Study on the Feasibility of a Harvesting, Transporting, and Chipping System for Forest Biomass Resources in Japan

Takuyuki Yoshioka*

Laboratory of Sustainable Forest Utilization, Department of Forest Science and Resources, College of Bioresource Sciences, Nihon University
1866 Kameino, Fujisawa 252-0880, Japan

Abstract

The aim of this study was to assess and discuss various aspects related to the feasibility of a harvesting, transporting, and chipping system for processing forest biomass resources in Japan. Within this framework, the author first comprehensively discussed the visions for introducing and diffusing woody bioenergy utilization in terms of the quantification of available woody biomass resources for energy, the development of low-cost harvesting and transporting systems, and the conversion processes. Second, a harvesting, transporting, and chipping system for logging residues was constructed, and the feasibility of the system was examined from the points of view of cost, energy balance, and carbon dioxide (CO2) emissions on the basis of field experiments at forestry operation sites. Third, the feasibility of the energy utilization of forest biomass resources in a mountainous region was assessed by analyzing the relationship between the mass and the procurement cost of forest biomass in the region with the aid of a geographic information system (GIS). The conclusions derived from this study will contribute to the practical implementation of the harvesting, transporting, and chipping system for forest biomass resources and to the realization of utilizing forest biomass for energy production in Japan.

Keywords

forest biomass resources, harvesting, transporting, and chipping cost, energy and carbon dioxide (CO2) balance, life cycle inventory (LCI) analysis, geographic information system (GIS)


Received on May 18, 2010

Accepted on October 18, 2010

Published online on March 31, 2011

*Corresponding author at:

Department of Forest Science and Resources, College of Bioresource Sciences, Nihon University

1866 Kameino, Fujisawa 252-0880, Japan

e-mail: yoshioka@brs.nihon-u.ac.jp


1. Introduction

1-1. Background of the study

The two oil crises that occurred in the 1970s spurred research on bioenergy worldwide. In Japan, the Ministry of Agriculture, Forestry and Fisheries implemented the "Biomass Conversion Project" during the fiscal period covering 1980 to 1990 (Agriculture, Forestry and Fisheries Research Council Secretariat (ed.) 1991). Various studies were carried out within the framework of this project, all focusing on the construction of a system of efficient bioenergy utilization. These included studies on methods of harvesting and transporting logging residues, i.e., tree tops and branches that are generated during limbing and bucking, considering logging residues to be a usable forestry product rather than a logging waste product (Forestry Science and Technology Promotion Center 1984 and 1985). Although promising results were obtained from such studies, the project was not implemented as a system at an actual site because the crude oil price stabilized at a lower level and the need for bioenergy decreased.

Now, many years later, the use of renewable energy is now being universally proposed as a countermeasure to global warming. Biomass as an alternative to fossil fuels is an environmentally friendly source of energy and is composed of organic materials, often generated as waste by-products. It is attracting widespread attention for its potential as an ideal primary energy resource in a sustainable society. Japan is currently promoting the use of bioenergy. In 2001, the government officially defined biomass as one of the new energy resources in the "Law Concerning Special Measures for Promotion of the Use of New Energy." The targets, based on the premise of maximum efforts from the government and the public in the fiscal year 2010, are 340,000 m3 crude oil equivalent with biomass power generation, corresponding to 330 MW capacity of electrical power generation, and 670,000 m3 crude oil equivalent with thermal utilization of biomass (Yokoyama 2002). Thus, the utilization of bioenergy is once again becoming an important political and scientific issue.

Among the various potential biomass resources that can be used to achieve these targets, woody biomass in particular is attracting a great deal of interest in Japan. A number of factors underlie this interest. First, woody biomass is abundant in Japan. Secondly, the energy utilization of woody biomass is expected to contribute to a revitalization of the forestry and forest products industries, which have long been depressed in Japan. Thirdly, woody biomass utilization will contribute towards maintaining the relevant ecological (including biological diversity), economic, and social functions of man-made forests, which are currently being neglected. However, in order to realize bioenergy utilization, programs for the introduction and implementation of bioenergy utilization should be adopted at a national level as soon as possible. These programs should be comprehensive in considering how to approach the quantification of available woody biomass resources for energy, the development of low-cost harvesting and transporting systems, and the conversion processes, as well as how these should meet the needs of the social system. To date, only a few studies on developing the necessary harvesting and transporting techniques have been carried out. In contrast, a number of energy-conversion technologies for woody biomass have already been developed to the level of practical use. In order to promote the introduction and diffusion of bioenergy utilization, therefore, it is necessary to establish a low-cost harvesting and transporting system for woody biomass as soon as possible.

The Japanese forestry industry has undergone major changes in the last years aimed at improving the productivity through mechanization, and the introduction of whole-tree logging systems has made rapid progress. However, due to the high productivity of the processors, a number of new problems have appeared, such as the large quantity of logging residues generated at landings. The use of forwarders has also made rapid progress, with the construction of low-grade strip access roads instead of expensive forest roads being promoted at the national level. Taken together, there is a golden opportunity for forwarders to haul slashes generated by processors, and these slashes can be converted into usable energy, such as heat, electricity, and liquid fuel, after they are transported by trucks and comminuted by chippers.

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1-2. Review of the studies on harvesting, transporting, and chipping for forest biomass resources

In this section, previous studies on the harvesting, transporting, and chipping of forest biomass resources are reviewed. The aim of this review is to identify the transitions that have occurred in the development and diffusion of the various relevant technologies and determine which of these may be appropriate for the development of a feasible and appropriate system in Japan (Yoshioka and Inoue 2006). The review is divided into two sections, namely, studies carried out "In the 1970s and 1980s" and those carried out "In and after the 1990s."

1-2A. In the 1970s and 1980s

In the 1970s and 1980s, when mainly only whole trees were harvested and utilized, many studies were conducted in North America (the United States and Canada) and Nordic countries (mainly Sweden and Finland), where forests grow on flat terrain. Most of the studies carried out in the 1970s investigated logging systems that consisted of felling trees using feller-bunchers, skidding the whole trees to forest roads using grapple skidders, limbing and bucking or chipping the whole trees at roadside landings, and then transporting the logs and wood chips. In the 1980s, researchers began looking at other logging systems as well.

Before the two oil crises in the 1970s, which stimulated studies on forest biomass harvesting, systems for chipping whole trees were researched and subsequently put into practice in the pulp and paper industries. In 1975 and 1976, four reports on chipping whole trees were published in the Technical Association of the Pulp and Paper Industry (TAPPI) Journal (Malac 1976, Morey 1975, Palenius 1976, Tufts 1976).

Morey in the United States reported that the process of whole-tree chipping had spread throughout North America when feller-bunchers and grapple skidders were introduced and technologies developed for separating clean wood chips for pulp production, with the result that increasingly more pulp mills accepted those wood chips (Morey 1975). The use of machines for felling, limbing, and bucking doubled the productivity in comparison to that of the conventional system by chain saws. In the mechanized system, a team of six operators produced 280–300 tons of wood chips a day, and the material cost at upon arrival at the mills was reduced from the conventional 20–30 US$ per ton to 6.22 US$ per ton. Morey also mentioned that mechanization reduced the expenses associated with cutting area, labor, and reforestation and that the chipping systems were effective for utilizing small-diameter thinned trees and low-quality logs of broad-leaved forests, which otherwise would be left unused.

Also in the United States, Tufts studied the productivity of whole-tree chipping and reported that although the system required a large initial investment, it was highly productive and could produce 800 tons of wood chips a week when applied to the thinning of a planted pine forest and transporting of the chips to a mill (by a team of 11 workers, a distance of 40–50 miles) and 150 tons of wood chips a day when used to clearcut a broad-leaved forest (by a team of 8 workers) (Tufts 1976). Malac reported that reforestation expenses were reduced by 33–65% in the United States when conventional shortwood logging was changed to mechanized whole-tree logging, although the expenses varied according to forest conditions (Malac 1976).

Palenius, however, reported that whole-tree chipping machines were introduced into Nordic countries due to insufficient manpower and the need both to produce the necessary amount of pulp wood and to appropriately thin forests (Palenius 1976). Therefore, according to this Finnish author, the background to the introduction of mechanized systems differed from that in North America. In Nordic countries, whole trees that were chipped were mainly thinned ones.

An FAO report that summarized the production and transport of wood chips supported the results and conclusions of these four studies (FAO 1976). This report, which also investigated the possibility of harvesting roots and logging residues left at cut-over areas in Nordic countries, concluded that the combined use of whole-tree chippers and separators of clean wood chips for pulp production was the most economical method for harvesting forest biomass and described various types of whole-tree chipping systems and mobile chippers. The chipping of small-diameter trees, such as those from forest thinning programs, was particularly mentioned as the only means by which whole-tree chipping could be profitable.

The utilization of forest resources as an energy source has also been studied. In Canada, Folkema compared two whole-tree chipping methods that used feller-bunchers and grapple skidders and reported that skidding whole trees directly to the chipper using the grapple skidder was more productive than moving the chipper along a forest road after skidding and accumulating whole trees along the roadside using the grapple skidder (Folkema 1977). Folkema reported that such a totally mechanized system was feasible only in large forests, in which the material cost, including expenses for transporting the wood chips to a mill, was 22.55–26.00 Canadian dollars per ton (45% of water content (wet basis), a distance of 50 km). Folkema indicated that total mechanization was difficult in medium to small forests where the optimal system for producing wood chips consisted of either (1) felling trees using chain saws, skidding the whole trees to forest roads using cable skidders, and chipping the trees at roadside landings using chippers or (2) felling trees using chain saws, chipping the whole trees using chippers connected to tractors, and hauling the chips to forest roads, and that the transportation distance by truck should not exceed 30 km (Folkema 1989).

Methods other than chipping whole trees have been studied by Stuart et al. in the United States (Stuart et al. 1981). These authors compared two systems:
(1) one that involved felling trees using feller-bunchers, skidding the whole trees using grapple skidders, intensively limbing and bucking, and then chipping or baling tree tops and branches, and (2) one that involved felling trees using chain saws, limbing and bucking, collecting the logs and logging residues separately using forwarders, and then chipping or baling the residues. They reported that whole-tree logging was the most economical approach and that collecting logging residues from forests required was expensive in terms of time, labor, and financial cost. Baling was reported to be more effective than chipping on a small scale.

Watson et al. compared the costs of producing logs and wood chips among the following three different systems (Watson et al. 1986):
1) Felling trees using feller-bunchers, limbing by chain saws, and skidding the tree-length logs using skitters;
2) Felling trees using feller-bunchers, skidding the whole trees using skidders, and limbing and bucking as well as chipping while separating the materials for logs and wood chips (one-pass system);
3) First felling small-diameter trees for wood chips using feller-bunchers, skidding the whole trees using skidders, and processing them into wood chips, and then producing logs in the same manner (two-pass system).

They reported that the one-pass system was the least expensive for producing logs and wood chips.

Typical studies in Nordic countries include the seven-year "Forestry Energy Project" by the Swedish University of Agricultural Sciences (Andersson and Falk (eds.) 1984). In this project, diverse studies were carried out on using logging residues as an energy source, including the history of using wood for fuel and the problem of removing nutrients from forests by harvesting tree tops and branches.

A "tree section" system was a main topic of the project, although other large-scale harvesting systems were also investigated, such as whole-tree logging that involved felling trees using feller-bunchers and skidding the whole trees using skidders, a collecting and chipping system that involved clearcutting by harvesters and producing wood chips from scattered logging residues using chipper-forwarders, and a chipping system that involved harvesting logging residues using forwarders and producing wood chips along forest roads or at terminals. The "tree section" system involved felling trees using feller-bunchers, cutting the trees into sections using grapple saws installed on forwarders, and collecting the sections (with branches) using the forwarders. This method was more productive than those systems that produced logs using harvesters. In order to load and transport "tree sections" or logging residues onto a trailer, the loads had to be compressed using the attached grapple; otherwise only 20–30% of the effective loading weight capacity of the trailer could be loaded.

In terms of small-scale systems, the study group reported that using materials from forest cleaning was an effective approach to improving the efficiency of subsequent forest operations. They recommended either felling trees using chain saws and then producing wood chips using chippers installed on agricultural tractors or collecting whole trees using cable skidders and producing wood chips at landings (a disadvantage of this method is the need for large landings). The report mentions the risks of work-related accidents caused by noise and striking of rebounded logs since logs must be put into chippers manually. Almqvist and Liss followed up this point and prepared a manual on chipping operations for small-scale forestry managers (Almqvist and Liss 1987).

Hakkila from Finland published a comprehensive review of studies on the utilization of forest biomass as energy that had been conducted prior to the end of the 1980s, including the aforementioned studies, studies by the U.S. Department of Energy (USDOE), and the "ENFOR Project" of the Canadian Forest Service (Hakkila 1989). With respect to forest biomass harvesting, which is the topic of this study, case studies were presented for diverse systems together with investigations and projects on harvesting, chipping, and transporting of whole trees, "tree sections," and logging residues.

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1-2B. In and after the 1990s

Studies carried out during and after the 1990s on harvesting of forest biomass can be broadly classified into IEA Bioenergy studies and others.

(a) IEA Bioenergy studies

The International Energy Agency (IEA) was established in 1974 under the auspices of the Organization for Economic Co-operation and Development (OECD), with the aim of achieving international cooperation in terms of all aspects related to energy. In 1978, the first biomass study project, "IEA Forestry Energy," was initiated. In 1986, the project was renamed "IEA Bioenergy" to include non-forest biomass resources. Thereafter, the word "bioenergy" has been widely used to refer to the utilization of biomass energy.

The first IEA Bioenergy study on forest biomass was conducted from 1986 to 1988 under the title "Development of Improved Methods for Harvesting, Processing and Transport of Forest Biomass (IEA Bioenergy Task III)." The main findings of this project were summarized in 1990. Research on harvesting forest biomass was summarized in the section entitled "Integrated Harvesting Systems to Incorporate the Recovery of Logging Residues with the Harvesting of Conventional Forest Products" by Goulding and Twaddle from New Zealand (Goulding and Twaddle 1990). Research on harvesting early thinnings was summarized in "Harvesting Early Thinnings of Energy" by Brenøe and Kofman from Denmark (Brenøe and Kofman 1990).

Goulding and Twaddle reviewed trials of harvesting whole trees that had been carried out in participating countries and presented a design for an "integrated harvesting" system that involved harvesting logging residues, such as previously wasted tree tops and branches, and using these for energy as well as harvesting conventional forestry products, such as logs and pulp wood (Goulding and Twaddle 1990). "Integrated harvesting" became a keyword of IEA Bioenergy projects on harvesting forest biomass in the early 1990s.

Brenøe and Kofman reviewed the eight tests on harvesting early thinnings conducted within the framework of the project, which also included tests on "integrated harvesting" (Brenøe and Kofman 1990). They classified the sites for processing whole trees into terminals, landings, and forests, and analyzed the feasibilities, advantages and disadvantages of each site. Their conclusion was that the only economically feasible integrated method for harvesting early thinnings was the "tree section" method used in Sweden and Finland.

From 1992 to 1994, studies were carried out under the theme "Harvesting and Supply of Woody Biomass for Energy (IEA Bioenergy Task IX)." In Canada, Puttock investigated "integrated harvesting" of whole trees by comparing the costs of collecting forest biomass to landings and chipping for the systems used in the participating countries and analyzing their advantages and disadvantages (Puttock 1995). The advantages of recovering logging residues included the reduced risk of pest insects and forest fire, improved efficiency of planting seedlings, and the resultant increases in the survival rate of planted young trees, although the economic benefits were difficult to quantify. The disadvantages included soil erosion caused by compaction and disturbance of the soil due to the increased work-associated activity in forests, removal of nutrients, and resultant adverse effects on tree growth. Puttock suggested that compaction and erosion of the soil could be avoided by restricting the routes of machines used in forests and that the fertility of the soil could be recovered by returning incineration ashes of forest biomass to prevent decreases in nutrients.

The main results of IEA Bioenergy Task IX were summarized in 1995. Culshaw and Stokes summarized the mechanization of short rotation forestry (SRF) (Culshaw and Stokes 1995), Hudson summarized the section on "integrated harvesting" (Hudson 1995), Gingras summarized the harvest of small-diameter trees and recovery of logging residues (Gingras 1995), and Angus-Hankin et al. summarized the section on forest biomass transportation (Angus-Hankin et al. 1995).

Hudson published a report on the efforts made by participating countries on "integrated harvesting" (Hudson 1995). Two different technologies, the chain flail method developed in North America and the "Massahake Method" developed in Finland, involve separating clean wood chips for pulp production from those for fuel during the production of whole-tree chips. Hudson reported that these technologies made thinning operations economically feasible. In comparison, the "tree section" system, which was developed in Nordic countries and was once the most popular "integrated harvesting" system, was used less frequently due to the increasing use of single-grip harvesters. According to Gingras, the multi-tree felling heads that were being developed in Nordic countries would be able to cut two or more small-diameter trees simultaneously, representing an option for mechanizing early thinning and improving its cost effectiveness (Gingras 1995). Angus-Hankin et al. compared the costs of transporting wood chips produced from logging residues, intact logging residues, and "tree sections" over a distance of 80 km on a trailer that could carry at least 100 m3 (Angus-Hankin et al. 1995). They also discussed the possibility of transporting baled logging residues. Comparative studies on the costs of the different harvesting methods of forest biomass, such as wood chips, logging residues, and baled residues, started during this period.

From 1998 to 2000, studies were conducted as part of the "Conventional Forestry Systems for Bioenergy (IEA Bioenergy Task 18)" project. It should be noted that SRF and "integrated harvesting," such as the chain flail technology (which are regarded as "one-pass systems"), were discussed within the framework of "Short Rotation Crops for Bioenergy (IEA Bioenergy Task 17)" mainly in the United States. Thus, Task 18 specialized in the use of bioenergy in forestry. The status and efforts of participating countries were reported from Finland (Nurmi 1999), Denmark (Heding 1999), the Netherlands (Vis 1999), and New Zealand (Hall 2000).

Nurmi reported that logging residues in Finland were usually transported after they had been processed into chips using chipper-forwarders in forests or at roadside landings and that harvesting of the logging residues could reduce reforestation costs by 100 US$ per hectare (Nurmi 1999). The transportation distance of forest biomass that formed a break-even point was 40–50 km when a cogeneration plant was assumed.

Heding reported that in Denmark wood chips were mainly a product of forest thinning, which involved felling trees in winter, leaving the trees in the forest during the summer to reduce the water content to one-third and return the leaves to the soil, and chipping the whole trees in the forest using chipper-forwarders (Heding 1999). The market price per gigajoule was 6 US$. Although the production of wood chips on its own was only just profitable, this method had greatly improved the efficiency of the final cutting of the thinned forests.

Vis reported that the mechanization of forestry in the Netherlands had reduced the production cost by 70% during final felling and by 66% during thinning (Vis 1999). Since there was no demand for low-quality materials other than for timber and pulp, mechanization provided a good opportunity for utilizing bioenergy. A harvesting system similar to that of Denmark was used, but logging residues after final cutting were also harvested.

Hall reported that forestry in New Zealand had shifted from collecting "tree sections" to harvesting whole trees and intensively limbing and bucking at landings, resulting in vast amounts of logging residues; consequently, methods for dealing with the residues had to be developed (Hall 2000). Four methods were investigated: (1) disposed of as waste; (2) burned at the site; (3) used as fuel in pulp mills; (4) used as material for producing fiberboard and pulp chips. Only method (4) was profitable.

Studies on the development of test balers and multi-tree felling heads were also carried out within the framework of Task 18. Balers process logging residues into cylindrical bales by compression, thereby enabling the bales to be handled as logs. A bale is also called a "bundle" or "composite residue log (CRL)." Multi-tree felling heads can cut two or more small-diameter trees simultaneously. The two harvesting systems that received the most attention were (1) a method that involved felling, limbing, and bucking trees in the forest using harvesters, collecting the logs using forwarders, and then harvesting forest biomass, and (2) whole-tree logging that involved limbing and bucking at roadside landings and transporting the forest biomass. These systems can be regarded as "two-pass systems" and are classified into several groups according to the location for producing wood chips.

This project was characterized by a number of comparative studies on harvesting cost per unit weight (or unit energy), which were conducted by assuming two or more systems for each type of forest biomass transportation. For example, the harvesting costs of non-chipped logging residues, wood chips, and bales of logging residues were investigated (Andersson 1999, Andersson et al. 2000, Eriksson 2000, Hudson and Hudson 1999, 2000, Hunter et al. 1999). In many studies, transporting non-chipped logging residues to energy-conversion plants on large-sized trailers and chipping intensively by large-sized chippers was found to be the least expensive method. However, Hudson and Hudson determined that baling would become relatively less expensive with increasing transportation distance, even though balers were still being used on an experimental basis (Hudson and Hudson 2000). Asikainen and Kuitto from Finland compared the harvesting costs between (1) collecting logging residues to roadside landings and then chipping and (2) chipping logging residues in the forest using chipper-forwarders or chipper-trucks (Asikainen and Kuitto 2000). Andersson and Eriksson tested multi-tree felling heads and reported that mechanization of early thinning, which was conventionally conducted using chain saws, would improve productivity, reduce costs, and enable utilization of early thinnings for energy (Andersson 1999, Eriksson 2000).

A summary of the results of Task 18 was published in 2002 (Richardson et al. (eds.) 2002), but the project continued for a further 6 years following 2001 under the auspices of the "Conventional Forestry Systems for Sustainable Production of Bioenergy (IEA Bioenergy Task 31)." Although Task 18 stayed in the pilot phase, the new Task 31 holds the promise of both practicality and business possibilities; for example, the bundler has been diffused in Finland (Hakkila 2004) and exported to other countries (Cuchet et al. 2004).

(b) Other studies

Studies have also been carried out on the harvesting of forest biomass outside of the framework of IEA Bioenergy Tasks. The majority of these studies on forest biomass focused on logging residues from final felling and small-diameter trees from early thinning.

Based on the findings of a Canadian study, Desrochers et al. reported that residues from shortwood logging, a type of logging widely performed in conventional forestry, were difficult to harvest due to technological problems, low productivity, and high costs (Desrochers et al. 1993). However, an energy-utilization system that involved collecting logging residues, producing chips at roadside landings, and transporting the chips would be feasible due to the spread of chippers for chipping residues and the advantages of removing residues from forest floors, including the reduction in reforestation costs. These authors verified a system of harvesting logging residues and collecting to roadside landings by chipping the residues using a newly developed chipper-forwarder and compared the results with that of a system used in Canada that consisted of collecting logging residues using a skidder installed with a loader and chipping the residues using a chipper mounted on a truck. A similar investigation on harvesting and chipping logging residues using chipper-forwarders was conducted by Asikainen and Pulkkinen in Finland (Asikainen and Pulkkinen 1998). Both studies showed that the use of chipper-forwarders was lower in terms of productivity and more expensive than producing chips at roadside landings.

