A Review of Biomass IGCC Technology - Application to Sugarcane Industries

A review of biomass integrated-gasifier/gasturbine combined cycle technology and its

application in sugarcane industries, with ananalysis for CubaEric D. Larson and Robert H. Williams

Center for Energy & Environmental Studies, Princeton University, Princeton, NJ, USA

M. Regis L.V. LealCentro de Tecnologia Copersucar, CP 162, Piracicaba, SP – Brazil – 13400-970

Biomass integrated-gasifier/gas turbine combined cycle (BIG/GTCC) systems will be capable ofproducing up to twice as much electricity per unit of biomass consumed and are expected to havelower capital investment requirements per kW of capacity than condensing-extraction steam turbine(CEST) systems, the present-day commercial technology for electricity production from biomass.The significant levels of biomass available as by-products of sugarcane-processing offer a potentiallyattractive application for BIG/GTCC systems. We review BIG/GTCC designs and ongoing demon-stration and commercial projects and present estimates of the performance of two differentBIG/GTCC plant configurations integrated into sugar or sugar-and-ethanol factories. Because ofthe importance of operating a cogeneration facility the year round in order to achieve attractiveeconomics, we present estimates of the availability of and collection cost for sugarcane trash (topsand leaves) as a fuel supplementary to bagasse. We present estimated costs for electricity generatedby commercially mature BIG/GTCC systems using sugarcane-biomass for fuel in a Southeast Bra-zilian context. The electricity costs are prospectively competitive with CEST-generated electricity,which motivates our analysis of how many BIG/GTCC units might need building (and at what cost)in order to reduce capital costs to competitive levels. We conclude with an assessment of the potentialimpacts on the Cuban energy sector of the introduction of BIG/GTCC cogeneration systems in thatcountry’s sugarcane industry. Cuba’s high per-capita production of sugarcane and its heavy de-pendence on oil for energy provide attractive conditions for a large-scale energy-from-sugarcaneprogram.

1. IntroductionThe biomass integrated-gasifier/gas turbine combined cy-cle (BIG/GTCC) technology was first identified over adecade ago as an advanced technology with the potentialto be cost-competitive with conventional condensing-ex-traction steam-turbine (CEST) technology using biomassby-products of sugarcane-processing as fuel, while dra-matically increasing the electricity generated per unit ofsugarcane processed [see, for example, Larson et al.,1990]. Bagasse, the fibrous residue of sugarcane-milling,is one major biomass by-product fuel. Trash, the tops andleaves of the sugarcane plant (Figure 1), is another sub-stantial energy resource. Bagasse and trash each accountfor about one-third of the above-ground energy stored bysugarcane, with the remaining one-third stored as sugar.

The raw energy value of bagasse and trash associatedwith the year-2000 global sugarcane harvest (1.3 billiontonnes of sugarcane spread across more than 100 coun-tries) is an estimated 8 EJ/year (or a continuous average

250 GWfuel), equivalent to 17 % of today’s total coal con-sumption in developing countries.[1]

During the past decade, there have been substantial ef-forts undertaken worldwide to develop BIG/GTCC tech-nology and carry out pilot, demonstration, and commercialprojects. This paper briefly reviews alternative BIG/GTCC system designs and technology commercializationefforts ongoing worldwide. We then present performanceestimates for BIG/GTCC designs integrated with sugar orsugar/ethanol factories. We also review estimates of theavailability and costs of sugarcane trash as a supplemen-tary cogeneration fuel in Brazil, Cuba, and some otherCaribbean countries. We estimate the prospective costs ofelectricity from BIG/GTCC systems under the assumptionthat the technology becomes commercially mature, andwe also estimate how many BIG/GTCC units would needbuilding before capital and operating costs can be ex-pected to reach commercially mature levels.

Finally, we present an analysis of the potential energy

Energy for Sustainable Development Volume V No. 1 March 2001

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Reproduced with permission from Energy for Sustainable Development

sector impacts of the widespread application ofBIG/GTCC systems at sugarcane-processing facilities ina major sugarcane-producing country, Cuba. Cuba is cur-rently the world’s 6th largest sugarcane producer, evenwith cane production levels less than half its peak pro-duction levels of the late 1980s. The relatively high per-capita sugarcane production in Cuba provides thepotential for sugarcane-derived electricity (and ethanol)to substantially reduce that country’s high fossil-fuel de-pendence.

2. BIG/GTCC technology2.1. Design conceptsThe basic elements of a BIG/GTCC power plant includea biomass dryer (ideally fueled by waste heat), a gasifierfor converting the biomass into a combustible fuel gas, agas cleanup system, a gas turbine-generator fueled bycombustion of the biomass-derived gas, a heat recoverysteam generator (HRSG) to raise steam from the hot ex-haust of the gas turbine, and a steam turbine-generator toproduce additional electricity (Figure 2). Three variationsof this basic configuration are under commercial devel-opment. Table 1 summarizes the main relative advantagesand disadvantages of the three variants. The principal dif-ferences among the variants arise from the design of thegasifier.

Variant 1 involves a fluidized-bed reactor operating atatmospheric pressure using air for partial oxidation of thebiomass. One of the leading atmospheric-pressure gasifierdevelopers, TPS (Sweden), uses a second gasificationstage with a catalyst (dolomite) to reduce the content ofheavy hydrocarbon products (“tars”) that are part of thegas produced in the first reactor. The elimination of tarsis required to prevent downstream operating difficultiesFigure 1. The sugarcane plant

Figure 2. Simplified schematic of a biomass integrated-gasifier/gas turbine combined cycle (BIG/GTCC) system


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that can arise from tar condensation. The product gas fromthe tar “cracker” is cooled from about 900ºC to near-am-bient temperature, cleaned, and compressed to the pres-sure needed for injection into the gas turbine combustor.

Variant 2 involves operating the gasifier near atmos-pheric pressure and using some form of indirect heatingof the biomass, rather than partial combustion. In oneleading design (Battelle Columbus Laboratory, USA), hotsand carries heat to gasify most of the biomass, leavingbehind some solid carbon (char). The char and sand arecirculated to a second reactor, where air is introduced toburn the char and thereby reheat the sand. The productgas passes through a tar cracking unit and is then cooled,cleaned and compressed to fuel the gas turbine. The heatin the combustion products leaving the char-burning re-actor is recovered to raise steam, to dry biomass fuel, or

for other useful purposes.Variant 3 involves operating a fluidized-bed gasifier un-

der elevated pressure using air for the partial oxidation.In this configuration, the gasifier product gas is cooledonly modestly, cleaned at elevated temperature using aceramic or sintered metal filter, and then passed to thegas turbine combustor. Leading developers of the pressur-ized gasifier concept include Foster-Wheeler (USA) andCarbona (Finland).2.2. Demonstration and commercial projectsSince the early 1990s, there have been considerable tech-nology development and demonstration efforts relating toBIG/GTCC commercialization, as summarized in Table 2.The first commercial BIG/GTCC project will produce 8MWe from wood chips grown on short-rotation planta-tions in the UK. Shakedown testing of the plant began at

Table 1. Relative advantages and disadvantages of BIG/GTCC systems based on three different gasifier designs

Gasifier design Advantages Disadvantages

Low-pressure,air blown(Variant 1)

- Easier fuel feed to gasifier than Variant 3- Conventional gas cleaning equipment- Economically suited for modest size

- Waste water produced from gas cleaning system- Fuel gas compressor adds cost, reduces efficiency- Limited economically to modest size

Low-pressure,indirectly-heated(Variant 2)

- Easier fuel feed to gasifier than Variant 3- Conventional gas cleaning equipment- Economically suited for modest size- Higher energy content fuel gas

- Waste water produced from gas cleaning system- Need fuel-gas compressor, but smaller than Variant 1- Limited economically to modest size- Gasifier operation more challenging than Variant 1

High-pressure,air blown(Variant 3)

- Higher efficiency due to lack of gas compressor- Dry hot-gas cleanup system- Economically suited to larger scale than others

- More difficult fuel feed to gasifier than others - More challenging gas cleaning than others- Higher NOx emissions than others- Limited economically to larger scale

Table 2. BIG/GTCC-related commercial and demonstration projects worldwide

Location Notes

Varnamo,Sweden

First fully-integrated BIG/GTCC demonstration plant: 6 MW electric plus 9 MW district heat from wood chips, usingAhlstrom (now Foster Wheeler) pressurized gasifier and ceramic hot gas filters for gas cleanup. Plant commissioningwas completed in 1995. Several thousand hours of successful integrated operation were completed by end of 1999.Decision taken early 2000 to “mothball” the facility due to high cost of continued operation.

