i small-scale gasification-based biomass power...
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10 January 1998, I
Small-Scale Gasification-Based Biomass Power Generation
Eric D. LarsonCenter for Energy and Environmental Studies
Princeton UniversityPrinceton, New Jersey, USA
Prepared for theBiomass Workshop
Changchun, Jilin Province, China12-13 January 1998
IntroductionGasifying biomass to produce a combustible gas provides the possibility for much more
efficient overall conversion of a given biomass resource into electric power than is possible withtraditional combustion-based technologies. In particular, gasified biomass can be used to powerinternal combustion engines (ICEs), gas turbines, and fuel cells, all of which are able to produceelectricity at considerably higher efficiency than boiler/steam-turbine systems of comparable size.In addition, ICEs, gas turbines, or fuel cells coupled with biomass gasifiers have the potential forconsiderably lower capital investment requirements than comparably-sized boiler/steam turbinesystems. In the size range below 5 MWe, spark-ignition or compression-ignition engines are thetechnologies of choice today for gasification-based power generation from biomass (Fig. I). Fuelcells and micro-gas turbines coupled with biomass gasifiers will offer considerably higherefficiencies at small scales compared to internal combustion engines [Williams, 1998], but suchadvanced technologies are still under development. This paper presents an overview oftechnology and economics of biomass-gasifier/internal combustion engine technology, with somediscussion of applications in the context of Jilin Province.
Historical Perspective on Biomass-Gasifier/Internal Combustion Engine (BiG/ICE) SystemsGasified wood-charcoal was widely used as a civilian fuel in Europe during the Second
World War [Anonymous, 1979], running several hundred thousand vehicles and poweringindustrial machinery (National Research Council, 1983]. The development of inexpensivepetroleum supplies after the war led to essentially total abandonment of BiG/ICE technology untilthe first oil price shock of the 1970s. Crash attempts were then made worldwide to resurrect and
: .install BiG/ICE systems for stationary power supply, especially in remote areas of developingcountries [Foley and Barnard, 1982]. Most such efforts failed, however, primarily becauselignocellulosic biomass was the preferred feedstock, rather than charcoal.. Significant amountsof tar can be produced during gasification of raw biomass. Condensation of tars on downstreamequipment causes system operating problems. Such problems were encountered in many of thegasifier-engine systems installed in the 1970s and 1980s (e.g., see Coovattanachai, et ai. [1982];Kumar, et al. [1985]; Zijp and Stassen [1984]). Tar and other problems [Stassen and Knoef,
I A substantial fraction of the energy content of the original raw biomass is lost in the process of convertingit to charcoal, particularly using charcoal conversion technologies that are commonly found worldwidetoday. When gasifiers were resurrected in the 1970s, these energy losses were generally consideredunacceptable from a resource supply standpoint. Hence the emphasis on lignocellulosic feedstocks.Similar concerns with over-utilization of the biomass supply during the Second World War led Sweden toban charcoal use in gasifiers toward the end of the war.
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1995], coupled with a resumption of low oil prices and an emphflSis on centralized powergeneration for rural electrification in developing countries, led to a second abandonment of effortsto commercially establish BiG/ICE technology by the end of the 1980s.
Research efforts continued, however, and led to the identification of gasifier and gascleanup system designs for eliminating tar and other technical problems. The process oftransferring these research findings into commercial products in the 1990s coincided with thegrowing recognition among developing country governments and multilateral lending agencies ofthe financial and environmental shortcomings of business-as-usual expansion of centralizedpublic-sector electricity supply to rural areas. Private power generation and renewable energyimplementation began to be strongly encouraged by many governments around the world. Today,interest has again revived worldwide in BiG/ICE technology for small-scale stationary powergeneration. Unlike with the previous resurrection efforts, BiG/ICE systems are now beingoffered commercially, with warranties and performance guarantees, by a growing number ofcompanies worldwide [e.g., see Anonymous, 1997 and Turnbull et al., 1996].