In New Zealand, Hall et al. compared the costs of harvesting logging residues in forests and at landings for each chipping location (including the introduction of chipper-forwarders) (Hall et al. 2001). Since the scale of chipping had a large effect on the costs, the least expensive method was to transport residues to energy-conversion plants and chip the residues intensively using large-sized chippers for residues both in forests and at landings.

In Finland, Malinen et al. conducted an analysis on the use of logging residues in forests generated during thinning and final felling based on calculations of the amount of forest biomass that could be utilized when it had to be hauled a distance of 250 m in the forest and transported a distance of 40 km on truck to an energy-conversion plant, with a focus on various upper limits in cost (Malinen et al. 2001). In Finland, logging residue is widely utilized as an energy source, and manuals for harvesting residues have been prepared (Alakangas et al. 1999).

In Spain, Delgado and Giraldo investigated the utilization of small-diameter trees from early thinning as boiler fuel by limbing and bucking in forest, collecting by tractors, producing chips at roadside landings, and transporting (Delgado and Giraldo 1995). For a maximum transportation distance of 30 km, the costs for harvesting and chipping were 1.45 and 2.45 pesetas per kg (water content was 15% (wet basis)), respectively.

In Sweden, Sennblad estimated the cost of producing wood chips for a regional heating plant by harvesting logging residues during thinning and final felling and small-diameter trees during early thinning for small- and large-scale systems (Sennblad 1994). For a hauling distance of 300 m in the forest and a transportation distance of 30 km on truck, a large-scale system was more profitable than a small-scale system. Sennblad proposed schedules of harvesting forest biomass for small-scale forestry managers, including the processes from early thinning to final felling, to help them overcome this disadvantage (Sennblad 1995).

A point worth noting is that since tree tops and branches on forest floors are decomposed and serve as nutrients for trees, harvesting logging residues may remove nutrients from the forest and adversely affect the growth of trees. This topic has been widely studied in Nordic countries, and Lundborg from Sweden has summarized the study results into a review (Lundborg 1997). Lundborg investigated the effects of harvesting logging residues and whole trees on organic matter and mineral nutrients in the soil and concluded that the harvesting of forest biomass had almost no effect on organic matter. In contrast, mineral nutrients are reduced by harvesting, although returning the incineration ash of forest biomass to the forest can prevent the soil acidification (Lundborg 1998). Börjesson from Sweden assessed the return of incineration ash in terms of cost (Börjesson 2000). In Sweden, the cost of harvesting logging residues was 3.8–4.2 US$ per gigajoule, but the cost of returning incineration ash was only 0.18–0.48 US$ per gigajoule. Moreover, when the environmental benefits of returning the ashes were converted into monetary value, the procurement cost of logging residues was estimated to be 1.1–4.6 US$ per gigajoule.

Studies on harvesting forest biomass in SRF have been conducted on separating clean chips for pulp production from chips for fuel using the chain flail technology (Hartsough et al. 2000, Stokes and Watson 1991), methods for chipping small-diameter trees and the development of baling machines (Felker et al. 1999), the performance of skidders and front-end loaders used in whole-tree logging (in Italy) and actual chipping operations (Spinelli and Hartsough 2001a, b). Spinelli and Hartsough (2001c) reviewed the Italian chipping operations in detail.

In summary, Fig. 1 illustrates the overview of the development and diffusion of harvesting technologies according to the kinds of forest biomass resources.


Fig. 1. Overview of the development and diffusion of harvesting technologies according to the kinds of forest biomass resources.

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1-3. Objective and framework of the study

The objective of this study is to discuss the feasibility of a harvesting, transporting, and chipping system for forest biomass resources in Japan. The subject is first approached by presenting a comprehensive discussion of the various visions on the introduction and diffusion of woody bioenergy utilization in terms of the quantification of available woody biomass resources for energy, the development of low-cost harvesting and transporting systems, and the conversion processes. Second, a harvesting, transporting, and chipping system for logging residues is constructed, and the feasibility of the system is examined from the points of view of cost, energy balance, and carbon dioxide (CO2) emissions on the basis of field experiments at forestry operation sites. Third, the feasibility of the energy utilization of forest biomass resources in a mountainous region is discussed by analyzing the relationship between the mass and the procurement cost of forest biomass in the region with the aid of a geographic information system (GIS). The following subjects are examined and discussed in six chapters and the conclusions derived from the chapters are summarized in the last chapter:

· Chapter 2: The feasibility of utilizing woody biomass as an energy resource in Japan is discussed based on amount and availability of woody biomass, and energy-conversion technologies;

· Chapter 3: The concept of a "harvesting system for logging residues by a processor and a forwarder" is examined for the purpose of constructing a system to harvest logging residues as a new resource for energy;

· Chapter 4: A "harvesting and transporting system for logging residues" is constructed with reference to three European countries where the utilization of bioenergy is making steady progress and examined on the basis of field experiments in Japanese forestry;

· Chapter 5: An experiment on the comminution of logging residues with a tub grinder is carried out in order to calculate the productivity and procurement cost of wood chips;

· Chapter 6: Using the method of a life cycle inventory (LCI) analysis, the energy balance and the CO2 emission of logging residues from Japanese conventional forestry as alternative energy resources is analyzed over the entire life cycle of the residues;

· Chapter 7: The feasibility of the energy utilization of forest biomass in a mountainous region in Japan is discussed with the aid of the GIS.

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2. Woody biomass resources and conversion in Japan: The current situation and projections to 2010 and 2050

In this chapter, the feasibility of utilizing woody biomass as an energy resource in Japan is discussed based on the amount and availability of this resource and energy-conversion technologies (Yoshioka et al. 2002b, 2005b). First, an overview of the present state of woody biomass is given, with an estimation of the amount of resources available for energy as well as a discussion of the future prospects of the resources. Secondly, the systems for logging residues are examined with respect to the development of low-cost harvesting and transporting systems, which is a key issue in the discussion on the introduction and diffusion of woody bioenergy utilization. Thirdly, the visions on the bioenergy utilization are presented in terms of 2010, which is the time frame for achieving the goals of the Kyoto Protocol on the reduction of greenhouse gas emissions, and 2050, when the problems on the depletion of fossil fuel resources are expected to worsen, as these years represent the targets for realization of the short-term and long-term visions, respectively. Finally, the utilization patterns, conversion processes, problems of technical development, and policy actions that the government should adopt are discussed on the condition that a small-scale and decentralized system and a large-scale and centralized system can coexist.

The following items are considered to be woody biomass (waste paper and black liquor are excluded):

· Logging residues, i.e., tree tops and branches that are generated during limbing and bucking operations;

· Thinned trees that are left in forests because the logging costs are higher than the timber price;

· Trees to be thinned from coniferous forests which are behind in tending;

· Coppice forests, i.e., broad-leaved forests that were formerly managed, mainly for fuelwood use, but are now left unutilized;

· Bamboo and bamboo grass (Sasa spp.);

· Mill residues, i.e., wood shavings and barks generated in the sawmill and plywood industries;

· Wood-based waste material;

· Trimmings of park trees, roadside trees, and garden trees.

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2-1. The present situation of woody biomass in Japan

2-1A. The amount of woody biomass

Various studies (New Energy Foundation 2000, Research Institute of Innovative Technology for the Earth 1999, Saka (ed.) 2001, Yamaji et al. 2000) have been conducted to estimate the amount of woody biomass in Japan. The annual potential amount here is based on the studies made by Harada (2000) and Honda (1986) as shown in Table 1. The value of 31.7 Tg/y given in Table 1 is in accordance with the estimations reported in the studies mentioned above. This amount of woody biomass has a calorific value of 634 PJ (176 TWh), corresponding to 2.8% of the national primary energy supply in the fiscal year 1999, 23.0 EJ (6.39 PWh) (Energy Data and Modelling Center (ed.) 2001).

The amount of logging residues (3.0 Tg/y, Table 1) was estimated based on the annual cut volume of 29 Mm3/y. Even subtracting this cut volume, the growing stock continues to increase by 69 Mm3 annually in Japan, mainly in the 10 million ha of the man-made forests which were afforested after the war. Therefore, the future available amounts of logging residues and thinned trees for energy are expected to increase considerably from a current total of 8.0 Tg/y, provided that policy-makers focus on bioenergy and the cutting of forests is promoted. In terms of the utilization of thinned trees, it is assumed that all of the cut material from thinning can be used for energy at the actual Japanese market value. However, this assumption may be unrealistic based on the "cascade use" or multistage use of wood (which means that wood fiber should be used for higher valued products as much as possible before it is recycled as an energy resource), so that further discussion is necessary.

Table 1. Annual potential amount of woody biomass in Japan on a dry-weight basis.1 Reprinted from Biomass and Bioenergy, 29(5), Yoshioka et al., Woody biomass resources and conversion in Japan: The current situation and projections to 2010 and 2050, 336–346, Copyright (2005), with permission from Elsevier.

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Broad-leaved forests are potential sources of large amounts of biomass annually (9.0 Tg/y). The rich ecosystems of coppice forests were traditionally maintained by periodic cutting (coppice forests were cut for charcoal for iron and steel as well as cooking). At the present time, however, broad-leaved forests are left unutilized, and degradation is progressing. Therefore, a new type of hardwood forest management that involves cyclic logging for the purpose of energy use is proposed so that the rich ecosystems of the broad-leaved forests can be restored.

The growth characteristics of bamboo and bamboo grass make it a valuable biofuel resource. A bamboo grass harvesting machine was developed in the oil crises of the 1970s, but never put into practical use. In field trials using this machine, the harvesting cost was calculated to be 17.5–20.8 US$/Mg on a dry-weight basis when the haulage distance was 200 m to forest roads (Agriculture, Forestry and Fisheries Research Council Secretariat (ed.) 1991); this cost is quite favorable compared to those of other existing technologies. Therefore, it should not be too difficult to introduce the machine into forests with gently undulating terrain on a trial basis and estimate the actual available amount of bamboo grass.

In addition to the total of 8.4 Tg/y of mill residues and wood-based waste material noted in Table 1, 1.90 Tg/y, 3.84–3.86 Tg/y, and 3.83–4.15 Tg/y of these materials are already used for compost and litter, industrial materials, and fuels, respectively (Harada 2000). However, it is supposed that there should be the following patterns of disagreeable waste recycling or disposal to no small extent:

1) Accepted free of charge by wood chip merchandisers as industrial materials and by stock farmers for compost and litter;

2) Disposed of by industrial waste disposal contractors with compensation;

3) Burned in private garbage incinerators unavoidably. The items listed above can be switched over to energy utilization by purchasing item 1) for a small amount of money and by collecting items 2) and 3) without charge.

Gardening companies are obliged to dispose of their trimmings as industrial wastes. Such wastes can also be used for energy by collecting them without charge.

The introduction of energy utilization of woody biomass is viewed as the next logical step in the sequence of recycling waste. As such, it is necessary to assess the actual amounts of mill residues, wood-based waste material, and trimmings that are available for energy purposes. However, there is also a need for establishing a collection system within a region prior to their use.

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2-1B. A harvesting and transporting system for woody biomass

In order to utilize logging residues and thinned trees for energy, it is necessary to harvest them from forests and transport them to energy-conversion plants. Three case studies on the costs of a harvesting and transporting system for logging residues are presented in this chapter as examples of a lowest cost system and its refinement:

· Case 1: The lowest cost system is constructed by using state-of-the-art machines that are currently coming into widespread use in Japanese forestry processes. This system, in which a mobile chipper is operated at the landing of a logging site (in a forest), is based on the field experiments carried out within the framework of ongoing studies (Yoshioka et al. 2000, 2002a);

· Case 2: In the transportation process, the shift from a transport contractor with a truck of 4 tons to the purchase an 18-ton trailer with 60 m3 of cubic capacity and an employed driver would be of interest because the transporting cost in Case 1 is too high (Yoshioka et al. 2002b). In Japan, trailers of this class are owned mainly by paper companies;

· Case 3: A bundler, which compresses logging residues into cylindrical bundles, has been recently developed in the Nordic countries. Bundles can be collected and transported in the same way as logs. Japanese forest engineers have shown a great interest in bundlers because they may improve the operational efficiencies of harvesting and transporting residues. Thus, in Case 3, the bundling process is incorporated into the system of Case 2 and examined with reference to the findings of Hudson and Hudson (2000).

The harvesting and transporting costs of the three cases listed above are shown in Table 2. The cost in Case 2 is almost half of that in Case 1. However, in order to realize a system similar to that of Case 2 in Japan, it is necessary to construct networks of high-grade forest roads so that large-sized trailers can travel directly to the landings of the logging sites. Additionally, for the purpose of enhancing the operational efficiencies of comminution and haulage, the introduction of bundlers or chipper-forwarders that have both chipping and forwarding functions needs to be considered.

Table 2. Harvesting and transporting costs of logging residues per Mg on a dry-weight basis. Reprinted from Biomass and Bioenergy, 29(5), Yoshioka et al., Woody biomass resources and conversion in Japan: The current situation and projections to 2010 and 2050, 336–346, Copyright (2005), with permission from Elsevier.

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The cost in Case 3 is lower than that in Case 2, suggesting the feasibility of incorporating bundlers into the low-cost harvesting and transporting system. A bundling system, however, is applicable only for gentle terrain like that found in Nordic countries; consequently, it will be necessary to develop a machine suitable for Japan where the topography is very steep.

The average transportation distance of the systems examined in this chapter is 40 km. Hudson and Hudson (2000) calculated the harvesting and transporting cost of logging residues in the U.K. to be 45.0 US$/Mg when the transportation distance was 100 km. This is a more favorable result than Case 3, which is the cheapest case of the three presented above. The calculation for Japanese conditions is based on field experiments complemented with data from studies performed outside of Japan. Therefore, it is still possible to reduce the harvesting and transporting cost in Japan if the introduction and diffusion of bioenergy utilization are promoted. The improvement of the system should include an accumulation of experience from the field experiments such as, for example, improvements in operating techniques.

Consequently, for the purpose of establishing a low-cost harvesting and transporting system for logging residues, it will be necessary that the infrastructure should be improved; however, the development of technology as well as the promotion of testing in field experiments should be considered as short-term tasks.

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2-2. Prospects for woody bioenergy utilization in Japan

The regulation of dioxin emissions by the already strengthened "Waste Management and Public Cleansing Law" and Japan's obligations under the Kyoto Protocol, with the first commitment period starting in 2008, are expected to be the driving forces for woody bioenergy utilization in both the waste recycling and energy production sectors. The Kyoto Protocol stipulates that Japan must reduce its greenhouse gas emissions by 6% from 1990. Therefore, 2010 is the target year for the short-term time frame. The long-term time frame extends to 2050, when the problems associated with the depletion of fossil fuel resources are expected to worsen. Thus, possible technological and infrastructure developments need to be put in the perspective of these time frames.

2-2A. Short-term vision (around the year 2010)

(a) A small-scale and decentralized system

In the year 2010, the following pattern of woody biomass utilization will be diffused: All of mill residues, wood-based waste material, and trimmings that formerly needed to be disposed of as waste products in addition to some of logging residues and thinned trees will be utilized as energy resources. There will be two aspects to the energy utilization of woody biomass, namely, waste recycling and energy production.

Unlike energy forest products that are cultivated and harvested systematically, many types of biomass generated as wastes are dispersed in low-density centers, necessitating collection and transportation for use at an energy-conversion plant. Converting biomass to energy directly at the location where waste biomass is actually generated is one option for reducing the costs of collection and transportation. Two possibilities, namely, "on-site" and "regional" types of energy-conversion processes feasible in Japan, are discussed here.

The present situation of energy-conversion processes of woody biomass in Japan is briefly outlined in Fig. 2. Bio-oil production by the process of fast pyrolysis is becoming of interest internationally, especially in Europe, but it has attracted less attention in Japan. Bio-oil as liquid fuel, for example, may be less available directly to vehicles and still needs technical development. Consequently, direct combustion or gasification is considered to be easier for the case of the small-scale energy-conversion technology of woody biomass. On the other hand, upgraded wood fuels, such as pellets and briquettes, are becoming popular in Japan, and more than ten pellet-production plants using mill residues, wood-based waste material, and trimmings are already in operation.


Fig. 2. Present R&D development and stages for energy-conversion processes of woody biomass in Japan. Reprinted from Biomass and Bioenergy, 29(5), Yoshioka et al., Woody biomass resources and conversion in Japan: The current situation and projections to 2010 and 2050, 336–346, Copyright (2005), with permission from Elsevier.

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(a-1) "On-site" type of energy-conversion process

This is the case where woody biomass is converted to energy and utilized at the site of waste biomass generation. In such a case, a company which experiences difficulty in disposing of wastes but which has a demand for heat and electrical power is expected to introduce this process into its own facility for waste recycling and energy production. According to the survey by the Japan Institute of Energy, the average amount of woody biomass generated per company in a Japanese sawmill, plywood, and gardening industry is 2–10 Mg/d on a dry-weight basis.

The following three processes are considered to be promising energy-conversion processes with the capability to cope with such amounts of biomass:

1) Thermal utilization by the direct combustion of woody biomass;

2) Power generation and thermal utilization, i.e., combined heat and power (CHP), by the direct combustion of woody biomass and a steam turbine;

3) CHP by a fixed bed gasifier and a gas engine.

Among the processes listed above, processes 1) and 2) are already at the level of introduction and diffusion. Process 3) is considered to be at the level of demonstration, since various types of technical developments have been promoted nationally and globally and/or in developed and developing countries. With regard to the small-scale gasification with a gas engine, however, a low-cost technology that treats tarry waste water from scrubbing has still to be developed.

In terms of the operational management and energy demand of a small-scale system, it is difficult for an "on-site" type of energy-conversion facility to operate around the clock; therefore, a system that starts and stops daily is desirable. In this case, the utility aspects of the energy-conversion facility are important; for example, such systems require a device for rapidly firing up and turning off the gasifier.

With respect to the scale of a plant, when the throughput of woody biomass, hours of operation, and thermal efficiency are 5 Mg/d on a dry-weight basis, 8 hours a day, and 8%, respectively, the net generation of power is calculated to be 420 kW. This output may provide all of the electricity needed to run the facility; moreover, there may be surplus. At the present time, Japanese electric power companies seldom buy electricity from small-scale biomass-based power generation plants. In order to diffuse the "on-site" type of energy-conversion process, it is essential to improve the system of trading surplus electricity.

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(a-2) "Regional" type of energy-conversion process

This is the case where biomass generated within a region is collected and converted to energy. In this scenario, the larger the collection area is, the greater the amount of biomass resources for energy can be collected, leading to some reduction in the investment and operation costs of a plant. On the other hand, the transportation cost increases with expansion of the collection area. Thus, in the case of the "regional" type of energy, there will always be a trade-off between these two factors in terms of the appropriate utilization of woody biomass and the technical development.

The relationship between the collection area and the amount of woody biomass cannot be defined completely. The net power output, however, is calculated as 4.2 MW when the throughput of woody biomass, hours of operation, and thermal efficiency are 50 Mg/d on a dry-weight basis, 8 hours a day, and 8%, respectively, by the process of direct combustion and a steam turbine, which is the available energy-conversion technology at the present moment. A grate-fired furnace is usually adopted to the process of direct combustion and a steam turbine. When a grate-fired furnace is used, the volume of steam is relatively stable to any variation in the components of the fuel. Therefore, power generation by direct combustion of woody biomass and a steam turbine is suitable for using various types of biomass within a region as fuel.

In this process, it is possible to utilize logging residues and thinned trees generated within a region as fuel, in addition to the mill residues, wood-based waste material, and trimmings that are the targets for the "on-site" utilization mentioned above. Moreover, it is realistic to deal with unutilized agricultural residues, such as rice straw and rice hull, generated within the same region together. Many kinds of agricultural residues are generated intensively in one specific period of the year, so it is not effective to establish an energy-conversion facility dedicated solely to processing these residues. Consequently, as the aim of the facility should be to convert all the biomass resources available within a region to energy, a power generation plant financially sponsored by joint public and private sector investment is desirable.

In order to realize the "regional" utilization, improvement of the energy-conversion technologies is necessary to obtain higher efficiency. Construction of low-cost harvesting and transporting systems for biomass is also necessary.

(b) A large-scale and centralized system

Co-firing of woody biomass with coal is expected to be the most feasible in the year 2010. Table 3 lists the advantages and disadvantages of the co-firing of woody biomass at an existing coal-fired power plant.

Table 3. Advantages and disadvantages of the co-firing of woody biomass with coal at an existing coal-fired power plant. Reprinted from Biomass and Bioenergy, 29(5), Yoshioka et al., Woody biomass resources and conversion in Japan: The current situation and projections to 2010 and 2050, 336–346, Copyright (2005), with permission from Elsevier.

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It is very important to adopt a vision that maximizes the advantages and minimizes the disadvantages toward energy utilization of woody biomass. When woody biomass is co-fired with coal at the 5–10% ratio of biomass, for example, a simple arithmetic calculation demonstrates that the carbon dioxide emissions will also be reduced by 5–10%. Although the harvesting and transporting cost of woody biomass is rather high as mentioned above, the effectiveness of the reduction is still substantially advantageous. Japan is so poor in fossil fuel resources that the self-sufficiency rate in the energy supply is around the 10% level. Therefore, the introduction of such an approach to bioenergy utilization will have a great effect not only on the self-sufficiency rate in the energy supply but also on the utilization of national forest resources and the conservation of the global environment.

In order to promote the diffusion of a large-scale and centralized system, it is essential that Japan establish a national consensus as well as a strategic scenario based on the international situation and to develop the energy-conversion process. These must be aimed at long-term development and should not remain in the short-term vision. Based on the forecast for future energy demand in Japan and the target for the conservation of global environment (including the measures against global warming), it is necessary to establish a program for the effective use of biomass that will guarantee a stable supply of energy resources of hydrocarbon origin, as well as to prioritize the direction of future research and development. It is also necessary to consider a scenario in which both the long-term vision is realized in the target year 2050 and bioenergy utilization is promoted. In this scenario, for example, a comprehensive system that includes the import of biomass from foreign countries will be proposed. In terms of a large-scale and centralized system, promotion of the design and development of the Integrated Gasification Combined Cycle (IGCC) and the clean liquid fuel production process, which substitute for coal and oil, respectively, is desirable from the point of view of a smooth transition to bioenergy utilization following the depletion of fossil fuel resources.

