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英国硕士烘焙的技术经济评价Assignment范文

论文价格: 免费 时间:2016-10-11 14:46:41 来源:www.ukassignment.org 作者:留学作业网
abstract摘要
 
预处理步骤具有生物能源链的性能有显著的影响,特别是在物流。烘焙,球团和热解技术,可在适度的尺度转化成生物质致密能源载体的便于运输和处理。烘焙是一个非常有前途的技术,由于相对于造粒(84%)和热解(64%)的高处理效率(94%)。1当焙干用制粒结合时,产物(TOP2)能量含量高达20.4 -22.7 GJ /吨。从拉丁美洲到鹿特丹港TOP交货的一次能源需求可能低至0.05 GJ / GJ,而相比之下,0.12 GJ / GJ的颗粒和0.08 GJ / GJHHV热解油。 TOP可以从现有的共烧植物递送到欧洲超过74的h /吨(3.3 H / GJ),电可制作廉价为4.4 hcent / kWhe。费舍尔Tropisch燃料成本6小时/ GJHHV为TOP,7小时/ GJ常规颗粒和9.5 H / GJHHV热解油。因此,来自TOP和常规粒料燃料生产是可比当前汽油生产成本为3〜7小时/ GJand柴油从2至7小时/ GJ,取决于油市场。3 HHV HHVThus,精心设计的供应链使国际从生物能源利用效率和经济的角度来看是可行的交易。与2008年保留爱思唯尔有限公司保留所有权利。The pre-treatment step has a significant influence on the performance of bioenergy chains, especially on logistics. Torrefaction, pelletisation and pyrolysis technologies can convert biomass at modest scales into dense energy carriers that ease transportation and handling. Torrefaction is a very promising technology due to its high process efficiency (94%) compared to pelletisation (84%) and pyrolysis (64%).1 When torrefaction is combined with pelletisation, the product (TOP2) energy content is as high as 20.4–22.7 GJ/ton. The primary energy requirement for TOP delivery from Latin America to Rotterdam harbour can be as low as 0.05 GJ/GJ, in contrast to 0.12 GJ/GJ for pellets and 0.08 GJ/GJHHV for pyrolysis oil. TOP can be delivered to Europe at over 74 h/ton (3.3 h/GJ) and electricity could be produced as cheap as 4.4 hcent/kWhe from an existing co-firing plant. Fisher Tropisch fuel costs 6 h/GJHHV for TOP, 7 h/GJ for conventional pellets and 9.5 h/GJHHV for pyrolysis oil. Consequently, fuel production from TOP and conventional pellets is comparable to the current gasoline production cost ranging from 3 to 7 h/GJand diesel from 2 to 7 h/GJ, depending on the oil market.3 HHV HHVThus, well designed supply chains make international trade of biomass feasible from energy efficiency and economic perspective. & 2008 Elsevier Ltd. All rights reserved. 
 
1. Introduction 介绍
 
Sustained energy supply is an essential objective to achieve and depends on ensuring secure and reliable energy sources. However, the European Union (EU) import dependency is rising. Unless domestic energy becomes more competitive in the next 20–30 years around 70% of the EU’s energy needs are expected to be met by imported products—some from regions threatened by insecurity [1]. On the other hand, fossil fuel consumption causes substantial environmental harm notably, climate change. Energy production and consumption account for 81.5% of the total green house gas (GHG) emissions in the EU-25 [2]. In addressing those threats, the EU is increasingly shifting towards policies favouring use of renewable energy sources. Currently biomass delivers around 4% of the EU’s primary energy (Eurostat) and in order to reach the future targets set out by the . Corresponding author at: Department of Science, Technology and Society, Copernicus Institute, Utrecht University, Heidelberglaan 2, 3584 CS Utrecht, The Netherlands. Tel.: +31 224212868; fax: +31 224291730. E-mail address: ayla.uslu@eea.europa.eu (A. Uslu). 1 Process efficiency includes sizing and drying of biomass. 2 TOP: torrefied and pelletised biomass. EU, significant amounts of biomass will be required. The renewable energy target in the EU’s overall mix is determined as 20% by 2020, which corresponds to 230–250 MtOE bioenergy depending on various assumptions [3].3 Furthermore as a substitute for transportation fuels, the EU set itself a minimum binding target of 10% biofuel use by 2020. Moreover, bioenergy contributes 22% of the primary energy supply in developing countries, and around 10% of global energy demand [4]. Since some countries have larger land areas used at lower densities compared to others, they may become net suppliers of renewable bioenergy. While biomass production costs in such countries may be relatively low, there will be additional logistic costs, energy uses and material losses [5]. However, several studies have given indications that international trade in biofuel could be economically feasible [6–8]. These studies, concerning long distance bio-energy transportation, analysed several cases to calculate biomass delivery and final energy production costs. Hamelinck developed a tool with which different bioenergy chains were analysed [5,6]. This work clarified that densification 3 The amount of bioenergy is dependent upon the total energy consumption growth, the increases in the other renewable energy sources and the end-use of the biomass. 0360-5442/$ -see front matter & 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2008.03.007  
A. Uslu et al. / Energy 33 (2008) 1206–1223 prior to international transportation of biomass is crucial, as converting biomass into a densified intermediate can save transport and handling costs. In addition, it can improve the efficiency of the final conversion stage. Subsequently, pretreatment is a key step in the total supply chain. Broadly, feedstock costs contribute around 20–65% of the total delivery cost whereas pre-treatment and transport contribute 20–25% and 25–40%, respectively, depending on the location of the biomass resources [5]. However, recent and potential future improvements of pre-treatment technologies and their subsequent impacts on the overall bioenergy chain have not been addressed in detail. Currently, the state-of-the-art (SOTA) biomass-to-energy chains are mostly based on pelletisation. However, the pretreatment technologies such as fast pyrolysis and torrefaction may improve the economics of the overall production chain. However, these technologies are still under development and their economic and technical performances are unclear. There are no normalised data sets available in literature and the available information mainly discusses the technology and the intermediate products, rather than their influence on the performances of the whole production chains. The main objective in this study is therefore to assess which pre-treatment method(s), at what point of the chain, with which conversion technology (ies) would give the optimal power and fuel (syngas) delivery costs for international biomass supply chains. The study focuses on detailed techno-economic analysis of key pre-treatment technologies, namely torrefaction, pyrolysis and pelletisation and their respective impacts, in terms of costs and energy uses in various chains for biomass production and use. 
 
2. Methodology and evaluation criteria 方法和评价标准
 
A technology review was performed to collect design data of pre-treatment technologies. Mass yields, energy yields and process efficiencies of each technology were evaluated, partly by building simple models to determine energy and mass balances. The economic evaluation of the technologies was based on component level cost data, which were obtained from literature and personal communication with experts. Since the capacities of the components affect the specific cost of a plant, economies of scales were analysed. These were done by identifying the base scales, base costs and the maximum scales of the equipment. Next, the equipment costs for designed scales were calculated using the scale factors per component obtained from literature. Capital investment requirements4 and production costs were calculated, and subsequently a sensitivity analysis was performed to identify the most important parameters that influence the production costs. Cost data were normalised using the OECD deflator and exchange rates of national currencies. Following the techno-economic assessment of each pretreatment technology, several biomass-to-energy chains were designed depending on the location and scale of the technology applied. The chain assumptions were based on feedstock harvested in South America (Brazil) and the final conversion applied in North-West Europe. Final conversion technologies comprise Entrained Flow Gasification for Fischer Tropsch liquid (EF-FT) production, biomass integrated gasification combined cycle (BIGCC), SOTA combustion and co-firing for power production. An existing model and database developed by Hamelinck was used to design the chains [5,6]. This tool enables chains to be set up with harvesting, transport, storage, handling, pre-treatment and final conversion steps considered in many ways. It also calculates energy and mass balances and economic performances of the chains selected. Chain analyses were followed by sensitivity analyses to test the robustness of the study results and assess the variation in fuel/power costs. The performance and economic impacts of pre-treated biomass on final conversion stage was not studied in this research, as this requires an extensive technoeconomic analysis which could however be the focus of future research. 
 