Selby, NorthYorkshire, UK

First fully-integrated commercial BIG/GTCC. Shakedown testing began in late 2000. The plant will produce 8 MWefrom short-rotation plantation wood (poplar) in a TPS atmospheric-pressure gasifier, with subsequent cracking of tars,cooling and filtering of raw gas, and wet scrubbing before compression to pressure needed for the gas turbine (ABBAlstom “Typhoon” model g.t.).

Southern Bahia,Brazil

A 32 MWe BIG/GTCC power plant using a scaled-up version of the Selby, UK, facility. Construction is expected tobegin in 2001. A General Electric LM2500 gas turbine modified for biomass-derived gas will be used. Fuel will beeucalyptus wood chips from dedicated plantations and from purchased plantation harvesting residues. Gasifier and gasturbine technology development has been ongoing for several years preceding start of construction.

Piracicaba,São Paulo, Brazil

Project initiated in 1997 at Copersucar Technology Center as an extension of the Bahia, Brazil, project. Overall goal isto evaluate and develop technology to enable BIG/GTCC to be used at sugarcane-processing facilities with bagasse andtrash as fuels. Work has included evaluating availability and quality of trash, agronomic routes to green cane harvestingwith trash recovery, gasification tests (at 2 MWth TPS pilot plant) of bagasse and trash, design integration ofBIG/GTCC into sugarcane facilities, and evaluation of overall environmental impact.

Burlington,Vermont, USA

Pilot plant demonstration of a 200 dry t wood/day Battelle Columbus Laboratory indirectly-heated gasifier. Testingstarted in 1998, with gas burned in existing boiler of a conventional wood-fired power plant. Plans are to install a gasturbine for testing with slipstream of gas.

Greve-in-Chianti,Italy

Two 15 MWth atmospheric-pressure TPS gasifiers operating commercially since 1993 on pelletized refuse-derived fuel(200 t/day RDF). Product gas is burned in cement kilns or boiler.


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the end of 2000. Additionally, construction of a 32 MWeBIG/GTCC system is expected to begin in 2001 in Bahia,Brazil. Both of these projects will utilize a design basedon the TPS atmopsheric-pressure gasifier (Design Variant1 in Table 1). The pilot-plant project in Varnamo, Sweden(Table 2), has demonstrated the feasibility of BIG/GTCCsystems based on pressurized gasifiers (Design Variant 3).The project in Burlington, USA is demonstrating a systembased on indirectly-heated gasification (Design Variant 2).

No demonstration projects are ongoing today involvingBIG/GTCC systems operating on sugarcane biomass.However, in preparation for a pilot demonstration project,extensive testing and analysis is being conducted at theCopersucar Technology Center (CTC) in the state of SãoPaulo, Brazil. Pilot scale atmospheric-pressure gasifica-tion tests with bagasse and trash are being carried outunder this program by TPS in Sweden. The objective ofthe CTC work is to understand in detail the key technicaland cost issues associated with introducing BIG/GTCCtechnology into sugarcane-processing facilities with theintention of designing and installing a pilot demonstrationunit in the next phase of the program.

3. The sugarcane-processing industriesUnderstanding how BIG/GTCC systems might be intro-duced into sugarcane-processing facilities requires an un-derstanding of present sugarcane-processing practices.The discussion here is based on current Brazilian prac-tices. The conversion of sugarcane into sugar or ethanolbegins with the crushing and washing of crushed canestalks, which results in separate streams of cane juice andbagasse containing about 50 % moisture. The bagasse issent to the mill’s cogeneration system, where current prac-tice is to burn it to generate the steam and electricityneeded to run the factory. Existing cogeneration facilitieshave typically been designed to be relatively inefficientin order to ensure that little or no bagasse disposal costsare incurred. The amount of bagasse available for fuel isactually far greater than the amount needed to meet allprocess energy demands. With efficient cogeneration sys-tems, a mill could generate electricity considerably in ex-cess of factory needs, while still meeting all processenergy demands (as discussed in Section 4). The optionof selling electricity to the grid was generally not avail-able when the factories were built, however, so there waslittle incentive to have efficient cogeneration systems.

Furthermore, rather than the current industry practiceof shutting down the cogeneration system during the timeof the year when sugarcane is not being harvested (5 to6 months of the year), a cogeneration system sellingpower to the grid could continue to operate during theoff-season if a supplementary fuel were available. Sugar-cane “trash”, the tops and leaves of the sugarcane plantthat are not used for fuel today, is a potentially attractivesupplementary fuel (as discussed in Section 5).3.1. Making sugar or sugar and ethanolIn sugar production, steam is used throughout the facilityin a sequence of processing steps to convert clarified canejuice into final sugar. The steps include juice concentra-

tion, sugar crystallization, centrifuging, and drying. Juiceconcentration is conducted in a continuous multiple-effectevaporator where the initial concentration of 14 to 16ºBrix (% solids by weight) is increased to 65 to 70º Brix.In this system “live” steam is fed to the first evaporatoreffect, and the vapor that results from evaporating waterin each effect is used as heating steam for the followingeffect and for other steps in the process. Normally fouror five effects are used.

The concentrated juice, now called syrup, is directedto the vacuum pans where it is further concentrated undervacuum to around 91-93º Brix in either a continuous ora batch process. This step produces a mixture calledmassecuite, consisting of around 50 % crystals surroundedby molasses (a sugar solution with remaining impurities).This massecuite, at a temperature of 65-75ºC, is dis-charged into crystallizers where a slow cooling takesplace, usually aided by water or air cooling.

The cooled massecuite is sent to the centrifuges wheremolasses and sugar crystals are separated. The process iscompleted by washing of the sugar crystals with pressur-ized water or steam inside the centrifuges to further re-move the molasses film from the crystal surface. Thesugar is discharged from the centrifuges at a temperatureof 65-85ºC and moisture content of 0.5-1.5 % and directedto a dryer/cooler. The latter uses steam to heat the dryingair, and it uses ambient air in the cooling section. Thesugar leaving this unit is delivered for packaging or bulkstorage.

The molasses collected from the centrifuges can be re-turned to the vacuum pans for recovery of residual dis-solved sugar. Depending on the degree of sucroserecovery desired, factories produce one, two or threemassecuites (also referred to as one, two, or three strikes).The exhausted molasses, called final molasses, has severalpotential uses.

At most sugar factories in Brazil, the final molasses isused as one of the feedstocks for production of fuel etha-nol at a distillery annexed to the sugar factory. The finalmolasses is blended with part of the raw cane juice toconstitute the fermentation feedstock. At a typical Brazil-ian sugar/ethanol production facility, 45-55 % of the su-crose entering the factory as cane is converted to sugar,with the balance being converted to ethanol. Such Brazil-ian factories use only one or two strikes for sugar, anddivert the remaining molasses for blending with raw canejuice to be converted to ethanol.3.2. Process energy demandsA cogeneration facility serving a sugar or sugar/ethanolfactory must always satisfy the demand for steam to runthe factory during the cane-crushing season. Cogenerationtechnologies that convert a high fraction of the biomassfuel input into electricity, such as BIG/GTCC, correspond-ingly convert a smaller fraction of the fuel input into proc-ess steam and cannot satisfy process steam demand viacogeneration unless measures are taken to improve theefficiency with which steam is consumed during sugar orethanol production.

