WrP? z q Xw jr-.- tA 4s O WORLD BANK TECHNICAL PAPER NUMBER 296 "117 ENERGY SERIES I nerp goi emlt A-,9tom VmLgl.mie Small-Scale Biomass Gasifiers for Heat and Power A Global Review Hubert E. Stassen Ii I >--fl- lltl95 kWel n.s 3.6 kg/kWh n.s. 7.1 Peat power gash.er Tora 36 kWei 23 kWel n.s. n.m. n.s. n.m. Wood heat gasifiers Rajamandala n.s. 600 kWth n.s. 0.30 kg/kWh n.s 68 Espara Feliz 2 x 670 kWth 2 x 522 kWth 0.45 kg/kWh 0.37 kg/kWh 75 76 St. Luzia 4,060 kWth 3,480 kWth 0.17 kg/kWh 0. 16 kg/kWh 80 77 n.s. = not stated. n.m. = not measurable. Note: kWh = kilowatt-hour; kWel = kilowatt electric; kWnie = kilowatt mechanic; kWth = kilowatt theri. Gasifier Performance 31 Specific Fuel Consumption Measured and manufacturer-specified values of the specific fuel consumption for different plants are given in Table 4.1. The BGMP data indicate that at full load, the specific wood consumption of wood gasifiers in combination with Otto engines is around 1.4 kg/kWh, which is marginally higher then the values stated by the gasifier manufacturers. Wood gasifiers operating with diesel engines (Balong) showed a somewhat lower specific wood consumption. The specific charcoal consumption of most charcoal gasifiers is measured at about 0.9 kg/kWh. This is somewhat higher than the values stated by the manufacturers. What happens to the specific fuel consumption when a gasification system is operated at very low loads is shown by the specific charcoal consumption (4 to 10 kg/kWh) of the Chacara plant in Brazil. The specific rice husk consumption of monitored rice husk gasifiers varied between 1.8 and 3.2 kg/kWh for different installations. Because of the low or even negative value of rice husks in most places and their abundant availability, the specific rice husk consumption is mostly not considered as an important decision factor in rice husk gasification. The measured specificfuel consumption of heat gasifiers was in good agreement with manufacturers data. System Efficiency Table 4.1 gives overall system efficiency values as measured by the BGMP. The systems employing wood gasifiers in combination with Otto engines showed full-load overall system efficiencies from 16 to 19 percent. These are reasonable values that are in good agreement with the theory. However, the values are low when compared with the efficiency ratings given by the manufacturers. For example, the Mahe gasifier was rated at about 24 percent efficiency by the manufacturer, but the de facto efficiency was only 16 percent. In practice, this means that the gasifier consumes about 50 percent more wood than the manufacturer's information indicates. Systems using wood gasifiers in combination with diesel engines show somewhat higher overall efficiencies because of the superior efficiency of the diesel engine compared with the Otto engine. In general, the charcoal systems show somewhat lower overall efficiencies than the wood systems. Values range between 10 and 15 percent. The intrinsic reason for this lower efficiency is the higher working temperature of charcoal gasifiers compared with wood gasifiers, which results in greater heat losses. Overall system efficiencies of rice husk gasifiers vary from 7 to 14 percent. The main reason for those low values is the incomplete burning of rice husks in this type of plant. Heat gasifiers show very reasonable efficiencies of 68 to 77 percent. In this respect it should be noted that the data for heat gasifiers in Table 4.1 refer to chemical energy in the gas. By adding the sensible heat in the hot gas to those values, the practical overall heat efficiency of heat gasifiers may be estimated as from 85 to 95 percent. 32 Small-Scale Biomass Gasifiers Diesel Fuel Substitution The BGMP monitored five systems that used dual-fuel diesel engines in combination with gasifiers (see Table 3.2). Measured diesel fuel substitution at full engine load ranged from about 60 percent (Majalengka and Balong) to about 70 percent (Bago and Bolo). The diesel engine of the quasi-functioning peat gasifier plant at Tora consumed at full engine load in dual-fuel mode only 20 to 30 percent less diesel than it did in full-diesel mode. The BGMP also measured diesel fuel substitution values at varying engine load levels. The outcome of those measurements is somewhat ambiguous, but it appears that up to a point decreasing engine loads resulted in decreased relative diesel fuel consumption. This tendency was reversed, however, when the engine load was still further decreased. For example, at full engine load (15 kWel), the diesel engine of the Balong plant consumed about 60 percent less diesel fuel than it would have in full-diesel operation. At 66 percent load (10 kWe,) and 40 percent load (6 kWel), diesel fuel substitution was measured at, respectively, about 90 percent and about 75 percent. Those data indicate that the practical diesel fuel savings of dual-fuel diesel plants depend very much on the plant load pattern. Of all dual-fuel plants monitored by the BGMP, only the Balong unit has succeeded in realizing overall diesel fuel savings of about 70 percent. All other plants have done considerably worse. Quality Performance Producer Gas Engines BGMP requirements included several measurements that bear on the lifetime that can be expected for engines that are operated on producer gas, including the amount of dust and tar in the gas, after cleaning, at the gas inlet manifold of the engine and the amounts of metal in the engine oil. Below, results are presented for six different BGMP- monitored plants. The engines of the first four plants worked well, requiring only normal service and maintenance. But the engines of the latter two plants were subject to abnormal wear, requiring frequent oil changes and frequent replacement of parts. Dust Content Table 4.2 gives values of dust concentrations that were measured on site at the engine inlets of specific plants. It also provides the "acceptable" and "preferable" dust concentrations usually quoted by engine manufacturers as guaranteeing normal engine operation and lifetime. Data indicate that most plants produce a fairly dust-free gas, although the values are generally somewhat worse then requested by engine manufacturers. The gas filter unit of the Onesua plant was undoubtedly the best with respect to dust, whereas the amount of dust in the gas from the Dogofiri gasifier may be on the borderline of what is acceptable in the long run. Gasifier Performance 33 Table 4.2 Factors Affecting Life Spans of Producer Gas Engines and Gasifiers at Six BGMP-Monitored Sites Life-span factor Gas dust content Gas tar content Metal amount Site (mg/Nm3)a (mg/Nm3)b in engine oil Balong 120-150 120-150 low Sebubuk 40-80 100-400 low Onesua <5 < 10 low Mab6 10-30 500-700 medium Dogofiri 250-300 3,000-4,000 high Majalengka < 100 1,000-2,000 high Note: Nm3 = normal cubic meter. a < 50 (acceptable); < 5 (preferable). b< 100 (acceptable);< 50 (preferable). Tar Content Table 4.2 presents also values for measured and specified tar concentrations at the engine inlet manifolds. It indicates a big difference between the wood gasifiers (Balong, Sebubuk, Onesua, and Mahe) and the rice husk gasifiers (Dogofiri and Majalengka). For the first group, the tar concentrations were more or less in line with the values requested by engine manufacturers. Values measured for the Onesua plant were especially low, but the amount of tar entering the engine of the Mahe plant was on the high side. The values for the rice husk gasifiers are 10 to 40 times higher than allowable, which means that the gas cleaning of those plants must be improved if long-term trouble-free engine operation is to be guaranteed. Engine Oil The results of the engine oil analyses, also detailed in Table 4.2, indicate that the oil of the engines from the rice husk gasifiers contained large amounts of metal (mainly iron and aluminum), indicating abnormal engine wear. Evaluation of the dust, tar, and engine oil measurements thus leads to the clear conclusion that the tar amount in the gas is the decisive factor governing wear and lifetime of producer gas engines. Turn-down Ratio The first four plants from Table 4.2 use downdraft reactors. This type of reactor is vulnerable to increased tar production at low load. Therefore, in order to establish the "turn-down ratio," the BGMP executed tar measurements at different reactor load levels. Those measurements indicated that all monitored downdraft reactors had acceptable turn- down ratios, of about 25 to 50 percent of full load. Gasifier and Other Nonmoving Parts The journals kept during operational monitoring show that almost all monitored power gasifier plants, especially during