3. Techno-economic evaluation 技术经济评价
 
3.1. Torrefaction 
Torrefaction is a thermal pre-treatment technology performed at atmospheric pressure in the absence of oxygen. Temperatures between 200 and 300 1C are used, which produces a solid uniform product with very low moisture content and a high calorific value compared to fresh biomass. Even though torrefaction is in its infancy, several studies show that torrefaction increases the energy density, hydrophobic nature and grindability properties of biomass [9–11]. Torrefied biomass typically contains 70% of its initial weight and 90% of the original energy content [9,11]. The moisture uptake of torrefied biomass is very limited, varying from 1% to 6%. #p#分页标题#e#
 
3.1.1. Torrefaction conditions and products 
Torrefaction process composes of initial heating, pre-drying, post-drying and intermediate heating stages. Above 200 1C, the torrefaction reaction occurs where devolatilisation takes place. Finally, the solid product is cooled to below 200 1C, which terminates the torrefaction process [9]. During torrefaction, biomass loses relatively more oxygen and hydrogen compared to carbon. Subsequently, the calorific value of the product increases. The net calorific value of torrefied biomass is in the range of 18–23 MJ/kg LHV5 (dry) or 20–24 MJ/kg HHV6 (dry) [9,11]. The moisture uptake of torrefied biomass is very limited due to the dehydration reactions during the torrefaction reaction. Destruction of OH groups in the biomass by dehydration reactions causes the loss of capacity to form hydrogen bonds with water. In addition, non-polar unsaturated structures are formed which makes the torrefied biomass hydrophobic [9]. The torrefied biomass also becomes more porous with a volumetric density of 180–300 kg/m3, depending on the initial biomass density and torrefaction conditions. It is more fragile as it looses its mechanical strength, making it easier to grind or pulverise. 
 
3.1.2. State-of-the-art (SOTA) system description 
Torrefaction technology is not yet commercially available. Pechiney has built the first demonstration unit that was in operation since 1987 with a capacity of 12 000 ton/yr of torrefied wood used as a reduction agent for the metallurgic industry [9].The process mainly consisted of a chopper, a drying kiln, and a torrefaction reactor (roaster) that required maximum 10% m.c. There were various problems with this reactor design when it was considered for bigger scales. The heat exchange area was a limiting factor. The feed moisture content was limited to 15% while the reactor throughput was limited to 2 ton/h. Higher moisture contents would drop the reactor throughput. Another disadvantage was that the reactor required free-flowing feed particles [9]. 45Capital costs consist of direct costs (equipment+total installation costs), LHV: lower heating value, untreated wood energy content is in the range of indirect costs (engineering and supervision, construction expense/contractor fee, 17–19 MJ/kg, charcoal is 30 MJ/kg and coal is 25–30 MJ/kg (LHVdry). 6contingency) and working capital. HHV: higher heating value.  
A. Uslu et al. / Energy 33 (2008) 1206–1223 Drying Torrefaction Cooling Heat exchange biomass Torrefied biomass Air utillity Fuel Fluegas Combustion DP Torrefaction gases Fluegas Fluegas gas recycle 
Fig. 1. General flow diagram of ECN torrefaction process [9] (DP: pressure drop recovery). 
 
3.1.3. Energy Research Centre of The Netherlands (ECN) torrefaction technology 
At ECN, a torrefaction process based on direct heating of the biomass by using the recycled hot gas has been designed. The torrefaction gas is re-pressurised and heated before it is recycled to the reactor. The moisture content of the feedstock in this process is extremely important since the feedstock property determines the required heat demand (Fig. 1). In this design, the combustion of torrefaction gas is expected to cover the energy demand of the dryer (without or with a minimal) utility fuel consumption. Thus, this results in a self supporting, high efficiency system. The calorific value of the produced gas ranges from 5.3 to 16.2 MJ/N m3 at the temperatures of 265 and 290 1C, respectively [9]. 
 
3.1.4. Torrefied biomass densification (torrefied and pelletised biomass, TOP) 
As described previously, torrefied biomass is a porous product with a low density. It is fragile, which makes it relatively easy to grind. However, decreased mechanical strength and increased dust formation, in addition to low volumetric density, makes further densification desirable. This is especially important when long distance transport is considered. In the ECN Laboratories, the mass density of torrefied biomass pellet has been measured at around 22 MJ/kg, whereas the energy density reaches up to 18 GJ/m3. Although this energy density is less than that of coal (20.4 GJ/m3), it is 20% higher than commercial wood pellets [9,12]. Thus, torrefaction in combination with pelletisation (TOP) offers significant advantages when the biomass logistics are considered. The pressure required for densification could be reduced by a factor of 2 at 225 1C, while the energy consumption of densification could be reduced by a factor of 2 compared to biomass pelletisation [9,13–15]. Torrefaction can reduce power consumption required for size reduction by up to 70–90% compared to conventional biomass pelletisation [16]. A simpler type of size reduction, such as cutting mills and jaw crushers, can be deployed instead of hammer mills 
 
3.1.5. Mass and energy balance 
Experiment and process simulations conducted by ECN have been combined to identify the energy and mass balance, thermal process efficiency, auto-thermal operations and combustibility of torrefaction gas. Torrefaction experiments are conducted in an indirectly heated screw reactor and a batch reactor. Willow and woodcutting are used as feedstock for these experiments. For the simulation-derived parameters, ASPEN simulations are performed on the basis of mass and energy yields of torrefaction that were experimentally determined. The flow sheet calculations in ASPEN are done for a production rate of 150 MWth torrefied biomass. The default moisture content of feedstock was 50%. Flue gas stack temperature was around 140 1C. The heat losses in drying and torrefaction were around 0.5% HHV of biomass feedstock. 
Fig. 2 represents the net energy flows of one of the points of operation in LHV. In order to dry the wet biomass (50%) to 15%, 22.2 MWth energy is used. This increases the calorific value resulting in an energy flow increase from 135.7 to 152.8 MWth (corresponding to a thermal efficiency of 96%). The thermal efficiency of torrefaction on the other hand is 100% since the torrefaction gas is fully utilised through combustion (neglecting heat losses to the environment). Moreover, the moisture content of the torrefied product is as low as 1–6% which decreases the difference between LHV and HHV significantly. The process efficiency (96.1%) is determined by the efficiency of drying, lowered by the heat losses to the environment during combustion and torrefaction. Net efficiency is around 91% when the utility consumption is included. The mass yield of the torrefaction process is around 70%. 
 
3.1.6. Economic evaluation 
The economic evaluation is based on estimations of required annual investment7 and total production costs. The total capital investment is calculated using the combination of 7 Annual investment cost is calculated as Iannual . a  It, a . r/(1 (1+r) L where a: the capital recovery factor, It: total investment, r: the discount rate and L: which are used for the conventional pelletising process [16]. the life time or depreciation period of the equipment.  
A. Uslu et al. / Energy 33 (2008) 1206–1223 Fluegas Drying Torrefaction HE biomass Torrefied biomass Combustion Fluegas 051152.8135.7156.1 22.2 21.4 7.97 5.47 27.7 14.7 Cooling 4.10 Torrefaction gas Fig.2.Netenergyflows(inMWth)correspondingwithtorrefactionofwoodcuttingsat2801Cand17.5minreactiontime(HE:heatexchanger)[9].[Itshouldbenotedthattheenergyflowsmentionedinthefigureareforwoodcuttingsandthiswoulddifferwhenadifferentfeedstockwithdifferenthemicellulosecompositionisapplied.]capacity-factored equipment-based estimates, and vendor quotes of the main plant items. The flow rates, heat duty, power equipment and capacity ratios are used in the capacity-factored estimation. The equipment-based estimations are done according to detailed design calculations [9]. The maximum capacity of a single torrefaction process line is estimated about 50–60 kton/a production capacity, corresponding to a fuel production of 30–40 MWth.8 Capital investment cost of a 60 kton/a production process is estimated at 5.2–7.5 Mh. Around 39% of the cost comprises the installation costs, while 31% comprises the equipment costs. When the feedstock cost is excluded, total production cost of torrefied biomass is calculated in the range of around 40–56 h/ton. 
 