BiG/ICE TechnologyA typical BiG/ICE power generating system includes three basic elements: a gasifier, gas
cooling/cleaning, and the engine/generator (Fig. 2):Gasification: The thermochemical processes of gasification include pyrolysis
(devolatilization) and char conversion.2 During pyrolysis, the volatile components of thefeedstock vaporize at temperatures between about 300°C and 600°C, leaving behind fixed carbon(char) and ash [Milne, 1979; Antal, 1983]. Biomass is high in volatile matter (typically 70-90%)in contrast to coal, so pyrolysis plays a large role in biomass gasification. Products of pyrolysisinclude carbon dioxide, carbon monoxide, hydrogen, methane, water vapor and complex organiccompounds (tars and oils) that condense at high temperatures and can be difficult to decompose("crack") into lighter permanent gases. In some gasifiers, the tars and oils constitute an importantenergy component of the product gas. A relatively small amount of char remains after pyrolysis,some of which burns to provide heat for pyrolysis of additional biomass and gasification of theuncombusted char. Since biomass chars react 10 to 30 times more rapidly than coal chars[Graboski, 1982], biomass gasifiers can typically operate at lower temperatures than coal gasifierswhile achieving the same char conversion.
The intended use of the gas and the particular feedstock to be gasified influence thedesign and operation of the gasifier and auxiliary equipment. Cost economies of scale usuallypermit large-scale systems to be more technologically sophisticated. Figure 3 shows several of themost prominent gasifier designs, and Fig. 4 shows the general range of applicability of each
design.The simplest gasifier design is the updraft reactor (Fig. 3a), named according to the
: .direction of airflow through a packed-bed of reacting biomass. Air is injected at the bottom and
biomass enters at the top, from which point it successively undergoes drying, pyrolysis, charcrasification and char combustion. The combustion releases heat and carbon dioxide that drive~asification and pyrolysis as the combustion products travel up through the bed. Updraft gasifiershave high energy conversion efficiencies due to the efficient counter-current heat exchange
2 A variety of names are associated with gasified biomass. "Producer gas" derives from the first "gas
producers" that were developed in the 1800s for gasifying coal [Ram bush, 1923]. Because of the lowheating value of such gas (4 to 6 MJ/Nm3, or 10% to 15% of the heating value of natural gas), its name is"poor gas" in French. Coal-derived producer gas was widely used in the 19th and early 20th centuries inurban areas (and continues to be used in some areas today) for domestic cooking, heating, and publiclighting, which led to its being labeled "town gas". The use of gasified biomass in vehicles in Europeduring World War II resulted in the name "suction gas," because engine suction is used to draw therequired air for gasification into the reactor.
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between the rising gases and descending solids. Condensing of pyrolysis tars from updraft \.gasifiers is problematic in applications where the producer gas must be cooled before it can beused, e.g. in internal combustion engines. Successfully removing tars from the gas before use cansignificantly penalize overall efficiency, since tars constitute an important fraction of the energyoutput of the gasifier. Thus, in practical operations, the use of updraft gasifiers has been limited todirect heating applications where no gas cooling is required, such as for producing a fuel that is -burned in a "close-coupled" boiler or kiln. "
Downdraft gasifiers produce an order of magnitude less tar [Brown, et al., 1987]. The -design shown in Fig. 3b was the dominant design used during World War II. In this design, the r
combustion zone is fixed at the point of air injection, and product gas is drawn out from below.Pyrolysis occurs above and continues within the combustion zone. All pyrolysis products areforced to pass through the hot char gasification zone, where a significant fraction of tar iscracked. In actual field experience in the 1970s and 1980s, it proved extremely difficult to reducetar to acceptable levels efficiently and cost-effectively, particularly at small scales [Parikh, et al.,1988]. Fairly elaborate and costly gas cleaning systems were recommended for applicationswhere a cool, tar-free gas was needed [Reed and Das, 1988].