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2-2B. Long-term vision (around the year 2050)

(a) A small-scale and decentralized system

Around the year 2050, almost all the woody biomass waste resources will be utilized for energy production in one way or another, so that the "on-site" type of energy-conversion process combining waste recycling and energy production will already have been diffused. Therefore, the "regional" utilization system targeted for unutilized resources is considered to be the main type of energy-conversion process at this time. The term "region" here is assumed to be an area smaller than the administrative unit (a city, town, or village). In this case, the comprehensive energy-conversion plant that accepts all of the biomass resources within a region and produces electrical power, heat, and liquid fuel according to the energy demand in the region will be realized.

In 2050, the depletion of oil will have become a reality, so the demand for liquid fuel which substitutes for oil is assumed to increase considerably. In towns and cities, building the infrastructure of natural gas and hydrogen will be promoted (but not in mountainous areas), and the shift to hydrogen and the like in the energy supply is expected to start.

In such a situation, it will be necessary to utilize biomass generated within a region as effectively as possible and to fulfill the energy demand in the region. Not only logging residues, thinned trees, and unutilized agricultural residues but also mill residues, wood-based waste material, and trimmings will be targeted for energy use. Moreover, the sustainable use of unutilized broad-leaved forests, bamboo, and bamboo grass, i.e., without damage to these ecosystems, will have started. With the aid of the global land use and energy (GLUE) model (Yamaji et al. 2000), the annual potential amount of biomass indicated above is estimated to be 1.44 EJ/y (400 TWh/y), corresponding to 6.3% of the national primary energy supply in the fiscal year 1999.

The scale of an energy-conversion plant is largely dependent on the amount of generated biomass. However, given the realization of a plant with throughput of biomass, hours of operation, and thermal efficiency of 200 Mg/d on a dry-weight basis, 8 hours a day, and 20%, respectively, the net power output is calculated as 33 MW, which is sufficient to fulfill the regional energy demand. Various types of combinations of energy-conversion technologies, such as a combination that supplies heat and power by gasification as well as liquid fuel by alcohol fermentation, should be developed. In order to realize such a combination, improvements in energy-conversion technologies and efficiency as well as reductions in the construction costs of a plant are necessary.

The management pattern of such an energy-conversion facility cannot be predicted at this time. However, a power generation plant financed by the joint investment of local residents, a municipality, and companies is regarded as one of the possibilities.

(b) A large-scale and centralized system

The population of Japan will decrease to about 105 million around the year 2050 (Energy Data and Modelling Center (ed.) 2001); however, energy consumption per capita may increase as the standard of living continues to rise. A reduction in the amount of carbon dioxide emissions will also be required, but this reduction will be difficult to achieve through the effective utilization of fossil fuel resources only, thus necessitating the changeover to renewable energies. Specifically, bioenergy as well as solar and wind energies must become the main sources of the primary energy supply. At the same time, given possible developments in utilizing existing solar and wind energies, hydrogen energy systems could be introduced and diffused. In such a situation, woody biomass and unutilized agricultural residues can contribute to the national primary energy supply only at the single-figure-% level at most, as mentioned above, so the utilization of foreign biomass resources must be considered.

The import of foreign biomass resources has been studied (Dote and Ogi 2001). In terms of carbon dioxide emissions related to the shipping of biomass, the amount of the emissions can be reduced by converting biomass to liquid fuel in foreign countries. In this case, however, potential environmental degradation in those countries supplying the biomass should be a point of great concern. It will therefore be necessary for Japan to make an import and export contract with each biomass supply country in which there is an explicit agreement that the forest cultivation program based on periodic biomass plantation is carried out in a sustainable way in that country. Japan will also be required to implement a policy that takes into account the curbing of global carbon dioxide emissions, such as through projects of revegetation in the desert, and others. Moreover, it will be important to work at the international level for approval of these activities, which are expected to reduce the amount of carbon dioxide emissions both nationally and globally as well as to protect the forests in developing countries from destruction, as part of the clean development mechanism (CDM). According to the GLUE model, North America, Latin America, the former USSR, and Eastern Europe are possible countries for biomass plantation use when the future increase in demand for food production is taken into consideration (Yamaji et al. 2000). The conflict between biomass plantation and food production must be prevented.

These foreign biomass resources and converted liquid fuel will be unloaded at sea ports in the same way as coal. Therefore, those energy-conversion plants located along the sea coast that are currently used to store and refine coal and oil can be converted into the large-scale and centralized type of biomass utilization facilities by increasing the biomass co-firing rate or by improving the device for biomass processing. Liquid fuels, such as ethanol, for transportation use will be supplied by utilizing the existing infrastructure.

In summary, Fig. 3 shows the prospects for woody bioenergy utilization in Japan in terms of time and the use of technologies and resources.


Fig. 3. Prospects for woody bioenergy utilization in Japan from the aspects of the time and the use of the technologies and the resources. Reprinted from Biomass and Bioenergy, 29(5), Yoshioka et al., Woody biomass resources and conversion in Japan: The current situation and projections to 2010 and 2050, 336–346, Copyright (2005), with permission from Elsevier.

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2-3. Further considerations

In the future, the government, municipalities, and private sector are expected to become promoters of and stake-holders in the woody bioenergy utilization. It is therefore important not only to assess the available woody biomass resources according to their harvesting and transporting costs but also to establish energy-conversion systems that can use various types of waste biomass together. Moreover, the construction of low-cost harvesting and transporting systems suitable for Japan is essential.

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3. Feasibility of a harvesting system for logging residues by a processor and a forwarder

In this chapter, a "harvesting system for logging residues by a processor and a forwarder" is examined with the aim of constructing a system to harvest slashes mainly for energy use (Yoshioka et al. 2000). In this system, which was designed with reference to the proposal by Sundberg and Silversides (1989), a forwarder hauls slashes generated by a processor from the landing of a logging site (in the forest) to another landing alongside a forest road.

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3-1. The harvesting system for logging residues by a processor and a forwarder

This system consists of whole-tree yarding/skidding, processor limbing and bucking at a landing of a logging site, and forwarder hauling of logs and slashes separately on a strip road (Fig. 4). In the proposal by Sundberg and Silversides, which is suitable for countries, such as Sweden, with a gentle terrain, forwarders are used to recover slashes for energy use, and a system consisting of harvesters and forwarders is suggested for collecting logging residues. However, Japan is characterized by a steep topography and the need for a high density of forest roads; as such, the "harvesting system for logging residues by a processor and a forwarder" is more suitable for Japan. Harvesters cannot be used on such steep terrain. Basic theoretical equations for several operations have been constructed here with reference to existing studies (Sakai 1987, Sakai et al. 1995) in order to analyze the feasibility of this type of system for harvesting slashes. The parameters of the equations (from (3.1) to (3.15)) are summarized in Table 4.


Fig. 4. Harvesting system for logging residues by a processor and a forwarder. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Feasibility of a harvesting system for logging residues as unutilized forest biomass. 5(2), 2000, 59–65. Yoshioka, T, Iwaoka, M, Sakai, H, Kobayashi, H, Fig. 1. © 2000, Springer Japan.

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Table 4. Parameters of the basic theoretical equations (from (3.1) to (3.15)). Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Feasibility of a harvesting system for logging residues as unutilized forest biomass. 5(2), 2000, 59–65. Yoshioka, T, Iwaoka, M, Sakai, H, Kobayashi, H, Table 1. © 2000, Springer Japan.

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3-1A. Processor limbing and bucking

The volume of logs (EP, m3/d) and the weight of slashes (EPS, kgDM/d; DM: dry mass) processed per day are expressed as:

EP = 3600·cP·DP ·VP/CTP (3.1)

EPS = 3600·cP·DP ·WP/CTP (3.2)

3-1B. Forwarder hauling of logs and slashes

The volume of logs (EF, m3/d) and the weight of slashes (EFS, kgDM/d) hauled by a forwarder per day from a landing of a logging site to another landing alongside a forest road per day are expressed as:

EF = 3600·cF·DF ·VF/CTF (3.3)

EFS = 3600·cFS·DFS ·WFS/CTFS (3.4)

One cycle consists of loading in the forest, running downward fully-loaded on a strip road, unloading alongside a forest road, and running upward with no load; the cycle times for hauling logs (CTF, s/cycle) and slashes (CTFS, s/cycle) are then expressed as:

CTF = L·(1/v1 + 1/v2) + TL + TU (3.5)

CTFS = L·(1/v1 + 1/v2) + TLS + TUS (3.6)

3-1C. Energy consumption

It is clearly not efficient to harvest the slashes if the energy input for harvesting slashes is more than the energy output of the slash biomass. In light of the conclusions from existing studies, such as the work edited by Shibata and Kitani (1981), which showed that energy input was several times more than the output in the case of alcoholizing wood, the energy consumption for collecting logging residues and the proportion of energy input to output must be evaluated carefully.

The energy input for harvesting slashes (HFS, MJ/d) is defined as the fuel consumption per day for hauling slashes (FFS, cm3/d) converted into the calorific value, so HFS is expressed as:

HFS = uFS ·(FFS/1000) (3.7)

and FFS is expressed as:

FFS = 3600·cFS·DFS ·CFFS/CTFS (3.8)

When the fuel consumption of each element operation is regarded as being proportional to the operating time, then the fuel consumption per cycle for hauling slashes (CFFS, cm3/cycle) is expressed as:

CFFS = a1·L/v1 + a2·L/v2 + aLS·TLS + aUS·TUS (3.9)

In terms of the calorific value of wood per unit weight, the more moisture the wood contains, the lower its calorific value (Forestry Experiment Station (ed.) 1982). However, the potential energy of slashes is examined by converting dry weight of slashes into calorific value.

The potential energy output of the slash biomass (HS, MJ/d) is defined as EFS converted into the calorific value, so HS is expressed as:

HS = uS·EFS (3.10)

The ratio of the energy input for harvesting slashes to the potential energy output of the slash biomass (p, %) is expressed as:

p = (HFS/HS)·100 (3.11)

p is defined as the "energy input rate" of hauling slashes. When p is greater than 100%, that is, energy input is in excess of output, then it is no longer efficient to harvest slashes as a source of energy.

3-1D. Cost estimation

The cost of hauling slashes per unit weight (CWFS, US$/kgDM) is expressed as:

CWFS = CFS/EFS (3.12)

and the cost of hauling slashes per day (CFS, US$/d) is expressed as:

CFS = (P + M + FDFS (3.13)

The longer the whole-tree yarding/skidding distance, the more likely it is that transportation energy and the cost of harvesting slashes will increase. However, it is assumed that the energy and cost of carrying slashes to the nearest landing of a logging site does not need to be considered since slashes are carried along with stems during whole-tree yarding/skidding.

3-1E. Weight of slashes

When the weight of slashes per whole tree (WP, kgDM/tree) is considered proportional to the volume of logs per whole tree (VP, m3/tree), WP is expressed as:

WP = k·VP (3.14)

where k is a proportional coefficient (kgDM/m3). Since k is interpreted as the weight of slashes per unit volume of logs processed, it can be regarded as a value specific to the type of tree. In the estimation of quantity of logging residues per annum in Japan performed by the Forestry Agency, residues are classified into "tops," "branches," and "others" (Forestry Science and Technology Promotion Center 1985). However, in this study, only "tops" and "branches" are considered as slashes generated during processor limbing and bucking, so k is expressed as:

k = mk·(r1 + r2)/{100 – (r1 + r2 + r3)} (3.15)

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3-2. Materials and methods

To test the theoretical equations (from (3.1) to (3.15)) at an actual logging site, a field experiment was carried out at the site of a thinning operation conducted by the Toyoma-cho Forest Owner's Association in Miyagi Prefecture on July 23–24, 1997 Table 5). Although the expected period of the thinning operation in Table 5 was from July 22 to August 12, trees to be thinned were felled in the previous spring to reduce the weight of the logs by allowing them to dry in the sun. The logging system at the site consisted of whole-tree skidding by one skidder, limbing and bucking by one processor (NIAB, Sweden), and hauling on a strip road by one forwarder (RMF-CH, Oikawa Motors Co., Ltd., Japan). There was one operator per machine, and two chain saws were used supplementally.

The operation times for processor limbing, bucking, and forwarder hauling of logs, respectively, and the volume of logs were measured. Tests were conducted using a forwarder to haul slashes (Fig. 5), and the operation times, weight of slashes, and fuel consumption of each operation were measured.

Table 5. Outline of the investigated site. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Feasibility of a harvesting system for logging residues as unutilized forest biomass. 5(2), 2000, 59–65. Yoshioka, T, Iwaoka, M, Sakai, H, Kobayashi, H, Table 2. © 2000, Springer Japan.

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Fig. 5. Experimenting with a forwarder hauling of slashes. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Feasibility of a harvesting system for logging residues as unutilized forest biomass. 5(2), 2000, 59–65. Yoshioka, T, Iwaoka, M, Sakai, H, Kobayashi, H, Fig. 2. © 2000, Springer Japan.

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3-3. Results

Table 6 shows the data collected from the field experiment.

3-3A. Processor limbing and bucking

Fourteen trees were limbed and bucked during the total observation time of 12,445 seconds. From the processor limbing and bucking data in Table 6 and given cP = 1 and DP = 6, the EP of Eq. (3.1) and EPS of Eq. (3.2) were calculated as 31.23 m3/d and 1,189 kgDM/d, respectively. Setting the modification coefficient, cP, equal to 1 indicates "standard" operations. In other words, when "standard" operations were conducted for 6 hours a day, the processing productivity was 31.23 m3/d and the weight of slashes generated simultaneously was 1,189 kg/d on a dry weight basis.

Table 6. Data collected from the field experiment. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Feasibility of a harvesting system for logging residues as unutilized forest biomass. 5(2), 2000, 59–65. Yoshioka, T, Iwaoka, M, Sakai, H, Kobayashi, H, Table 3. © 2000, Springer Japan.

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3-3B. Forwarder hauling of logs

Three cycles of hauling were observed during 8,590 seconds. Using the data in Table 6 for forwarder hauling of logs, the cycle time, CTF (s/cycle) of Eq. (3.5), was calculated as:

CTF = 2.28·L + 1821 (3.16)

Using Eq. (3.16) and Table 6, the volume of logs hauled per day, EF (m3/d) of Eq. (3.3), was calculated as:

EF = 3600·cF·DF ·5.53/(2.28·L + 1821) (3.17)

3-3C. Experiment on forwarder hauling of slashes

(a) Operating time

One cycle of forwarder hauling of slashes was observed during 3,651 seconds. From the data in Table 6, the cycle time, CTFS (s/cycle) of Eq. (3.6), was calculated as:

CTFS = 2.28·L + 2874 (3.18)

Using Eq. (3.18) and Table 6, the weight of slashes hauled per day, EFS (kgDM/d) of Eq. (3.4), was calculated as:

EFS = 3600·cFS·DFS ·425.3/(2.28·L + 2874) (3.19)

(b) Fuel consumption

Fuel (light oil) consumption of each operation was measured and divided by the time for each operation to calculate the fuel consumption per unit time (see Table 6). Based on this fuel consumption data, the fuel consumption per cycle for hauling slashes, CFFS (cm3/cycle) of Eq. (3.9), was calculated as:

CFFS = 2.58·L + 1351 (3.20)

Using Eqs. (3.18) and (3.20), the fuel consumption per day for hauling slashes, FFS (cm3/d) of Eq. (3.8), was calculated as:

FFS = 3600·cFS·DFS ·(2.58·L + 1351)/(2.28·L + 2874) (3.21)

(c) Cost calculation

Given that the price of light oil per liter was 0.70 US$ and the relative prices of other oils, such as a ratio of machine oil cost to fuel cost of 0.2 (Sakai 1987), the fuel cost per hour, F (US$/h), was calculated as:

F = 8.4 × 10–4·FFS/ DFS (3.22)

Labor cost per hour, P, was 25.77 US$/h (from personal communication) and machine cost per hour, M, was 34.43 US$/h from the machine price (Forestry Mechanization Society (ed.) 1996) and the standard productivity list (Umeda et al. 1982). Therefore, using Eq. (3.22), P = 25.77 US$/h, and M = 34.43 US$/h, the cost of hauling slashes per day, CFS (US$/d) of Eq. (3.13), was calculated as:

CFS = (60.20 + 8.4 × 10–4·FFS/ DFSDFS (3.23)

(d) Weight of slashes

In this chapter, the weight of slashes is considered on a dry weight basis. However, during the field experiment, the green weight of slashes (dried in the sun for a few months after felling) was measured and converted into dry weight by estimating the water content. Based on five samples of logs, the green weight of logs per cubic meter was calculated to be 485.7 kg/m3. Therefore, assuming that the water content was 50% (Forestry Experiment Station (ed.) 1982), the dry weight of logs of the Cryptomeria japonica D. Don ("sugi," or Japanese cedar) at the site per cubic meter, mk, was calculated to be 323.8 kg/m3.

In the field, some limbing had been done at felling during the previous spring and the trees left to dry in the sun; consequently, the exact ratio of the weight of tops and branches to the whole-tree weight could not be obtained. The ratios of the weight of tops, r1, branches, r2, and others, r3, to the weight of a whole tree of the Cryptomeria japonica D. Don are considered to be 2, 8, and 5%, respectively, on the basis of data used by the Forestry Agency to calculate the quantity of logging residues (Forestry Science and Technology Promotion Center 1985). From mk = 323.8 kgDM/m3, r1 = 2%, r2 = 8%, and r3 = 5%, the weight of slashes per unit volume of logs processed, k of Eq. (3.15), was calculated to be 38.1 kgDM/m3. Using k = 38.1 kgDM/m3 and data from Table 6, the weight of slashes per whole tree, WP of Eq. (3.14), was calculated to be 45.7 kgDM/tree.

In this experiment, the green weight of slashes hauled during one cycle was measured as 638.0 kg. Therefore, taking the water content of both slashes and logs into account, the dry weight of slashes hauled per cycle, WFS, was calculated as 425.3 kgDM/cycle.

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3-4. Discussion

3-4A. The harvesting system for logging residues by a processor and a forwarder

Given that one operator is in charge of the processor for limbing and bucking and a second operator is in charge of the forwarder hauling of logs and slashes, the relation between DP (effective working time of processor per day), DF (effective working time of forwarder hauling of logs per day), and DFS (effective working time of forwarder hauling of slashes per day) is expressed as:

DP = DF + DFS (3.24)

The volume of logs hauled by the forwarder per day never exceeds the volume of logs limbed and bucked by the processor per day. If the efficiency of the forwarder is higher than that of the processor, the forwarder still has time to spare after hauling all the logs processed and can haul slashes during this spare time. Given that the forwarder hauls all the logs processed during the day, the relation between EP (volume of logs processed per day) and EF (volume of logs hauled per day) is expressed as:

EP = EF (3.25)

The weight of slashes generated during limbing and bucking is considered to be proportional to the volume of logs processed and a proportionality coefficient, k (weight of slashes per unit volume of logs processed), is used to express the relation between EP and EPS (weight of slashes processed per day):

EPS = k·EP (3.26)

The relation between EPS and EFS (weight of slashes hauled per day) is expressed as:

EFS = α·EPS (3.27)

where α is defined as the "rate of slash harvesting," and equals 1 when the forwarder hauls all of the slashes generated by the processor.

If the value of α is known, the ratio of the weight of slashes hauled to that of slashes processed can be estimated (hauling of slashes by the forwarder is carried out during spare time, as mentioned above). Therefore, α is regarded as an index of the capability to haul slashes by utilizing the spare time of the forwarder.

From Eqs. (3.17), (3.19), (3.24), (3.25), (3.26), and (3.27), the volume of logs hauled per day, EF (m3/d), is calculated as:

EF = cF·cFS· DP/{(1.15 × 10–4·cFS + 1.49 × 10–6·α·k· cFL

+ (9.15 × 10–3·cFS + 1.88 × 10–3·α·k· cF)} (3.28)

Therefore, EF can be expressed as a function of L (hauling distance).

Using k = 38.1 kgDM/m3 and given cF = cFS = 1 and DP = 6, which means that the "standard" (as modification coefficients cF = cFS = 1) operation of the forwarder is carried out for 6 hours a day, the relation between L and EF is shown in Fig. 6 for rates of slash harvesting of α = 0, 0.5, and 1. The value of k is specific to the kind of tree, and k in Eq. (3.28) can be adjusted for various types of trees, such as for pines and broad-leaved trees. The modification coefficients cF and cFS should be adjusted for type of tree, volume of logs, and weight of slashes hauled by the forwarder.


Fig. 6. Relationship between hauling distance of forwarder, L, and volume of logs hauled per day, EF. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Feasibility of a harvesting system for logging residues as unutilized forest biomass. 5(2), 2000, 59–65. Yoshioka, T, Iwaoka, M, Sakai, H, Kobayashi, H, Fig. 3. © 2000, Springer Japan.

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α = 0 means that the forwarder hauls only logs and no slashes at all. At a site where a highly productive machine, such as a single-grip processor, is used, it is possible that the operating point in Fig. 6 would have an EP coordinate above the curved line for α = 0. In such a case, the performance of the processor is higher than that of the forwarder, so some logs remain at the landing of the logging site when both machines are operated for the same amount of time. Therefore, the forwarder must be operated longer than the processor. Examples of possible measures for resolving this problem are listed as follows:

1) Shorten the hauling distance until the coordinate of the operating point (L, EP) shown in Fig. 6 is below the curved line for α = 0;

2) Introduce a large-sized forwarder capable of coping with the high productivity of the processor;

3) Add another forwarder.

α = 1 means that the forwarder hauls all of logs and all slashes. Therefore, the curved line for α = 1 in Fig. 6 indicates the relation between the hauling distance and the volume of logs hauled per day when the forwarder is expected to haul all of the slashes as well as all of the logs. When the productivity of the processor is plotted below the curved line for α = 1, the performance of the forwarder is higher than that of the processor. So, even if the forwarder hauls all logs and all slashes, there is still spare time.

EF in Fig. 6 can be replaced with EP under the condition that the forwarder hauls all of the logs limbed and bucked by the processor during the day. In the case where L and EP are given, the point (L, EP) can be plotted on this graph. If the point (L, EP) is below the curved line for α = 1, then all of the slashes processed in the site can be hauled by the forwarder. If the point (L, EP) is between the curved lines for α = 0 and α = 1, the ratio of the weight of slashes harvested to the weight of slashes generated can be found by estimating the value of α from the graph. For example, at a site where L = 500 m and EP = 30 m3/d, α is approximately 0.5; it can therefore be estimated that about 50% of slashes processed can be hauled to a landing alongside a forest road. At the investigated site, α was found to be about 0.95 when L = 191.4 m and EP = 31.23 m3/d were used in Fig. 6, thereby ascertaining that almost all the slashes could be hauled.