3.2. Pyrolysis 
3.2.1. Process definition 
Pyrolysis can be described as the direct thermal decomposition of biomass in the absence of oxygen [17]. Temperatures employed in pyrolysis are 400–800 1C [18]. The products are gas, liquid and solid char, and their relative proportions depend on the pyrolysis method, the characteristics of the biomass and the reaction parameters. Fast pyrolysis is one of the methods where very high heating rates (around 500 1C) at moderate temperatures and rapid product quenching are employed to produce pyrolysis oil (bio-oil) [19]. It generates mostly vapours and aerosols. Generally, the yields are 40–65 wt% organic condensates, 10–20% char, 10–30% gases and 5–15% water based on dry feed [20]. The energy content of the pyrolysis oil is around 15–18 MJ/kg with a moisture content around 25%. The LHV of gas is around 15 MJ/N m3 and the char is around 32 MJ/kg [20].9 The char produced in fast pyrolysis is very flammable due to its small particle size and high volatility. Therefore, hot char from the process should be properly handled to avoid ignition. #p#分页标题#e#
 
3.2.2. SOTA technology 
Fast pyrolysis of biomass is on the verge of development and demonstration stage (in power production) [21–25]. Fluidised and transported bed reactors have gained acceptance for being reliable thermal reaction devices capable of producing bio-oil with relatively high yields. However, other reactor types such as ablative, rotating cone and vacuum reactors have varying benefits and drawbacks compared to each other. Both bubbling and circulating fluidised bed reactors are commercially available with the capacities of 20–400 kg/h10 for bubbling and 20–1700 kg/h for circulating bed type,11 however, currently deployed pyrolysis systems are relatively small ranging from 20 to 3500 kg/h (in dry feed bases). Even though Fluidised Bed (FB) reactors are reliable (they have a long history and are commercially applied) one of the main constraints they have is their requirement for very small feedstock sizes (1–2 mm). Another constraint is the dependency of the reactor throughput on the amount and efficiency of the heat supplied. Even though in some reactor types the fluidising gas can be preheated and recycled back to the system (as in Fig. 4), this usually results in scale up difficulty. On the other hand ablative reactors can handle feedstock sizes up to 20 mm, however, they are subject to erosion risk due to high entering velocities. Vacuum reactors are not promising since they have relatively lower bio-oil yields (30–45%) even though the bio-oil produced is very clean [19,26–29]. A rotating cone reactor has been developed at the University of Twente. This reactor is based on mixing of biomass feedstock with hot sand near the bottom of the cone and transportation upwards by the rotating action of cone. It is scaled up to 200 kg/h as a pilot plant. This technology does not require a carrier gas for pyrolysis and this makes bio-oil recovery easier. Moreover it is a compact technology with a good integration of heat [29]. 
 
3.2.3. Mass and energy balance 
The mass and energy yield of rotating cone pyrolysis technology is presented in Fig. 3. The mass yield of bio-oil is around 70%, while non-condensable gas mass yield and char yield are around 20% and 10%, respectively. The energy yield of this fast pyrolysis process is determined to be around 66% [30]. 
 
3.2.4. Economic evaluation 
Since the cost data for pyrolysis plants varies significantly, rotating cone pyrolysis plant (25 MWth) cost data from reference [30] is compared to a reference pyrolysis plant calculated in this study in order to identify the possible lowest and highest cost ranges for the same scale. The reference plant calculation is based 8 [9]. 9 10When the fast pyrolysis reactor operation is in favour of maximum liquid RTI, Canada and Dynamotive. 11production with a minimum of vapour cracking. Ensyn Design.  
A. Uslu et al. / Energy 33 (2008) 1206–1223 0.7 kg/hr fluegas bio-oil4 tons/hr 5.5 tons/hr 5.5 tons/hr7.5 tons/hr 16.5 MWLHV 25 MWLHV 25 MWLHV25 MWLHV gas 0.75 tons/hr Dryer Pyrolysis unit 2.1MWLHVHammer mill ash 0.05 tons/hr 
Fig. 3. The mass and energy balance of a 5-tondry feed/h pyrolysis plant [30]. on the cost data obtained from literature for feedstock preparation unit, dryer, hammer mill12 and the pyrolysis reactor.13 As a result, 25 MWth capacity pyrolysis plant capital investment cost is calculated as being in the range of 4.5–11.5 Mh. In addition, when the feedstock cost is excluded, the production cost is calculated as being around 75–150 h/ton (6–12 h/GJ).14 
 
3.3. Pelletisation 
Pelletisation can be defined as drying and pressing of biomass under high pressure to produce cylindrical pieces of compressed and extruded biomass. Pellets have a smaller volume and a higher volumetric energy density compared to wood chips and are hence more efficient to store, ship and convert into energy [31]. Pelletisation not only produces a uniform and stable fuel, but also the amount of dust produced is minimised. Another advantage of pelletisation is that it enables free flowing,15 which facilitates material handling and rate of flow control important for loading and unloading operations [32]. The production of pellets requires small feedstock particles, maximum 3–20 mm and moisture content below 10–15%[33]. However, piston press pelletisation can handle up to 20% moisture content [34–37]. Pelletisation is performed at a temperature of around 150 1C. Water plays an important role in densification. If the feedstock is either too dry or too wet, the pressure required for densification increases dramatically. In fact, moisture content of 10–25% is considered optimal [14]. Thus, the feedstock is heated to 50–100 1C to soften the lignin and obtain the desired moisture content and at approximately 150 1C mechanical densification is applied. 12 The base scales of 100 ton/h rotary drum dryer with 5 Mh capital cost, a 50 ton/h hammer mill with 0.37 Mh capital cost and 5000 m3 silo with 0.331 Mh from reference [5] are applied to calculate the 25 MWth reference pyrolysis plant. The scaled factor used is 0.7. 13 The pyrolysis reactor cost data is calculated by the below equation derived from reference [19]. TPC, kECU2000 . 40.8  (Q(kg-dry/h) where TPC: total plant cost of the pyrolysis reactor, Q: the mass flow rate of prepared wood feed into the reactor. However, in this study five different pyrolysis plant cost data are plotted to a graph and the equation, TCI, 2004 . 94.126  Q (kg-dry/h) is derived. These plants are from Ensyn (transported bed reactor), Egemin (entrained flow), Interchem (NA) Industries (ablative), BTG (rotating cone) and ASR (vacuum). Since the cost data calculated by Bridgwater’s equation is higher, it is used as the maximum cost data. 14 Assumptions are: 70% bio oil yield with 17. 5 MJ/kg LHV, 7500 h/year biomass availability. 15 Free flowing: particles having the same shape ensuring that they can flow pelletisation biomass screening drying grinding pellet storagecooling 
Fig. 4. State-of-the-art pellet production process diagram. 
3.3.1. State-of-the-art (SOTA) system description 
Pelletising has been commercialised. For example, a 120-ton/ day plant has been operating since 1976 in Oregon [14].In addition, Finland and Sweden are the two leading countries in pelletising technology in Europe. Pellet production basically consists of at least four steps: drying, milling (grinding), pelletising and cooling (Fig. 4). 3.3.2. Product The produced pellets have a net calorific heating value in the range of 16–18 MJ/kg. The actual value largely depends on the moisture content which varies between 5% and 10% (Table 1). 3.3.3. Improvements in pelletising technology Currently there are two different processes, under development in order to improve the quality of the pellets and to decrease the energy consumption during the pelletisation process. The first of these is a steam explosion process tested in a demonstration unit [37]. The aim is to produce pellets which are much harder, have a higher specific weight (a bulk density of 850 kg/m3) and are less sensitive to moisture and separation of fines. The research is being carried out in Norway at the Cambi Bioenergi Vestmarka. The raw material is preconditioned in this technology by heating a steam-compression reactor to release the natural lignin. After a certain exposure time, the pressure is reduced, which causes the material to explode. In the literature, it is mentioned that the pre-treatment process increases the pellet mill capacity 100%. However, the plant in Norway is a prototype plant, it is not yet commercial and the economic data is not available. The second technology has been developed by the Italian company EcoTre System. In this new technology, electricity freely. consumption ranges between 0.025 and 0.045 kWh/kg, depending  
A. Uslu et al. / Energy 33 (2008) 1206–1223 
Table 1 Characteristics of wood pellets (sawdust, cutter shavings, and wood-grinding dusts as raw materials) [38] Variables Unit Value Size Diameter mm 6– 10 Length mm 10– 13 Energy content MJ/kg 16.9– 18.0 Moisture content % 7– 12 Ash content % 2 Bulk density kg/m3 650– 700 Space demand m 3/ton 1.5 on the type of wood. The process operates at low temperatures (55–60 1C) and without any additives. The main advantage of this system is its simplicity and lower investment costs. The pelletiser in this process can handle biomass with 30–35% moisture content, which means that a simple dryer can be employed or a dryer might not be required [37]. Energy consumption and investment costs are reduced significantly. The energy consumption of a rotary drum dryer is stated as being around 20 kWhe/ton [5]. 3.3.4. Mass and energy balance During pelletisation process, biomass is dried and pressurised to produce pellets with a moisture content of 10%. Thus, the mass yield is determined by the dryer efficiency. The thermal efficiency is calculated as around 94%,16 while the net efficiency is around 87% when the utility fuel is included [39]. 3.3.5. Economic evaluation A 24,000 tonpellet/yr pelletisation process cost data [39] are used as reference data.17 In addition, the cost data obtained from [5] are normalised so that a comparison can be made. The total investment cost of a 24,000 tonpellet/yr plant is calculated to be in the range of 2 Mh18–2.6 Mh.19 In another study, the investment cost of a 80,000 tonpellet/yr plant is given as 5.9 Mh20 [16]. Thus, the normalised specific 0.15–0.25 Mh/MWth(input). investment cost is in the range of #p#分页标题#e#
 