the startup period directly after commissioning, 34 Small-Scale Biomass Gasifiers were subject to a continuing series of more or less serious technical defects. Examples ranged from badly fitting fuel and ash removal covers, warped service hatches, leaking gaskets, and blocked valves, pipes, and filters to completely destroyed high-temperature sections and burned grates as well as accelerated corrosion of many parts of the reactor, gas-cleaning sections, and connecting piping. This suggests that the plants were not fully commercial and mature technical concepts. In fact, they were prototypes, developed and tested in the laboratory but not subjected for a sufficient time to the rigors of daily use. Manufacturers had received insufficient feedback on how to improve designs and materials in order to achieve sufficient quality. The BGMP reports indicate that this initial deficit in quality, especially with respect to factors such as resistance to heat and corrosion, appears to be a major reason for project failure. The small and large technical problems that were caused by the poor quality of materials and design resulted in unreliable operation that discouraged and demoralized operators and owners. Thus, only the small number of installations that had sufficient and sustained technical backup were able to overcome this quality problem by installing better-designed or -fabricated parts; it was they who thus could evolve to more or less trouble-free operation. Behind this scenario of trouble lies the fact that the commercial market for small- scale gasifiers has never been large enough to carry the expenses associated with development from prototype to mature commercial plant. Developers of gasifiers in developed and developing countries were able, however, to get grant money to design prototypes and to test them under operational circumstances. Under these circumstances, technical and operational problems were to be expected, especially because the performance of power gasifiers appears to be sensitive to relatively small changes in fuel- and energy-demand-related parameters. Even so, the results of the BGMP show that some small-scale wood gasifiers did achieve reliable and relatively trouble-free operation, and this means that experience and expertise in building and operating reliable, safe, and pollution-free wood gasifiers is now definitely available, at least in some locations. Operational Performance Labor The labor necessary for operating a gasification plant is considerably different from the input required for running an equivalent diesel engine. This difference is both quantitative and qualitative. During operation, the gasifier operator must frequently check a number of temperature and pressure meters and, based on this information, make decisions on actions such as adding new fuel, shaking the grate, deblocking filters, and adjusting valves. At the end of daily operation the operator must normally clean reactor and filters from ash and dust. Finally, the operator may be also in charge of fuel preparation and fuel quality control. Thus, unlike diesel engine operations in which the engine driver may also be given other, unrelated tasks, the running of a small-scale gasification system is basically a full-time job. Gasifier Performance 35 The operational history of the gasifiers monitored under the BGMP shows that not every operator is easily able to attain the required level of competence. Motivation and discipline are necessary, but the ability to react adequately to two or three input parameters and some basic technical skills are also crucial. Achieving this level of expertise and quality of operation appears to require not only an adequate initial training programme but also continuous technical backup for a period of at least a year. Recent developments in the automotive industry have resulted in mass-produced hardware and software that may greatly increase possibilities for automatic control of gasifiers. The auto industry manufactures and uses a number of inexpensive as well as temperature- and shock-resistant sensors and attenuators. In combination with their corresponding multi-parameter input logic software, such instruments could conceivably monitor and control gas engines and reactors, correspondingly reducing or eliminating the need for highly trained and experienced gasifier personnel. Such a development would improve the current economic competitiveness of small wood and charcoal gasifiers only marginally, but it would certainly increase the possibilities for speedy introduction of the technology. Health and Safety To assess the danger of carbon monoxide poisoning, the BGMP measured carbon monoxide concentrations at the gasifier site. On all sites except one, the concentrations were found to be around or below 20 parts per million (ppm), which means that there are no health signs or symptoms. At one site (Sebubuk), a CO concentration of 1,000 ppm was measured during gasifier refueling. Operators at this site complained of headaches. Another CO poisoning incident was reported from Itamarandiba, Brazil. It resulted from working on a hot reactor, in defiance of safety regulations. Gas explosions may occur in a reactor when, because of leakages, a hot combustible gas is mixed with sufficient air to cause spontaneous combustion. The heat gasification system of S. Lucia, Brazil, reported a number of gas explosions, but none caused fatalities or major equipment damage. Fires may result from the high surface temperatures of equipment and from sparks emitted during refueling, but no fires were recorded in any plant monitored by the BGMP. Environmental Pollution Biomass gasifiers may produce tar/phenol-containing condensates. The amounts produced depend on fuel and reactor type. Condensate analyses from different BGMP plants show a wide range of carcinogenic compounds in different concentrations. Not all those compounds are biodegradable. None of the plants that were monitored took special measures in dealing with the condensates. In all cases the pollutants were freely discharged to the enviLonment. None of the operators dealing with contaminated condensates used protective clothing or hand gloves. Table 4.3 compares the toxic effluent production at the Onesua downdraft wood gasifier with that at the Dogofiri open-core rice husk gasifier. The Onesua gasifier 36 Small-Scale Biomass Gasifiers Table 4.3 Comparison of Toxic Effluents at Two Gasifier Sites Site Amount (I/hour) Phenols (mg/i) Phenols (kg/hour) Phenols (kg/kWhel) Onesuaa 0.5 100-200 0.05-0.10 0.002-0.004 Dogofirib 500 30 15 0.167 Note: kg = kilogram; kWhel = kilowatt-hour electric; I = liter. a Downdraft wood gasifier. bOpen-core rice-husk gasifier. produces small amounts of tar that are relatively easy to deal with. But the Dogofiri plant produces and discharges 500 liters of contaminated condensates, containing 15 kilograms of toxic phenols, each hour. Without the addition of effective effluent treatment facilities, the operation of this and similar plants gives rise to a major environmental pollution problem. Summary A summary of the performance that may be expected from different types of gasification plants is provided in Table 4.4. Table 4.4 Performance of Gasifier Plants System Engine Specific fuel overall Diesel Engine Problems derating consumption efficiency savings life- Gasifier Health Environ- Gasifier type (%) a kg/kWh b (%) b (%) c time quality and safety mental Power gasifiers Wood Otto 50-60 1.4 > 16 n.a. 4 ? none minor Wood diesel 60-90 1.1 > 21 60-90 4 ? none minor Charcoal Otto 50 0.9 > 10 n.a. 4 ? none none Charcoal diesel 50-80 0.9 > 12 40-70 ? ? none none Rice husk Otto 50-60 > 3.5 > 7 n.a. ? V none major Rice husk diesel 60-90 > 2.0 > 12 50-75 - ? none major Peat diesel 20-50 high very very - X possible major low little probable Heat gasifiers Wood n.a. 0.30-0.35d > 75e n.a. n.a. + none none Charcoal n.a. 0 15-0.17d > 75e n.a. n.a. + none none > 90f 4 = normal; + = good; ? = doubtful; - = shortened; X bad; n.a. = not applicable. Note. kg = kilogram; kWh = kilowatt-hour. aMaximum engine output on producer gas as a percentage of maximum power output on gasoline/diesel. bAt full engine load. CAs a percentage of equivalent diesel engine fuel consumption at equivalent engine load. dFuel consumption per kWhth. eEfficiency with respect to chemical energy in the gas. fOverall heat energy efficiency. 