A number of researchers have contributed to developing an understanding of the scienceof what was previously the ill-defined art of gasification[Groeneveld, 1980; Reed and Markson,1982; Shrinivasa and Mukunda, 1983; Kaupp, 1984; Susanto, 1984; Parikh et al., 1988; Reed andDas, 1988; Mukundaetal., 1984, 1993, 1994a, 1994b;Sasidharanetal., 1995]. Such work led tothe identification of specifications for modified downdraft gasifier designs and gas cleaningsystems that enable acceptable tar levels to be achieved under commercial operating conditions[Mukunda et aI., 1994b]. One such design is the open-top reactor (Fig. 5). The most obviousdifferences between this design and the traditional downdraft gasifier (Fig. 3b) are the open top -and the lack of a flow restriction at the "throat," but many differences in details that wereidentified through theoretical and experimental research, including an understanding of requiredfuel physical and chemical characteristics, have contributed to the development of this design[Mukunda et al., 1993].
For larger-scale applications, various fluidized bed designs derived from coal gasifiersand combustors are used. The bubbling-bed (Fig. 3c) was the first fluidized-bed gasifier designdeveloped. The circulating fluidized-bed (CFB) (Fig. 3d), is an increasingly popular commercialvariant. In a fluidized bed, an inert material (like sand) constitutes the bed into which biomassfuel is continuously fed. Air, oxygen and/or steam are injected from below to keep the bedfluidized. Turbulence leads to excellent heat and mass transfer, producing relatively uniformtemperatures throughout and overall faster reactions than in updraft or downdraft reactors. Thehigher reaction rates lead to higher throughput capabilities per unit volume, and hence lower
.capital costs per unit of capacity. Fluidized-beds are generally more expensive than fixed-beds at: smaller scales due to the high costs for blowers, continuous feed systems, control systems and
other instrumentation [Larson et al., 1989]. Indirectly-heated gasifiers, designed specifically totake advantage of the higher reactivity of biomass compared to coal, are also being developed[Wyman, et al., 1993; Katofsky, 1993]. In these designs, biomass is heated by an inert heat-carrying material such as sand (Fig. 3e) or through a heat exchanger (Fig. 3t). The indirectdesigns rely on the high reactivity of biomass feedstocks to compensate for the generally loweroperating temperatures that can be achieved using indirect heating. A primary attraction of theindirect design is that it produces a much higher energy content product gas than air-blowngasifiers, since there is no nitrogen dilution.
Gas Cooling/Cleaning: Gas from the gasifier must be cleaned to avoid contaminantdeposition and erosion or corrosion damage to the engine. The gas must also be cooled toincrease its density for injection into the engine cylinders. Properly designed and operated, thebest commercial gasifiers available today minimize tar production, such that a direct-contactwater quench followed by a filtration system for particulate removal can be used [Anonymous,
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1997; Mukunda et al., 1994a]. Careful design of the scrubber and filter are critical to ensuringadequate gas cooling and cleaning, as well as ease of maintenance and operation of the
cooling/filter system.Engine/Generator: Gasified biomass can fuel either compression ignition (diesel) engines
or spark ignition (gasoline) engines. Diesel engines are favored because of their higherefficiency, greater durability and reliability, simpler maintenance, and because diesel fuel isreadily available in most developing countries. Producer gas can replace 65-85% of the dieselfuel requirements of an engine-some diesel fuel is needed to assist ignition. Commercial dieselengines require only minor modifications to the air intake system so that engine suction drawsboth air and fuel gas simultaneously. Decreasing air flow with a control valve permits the fuel-airratio to be adjusted.
Crop Residues for Big/ICE Systems in Jilin ProvinceA wide variety of biomass feedstocks can be used to fuel BiG/ICE systems, but the
physical and chemical characteristics (size, texture, moisture content, fixed carbon content, etc.)of the feedstock are important in determining performance. In general, a BiG/ICE technologysupplier sets feedstock specifications that must be met to insure successful operation, since agasifier's design and operation varies with the feedstock being used. Commercial BiG/ICEsystems are available today that will operate on wood chips, maize cobs, cotton stalks, rice hulls,soy husks, coconut shells, palm nut shells, sawdust, and other fuels. Residue fuels, which areavailable today in most regions of the world, are an attractive fuel source for BiG/ICE systemsbecause of their generally low cost.