3.4. Techno-economic comparison of the processes 
Technical and economic comparison of the pre-treatment technologies are presented in Tables 2 and 3. 
3.5. Sensitivity analyses and economy of scale for pre-treatment technologies 
The key parameters that affect the performance of torrefaction, pyrolysis and pelletisation were analysed by means of sensitivity analysis.

Table 4 shows the parameters and the ranges these parameters may vary. 16 The moisture content of the fresh biomass is assumed to be around 35% and the LHV(dry) as 16.5 MJ/kg. The moisture content of the pellet is around 10%. 17 The assumptions are: 6 ton/h fresh biomass with 55% w.b, LHVar is 6.2 GJ/ ton. The biomass leaves the dryer has got 15% m.c. 18 This is the total investment cost mentioned in reference [39]. 19 The cost data for dryer, hammer mill and pellet press are collected from reference [5] and normalised for the 6 ton/h fresh biomass input data. Besides, storage peripheral equipment and general investments which includes mainly construction costs are calculated as the percentages of the total main equipment costs. These percentages are obtained from reference [39]. 20 This value was calculated for greenwood, when sawdust is considered, the cost data is given as 3.9 Mh [16]. The production costs of the three technologies are influenced strongly by biomass costs, investment costs, load factor and the life time. Torrefaction and pyrolysis production costs are more sensitive to the capital investment costs than pellet production (Figs. 5–10). Increasing the capital investment cost 40% increases the torrefied biomass production cost and bio-oil cost around 12%, while it increases pellet production cost 8%. Another important factor that needs further consideration is the scale effect. Economies of scale have a considerable influence on the production costs. The torrefaction and pyrolysis processes are capital-intensive; hence investment costs are key to the establishment of production costs. In Fig. 8, the economy of scale on capital investment costs are displayed. After 40 MWth input, the specific investment cost do not decrease any longer. In contrast, when the capacity is smaller than 40 MWth, production costs will increase. For the pyrolysis process, smaller scales are more favourable. As shown in Fig. 9, capacities larger than 20–25 MWth input do not benefit significantly from economies of scale. 
 
3.6. Final conversion 
Biomass is eventually considered for production of electricity and transportation fuels. In this study, state-of-the-art ‘SOTA’ combustion, co-firing, BIGCC and FT technologies are considered as the final conversion steps. 
 
3.6.1. Impact of pre-treated biomass on gasification systems 
Torrefied biomass has several advantages; prior to gasification, electricity consumption for milling decreases significantly. The fibrous structure and the tenancy of biomass are reduced by hemicellulose decomposition together with the depolymeristation of cellulose during the torrefaction reaction. The power consumption in size reduction is decreased 85% when the biomass is first torrefied. The energy consumption required for milling biomass into 100 mm decreases from 0.08 kWe/kWth(dry) to 0.01–0.02 kWe/kWth when torrefaction is applied [42]. Moreover the capacity of the mill increases in proportion to the particle size. When the 0.2 mm particle size is considered, the chipper capacity for torrefied willow is up to 6.5 times the capacity of untreated willow [42]. For both torrefied pellets and conventional pellets, drying is not needed. In the case of bio-oil, the pre-treatment section needs to be adjusted depending on the bio-oil characteristics. Sizing is not necessary anymore and the feeding system can be similar to the liquid fuel feeding systems for CFB gasification instead of those that are suitable for solid fuel feeding. 
 