5 Economics of Biomass Gasifiers Because producer gas is an alternative to gasoline or diesel, the financial and economic feasibility of biomass gasifiers depends on the cost savings that are realized by switching from those petroleum fuels to biomass. Those cost savings must be measured against the higher capital and operational costs of the biomass system. This chapter presents capital and operational costs for gasifier plants based on field data and a simple cost model. Comparison with the costs of petroleum-based alternatives results in break-even figures as a function of fuel prices and number of operating hours. It must be stressed that in practice the outcome of financial and economic evaluations depends also on the values of a number of other site-specific parameters. The figures presented below are therefore useful to illustrate trends, but they should not be taken as absolute. Financial Cost and Performance of BGMP Gasifiers Table 5.1 presents investment costs, as established during baseline monitoring, for the gasifier plants monitored by the BGMP. Because of the large differences, a distinction is made between gasifier power plants made in developed countries (imported systems), plants made in developing countries (local systems), and heat gasifiers. Although in practice the plants were paid for in many different currencies, for reasons of comparison, all costs have been converted to U.S. dollars (1990). So far as possible, the data take the following investments into account: * Cost of gasifier, fuel handling system, gas cleanup system, and all other related auxiliary and control equipment * Cost of diesel engine or Otto engine, including all auxiliary and control equipment * Cost of generator, water pump, or compressor * Cost of freight, insurance, installation, and civil works. The cost data indicate that imported power gasifiers tend to be more expensive then domestically manufactured systems. In both categories, however, the most expensive systems (Onesua and Balong, respectively) performed technically best. The 37 38 Small-Scale Biomass Gasifiers Table 5.1 BGMP Gasifier Costs and Profitability Total investment Specific investment Operational costs Site US$ (1990) US$/kWel a US$/kWei b (US$/kWh) Profitability Imported power gasifiers Sebubuk 60,000 2,000 2,300 0.07 nil Onesua 100,000 3,600 4,200 0.09 nil Mahe 30,000 850 850 0.25 marginal Dogofiri 415,000 2,600 2,600 0.23 marginal Tora (15,000)C (425)c (650)C 0.12 nil Local power gasifiers Balong 23,000 1,150 1,550 0.08 marginal Majalengka 10,000 650 650 0.06 marginal Lembang 6,500 650 500 0.12 nil Bago 12,000 425 1,400 0.04 nil Bolo 12,000 300 750 0.03 nil Itamarandiba 8,000 200 400 0.11 nil Heat gasifiers Rajamandala 40,000 66d 65d 41.6e marginal Espara Feliz 30,000 25d 30d 3.27e profitable Santa Luzia 310,000 75d god nil Note: kWh = kilowatt-hour; kWel = kilowatt electric. a Specific investment cost based on manufacturer maximal power output. b Specific investment cost based on BGMP measured maximal power output. c Gasifier not properly working. d As kW thermal. e In US$ per tonne biomass fuel. exception was the ferrocement charcoal gasifier (Lembang), which was cheap but still had good performance. Although less price information is available for heat gasifiers, it appears that this equipment can also be divided between relatively low- and high-cost installations. Gasifier operating costs, as established for different plants during baseline monitoring, are presented in Table 5.1. Operating costs include personnel costs, fuel costs, and costs of service and maintenance. The data are thus very site-specific, but they still indicate the operational cost values that can be attained in power and heat gasifier operation. Table 5.1 also indicates that only one heat gasifier (Espara Feliz) operat. profitably compared with a liquid-fuel-system alternative. A few power plants we. marginally profitable. On most sites, operating a gasifier turned out to be more expensivL than using an equivalent diesel engine. The most important causes of unprofitability were the high cost of biomass fuel (especially charcoal), high capital cost, low diesel fuel savings, and low number of operating hours. Economics of Biomass Gasifiers 39 Power Gasifiers Cost Model A simple cost model was developed for a general investigation of power gasifier economics. The model is based on the BGMP observation that costs of locally manufactured acceptable power gasifiers (e.g., Lembang) can be considerably lower than those of imported plants (e.g., Onesua). Capital Costs. Tables 5.2 and 5.3 present estimated installed investment for different power gasifiers of variable power output. Table 5.2 shows total investments for imported expensive systems, which were obtained by adding estimated costs of the different major parts of the plant. Estimates are based on actual data from the BGMP. Costs of freight, installation, and training were taken as part of the investment and therefore incorporated into the capital costs. Table 5.3 repeats the same exercise for local, inexpensive plants. Both tables also indicate effective investments required to establish equivalent diesel plants. For example, the installed cost of a 30 kW imported wood gasifier plant with an Otto engine is estimated at US$61,800 (US$2,060/kW), whereas a locally manufactured plant is estimated at US$31,380 (US$1,046/kW). The cost of an equivalent diesel engine plant is estimated at US$18,570 (US$619/kW). Operating Costs. Operating costs for both biomass and diesel systems were based on costs of fuel, labor, and maintenance measured by the BGMP. Economy Break-Even Diesel Fuel Price. One way to evaluate the viability of a gasification system is to establish the break-even diesel fuel price (BEDP). This is diesel fuel price at which an equivalent diesel engine system would produce power at the same cost as the gasifier system. Three important parameters influencing BEDP of gasifiers are gasifier cost, number of full-load operating hours per year, and cost of woodfuel. Figures 5.1 and 5.2 show BEDP values for different gasifiers. Wood Gasifiers. Figure 5.1 establishes BEDP for low-cost wood gasifiers working with Otto engines. It presents data for gasifiers with three different capacities (10 kWel, 30 kWe,, and 100 kWel) and shows how BEDP values vary with the annual number of operating hours and the cost of woodfuel. For example, economic operation of a 10 kWel wood gasifier generator set working for 1,000 hours per year with free wood (US$0/tonne), results in a BEDP of US$600/tonne. On the other hand, a 100 kWel wood gasifier plant, operating for 4,000 hours per year and working with wood priced at US$20/tonne, has a BEDP of about US$225/tonne. When high-cost imported gasifier plants are used, BEDP values incre- enormously. For example, the BEDP of a 30 kW high-cost wood gasification system 1. is operated for 3,000 hours per year is approximately US$300/tonne higher than til equivalent BEDP of a low-cost gasifier plant. Retrofitting existing engines with gasifiers 40 Small-Scale Biomass Gasifiers is an option that can be realized at lower diesel prices. The BEDP of a 100 kWel plant operating 3,000 hours per year is about US$100/tonne lower than the BEDP of an equivalent low-cost gasifier system. Finally, the model shows that below 80 percent diesel substitution, dual-fuel diesel engine plants always have higher BEDPs than equivalent Otto plants. Only very high diesel substitutions (in excess of 80 percent), in combination with high wood costs and few operating hours, result in a BEDP that is somewhat lower than that of an equivalent Otto plant. Small Charcoal Gasifiers. Figure 5.2 presents BEDPs for two small 10 kWel charcoal gasifier plants locally made, from steel and ferrocement, respectively. At a charcoal cost of US$50/tonne, and at 4,000 operating hours, the BEDP of the steel system and the ferrocement system were about US$425/tonne and US$380/tonne, respectively. The small difference between the two systems follows from the relatively small cost difference (about 15 percent) between locally made steel charcoal gasifiers and ferrocement gasifiers. The BEDP of small-scale high-cost gasifier plants is again much higher than that of equivalent low-cost plants. At 3,000 operating hours, the BEDP increases by approximately US$250/tonne. Retrofitting decreases the BEDP by 200 to US$450/tonne depending on the number of operating hours. At diesel substitution rates below 80 percent, BEDPs from dual-fuel plants will always be higher then those of equivalent Otto plants. Rice Husk Gasifiers. Figure 5.2 also presents BEDP values for rice husk gasifier plants with outputs ranging from 30 kWe, to 100 kW,,. Low-cost rice husk gasification systems at 1,000 full-load operating hours have BEDPs of US$290/tonne to US$430/tonne. At 3,000 annual operating hours, the BEDP values for low-cost systems drop considerably, ranging from US$150/tonne