Factories producing sugar alone or co-producing sugar


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and ethanol today consume similar levels of process steamper tonne (t) of sugarcane crushed. A typical level of proc-ess steam consumption almost anywhere in the world to-day is 400 to 500 kg steam/t of sugarcane crushed (kg/tc).

As noted earlier, sugar factories have historically hadlittle incentive to minimize process steam demands. Incontrast, the process steam consumption in beet-sugar fac-tories or corn-ethanol distilleries is far lower than in cane-based factories, because in those factories process energyis provided using costlier fossil fuels. Adopting some ofthe technologies commonly used in the beet-sugar or corn-ethanol industries would lead to substantial reductions inprocess steam demand in cane-processing industries. Thisin turn would enable a cogeneration system at a mill togenerate larger amounts of electricity. The possibility ofexporting electricity to earn additional revenue providesan incentive for adopting process steam reductions atcane-processing facilities. The return on investment fromadded electricity sales would typically be attractive.

Detailed studies have shown that there is a potentialfor reducing the process steam consumed in sugar andethanol production by up to half levels typical for theindustry today [Ogden et al., 1990; 1991]. As interest inthe export of electricity from sugar mills has risen, anincreasing number of feasibility studies of process steamuse reductions have been undertaken at specific mills. Onesuch study was carried out for the Hector Molina mill inCuba, where a CEST cogeneration system will be installedas part of a project co-financed by the Global Environ-ment Facility (GEF). The plan for the Hector Molina pro-ject includes a 32 % reduction in process steamconsumption, from 500 kg/tc to 340 kg/tc [Guzman andValdes, 2000].

Engineers at the CTC have assessed the potential forreducing process steam demand in typical Brazilian cane-processing facilities [CTC, 1998]. They developed de-tailed designs for modifications required to reduce process

steam use and estimated the capital investments requiredto implement such modifications. Table 3 summarizes re-sults from the CTC analyses.

4. BIG/GTCC performance estimatesEngineers at the CTC have also developed detailed per-formance calculations for alternative cogeneration systemsoperating on bagasse and trash and integrated into a sug-arcane-processing facility. On the basis of the CTC’s cal-culations, we illustrate the key differences between steamturbine-based and gas turbine-based cogeneration. In allcases, we consider a cogeneration facility at a factory witha maximum crushing rate of 7000 tc/day and a capacityfactor of 87 %. Most of our analysis assumes a crushingseason lasting 214 days (as in Southeast Brazil), but wealso examine the impact of a 150-day season (as in Cuba).A uniform mixture of bagasse and trash is assumed to bethe fuel throughout the year in all cases. A uniform fuelcomposition simplifies the design and operation of thegasifier or boiler to which it is fed.[2] It also facilitatesseasonal fuel storage by increasing the average moisturecontent of the stored fuel. (The low moisture content oftrash by itself increases fire risks.)4.1. Partial BIG/GTCC design

Until sufficient confidence in the reliability ofBIG/GTCC technology is developed, it is unlikely that asugar or sugar/ethanol producer will be willing to relyentirely on a BIG/GTCC cogeneration system to meet itsprocess energy demands. In this context, a “partial”BIG/GTCC design can be envisioned that would utilizesome of the existing cogeneration equipment at a typicalexisting factory to provide process steam requirements.The particular design considered here assumes that theprocess steam demand is fully met by an existing 22-barbagasse-burning boiler.[3] The steam from this boiler isexpanded to 2.5 bar in back-pressure steam turbines thatrun mechanical equipment in the factory (cane knives,

Table 3. Alternative factory process energy demands and capital investments required to reduce energy demands to the indicatedlevels at a facility processing 7000 tc/day

Sugar-onlyfactory[1]

Sugar factory with annexed ethanoldistillery[2]

Typicaltoday

Steamsaving I

Steamsaving II

Typicaltoday

Steamsaving I

Steamsaving II

Process steam consumption, kg/tc 500 340 280 500[3] 340[4] 280[5]

Process electricity consumption, kWh/tc 20 28 29 20 28 29

Total capital investment (million US$) - 1.60 2.20 - 3.33 4.86

Source: CTC estimates

Notes

1. These are rough estimates, since there are very few factories in the Copersucar cooperative that produce only sugar.

2. Based on 7000 tc/day milling rate, 14.1 % sucrose on cane, 13.8 % fiber on cane, 400 t/day sugar production, 353 m3/day ethanol production. Process steam condition is 2.5 bar,saturated.

3. Mill with 5-effect evaporator, vacuum pan heated with steam bled from 1st evaporator effect, 6-bar steam for centrifuges, 10 kg/tc steam losses.

4. Mill with vapor bleeding from 1st, 2nd, and 3rd evaporator effects for juice heating, regenerative heat exchangers for juice heating (using stillage and juice as heat source), mechanicalstirrers for vacuum pans, 2nd stage evaporator bleeding for vacuum pans, and use of Flegstil technology and molecular sieves in the distillery.

5. In addition to modifications to achieve 340 kg/tc, the following changes are introduced: vapor bleeding from 4th effect for juice heating, additional set of juice heaters, vapor bleedingfrom 5th effect for vacuum pans.


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shredders, and crushers) and generate a small amount ofelectricity. The process steam consumption in the factoryis assumed to be reduced to 340 kg/tc from the typicalpresent-day level of 500 kg/tc, as a result of steam con-servation investments in the factory. In parallel to the 22-bar boiler, the design includes a gasifier supplying fuelto a gas turbine-generator, the hot exhaust from which isused in a heat recovery steam generator to produce 82-barsteam that drives a steam turbine-generator. Also, a smallamount of bagasse is burned in a furnace for drying thegasifier fuel to an average of 10 % moisture content (Fig-ure 3).[4] The performance estimates for the gasifier, gasturbine, and heat recovery steam generator portion of theplant were provided to the CTC by TPS, the Swedish gasi-fier supplier and system integrator. The TPS design in-cludes an atmopheric-pressure gasifier coupled with araw-gas tar cracker and followed by a wet scrubber forgas cleaning and cooling. An intercooled fuel gas com-pressor is used to bring the gas to the pressure neededfor injection into a General Electric LM2500 gas turbinemodified for biomass-derived gas [Neilson et al., 1999].The TPS design is based on the design of the BIG/GTCCcommercial demonstration plant planned for Bahia, Bra-zil [Waldheim and Carpentieri, 2001].

For comparison purposes, CTC engineers also devel-oped performance calculations for a high-pressure steamturbine cogeneration system (Figure 4). The CTC designfor this system includes a boiler producing 82-bar steamthat is expanded through a condensing extraction steam

turbine (CEST). Some steam is extracted at 22 bar to drivethe existing back-pressure mechanical steam turbinedrives and turbine-generator, after which the expandedsteam is delivered for process use. The CEST was de-signed with the same process steam demand and sametotal biomass consumption as the BIG/GTCC design.