3.6.2. Impacts of pre-treated biomass on combustion 
Combustion reactivity of the torrefied biomass has been evaluated21 [9]. The carbon conversion of woodcuttings was measured as 96.1%, while torrefied woodcutting was measured as 96.6%, low volatile coal as 64% and high volatile coal as 81%. It was observed that the carbon conversion of torrefied biomass was comparable to that of woodcuttings and significantly higher compared to low-or high volatile coal [9]. When bio-oil is combusted, the quality of the bio-oil influences the combustion efficiency significantly. The most important parameters for bio-oil combustion are viscosity, water and particulates content, bio-oil raw material, bio-oil age and amount of methanol addition (up to 10% wet) [43]. Methanol addition homogenises poor 21 The LCS experiments were done under typical combustion conditions in coal fired boiler, conversion measurements were obtained after 1000 ms residence time. Results were w.t, ash free.  
A. Uslu et al. / Energy 33 (2008) 1206–1223
Table 2 Technical comparison of torrefaction, TOP, pyrolysis and pelletisation processes UnitTorrefactionTOPprocessPyrolysisPelletisationFeedstocktypeWoodcuttingschipsGreenwoodchipsCleanwoodwasteaGreenwoodchipsMoisturecontent(m.c.)wt%50%57%–57%LHVa.rMJ/kg6.26.26.26.2ProducttypeTorrefiedbiomassPelletsBio-oilPelletsProductm.c.wt%31–520–30( 22%)7–10ProductLHV—a.r-dryMJ/kg19.9(20.4)19.9–21.6(20.4–22.7)1715.8(17.7)Massdensity(bulk)kg/m3230750–8501200500–650Energydensity(bulk)GJ/m34.614.9–18.420–30b7.8–10.5ThermalefficiencybLHVa.r96%92–97%66%92,2%NetefficiencycLHVa.r92%d90–95%e64%f84%ga Three millimetre pine wood, sawdust residues from wood waste supplier, poplar, beech, wheat straw, rice husks, beech/oak and several organic waste materials have been successfully converted to bio-oil. b Thermal efficiency indicates the efficiency where utility use is not included (energy cap. product/energy cap. feedstock). Net efficiency includes the primary energy use to produce power necessary for components in the plant. d The electrical input to the system is given as 2.61 MWe for 517 kton/yr feedstock input [9]. e Utility fuel consumption is measured as 4.7 MWth and electricity consumption as 1.01 MWe for 170 kton/yr feedstock input [9]. When sawdust is used as feedstock, the efficiency is around 93.7% [9]. f Pyrolysis electricity consumption is accepted as 0.0150 MWe/MWth, in reference [40], electricity is assumed to be generated with 40% efficiency. g The utility fuel consumption is measured as 11.3 MWth and electricity consumption as 1.84 MWe for a 170 kton/yr input. When sawdust is used, the net efficiency is around 88% [16]. Table 3 Economic comparison of torrefaction, TOP, pyrolysis and pelletisation processes UnitTorrefactionTOPprocessPyrolysisPelletisationNormalisedcapacityaMWth(input)40404040CapitalinvestmentMh6.57.8b6.2–15.9c6.2dSpecificinvestmentMh/MWth(input)0.160.201.16–0.400.15O&M%554e5Energy—ekWh/toninput92f102g75h129Energy—hGJ/tonProduction costsi h/ton 58 45 75–150 41 h/GJ 3.2 2.5 6–12 3.4 a All the base capacities are scaled up to 40 MWth input. This scale is the optimal scale for torrefaction and TOP. For pyrolysis, economy of scale is obtained up to about 40 MWth input [41]. See also the section on economies of scale (Section 3.5). b Greenwood (woodchips) input (37 MWth) TOP process was calculated as 7.4 Mh [16]. The cost data was calculated in the range of 4.5–11.5 Mh for the 25 MWth input capacity pyrolysis plant. d For a 37 MWth input investment cost is given as 5.9 Mh (for woodchips). This figure is scaled up to 40 MWth. e Data is obtained from reference [5]. f The energy consumption of a moving bed torrefaction process is given as 92 kWh [16]. g Data include drying, torrefaction, size reduction and densification; steam for drying is obtained from the torrefaction gas. h Electricity consumption is accepted as 0.0150 MWe/MWth input [40]. i Assumptions for TOP and torrefaction, 8000 h load factor, 10-year depreciation [40] for pyrolysis 7500 h/yr load factor, 15-year depreciation [30] and for pelletisation 7884 h/yr load factor [16]. Feedstock cost is excluded in the production calculations to see the influence of the capital investments on production. Table 4 Main parameters used and ranges for sensitivity analysis Parametersa TorrefiedbiomassBio-oilPelletValueRangeValueRangeValueRangeBiomasscosts(h/tondry)300–50300–50300–50Capitalcosts(Mh)2512–306.54.5–7.82.031.6–2.4Discountrate(%)12.55–17.512.55–17.512.55–17.5Loadfactor(h/yr)75006750–800075006750–800075006750–8000Depreciationperiod(years)105–20105–20105–20a The values and the ranges are based on literature studies mentioned in technology section. quality oil and decreases particulate emissions. The high viscosity of than a regular biomass pre-treatment section, which is mainly the bio-oil can cause blockages of the burner pipe and the high biomass sizing; the bio-oil pre-treatment step consists of filtering water content of bio-oil makes it difficult to ignite [30]. Therefore, the oil to a maximum particle size of 40 mm and pre-heating the biothe bio-oil needs to be pre-treated before it is combusted. Different oil to roughly 60 1C, depending on the bio-oil quality [30].Another  
A. Uslu et al. / Energy 33 (2008) 1206–1223 1213 Sensitivity analysis of torref. biomass production Torrefaction economy of scale 85 60 50 Biomass cost Capital cost Interest rate Load factor Depr. period Specific production cost (Euro/ton) Specific production cost (Euro/ton) Specific Investment Costs (Euro/ton) Pellet production cost (Euro/ton) Bio-oil production cost (Euro/GJ)Production cost (Euro/ton)40 30 20 10 0 0 50 100 150 200123456 MWthVariables Fig. 8. Scale effect on torrefied investment costs. Fig. 5. Torrefied biomass production sensitivity. Sensitivity analysis of bio-oil production costs Pyrolysis economy of scale 300 Biomass cost Capital cost Interest rate Load factor Depreciation 14 12 10 250 200 150 100 50 0123456 0 20406080Variables MWth Fig. 6. Bio-oil production costs sensitivity. Fig. 9. Scale effect on bio-oil production costs. Sensitivity analysis of pelletisation Pelletisation economy of scale120 80 Biomass cost Cap. invest. cost Interest rate Load factor Depcreciation period 100 70 60 50 40 123456 Variables Fig. 7. Pellet production sensitivity analysis. experimental study has shown that some important modifications in the injection system of the gas turbine need to be done due to the high viscosity of bio-oil [44]. Since the related cost data for filtering and pre-heating bio-oil could not be obtained, the influence on combustion cost data cannot be determined. The cost data used in this study is presented in#p#分页标题#e#

Table 5. 0 10 30 5020 40 MWth Fig. 10. Scale effect on pellet production costs (local transportation is not included in the production cost calculations. Biomass feedstock is assumed to be 30 h/ton and a 0, 7 scale factor is used). 
4. Chain analysis 供应链分析
 
4.1. Approach and methodology 
There are several factors influencing the overall production costs when international bio-energy trade is considered. The location of  
A. Uslu et al. / Energy 33 (2008) 1206–1223 Table 5 Final conversion cost figures to be used for TOP, pellet and pyrolysis oila Unit BIGCCb FB-combustionc Co-firingd EF gasificatione Base scale MWth 105 200 100 1000 Maximum scale MWth 408 200 100 – R factor 0.61 0.77 0.7 0.7 Efficiency % 57 35 40 71% Life time Year 25 25 10 25 Total capital req. Mh 90 124 16.7 83–134 Spec. capital req. Mh/MWth(input) 0.86 0.62 0.16 0.083–0.134 O&M % 4 4 0 6–8 a Data mentioned do not include the possible impacts of pre-treated biomass on those technologies. b [45]. [46]. d Extra (non-fuel) costs for coal load are mentioned as 13.7 h/MWhLHV for pellets and 6.3 h/MWhLHV for pyrolysis oil. This cost is accepted as capital cost and O&M accepted as 0. The depreciation is done for 10 years [5]. e EF gasifier investment (including fuel feeding and syngas cooler) is estimated to be from about 41 to 75 h/kWth with pyrolysis oil as feed, the lower end of the range being for large-scale plants (1000 MWth) while the higher cost corresponds to capacities around 300 MWth. In this study, 41 h/kWth is applied for pyrolysis oil and 45 h/kWh for pellets. Figures include syngas conditioning (syngas cleaning, water gas shifting and CO2 removal) [40]. the pre-treatment process is one important factor since it influences the scale of the subsequent processes which are capital-intensive. Moreover it influences the further transportation and storage options. In this study, five transfer points were considered, namely: local biomass production site, central gathering point, export and import terminals and a final conversion unit. As mentioned previously various chains have been designed using a tool developed by Hamelinck et al. [5]. This tool enables to calculate energy and mass balance, and economic performance of the chains (Table 6). 
 
4.2. Logistic operations 
Latin American22 energy crops are chosen as the biomass source since Latin America offers high yield of biomass with low production costs [5]. The crop characteristics applied in the chain analysis are presented in

Table 7. Harvesting is assumed to be done by harvest bundlers. Further in the chain, biomass is cut to the desired feedstock particle size depending on the pre-treatment process type. From bundles (3000 mm) to chips (30 mm), roll crushers are employed and for smaller sizes (2 mm for pyrolysis and 3–10 mm for pellets) hammer mills are considered. Biomass is dried up to 15% moisture content for torrefaction and pelletisation and to 7% for pyrolysis process. Following the pre-treatment, product is stored either in silos or special lined carbon steel tanks depending on its form. 
 