3-4B. Energy analysis

From Eqs. (3.7), (3.10), (3.19), and (3.21), the "energy input rate" of hauling slashes, p (%) of Eq. (3.11), is calculated as:

p = (uFS/uS)·(6.07 × 10–4·L + 3.18 × 10–1) (3.29)

Therefore, p can be expressed as a function of L. Since the value of uS is specific to the type of tree, Eq. (3.29) can be applied for various kinds of trees.

The hauling distance at the investigated site was 191.4 m. When the calorific value of light oil (fuel of the forwarder) per unit volume and the higher calorific value of the Cryptomeria japonica D. Don (dried thoroughly) per unit weight are considered to be 38.49 MJ/dm3 and 19.54 MJ/kgDM, respectively (Honda 1986), using L = 191.4 m, uFS = 38.49 MJ/dm3, and uS = 19.54 MJ/kgDM, the p of Eq. (3.29) is calculated as 0.85%. Consequently, it was confirmed that there is a potential for the efficient energy utilization of slashes. By fixing the desired "energy input rate" of hauling slashes by a hauling distance beforehand, the optimum hauling distance can be decided, enabling effective planning of a forest road system.

In this chapter, only the simplest case, where thoroughly dried slashes are converted directly into energy, is considered. With respect to energy input, the energy consumption of the forwarder operator must also be taken into account. Energy conversion efficiency must be strictly examined for the practical realization of a system to harvest logging residues for energy use.

3-4C. Cost analysis

From Eqs. (3.19), (3.21), and (3.23), the cost of hauling slashes per unit weight, CWFS (US$/kgDM) of Eq. (3.12), is calculated as:

CWFS = {(8.96 × 10–5 + 5.06 × 10–6·cFS L

+ (1.13 × 10–1 + 2.65 × 10–3·cFS)}/ cFS (3.30)

Therefore, CWFS can be expressed as a function of L.

Using L = 191.4 m and given cFS = 1, which means that the "standard" operation of the forwarder is carried out, CWFS of Eq. (3.30) is calculated as 0.134 US$/kgDM. By considering the value of cFS with regard to the load of slashes, Eq. (3.30) can be applied for various kinds of trees.

It has been reported that in Japan, slashes as fuel are worth several yen per kg on a green weight basis (Honda 1986; the exchange rate was roughly 115 yen to the U.S. dollar as of July 1997), so the cost per unit weight for hauling slashes must be reduced. To increase the hauling efficiency, it may be effective to enhance the load capacity of the forwarder. In the field experiment, the average volume of logs hauled in one cycle, 5.53 m3, was converted into 1,791 kg on a dry weight basis, which was 4.21-fold greater than the weight of logging residues hauled per cycle, 425.3 kg; therefore, the efficiency of hauling the residues was less than 25% of that for hauling logs. One proposed solution to this problem is that the volume of slashes be decreased by introducing a chipper. In the future, another forwarder which has chipping capability and is dedicated to harvesting only slashes needs to be developed and examined in terms of energy and cost.

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3-5. Further considerations

Steady progress in the utilization of forest biomass is being made in Nordic countries in general and in Sweden in particular where woody biomass accounts for more than 20% of the primary energy supply. Within the framework of a project for the expansion of biomass utilization, several studies on a chipper (Asikainen and Pulkkinen 1998) are ongoing as basic research on the energy utilization of slashes. However, these systems are for countries with a gentle terrain; a system suitable for countries with a steep terrain, such as Japan, needs to be developed.

It is also desirable that a method for the efficient use of slashes is developed and used in practical applications. It is effective to harvest slashes in and around an operating site as a source of local energy, although this approach is associated with concern that nutrients would be removed from the forest. Possible solutions to this problem, such as, returning slashes to forest areas to conserve the nutrients and control weeds, need to be examined.

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4. A case study on the costs and fuel consumption of harvesting, transporting, and chipping chains for logging residues in Japan

As a follow-up to the analysis in Chapter 3, the focus of Chapter 4 is an examination of a "harvesting and transporting system for logging residues" based on data collected from field experiments and existing studies (Yoshioka et al. 2002a, 2006a). This system, in which the process of chipper comminuting is newly introduced and a truck transports biomass to an energy-conversion plant, was constructed with reference to three European countries, i.e., the U.K. (Hunter et al. 1999), Sweden (Andersson 1999), and Finland (Korpilahti 1998). Utilization of bioenergy is making steady progress in these countries. The feasibility of the system in Japan is discussed from the standpoints of cost and energy, and the system is compared with those of these European countries. A preliminary sensitivity analysis to the system is also carried out, followed by a discussion of the problems for realization.

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4-1. Materials and methods

4-1A. A harvesting and transporting system for logging residues

This system, which was designed taking due consideration of the present situation of Japanese forestry, includes the following processes (Fig. 7):

1) Whole-tree yarding/skidding: The machine used in this process is not particularly limited here, while the operation is usually conducted by yarders, tower-yarders, or tractors in Japan. Compared with conventional machines like yarders and tractors, the use of tower-yarders has been increasing in Japanese forestry, especially for the purpose of thinning;

2) Processor limbing and bucking: This operation is conducted at the landing of a logging site (in a forest);

3) Forwarder hauling: A forwarder hauls logs and slashes/chips on a strip road from the landing of a logging site to another landing alongside a forest road. In Japan, low-grade strip roads complement the low density of forest road networks because the construction cost of forest roads is too high. However, trucks cannot travel on such low-grade strip roads, so two landings are inevitably essential for this system;

4) Truck transporting: A 4-ton truck transports slashes/chips on a forest road and a public road;

5) Energy-conversion: There is no energy-conversion plant in Japan that is suitable for receiving logging residues as fuel; this process is therefore only provisional here.


Fig. 7. Harvesting and transporting system for logging residues. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Cost, energy and carbon dioxide (CO2) effectiveness of a harvesting and transporting system for residual forest biomass. 7(3), 2002, 157–163. Yoshioka, T, Aruga, K, Sakai, H, Kobayashi, H, Nitami, T, Fig. 1. © 2002, Springer Japan.

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In terms of the distances of hauling and transporting, these are assumed to range from 100 to 1,000 m and from 20 to 80 km for the case discussed in this chapter, respectively, on the basis of the actual situation of Japanese forestry and the results of a past questionnaire sent to logging enterprises (Nitami and Kamiizaka 1982).

In addition to the five processes listed above, chipper comminuting is incorporated into the system with the dual purpose of enhancing the hauling and transporting efficiency of logging residues and carrying the residues in the form of chips to an energy-conversion plant. Chipper comminuting, however, increases the cost and energy of the system. Therefore, the system is classified into three types, namely, "In-forest," "Landing," and "Plant," according to the operating sites of chipper comminuting, i.e., a landing in a forest, a landing alongside a forest road, and an energy-conversion plant, respectively (Fig. 8). Mobile chippers are used in the "In-forest" and "Landing" systems, while a large-sized chipper is used in the "Plant" system. The effect of the difference between the operating sites of chipper comminuting on the system's cost and fuel consumption per unit mass of biomass on a dry basis is also examined.


Fig. 8. Three types of the systems classified according to the operating sites of chipper comminuting. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Cost, energy and carbon dioxide (CO2) effectiveness of a harvesting and transporting system for residual forest biomass. 7(3), 2002, 157–163. Yoshioka, T, Aruga, K, Sakai, H, Kobayashi, H, Nitami, T, Fig. 2. © 2002, Springer Japan. Reprinted from Biomass and Bioenergy, 30(4), Proceedings of the third annual workshop of Task 31 'Systainable production systems for bioenergy: Impacts on forest resources and utilization of wood for energy' October 2003, Flagstaff, Arizona, USA, Yoshioka et al., A case study on the costs and the fuel consumption of harvesting, transporting, and chipping chains for logging residues in Japan, 342–348, Copyright (2006), with permission from Elsevier.

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4-1B. Description of machines

With regard to forwarder hauling, the experiment on hauling logging residues by a wheel-type forwarder with a 2,000 kg load capacity (RM8WDB-6HG, Oikawa Motors Co., Ltd., Japan) was carried out in the Takizawa Experimental Forest of Iwate University, Iwate Prefecture (Fig. 9). The logging residues were fresh tops and branches of a 26-year-old Cryptomeria japonica D. Don ("sugi," or Japanese cedar). The mass of logging residues at the experimental site was about 50 Mg/ha on a dry basis. The operation time, mass of slashes, and fuel (light oil) consumption of each operation were measured, and the water content of slashes was estimated by drying several samples thoroughly.

An experiment on comminuting slashes by a mobile chipper was also carried out. The chipper used in this experiment was a test model manufactured by the Oikawa Motors that was equipped with an Isuzu 6BD1 diesel engine (displacement and power output are 5,785 cm3 and 79.4 kW/2,200 rpm, respectively). As in the experiment on forwarder hauling, the operation time, mass of chips, and fuel (light oil) consumption were measured, and the water content of chips was estimated. An additional parameter, the "volume reduction rate" (see Table 9), was also measured for the purpose of determining how the efficiency of hauling and transporting logging residues was enhanced by chipper comminuting.

This is the first time that such a large-sized chipper as the one described here has ever been put into operation in Japanese forestry. Therefore, the process of comminuting by a large-sized chipper is discussed taking the results of an existing study into account in which the performance of a tub grinder (TG 400A, Vermeer Manufacturing Company, USA) was investigated at a grading site. The tub grinder was introduced in order to recycle logged trees effectively at the site.


Fig. 9. Experimenting with a forwarder hauling of slashes. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Cost, energy and carbon dioxide (CO2) effectiveness of a harvesting and transporting system for residual forest biomass. 7(3), 2002, 157–163. Yoshioka, T, Aruga, K, Sakai, H, Kobayashi, H, Nitami, T, Fig. 3. © 2002, Springer Japan. Reprinted from Biomass and Bioenergy, 30(4), Proceedings of the third annual workshop of Task 31 'Systainable production systems for bioenergy: Impacts on forest resources and utilization of wood for energy' October 2003, Flagstaff, Arizona, USA, Yoshioka et al., A case study on the costs and the fuel consumption of harvesting, transporting, and chipping chains for logging residues in Japan, 342–348, Copyright (2006), with permission from Elsevier.

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4-2. Results

Tables 7, 8, 9 present the data collected from the field experiments and existing studies. The total cost of each process, namely, hauling, transporting, and comminuting, was calculated separately by aggregating the labor, machine, and fuel costs in these tables.

Table 10 presents the cost and fuel consumption in each of the three systems (the distances of forwarder hauling and truck transporting are 100–1,000 m and 20–80 km, respectively) as well as the "energy input rate" (see footnote of the table), the cost per MWh of bioenergy, and the results of a preliminary sensitivity analysis. In Table 11, data on the cost and CO2 emission, which are obtained from the fuel consumption, per MWh of bioenergy are compared to data for three European countries, i.e., the U.K., Sweden, and Finland.

Table 7. Data collected from the field experiments and existing studies: (a) Forwarder hauling. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Cost, energy and carbon dioxide (CO2) effectiveness of a harvesting and transporting system for residual forest biomass. 7(3), 2002, 157–163. Yoshioka, T, Aruga, K, Sakai, H, Kobayashi, H, Nitami, T, Table 1(a). © 2002, Springer Japan. Reprinted from Biomass and Bioenergy, 30(4), Proceedings of the third annual workshop of Task 31 'Systainable production systems for bioenergy: Impacts on forest resources and utilization of wood for energy' October 2003, Flagstaff, Arizona, USA, Yoshioka et al., A case study on the costs and the fuel consumption of harvesting, transporting, and chipping chains for logging residues in Japan, 342–348, Copyright (2006), with permission from Elsevier.

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Table 8. Data collected from the field experiments and existing studies: (b) Truck transporting.1 Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Cost, energy and carbon dioxide (CO2) effectiveness of a harvesting and transporting system for residual forest biomass. 7(3), 2002, 157–163. Yoshioka, T, Aruga, K, Sakai, H, Kobayashi, H, Nitami, T, Table 1(b). © 2002, Springer Japan. Reprinted from Biomass and Bioenergy, 30(4), Proceedings of the third annual workshop of Task 31 'Systainable production systems for bioenergy: Impacts on forest resources and utilization of wood for energy' October 2003, Flagstaff, Arizona, USA, Yoshioka et al., A case study on the costs and the fuel consumption of harvesting, transporting, and chipping chains for logging residues in Japan, 342–348, Copyright (2006), with permission from Elsevier.

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Table 9. Data collected from the field experiments and existing studies: (c) Chipper comminuting. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Cost, energy and carbon dioxide (CO2) effectiveness of a harvesting and transporting system for residual forest biomass. 7(3), 2002, 157–163. Yoshioka, T, Aruga, K, Sakai, H, Kobayashi, H, Nitami, T, Table 1(c). © 2002, Springer Japan. Reprinted from Biomass and Bioenergy, 30(4), Proceedings of the third annual workshop of Task 31 'Systainable production systems for bioenergy: Impacts on forest resources and utilization of wood for energy' October 2003, Flagstaff, Arizona, USA, Yoshioka et al., A case study on the costs and the fuel consumption of harvesting, transporting, and chipping chains for logging residues in Japan, 342–348, Copyright (2006), with permission from Elsevier.

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Table 10. The harvesting cost and the fuel consumption in each of the three systems, including the harvesting cost per MWh of bioenergy, the "energy input rate," and the preliminary sensitivity analysis. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Cost, energy and carbon dioxide (CO2) effectiveness of a harvesting and transporting system for residual forest biomass. 7(3), 2002, 157–163. Yoshioka, T, Aruga, K, Sakai, H, Kobayashi, H, Nitami, T, Table 2. © 2002, Springer Japan. Reprinted from Biomass and Bioenergy, 30(4), Proceedings of the third annual workshop of Task 31 'Systainable production systems for bioenergy: Impacts on forest resources and utilization of wood for energy' October 2003, Flagstaff, Arizona, USA, Yoshioka et al., A case study on the costs and the fuel consumption of harvesting, transporting, and chipping chains for logging residues in Japan, 342–348, Copyright (2006), with permission from Elsevier.

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Table 11. Comparison with three European countries in terms of harvesting cost and CO2 emission per MWh of bioenergy. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Cost, energy and carbon dioxide (CO2) effectiveness of a harvesting and transporting system for residual forest biomass. 7(3), 2002, 157–163. Yoshioka, T, Aruga, K, Sakai, H, Kobayashi, H, Nitami, T, Table 3. © 2002, Springer Japan.

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4-3. Discussion

4-3A. Cost

Of the three systems proposed in the chapter, the "In-forest" type has the lowest cost per unit weight of logging residues and the "Plant" type has the highest (Table 11). In other words, the earlier chipper comminuting can be incorporated into the system, the lower the total cost of the system. Consequently, the margin of chips to slashes in forwarder hauling and truck transporting is larger than that of large-sized to mobile in chipper comminuting.

In Japan, the unit price of electricity was 148 US$/MWh as of 2000. A considerably high proportion of the costs per MWh of bioenergy in the three systems can be accounted for by the price of electricity. This factor is especially relevant in the "Plant" type where it is possible that the cost exceeds the price of electricity depending on the hauling conditions and transporting distances of the system. The underlying reasons for this development are:

· The very small load capacities and chipper power on studied machines compared to European machines;

· Machinery that is not fully adapted to the work;

· Operators with little experience with forest fuel recovery.

Therefore, at the moment, the outlook for realization of a harvesting and transporting system for logging residues in Japan is not favorable from the standpoint of cost. This is relevant to forestry conditions in Japan and shows that the studied system has low productivity and is not financially sound. However, implementation of better machines and well-trained operators might change the results substantially. The conclusion to be drawn is, therefore, that improvement of the system, including the accumulation of field experience, such as increased skills in operating the machines and technological improvements in machinery, is essential. Nationwide field trials are currently ongoing.

Hektor (1998) reported that the energy generation costs per MWh for fossil fuels and for logging residues from final felling were 5.33–18.7 US$/MWh and 16.0 US$/MWh, respectively. The energy generation costs consisted of the capital, R&M (repair and maintenance), and operating costs, with all these costs being almost at the same level and very small compared with the costs for logging residues listed in Table 10. This comparison indicates that the procurement cost greatly influences the total cost with regard to logging residues for energy and that in order to realize the energy utilization of logging residues in Japan, it is essential to develop low-cost harvesting, transporting, and chipping techniques. The introduction of multifunctional machines is one possibility. For example, a chipper-forwarder has both chipping and forwarding functions, while a chipper-truck carries out both chipping and transporting operations. Implementation of such machines will increase productivity.

Table 11 shows that there is a large difference between Japan and the three European countries in terms of the cost per MWh of bioenergy, with almost all the costs given for the European countries being around 10 US$/MWh regardless of the operation site of chipper comminuting and the type of machine. According to Hunter et al. (1999), the procurement cost per unit energy of biomass to an energy-conversion plant is the same level as those of fossil fuels, i.e., coal, oil, and gas. This can be interpreted to mean that biomass as an energy resource is rather competitive against fossil fuels in these European countries. Accordingly, the cost of 10 US$/MWh level is a target for the system described in this chapter.

In the European countries, for example, bundlers for compressing logging residues (see Table 11) and trailers of the 30-ton class for transporting are used so that the hauling and transporting efficiency is fairly high. Therefore, it is still possible to reduce the differential of the cost between Japan and the European countries by introducing the process of compressing into the system. The bundler will reduce the total cost. However, the bundler is applicable only for gentle terrain, such as that found in Nordic countries, so the development of a machine and a system suitable for the steep topography of Japan is necessary.

4-3B. Fuel consumption and CO2 emission

The "Plant" type has the highest fuel consumption per unit weight of logging residues, with the "In-forest" and "Landing" types being lower and almost at the same level (Table 10). This indicates that the margin of the landing alongside a forest road to the landing in a forest at the site of chipper comminuting is practically equal to the margin of chips to slashes in forwarder hauling.

In terms of "energy input rate," all three systems are generally at single-figure-% levels. Consequently, the realization of the harvesting and transporting system for logging residues in Japan presents no specific problem from the point of view of the "energy input rate," i.e., the input and output of energy in the system

In terms of the CO2 emission per MWh of bioenergy (Table 11), Japan is almost on the same level as Finland. According to Korpilahti (1998), if the target of substituting 1.5 million toe (tons of oil equivalent) of fossil fuels in Finland by 2010 is fulfilled by increasing the use of bioenergy, the reduction in CO2 emissions will be 6.9% of the total emissions in 1996. Korpilahti also shows that CO2 emissions are 341 kgCO2/MWh for coal and 304 kgCO2/MWh for oil. Therefore, it is possible for Japan to reduce domestic CO2 emissions by utilizing logging residues as alternative energy resources.

However, in all of the European countries discussed in this chapter, biomass provides a share of the domestic energy supply, and the governmental target to promote the use of bioenergy is consistently held up. These facts suggest that realization of bioenergy utilization in Japan necessitate government support in various forms such as, for example, taxing CO2 emissions from fossil fuels. Development of the machines and systems as a government-subsidized project focused on global warming countermeasures is also a possibility.

4-3C. Preliminary sensitivity analysis

Increasing the efficiency in the process of transporting is examined (see Table 10 and footnotes), especially because the transporting cost is too high. As a result, the total costs are reduced almost to half (Table 10) and the differential between Japan and the European countries is also reduced (Table 11), which in turn indicates the importance of the load size of hauling and transporting vehicles. Therefore, the introduction of large-sized trailers, as shown in Table 10, and the construction of a network of high-grade forest roads so that large-sized trailers can travel directly to the landings of logging sites are necessary. In addition, the introduction of bundlers or chipper-forwarders should be considered as a measure to reduce the total harvesting cost by increasing the efficiency of the comminuting and hauling process.

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4-4. Further considerations

The harvesting cost must be reduced by various measures, such as introducing the process of compressing slashes into the system. The bundler, for example, will reduce the total cost. However, the current bundling system is applicable only for gentle terrain, such as that found in Nordic countries, necessitating the development of a machine and a system suitable for the steep topography of Japan. On the other hand, in terms of the input and output of energy, a more detailed analysis, such as an LCI analysis that considers the life cycle assessment (LCA) method, is necessary to provide a scientific basis for the premise that biomass as an energy resource has a much lower environmental impact over its entire life cycle than fossil fuels.

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5. Comminution of logging residues with a tub grinder: Calculation of the productivity and procurement cost of wood chips

For logging residues to be utilized as sources of energy, it is necessary to comminute them so that their forwarding and transporting efficiency can be enhanced. In addition, residues should be pretreated, i.e., chipped or crushed, in an energy-conversion plant before being converted into usable energy in the form of, for example, heat, electricity, and liquid fuel.

Logging residues can be comminuted in a forest, at a roadside landing, or at an energy-conversion plant. Various kinds of chippers and crushers for logging residues have been developed and examined worldwide under field conditions (Asikainen and Pulkkinen 1998, Delgado and Giraldo 1995, Desrochers et al. 1993, Hall et al. 2001). In several countries, the technique has already taken final form, and operating manuals have been published (Alakangas et al. 1999, FAO 1976, Folkema 1989). In recent years, chippers and crushers for comminuting logging residues and non-marketable thinned trees have been being diffused in Japanese forestry. Increasing nationwide interest in bioenergy utilization is one reason for this development, and some small-sized and medium-sized chippers have been tested at the local government level in order to define the productivity of these machines and the quality of the chips obtained.

When a large-sized chipper or crusher is introduced, economies of scale will be achieved, i.e., the comminuting cost of a large-sized chipper or crusher is expected to be lower than that of a small-sized one. However, few trials on comminuting logging residues by a large-sized chipper or crusher with an engine output higher than approximately 150 kW have been carried out in Japan. Data presented in Chapter 4, in which the appropriate site for comminuting logging residues from the viewpoint of the total procurement cost of wood chips was discussed, showed that the comminuting cost of a large-sized crusher was lower than that of a small-sized chipper. In the discussion of comminution by a large-sized crusher, reference was made to a study in which the performance of a tub grinder (TG400A, Vermeer Manufacturing Company, USA) was investigated at a grading site. In the cost calculation of the tub grinder, however, only the labor cost, the machine cost (expenses for depreciation and supplies), and the fuel cost incurred by the operation of the tub grinder itself were considered. Moriguchi et al. reported, based on their study of comminution by a medium-sized chipper with an engine output of 60.3 kW, that the sum of the cost of a grapple loader to feed logging residues into the chipper, that of carrying in, installing, and carrying out the chipper and the loader, and that of constructing a landing for the operation accounted for a considerably high proportion of the total chipping cost (Moriguchi et al. 2004). The results of this study suggest that those additional costs should be considered, particularly when calculating the cost of comminuting logging residues with a large-sized crusher, such as a tub grinder.