to US$250/tonne. Conclusion At world market oil prices of approximately US$18/barrel, the cost price of diesel is about US$190/tonne. International and local transport costs can add a maximum of about US$60/tonne. Therefore, the maximum economic cost of diesel at most locations in the world is about US$250/tonne. These BEDP values make it clear that biomass gasification is not economically attractive at current oil prices. World market oil prices must rise by a factor one-and-a-half to two for biomass gasification to become attractive again. The possible exception to this statement may be low-cost wood and rice husk gasifiers, which may have BEDP values ranging from 150 to US$250/tonne. But low- cost rice husk gasification systems are not yet technically proven, and wood is not usually available for free. The situation may be different when biomass gasification is approached from a financial point of view, however. Local taxes may cause actual market prices for diesel oil to be substantially higher then US$250/tonne. At diesel oil market prices of US$400/tonne to US$500/tonne, then, low-cost gasifier plants that run for long periods, as in some industrial applications, may be financially viable. Economics of Biomass Gasifiers 41 Heat Gasifiers Cost Model Capital Costs. On basis of real heat gasifier costs (Table 5.1), a simple capital cost model was developed for heat gasifiers. Because of the fairly wide variations in specific investment found in practice, the model makes a distinction between low-cost and high-cost systems. Table 5.4 presents cost estimates for both categories at three output levels (500 kWth, 1,000 kWth, and 4,000 kWth). The model arrives at specific capital costs ranging from US$34/kWth to US$44/kWth for low-cost systems and US$130/kWth to US$152/kWth for high-cost systems. Those values are conservative. A Biomass Technology Group (1989) study documented that in Thailand complete heat gasification systems, including burner, have been delivered and installed for US$12 to 14/kWth. A World Bank study (ESMAP 1990) quotes local installed costs of heat gasifiers ranging from 250 kWth to 1,000 kWth at US$12.5/kWth. Operating Costs. Operating costs of heat gasifiers depend on fuel costs, labor costs, and costs of service and maintenance. On basis of the data collected by the BGMP, values have been estimated for costs. Economy Figure 5.3 presents the outcome of the model calculations for low-cost heat gasification systems at three different capacity levels, respectively, of 500 kWth, 1,000 kWth, and 4,000 kWth. It is also assumed that the overall system efficiency (gasifier/furnace) is 75 percent, whereas for an oil-fired system 85 percent is assumed. Such low-cost wood heat gasifiers, using wood at a cost of US$20/tonne and operating between 2,000 and 4,000 hours per year, appear to have BEDP values of about US$120/tonne. In equivalent operation, BEDP values for high-cost heat gasification systems are about US$160/tonne. At a wood cost of US$10/tonne, the low-cost and the high-cost systems have BEDP values, respectively, of about US$75/tonne and US$115/tonne. Conclusion At a world oil market price of about US$18/barrel, the price of fuel oil is approximately US$120/tonne. Adding US$60/tonne for international and local transport, the maximum economic price of fuel oil is about US$180/tonne. Some care must be taken in drawing too-optimistic conclusions because the technical feasibility of heat gasifiers has not been proven on a very large scale for all conditions assumed in the model. Nevertheless it appears that a considerable array of practical combinations of heat demand, gasifier cost, and wood fuel costs possible, specifically in the agro-industrial sector in developing countries, where biomass gasification for heat applications is attractive. Table 5.2 Capital Costs and Performance Parameters for Small Diesel and Biomass Gasifier Power Plants (High Cost Systems) Capital investment estimate Specific equipment cost (US$/kWet) Other investment Other cost and performance parameters Generator, Training, Freight, Maintenance Installed control, commis- installation, Total capital Economic System Number and service capacity Gasifier and sioning and other investment lifetime efficiency of cost (% per System type (kWel) system Engine electrical Total (US$) (US$1kWel) (US$/kWel) (years) (%) operators 1,000 hours) Diesel 10 n.a. 325 402 727 1,000 182 1,009 10 23 1 4 Full gas Charcoal/ferrocement 10 57 466 402 925 2,000 231 1,356 7 12 2 4 Charcoal/steel 10 1,001 466 402 1,868 2,000 467 2,535 7 12 2 4 Wood/steel 10 1,201 466 402 2,069 2,000 517 2,786 7 12 2 4 Dual fuel Charcoal/ferrocement 10 40 387 402 828 2,000 207 1,235 7 15 2 4 4~b Charcoal/steel 10 731 387 402 1,520 2,000 380 2,100 7 15 2 4 M3 Wood/steel 10 877 387 402 1,666 2,000 416 2,282 7 15 2 4 Diesel 30 n.a. 210 259 469 1,000 117 619 10 25 1 4 Full gas Wood/steel 30 1,035 300 259 1,594 2,000 399 2,060 7 16 2 4 Rice husk/steel 30 1,553 300 259 2,112 2,000 528 2,707 7 9 3 4 Dual fuel Wood/steel 30 756 249 259 1,265 2,000 316 1,647 7 18 2 4 Rice husk/steel 30 1,134 249 259 1,643 2,000 411 2,120 7 10 3 4 Diesel 100 n.a. 130 160 290 1,000 72 372 10 28 1 4 Full gas Wood/steel 100 880 185 160 1,225 2,000 306 1,552 7 17 3 4 Rice husk/steel 100 1,320 185 160 1,665 2,000 416 2,102 7 10 4 4 Dual fuel Wood/steel 100 643 154 160 957 2,000 239 1,216 7 19 3 4 Rice husk/steel 100 964 154 160 1,278 2,000 320 1,618 7 11 4 4 Note: kWel = kilowatt electric. Table 5.3 Capital Costs and Performance Parameters for Small Diesel and Biomass Gasifier Power Plants (Low Cost Systems) Capital investment estimate Specific equipment cost (US$/kWel) Other investment Other cost and performance parameters Generator, Training, Freight, Total Maintenance Installed control, commis- installation, capital Economic System Number and service capacity Gasifier and sioning and other investment lifetime efficiency of cost(% per System type (kWel) system Engine electrical Total (US$) (US$/kWei) (US$/kWel) (years) (%) operators 1,000 hours) Diesel 10 n.a. 325 402 727 1,000 182 1,009 10 23 1 4 Full gas Charcoal/ferrocement 10 57 466 402 925 2,000 231 1,356 7 12 2 4 Charcoal/steel 10 217 466 402 1,085 2,000 271 1,556 7 12 2 4 Wood/steel 10 261 466 402 1,128 2,000 282 1,610 7 12 2 4 Dual fuel Charcoal/ferrocement 10 40 387 402 828 2,000 207 1,235 7 15 2 4 Charcoal/steel 10 159 387 402 947 2,000 237 1,384 7 15 2 4 Wood/steel 10 190 387 402 979 2,000 245 1,424 7 15 2 4 Diesel 30 n.a. 210 259 469 1,000 117 619 10 25 1 4 Full gas Wood/steel 30 225 300 259 784 2,000 196 1,046 7 16 2 4 Rice husk/steel 30 225 300 259 784 2,000 196 1,046 7 9 3 4 Dual fuel Wood/steel 30 164 249 259 672 2,000 168 907 7 18 2 4 Rice husk/steel 30 164 249 259 672 2,000 168 907 7 10 3 4 Diesel 100 n.a. 130 160 290 1,000 72 372 10 28 1 4 Full gas Wood/steel 100 159 185 160 505 2,000 126 651 7 17 3 4 Rice husk/steel 100 159 185 160 505 2,000 126 651 7 10 4 4 Dual fuel 2 2 Wood/steel 154 160 453 2,000 113 587 7 19 3 4 Rice husk/steel 154 160 453 2,000 113 587 7 11 4 4 Note: kWel = kilowatt electric. Table 5.4 Capital Costs and Performance Parameters for Heat Gasification Plants Minimum capital investment estimate Other cost and performance parameters Freight, Maintenance Installed Gasifier Fuel Total installation, Total capital Economic System Number and service capacity system handling equipment and other investment lifetime performance of cost (% per System type (kW[h) (US$/kWth) (US$/kWth) (US$MkWth) (US$/kWth) (US$IkWth) (years) (%) operators 1,000 hours) High-cost system 500 117 0 117 35 152 12 85 2 2 1,000 106 0 106 32 138 12 85 3 2 4,000 88 12 100 30 130 12 85 3 2 Low-cost system 500 29 0 29 9 37 5 85 2 2 1,000 26 0 26 8 34 5 85 3 2 4,000 22 12 34 10 44 5 85 3 2 Note: kWth = kilowatt therrnal. Economics of Biomass Gasifiers 45 Figure 5.1 Break-Even Diesel Price: Gasifier Systems Using Wood Wood gasifier, 10 kW Wood gasifier, 30 kW 200 2800 600 1100 ___ _____ _____ N 700 _____ ____30 4 000 300 2600 200 __ 100~~~~~~~~~~~~~~~~~~~~~~~~~~~~~0 0 400 0 1000 2000 3000 4000 5 000 6000 7000 8 000 0 1000 2 1100 3000 4000 5000 6000 7000 H000 Annual full powfer hours Annual full powler hours _Wood price 0 U$S/l - Wood price 20 Ut/t K- Wood price 40 Ut/l Wood price 0 US/t e Wood price 20 U$/t Wood price 40 US/I ---Wood price 60 US/l Wood price 80 US/l A Wood price 100 US/t Wood price 60 Ut/t -X-Wood price 80 U$/l Wood price I100 US/1 Wood gasifier, 100 kW 2400 - \20= \7200 I _ _ _ _ _ __ 0 1000 2000 3000 4000 5000 6000 7000 8000 Annual full powler hoursAnulfl wehor |~- Wood price 0 US/I -+-- Wood price 20 US/Il~- Wood price 40 US/ t -Wo rc S/ -Wo rc 0U/I -Wodpie4Ill/| -6- Wood price 60 Ut/Il)- Wood price oO US/I t Wood price 100 US/ H odpie6 SI--Wo rc 0u/I & odpielO |1/ ~~~~~Wood gasifier , syte s 00fct kWdfeethrwr ofgrtin nbekee islpie -3 00___ 0 000 2000 3000 4000 5000 6000 7000 8000 Annual full powier hours -U- Wood price 0 US/I -4-- Wood price 20 U$/I f Wood price 40S/ -3-- Wood price 60 Ua/b -u Wood price 80 U3/I UDt Wood price 100 US/I Wood gasifier systems; effects of different hardware configurations on break-even diesel price: 10 kW 30 kW 100 kW High cost rather than low cost gasifier system Required increase of diesel price for break-even: 1000 hours/year 600-700 USD/ton about 600 USD/ton about 600 USD/ton 3000 hours/year about 300 USD/ton about 300 USD/ton about 300 USD/ton Back-fitting to existing generator set: Reduction of diesel price for break-even: 1000 hours/year about 500 USD/ton about 350 USD/ton about 200 USD/ton 3000 hours/year about 200 USD/ton about 150 UISD/ton about 100 USD/ton Dual-fuci rather than full-gas system At 80% diesel substitution, dual-fuel is marginally more economic for high biomass fuel price and few annual operating hours. If less than 80% substitution is achieved, break-even diesel price will be higher. 