As detailed in Table 4, the partial BIG/GTCC systemdesigned by CTC engineers generates 28 MW of export-able electricity (i.e., electricity in excess of process elec-tricity needs) during the milling season and 29 MW inthe off-season. The CEST generates 22 MW of exportableelectricity throughout the year. All of the bagasse gener-ated during the crushing season (140 kg dry matter/tc) isconsumed over the course of the year, and additionallyabout 58 kg (dry matter) of trash is required as fuel/tc.[5]

4.2. Pure BIG/GTCC designOnce sufficient confidence has developed in the reliabilityof the BIG/GTCC technology, “pure” BIG/GTCC cogen-eration systems would likely be introduced. The perform-ance of such a system (Figure 5) has been estimated byCTC engineers. In contrast to the “partial” BIG/GTCCdesign, there is no bagasse-burning boiler in this system.Additional fuel is then available for the gasifier, enablinga larger gas turbine to be utilized. For simplicity, CTCengineers modeled this design assuming it includes twoBIG/GTCC modules identical to the one used in the “par-tial” BIG/GTCC configuration. Steam at 82 bar pressurefrom the heat recovery steam generator is expandedthrough a condensing extraction steam turbine, with one

Figure 3. Schematic diagram for the “partial BIG/GTCC” system discussed in the text. All process steam demand is provided from the exhaust steamof the back-pressure turbine drives. The electrical output of the gas turbine/steam turbine combined cycle augments the process mechanical andelectrical power provided by the back-pressure drives. Remaining electricity is available for export to the grid.


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Table 4. Energy balances for “partial” BIG/GTCC and for CEST cogeneration at a mill processing 7000 tc/day during a crushing season lengthcharacteristic of SE Brazil. The crushing season length is 214 days, during which the mill and cogeneration system operate with 87 %capacity factor (total of 1.3 million tc crushed per year). Total biomass fuel consumption is the same for each cogeneration system.

CEST (82 bar steam) Partial BIG/GTOn-season Off-season Annual On-season Off-Season Annual

Electricity generationGas turbine, kW - - - 16,800 16,800 -Condensing steam turbine, kW 23,910 21,976 - 13,033 12,432 -Back-pressure steam turbine, electricity, kW 2,260 - - 2,483 - -Back-pressure steam turbine mech. power, kW 4,045 - 4,045 -

Total, kW 30,215 21,976 - 36,361 29,232 -Total, GWh 135 69 204 162 92 255Total, kWh/tc 104 57 157 125 71 196

On-season process energy consumptionSteam (130ºC, 2.5 bar), kg/tc 340 - - 340 - -

kg/hr 99,200 - - 99,200 - -Electrical & mechanical power, kW 8,239 - - 8,239 - -

kWh/tc 28 - - 28 - -Exported electricity, kW 21,976 21,976 - 28,122 29,232 -

GWh 98 69 167 126 92 218kWh/tc 75 53 129 96 71 167

Hourly biomass fuel consumption[1]

Bagasse, t50/hr 55.6 31.1 - 63.0 20.5 -Trash, t15/hr 14.4 8.0 - 11.7 11.8 -

Total biomass fuel consumption[1]

Bagasse, thousand t50 per year 261 103 365 296 68 365Trash, thousand t15 per year 64 25 90 52 37 89

Biomass dry matter consumed/tc[1]

Bagasse, t0/tc 0.100 0.040 0.140 0.114 0.026 0.140Trash, t0/tc 0.042 0.017 0.059 0.034 0.024 0.058

Cogeneration efficiencies (%, HHV basis)Electricity generation 14.3 18.6 15.5 16.5 28.1 19.4Process steam generation 31.8 - 22.8 30.4 - 22.8Electricity plus steam 46.1 18.6 38.3 46.9 28.1 42.2

Cogeneration efficiencies (%, LHV basis)Electricity generation 17.3 22.6 18.8 20.1 33.3 23.5Process steam generation 38.5 - 27.6 37.1 - 27.6Electricity plus steam 55.8 22.6 46.4 57.1 33.3 51.1

Source: CTC calculations

Note

1. The subscript refers to the moisture content of the fuel. For example, t50 is tonnes of material with 50 % moisture content, and t0 is tonnes of dry material (zero moisture content).

Figure 4. Schematic diagram for a condensing-extraction steam turbine (CEST) cogeneration system. The design shown here is the same for the CESTsystems discussed in both Sections 4.1 and 4.2 in the text. All process steam demand is provided from the exhaust steam of the back-pressure turbinedrives. The electrical output of the condensing steam turbine augments the process mechanical and electrical power provided by the back-pressuredrives. Remaining electricity is available for export to the grid.


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extraction at 22 bar. The extracted steam is expanded inback-pressure mechanical turbine drives and a small tur-bine-generator. The exhaust steam from these back-pres-sure units is used as process steam. The process steamdemand in this case was assumed to be reduced to 280kg/tc through capital investments in steam conservation.

For comparison purposes, CTC engineers also calcu-lated the performance of a high-pressure steam turbinesystem with the same process steam demands and biomassconsumption as for the pure BIG/GTCC case.

As detailed in Table 5, the pure BIG/GTCC system pro-duces about 43 MW of exportable electricity during themilling season and 58 MW during the off-season. Themain reason for the higher off-season production of export-

able electricity in this case is that process steam is notneeded during the off-season. As a result, a much largeramount of steam is expanded fully through the steam tur-bine in the off-season. In this configuration, all of thebagasse generated during the crushing season is consumedover the course of the year, and additionally about 103kg (dry matter) of trash are required per tc.

The CEST system consumes the same amount of fuelannually as the BIG/GTCC system and produces about31 MW of exportable power the year round.

Figure 6 summarizes the power export potential interms of kWh/tc for both the “partial” and “pure”BIG/GTCC cases and their counterpart CEST systems.The partial BIG/GTCC produces 167 kWh/tc of exported

Table 5. Energy balances for “pure” BIG/GTCC and for CEST cogeneration at a mill processing 7000 tc/day during a crushing season lengthcharacteristic of SE Brazil. The crushing season length is 214 days, during which the mill and cogeneration system operate with 87 %capacity factor (total of 1.3 million tc crushed per year). Total biomass fuel consumption is the same for each cogeneration system.

CEST (82 bar steam) “Pure” BIG/GTCCOn-season Off-season Annual On-season Off-season Annual

Electricity generationGas turbine - - - 33,600 33,600 -Condensing steam turbine 33,651 30,638 - 12,270 24,877 -Back-pressure steam turbine, electricity 2,850 - - 3,250 - -Back-pressure steam turbine, mech. power 2,567 - - 2,567 - -

Total, kW 39,068 30,638 - 51,687 58,477 -Total, GWh 174 97 271 230 185 415Total, kWh/tc 134 75 209 177 142 320On-season process energy consumption 280 - - 280 - -Steam (130ºC, 2.5 bar), kg/tc

kg/hr 81,700 - - 81,700 - -Electrical & mechanical power, kW 8,403 - - 8,403 - -

kWh/tc 29 - - 29 - -Exported electricity, kW 30,665 30,638 - 43,284 58,477 -

GWh 137 97 234 193 185 378kWh/tc 105 75 180 148 142 291


Bagasse, t50/hr 52.8 35.1 - 45.4 45.4 -Trash, t15/hr 24.1 16.0 - 20.7 20.7 -


Bagasse, thousand t50 per year 248 117 365 213 151 365Trash, thousand t15 per year 107 50 158 92 65 158


Bagasse, t0/tc 0.095 0.045 0.140 0.082 0.058 0.140Trash, t0/tc 0.070 0.033 0.103 0.060 0.043 0.103

Cogeneration efficiencies (%, HHV basis)Electricity generation 16.1 19.1 17.1 24.8 28.1 26.2Process steam generation 22.8 - 15.5 26.5 - 15.5Electricity plus steam 38.9 19.1 32.6 51.3 28.1 41.7

Cogeneration efficiencies (%, LHV basis)Electricity generation 19.2 22.8 20.4 29.6 33.5 31.2Process steam generation 27.2 - 18.5 31.7 - 18.5Electricity plus steam 46.5 22.8 38.9 61.3 33.5 49.8

Source: CTC calculations

Note



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Figure 5. Schematic diagram for the “pure BIG/GTCC” system discussed in the text. All process steam demand is provided from the exhaust steam ofthe back-pressure turbine drives. The electrical output of the combined gas turbine/steam turbine cycle augments the process mechanical and electricalpower provided by the back-pressure drives. Remaining electricity is available for export to the grid.