Therefore, the objective of this chapter is to investigate the following items by testing the comminution of logging residues with a tub grinder (Yoshioka et al. 2006b):

· Productivity of a large-sized crusher;

· Proportion of the total costs accounted by the cost of auxiliary machines, for example, a grapple loader, the cost of carrying in, installing, and carrying out the crusher and auxiliary machines, and the cost of constructing a landing;

· Calculation of the cost of comminuting logging residues collected at a landing and transporting wood chips;

· Balance of the processing capacity between the large-sized crusher and other machines, such as a yarding machine and auxiliary ones.

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5-1. Materials and methods

5-1A. Experimental site

The experiment was conducted at the Fukashiro Dam construction site, Yamanashi Prefecture, which is situated to the west of Tokyo. The site is located at the upper reaches of the Kazuno River, which forms part of the Sagami River system. Pulpwood was extracted from scrap trees generated during the course of building the dam, and residual material was comminuted by a tub grinder. In other words, the residual material was regarded to be logging residues. The scrap trees, which had to be disposed of in accordance with local government regulations, were collected from 18 ha Japanese cedar (Cryptomeria japonica D. Don) and broad-leaved tree stands that were to be submerged.

5-1B. Description of systems

The operation was divided into two systems, that is, a "COLLECT and SORT" system and a "COMMINUTE and TRANSPORT" one. After a certain amount of logging residues had been collected, the comminuting operation was carried out.

The "COLLECT and SORT" system consisted of felling with chain saws, collecting with a yarder (cable yarding system: endless Tyler system; maximum yarding distance: 460 m), bucking with chain saws, and sorting with a grapple loader. Pulpwood and logging residues were sorted and piled into separated heaps of pulpwood and residues, respectively. Here, logging residues were considered to be by-products of pulpwood production. In this sense, all of the costs associated with this system are attributed to the pulpwood produced. A time study of a yarder was carried out, and the balance of the processing capacity between this system and the "COMMINUTE and TRANSPORT" one is discussed.

In the "COMMINUTE and TRANSPORT" system, a grapple loader fed logging residues into a tub grinder, a tub grinder comminuted the logging residues (the screen size opening of a tub grinder was set at 5.0 cm), a bucket loader (a digging bucket of an excavator was replaced with a larger-sized bucket for the purpose of loading wood chips) loaded wood chips onto a truck, and a truck transported the wood chips. Therefore, these two loaders were regarded as auxiliary machines for the tub grinder in this system. The tub grinder was equipped with a conveyor to take wood chips directly into a truck. However, a bucket loader for loading chips was introduced because the mobility of the truck was considered to have priority. Time studies of the tub grinder and the two loaders were conducted, and the volume of the processed chips and fuel (light oil) consumption of each machine was measured. A bin (0.60 m long, 0.50 m wide, 0.60 m high, with a weight of 3.6 kg) was filled with chips, and the weight of the bin was also measured (scales: MODEL DS-261, Teraokaseiko Co., Ltd., Japan). Consequently, the green weight of the chips per unit volume could be calculated. Ten chip samples were taken to determine the moisture content of the chips. The green mass of each sample was measured, and the samples were then dried at 103 degrees Celsius for more than 24 h. The moisture content was determined by dividing the mass of water contained within the sample by the dry mass of the sample.

5-1C. Description of machines

The tub grinder (HD-9 Industrial Tub Grinder, DuraTech Industries International, Inc., USA, Fig. 10) is 7.72 m long, 2.49 m wide, and 2.62 m high and weighs 8,760 kg. Its engine (275 HP John Deere) has an output of 205.1 kW. The tub is 1.02 m deep, with a diameter at the top and bottom of 2.91 m and 2.29 m, respectively. A hammer mill crusher is positioned at the bottom of the tub. The grapple loader (base machine: EX120-5, Hitachi Construction Machinery Co., Ltd., Japan; grapple: GS90LHV, Iwafuji Industrial Co., Ltd., Japan, Fig. 11) is 7.58 m long, 2.50 m wide, and 2.72 m high and weighs 11,800 kg. Its engine output is 67.1 kW. The bucket loader (312B, Shin Caterpillar Mitsubishi Ltd., Japan, Fig. 12) is 7.57 m long, 2.89 m wide, and 2.83 m high and weighs 12,300 kg. Its bucket capacity and its engine output are 0.5 m3 and 66.9 kW, respectively. The maximum load volume of the truck was 40 m3. The operators of the respective machines had a significant amount of relevant work experience, and the landing was large enough for the operators to maneuver the machines at will.


Fig. 10. Tub grinder. Reprinted with permission from Croatian Journal of Forest Engineering, 27(2), Yoshioka, T et al., Comminution of logging residues with a tub grinder: Calculation of productivity and procurement cost of wood chips, 103–114, Fig. 1, © 2006, Forestry Faculty of Zagreb University.

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Fig. 11. Grapple loader. Reprinted with permission from Croatian Journal of Forest Engineering, 27(2), Yoshioka, T et al., Comminution of logging residues with a tub grinder: Calculation of productivity and procurement cost of wood chips, 103–114, Fig. 2, © 2006, Forestry Faculty of Zagreb University.

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Fig. 12. Bucket loader. Reprinted with permission from Croatian Journal of Forest Engineering, 27(2), Yoshioka, T et al., Comminution of logging residues with a tub grinder: Calculation of productivity and procurement cost of wood chips, 103–114, Fig. 3, © 2006, Forestry Faculty of Zagreb University.

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5-1D. Cost calculation

The total comminuting cost per m3 of the processed wood chips, TC (US$/m3), is expressed as:

where LAi (US$/h), Mi (US$/h), and Fi (US$/h) are the labor, machine, and fuel costs per hour, respectively, of each machine (i represents each machine, i.e., a tub grinder, a grapple loader, and a bucket loader); Pi (m3/h) is the productivity of each machine; CAi (US$) is the cost of carrying in, installing, and carrying out each machine; W (m3) is the whole amount of wood chips processed at the investigated site; CO (US$) is the cost of constructing a landing. The machine cost (expenses for depreciation and supplies), Mi, and the fuel cost, Fi, are calculated on the basis of the following two equations:

where MPi (US$), Hi (h/d), Di (d/y), and LIi (y) are the machine price, hours of operation per day, days of operation per year, and life of each machine, respectively; Si (US$/h) is the expense for supplies; FCi (dm3/h) is the fuel (light oil) consumption; 0.76 (US$/dm3) is the unit fuel price. Pi and FCi are calculated based on the results of the field experiment. LAi, CAi, W, CO, Hi, and Si were gathered by means of a questionnaire (note: the expense associated with the supplies of a tub grinder should have been investigated in detail (such as, what is the frequency of replacing old worn-out hammers with new ones?); this aspect needs further discussion).

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5-2. Results

This time study was considered to be finished when the tub grinder had comminuted almost all of the logging residues collected at the landing and the truck had transported three full loads of wood chips. Therefore, each quantity processed by the tub grinder and the two loaders during the time study was considered to be 120 m3 in terms of the loose volume of chips (the volume of chips is expressed in loose measures).

During the time study, the effective working time of the tub grinder was 7,196 seconds; thus, the productivity of the grinder was calculated to be 60.0 m3/h (the effective time does not include any delays). In comparison, the effective working time of the grapple loader and that of the bucket loader were 6,779 s and 7,127 s, respectively. Consequently, the performances were calculated to be 63.7 m3/h for the grapple loader and 60.6 m3/h for the bucket loader. Table 12 provides detailed information on the calculations of the total comminuting cost. The cost of constructing the landing per m3 of chips in Table 12, 0.732 US$/m3, was calculated by dividing the cost of constructing the landing, 2,857 US$, by the whole amount of wood chips processed at the investigated site, namely, 3,903 m3. However, as 361.8 m3 of pulpwood was also produced at the site, the cost of constructing the landing should have been distributed between the amounts of pulpwood and wood chips according to their economic values. During the collection of materials for the time study of the tub grinder and the two loaders, the yarder was in operation for 39,424 s, and the amount of the collected materials was equivalent to 40 m3 of pulpwood and 120 m3 of wood chips.

The bin filled with the processed wood chips (Fig. 13) weighed 61.4 kg at the experimental site. The bin weighed 3.6 kg and had a volume of 0.18 m3; therefore, the green weight of the chips per unit volume was calculated to be 321 kg/m3. Finally, the average moisture content of the chips measured 120.4% (on a dry-mass basis, with a standard deviation of 12.6%), and the dry weight of the chips per unit volume was estimated to be 146 kgDM/m3.

Although the moisture content of logging residues to be comminuted and the screen size opening of a tub grinder would influence the productivity of the tub grinder, only one instance (moisture content: 120.4%; screen size opening: 5.0 cm) was examined here. Thus, there is no further discussion on the quality of wood chips in terms of whether the processed wood chips shown in Fig. 13 are suitable as a bioenergy source.

Table 12. Details on the calculations used for the total comminuting cost. Reprinted with permission from Croatian Journal of Forest Engineering, 27(2), Yoshioka, T et al., Comminution of logging residues with a tub grinder: Calculation of productivity and procurement cost of wood chips, 103–114, Table 1, © 2006, Forestry Faculty of Zagreb University.

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Fig. 13. Processed wood chips. Reprinted with permission from Croatian Journal of Forest Engineering, 27(2), Yoshioka, T et al., Comminution of logging residues with a tub grinder: Calculation of productivity and procurement cost of wood chips, 103–114, Fig. 4, © 2006, Forestry Faculty of Zagreb University.

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5-3. Discussion

5-3A. Total comminuting cost

When only the labor cost, the machine cost, and the fuel cost of the tub grinder were considered on the basis of data presented in Chapter 4, the comminuting cost per m3 of the processed wood chips was calculated to be 2.663 US$/m3 (Table 12). This value corresponds to 18.2 US$/MgDM (=2.663 [US$/m3] × 1000 [kg/Mg]/146 [kgDM/m3]; with 1,000 kg/Mg being the conversion coefficient) in terms of the cost per dry mass of chips and is lower than the comminuting cost examined in Chapter 4, i.e., 22.7–45.5 US$/MgDM. The moisture content observed in the system analyzed in this chapter, 120.4%, was quite similar to that in Chapter 4, 119.3%, and typical of green logging residues (Asikainen and Pulkkinen 1998). On the other hand, the bulk density, 146 kgDM/m3, was higher than that in Chapter 4, 113.9 kgDM/m3. The reason for this difference is the composition of the processed wood chips, which in the system described in this chapter included coniferous and broad-leaved species, while in that described in Chapter 4 included only chips from Japanese cedar. In general, a broad-leaved tree is heavier than a coniferous one from the viewpoint of weight per unit volume. Consequently, the higher bulk density can be considered to be one of the reasons that the comminuting cost in this chapter was lower than that reported in Chapter 4 in terms of cost per dry mass of chips.

The cost of the two loaders, that of carrying in, installing, and carrying out the machines, and that of constructing the landing, are also given in Table 12, and the breakdown of the total comminuting cost is shown in Fig. 14. The percentage of the sum of the cost of the loaders, that of carrying in, installing, and carrying out the machines, and that of constructing the landing is 53% of the total comminuting cost. These costs have to be reduced in order to improve the total cost. The cost of the two loaders represents 30% of the total cost (Fig. 14). However, instead of the operational system used in this chapter, other operation patterns, such as different combinations of machines, could have been adopted at the experimental site. Given this possibility, a comparison between the calculated total cost and the cost of the cases described below is necessary:

· Case 1: Instead of a grapple loader, the operator of a tub grinder manipulates a grapple by installing it in the tub grinder or introducing another chipper or crusher equipped with a grapple;

· Case 2: Instead of a bucket loader, a tub grinder dumps wood chips directly into a truck with its conveyor;

· Case 3: Instead of two loaders (and a truck), a chipper truck, which can comminute logging residues and transport chips, is introduced. When only one machine works at a landing, there is no interaction between machines. Therefore, the operator of the chipper truck can control the entire "COMMINUTE and TRANSPORT" system. Although the operation rates of both the chipping and transporting functions of the chipper truck will be lower than those of a tub grinder and a truck, it is easier to plan and carry out the operation of one machine than the operations of two or three machines from the point of view of management.

The cost of carrying in, installing, and carrying out the machines (10%) and that of constructing the landing (13%) shown in Fig. 14 are calculated by dividing their original cost by the whole amount of the wood chips processed at the investigated site. In order to reduce these two costs, therefore, it is necessary to produce as many wood chips as possible at one landing—in other words, as many logging residues as possible should be collected at one landing. For example, if a 10% greater amount of wood chips were to be produced at the landing, the percentage of the two costs to the total cost would decrease to 21.3% and the total cost would decrease by 2.1%. Moreover, if 10,000 m3 of wood chips were to be produced, the percentage of the two costs would decrease to 11.2% and the total cost would decrease by 13.3%.


Fig. 14. Breakdown of the total comminuting cost. Reprinted with permission from Croatian Journal of Forest Engineering, 27(2), Yoshioka, T et al., Comminution of logging residues with a tub grinder: Calculation of productivity and procurement cost of wood chips, 103–114, Fig. 5, © 2006, Forestry Faculty of Zagreb University.

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The total comminuting cost is calculated as 5.637 US$/m3 (Table 12). In a Finnish case study, the cost of comminution with a tub grinder was 1.7 US$/m3 despite the productivity being similar to that reported in this chapter (Asikainen and Pulkkinen 1998). The reason for this difference would appear to be the use of only one machine in the Finnish system as the tub grinder was equipped with both a grapple and a conveyor. The grapple put logging residues into the tub, and the conveyor took wood chips directly into a truck; in other words, the tub grinder required no auxiliary machines. On the other hand, the mobility of a truck for transportation was probably restricted. This study and the Finnish one should have been compared from the standpoint of the sum of the costs of comminution and transportation. It should be noted that the total comminuting cost of the system described in this chapter, 5.637 US$/m3, corresponds to 38.6 US$/MgDM in terms of the cost per dry mass of chips. The cost of a small-sized chipper, which would be suitable for tree tops and branches with a maximum diameter of 15 cm, was calculated to be 66.5 US$/MgDM in Chapter 4. Therefore, the comminuting cost of a large-sized crusher is lower than that of a small-sized chipper.

Based on personal communication, the cost of a truck was shown to be 571 US$ per day at the investigated site. Figure 15 shows the relationship between the number of truck transportation events per day and the costs of comminution and transportation per dry mass of chips. The sums of the costs of comminution and transportation were 136.4 US$/MgDM, 87.5 US$/MgDM, and 71.2 US$/MgDM when the truck transported wood chips once per day, twice per day, and three times per day, respectively (a truck will transport three times per day when its running speed, hours of operation per day, operation time of loading and unloading per cycle, and one-way running distance are 30 km/h, 6 h/d, 40 minutes per cycle, and 20 km, respectively). The cost of 71.2 US$/MgDM, for example, corresponds to 3.56 US$/GJ or 12.8 US$/MWh in terms of the cost per calorific value of chips, and it is almost on a par with those of European countries in which the energy utilization of logging residues is making steady progress (see Chapter 4). In terms of the energy utilization of logging residues, Fig. 15 may be of use in designing the arrangement of landings around an energy-conversion plant and the order of truck transportation, while the cost of a truck must be investigated and analyzed in detail.


Fig. 15. Relationship between the number of daily instances of truck transportation and the costs of comminution and transportation per dry mass of chips. Reprinted with permission from Croatian Journal of Forest Engineering, 27(2), Yoshioka, T et al., Comminution of logging residues with a tub grinder: Calculation of productivity and procurement cost of wood chips, 103–114, Fig. 6, © 2006, Forestry Faculty of Zagreb University.

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5-3B. Balance of the processing capacity between a tub grinder and other machines

The productivity of a tub grinder ranges from 14–24 to 100–150 m3/h in published studies (Asikainen and Pulkkinen 1998). The difference in the results is said to be due to difficulties in feeding logging residues into the tub grinder. The productivity of the tub grinder during the time study, 60.0 m3/h, is quite similar to that of the Finnish case study, 60–70 m3/h (Asikainen and Pulkkinen 1998), demonstrating the high performance of the tub grinder investigated.

In order to collect materials for the experiment, the yarder was in operation for about 11 h (39,424 s), while the tub grinder comminuted the sorted logging residues for almost 2 h (7,196 s). During the whole period (361.8 m3 of pulpwood and 3,903 m3 of wood chips were processed), the yarder and the tub grinder operated 105 days and 21 days, respectively. Not all of the operation hours of the yarder were for collecting wood chips because the yarder collected pulpwood material at the same time by whole-tree yarding. However, the yarder had to work for a much longer time than the tub grinder to cope with the relatively higher productivity of the grinder.

The percentage of time the grapple loader and bucket loader spent for idling was 6.2% and 4.6% of the total observed time, respectively. There was little time for both machines to idle, so it is supposed that the two loaders were running almost non-stop to cope with the high performance of the tub grinder.

Based on personal communication, the net productivity of the tub grinder during the whole period was 26.6 m3/h, which is 44% of the productivity based on the time study, namely, 60.0 m3/h. This leads to the interpretation that the rate of operation of the tub grinder was less than 50% even when the grinder worked at the site and is likely due to the relatively higher productivity of the tub grinder than that of the yarder. As a result, the rate of operation of the tub grinder will not be enhanced unless large amounts of logging residues are collected for comminution. This aspect is further examined in a comparison of the costs of comminution and transportation between the two cases, as described below:

· Case 1: A large amount of logging residues is collected to counterbalance the high productivity of the tub grinder. The total comminuting cost will be reduced because a larger amount of wood chips will be produced at one landing and the cost of carrying in, installing, and carrying out the machines and that of constructing a landing will be reduced. However, a landing that is large enough to operate the auxiliary machines for the tub grinder and accommodate the large amounts of collected logging residues and processed wood chips must be constructed. Moreover, it would be necessary to build a network of high-grade forest roads on which large-sized trucks that can carry loads of as much as 40 m3 of wood chips can travel directly to the landing;

· Case 2: Another smaller-sized tub grinder is introduced. In order to keep the rate of operation of the tub grinder high, the size of the grinder should be determined in accordance with the amount of logging residues that can be collected at one landing, the processing capacity of a yarding (or skidding) machine and auxiliary ones, and the degree of preparation of the network of high-grade forest roads.

In both of these cases, the productivity of a tub grinder is expected to be still higher, so it would be realistic for Japanese forestry to consider the sharing of one tub grinder among several logging sites. If this were to be the case, i.e., machines were to be transferred from one site to another, the planning and management of an operational system at each site will need to take the total comminuting cost into account, since the proportion of the sum of the cost of carrying in, installing, and carrying out machines and that of constructing a landing to the total cost is not negligible.

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6. Energy and carbon dioxide (CO2) balance of logging residues as alternative energy resources: System analysis based on the method of a life cycle inventory (LCI) analysis

Biomass is carbon-neutral. For example, forest biomass is neutral in terms of the balance of carbon dioxide (CO2), which has been implicated in the ongoing changes in global climate. This neutrality can be maintained if the management of naturally regenerated and planted forests is carried out on a truly sustainable basis. However, the veracity of this statement should be challenged. In forest management programs, various operations are carried out that involve the use of forestry machines, and these forestry machines, when in operation, usually consume liquid fossil fuel and exhaust CO2. Therefore, in any evaluation of the energy and CO2 balance of forest biomass, not only the sequestration and consumption of biomass itself but also the consumed fuel and the exhausted CO2 gas need to be discussed. The study on fuel consumption for chipping, forwarding, and transporting logging residues (see Chapter 4) indicated that there was no specific problem from the point of view of the input and output of energy, and the results suggested that Japan could reduce its domestic CO2 emission by using biomass as an alternative energy resource. To conduct a fair evaluation of the balance of energy and CO2, however, it will be necessary to examine not only the fuel consumption by forestry machines but also the energy balance of the entire system, which would include materials, construction, and the repair and maintenance of machines used in forestry as well as the costs associated with an energy-conversion plant.

Therefore, a more detailed analysis of the system will be required to provide scientific evidence that logging residues could serve as an efficient alternative energy source and one that would have a lower environmental impact than fossil fuels. Such an analysis method is called a life cycle inventory (LCI) analysis and is based on a method called a life cycle assessment (LCA). This type of analysis is essential when the aim is to obtain the necessary scientific evidence. LCI has been used to compare different options. Methodologies on how to perform the LCI are defined in the ISO 14000 standard, which also applies to LCA (ISO 14040/JIS Q 14040 1999, ISO 14041/JIS Q 14041 and ISO TR 14049/JIS Q TR 14049 2001). LCI is an intrinsic part of the complete LCA.

With regard to the analysis of a bioenergy production system that considers all of the processes, many studies based on the LCI analysis method have been conducted in Europe (Boman and Turnbull 1997, Börjesson 1996a, b, Börjesson and Gustavsson 1996, Faaji et al. 1997, Forsberg 2000, Gustavsson et al. 1995, Hektor 1998, Jungmeier et al. 1998). Hektor (1998) analyzed the difference in the amount of CO2 emitted by a combined heat and power (CHP) system fueled by fossil fuels and one fueled by various forest biomass resources, e.g., logging residues and thinned trees from conventional forestry and whole-tree chips from short rotation forestry (SRF). Boman and Turnbull (1997) calculated the reduction in the amount of CO2 emission by replacing coal-fired power generation systems with biomass-fired power generation systems. A number of Japanese research groups have analyzed a bioenergy system based on LCI analysis or LCA (Dote and Yokoyama 1994, Dowaki et al. 2000, 2001, Tahara et al. 1998). All of these, however, regarded forest biomass from SRF in foreign countries as an energy resource for the purpose of trading greenhouse gas emissions, taking the clean development mechanism (CDM) into account. Moreover, all the studies on the energy conversion of biomass mentioned above targeted large-scale plants whose net power output were tens to hundreds MW.

In Japan, the energy utilization of forest biomass is expected to improve the health of domestic man-made forests. However, a large-scale energy-conversion plant using forest biomass as the fuel source is not feasible due to the small working unit of forest management as well as the expensive harvesting and transporting cost of the biomass. Forest biomass from Japanese conventional forestry will therefore have to be converted to energy in a small-scale plant. The results from existing studies on the evaluation of a large-scale system cannot be applied to a small-scale system where the net power output of an energy-conversion plant is at most several MW for two primary reasons: (1) differences in the type and size of forestry machines between foreign countries and Japan; (2) the difference in thermal efficiency between a large-scale plant and a small-scale one. Therefore, it is essential to evaluate a small-scale system suitable for Japanese conventional forestry.

In this chapter, the input and output of energy and CO2 emission of the forest biomass are analyzed over the entire life cycle of the biomass within the context of an LCI analysis, with the aim of determining whether a small-scale energy-conversion system that uses forest biomass from Japanese conventional forestry as fuel is feasible from the point of view of energy and CO2 balance (Yoshioka et al. 2005a).