46 Small-Scale Biomass Gasifiers Figure 5.2 Break-Even Diesel Price: Gasifier Systems Using Charcoal or Rice Husks Low cost charcoal system, 10 kW Ferrocement charcoal system, I 0 kW j800 Ferocmel_hacol_ysem_1_k !,°0 ' _ ,,, - Ž7800- 00 00 'o200 l__ l__ l00-_ 40040 300 3~~~~~~~~~~~~~~~~00 jxoo-== lllAoo -,- 0 1000 2000 3000 4000 5000 6000 7000 8000 0 1000 2000 3000 4000 s000 6000 7000 8000 Annual full power hours Annual full power houm -mU- 0 US/t -+ 50 US/i - 100 U1$/li -U-0 S/I-4S VS/i I DO u$/i -f 150 US$/1 High and low cost rice husk systems Rice husk fuel price: 0 USO/lon jBOO T ".1700 r __ 5~00I -_ _ D X _ __ _ 400 ___ 300 -- 0 0 1000 2000 3000 4000 5000 6000 7000 0oo0 Annual Cull power hoDus -|- High cosf, 100 kW I Low cost, 30 kW --- Low cost, I00 kW Effects of different hardware configurations on break-even diesel price for charcoal systems: 10 kW steel system 10 kW ferrocement system High cost rather than low Required increase of diesel price for break-even: cost gasifier system 1000 hours/year about 550 USD/ton not applicable 3000 hours/year about 250 USD/ton not applicable Back-fitting to existing Reduction of diesel price for break-even: generator set: 1000 hours/year about 450 USD/ton about 500 USD/ton 3000 hourstyear about 200 USD/ton about 200 USD/ton Dual-fuel rather than full- At 80% diesel substitution, dual-fuel is marginally more economic for high biomass fuel gas system price and few annual operating hours. If less than 80% substitution is achieved, break- even diesel price will be higher. Economics of Biomass Gasifiers 47 Figure 5.3 Break-Even Fuel Oil Price: Low-Cost Heat Gasifier Systems Using Wood Heat gasifier, 500 kW ___00 Heat gasifier, 1000 kW Soo~~~~~~~~~~ 600 ______ 300 100 0.Q0. o -000 2000 3000 4000 sooo 6000 7000 8000 0 300 zooo2 3000 4000 sooo eooo 7000 8000 Annual hzi power hours Aninual full power hours Wood price 0 US/t Wood price 20 us jt - Wood price 40 US/I _ Wood price 0 US/I + Wood price 20 U$/i -~ Wood price 40 US/ Wood pric 60 U$/t Wood price 80 US/t - Wood price Io 00uS/t -I-Wood price 60 US/t --Wood price 80 uS/t -A-Wood price Io 00UV/ 2e0t gasifier, 4000 kW 30-~~~~~~~~~~~~~~~~~~~~~~ ;~~~~~~~~ 50 __ 0 1000 2000 3000 4000 5000 6000 7000 8000 Annual full power hours - Wood price 0 U S/lW 40Wo Wood price 20 US/I --Wood price 40 US/t -e- Wood price 60 US/I -04- Wood price 80 US/i -r- Wood price l00 US/I Heat gasifiers; effects of different hardware configurations on break-even diesel price: 500 kW I1000 kW 4000 kW High cost rather than low Required increase of diesel price for break-even: cost gasifier system 1000 hours/year about 100 USD/ton about 150 USD/ton about 50 USD/ton 3000 hours/year about 50 USD/ton about 40 USD/ton about 30 USD/ton 5000 hours/year about 35 USD/ton about 30 USD/ton about 25 USD/ton Fuel: wood Efficiency oil fired installation: 85% Heat gasifier system efficiency: 75% 6 Conclusions and Recommendations Small-Scale Power Gasifiers Gasification combined with use of the gas in an internal combustion engine is the most efficient way of converting solid fuels into shaft power or electricity. Small-scale power gasification allows the use of biomass instead of petroleum derivatives in small internal combustion engines. Gasifiers use a renewable energy resource, one that is available almost everywhere in one form or another. Therefore, biomass gasification presents a local fuel alternative for countries that have no fossil fuel resources. Providing that the biomass used for gasification is grown on a sustainable basis, its use does not increase the amount of CO2 in the atmosphere and hence does not add to the "greenhouse effect." The technology may find application where petroleum fuels are either unavailable or where the cost of power from engines fueled by producer gas is lower than from diesel- or gasoline-fueled engines. Commercial Status of Small-Scale Power Gasifiers Although a number of equipment manufacturers in Europe and the United States sell small-scale biomass power gasification systems, only a few units have been installed in developed and developing countries during the last five years. The situation is somewhat different in India and China, where manufacturers of small-scale wood power gasifiers and rice husk gasifiers, respectively, appear to maintain at least some level of production. At present, only a few commercial small-scale biomass power gasifiers are operating globally. The majority are about a hundred rice husk gasifiers, located primarily in China. A declining number of charcoal gasifiers continue operation in Latin America, primarily Brazil. A few wood-fueled power gasifiers are in commercial operation in Latin America as well. The largest unit, about 1 MWeI, is installed in Paraguay. The short-term commercial prospects of small-scale biomass power gasifiers in developing countries at present appear limited. Three major factors can be cited: Unfavorable economics compared with fossil-fuel alternatives 49 50 Small-Scale Biomass Gasifiers * Low quality and reliability of equipment, resulting in operational difficulties * Inherent difficulties in training sufficiently qualified or experienced personnel, resulting in substandard operation of units. Longer-term prospects depend on the long-term price developments in world oil markets as well as on the progress that can be made in improving the quality of the equipment and in simplifying operating procedures. Power Gasifier Economics The economics of biomass gasification are highly dependent on the price of diesel fuel. At world market oil prices of approximately US$18/barrel, diesel costs about US$190/tonne. International and local transport costs can add a maximum of about US$60/tonne. Therefore, the maximum cost of diesel at most locations in the world is about US$250/tonne. Charcoal and Wood Gasifiers. At a diesel cost of US$250/tonne, small charcoal gasifiers are not economic. Such plants require at least a 100 percent increase in diesel-fuel cost even to be considered as an alternative to diesel power. Low-priced wood gasifiers of local manufacture and relatively large capacity (> 100 kWei) require low woodfuel prices (< US$20/tonne), high load factors (close to 1), and high total operating hours (about 4,000 hours per year) for them to recover, through fuel cost savings, the additional capital investments associated with the current gasification systems. Only a regular and fairly constant power demand would make the such power gasifiers economically attractive. The latter two factors alone invalidate the economic application of those gasifier plants at most rural power applications in developing countries. Better possibilities may exist in relatively isolated agro-industries. Also, the economics of small-scale biomass gasifiers for base-load power generation in small local grids in developing countries should be studied. Rice Husk Gasifiers. The economic data from the BGMP suggest that the biomass power gasifiers that may be closest to commercialization are low-cost "open core" rice husk gasifiers. At 3,000 to 4,000 annual operating hours and high load factors, these plants require for diesel prices of only US$150 to 250/tonne to break even. It is probable that operating and load conditions of this sort exist in large rice mills in some developing countries. The potential for this technology therefore may be significant. Although high-cost rice husk gasifiers of Chinese design and manufacture are a proven technology, they are still