Maize production is a major residue generating activity in Jilin Province: an estimated 9million tonnes of residues are available annually for non-field use.3 Figure 6 shows a roughestimate of the annual quantity of maize residues that would be needed to fuel BiG/ICE powerplants of up to 500 kWe capacity. Also shown is the estimated area of maize that must beharvested annually to provide these residues, assuming a maize yield of 6 tonnes/ha and a ratio ofdry residues to primary maize production of I: I, and that one-third of the residues must remain011 the land to provide organic matter and nutrients. To operate a 200 kWe system with a 65%capacity factor would require residues from about 300 ha of maize production. The total tonnageof ecologically-recoverable maize residues in Jilin province would support an installed BiG/ICEgenerating capacity of some 1500 MWe.
Energy Crops for BiG/ICE SystemsIn addition to residue fuels, biomass can be grown specifically for energy purposes. Such
fuel will generally be more costly than residues, but much greater quantities can be generatedfrom a given land area, and lands not well suited for crop production (marginal or degraded
; .lands) might be suitable for growing energy crops. Woody crops, which can be harvested asneeded and stored more easily after harvesting than herbaceous crops, might supplement seasonalresidue fuels, or replace them entirely in the longer term.
It is often assumed that large plantations (tens of thousands of hectares) of energy cropsare needed in order to produce dedicated biomass energy competitively. However, an alternativesmall-scale biomass supply system, "farm forestry," might be ideally suited to providing biomassto supplement or replace residue fuels in rural applications where large blocks of land cannot bededicated to energy crop production. Farm forestry is increasingly being implemented in Brazil(see box), and similar activities have been reported elsewhere.
3 Based on maize production of 13.5 million tonnes/year (as reported in transparencies prepared by Ralph
Overend for this workshop), a residue-to-maize ratio of I: I, and a requirement that '/3 of residues are left onthe field for maintenance of nutrients and organic matter status.
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BOX: Farm Forestry in Brazil
In a typical fann-forestry program in Brazil, a forestry company provides the materialinputs and technical know-how for establishing trees on a fanner's land (I to 50 hectares of treesper farm) and contracts with the fanner to buy some or all of the first harvest for an agreed uponprice that incorporates repayment for the initial inputs and services. The inputs include saplings(typically some species of eucalyptus in Brazil), fertilizers (applied at planting), herbicides(applied at some point after planting), and pesticides. The company samples the farmer's soil andprovides inputs "tuned" to that farmer's soil.
Under programs ongoing in Brazil, biomass yields reported for small-farm plantings arenot much below those reported for large-scale plantations owned and operated by forestrycompanies. This success is attributed to a combination of sophisticated material inputs and careful(typically-manual) tending by the fanner. Yields can be expected to increase as both farmers andtheir contracting companies learn improved methods and approaches (most programs in Brazilstarted less than a decade ago.) Yield reductions are often offset by substantially lower costs tocompanies for establishing farm forests. Limited survey data indicate that the per hectare cost forfanner-contracted land is substantially less than half the cost for company-owned land [Larsonand Williams, 1995]. Limited data also suggest that delivered costs for biomass are not muchdifferent between farm-forests and large-scale plantations.
Farm forestry is growing rapidly in Brazil, with encouragement from the private sector;from federal, state and local governments; and from farmers. Several hundred thousand hectareshave been established in less than a decade. This compares favorably with the estimated 6 to 7million hectares of large-scale plantations established in Brazil since the 1960s. Farmer-ownedplantations account for as much as 20 percent of some forestry companies' total planted area, andsome companies have a goal of raising this fraction to 50 percent or more.
The overall results of the small-fann forestry programs in Brazil have been minimalchanges in land ownership and use patterns (large forestry companies are not buying out smallfanners), while local wood supplies at reasonable costs have increased, and farmers (includingfonnerly subsistence farmers) have gained a revenue source.
Regardless of the scale at which dedicated biomass energy crops are produced, they arelikely to be more costly to use in BiO/ICE applications than residue fuels. Costs will vary withlocal soil, climate, labor costs, and other factors. Some indication of costs can be derived from anextensive assessment of expected productivities and costs for plantation-grown biomassundertaken for the nine states (covering 155 million hectares) that comprise the semi-arid regionof Northeast Brazil [Carpentieri, et al., 1993]. Large areas of the Northeast have been identifiedthat are suitable and potentially available for energy crop production (Fig. 7). The total estimatedbiomass production potential is substantial: it is estimated to be sufficient to generate 20 to 40
.-times the current electricity consumed in the Northeast region. Average projected plantation.yields vary from region to region within the Northeast, and costs vary accordingly (Fig. 8).