4.3. Biomass transportation 
Transport distance is determined depending on the pretreatment process capacity, the percentage of the land occupied with crops and the biomass yield. Pre-treatment plants are assumed to be located at the centre of the farming areas. In this study, 20% of land under energy cropping and 22.4 tondry/ha yr yield is accepted.23 The first truck transport distance24 is 22 Latin American electricity price is considered as 35 h/MWhe and labour price as 6 h/man-h [47], while for Western Europe electricity price is considered as 60 h/MWhe [5] and labour price as 25 h/man-h (average salary in Western Europe is in the range of 14–40 h/man-h [5,19]). 23 Yield for Latin American energy crops are in the range of 22.4–28 tondry/ ha yr (short–long term) at a harvest rotation of 6 year and 60% m.c. m.c. decrease to 20% after 4 weeks drying in the field [5]. Bulk density of stacked eucalyptus stems is 0.28 ton dry/m3 bulk (0.47 m3 solid/m3 bulk and 0.59 ton dry/m3 solid) [48]. 24 The transport distance is calculated as: R . O(P/(2  p  Y  C)) where P is plant capacity (tons/year), Y is crop yield (tons/km2) and C is % of total area covered by energy crops. calculated as the radius of the circle (Fig. 11) [45,46]. A generic distance (100 km) to the harbour is assumed in this study, since the biomass production stage including the possible locations is not considered within the scope of this work. However, this issue is considered in the sensitivity analysis.

Table 8 illustrates the average transportation distances from harvested area to the transfer point in relation to the capacity of pre-treatment unit. Following the pre-treatment step intermediate biomass is transported by trucks to the harbour. Shipment distance from Latin America to West Europe is assumed as 11.500 km. Suezmax tanker (125,000 ton) is considered for bio-oil shipment and Suezmax bulk carrier or tank is employed for pellets. Cost figures and energy use data for truck transport and shipment are derived from references [5]. 
 
4.4. Designed chains 
Fig. 12 outlines the chains that are modelled in this study. In the local processing steps, smaller pre-treatment units are assumed whereas in the central gathering points relatively larger pre-treatment options (150 MWth) are considered. The mentioned pre-treatment processes include sizing and drying. Therefore, these options are not renamed in the designed chains. The first and the second chain show the transport cost differences between torrefied biomass and torrefied+pelletised (TOP) biomass. The last chain is considered as the reference scenario. 
 
4.5. Results 
 
4.5.1. Energy use of chains delivering solid energy carrier 
 
Fig. 13 shows the primary energy use of the chains delivering biomass. Energy use ranges from 1.98 GJ/tondm (for TOP process having a relatively small scale) to 2.46 GJ/tondm (for torrefied biomass without pelletisation). This difference occurs due to the energy used during shipment. Total energy use of the ship is assumed to be 4516 MJ/km [5]. Since the ship is filled volumetrically before it is filled down to its load mark by weight, due to the low density of torrefied wood high energy use occurs. The primary energy use for TOP delivery is approximately 8.5% of the delivered LHV. Only torrefied and delivered biomass requires 12% of the delivered LHV. Reference case primary energy requirement for energy is 11% of delivered. 
 
4.5.2. Energy use of chain delivering liquid 
The energy use of bio-oil delivery to West Europe is approximately 0.09 GJprimary/GJHHV (Fig. 14). The energy  
A. Uslu et al. / Energy 33 (2008) 1206–1223 Table 6 Bio-energy chain operation steps, options and variables included in the chains model [5] aOperation window (OW) is defined by the annual period that the equipment is available/used for processing. bLoad factor is defined as the percentage of the time the equipment can be used within the operation window [6]. Table 7 Crop characteristics (ranges indicate short and long term) [5,6] Type Logs ShipPosition Roadside Biomass cost (h/tonw.b) 10.2– 16.8 (h/GJ) 1– 1.8 Harbour Energy fuel (MJHHV/ton) 49– 60 Yield (tondry/ha yr) 22.4– 28 Density (kg/m3 324bulk) HV (GJHHV/tondry) 19.4 Dm loss/month 0.5% Supply Whole year Transfer point (Pre-treatment) Truck Biomass collection area w.b: wet bases; Dm: dry matter; Avg ps: average particle size; HV: heating value. Fig. 11. Schematic presentation of transportation distances.  
A. Uslu et al. / Energy 33 (2008) 1206–1223 Table 8 Logistics of biomass from harvesting to the pre-treatment process point Pre-treatmentcapacityMWthinput194177414141BiomassLHVdry(MJ/kg)17.717.717.717.717.717.7Fuelinputplant(ktonwet/yr)47.9102.2191.6102.2102.2102.2Moistercontent(%)353535353535Fuelinputplant(ktondry/yr)31.166.4124.566.466.466.4Yield(tondry/hayr)22.422.422.422.422.422.4Numberofhaenergycrops139029655559296529652965Landavailableforenergyfarming0.20.20.20.10.30.5Numberofsquarekmenergycrops69.5148.2277.9296.598.859.3Averagedistancetotransferpoint(km,oneway)357743Harvesting (felling) Storage Storage Open air pile (bales) Open air pile (bales) Storage Open air pile (bales) Storage Open air pile (bales) Base Case Scenario Storage Open air pile (bales) Storage Open air pile (bales) truck transp. truck transp. truck transp. truck transp. truck transp. truck transp. Chipper Torrefaction Storage (Silo) Chipper Torrefaction Pelletisation Storage (Silo) Hammermill Pyrolysis Storage (Tank) ChipperChipper Pelletisation Storage (Silo) Torrefaction Chipper Hammermill Storage (Tank) Pyrolysis Hammermill truck transp.truck transp. truck transp. truck transp. truck transp. truck transp. Storage Chipper Export Harbour Pelletisation locallocal centralcentral ship transport Import Harbour Combustion truck transp. Final conversion BIGCC Co-firing EF-Fischer Tropsch Storage (silo/tank) Preparation Fig. 12. Modelled bio-energy chains from Latin America to West Europe. is mainly required in the pre-treatment and transportation #p#分页标题#e#
 
4.5.3. Energy use of chains delivering electricity step. 
The energy requirement for the chains that produce electricity is On the other hand, FT fuel chains consume on average in the range of 0.15–0.25 GJprimary/GJHHV (Fig. 16). The main steps 0.26 GJprimary/GJHHV for TOP, whereas it consumes around that use primary energy are the energy requirement for densifica0.16 GJprimary/GJHHV for bio-oil chains and 0.17 GJprimary/GJHHV for tion and fuel consumption stages. Approximately 40% of the energy pellet chains (Fig. 15). use is due to the pre-treatment (mentioned as densification) step.  
A. Uslu et al. / Energy 33 (2008) 1206–1223 Energy use of chains delivering biomass 0.0 0.5 1.0 1.5 2.0 2.5 3.0Energy use (GJ/tonne dry delivered) Densification Sizing Ship Truck Biomass Fig. 13. Energy use of chains delivering biomass to Rotterdam harbour. Energy use of chain delivering bio-oil Energy use (GJ/GJHHV liquids delivered)0.10 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0.00 Pyro (Rot.Cone)-ship Densification Sizing Ship Truck Biomass Fig. 14. Energy use of bio-oil delivered to West Europe in GJ/GJHHVbio oil. 
 
4.5.4. Overall chain efficiency 
Chains supplying pre-treated biomass have an overall efficiency of some 95% for TOP, 85% for pellets and 68% for bio-oil (Fig. 17). When the chains supplying electricity and FT liquid are considered, TOP-BIGCC (52%) and TOP-FT (61%) chains have the highest efficiency (the BIGCC efficiency is around 57% and the EF gasification efficiency is around 71%). 
 