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6-1. Materials and methods

Logging residues, i.e., tree tops and branches, are produced during limbing and bucking; these materials are considered here to be the sources of energy. Residues are supposed to be chipped, forwarded, and transported by forestry machines, and then converted to electricity in a biomass-fired power generation plant; the entire system is analyzed in this chapter. Basic data on a harvesting and transporting system for logging residues and an energy-conversion plant are collected from the field experiments (see Chapters 3, 4, and 5) and from published studies on biomass-fired and coal-fired power generation plants (Ogi et al. 2002, Uchiyama and Yamamoto 1991, 1992), respectively. Calculations of the energy input required by each process of the system and the output from an energy-conversion plant were made to determine the energy balance. In addition, the ratio of energy output to input was analyzed based on the LCI analysis. The CO2 emission from each process was calculated by multiplying the energy input into each process and the CO2 emission per unit energy. Finally, the CO2 emission per unit of bioenergy was estimated from the total CO2 emissions and the energy output was measured in the form of electricity.

6-1A. System components

The chipping, harvesting, and transporting chain for logging residues (see Chapter 4) and the operations to reduce the water content of residues are combined in this analysis. In terms of the energy-conversion system, the state-of-the-art power generation technology available in Japan is supposed to be introduced; therefore, a power generation system that supplies electricity by utilizing logging residues from domestic conventional forestry as fuel is assumed in this chapter. Figure 16 illustrates the process tree of a biomass procurement and bioenergy supply system.


Fig. 16. Process tree of a biomass procurement and bioenergy supply system. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Energy and carbon dioxide (CO2) balance of logging residues as alternative energy resources: System analysis based on the method of a life cycle inventory (LCI) analysis. 10(2), 2005, 125–134. Yoshioka, T, Aruga, K, Nitami, T, Kobayashi, H, Sakai, H, Fig. 1. © 2005, Springer Japan.

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Trees are felled by chain saws and left in forests for a few months to dry in the sun; this is called "sour" felling, and it reduces the water content to 50% (dry basis). The operation of whole-tree yarding/skidding is then conducted by tractors, yarders, or mobile yarders. Trees are limbed and bucked by a processor at a landing of a logging site in a forest. A large quantity of tops and branches are generated because of the high performance of the processor. These logging residues are the sources of energy.

With regard to the harvesting and transporting system for logging residues, the least costly system (see Chapter 4) was adopted. Biomass is comminuted at the landing of the logging site by a mobile chipper, hauled on a strip road to another landing alongside a forest road by a forwarder (haulage distance is 191.4 m), and transported on a forest road and a public road to a power generation plant in a 4-ton truck. The comminuted biomass is then dried in a plant stockyard, and the water content is reduced to 15% (dry basis).

The scale of the plant discussed in this chapter is based on a survey by Ogi et al. (2002) of nine biomass-fired power generation plants that were in operation in Japan as of 2002. These plants mainly used mill residues as fuel. The average values of the net power output and thermal efficiency of the nine plants surveyed were 3 MW and 12%, respectively. The plant used as an example in this chapter is supposed to be in operation 24 hours per day and 256 days per year (the annual rate of operation is 70%), and the life of the plant is 30 years. Table 13 shows the basic data on the biomass-fired power generation plant.

Table 13. Basic data on a biomass-fired power generation plant.(1) Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Energy and carbon dioxide (CO2) balance of logging residues as alternative energy resources: System analysis based on the method of a life cycle inventory (LCI) analysis. 10(2), 2005, 125–134. Yoshioka, T, Aruga, K, Nitami, T, Kobayashi, H, Sakai, H, Table 1. © 2005, Springer Japan.

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6-1B. System boundary

The system boundary defined in this chapter is also shown in Fig. 16. Bioenergy is considered as a by-product to conventional forestry practices. In this sense, forestry activities are not influenced by the existence of a downstream bioenergy system. Therefore, the bioenergy system boundary starts with the comminution of logging residues at the landing of the logging site by a mobile chipper. All environmental impacts up to this point are accredited to forestry.

Basic data on the forestry machines and required materials for the biomass-fired power generation plant that are used to calculate the energy input into the system are listed in Tables 14, 15, respectively. The data contained in these tables have been obtained from field experiments and published studies (see footnotes of respective tables). Table 16 shows the energy density of the required materials and fuel.

Table 14. Basic data on the forestry machines.1 Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Energy and carbon dioxide (CO2) balance of logging residues as alternative energy resources: System analysis based on the method of a life cycle inventory (LCI) analysis. 10(2), 2005, 125–134. Yoshioka, T, Aruga, K, Nitami, T, Kobayashi, H, Sakai, H, Table 2. © 2005, Springer Japan.

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Table 15. Required materials for a biomass-fired power generation plant.* Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Energy and carbon dioxide (CO2) balance of logging residues as alternative energy resources: System analysis based on the method of a life cycle inventory (LCI) analysis. 10(2), 2005, 125–134. Yoshioka, T, Aruga, K, Nitami, T, Kobayashi, H, Sakai, H, Table 3. © 2005, Springer Japan.

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Table 16. Energy density of the required materials and fuel.* Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Energy and carbon dioxide (CO2) balance of logging residues as alternative energy resources: System analysis based on the method of a life cycle inventory (LCI) analysis. 10(2), 2005, 125–134. Yoshioka, T, Aruga, K, Nitami, T, Kobayashi, H, Sakai, H, Table 4. © 2005, Springer Japan.

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6-1C. Calculation methods

The goal of this chapter is to investigate three environmental load profiles of the defined biomass procurement and bioenergy supply chain. The first is the energy balance factor (EBF), which is the ratio of energy output to input and used to confirm whether or not the system is feasible as an energy production system. The second is the energy payback time (EPT), which is the index that accounts, by energy production, for the number of years required to recover the total energy input into the system over an entire life cycle. Logging residues are compared with fossil and renewable resources from the perspectives of EBF and EPT, respectively. The third is the CO2 emission factor (CEF), which is the CO2 emission per unit of electricity generated. The CEF of the biomass-fired power generation plant is compared with that of a coal-fired power generation plant, which has been reported to have the highest environmental impact among various power generation technologies. The reduction in the amount of CO2 emission in Japan that will result from replacing coal-fired generation systems with biomass-fired generation systems is calculated to evaluate to which extent logging residues as alternative energy resources can contribute to achieving the goals of the Kyoto Protocol in the first period of commitment starting in the year 2008, when Japan must reduce its greenhouse gas emissions by 6% of the amount recorded in 1990.

After the goal and scope of this section have been defined, an inventory analysis is carried out based on the collected and processed data. The parameter that has the most impact on the LCI results, i.e., EBF, EPT, and CEF, is evaluated with a sensitivity analysis so that problems and improvements of the system can be revealed.

Basic theoretical equations of three environmental load profiles defined here (EBF, EPT, and CEF) are based on the rule made by Uchiyama and Yamamoto (1991) and expressed as:

where LCEO is the energy output from an energy-conversion plant over its entire life cycle; LCEEi and LCOEi are the "equipment" and "operation" energies over the life cycle of each process of the system, respectively (i: each process, i.e., comminuting, hauling, transporting, and power generation); AEO is the annual energy output; AOEi is the annual "operation" energy of each process; LCEEEij and LCOEEij are the "equipment" and "operation" energies, respectively, of each kind of energy resources, e.g., electricity, coal, and oil, over the life cycle of each process (j: each kind of energy resources); CEEj is the CO2 emission per unit energy of each energy resource.

In this chapter, the energy input consists of the "equipment" and "operation" energies. Consequently, the denominator of the right-hand side of Eq. (6.1) represents the energy input into the system over its entire life cycle.

"Equipment" energy is defined as the energy necessary for manufacturing equipment, which constitutes a system, i.e., forestry machines and a biomass-fired power generation plant, and is composed of the "material," "production," "transportation," and "construction" energies. "Material" energy is the energy necessary for refining raw materials, e.g., steel, aluminum, and concrete. "Production" energy is the energy necessary for producing the parts of equipment, e.g., machine engines and a plant generator. "Transportation" energy is the energy necessary for transporting the parts. "Construction" energy is the energy necessary for constructing equipment from the parts transported. On the other hand, "operation" energy is defined as the energy necessary for operating a system and consists of the fuel consumption of forestry machines and the "repair and maintenance" energy of a power generation plant. Fuel consumption was measured in the field experiments on chipping, forwarding, and transporting logging residues at forestry operating sites in Japan (see Chapters 3, 4, and 5). "Repair and maintenance" energy is the energy necessary for the repair of parts and the maintenance of a plant.

With regard to the calculation of the energy input, this chapter adopts a process analysis in which the object is divided into its component elements and the energies required for the formation of each element are integrated. The following three equations are used to calculate the "equipment" energy over the entire life cycle of the system:

where MEi, PEi, TEi, and CEi are the "material," "production," "transportation," and "construction" energies of each process, respectively; MWk is the weight of each kind of necessary materials (k: each kind of necessary materials); EDMkj is the energy density of each necessary material (the calorific value of each energy resource per unit weight of each material). Equation (6.6) shows an assumption that the sum of the "production," "transportation," and "construction" energies is equivalent to 20% of the total "material" energy according to Uchiyama and Yamamoto (1991). The "operation" energy over the entire life cycle of the system (LCOEsystem) is calculated on the basis of the following three equations:

where FCmachine is the total fuel consumption of forestry machines; RMEplant is the "repair and maintenance" energy of a power generation plant; FCi is the fuel consumption of each machine; EDF is the energy density of fuel consumed; LCEEplant is the "equipment" energy over the life cycle of the plant. Equation (6.9) indicates that RMEplant is equivalent to 5% of LCEEplant on the condition that the repair and maintenance of the plant is performed every year so that all parts of the plant may be updated in 20 years (Uchiyama and Yamamoto 1991).

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6-2. Results and discussion

6-2A. Inventory analysis

(a) Energy balance

From the data in Tables 14, 15, 16, it is possible to calculate the "equipment" and "operation" energies using Eqs. (6.4), (6.5), and (6.6) and Eqs. (6.7), (6.8), and (6.9), respectively, thereby clarifying the energy inputs into all the processes of the system. The life cycle inventory of the logging residues in terms of the energy balance can then be completed, the results of which are given in Table 17 (the life cycle inventory explains the details of a specific item inside the system boundary).

The energy input into the system can be analyzed by aggregating the "equipment" and "operation" energies of each process in Table 17.Figure 17 illustrates the breakdown of the annual energy input into the system. In this figure, 82.2% of the total energy input is the "operation" energy, with the "equipment" energy corresponding to the other 17.8%; that is, the amount of energy required for operating the system is much larger than the amount of energy required by the equipment that makes up the system. With respect to the "operation" energy, the fuel consumption of the forestry machines accounts for 73.2% of the total energy input, with the processes of comminuting and transporting being primarily responsible for these especially high rates of consumption. The essential first step towards reducing the total energy input is to reduce the fuel consumption of the mobile chipper and the truck per unit weight of logging residues by taking such measures as developing efficient techniques and improving the operational efficiency of both processes (in this chapter, 0.450 MgDM/h for a mobile chipper and 0.679 MgDM/h for a truck; see Table 14). For example, if the efficiency of a mobile chipper increases by 25% and the fuel consumption per unit weight of residues decreases by 20%, the total energy input will be reduced by 7.6%.

Table 17. Life cycle inventory of logging residues: (I) Energy balance.* Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Energy and carbon dioxide (CO2) balance of logging residues as alternative energy resources: System analysis based on the method of a life cycle inventory (LCI) analysis. 10(2), 2005, 125–134. Yoshioka, T, Aruga, K, Nitami, T, Kobayashi, H, Sakai, H, Table 5. © 2005, Springer Japan.

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Fig. 17. Breakdown of the annual energy input into the system. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Energy and carbon dioxide (CO2) balance of logging residues as alternative energy resources: System analysis based on the method of a life cycle inventory (LCI) analysis. 10(2), 2005, 125–134. Yoshioka, T, Aruga, K, Nitami, T, Kobayashi, H, Sakai, H, Fig. 2. © 2005, Springer Japan.

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Table 17 also shows the EBF and the EPT calculated from Eqs. (6.1) and (6.2), respectively. The EPT in Table 17 is 1.09 years, which represents the total energy input into the system consisting of a plant with an operating life of 30 years that can be recovered for a short period of 1.09 years with power generation; this results suggests that residual forest biomass is relatively superior to other renewable energy resources, such as wind (1.99 years) or solar energy (10.00 years) (Uchiyama and Yamamoto 1991). On the other hand, the EBF in Table 17 is 5.69, which means that 5.69-fold more energy than that required for the total energy input can be produced during the entire life cycle of the system. This result indicates that the system in this chapter is feasible as an energy production system. From the perspective of EBF, however, residual forest biomass is inferior to fossil energy resources such as coal (17.15) or oil (20.75) (Uchiyama and Yamamoto 1991). The average net power output of power generation plants of those fossil resources is 1,000 MW; a large-scale power generation system can supply a huge amount of electricity steadily, while a small-scale system enables on-site or regional energy utilization. Both systems have advantages (and disadvantages), so a small-scale 3 MW biomass-fired plant should not be compared with a large-scale one in the 1,000-MW class from the aspect of energy balance alone.

(b) CO2 emission

The CO2 emissions from all of the processes of the system are calculated from Table 17 and the CO2 emission per unit energy of each energy resource is determined (see footnote of Table 18). The life cycle inventory of logging residues in terms of CO2 emission is then completed and is listed in Table 18. The CO2 emissions from the "equipment" energy and the "operation" energy account for 38% and 62%, respectively, of the total CO2 emission from the system, resulting in a smaller difference between both energies than that in the case of the energy input into the system discussed above.

Table 18. Life cycle inventory of logging residues: (II) CO2 emission.* Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Energy and carbon dioxide (CO2) balance of logging residues as alternative energy resources: System analysis based on the method of a life cycle inventory (LCI) analysis. 10(2), 2005, 125–134. Yoshioka, T, Aruga, K, Nitami, T, Kobayashi, H, Sakai, H, Table 6. © 2005, Springer Japan.

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Table 18 also shows CEF calculated from Eq. (6.3). The CEF of the biomass-fired power generation system is 61.8 kgCO2/MWhe (e: electricity), while that of the coal-fired power generation system in Japan is 960 kgCO2/MWhe (the net power output is 1,000 MW, the annual rate of operation is 75%, and the life of a plant is 30 years (Uchiyama and Yamamoto 1992)). Therefore, through the system analysis based on LCI, it can be determined that residual forest biomass from Japanese conventional forestry has a much lower environmental impact than coal from the viewpoint of the amount of CO2 emitted in power generation. Moreover, the reduction in the amount of CO2 emission in Japan that will result from replacing coal-fired power generation plants with biomass-fired ones is calculated from the CEFs of biomass and coal shown above, the generated electricity per biomass-fired plant per year, 18,432 MWhe/y, and the number of the plants that can be constructed in Japan, 100, as follows:

{(960 – 61.8) [kgCO2/MWhe]/1000 [kg/Mg]}

× 18432 [MWhe/y] × 100 = 1655562 [MgCO2/y]

where 1,000 kg/Mg is the conversion coefficient. This amount corresponds to 0.142% of the national CO2 emission estimated for 2000, i.e., 1.162 PgCO2/y (Energy Data and Modelling Center (ed.) 2002).

Boman and Turnbull (1997) analyzed the CEFs of forest biomass and coal. In their analysis, the CEF of coal was calculated to be over 100 kgC/GJe (equivalent to 1,319 kgCO2/MWhe), while that of forest biomass was less than 10 kgC/GJe (131.9 kgCO2/MWhe); the results of the calculations performed in this chapter are roughly in accordance with those of that analysis. Moreover, were all of the fuel to be replaced with biomass in a 108 MW coal-fired power generation plant, the reduction in the amount of CO2 emission per GJe would be eight-fold greater than when only 10% of the fuel would be replaced (in terms of the co-firing of forest biomass with coal, there is still an advantage that biomass can be converted to electricity with high efficiency, so further discussion of this aspect will be necessary). Their analysis can be regarded as a practical one because they took the utilization of the existing coal-fired plant into consideration. On the other hand, in this chapter, it is assumed that the large-scale 1,000-MW class coal-fired system is replaced with the small-scale 3-MW class biomass-fired system. However, these systems differ not only in scale but also in suitable location (along the sea coast for coal and mountainous regions for forest biomass). Just how the system is to be replaced within the present social framework needs to be well discussed.

6-2B. Sensitivity analysis

In this section, the degree to which the LCI results in this study, i.e., EPT, EBF, and CEF, will be influenced by changes in values of the parameters is evaluated by a sensitivity analysis. Figure 18 illustrates the results of this analysis, in which the life span, net power output, and thermal efficiency of the biomass-fired power generation plant are chosen the primary determinants.


Fig. 18. Sensitivity analysis to the LCI results. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Energy and carbon dioxide (CO2) balance of logging residues as alternative energy resources: System analysis based on the method of a life cycle inventory (LCI) analysis. 10(2), 2005, 125–134. Yoshioka, T, Aruga, K, Nitami, T, Kobayashi, H, Sakai, H, Fig. 3. © 2005, Springer Japan.

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The shorter the life of the plant, the lower the EPT─which is a favorable tendency. However, the EBF decreases and the CEF increases if the life of the plant is shortened, both of which are unfavorable tendencies. From the viewpoint of the input and output of energy, which is one of the main subjects of this study, EBF is the most important parameter. Therefore, these findings suggest that the plant should be operated for as long a period as possible. The more the net power output increases, the more EPT and CEF will increase and EBF will decrease, which are unfavorable tendencies. The chipping, forwarding, and transporting costs of logging residues will increase when the scale of an energy-conversion plant is expanded. For example, the average transporting distance of a 4-ton truck is calculated to be 45.6 km when an 8 MW biomass-fired power generation plant is constructed. Therefore, from the aspects of energy and CO2 balance as well as the procurement cost, a larger-scale plant is unrealistic for logging residues. The thermal efficiency of the plant has the greatest influence on the LCI results. The EPT and CEF will decrease and the EBF will increase when the thermal efficiency increases, which are favorable tendencies. If the energy-conversion technology of biomass whose thermal efficiency is 40% is realized, the reduction in the amount of CO2 emission in Japan is expected to be equivalent to 0.481% of the national CO2 emission. Consequently, with the aim of making residual forest biomass more advantageous to fossil resources, it is proposed that a small-scale and efficient energy-conversion technology of biomass should be developed.

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6-3. Further considerations

There are additional problems that will require more detailed study in the future. In terms of the methodologies, for example, the allocation of the energy inputs and the CO2 emissions of the felling, yarding/skidding, limbing and bucking processes to logs and logging residues will be necessary when logging residues as energy resources are regarded not as by-products to conventional forestry but as forestry products equal in value to logs. From the perspective of the standards set by the Kyoto Protocol, the results of this study, in which only logging residues are taken into account, are not necessarily satisfactory; therefore, the amount of CO2 emissions of the other woody biomass resources, such as thinned trees, broad-leaved forests, mill residues, wood-based waste material, and trimmings, over their entire life cycles should also be evaluated.

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7. A GIS-based analysis of the relationship between the annual available amount and the procurement cost of forest biomass in a mountainous region in Japan

Detailed data on the annual available amounts of forest biomass, including spatial data, as well as those on harvesting and transportation costs (procurement costs) are necessary prerequisites for the optimal and sustainable utilization of forest biomass for energy. van Belle et al. (2003) conducted such analyses using a geographic information system (GIS). The GIS has been used in a number of studies on forestry operations and forest road planning (Dean 1997, Eriksson and Rönnqvist 2003, Forsberg and Rönnqvist 2003, Kluender et al. 2000, Martin et al. 2001, Pentek et al. 2004, 2005) and for estimating the amount of domestic forest biomass resources in sufficient detail (Nord-Larsen and Talbot 2004, Ranta 2003, 2004, Talbot and Nord-Larsen 2003).

In this chapter, the feasibility of the energy utilization of forest biomass in a mountainous region in Japan is discussed based on an analysis of the relationship between the mass and the procurement cost of biomass in the region using a GIS (Yoshioka and Sakai 2005). A model region was selected, and logging residues, thinned trees, and trees from broad-leaved forests were defined as forest biomass for energy. Mechanization in forestry for the energy utilization of forest biomass was assumed to be available. The objective was to determine the actual situation of the region in terms of possible utilization of forest biomass for bioenergy production by investigating the distribution of forest resources, the topography, and the alignment of forest and public roads as exactly as possible.

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7-1. Materials and methods

The model region selected is a county located in the middle of Japan. It has a gross surface area of 493.28 km2, with a population of 72,862 distributed in 21,769 households. It is subject to an inland and basin-type climate; the annual average temperature is 13–14 degrees Celsius, and the annual precipitation is 1,500–1,600 mm/y. The forests belong to the lucidphyllous forest zone, covering an area of 37,202 ha (75% of the gross area of the county). Coniferous plantation forests cover 58% of the forested area. The 43 sawmills in the region annually consume 78,992 m3 of sawlogs. The county leads the prefecture in terms of forestry and timber business, but annual fellings have dropped by almost 50% in the past 5 years. The amount of forest stands left tending is increasing. The slow progress of mechanized forestry in this region is assumed to be one of the major reasons for this decline in productivity.

The forest survey data, statistics on the forest industries, and guides to forestry practice were offered from the prefectural office. Using these data and the GIS (software: TNTmips®; MicroImages, Inc., USA), the annual available amount of biomass resources was calculated, and a distribution map was made. The shapes and the locations of sub-compartments are the vector data, which are managed by the prefecture. The digital elevation model (DEM) was utilized to calculate the heights above sea level and the angles of inclination. Forest and public roads were traced on the digital topographic map of the region and converted to vector data. These data were integrated on the software and processed. Harvesting and transportation systems for forest biomass were classified depending on the fraction of the tree for energy and the topographical conditions, and the equations for calculating costs were made.

This section includes the methodology used to assess the forest biomass resources, to prepare topographic information, and to select an optimal harvesting and transportation systems, with reference to the methodology of three European studies, i.e., Belgium (van Belle et al. 2003), Denmark (Nord-Larsen and Talbot 2004), and Finland (Ranta 2004).