About one-third of the potential biomass production has delivered costs below $1.2/0J in 1988US$ (Fig. 9)--about $1.6/0J in 1997 US$. An additional fifty percent of the potential regionalplantation-biomass supply would have an average delivered cost of $1.3/0J (1988$) or $1.7 /OJ
( 1997$).Local assessment in Jilin Province is needed to estimate what local costs might be for
production and delivery of dedicated energy crops. The growing season is shorter in Jilin than inNortheast Brazil, which will tend to lower yields, but higher rainfall may be a compensatingfactor. Differences in labor costs between Jilin and NE Brazil could also be important.
The higher cost associated with plantation biomass provides a strong incentive forpursuing higher efficiency in converting the biomass to electricity. Higher efficiency alsoreduces the land requirements for providing each kWh of electricity. Figure 10 shows land arearequirements for small biomass power generating systems. Area is shown as a function of power
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plant capacity up to 500 kWe, for assumed plantation yields of5, 10, and 15 dry tonnes perhectare per year. Curves are shown for conversion efficiencies representing the performance ofBiG/ICE technology and for a technology that might have twice this efficiency.
Costs for BiG/ICE SystemsThe overall economics of BiG/ICE technology are illustrated here in terms of the
lifecycle cost of power generation.Mukunda et af. [1993] provide one detailed estimate of capital and operating costs for
BiG/ICE technology at a scale of96 kWe. This particular system utilizes the gasifier designed atthe Indian Institute of Science (Bangalore) and now being pursued for commercialization by anIndian-Swiss joint venture company [Anonymous, 1996]. Mukunda et af. project a total first costfor an installed system (in 1997 US$) to be about $460/kWe, but key components of such asystem (for example, the gasifier and the engine) require replacement at regular intervals. Over a25-year investment period, the present value of total installed equipment costs (includingreplacement of the gasifier and engine every 6 years and the cleanup and control systems every10 years) is an estimated $800/kW (using a 12% discount rate).
Another BiG/ICE system is offered commercially by EnergyWorks through ajointventure with Ankur Scientific, an Indian gasifier manufacturer [Anonymous, 1997]. DeLaquil[1998] estimates an installed cost of about $ 1200/kWe for such a system today. This estimateincludes manufacture of the system in a developing country, such as India or Indonesia, but it isfor a newly commercial technology. It is conceivable that costs would fall in the future (perhapsas low as the estimate by Mukunda, et af.) once demand grows such that high production volumeis achieved. In any case, the assumed capital investment has relatively little impact on the overalleconomics of BiG/ICE power generation, as illustrated below. Fuel costs are more critical.
Fuel consumption is estimated by Mukunda et af. at full load to be 1.3 kg/kWh ofbiomass (with 15% moisture content) and 0.1 liters/kWh of diesel fuel (representing adisplacement of 70% of the full diesel consumption in diesel-only operation). DeLaquil estimatesbiomass and diesel consumption at 1 kg/kWh (20% moisture content) and 0.1 liters/kWh.
Table 1 shows the calculated cost of electricity generation for a 96 kWe BIG/ICE system,assuming a capital cost of $800/kWe, an internal rate of return to the investor of 12%, a capacityfactor of 65%, operating labor costs representing a rural Indian context, diesel fuel costing$0.26/liter ($6.7 /GJ), and biomass costing $20/tonne with 15% moisture content ($I/GJ). Withthese assumptions. the total cost of power generation is 7.4 e/kWh. One-third of the total cost isfor diesel fuel; one-quarter is for biomass fuel (Fig. 11). Generating costs compare veryfavorably with stand-alone diesel power generation at the same scale, even at relatively low dieselfuel prices (Fig. 12).