Figure 6. Electricity generated in excess of process electricity consumption at cane-processing facilities for milling season length typical for SE Brazil.Results are shown for the alternative cogeneration systems shown in Figures 3-5. The amount of bagasse and trash consumed in each case is indicated.(See Tables 4 and 5 for details.)


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electricity on an annual basis, or 29 % more than the 129kWh/tc produced by its counterpart CEST system. Thepure BIG/GTCC produces 62 % more exportable powerthan its counterpart CEST system (291 kWh/tc versus 180kWh/tc).4.3. Cogeneration performance in the Cuban contextThe performance results in Figure 6 would be differentfor cogeneration systems integrated into Cuban sugar fac-tories, primarily because of the shorter crushing seasonin Cuba. The requirement for fuel to supplement bagasseat a sugar factory with a processing capacity of 7000tc/day would be greater in Cuba than in Brazil. If an ade-quate amount of supplementary fuel were available, how-ever, a cogeneration facility associated with a factorycrushing for 150 days would generate larger amounts ofelectricity (on an annual basis) per tc than with the samefactory crushing for 214 days (Figure 7 and Table 6). Thetrash requirement in this case (220 dry kg/tc for the “pureBIG/GTCC” case) is more than double the trash requiredwith the longer crushing season.4.4. Performance estimates for the long termThe BIG/GTCC performance shown in Table 5 is used asthe basis for subsequent analysis in this paper. It repre-sents a conservative system design that could be the basisfor initial introduction of BIG/GTCC systems into thesugar industry. Once a commercial BIG/GTCC industryis established, however, performance could improve con-siderably over the levels shown in Table 5 as a result ofcomponent and system optimization. For example, thestrategy for drying the biomass feed to the gasifier in the

design of Table 5 requires about 4 % of the fuel consumedat the plant to be burned to generate hot gas for drying.A more integrated system design would recover wasteheat from the HRSG and other sources to dry thebiomass.[6] Other design changes, such as optimizing thesteam pressure from the HRSG and better overall thermalintegration, could further improve efficiency.

The potential for increasing electricity generating effi-ciency through such improvements can be assessed froma detailed calculation presented by Consonni and Larson[1996] for an optimized BIG/GTCC system using thesame gasifier design considered for Table 5. The electricgenerating efficiency of a 26 MW stand-alone BIG/GTCCsystem in that case was 34 % (higher heating value basis).For comparison, the electric efficiency in Table 5 (for a59 MW system) for the off-season operating period,which would be equivalent to a stand-alone power gen-erating efficiency, is 28 % (HHV basis).[7]

In the longer term, additional technological innovationswill further improve performance. An indication of thepossibilities in this regard is the calculated electrical ef-ficiency of 40 % (HHV) for a 76 MW electric BIG/GTCCsystem utilizing a pressurized gasifier (instead of the non-pressurized gasifier in Table 5) and an advanced gas tur-bine.[8]

5. Biomass fuels for cogeneration at a sugar orethanol factoryThis section examines whether there would be suffi-cient sugarcane biomass available at a facility to fuel

Figure 7. Electricity generated in excess of process electricity consumption at cane-processing facilities for milling season length typical for Cuba.Results are shown for the alternative cogeneration systems shown in Figures 3-5. The amount of bagasse and trash consumed in each case is indicated.Additional details for the right-hand set of bars is given in Table 6.


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the cogeneration systems described in the previous sec-tion.5.1. BagasseThe percentage of the bare cane stalk that is bagasse var-ies with the cane variety. A typical level in Brazil is 140dry kg of bagasse per tonne of milled cane stalk (140kg0/tc).[9] After milling, the bagasse contains about 50 %water, so bagasse availability is often quoted in terms ofbagasse with 50 % moisture content. In this case, the Bra-zilian figure is 280 kg50/tc. This level of bagasse is fairlytypical for sugarcane worldwide.5.2. TrashThe practice in most countries where sugarcane is grown

is to burn off the trash just before the harvest to facilitateharvesting of the stalks. Pollution from burning of canefields is leading to restrictions on this practice in someparts of the world. For example, in Brazil a 1998 lawestablished a timetable for eliminating pre-harvest burn-ing: for areas with a grade under 12 % (considered har-vestable by machine), all burning must end by 2006; forareas with a grade above 12 %, all burning must end by2013. Such restrictions are likely to be introduced in manycountries in the future.

Motivated by the growing awareness of the negativeenvironmental impacts of cane-burning and, especially, bythe recognition of the potential energy value of sugarcane

Table 6. Energy balances for “pure” BIG/GTCC and for CEST cogeneration at a mill processing 7000 tc/day during a crushing season lengthcharacteristic of Cuba. The crushing season length is 150 days, during which the mill and cogeneration system operate with 87 % capacity

factor (total of 0.896 million tc crushed per year). Total biomass fuel consumption is the same for each cogeneration system.

CEST (82 bar steam) “Pure” BIG/GTCCOn-season Off-season Annual On-season Off-season Annual

Electricity generationGas turbine - - - 33,600 33,600 -

Condensing steam turbine 37,308 34,322 - 12,270 24,877 -

Back-pressure steam turbine, electricity 2,850 - - 3,250 - -

Back-pressure steam turbine, mech. power 2,567 - - 2,567 - -

Total, kW 42,725 34,322 - 51,687 58,477 -

Total, GWh 130 157 287 159 267 425

Total, kWh/tc 147 175 321 177 298 475

On-season process energy consumptionSteam (130ºC, 2.5 bar), kg/tc 280 - - 280 - -

kg/hr 81,700 - - 81,700 - -

Electrical & mechanical power, kW 8,403 - - 8,403 - -

kWh/tc 29 - - 29 - -

Exported electricity, kW 34,322 34,322 - 43,284 58,477 -

GWh 105 157 262 133 267 400

kWh/tc 118 175 292 148 298 446


Bagasse, t50/hr 38.4 26.5 - 31.2 31.2 -

Trash, t15/hr 36.8 25.4 - 30.0 30.0 -


Bagasse, thousand t50 per year 124 127 251 101 150 251

Trash, thousand t15 per year 113 115 228 92 137 229


Bagasse, t0/tc 0.069 0.071 0.140 0.056 0.084 0.140

Trash, t0/tc 0.107 0.110 0.217 0.088 0.130 0.218

Cogeneration efficiencies (%, HHV basis)Electricity generation 16.9 19.7 18.3 25.0 28.3 27.0

Process steam generation 21.8 - 10.8 26.7 - 10.8

Electricity plus steam 38.7 19.7 29.1 51.7 28.3 37.7

Cogeneration efficiencies (%, LHV basis)

Electricity generation 19.7 23.0 21.3 29.2 33.0 31.5

Process steam generation 25.5 - 12.6 31.2 - 12.6

Electricity plus steam 45.1 23.0 33.9 60.4 33.0 44.0Source: CTC calculations

Note



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trash, efforts have been made over the past 15 years todevelop the capability for recovering and using trash asa fuel for electricity generation in a number of countries,including Australia [Schembri and Carson, 1997], Brazil[Leal, 1995], Colombia [Cock et al., 2000], the Domini-can Republic [Lopez, 1987], India [Anonymous, 2000],the Philippines [Varua, 1987], Puerto Rico [Phillips, 1987;Allison, 1987], Thailand [Winrock, 1991], and elsewhere.5.2.1. BrazilOne of the most intensive efforts to understand and designtrash recovery and transport systems is the program beingcarried out at the CTC. Measurements there indicate thatthe total amount of trash produced by sugarcane varietiescommonly grown in Southeast Brazil ranges from 110 to170 kg0/tc, with an average of 140 kg0/tc [Macedo et al.,2001].