associated with unacceptable environmental pollution. The same drawbacks apply to low-cost rice husk gasifiers, and they are also burdened by low quality and reliability. Nonetheless, experiences with low-cost rice husk gasifier designs in Indonesia have been encouraging. The pollution problem may be overcome by employing the same high-temperature catalytic tar-cracking techniques that have been developed for the large fluidized-bed biomass gasifiers. In view of their potential, low-cost, low-tar fixed-bed Conclusions and Recommendations 51 rice husk gasifiers, ranging in output from 100 kWei to 500 kWel, should be developed further. Once the environmental problems have been solved, "open core" gasifiers may be adapted for using other agricultural residues such as coffee husks, maize cobs, and cotton gin trash. Equipment Performance Several aspects of gasifier power plant performance were much below manufacturers' specifications. Specifically, maximum engine power output and diesel- fuel savings (in dual-fuel systems) of some plants were much lower than would be expected from the manufacturers' information. In addition, although most wood and charcoal plants produced a gas that can be used in internal combustion engines without considerably worsening their lifetime and maintenance needs, this was not the case for rice husk gasifiers, which at present only work with special sturdy low-speed engines that must have frequent maintenance. Because they were prototypes, almost all plants experienced significant problems relating to material selection and corrosion. Staff at some installations were able to overcome those problems, but most did not. None of the plants presented serious dangers with respect to operator health and safety, but operation of even state-of-the-art open-core rice husk plants still results in serious environmental pollution. Other gasifier types produced much more manageable environmental problems that can be overcome relatively easily. Equipment Reliability A comparison of relatively successful and unsuccessful projects reveals that both sorts experienced problems during the initial period after startup, but the successful projects were those that had the expertise and resources to modify and "debug" their plants and-in the end-arrive at more-or-less trouble-free operation. Successful projects had the commitment of the gasifier manufacturer for a prolonged period to help the local operators immediately with technical, material, or spare-part supply problem. The successful projects also evidenced a strong (usually financial) motivation of management and operator alike to keep the gasifier working. Equipment Quality The commercial market for small-scale gasifiers has never been large enough to carry the expenses of development from prototype to mature commercial plant. Plants that were installed were generally prototypes funded by grants. Under such circumstances, technical and operational problems are to be expected, especially because the performance of power gasifiers appears to be sensitive to relatively small changes in fuel- and energy-demand-related parameters. Nevertheless, the results of the BGMP show that some small-scale wood gasifiers finally achieved reliable and relatively trouble-free operation. Experience and expertise in building and operating reliable, safe, and pollution-free wood gasifiers is thus now available. 52 Small-Scale Biomass Gasifiers Operating Personnel Properly operating a biomass gasification system requires training and experience. The labor required to operate a gasification plant is quite different from that required to run a diesel engine of equivalent output. This difference is not only quantitative but qualitative. During operation, the operator must frequently check a number of temperature and pressure meters and use the information so gleaned to make decisions on adding fuel, shaking the grate, deblocking filters, and adjusting valves. At the end of daily operation the operator normally cleans reactor and filters of ash and dust. The operator may also be in charge of fuel preparation and fuel quality control. All this means that, contrary to diesel engine operation, where the engine driver has time to take on additional unrelated tasks, a small-scale gasifier requires a full-time operator. The operational history of the gasifiers in the BGMP shows that not every operator can master the required competencies. Motivation and discipline are necessary, but the operator also must be able to react adequately on two or three input parameters and must master some basic technical skills. Biomass gasifier operations thus appear to require not only an adequate initial training program for operators but also continuous technical backup for a period of at least a year. Recent developments in the automotive industry have resulted in mass-produced hardware and software that may greatly increase possibilities for automatic control of gasifiers. The automotive industry manufactures and uses a number of inexpensive temperature- and shock-resistant sensors and attenuators. In combination with the corresponding multiparameter input logic software, such instruments could conceivably monitor and control a biogas engine and reactor, thereby largely reducing or eliminating the need for highly trained and experienced gasifier personnel. Although such a development would improve the current economic competitiveness of small wood and charcoal gasifiers only marginally, it would certainly increase the possibilities for speedy introduction of the technology. Environmental Pollution Biomass gasification systems produce solid, liquid, and gaseous wastes, which, if not adequately controlled, harm the environment. Solid wastes are primarily residue ash. The amount produced may vary between 1 and 20 percent, depending on the biomass fuel. In most cases, disposal of this ash is not a problem, and in some cases, such as rice husks, the ash may have value for use by steel or cement industries. Gaseous emissions from biomass gasifiers are also not a significant factor except possibly in the immediate vicinity of the system, where CO leakages could be hazardous to workers. Compared with alternatives-especially fossil-fuel-based systems-biomass gasifiers are relatively benign in their environmental emissions, producing no sulfur oxides and only low levels of particulates. The situation is not as encouraging when large quantities of liquid effluents are produced, as is the case in updraft and "open core" power gasifiers. The situation is Conclusions and Recommendations 53 exacerbated if wet-gas cleaning systems are used, which can dramatically increase the volumes of contaminated liquid effluent. In all cases, the effluent can be highly toxic, and untreated disposal of such effluent can lead to contamination of drinking water, fish kills, and other negative impacts. At present, additional research and development are needed to find solutions to this problem. Fortunately, most downdraft and cross-draft power gasifiers can be equipped with dry-gas clean-up systems, which drastically reduce the quantity of liquid effluent produced. As a result, disposal can be accomplished in a more controlled and acceptable manner. The problem does not arise in heat gasifiers, because such systems usually combust the dirty hot producer gas completely-that is, inclusive of the tarry components, which are gaseous at higher temperatures. Health and Safety Operation of biomass gasifiers may result in exposure to toxic gaseous emissions (i.e., carbon monoxide); fire and explosion hazards; and toxic liquid effluents. Avoiding poisoning by toxic gases is mainly a matter of following sound workplace procedures, such as avoiding inhalation of the exhaust gas during startup and ensuring good Ventilation of gas-filled vessels before personnel enter them for service and maintenance. Avoiding fires and explosions is also primarily a matter of following sound procedures. In addition, however, it is important that the system is designed so that any internal explosion that may occur can be relieved to avoid damage to the system. Avoiding contact with carcinogenic compounds in the condensates requires the use of protective gloves, clothing, or both. From the above, it may be concluded that with proper operator training, equipment and procedures, health and safety hazards can be minimized or even eliminated. A Long-Term Approach to Technology Transfer From the BGMP it becomes clear that the gasifier programs that have adopted strategies for sustainability and long-term development have shown the best results. Donor agencies should concentrate on building local capability through training and transfer of technology rather than on simply providing expertise and equipment. Building local capacity is a slow process, but it is the only one that will lead to successful projects that benefit rural communities. Simply setting up a project and then leaving is a waste of time and money. Any activity not carried out with a motivated local partner is also destined to have no future. The most effective gasification programs have resulted from the formation of strong and experienced local organizations that enable the training of local personnel in different aspects of the technology and the adaptation of the process to suit local circumstances. Therefore, an in-country group of competent and dedicated professionals with experience in technology development and implementation seems an essential starting point for any sustained expansion in the use of biomass gasification. Any long- term program should probably start with setting up a national center of expertise. 