The analyses in Table 1 and Fig. 12 assume a capacity factor of 65%. Capacity factors in; .the 25-50% range might be more representative of power demands in a rural village at a relatively
early stage of electrification. At lower capacity factors, the cost of power increases substantially(Fig. 13). However, to reduce power costs at the early stages of electricity demand developmentin rural areas, one strategy might be to export baseload electricity to urban demand centers[Kartha et af., 1997]. Low power demands in rural areas lead to high costs for power delivered tosuch regions over the central electricity grid from power plants located near urban centers,because transmission line capacity is vastly underutilized in such situations [Sinha and Kandpal,1991]. Nevertheless, it may be economically feasible to transmit power from, rather than to, therural area until local demand grows, since transmission lines could then be utilized with highcapacity factors. It is noteworthy that remote hydroelectric sites and mine-moutl1 coal-firedpower plants provide power to urban centers under such arrangements.
As noted earlier, power generating costs are not especially sensitive to capital costs-acapital cost of$1200/kWe instead of$800/kWe increases per-kWh generating costs by about 15%at a 65% capacity factor. However, the cost of fuel, both diesel and biomass, has a large impact
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" on total cost. Even at the low end of diesel fuel costs, diesel fuel still accounts for one-third of, the total cost of power (Fig. 11). With the diesel cost fixed at $0.26/liter, Fig. 14 shows power
generating cost for a range of biomass costs, from zero (negative fuel costs are conceivable insome situations, e.g., where disposal costs can be avoided) to $2/GJ, which might be a high-endestimate of the costs of dedicated energy crop production in Jilin Province.
At the high end of the biomass cost range shown in Fig. 14, power generating costsexceed 10 e/kWh. More efficient technologies are desirable, especially for use with such higher-cost biomass. Such technologies could become available in the future. One such technology is ahybrid system involving gasification to power a fuel cell and recuperated gas turbine. Capitalcosts for such a system are projected to be modestly higher than costs for BiG/ICE today, whileefficiencies4 above 40% (at least double the BiG/ICE) are projected at a scale of200 kWe [Karthaet al., 1997].- This efficiency corresponds to a biomass consumption of about 0.5 kg/kWh (15%moisture content). With such high efficiency systems (that also require no diesel fuel), the cost ofelectricity generation would be under 6 e/kWh with biomass costing $2/GJ and assuming acapital cost of$1200/kWe (Fig. 1 5).
Institutional and Infrastructure IssuesWhile advanced technologies, such as gasifier/fuel cell systems, promise improved
economics for small-scale biomass power generation in the future with dedicated biomass energycrops as fuel, the economic analysis above indicates that BiG/ICE systems that are commercially-available today can be competitive for rural power generation today in a variety of situations. Inparticular, where low-cost biomass residue fuels are available, BiG/ICE technology would appearto be very competitive with stand-alone diesel generation.
To maximize the potential economic benefits of introducing BiG/ICE, some importantinstitutional and infrastructure development challenges must be addressed. Successfullyaddressing such issues using technology available today (BiG/ICE) will greatly facilitate theintroduction of advanced technologies in the future (e.g., gasifier-fuel cell systems) that promisestill greater benefits for rural development.
One challenge is to put into place production and delivery infrastructures for residuefuels. Where conditions are especially favorable, dedicated energy crop production systemsmight also start to be developed.
Another challenge is developing a diversified electric load with an isolated (non-grid-connected) system in order to achieve high system capacity factors and thereby lower the cost ofgenerated power. If a BiG/ICE system were able to connect to the grid, then the possibility existsfor exporting power to urban demand centers until such time as local power demands can beexpanded and diversified. Institutional arrangements for allowing small-scale power supply tothe utility grid would need to be worked out. Revenue collection systems would also need to be
..put in place..The introduction of BiG/ICE systems would also provide opportunities to develop
technology transfer and certification mechanisms, as well as for the development of a rural-focussed independent power producer industry and associated technology marketing,maintenance, and operator training infrastructures.
Potential Rural Development BenefitsSmall-scale gasification-based biomass power generation is a potentially attractive
strategy for sustainable electricity supply in rural areas. Gasifier/internal combustion enginesystems are commercially available today, and advanced systems under development promise stillbetter economics in the longer-term,
" Efficiency is defined here as the fraction of the higher heating value of biomass converted to electricity.