4.5.5. Cost data for chains delivering solid energy carriers 
The size of the pre-treatment unit plays a significant role in the biomass logistics since it influences both the first truck transport distance, and the costs of the transportation. In Fig. 18, the torrefaction option is analysed for different scales. The logistics of torrefied biomass for a smaller scale (18.75 MWth) is conducted to determine the differences between transporting it in the form of pellets or torrefied biomass. The cost difference is significant, the main cause of which is the shipment. Torrefied biomass bulk density is very low (230 kg/ton) compared to TOP (750 kg/ton). Transportation of torrefied biomass as pellets is much cheaper. Therefore, torrefaction is only considered in combination with pelletisation and here is referred to as TOP. When the scales 18.75 MWth–40 MWth–75 MWth and 150 MWth are compared, it is seen that the delivery costs of smaller scales are relatively cheaper, however, in the 40 MWth system (named as TOP process), the cost reaches a minimum of 75.5 h/tondry delivered. The cost of delivering biomass in the form of TOP is very close to that of pellets. The delivery cost of TOP and pellet is 73.5 and 69.7 h/tondry, respectively. When the cost data is considered for the energy content, the TOP delivery cost is found to be cheaper than the pellet (by 3.3–3.9 h/GJLHV). The major steps contributing to the overall delivery cost are the biomass source, truck transport and pre-treatment step. The pre-treatment step contributes to approximately one quarter of the total delivery cost, while truck transport and the biomass production both contribute similar amounts.  
A. Uslu et al. / Energy 33 (2008) 1206–1223 Energy use of chains delivering FT-liquids 0.00 0.05 0.10 0.15 0.20 0.25 0.30 Energy use (GJ/GJHHV liquids deliveredConversion Sizing Ship Truck Biomass LA1-TOP-ship-FT(EF) LA1-Pellet-ship-FT(EF) LA1-pyro-ship-FT(EF) *Conversion includes pre-treatment + EF-FT Fig. 15. Energy use of the chains delivering FT liquid. Energy use of chains delivering electricity0.3 0.25 0.2Energy use (GJ/GJ power delivered)De Sizing Desnification Ship Truck Biomass 0.15 0.1 0.05 0 LA1-TOPBIGCC LA1-pellet-LA1-TOPLA1-pelletLA1-pyro-LA1-TOPLA1-pellet-BIGCC co-firing co-firing co-firing com. comb Fig. 16. Primary energy uses for chains delivering electricity. 
 
4.5.6. Cost data for chains delivering liquid energy carriers 
A capacity rotating cone technology (25 MWth) and a reference technology with the same scale are analysed. Cost figures for reference technology are based on literature data whereas cost figure for rotating cone technology is based on reference [29]. Fig. 19 illustrates that significant cost differences occur even for same scale of pyrolysis processes. This is one of the drawbacks of this technology. The delivery cost of bio-oil ranges between 4.7 and 7 h/GJHHV when the investment costs are calculated based on rotating cone technology and the reference technology described in the pyrolysis sub-section. Pre-treatment accounts for approximately 30–50% of the total cost of bio-oil delivery. In contrast, when FT liquid production is considered, the conversion to FT liquid stage is assumed to be applied in West Europe with a large scale (1000 MWth) since FT liquid production is more cost effective at larger scales [5,40,49]. The FT liquid costs around 7.4 h/GJHHV for TOP whereas it costs in the range of 9.8–12.6 h/GJHHV for bio-oil (see Fig. 20). The cost of liquid production in the reference case (pelletisation) is 7.9 h/GJHHV. 
 
4.5.7. Cost data for chains producing electricity 
Electricity is assumed to be produced either by BIGCC, FB combustor-steam turbine or by co-firing in a PC boiler. The electricity costs for TOP and pellet chain are 13.05 h/GJ (4.6 hcent/kWhe)and 15.24 h/GJ (5.5 hcent/KWhe), respectively, when the BIGCC option is considered. The conversion step contributes to approximately 50% of the total power cost while the second major contributor is transportation ( 25%). The storage costs following the TOP process have not been considered. As torrefied biomass is hydrophobic in nature, it may be stored in the open air and not in silos. When FB-combustion is used, cost of chains delivering electricity are: 21.64 h/GJ (7.7 hcent/kWhe) for the TOP chain, and 22.84 h/GJ (8.2 hcent/kWhe) for the reference chain. Similarly as for the electricity production by BIGCC, the costs are mainly influenced by the conversion steps followed by transportation and biomass harvesting steps. It accounts for approximately 60% of the total cost. On the other hand, electricity costs are 12.2 h/GJ (4.4 hcent/kWhe) and 16.2 h/GJ (5.8 hcent/kWhe) for the TOP chain and pyrolysis chain, respectively, when co-firing is applied. Approximately 10–15% of wood pellets can be co-fired by mass [5] and the costs associated  
A. Uslu et al. / Energy 33 (2008) 1206–1223 Energy efficiencies 0 10 20 30 40 50 60 70 80 90 100 TOP-shipPellet-ship Pyro-ship TOP Pellets TOP Pellet Pyro TOP Pellet TOP Pellet Pyro Co-f iringBIGCC Comb . FT -liq.(EF) Cost of chains delivering pellets 0 20 40 60 80 100 120 Costs (€/tonne dry delivered) PelletisationTorrefaction+pelletisationTorrefaction Storage Densification Sizing Ship Truck Biomass (pre-treatment) (%) Fig. 17. Overall energy efficiencies. Fig. 18. Cost data of chains delivering pellets in h/tondry delivered. with feedstock handling account for 6.3 h/MWhLHV for bio-oil and 13.7 h/MWhLHV for pellets [5] (Fig. 21). As seen, the chains including TOP process with BIGCC and EF-FT liquid production are identified as the optimal chains. BIGCC efficiency is much higher (56%) compared to combustion (35%) and co-firing (40%) and it gains from bigger scales (105–408 MWth), whereas EF gasification efficiency is 71% at a 1000 MWth capacity. 
 
4.6. Sensitivity analysis 
The biomass supply chains analysed in this work are highly dependent on the plantation yield, interest rate, load factor and the plantation distance to the harbour. Therefore, they require further evaluation. The base values presented in

Table 9 are analysed within the range of 50–250% and the results are illustrated in Fig. 22. The most significant factor in terms of fuel cost is the operation window. Reducing OW from 12 months to 6 months increases the TOP production cost from 60 to 80 h/ton. The cost changes mainly depend on the storage and operational costs. In fact, the number of storage units increases significantly when the biomass is harvested for a shorter period of time. The operation cost increases because the equipment is not fully utilised throughout the year. The storage contributes about 6.75 h/tondry for a 6 months OW. When the interest rate is increased from 5% to 20%, the fuel cost increased from 64 to 86 h/ton. This is directly related to the  
A. Uslu et al. / Energy 33 (2008) 1206–1223 8 Cost of chains delivering bio-oilStorage Densification Ship Truck Biomass Cost of chains delivering electricity 0 5 10 15 20 25 Costs (€/GJ power delivered) BIGCC Co-firing FB-combustion Conversion Storage Ship Truck Biomass +pre-treatm. Costs (€/GJHHV Liquids)7 6 5 4 3 2 1 0 LA1-pyro (rot.cone)-ship LA1-pyro(ref)-ship Fig. 19. Cost of bio-oil delivered to West Europe (h/GJHHV). Cost of chains delivering FT-Liquids 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Costs (?/GJHHV Liquids) Conversion Storage Ship Truck Biomass LA1-TOPLA1-PelletLA1-pyroLA1-pyro(rot cone)ship-FT(EF) ship-FT(EF) ship-FT(EF) ship-FT *Conversion step includes both pre-treatment and final conversion Fig. 20. Costs of FT liquid for different pre-treated feedstock (conversion in the graph comprises pre-treatment and FT processes). LA1-TOP-LA1-pellets-LA1-TOP-co-LA1-pellet-co-LA1-pyro-co-LA1-TOP-LA1-pellet-BIGCC BIGCC firing firing firing combustion combustion Fig. 21. The power cost delivery figures for chains considered within this study. cost of capital investment in the various equipment employed at in biomass yield decreases the biomass costs; however, since various stages of the fuel chain. the biomass plantation and harvesting is not the focus of this Varying biomass yield to 33.6 tondry/ha decreases the fuel cost study, this cost difference is not considered in the scope of the to 69 h/tondry while decreased yield to 11.2 tondry/ha results in analysis. increased fuel cost of 76 h/tondry. When the biomass yield is When the distance to the harbour is increased from 50% of the increased smaller areas are required to harvest biomass and thus base value to 200%, the fuel cost increases up to 79 h/tondry and shorter first truck transport distances. Furthermore, the increase the truck transport cost corresponds to around 26 h/tondry.  #p#分页标题#e#
A. Uslu et al. / Energy 33 (2008) 1206–1223 In conclusion, changing the operation period from 6 months to 12 months decreases the TOP delivery cost 25%, while variation of interest rates from 5% to 20% results in fuel cost changes of about 33%. Similarly, changing the biomass yield from 50% to 150% of the base value results in a fuel cost change of about 11%. When the transportation distance is considered, increasing the truck distance from 50% to 200% of base values increases the fuel costs by around 20%. 
 