54 Small-Scale Biomass Gasifiers Heat Gasifiers The commercial potential for heat gasifiers is significant. The technical performance is generally proven and reliable. Heat gasifiers are economically attractive compared with conventional alternatives. In addition to their excellent prospects in the agro-industrial sector, heat gasifiers can be applied in non-biomass-producing industries requiring process heat if acceptable and affordable biomass fuels are available. Potential heat gasifier markets include retrofits for oil-fired boilers, ovens, kilns, and dryers used in various industries. A complete evaluation of the market potential of heat gasifiers would require a separate study. Annex: Criteria for Preliminary Project Identification The experiences from World War II as well as from several more recent projects in developing countries demonstrate that under certain conditions, wood gas from biomass can substitute for petroleum fuels. However, this does not mean that biomass gasification is a technically, economically, ecologically, or socially feasible alternative to petroleum fuels under all circumstances. Using the Checklist Reasonable assurance about the feasibility of a biomass gasifier installation can only be obtained after a careful technical and economic evaluation that takes into account site-specific requirements and conditions. For a first screening, however, a checklist (Figure A1.1) can be used to indicate whether biomass gasification is worth considering. If all questions on the list are answered positively, the evaluator can be reasonably sure of good prospects for a biomass gasification project. Any negative answer should prompt the evaluator to look for ways to eliminate the obstacles to a successful biomass gasification project or to examine alternative ways of meeting power requirements. The decision tree in Figure Al .1 is based on simple positive/negative answers to a number of questions. Some background information to these questions is given in the following paragraphs. This information is summarized in Table A 1. 1. Capacity Range The largest fixed-bed gasifier power plant reporting more-or-less reliable operation uses two wood gasifiers to fuel three wood-gas engines of 330 kWe, each. The BGMP was not able to monitor this plant, which is in a Mennonite community in Loma Plata, Paraguay. Single gasifier units in capacities above 500 kWe, are not commercially proven. Moreover, upscaling of fixed-bed power gasifiers above 500 kWe, may be difficult for technical and environmental reasons. Most recent biomass gasification experience stems from plants operating generators in the 10 to 100 kWe, range. Probably the largest feasible capacity for fixed-bed heat gasifiers is in the range of 5 MWth. Larger heat gasifiers are in operation, but the reactors are mostly of the fluidized-bed type, which is outside the scope of this report. 55 56 Small-Scale Biomass Gasifiers Figure A1.1 Decision Tree for Small-Scale Biomass Gasifier Projects Is your capacity demand in the following range? Small scale gasifiers are Below 500 electrical or mechanical kW or commercially unproven outside this range. below 5 thermal MW ,, Large risk for project failure 4111K Small scale fixed bed gasifiers are (Do you have the following biomass available ? icommercially unproven for other fuels. E Charcoal, ood, ricehusks, cocnut shell Are you prepared to run extensive fuel tests Charcoal, wood, lice husks, coconut shells ____ and adapt system design if neccessary ?n 0 Is your supply of biomass sustainable at the Can you supplement your supply with a required daily, monthly, and annual level for similar biomass from other sources to meet \ the expected duration of your p needs? 0 40 Are you willing to invest twice the capital _______________O______ as is required for a petroleum system ?7 . Potential of economic feasibility is uncertainw ___________________ _ and dependent on other factors (i.e., actual | Is the biomass fuel price below 60 c capital and other operating costs). Xv USS/ton and the petroleum price above m~..V2 Are you still prepared to spend time to < ~~300 US$/ton ? ) analyze the costs in more detail? J It is unlikely that recovery of capital costs S can be achieved through fuel cost savings a Can more than 1,000 annual operating E in less than I ,000 hours per year. K C hours be expected? w.V Are you still prepared to spend time % analyzing the fuel costs in more detail? K Is te expected average load of the system I 0 t during operation greater than 50 percent? J t Low load factors can lead to operational problems. C\ Have you found a system design with proven performance over your load range? c Are you willing to accept somewhat lower reliability than normally associated with a Are you prepared to invest in a back-up diesel system operating in your environment? system? (A Is tere aboravaiableto oerat a 0) ( Is there labor available to operate and Do you think that better incentives for the co maintain the gasifier system, and are the operators would improve the situation, and are E E operators willing to deal with the dirtier you prepared to accept the financial O Kworking conditions associated with gasifiers ? ) o reae tonsaecept th fiania_ consequence-s? i C Are there any other successful gasifler pro- Are you prepared to be a pioneer and to jects currently operating in your country from EO establish the support infrastructure E<> which you can obtain information? that will be needed? r Are you confident that you have answered v) E Review the data in this handbook all the above questions coffectly? J ..-y and/or seek technical assistance. l 41K Prospects are good for successful applications of biomass gasification, and a more detailed analysis should be conducted. Annex 57 Biomass Fuels Charcoal, many types of wood, rice husk, and coconut shells are the only fuels that can be considered as commercially proven in fixed-bed power gasifiers. Depending on the gas producer design and the form in which the fuel is available, preprocessing of the fuel may be required. The same fuels work well in fixed-bed heat gasifiers. However, indications are that the performance of these plants is less critical with respect to specific fuel characteristics, so that other biomass fuels (e.g., maize cobs, coffee husks, coconut husks, cotton gin trash) also may be considered in this application. Sustainable Fuel Supply For successful application of a biomass gasifier, a suitable quantity of biomass fuel must be available to fuel the installation during its lifetime. Table AL.I gives biomass fuel consumption figures for plants operating on full power that were measured during the BGMP. In conjunction with actual power or heat demand figures, those data can be used to estimate the minimum necessary biomass supply. Investment The cost of an installation with a biomass gasifier compared with one using petroleum fuel will obviously depend on choice of equipment and supplier. Data from the BGMP show very large variations in specific costs (US$/kW). However, experience from recent units indicates that as a rule-of-thumb the installed cost of a gasifier power plant tends to be two to four times the cost of a similar installation operating on petroleum fuel and that the installed cost of a heat gasifier may be one and a half to two times the cost of an oil-fueled plant. Local Conditions The feasibility of small-scale biomass gasifiers hinges on the savings that can be gained by switching from relatively high-cost petroleum fuels to low-cost biomass fuels. A detailed and accurate financial feasibility study can only be carried out late in a project study, after the operating conditions have