The CTC has analyzed a number of concepts for ma-chine harvesting and delivering of trash to a mill’s cogen-eration facility. It estimates that the maximum amount oftrash that can physically be recovered and delivered to acogeneration facility is about 89 % of the total trash pro-duced [Macedo et al., 2001]. This corresponds to about125 kg0/tc on average, which is well above the level re-quired to fuel the cogeneration systems described in Ta-bles 4 or 5, but below that required with the shortercrushing season (as in Table 6).

The CTC estimates the direct cost of collecting trashfrom the field, baling it, and transporting the bales to themill to be $ 10.9/dry t ($ 10.9/t0), or $ 0.64/GJHHV[Macedo et al., 2001].[10] The total net cost of deliveredtrash must also account for the substantial agronomic im-pacts of removing trash, including loss of recycled nutri-ents. The largest component of the agronomic cost isadditional herbicide used to replace the weed-suppressingtrash blanket that remains on the field after conventionalmachine harvesting. Agronomic costs add an additional80 % to the direct recovery costs, resulting in a total netcost of delivered trash bales of $ 1.2/GJHHV (Table 7).5.2.2. CubaThe sugarcane harvesting system in Cuba is unique amongcane-producing countries in two important respects. First,an estimated 70 % of the sugarcane crop is harvested bymachine without prior burning, which is far higher thanfor any other country. For example, only 20 % of Brazil’ssugarcane is machine harvested at present. The secondunique feature of Cuban harvesting practice is the long-standing commercial use of “dry cleaning stations” to re-move trash from the cane stalks before the stalks aretransported to the crushing mills. Cuba has over 900cleaning stations to serve its 156 sugar mills. The cleaningstations are generally not adjacent to the mills, but areconnected to mills by a low-cost cane delivery system –a dedicated rail network with more than 7000 km of track.The cleaning stations take in green machine-cut or manu-ally cut cane. Trash is removed from the stalk and blownout into a storage area. The stalks travel along a conveyorto waiting rail cars. The predominant practice today is toincinerate the trash at the cleaning station to reduce the“waste” volume.

Detailed estimates developed by the Cuban Ministry ofSugar [Egusquiza, 1994; Egusquiza and Gonzalez, 2000]indicate that the total trash production of Cuban sugarcanevarieties is considerably higher per tc than those found inBrazil. The estimated trash production in Cuba is nearly200 kg0/tc (Table 8), compared with 140 kg0/tc in Brazil.In Cuba today, about half of the trash (97 kg0/tc in thecase of machine-harvested cane) is left on the field afterharvest, about one-quarter (47 kg0/tc) is concentrated atthe cleaning stations, and an additional one-quarter (46kg0/tc) is delivered to the mill with the cane (Table 8).

If a trash recovery level similar to that achieved in Bra-zil (89 %) could be realized in Cuba, the total trash thatcould be delivered to a cogeneration facility would besome 174 kg0/tc on average. Such a level is still shy ofthe level needed to operate the cogeneration systems de-scribed in Table 6, where the crushing season lasts only150 days.

The costs for recovering and delivering trash to a millsite in Cuba are likely to be considerably lower than thecosts estimated in Table 7 for Brazil since some trash isalready concentrated at cleaning stations and since railtransport of trash to the mill site is feasible. Our “guess-timate” is that direct costs per t of trash delivered to amill can be reduced by 50 % relative to the $ 10.9/t0estimated for Brazil. Assuming the costs of agronomicimpacts are the same as in Brazil, the total cost of deliv-ered bales in Cuba would then be $ 14.1/t0, or $0.83/GJHHV.5.2.3. Other Caribbean countriesMeasurement of trash production by cane species typi-cally grown in some other Caribbean countries show ra-tios of trash-to-millable stalk that are even higher than

Table 7. Estimated cost of trash bales delivered to a sugar/ethanolfactory (São Paulo state, Brazil)

Activity Cost, US$ Fractionof totalcost, %Per dry t Per GJ

Windrowing 0.68 0.040 3.5

Baling[1] 4.43 0.260 23

Loading of bales 1.64 0.097 8.4

Field tractor/trailering 1.35 0.079 6.9

Transport to mill 2.20 0.129 11

Unloading 0.59 0.035 3.0

Total direct cost 10.89 0.640 56

Agronomic cost2 8.66 0.510 44

Total net cost 19.55 1.150 100

Source: Macedo et al., 2001.

Notes

1. Rectangular bales (0.8×0.87×1.90 meters) with an average weight of 306 kg and with15 % moisture content and 5 % soil. The higher heating value of trash with 15 %moisture content is 14.5 MJ/kg15. The lower heating value is (13.0 MJ/kg15).

2. The main agronomic cost of trash removal considered here is the additional herbiciderequired when there is an insufficient trash blanket on the field. Other costs include areduction in cane productivity due to compaction, and a lower degree of field terracingthat can be done. One positive agronomic impact (resulting in a cost reduction) is thatsoil preparation is easier without a trash blanket present.


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those reported for Cuba. Phillips [1987] cites a study donein the Dominican Republic for the Dominican ElectricCorporation which indicated, on the basis of measure-ments, “a rather consistent correlation between cane ton-nage and barbojo (trash) tonnage per hectare. On theaverage, for each ton of cane there is 0.66 ton of barbojoat a field moisture content of 50 % (by weight) whenharvested,” i.e., 330 kg0/tc. Phillips also presents results

of measurements made for several Puerto Rican cane va-rieties that show an average of 340 kg0/tc (Table 9). Insome of the first work published about the potential forutilizing trash for energy, Alexander [1985] indicates anaverage trash production associated with typical PuertoRican sugarcane in the early 1980s to be 280 kg0/tc.[11]

5.3. Energy caneAlexander also indicates that there is a potential for evenlarger trash production via breeding of “high-tonnagecane”, which he refers to as “energy cane”. He observesthat energy cane can yield more trash and more sugar perhectare than conventional sugarcane, even though sugarcontent per tc would be lower than with conventionalcane. The high yields of both components result from acombination of denser spacing of cane plants and selectivebreeding for high fiber production. On the basis of meanyield values of energy-cane trials over five crop years andusing four varieties and two row spacings, Alexandershows that total dry matter per ha with energy cane couldbe 3 to 4 times as large as with conventional Puerto Ricansugarcanes, while the total fermentable solids (sugar) pro-duction per ha will more than double. [See Figures 3-7in Alexander, 1985].

Alexander points out that sugar producers historicallyhave dismissed the idea of milling high-fiber cane, despitehigher sugar production per ha, because much more ton-nage must be milled than with conventional sugarcane toextract a comparable amount of sugar. The possibility ofrevenues from increased sale of electricity with higher-fiber sugarcanes have not been considered in such think-ing. For certain market conditions (prices of electricityand sugar and/or ethanol), the added revenue from elec-tricity sales may make the high-fiber cane option attrac-tive.

6. Cogeneration economicsHere we assess the prospective economics associated withelectricity production from sugarcane biomass in association

Table 9. Trash production per tonne of millable cane for differentcane varieties and locations, as measured in Puerto Rico

Location Canevariety[1]

Millablecane(t/ha)

Trash(dryt/ha)

Ratio of trashto millable

cane (dry t/tc)

BarahonaPR 980 123.1 44.8 0.36

PR 980 71.3 25.4 0.35

PR 980 34.7 29.1 0.84

QuisqueyaPR 1028 86.2 23.5 0.27

PR 1028 33.3 14.6 0.44

Consuelo

PR 980 69.7 21.3 0.31

PR 980 60.7 22.8 0.38

PR 1028 52.6 13.5 0.26

CP 5243 52.1 18.3 0.35

CP 5243 46.9 16.5 0.35

CP 5243 39.2 11.0 0.28

Average[2] 0.34

Source: Phillipps, 1987.