7-1A. Calculation of the annual available amount of forest biomass

There were 2,168 sub-compartments in the region and 7,841,851 m3 of total growing stock. This high average value of growing stock, i.e., 211 m3/ha, is due to the fact that many of the forests in the region were just maturing. Among the sub-compartments, there were 1,113 coniferous plantation stands and 398 naturally regenerated broad-leaved stands; these stands were targeted for harvesting logs and energy fractions. Protection forest stands for the purpose of sediment disaster prevention and water conservation were excluded. Thinning and clearcutting were supposed to be carried out in the coniferous forests, and selection felling in the broad-leaved forests. The representative tree species in the region are "hinoki" or a cypress (Chamaecyparis obtusa) in coniferous stands and "keyaki" or a zelkova (Zelkova serrata) in broad-leaved stands. Table 19 lists the operation patterns of the sub-compartments to be felled. In the coniferous plantation forest, the annual cut volume was supposed to equal the annual increment. Thus, the cutting cycle was calculated as 9.2016 years by dividing the total allowable volume, 1,158,796 m3, according to the regional forest survey records (see Table 19) by the annual increment, 125,934 m3/y.

The total stem volume of each sub-compartment is recorded in the forest register. Thus, if a coefficient for converting stem volume to dry mass is known, the amount of biomass resources can be calculated. Coefficients for the calculation of total tree biomass resources are listed in Table 20. The coefficients shown in Table 20 have been basically standardized by the Japanese government (Agriculture, Forestry and Fisheries Research Council Secretariat (ed.) 1991). By applying the data shown in Tables 19, 20 to the forest register and considering the cutting cycles of coniferous and broad-leaved forests, the annual available amount of forest biomass in the region can be calculated.

The amount of biomass in each sub-compartment was also calculated using the GIS in order to describe the spatial distribution of the resources.

Table 19. Operation patterns of sub-compartments to be felled. Reprinted with permission from Croatian Journal of Forest Engineering, 26(2), Yoshioka, T, Sakai H, Amount and availability of forest biomass as an energy resource in a mountainous region in Japan: a GIS-based analysis, 59–70, Table 1, © 2005, Forestry Faculty of Zagreb University.

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Table 20. Methods for calculating the amount of biomass resources.* Reprinted with permission from Croatian Journal of Forest Engineering, 26(2), Yoshioka, T, Sakai H, Amount and availability of forest biomass as an energy resource in a mountainous region in Japan: a GIS-based analysis, 59–70, Table 2, © 2005, Forestry Faculty of Zagreb University.

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7-1B. Preparation for topographic information

First, the vector data on the shapes and the locations of the sub-compartments were entered into the GIS software together with the corresponding forest register data. Second, the digital topographic map of the region (1:25,000 scale; the Geographical Survey Institute, Japan) was entered into the software, and all roads exceeding 3 m width were traced and converted to vector data (Fig. 19). Third, the DEM of the region (50 m mesh; the Geographical Survey Institute, Japan) was entered into the software to calculate the slope of each sub-compartment and to judge the skidding/yarding direction (uphill or downhill) (Fig. 20). Fourth, all of the vector data were converted to raster data, and the mesh of the raster data was based on the mesh of the DEM, i.e., 50 m mesh. These layers were integrated according to the International Terrestrial Reference Frame (ITRF). Figure 21 shows the vector data projected on a digital topographic map (Fig. 21(a)), the converted raster data on the shapes and the locations of sub-compartments (Fig. 21(b)), and the converted raster data on forest and public roads (Fig. 21(c)).


Fig. 19. Conversion of forest and public roads into vector data. Reprinted with permission from Croatian Journal of Forest Engineering, 26(2), Yoshioka, T, Sakai H, Amount and availability of forest biomass as an energy resource in a mountainous region in Japan: a GIS-based analysis, 59–70, Fig. 1, © 2005, Forestry Faculty of Zagreb University.

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Fig. 20. Digital elevation model (DEM, right) corresponding to a contour map (left). The vertical interval of the contour map is 10 m. The mesh size of the DEM is 50 m, and the numerical value in each mesh indicates the height above sea level at the top-left grid point of the mesh (unit: m). Reprinted with permission from Croatian Journal of Forest Engineering, 26(2), Yoshioka, T, Sakai H, Amount and availability of forest biomass as an energy resource in a mountainous region in Japan: a GIS-based analysis, 59–70, Fig. 2, © 2005, Forestry Faculty of Zagreb University.

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Fig. 21. Conversion of vector data into raster data. Reprinted with permission from Croatian Journal of Forest Engineering, 26(2), Yoshioka, T, Sakai H, Amount and availability of forest biomass as an energy resource in a mountainous region in Japan: a GIS-based analysis, 59–70, Fig. 3, Fig. 4, © 2005, Forestry Faculty of Zagreb University.

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The GIS software was used to generate transport solutions from the forest to the energy plant. The skidding/yarding distance of each sub-compartment was determined by calculating the distance from the "center of gravity" mesh of a sub-compartment to the nearest road mesh. A landing was to be arranged in the respective road mesh. Road transportation distance was determined by calculating the distance from the "landing" road mesh to the energy-conversion plant, located in the center of the region, using the Dijkstra's Algorithm. Finally, the average angle of inclination of each sub-compartment was calculated, and skidding/yarding direction (uphill or downhill) was assessed by comparing the altitudes of the "center of gravity" mesh with those of the "landing" road mesh.

7-1C. Classification of harvesting and transporting systems for forest biomass

The engine for the chipper used for comminuting whole trees (see Table 19) must be larger than that used for comminuting logging residues. A small-sized chipper (engine power: 23 PS/17.2 kW) was supposed to be used for comminuting logging residues, and a middle-sized chipper (200 PS/149 kW) for comminuting whole trees from thinnings and broad-leaved forests. Harvesting and transportation systems for forest biomass were classified into two types depending on the parts of a tree used for energy (logging residues or the whole tree) (Fig. 22). The type of machine used for skidding/yarding is usually decided upon following consideration of the topographical conditions, i.e., slope, distance, and direction (uphill or downhill). Here, tractors (skidders), tower yarders (mobile yarders), and yarders are to be used for the skidding/yarding process. Figure 23 shows how skidding/yarding machines were classified according to the topographical conditions of sub-compartments.

Table 21 presents the cost functions for harvesting and transporting forest biomass taking the variables slope, skidding/yarding distance, and transportation distance into account. The performance of forestry operations in Japan have been partly standardized by Sakai (1987) and Sawaguchi (1996), and their studies were referred to in order to formulate biomass harvest and transport operations. The costs of labor, machinery, and fuel were considered to be basically the same as those used in the previous study by the author (Yoshioka et al. 2006a). The procurement costs of forest biomass were calculated by applying the cost functions to the spatial data for each sub-compartment in the region.


Fig. 22. Classification of systems according to the parts of a tree for energy. Reprinted with permission from Croatian Journal of Forest Engineering, 26(2), Yoshioka, T, Sakai H, Amount and availability of forest biomass as an energy resource in a mountainous region in Japan: a GIS-based analysis, 59–70, Fig. 5, © 2005, Forestry Faculty of Zagreb University.

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Fig. 23. Classification of machines according to the topographical conditions. Reprinted with permission from Croatian Journal of Forest Engineering, 26(2), Yoshioka, T, Sakai H, Amount and availability of forest biomass as an energy resource in a mountainous region in Japan: a GIS-based analysis, 59–70, Fig. 6, © 2005, Forestry Faculty of Zagreb University.

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Table 21. Cost functions for harvesting and transportation of forest biomass.* Reprinted with permission from Croatian Journal of Forest Engineering, 26(2), Yoshioka, T, Sakai H, Amount and availability of forest biomass as an energy resource in a mountainous region in Japan: a GIS-based analysis, 59–70, Table 3, © 2005, Forestry Faculty of Zagreb University.

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7-2. Results

7-2A. Annual available amount of forest biomass

The annual available amount of biomass resources in the region was calculated by the method described in Section 7-1A (Table 22). About half of the sub-compartments in the region were targeted for harvesting logs and energy sources, and the total annual available amount was calculated to be 52.206 GgDM/y. Both coniferous plantation forests and naturally regenerated broad-leaved forests will be felled in a sustainable way, i.e., by considering the cutting cycles of the forests. Therefore, the health of the forests is expected to be improved by utilization of biomass resources for energy. At least 143 MgDM (=52,206 [MgDM/y]/365 [d/y]) of biomass can be supplied to an energy-conversion plant every day (the mass varies with the days of operation). On the other hand, 57,162 m3/y of the cut volume of logs corresponds to 72% of the annual consumption of logs for timber in the region, and the total amount of logs and energy sources to be harvested is sufficient enough to sustain the introduction of large efficient forestry machines.

Table 22. Annual available amount of forest biomass in the region. Reprinted with permission from Croatian Journal of Forest Engineering, 26(2), Yoshioka, T, Sakai H, Amount and availability of forest biomass as an energy resource in a mountainous region in Japan: a GIS-based analysis, 59–70, Table 4, © 2005, Forestry Faculty of Zagreb University.

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7-2B. Relationship between the mass and the procurement cost of forest biomass

The masses and the procurement costs of all sub-compartments were obtained using the data on the topography prepared in Section 7-1B and the cost functions described in Section 7-1C. Figure 24 shows the distribution map of the procurement cost of forest biomass from each sub-compartment, and Fig. 25 shows the relationship between the annual available amount and the cost of harvesting and transporting forest biomass in the region.

Logging residues were the cheapest, followed by trees from broad-leaved forests; thinned trees were the most costly. Logging residues, i.e., tree tops and branches generated during limbing and bucking, are regarded as by-products of logging operations (see Fig. 22). Therefore, the procurement costs of the residues, which were calculated by considering only the chipping and transportation processes, were the cheapest. Although the procurement cost of thinned trees was roughly the same as that of broad-leaved forests per cubic meter, broad-leaved forests can be seen to be cheaper than thinned trees in Fig. 25 because of the higher bulk density of a broad-leaved tree compared to a coniferous tree. (As such, broad-leaved trees are expensive due to the selective cutting regime, leading to low volume per machine position, and performance is decreased by having to consider the remaining trees; the same is true for thinnings since the small size of the harvested trees may lead to high costs. In the future, however, once the choice is made to harvest logging residues, a portion of the logging cost for the main operation could be allocated to the residues based on net value or, possibly, volume. This will marginally improve the profitability of the main logging operation.).

In terms of realizing the energy utilization of forest biomass in the region, there are three advantages to the relationship mentioned above:

1) A set maximum purchase price of forest biomass can be used to determine the annual available amount;

2) In analogy to 1), the price needed to procure a certain necessary annual amount of forest biomass can also be determined;

3) The procurement costs from all sub-compartments in the region are calculated. Therefore, in both 1) and 2) above, the relationship can be used for prioritizing stands for harvesting in operational planning.


Fig. 24. Distribution map of the procurement cost of forest biomass (unit: US$/MgDM). Reprinted with permission from Croatian Journal of Forest Engineering, 26(2), Yoshioka, T, Sakai H, Amount and availability of forest biomass as an energy resource in a mountainous region in Japan: a GIS-based analysis, 59–70, Fig. 7, © 2005, Forestry Faculty of Zagreb University.

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Fig. 25. Relationship between the mass and the procurement cost of forest biomass. Reprinted with permission from Croatian Journal of Forest Engineering, 26(2), Yoshioka, T, Sakai H, Amount and availability of forest biomass as an energy resource in a mountainous region in Japan: a GIS-based analysis, 59–70, Fig. 8, © 2005, Forestry Faculty of Zagreb University.

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7-3. Discussion

7-3A. Assessment of the relationship between the mass and the procurement cost

The construction of a power-generation plant that uses forest biomass as fuel and supplies electricity to the region is discussed here. In terms of the scale of the plant, the net power output, the thermal efficiency, and the operating rate are supposed to be 3 MW, 12%, and 70%, respectively (see Chapter 6), and the power-generation cost of the plant (costs for investment and operation at the plant) is 66.7 US$/MWhe (e: electricity). In terms of scale, this plant will provide electricity to 5,400 households, i.e., 24.8% of the households in the region, and consume 30.106 GgDM/y of forest biomass. Therefore, the ceiling on a purchase price of biomass can be read as 108.6 US$/MgDM from Fig. 25, and plans to harvest and transport biomass from the sub-compartments at a cost of less than 108.6 US$/MgDM can be developed.

Figure 25 also shows the average cost, which is calculated by dividing the sum total of the purchase price of forest biomass by the amount of biomass to be purchased. The average cost for the supposed plant can be read as 86.5 US$/MgDM from the figure, which is equivalent to 141.3 US$/MWhe. From the viewpoint of cost, it would appear that the utilization of forest biomass as an energy resource in this region is difficult because the unit price of electricity per MWh in Japan is 151.4 US$/MWhe while the power-generation cost is 66.7 US$/MWhe. However, the feasibility of utilizing forest biomass for energy should not be discussed only from the viewpoint of cost. A comprehensive analysis must also include the effects on the reduction in the amount of CO2 emission and job creation in the region. Furthermore, learning curves of most complex operations, such as forest fuel procurement, indicate that there will be a considerable potential for cost reductions through performance improvements and everyday rationalization once the system is implemented on a full scale.

In a case study in Denmark in which the technical and economical availability of forest fuel resources was estimated based on a GIS analysis, the mean delivery cost of wood chips ranged from 672 €/TJ to 716 €/TJ for the three "Average" consumption scenarios (Nord-Larsen and Talbot 2004), corresponding to 18.1–19.3 US$/MgDM when 1 € = 1.35 US$ and 1 MgDM = 20 GJ. The average cost in this section, 86.5 US$/MgDM, is over fourfold more expensive than in the Danish study. This difference has the same tendency as that reported in a previous study by the author (Yoshioka et al. 2006a), which examined the feasibility of a harvesting and transporting system for logging residues in Japan by comparing the calculated harvesting and transportation costs with those of Nordic countries. In the earlier study, the authors emphasized the importance of not only introducing technical developments into the harvesting process, e.g., introducing a bundler, but also of improving the logistics. When 30.106 GgDM/y of forest biomass is harvested for the operation of the above-mentioned plant, the average skidding/yarding and transportation distances are 262 m and 14.5 km, respectively (362 m and 13.2 km for logging residues, 146 m and 13.1 km for thinned trees, 275 m and 15.1 km for trees from broad-leaved forests). For example, the procurement cost of wood chips from broad-leaved trees in the case of average yarding (by a tower yarder, 275 m) and transportation (15.1 km) distance is calculated 82.0 US$/MgDM, which consists of 15.5 US$/MgDM for felling, 33.2 US$/MgDM for yarding, 16.7 US$/MgDM for comminution, and 16.6 US$/MgDM for transportation. These costs are so high that the total procurement cost cannot be economically competitive. The authors of the earlier study therefore suggest (reiterated in this chapter) that technical development, especially for the skidding/yarding process, as well as the improvement of logistics should receive high priority in terms of optimizing forest fuel utilization in Japan.

In addition to the forest biomass discussed here, it would be realistic and valuable to utilize mill residues (wood shavings and barks generated in sawmills and plywood plants), wood-based waste material, and trimmings of park trees, roadside trees, and garden trees together. If half the amount of biomass necessary for the supposed plant (15.053 GgDM/y) is covered by mill residues, wood-based waste material, and trimmings generated in the region, the average cost of forest biomass will be reduced to 73.1 US$/MgDM (Fig. 25). Moreover, at the present time in Japan, many of the mill residues, wood-based waste material, and trimmings can be obtained free of charge, so the effectiveness of the reduction in the procurement cost of biomass will be greater on the whole; for example, (15.053·73.1 + 15.053·0)/30.106 = 36.5 [US$/MgDM]. However, as this will not be the case once a market has been established and there is a clear demand for biomass for fuel, further discussion on this aspect will be necessary.

7-3B. Assessment of the resolution of the geospatial data

With respect to the analytical method using the GIS, one of the main obstacles for integrating multiple layers of geospatial information is to bring all data to manageable spatial resolution and data format, i.e., vector or raster. In the analysis described in this chapter, all of the vector data (shapes and locations of sub-compartment, forest and public roads) were converted to the raster based on the mesh of DEM, i.e., a 50-m-cell grid; in other words, a 3-m-wide road in vector format was rasterized to a 50-m grid. GIS is scale dependent, and it is necessary to consider the appropriate spatial scale for addressing the problem at hand (Graham et al. 2000). From this point of view, there may be a lack of locational accuracy in any analysis involving the road system, necessitating a more detailed analysis.

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7-4. Further considerations

The relationship between the mass and the procurement cost of forest biomass analyzed in this chapter targeted only the situation at the present time. Further study and discussion of the long-term feasibility of utilizing forest biomass in a sustainable way are essential.

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8. Conclusions

The feasibility of a harvesting, transporting, and chipping system for forest biomass resources in Japan has been discussed in this study. First, the visions for introducing and diffusing woody bioenergy utilization in Japan were comprehensively discussed in terms of the quantification of available woody biomass resources for energy, the development of low-cost harvesting and transporting systems, and the conversion processes. Second, a harvesting, transporting, and chipping system for logging residues was constructed and the feasibility of the system was examined from the points of view of cost, energy balance, and carbon dioxide (CO2) emissions based on the results of field experiments in forestry operation sites. Third, the feasibility of the energy utilization of forest biomass resources in a mountainous region was discussed based on an analysis of the relationship between the mass and the procurement cost of forest biomass in the region with the aid of a geographic information system (GIS). The following conclusions were derived from the results of this study:

· Chapter 2: The feasibility of the utilization of woody biomass as an energy resource in Japan was discussed based on the amount and availability of woody biomass and energy-conversion technologies. The amount currently available was estimated to be 31.7 Tg/y on a dry-weight basis, corresponding to 2.8% of the national primary energy supply. An analysis of the current systems for the harvest and transport of logging residues showed that improvement were needed for such systems to be sustainable/economic. The prospects for woody bioenergy utilization around the years 2010 and 2050 were also discussed based on the present state-of-the-art energy-conversion technologies. Around 2010, both "on-site" utilization and "regional" utilization are expected to be feasible as a small-scale and decentralized system. The co-firing of woody biomass with coal at an existing coal-fired power plant is expected to be feasible as a large-scale and centralized system. Around 2050, "regional" utilization is expected to be the main energy utilization for the small-scale and decentralized system. Biomass plantations in foreign countries would be needed for a large-scale and centralized system in Japan;

· Chapter 3: The concept of a "harvesting system for logging residues by a processor and a forwarder" was examined with the aim of constructing a system to harvest logging residues (or slashes) as a new resource for energy. The rate of slash harvesting, α, and the "energy input rate" of hauling slashes, p (%), were defined as indices of the possibility of harvesting slashes and the utilization of slashes for energy, respectively. From an analysis of the field experiment, both the volume of logs hauled by the forwarder per day, EF (m3/d), and p are expressed as functions of the hauling distance, L (m). The productivity of the processor, EP (m3/d), and L were used to calculate α. The results showed that α was approximately 0.95 for the experiment site, indicating that almost all the slashes could be hauled. It was recognized that the energy utilization of slashes was feasible for this site because p was less than 1%. The hauling cost per unit weight of slashes was calculated to be 0.134 US$/kgDM (DM: dry mass). This high cost demonstrates that the cost must be reduced by taking measures such as enhancing the hauling efficiency of the forwarder;

· Chapter 4: A "harvesting and transporting system for logging residues" was constructed with reference to three European countries where the utilization of bioenergy is making steady progress and examined on the basis of field experiments in a Japanese forestry situation. The feasibility of the system was discussed from the standpoints of cost and energy, and the system was compared with those of the three European countries. In terms of costs, the incorporation of chipper comminuting into the system as early as possible was desirable given the trends of harvesting cost and fuel consumption per unit weight of logging residues. Such a system is not particularly feasible from the standpoint of the harvesting cost per MWh of bioenergy. However, no specific problems were found from the point of view of the "energy input rate," and it was demonstrated that it is possible for Japan to reduce domestic carbon dioxide emissions by utilizing biomass as an energy resource. A comparison with the three European countries and a preliminary sensitivity analysis of the system demonstrated that technical developments aimed at reducing the harvesting cost (e.g., improving the forwarding and transporting efficiency) and wide-scale governmental support are essential for realizing bioenergy utilization in Japan;

· Chapter 5: An experiment on the comminution of logging residues with a tub grinder was carried out in order to calculate the productivity and procurement cost of wood chips. At the investigation site, there was a tub grinder equipped with a hammer mill crusher at the bottom of the tub, and a grapple loader and a bucket loader were used as auxiliary machines for the grinder. The productivity of the tub grinder was 60.0 m3 per effective hour, and the total comminuting cost was calculated as 5.637 US$/m3, indicating that the comminuting cost of a large-sized crusher was lower than that of a small-sized chipper. The sum (in percentage) of the cost of the loaders, the cost of carrying in, installing, and carrying out the machines, and the cost of constructing a landing was 53% of the total comminuting cost. When a truck with a cubic capacity of 40 m3 transported wood chips three times per day, the sum of the costs of comminution and transportation was 71.2 US$/MgDM, which was almost on a par with those of European countries in which the energy utilization of logging residues was making steady progress. Based on the discussion weighing the advantages and disadvantages of the processing capacity of the tub grinder and that of other machines, a realistic option for Japanese forestry would be to consider the sharing of one tub grinder among several logging sites;

· Chapter 6: Using the method of a life cycle inventory (LCI) analysis, the energy balance and the carbon dioxide (CO2) emission of logging residues from Japanese conventional forestry as alternative energy resources were analyzed over the entire life cycle of the residues. The fuel consumption of forestry machines was measured in field experiments on harvesting and transporting logging residues at forestry operating sites. In addition, a total audit of energy consumption was undertaken that involved an assessment of materials, construction, and the repair and maintenance of forestry machines as well as the costs associated with an energy-conversion plant. As a result, the ratio of energy output to input was calculated to be 5.69, indicating that the system could be feasible as an energy production system. The CO2 emission per MWhe (e: electricity) of the biomass-fired power generation plant was calculated to be 61.8 kgCO2/MWhe, while that of coal-fired power generation plants in Japan was 960 kgCO2/MWhe. Therefore, the reduction in the amount of CO2 emission that would result from replacing coal with biomass by the power generation of as much as 3.0 Tg/y of logging residues in Japan was estimated to be 1.656 TgCO2/y, corresponding to 0.142% of the national CO2 emission. The analysis in Chapter 6 provides evidence that Japan could reduce its domestic CO2 emission by using logging residues as alternative energy resources;

· Chapter 7: The feasibility of utilization of forest biomass for energy in a mountainous region was discussed based on analyses with the GIS. In Chapter 7, "forest biomass" denotes logging residues, thinned trees, and trees from broad-leaved forests. First, using the GIS, a complete distribution map of biomass resources was compiled and the topographical information of each sub-compartment was prepared for analysis. Second, harvesting and transportation systems were classified into six types based on the fraction of the tree for energy used (two types) and by topographical conditions (three types). Equations for cost calculations were developed and included the variables slope, skidding/yarding distance, and transportation distance. Finally, the relationship between the mass and the procurement cost of forest biomass in the region was analyzed. The results show that logging residues (the available amount was 4.035 GgDM/y) were the least costly followed by broad-leaved forests (20.317 GgDM/y), while thinned trees (27.854 GgDM/y) were the most costly. The analysis may support operational planning, especially the decision of selecting sub-compartments to be felled. For example, the amount of biomass needed to supply a power-plant that could supply 24.8% of the electrical needs of the region was calculated to 30.106 GgDM/y. This amount of forest biomass could optimally be harvested from sub-compartments where procurement costs were lower than 108.6 US$/MgDM.