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Biomass-derived power could contribute to rural development in a number;;,ofways. Inaddition to direct employment in fuel gathering, delivery, and power plant operation, theeconomically competitive electricity that could be produced by such systems could draw otheremployment- and income-generating activities into rural areas, especially energy-intensiveindustries that offer well-paid jobs. Until sufficiently-high levels of electricity demand developlocally, biomass-derived power might be economically exported to urban demand centers toachieve the high plant capacity factors that lead to lower generating costs. Privatized biomass-power generation and the industrial activities it attracts might provide a tax base to help financerural infrastructure building that would serve to attract additional economic activities. Such ta.xrevenues could also be used to subsidize the provision of basic human needs to communities thatremain outside of the cash economy. Building on an initial residue fuel supply, production ofdedicated energy crops in the longer term might be a strategy for restoring marginal or degraded .
lands to more productive use.
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T.B. Reed and M. Markson, "Biomass Gasification Reaction Velocities," in Fundamentals of Thermochemical BiomassConversion, Overend, Milne, and Mudge (eds.), Elsevier Applied Science, New York, 1982, pp. 951-965.
P. Sasidharan, K.P. Murali, and K. Sasidharan, "Design and Development of a Ceramic-Based Biomass Gasifier-anR&D Study from India." Energy for Sustainable Development, 11(4), November 1995, pp. 49-52.
U. Shrinivasa, and H.S. Mukunda, "Wood Gas Generators for Small Power Requirements," Current Science, 52(23), Dec.
5:1094-1098,1983.
C.S. Sinha and T.C. Kandpal, "Decentralized versus Grid Electricity for Rural India: the Economic Factors," EnergyPolic,v, 19. pp. 441-448.
9
-~~
I
H.E.M. Stassen and H.A.M. Knoef. "UNDP/World Bank Small-Scale Gasifier Monitoring Programme -FinalFindings:' Energy for Sustainable Development, II( I), May 1995, pp. 41-48.
H. Susanto, "Moving Bed Gasifier with Internal Recycle and Separate Combustion of Pyrolysis Gas," Ph.D. thesis, InstitutTeknologi, Bandung, Indonesia. 1984.
J.H. Turnbull, S. Hulkkonen, and R. Dracker, "Development of Small Modular Biomass Power Systems:' Proceedingsof Bioenergy '96, Southeastern Regional Biomass Program, Nashville, Tennessee, 1996, pp. 605-611.
R.H. Williams, paper on biomass-gasifier fuel cell/gas turbine power system presented at this workshop, Jan. 1998.
C.E. Wyman, R.L. Bain, N.D. Hinman, D.J. and Stevens, "Ethanol and Methanol from Cellulosic Materials," in T.B.Johansson. H. Kelly, A.K.N. Reddy, R.H. Williams, and L. Burnham (eds), Renewable Energy: Sources for Fuels andElectricity. Island Press, Washington, 1993.
T. Zijp and H.E.M. Stassen, Operating £Tperience Ivith Producer Gas Plants in Tan=anian Villages, Dept. of ChemicalEngineering, Twente University of Technology, Enschede, The Netherlands, 1984.
10
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, Table 1. Perfonnance and costs fora 96 kWe BiG/ICE system, based on Mukunda, eta/. [1993].
Perfonnance Parameters
Installed Electric Capacity (kW) 96Capacity factor (%) 65Annual kWh production 546,624
Specific fuel useDiesel (kgihr): 70% of 0.28 kg/kWh replaced 8.06
(MJ/hr) 367Biomass (kg/kWh), 15% moisture content 1.1
(kg/hr) 106(MJ/hr) 1795
Lubricating oil use (grams/kWh) 1.36Costs -1997 US$ (a) 0
Capital investment, $/kW (b) 800Maintenance, Siyear (c) 2511Lube oil, $/year (d) 2624Labor, S/operating hour (e) 0.23Fuel, S/operating hour (f)
Diesel 2.4Biomass 2.1
Lifecycle Costs, 1997 US cents per kWh (g)Capital 1.8Maintenance and lube oil 0.9Operating labor 0.2Diesel fuel 2.5Biomass fuel 1.9TOTAL (cents/kWh) 7.4Notes:(a) COSIS given by Mul..-undaetal. [19931 are converted from 1991 Indian Rupees at 20 Rs/US5 and then from 1991 USS to 1997 USS
using the Gross Domestic Product deflator for the USA (1.15 in 1997 relative to 1991).(b) A 25-year analysis period is considered. A 12% discount rate is assumed to calculate the present value of future replacement unilS
that mUst be purchased over this period. The gasifier and engine-generator are assumed to be replaced at 6-year intervals. Thecooling/cleaning and control systems are replaced at 100year intervals. The building does not require replacement.