Notes

1. The same cane varieties give a wide range of production per hectare, depending oncultivation practices. For example the PR 980 variety at Barahona yielding 123 t/ha iswith irrigation.

2. This is the average of all values in the table, excluding the anomalous 0.84 value.

Table 8. Mass balance of sugarcane biomass in Cuba. This table shows the disposition of sugarcane stalks and cane trash throughout theharvesting, transport, and milling cycle, as presently practiced in Cuba. About 89 % of the cane standing on the field before harvest actually

reaches the crushing mills. About half of the trash produced by the sugarcane crop is left behind on the field after harvest. An additional24-30 % is left at the cane cleaning stations, and 17 % to 24 % is crushed in the mills with the cane.

Machine harvested fields Manually harvested fields

Cane stalks(%)

Trash(%)

Trash(dt/tc)[1]

Bare stalks(%)

Trash(%)

Trash(dt/tc)[2]

Standing in the field before harvest 100 100 0.195 100 100 0.195

Left in field after harvest 5.50 50.0 0.097 1.88 47.3 0.092

Diverted for seed 2.49 1.32 0.003 6.11 5.50 0.011

Losses in transport to cleaning station 0.94 0.50 0.001 0.92 0.47 0.001

Left at cleaning station 0.94 24.0 0.047 1.64 29.5 0.058

Losses in transport to mill 0.90 0.24 0.001 0.89 0.17 0.000

Delivered to and crushed at the mill 89.2 23.9 0.046 88.6 17.1 0.033

Source: Egusquiza, 1994. See also [Egusquiza and Gonzalez, 2000].

Note

1. This is tonnes of dry trash per tonne of machine-harvested cane delivered and crushed at the mill.

2. This is tonnes of dry trash per tonne of manually-harvested cane delivered and crushed at the mill.


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Table 10. Inputs to cost analysis

Factory characteristics

Cane crushing capacity, tc/day 7000

Total amount of sugarcane crushed, tc/year 1,300,000

Sugar yield from cane, tonnes of sugar per tc[1] 0.13

Ethanol yield from cane, liters per tc[1] 85

Cane processing costs[2,3]

Capital investment to install an ethanol distillery[4] (million $) 6.39

Operating and maintenance costs

Cane crushing, $ per tonne of cane crushed[5] 1.88

Sugar factory (cane juice processing to sugar), $ per tonne of sugar[6] 38.2

Ethanol distillery (annexed to sugar factory), $ per m3 ethanol[7] 72.3

Cost of sugarcane delivered to crushing mill, $ per tonne cane[8] 12

Cogeneration capital costs, O&M costs, and fuel consumption CEST BIG/GTCC

Installed generating capacity, MW[9] 33.7 58.5

Capital investments charged to cogeneration plant

Cogeneration plant, million $ 50.4 86.8

For process steam reductions at sugar-only factory,[10] million $ 2.20 2.20

For process steam reductions at sugar/ethanol factory,[10] million $ 4.86 4.86

Operating and maintenance costs, million $ per year[11] 1.457 2.478

Operating labor, million $ per year 0.343 0.382

Fixed maintenance, million $ per year 1.008 1.736

Consumables (excluding fuel), million $ per year 0.106 0.361

Biomass fuel consumed, thousand dry t per year[12]

Bagasse 126 126

Trash 194 194

Products sold for revenue, sugar-only factory

Sugar, tonnes per year 168994 168994

Export electricity, GWh per year[13] 234 378

Products sold for revenue, sugar-ethanol factory

Sugar, tonnes per year 84497 84497

Ethanol, m3 per year 55248 55248

Export electricity GWh per year[13] 234 378Notes

1. These yields refer to production of either sugar only or ethanol only. Thus, for a mill producing both sugar and ethanol, the yields apply only to that fraction of the total cane crushedthat goes toward making each product. The yield values here are typical of what are achieved in Southeast Brazil today. Brazil is generally acknowledged to have one of the mostadvanced sugarcane-processing industries in the world. The levels shown here for Brazil should be achievable elsewhere over time.

2. These costs are based on typical current practice in Southeast Brazil. They exclude the costs for process steam and electricity, which are accounted for elsewhere in the cost analysis.

3. Because new sugar mills are rarely built, no initial capital cost is factored into the cane processing cost. However, capital replacement (12 %/year) is included as part of the O&Mcosts.

4. For a distillery with the capacity to convert about half of the sucrose in the incoming cane into ethanol. See Table 13.

5. These costs include capital replacement costs (12 %/year).

6. These costs include capital replacement costs (12 %/year). The costs are for a sugar factory that processes about half of the sucrose in the incoming cane into sugar (with the otherhalf being converted to ethanol). However, the cost per tonne of sugar would be approximately the same if the factory were instead converting all of the sucrose to sugar.

7. These are based on the average operating and maintenance costs (excluding capital replacement costs) for Copersucar mills.

8. Brazil is acknowledged to have one of the lowest sugarcane production costs in the world. The indicated cost is widely achieved in Southeast Brazil. Costs as low as $ 8/tc areachieved in some parts of Southeast Brazil.

9. These are the combined capacities of the condensing steam turbine plus gas turbine, as shown in Table 5. The capacities shown in Table 5 exclude parasitic power consumed withinthe steam cycle or gas turbine cycle.

10. See Table 3.

11. Operating labor costs are based on estimates by CTC using Brazilian wage rates (Table 11). Annual fixed maintenance cost is estimated as 2 % of initial capital investment.Consumables are as estimated by CTC engineers (Table 12).

12. From Table 5, these are the dry matter contained in the bagasse and trash that are consumed. The bagasse and trash are assumed to be delivered to the cogeneration plant gatewith 50 % and 15 % moisture content, respectively. In reality, since a mix of bagasse and trash would be stored for off-season use, some further air-drying is likely. In that case,efficiencies would be higher than those indicated in Table 5.

13. From Table 5.


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with sugar production. We also consider electricity pro-duction in conjunction with combined sugar and ethanolproduction, when half of the sucrose in the cane is con-verted to sugar and half to ethanol. We compare the over-all economics for BIG/GTCC cogeneration with that forCEST cogeneration. Our assessment uses capital and op-erating cost estimates for commercially mature BIG/GTCC technology, i.e., costs that are projected forBIG/GTCC technology after several systems have beeninstalled. (BIG/GTCC cost reduction trajectories are dis-

cussed in Section 7.) Table 10 summarizes key inputs toour cost analyses. The notes in Table 10 refer to additionaldetailed breakdowns of investment costs to achieve proc-ess steam use reductions (Table 3), cogeneration operatinglabor and consumables costs (Tables 11 and 12, respec-tively), and ethanol distillery investment costs (Table 13).

Total installed capital costs for the CEST andBIG/GTCC facilities are especially important inputs. Thetotal investment for the CEST system, $ 1500/kW, isbased on the estimate in a feasibility study for a 33 MWCEST project planned for the Hector Molina sugar millin Cuba [MINAZ, 1999]. The capital cost for theBIG/GTCC plant is based on estimates by engineers atthe CTC and on the analysis in Section 7 of the likelycosts for commercially mature stand-alone electric-powerBIG/GTCC systems. In Section 7 the cost for such sys-tems are estimated to be $ 1400/kW at a scale of 60 MW.This estimate is consistent (within the accuracy range ofpreliminary cost estimation) with cost estimates that havebeen made by several others for commercially matureplants [Carpentieri and Macedo, 2000; Craig and Mann,1996; Elliott and Booth, 1993; Faaij et al., 1998; Weyer-haeuser et al., 1995]. For the same electric output capacity,a BIG/GTCC cogeneration system will have a higher costper kW than a stand-alone system due to added costs as-sociated with process steam production. The cost estimateshown in Table 10 for the BIG/GTCC cogeneration sys-tem is $ 1480/kW.