5. Discussion and conclusion 讨论和总结
 
The main objective of this study was to identify the optimum biomass-to-energy chains by analysing the pre-treatment technologies (torrefaction, pyrolysis and pelletisation) each of which differ significantly in terms of their impacts on transportation, storage and conversion. The potential and future technical and economic performance of these technologies was analysed. The influences of intermediate products (pre-treated biomass) on transportation cost and energy use were evaluated. The impacts of Table 9 Parameter used for sensitivity analysis ParametersBasevalueInterestrate(%)10Yield(tondry/hayr)22.4Harvestoperationperiod(OW)(months)8Distance(km)100Sensitivity analysis-TOP delivery 50 60 70 80 90 TOP delivery cost (€/ton-dryOW Ir Yield Tran. 50% 100% 150% 200% Parameter variation Fig. 22. Sensitivity analysis for TOP process (OW: harvest operation period).

Table 10 Techno-economic comparison of torrefaction, TOP, pelletisation and pyrolysis intermediate products on the performance of power and syngas conversion technologies require an extensive analysis, which was not the scope of this research. However, those impacts can have significant impacts not only on costs but also performances of the final conversion technologies. 
 
5.1. Pre-treatment technologies 
Torrefaction, pyrolysis and pelletisation were evaluated in terms of their technical and economic performances. Results are summarised in

Table 11. Table 10 illustrates that torrefaction, TOP and pelletisation process efficiencies were found to be high compared to pyrolysis technology. The energy density of TOP pellets is approximately 1.75 times higher than conventional pellets and 3 times higher than torrefied biomass. When the specific capital investment of pyrolysis technology is considered, there is a significant variation between the cost figures found in scientific literature. This variation could due to the range of technologies reported. However, cost data for specific process designs in literature varies widely. Therefore, in this study, two scenarios were considered, one assuming low and one assuming relatively high capital costs. The resulting bio-oil production cost estimates are in the range of 6–12 h/GJHHV (feedstock cost is accepted as 0) in the Western Europe conditions. Economy of scale plays a significant role in the pre-treatment costs. This study shows that torrefaction plant capacity exceeding 40 MWth does not gain from an economy of scale. A similar conclusion can be drawn for the pelletisation process, 35–40 MWth does not result in further gains from the economies of scale. Consequently, this study indicates that torrefaction in combination with a pelletisation process is more advantageous than pelletisation. Pyrolysis, as an alternative, has drawbacks in terms of process efficiency and economy when compared to the other technologies. However, this performance should be evaluated as part of the overall bioenergy supply and conversion chains considered. 
 
5.2. Chain analysis Energy crops (eucalyptus) produced in Latin 
America are considered to be imported to the Netherlands. In order to investigate the optimal location for the pre-treatment processes, different scales were applied in the chains. These chains were then compared. Biomass supply chain elements for TOP biomass, pellets and bio-oil included harvesting, storage, pre-treatment, transportation and final conversion stages. The final energy conversions considered were FT fuels, and power production by means of BIGCC, combustion and co-firing. The pre-treatment technologies were assumed to operate with a high load factor, which however sets high organisational requirements for the UnitTorrefactionTOPPelletisationPyrolysisProcessefficiencya%9290.884–8766–70Energycontent(LHVdry)MJ/kg20.420.4–22.717.717Massdensitykg/m3230750–8501200500–650EnergydensityGJ/m34.614.9–18.47.8–10.520–30SpecificcapitalinvestmentsMh/MWth0.170.190.150.19–0.42Productioncostsh/ton58505475–104a This is the overall efficiency of the technology which includes utility fuels  
A. Uslu et al. / Energy 33 (2008) 1206–1223 Table 11 Costs of chains delivering fuel and power Intermediate delivered to FT-liquid fuel Power (BIGCC) Power (combustion) Power (co-firing) harbour (h/GJHHV) (h/GJHHV) (h/kWh) (h/kWh) (h/kWh) TOP3.37.44.67.74.6Pellet3.97.95.58.24.8F.pyrolysis4.7–7.09.8–12.65.9biomass supplies. In addition, the bioenergy supply chain costs are very sensitive to the harvest operation period. In this study, 8 months harvesting is considered. Shorter harvesting periods result in increased biomass production costs. The calculation results are summarised in Table 11. TOP pellets can be delivered at costs as low as 73.5 h/ton (3.3 h/GJ) with a biomass cost of 10 h/ton. One of the reasons for the relatively low delivery cost is the approximately 15% higher bulk density compared to conventional pellets, which lowers both the road and sea transport costs. Another reason is the plant scale applied. As mentioned previously, with a 40 MWth plant scale it was possible to obtain lower production costs. When TOP is considered for smaller scales such as 18.75 MWth, the delivery cost increased by 16%. On the other hand, when the base scale is increased around 80%, the delivery cost increases by 10% because of longer first truck transport distances. Pyrolysis oil delivery costs were found to be in the range of 4.7–7 h/GJ, depending on the scenarios mentioned above. This study shows that it is possible to deliver 80% of the initial amount of biomass to Rotterdam harbour by means of TOP pellets, whereas it is 70% for pellets and 50% for pyrolysis oil. The chain efficiency in this study is defined as the ratio of the biomass delivered to the total of biomass and primary energy input in every step of the chain. These efficiencies are highly influenced by the pre-treatment process efficiencies and the dry matter losses during transport. FT fuel production cost can be as low as 7.4 h/GJHHV, when the final conversion takes place at large centralised facility. The EF gasifier assumed here had a 1000 MWth capacity. When pyrolysis oil is converted into FT liquids, the production cost is in the range of 9.8–12.6 h/GJHHV. The truck transport, the storage and the pretreatment costs are the major cost factors. Table 11 indicates that power production costs can be as low as 4.6 h/kWh either with a large scale BIGCC facility or with an existing co-firing plant. BIG/CC benefits from its high efficiency (which is assumed to be 57%), whereas it is 35% for combustion and 40% for co-firing. As described earlier, cost data for co-firing does not include the facility capital investment cost but it does include extra costs for pellets and pyrolysis oil handling. The implication of this is that when a new facility is considered, the cost of electricity will be higher. The primary energy required to deliver the fuel to the Rotterdam harbour is 8% (of their initial energy content) for delivered TOP, 10% for pellet and 8–9% for pyrolysis oil (HHV). The chain efficiency of TOP for electricity generation by BIGCC is around 55% where as it is around 61% for FT. Consequently, according to the parameters used in this study:   Torrefaction in combination with pelletisation (TOP), in plants with a scale of 40 MWth, is the optimum supply chain from the economic and energy efficiency perspective,   TOP supply converted to the FT-liquid is the optimal synfuel production chain and   TOP supply converted to power either by BIGCC or existing co-firing facility are the optimal chains. Further conclusion of this study is that pyrolysis, even assuming optimistic performance and cost cannot compete in energy efficiency terms with the TOP and pelletisation pre-treatment technologies (and also when the total chain from biomass production to final conversion is considered). Since torrefaction has not been demonstrated yet, its performance is still uncertain and verification is needed. Pelletisation has already been commercialised and there is further room to improve the technology. This indicates that pelletisation should still be considered as an important option for the near future. Pyrolysis technology, in contrast needs further improvements that it can be cheaper. In conclusion, this study has indicated that intercontinental bioenergy transport is economically and energetically feasible, when associated pre-treatment stages are considered in the chain. Furthermore, torrefaction in combination with pelletisation appears a very promising technology that of course requires further development and commercialisation. Thus, well-designed supply chains make international trade of biomass feasible from the energy efficiency and economic perspectives. Torrefaction hence seems a very promising option for minimising logistic costs and improving energy use. #p#分页标题#e#
 
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