The conclusions drawn in this study will contribute to the practical implementation of the harvesting, transporting, and chipping system for forest biomass resources and to the realization of utilizing forest biomass for energy production in Japan.

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Acknowledgments

This study is based on the author's doctoral dissertation submitted to the University of Tokyo in 2003. The author first of all would like to express his deep-felt gratitude to his dissertation supervisor Professor Emeritus Dr. Hiroshi Kobayashi of the University of Tokyo for inspiring and encouraging him to pursue a career in the field of Forest Engineering. His gratitude is also extended to four co-supervisors, Professor Dr. Hideo Sakai, Associate Professor Dr. Toshio Nitami, and Professor Emeritus Dr. Mitsuhiro Minowa of the University of Tokyo, and Professor Dr. Katsumi Toyokawa of Tokyo University of Agriculture, for their guidance and criticism during the review of the dissertation.

Many people have been involved in the practical aspects that have contributed to the completion of this study and, unfortunately, space requirements do not allow the author to mention them all by name. He sincerely thanks Professor Dr. Koki Inoue, who is his current supervisor at Nihon University, Associate Professor Dr. Masahiro Iwaoka of Tokyo University of Agriculture and Technology, and Associate Professor Dr. Kazuhiro Aruga of Utsunomiya University for their excellent understanding, great cooperation, and valuable advice. His sincere thanks are also extended to the members of the Laboratory of Forest Utilization of the University of Tokyo, the technical officers of the University Forest in Chichibu of the University of Tokyo, the technical officers of the Takizawa Experimental Forest of Iwate University, the technical officers of the Toyoma-cho Forest Owner's Association, and the members of the Biomass Division of the Japan Institute of Energy for their cooperation in the experimental work, fruitful discussions, and helpful advice.

This study was financially supported by the Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan (Nos. 10460061, 14-07654, 16-10303, and 18780121), the National Fund for Forest Greenery and Waters from the National Land Afforestation Promotion Organization of Japan, and Nihon University.

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Yoshioka T, Iwaoka M, Sakai H, Kobayashi H. Feasibility of a harvesting system for logging residues as unutilized forest biomass. Journal of Forest Research 2000; 5: 59–65.

Yoshioka T, Aruga K, Sakai H, Kobayashi H, Nitami T. Cost, energy and carbon dioxide (CO2) effectiveness of a harvesting and transporting system for residual forest biomass. Journal of Forest Research 2002a; 7: 157–163.

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Yoshioka T, Aruga K, Nitami T, Kobayashi H, Sakai H. Energy and carbon dioxide (CO2) balance of logging residues as alternative energy resources: System analysis based on the method of a life cycle inventory (LCI) analysis. Journal of Forest Research 2005a; 10: 125–134.

Yoshioka T, Hirata S, Matsumura Y, Sakanishi K. Woody biomass resources and conversion in Japan: The current situation and projections to 2010 and 2050. Biomass and Bioenergy 2005b; 29: 336–346.

Yoshioka T, Aruga K, Nitami T, Sakai H, Kobayashi H. A case study on the costs and the fuel consumption of harvesting, transporting, and chipping chains for logging residues in Japan. Biomass and Bioenergy 2006a; 30: 342–348.

Yoshioka T, Sakurai R, Aruga K, Nitami T, Sakai H, Kobayashi H. Comminution of logging residues with a tub grinder: Calculation of the productivity and procurement cost of wood chips. Croatian Journal of Forest Engineering 2006b; 27: 103–114.

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List of Figures

Fig. 1. Overview of the development and diffusion of harvesting technologies according to the kinds of forest biomass resources.

Fig. 2. Present R&D development and stages for energy-conversion processes of woody biomass in Japan. Reprinted from Biomass and Bioenergy, 29(5), Yoshioka et al., Woody biomass resources and conversion in Japan: The current situation and projections to 2010 and 2050, 336–346, Copyright (2005), with permission from Elsevier.

Fig. 3. Prospects for woody bioenergy utilization in Japan from the aspects of the time and the use of the technologies and the resources. Reprinted from Biomass and Bioenergy, 29(5), Yoshioka et al., Woody biomass resources and conversion in Japan: The current situation and projections to 2010 and 2050, 336–346, Copyright (2005), with permission from Elsevier.

Fig. 4. Harvesting system for logging residues by a processor and a forwarder. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Feasibility of a harvesting system for logging residues as unutilized forest biomass. 5(2), 2000, 59–65. Yoshioka, T, Iwaoka, M, Sakai, H, Kobayashi, H, Fig. 1. © 2000, Springer Japan.

Fig. 5. Experimenting with a forwarder hauling of slashes. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Feasibility of a harvesting system for logging residues as unutilized forest biomass. 5(2), 2000, 59–65. Yoshioka, T, Iwaoka, M, Sakai, H, Kobayashi, H, Fig. 2. © 2000, Springer Japan.

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Fig. 6. Relationship between hauling distance of forwarder, L, and volume of logs hauled per day, EF. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Feasibility of a harvesting system for logging residues as unutilized forest biomass. 5(2), 2000, 59–65. Yoshioka, T, Iwaoka

Fig. 7. Harvesting and transporting system for logging residues. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Cost, energy and carbon dioxide (CO2) effectiveness of a harvesting and transporting system for residual forest biomass. 7(3), 2002, 157–163. Yoshioka, T, Aruga, K, Sakai, H, Kobayashi, H, Nitami, T, Fig. 1. © 2002, Springer Japan.

Fig. 8. Three types of the systems classified according to the operating sites of chipper comminuting. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Cost, energy and carbon dioxide (CO2) effectiveness of a harvesting and transporting system for residual forest biomass. 7(3), 2002, 157–163. Yoshioka, T, Aruga, K, Sakai, H, Kobayashi, H, Nitami, T, Fig. 2. © 2002, Springer Japan. Reprinted from Biomass and Bioenergy, 30(4), Proceedings of the third annual workshop of Task 31 'Systainable production systems for bioenergy: Impacts on forest resources and utilization of wood for energy' October 2003, Flagstaff, Arizona, USA, Yoshioka et al., A case study on the costs and the fuel consumption of harvesting, transporting, and chipping chains for logging residues in Japan, 342–348, Copyright (2006), with permission from Elsevier.

Fig. 9. Experimenting with a forwarder hauling of slashes. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Cost, energy and carbon dioxide (CO2) effectiveness of a harvesting and transporting system for residual forest biomass. 7(3), 2002, 157–163. Yoshioka, T, Aruga, K, Sakai, H, Kobayashi, H, Nitami, T, Fig. 3. © 2002, Springer Japan. Reprinted from Biomass and Bioenergy, 30(4), Proceedings of the third annual workshop of Task 31 'Systainable production systems for bioenergy: Impacts on forest resources and utilization of wood for energy' October 2003, Flagstaff, Arizona, USA, Yoshioka et al., A case study on the costs and the fuel consumption of harvesting, transporting, and chipping chains for logging residues in Japan, 342–348, Copyright (2006), with permission from Elsevier.

Fig. 10. Tub grinder. Reprinted with permission from Croatian Journal of Forest Engineering, 27(2), Yoshioka, T et al., Comminution of logging residues with a tub grinder: Calculation of productivity and procurement cost of wood chips, 103–114, Fig. 1, © 2006, Forestry Faculty of Zagreb University.

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Fig. 11. Grapple loader. Reprinted with permission from Croatian Journal of Forest Engineering, 27(2), Yoshioka, T et al., Comminution of logging residues with a tub grinder: Calculation of productivity and procurement cost of wood chips, 103–114, Fig. 2, © 2006, Forestry Faculty of Zagreb University.

Fig. 12. Bucket loader. Reprinted with permission from Croatian Journal of Forest Engineering, 27(2), Yoshioka, T et al., Comminution of logging residues with a tub grinder: Calculation of productivity and procurement cost of wood chips, 103–114, Fig. 3, © 2006, Forestry Faculty of Zagreb University.

Fig. 13. Processed wood chips. Reprinted with permission from Croatian Journal of Forest Engineering, 27(2), Yoshioka, T et al., Comminution of logging residues with a tub grinder: Calculation of productivity and procurement cost of wood chips, 103–114, Fig. 4, © 2006, Forestry Faculty of Zagreb University.

Fig. 14. Breakdown of the total comminuting cost. Reprinted with permission from Croatian Journal of Forest Engineering, 27(2), Yoshioka, T et al., Comminution of logging residues with a tub grinder: Calculation of productivity and procurement cost of wood chips, 103–114, Fig. 5, © 2006, Forestry Faculty of Zagreb University.

Fig. 15. Relationship between the number of daily instances of truck transportation and the costs of comminution and transportation per dry mass of chips. Reprinted with permission from Croatian Journal of Forest Engineering, 27(2), Yoshioka, T et al., Comminution of logging residues with a tub grinder: Calculation of productivity and procurement cost of wood chips, 103–114, Fig. 6, © 2006, Forestry Faculty of Zagreb University.

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Fig. 16. Process tree of a biomass procurement and bioenergy supply system. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Energy and carbon dioxide (CO2) balance of logging residues as alternative energy resources: System analysis based on the method of a life cycle inventory (LCI) analysis. 10(2), 2005, 125–134. Yoshioka, T, Aruga, K, Nitami, T, Kobayashi, H, Sakai, H, Fig. 1. © 2005, Springer Japan.

Fig. 17. Breakdown of the annual energy input into the system. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Energy and carbon dioxide (CO2) balance of logging residues as alternative energy resources: System analysis based on the method of a life cycle inventory (LCI) analysis. 10(2), 2005, 125–134. Yoshioka, T, Aruga, K, Nitami, T, Kobayashi, H, Sakai, H, Fig. 2. © 2005, Springer Japan.

Fig. 18. Sensitivity analysis to the LCI results. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Energy and carbon dioxide (CO2) balance of logging residues as alternative energy resources: System analysis based on the method of a life cycle inventory (LCI) analysis. 10(2), 2005, 125–134. Yoshioka, T, Aruga, K, Nitami, T, Kobayashi, H, Sakai, H, Fig. 3. © 2005, Springer Japan.

Fig. 19. Conversion of forest and public roads into vector data. Reprinted with permission from Croatian Journal of Forest Engineering, 26(2), Yoshioka, T, Sakai H, Amount and availability of forest biomass as an energy resource in a mountainous region in Japan: a GIS-based analysis, 59–70, Fig. 1, © 2005, Forestry Faculty of Zagreb University.

Fig. 20. Digital elevation model (DEM, right) corresponding to a contour map (left). The vertical interval of the contour map is 10 m. The mesh size of the DEM is 50 m, and the numerical value in each mesh indicates the height above sea level at the top-left grid point of the mesh (unit: m). Reprinted with permission from Croatian Journal of Forest Engineering, 26(2), Yoshioka, T, Sakai H, Amount and availability of forest biomass as an energy resource in a mountainous region in Japan: a GIS-based analysis, 59–70, Fig. 2, © 2005, Forestry Faculty of Zagreb University.

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Fig. 21. Conversion of vector data into raster data. Reprinted with permission from Croatian Journal of Forest Engineering, 26(2), Yoshioka, T, Sakai H, Amount and availability of forest biomass as an energy resource in a mountainous region in Japan: a GIS-based analysis, 59–70, Fig. 3, Fig. 4, © 2005, Forestry Faculty of Zagreb University.

Fig. 22. Classification of systems according to the parts of a tree for energy. Reprinted with permission from Croatian Journal of Forest Engineering, 26(2), Yoshioka, T, Sakai H, Amount and availability of forest biomass as an energy resource in a mountainous region in Japan: a GIS-based analysis, 59–70, Fig. 5, © 2005, Forestry Faculty of Zagreb University.

Fig. 23. Classification of machines according to the topographical conditions. Reprinted with permission from Croatian Journal of Forest Engineering, 26(2), Yoshioka, T, Sakai H, Amount and availability of forest biomass as an energy resource in a mountainous region in Japan: a GIS-based analysis, 59–70, Fig. 6, © 2005, Forestry Faculty of Zagreb University.

Fig. 24. Distribution map of the procurement cost of forest biomass (unit: US$/MgDM). Reprinted with permission from Croatian Journal of Forest Engineering, 26(2), Yoshioka, T, Sakai H, Amount and availability of forest biomass as an energy resource in a mountainous region in Japan: a GIS-based analysis, 59–70, Fig. 7, © 2005, Forestry Faculty of Zagreb University.

Fig. 25. Relationship between the mass and the procurement cost of forest biomass. Reprinted with permission from Croatian Journal of Forest Engineering, 26(2), Yoshioka, T, Sakai H, Amount and availability of forest biomass as an energy resource in a mountainous region in Japan: a GIS-based analysis, 59–70, Fig. 8, © 2005, Forestry Faculty of Zagreb University.

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Table 1. Annual potential amount of woody biomass in Japan on a dry-weight basis.1 Reprinted from Biomass and Bioenergy, 29(5), Yoshioka et al., Woody biomass resources and conversion in Japan: The current situation and projections to 2010 and 2050, 336–346, Copyright (2005), with permission from Elsevier.

Table 2. Harvesting and transporting costs of logging residues per Mg on a dry-weight basis. Reprinted from Biomass and Bioenergy, 29(5), Yoshioka et al., Woody biomass resources and conversion in Japan: The current situation and projections to 2010 and 2050, 336–346, Copyright (2005), with permission from Elsevier.

Table 3. Advantages and disadvantages of the co-firing of woody biomass with coal at an existing coal-fired power plant. Reprinted from Biomass and Bioenergy, 29(5), Yoshioka et al., Woody biomass resources and conversion in Japan: The current situation and projections to 2010 and 2050, 336–346, Copyright (2005), with permission from Elsevier.

Table 4. Parameters of the basic theoretical equations (from (3.1) to (3.15)). Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Feasibility of a harvesting system for logging residues as unutilized forest biomass. 5(2), 2000, 59–65. Yoshioka, T, Iwaoka, M, Sakai, H, Kobayashi, H, Table 1. © 2000, Springer Japan.

Table 5. Outline of the investigated site. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Feasibility of a harvesting system for logging residues as unutilized forest biomass. 5(2), 2000, 59–65. Yoshioka, T, Iwaoka, M, Sakai, H, Kobayashi, H, Table 2. © 2000, Springer Japan.

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Table 6. Data collected from the field experiment. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Feasibility of a harvesting system for logging residues as unutilized forest biomass. 5(2), 2000, 59–65. Yoshioka, T, Iwaoka, M, Sakai, H, Kobayashi, H, Table 3. © 2000, Springer Japan.

Table 7. Data collected from the field experiments and existing studies: (a) Forwarder hauling. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Cost, energy and carbon dioxide (CO2) effectiveness of a harvesting and transporting system for residual forest biomass. 7(3), 2002, 157–163. Yoshioka, T, Aruga, K, Sakai, H, Kobayashi, H, Nitami, T, Table 1(a). © 2002, Springer Japan. Reprinted from Biomass and Bioenergy, 30(4), Proceedings of the third annual workshop of Task 31 'Systainable production systems for bioenergy: Impacts on forest resources and utilization of wood for energy' October 2003, Flagstaff, Arizona, USA, Yoshioka et al., A case study on the costs and the fuel consumption of harvesting, transporting, and chipping chains for logging residues in Japan, 342–348, Copyright (2006), with permission from Elsevier.

Table 8. Data collected from the field experiments and existing studies: (b) Truck transporting.1 Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Cost, energy and carbon dioxide (CO2) effectiveness of a harvesting and transporting system for residual forest biomass. 7(3), 2002, 157–163. Yoshioka, T, Aruga, K, Sakai, H, Kobayashi, H, Nitami, T, Table 1(b). © 2002, Springer Japan. Reprinted from Biomass and Bioenergy, 30(4), Proceedings of the third annual workshop of Task 31 'Systainable production systems for bioenergy: Impacts on forest resources and utilization of wood for energy' October 2003, Flagstaff, Arizona, USA, Yoshioka et al., A case study on the costs and the fuel consumption of harvesting, transporting, and chipping chains for logging residues in Japan, 342–348, Copyright (2006), with permission from Elsevier.

Table 9. Data collected from the field experiments and existing studies: (c) Chipper comminuting. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Cost, energy and carbon dioxide (CO2) effectiveness of a harvesting and transporting system for residual forest biomass. 7(3), 2002, 157–163. Yoshioka, T, Aruga, K, Sakai, H, Kobayashi, H, Nitami, T, Table 1(c). © 2002, Springer Japan. Reprinted from Biomass and Bioenergy, 30(4), Proceedings of the third annual workshop of Task 31 'Systainable production systems for bioenergy: Impacts on forest resources and utilization of wood for energy' October 2003, Flagstaff, Arizona, USA, Yoshioka et al., A case study on the costs and the fuel consumption of harvesting, transporting, and chipping chains for logging residues in Japan, 342–348, Copyright (2006), with permission from Elsevier.

Table 10. The harvesting cost and the fuel consumption in each of the three systems, including the harvesting cost per MWh of bioenergy, the "energy input rate," and the preliminary sensitivity analysis. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Cost, energy and carbon dioxide (CO2) effectiveness of a harvesting and transporting system for residual forest biomass. 7(3), 2002, 157–163. Yoshioka, T, Aruga, K, Sakai, H, Kobayashi, H, Nitami, T, Table 2. © 2002, Springer Japan. Reprinted from Biomass and Bioenergy, 30(4), Proceedings of the third annual workshop of Task 31 'Systainable production systems for bioenergy: Impacts on forest resources and utilization of wood for energy' October 2003, Flagstaff, Arizona, USA, Yoshioka et al., A case study on the costs and the fuel consumption of harvesting, transporting, and chipping chains for logging residues in Japan, 342–348, Copyright (2006), with permission from Elsevier.

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Table 11. Comparison with three European countries in terms of harvesting cost and CO2 emission per MWh of bioenergy. Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Cost, energy and carbon dioxide (CO2) effectiveness of a harvesting and transporting system for residual forest biomass. 7(3), 2002, 157–163. Yoshioka, T, Aruga, K, Sakai, H, Kobayashi, H, Nitami, T, Table 3. © 2002, Springer Japan.

Table 12. Details on the calculations used for the total comminuting cost. Reprinted with permission from Croatian Journal of Forest Engineering, 27(2), Yoshioka, T et al., Comminution of logging residues with a tub grinder: Calculation of productivity and procurement cost of wood chips, 103–114, Table 1, © 2006, Forestry Faculty of Zagreb University.

Table 13. Basic data on a biomass-fired power generation plant.(1) Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Energy and carbon dioxide (CO2) balance of logging residues as alternative energy resources: System analysis based on the method of a life cycle inventory (LCI) analysis. 10(2), 2005, 125–134. Yoshioka, T, Aruga, K, Nitami, T, Kobayashi, H, Sakai, H, Table 1. © 2005, Springer Japan.

Table 14. Basic data on the forestry machines.1 Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Energy and carbon dioxide (CO2) balance of logging residues as alternative energy resources: System analysis based on the method of a life cycle inventory (LCI) analysis. 10(2), 2005, 125–134. Yoshioka, T, Aruga, K, Nitami, T, Kobayashi, H, Sakai, H, Table 2. © 2005, Springer Japan.

Table 15. Required materials for a biomass-fired power generation plant.* Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Energy and carbon dioxide (CO2) balance of logging residues as alternative energy resources: System analysis based on the method of a life cycle inventory (LCI) analysis. 10(2), 2005, 125–134. Yoshioka, T, Aruga, K, Nitami, T, Kobayashi, H, Sakai, H, Table 3. © 2005, Springer Japan.

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Table 16. Energy density of the required materials and fuel.* Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Energy and carbon dioxide (CO2) balance of logging residues as alternative energy resources: System analysis based on the method of a life cycle inventory (LCI) analysis. 10(2), 2005, 125–134. Yoshioka, T, Aruga, K, Nitami, T, Kobayashi, H, Sakai, H, Table 4. © 2005, Springer Japan.

Table 17. Life cycle inventory of logging residues: (I) Energy balance.* Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Energy and carbon dioxide (CO2) balance of logging residues as alternative energy resources: System analysis based on the method of a life cycle inventory (LCI) analysis. 10(2), 2005, 125–134. Yoshioka, T, Aruga, K, Nitami, T, Kobayashi, H, Sakai, H, Table 5. © 2005, Springer Japan.

Table 18. Life cycle inventory of logging residues: (II) CO2 emission.* Reprinted with kind permission from Springer Science + Business Media: Journal of Forest Research, Energy and carbon dioxide (CO2) balance of logging residues as alternative energy resources: System analysis based on the method of a life cycle inventory (LCI) analysis. 10(2), 2005, 125–134. Yoshioka, T, Aruga, K, Nitami, T, Kobayashi, H, Sakai, H, Table 6. © 2005, Springer Japan.

Table 19. Operation patterns of sub-compartments to be felled. Reprinted with permission from Croatian Journal of Forest Engineering, 26(2), Yoshioka, T, Sakai H, Amount and availability of forest biomass as an energy resource in a mountainous region in Japan: a GIS-based analysis, 59–70, Table 1, © 2005, Forestry Faculty of Zagreb University.

Table 20. Methods for calculating the amount of biomass resources.* Reprinted with permission from Croatian Journal of Forest Engineering, 26(2), Yoshioka, T, Sakai H, Amount and availability of forest biomass as an energy resource in a mountainous region in Japan: a GIS-based analysis, 59–70, Table 2, © 2005, Forestry Faculty of Zagreb University.

Table 21. Cost functions for harvesting and transportation of forest biomass.* Reprinted with permission from Croatian Journal of Forest Engineering, 26(2), Yoshioka, T, Sakai H, Amount and availability of forest biomass as an energy resource in a mountainous region in Japan: a GIS-based analysis, 59–70, Table 3, © 2005, Forestry Faculty of Zagreb University.

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Table 22. Annual available amount of forest biomass in the region. Reprinted with permission from Croatian Journal of Forest Engineering, 26(2), Yoshioka, T, Sakai H, Amount and availability of forest biomass as an energy resource in a mountainous region in Japan: a GIS-based analysis, 59–70, Table 4, © 2005, Forestry Faculty of Zagreb University.