been determined and the equipment has been specified. In the early project identification phase, a first rough estimate is desirable; hence, the three listed items in the decision tree (i.e., fuel cost, operating hours, and load factor) address this issue. It should be borne in mind however, that the three factors are interrelated (i.e., a high number of annual operating hours or a high value of the load factor can compensate for too-low petroleum fuel costs on site or too-high processed biomass fuel costs. Fuel Costs Obviously the possibilities to regain the additional investment through savings on the fuel bill are highest when petroleum costs are high and biomass fuel costs are low. 58 Small-Scale Biomass Gasifiers Table Al.1 Background Information to the Checklist When Considering Biomass Gasification Power gasifiers Heat gasifiers Evaluation factor (capacity range < 500 kWeI) (capacity range < 5.0 MWth) Biomass fuels Charcoal Wood Wood Charcoal Rice husks Rice husks Coconut shells Coconut shells Limited experience with a number of other biomass fuels Fuel consumption Wood: 1.3-1.4 kg/kWel Wood: 0.4 kg/kWth Charcoal: 0.7-0.9 kg/kWel Charcoal: 0.15-0.17 kg/kWth Investment 2-4 times the investment in 1.5-2.0 times the investment in oil- petrol/oil-fueled plant fueled plant Local conditions Fuel cost Petrol/diesel > 300 US$/tonne Processed biomass fuel < 60 US$/tonne Operating hours > 1,000 hour per year Load factor > 50 Reliability 10-20 downtime caused by Less than 5 downtime caused by technical problems technical problems Labor Motivated and skilled labor No special labor requirements required Other projects Initial support needed No special requirements Note: kg = kilogram; kWel = kilowatt electric; kWth = kilowatt thermal; MWth = megawatt thermal. However, the data from the BGMP show that it is unlikely that biomass gasification will be financially feasible if the cost of petroleum fuel on site is less than about US$300/tonne and the cost of processed biomass fuel on site is more than about US$60/tonne. Operating Hours If the additional investment in a gasifier is to be recovered within a reasonable time, the unit must be operated frequently. After all, only in operation can comparative savings on fuel cost be realized. Consequently, the possibility of recovering the additional investment depends greatly on the operating time. Data from the BGMP indicate that recovery of the additional capital investment is unlikely when the gasifier is used for less then 1,000 hours per year. Load Factor The load factor of an energy system is defined as the ratio of the actual energy output and the nominal (maximum possible) power output. Low load factors in gasifier Annex 1 59 systems may have both economic and technical consequences. If the average load factor is low, reclaiming of the additional capital investment as compared to a conventional petrol- or oil-fueled system will become increasingly difficult. Also, certain type of power gasification systems (i.e., downdraft fixed-bed gasifiers) are technically not suitable for prolonged operation on low loads. Therefore, evaluation of the gasifier option only makes sense when the expected average load factor is above 50 percent. Reliability The data of the BGMP make it clear that gasifier power plants are less reliable than comparable petrol- or oil-fueled systems. On the one hand, this is caused by a lag in development that may well be remedied over time. On the other hand, the complexity of adding a gas producer to an engine is an intrinsic reason for lower reliability. The data indicate that at present the more developed small-scale biomass gasifier power plants are down for 10 to 20 percent of the time because of technical problems or scheduled maintenance. Heat gasifiers have fewer technical problems and consequently are more reliable. Labor Operating an installation with a biomass gasifier means additional fuel processing, fuel handling, and system service compared with using liquid fuel. In particular, the regular cleaning of gas filters can be a dirty and therefore less attractive job. Service intervals for biomass gasifier plants are shorter than for plants using liquid fuels, which means that the requirements on operator discipline are higher if operational disturbances are to be minimized. Operation itself also requires a higher time input, since high-tech control and safety systems that allow unattended operation are more difficult to justify financially for small-scale installations. Even with regular service, some operational disturbances-such as those that may be caused by irregularities in fuel properties-are likely to occur at irregular intervals. Such disturbances will demand intervention of higher skill and understanding of the process from the operator than is normally the case in liquid fuel operation. These skills can be transferred through proper training if the trainee has a reasonable level of diagnostic aptitude and ability. The implication is that successful operation of a small-scale gasifier power installation calls for a more skilled, motivated, and disciplined operator than is normally needed for diesel engine operation. In addition, this operator must be willing to do dirty work. The BGMP has learned that such operators are sometimes difficult to find on sites and in situations where small-scale power gasifiers are financially feasible. Some plants would have performed much better had the operators shown more skill and dedication in their tasks. More specifically, the BGMP indicated that it is not easy to transform engine drivers into gasifier operators, especially without adequately adapting their salary to the new and more demanding tasks, introducing an incentive scheme based on fuel-cost savings, or both. 60 Small-Scale Biomass Gasifiers The above-mentioned labor problems were not encountered at heat gasifier plants, probably because operating a heat gasifier intrinsically calls for less skill, motivation, and discipline than are needed for running a power gasifier. Other Projects Since it is more complex to fuel an engine with producer gas than with liquid fossil fuel, it is very likely that advice and technical support will be needed in the initial phase of the project, which may last for a year. If other similar installations are operated in the neighborhood, the necessary support may be obtained from the users of these installations. In pioneer installations, however, support must be arranged either through the equipment manufacturer or through a technical consultant. This initial support must not be neglected or underestimated. Many if not most failures of biomass gasifier projects in developing countries can be attributed to lack of sufficient technical assistance. Detailed Evaluation If careful consideration of the questions in the checklist have led to the conclusion that there are good prospects for a successful application of the technology, a preliminary project design should be made. References Biomass Technology Group. 1992. State of the Art: Rice Husk Gasification, Enschede, The Netherlands. ESMAP (Joint UNDP/World Bank Energy Sector Management Assistance Programme). 1990. Costa Rica: Forest Residues Utilization Study. ESMAP Report 108/90. 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Water Policy and Water Markets: Selected Papers and Proceedingsfrom the World Bank's Antiual Irrigation and Drainage Seminar, Annlapolis, Maryland, December 8-10, 1992 No. 250 Rangeley, Thiam, Andersen, and Lyle, International River Basin Organizations in Sub-Saharan Africa No. 251 Sharma, Rietbergen, Heimo, and Patel, A Strategyfor the Forest Sector in Sub-Saharan Africa No. 252 The World Bank/FAO/UNIDO/lndustry Fertilizer Working Group, World and Regional Supply and Demand Balancesfor Nitrogen, Phosphate, and Potash, 1992/93-1998/99 No. 253 Jensen and Malter, Protected Agriculture: A Global Reviewv (List continues on the inside back cover) THE WORLD BANK A partner in strengthening economies and expanding markets to improve the quality of life for people everywhere, especially the poorest Headquarters European Office Tokyo Office 1818 H Street, N.W. 66, avenue d'1ena Kokusai Building Washington, D.C. 20433, U.S.A. 75116 Paris, France 1-1, Marunouchi 3-chome Chiyoda-ku, Tokyo 100, Japan Telephone: (202) 477-1234 Telephone: (1) 40.69.30.00 Facsimile: (202) 477-6391 Facsimile: (1) 40.69.30.66 Telephone: (3) 3214-5001 Telex: mci 64145 WORLDBANK Telex: 640651 Facsimile: (3) 3214-3657 MCI 248423 WORLDBANK Telex: 26838 Cable Address: INTBAFRAD WASIINGTONDC World Wide Web: http://www.worldbank.org E-mail: books@worldbank.org i- 7S0-8213-337137 I. 1. ~~~~~~~~~~~ISBN 0-8213-3371-2