(c) Annual maintenance cost is estimated as 5% of the first cost of the gasifier and building plus 100/0 of the first cost of the engine-generator set.
(d) lubricating oil is assumed to cost S3/1iter.(e) Operating labor is assessed at4 Rs/operating hour (1991 Rs).(f) Diesel fuel is priced at SO.26/liter (1997S), or S665/GJ. Biomass is S20 per toMe (19975) containing 15% moisture, or $I/GJ.(g) This is the revenue required to achieve a 12% internal rate ofretum on a 25-year investment
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Figure Captions
Fig. I. Scales of application for prime mover technologies in combination with biomass gasification. Gasengine refers to spark-ignited internal combustion engine. IGCC refers to integrated gasifier-gasturbine/stearn turbine combined cycle. Source: TPS, Inc., Nykoping, Sweden.
Fig. 2. Typical equipment layout for a biomass-gasifier/internal combustion engine power generating system.
Fig. 3. Alternative designs for biomass gasification: (a) updraft fIXed-bed, (b) downdraft fIXed-bed, (c)bubbling fluidized bed, (d) circulating fluidized bed, and (e,f) indirectly-heated fluid beds. Source: Larson,1993.
Fig. 4. Scales of application for alternative biomass gasifier designs. Source: TPS, k8e.,..-N,ykoping, Sweden.
Fig. 5. Two variants of the open-core downdraft biomass gasifier [Mukunda, et ai., 1993].
Fig. 6. Approximate maize residue requirements (and associated maize growing area) for biomass-gasifier/internal combustion engine power generation up to 500 kW. in size.
Fig. 7. Regions in Northeast Brazil identified as suitable and potentially available for biomass energy cropproduction [Carpentieri, et ai., 1993]. The inset shows the location of the Northeast region relative to theAmazon jungle.
Fig. 8. Estimated delivered cost of eucalyptus that would be grown for energy in Northeast Brazil as afunction of yield [Carpentieri et ai., 1992]. The average yield in each of the nine states of the Northeast areindicated, as are average yields by bioclimatic region.
Fig. 9. Estimated potential cost-supply curve for biomass energy from plantations in Northeast Brazil[Carpentieri et ai., 1992].
Fig. 10. Approximate planted area for energy crop production required to fuel gasifier-engine systems up to500 kW. in size. Area requirements are shown for BiG/lCE technology and for future technology with doublethe efficiency of BiG/lCE systems. For each technology, the area is shown for crop yields of 5, 10, and 15 drytonnes per hectare per year.
Fig. 11. Oisn-ibution of power generating cost for a 100-kW. scale BiG/GT system.
Fig. 12. Cost comparison between 100-kW. scale BiG/lCE and stand-alone diesel-only power generatingsystems as a function of diesel fuel cost.
Fig. 13. Calculated electricity generating cost for 100 kW. BiG/lCE systems as a function of system capacity; -factor. Results are shown for two levels of initial capital investment. See Table 1 for additional details.
Fig. 14. Calculated electricity generating cost for a 100 kW. BiG/lCE system as a function of assumedbiomass fuel cost. Results are shown for two levels of initial capital investment. See Table 1 for additionaldetails.
Fig. 15. Calculated electricity generating cost for small-scale biomass power systems as a function of thebiomass required per kWh generated, assuming two different capital investment levels and two differentbiomass fuel costs. (For simplicity, diesel fuel consumption is assumed to be zero.) The shaded boxes alongthe x-axis indicate the biomass utilization range that can be expected for presently-available BiG/lCE systemsand for future systems coupling gasification with fuel cells.
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