Our cost analysis considers a 7000 tc/day capacity fa-cility operating in a Southeast Brazil context, i.e., with a214-day crushing season and 87 % capacity factor. Thus,1.3 million t (Mt) of cane are crushed annually at the mill.Figure 8 illustrates the financial model we consider here.We assume that the sugar or sugar-and-ethanol producerpays the cost of delivered sugarcane. The cogeneratorpays for collection and delivery of trash. Bagasse is de-livered from the cane-crushing mills to the cogenerator in

Table 11. Operating labor costs for cogeneration systems, based on Brazilian wage rates[1]

Job description Monthlyrate ($)[2]

CEST BIG/GTCC

Jobs[3] $/yr Jobs[3] $/yr

Manager 5320 1 63840 1 63840

Supervisor 2090 3 75240 3 75240

BIG/GT operators 532 - - 14 89376

Boiler operators 532 9 57456 - -

Operator (front-end loader) 532 6 38304 6 38304

Operator (bale shredder) 532 3 19152 3 19152

Conveyor operator 532 3 19152 3 19152

Fuel-feeder operator 532 6 38304 6 38304

Auxiliaries and relief 532 5 31920 6 38304

Totals 36 343368 42 381672

Notes

1. For the cogeneration plant configurations described in Table 5 operating with three shifts of workers, plus one auxiliary/relief person for each group of 6 operators.

2. Total compensation, which includes salary plus additional amount equal to 90 % of salary to cover benefits, social costs, etc.

3. Full-time equivalent.

Table 12. Cost of consumables for cogeneration systems

Unitquantity

Annualquantity

Cost$/unit

Cost$/year

BIG/GTCC[1]

Materials[2] 254300

Diesel fuel (baler), l/hr 15 66929 0.35 23600

Diesel fuel (tractor), l/hr 21 160630 0.35 56700

Lube oil, m3/hr 8 8 1014 8100

Treated water, m3/hr 13 99177 0.18 17900

Total 360600

CEST[1]

Treated water, m3/hr 13 99177 0.18 17900

Lube oil, m3/hr 8 8 1014 8100

Diesel fuel (baler), l/hr 15 66929 0.35 23600

Diesel fuel (tractor), l/hr 21 160630 0.35 56700

Total 106200

Notes

1. For Nth plant versions of the cogeneration plant configurations described in Table 5.No active control of NOx emissions is assumed for either case.

2. Includes gasifier bed material, filter material, chemicals, and miscellaneous other con-sumables


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exchange for process steam and electricity, which is ef-fectively the arrangement at most sugar or sugar/ethanolfactories today. We use a capital charge rate of 20 % peryear in all calculations. Investments to reduce processsteam consumption are charged to the cogenerator, sincethe benefit arising from such investments is an increasedlevel of electricity generation.6.1. Production costs for electricity and sugarFigure 9 shows the busbar production cost for electricitycogenerated at a BIG/GTCC facility and at a CEST facil-ity as a function of the cost of trash to the cogeneratorin the case where the factory is one that makes sugar only.The BIG/GTCC yields a lower busbar cost over the entire

range of trash costs shown. The gap in generating costbetween the two systems grows as the trash price in-creases due to the higher efficiency of the BIG/GTCCsystem. As a reference, the shaded vertical bar on the leftin Figure 9 indicates the range in required electricity saleprice for the Hector Molina CEST project: 5.8 to 7.5¢/kWh [MINAZ, 1999]. The generating costs calculatedfor the BIG/GTCC and CEST systems both fall withinthis range for the trash prices shown.

Table 14 shows sub-components of the cost of electric-ity when the trash price is $ 1.2/GJHHV, the average costestimated for Southeast Brazil (Table 7). The busbar costis dominated by capital charges, which are slightly higherfor the BIG/GTCC than for the CEST. Total generatingcost is lower for the BIG/GTCC than for the CEST, how-ever, due to the much lower cost per kWh for trash arisingfrom the higher efficiency of the BIG/GTCC. The cost ofsugar production shown in Table 14 is representative ofcurrent average production costs in Southeast Brazil.

Busbar electricity costs would be reduced if carbon di-oxide emission reductions were credited against generat-ing costs. Electricity from sugarcane biomass would haverelatively low levels of associated net emissions of carbondioxide: on average, the CO2 emitted at the cogenerationfacility would be completely reabsorbed in subsequent re-growth of the sugarcane, and the only net CO2 emissionsto the atmosphere would be the relatively small amountsarising from use of fossil fuel-based fertilizers and agri-cultural machinery operations [Moreira, 2000]. If the su-garcane-derived electricity were to displace electricitygenerated from fossil fuels, there would be net savings inCO2 emissions per kWh generated. If the net CO2 emis-sion reductions correspond to those avoided by not burn-ing oil to generate electricity, a scenario appropriate forCuba, then the saved CO2 would be 0.22 kgC/kWh gen-erated. If a carbon credit of $ 20/tC displaced were avail-able – a value currently offered by the Prototype CarbonFund of the World Bank[12] – cost of electricity shown inFigure 9 would be reduced by 44 mills/kWh ($0.0044/kWh). The impact of such a carbon credit is alsoshown in Table 14.6.2. Production costs for electricity, sugar, and ethanolIn conjunction with a factory producing both sugar andethanol from sugarcane, the cost of cogenerated electricitywould be slightly higher than with a sugar-only factory,because steam conservation investments, which arecharged against electricity production, are higher for asugar/ethanol factory than for a sugar-only factory. (SeeTable 3.) Also, the difference between the cost ofBIG/GTCC and CEST electricity would be slightlygreater, because the same steam conservation investmentswould be spread over a higher number of kWh with theBIG/GTCC.

Table 15 gives a breakdown of sugar/ethanol/electricitycosts when sugarcane trash costs $ 1.2/GJ. The ethanolcost shown there ($ 0.26/liter (l), without carbon credit),would enable ethanol to compete as a gasoline blend-stock when the crude oil price is close to $ 30 per barrel(bbl).[13] This ethanol cost is representative of current

Table 13. Capital investment required to add an ethanol distillery toan existing sugar factory.[1] The capacity of the distillery is 300 to

350 m3 anhydrous ethanol per day, which is approximately thecapacity of a distillery attached to a 7000 tc/day crushing mill

converting half of the available sucrose into ethanol.

Thousand US$

Fermentation and distillation plants 4577

Ethanol storage tanks 1220

Stillage handling and storage 464

Laboratory 6

Spare parts warehouse 6

Fuse oil system 15

Cooling water system 100

Total 6388

Note

1. Estimated by CTC engineers. The estimate is consistent with an independent quotefrom NG (a packaged distillery supplier in São Paulo state, Brazil) provided to the CTC.The NG quote was for US$ 5.5 million for a 350 m3/day facility, including fermentation,distillation, molecular sieve dehydration, and buildings, but excluding foundations andethanol storage tanks.

Figure 8. Cost model for electricity production in conjunction with sugarproduction. The sugar producer buys sugarcane and sells sugar. The co-generator buys trash and sells electricity. The sugar producer and cogen-erator exchange bagasse for process steam and electricity.


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average production costs in Southeast Brazil. Many pro-ducers in Brazil can make ethanol at lower cost. The keyvariable is the cost of the sugarcane. At $ 12/tc, cane ac-counts for over half the cost of the ethanol in Table 15.Cane costs as low as $ 8/tc are achieved in some partsof SE Brazil and should be achievable elsewhere overtime. A cane cost of $ 8/tc would lower the cost of ethanolby $ 0.05/l compared with the cost in Table 15. Underthis condition, ethanol would be competitive with gasoline

when crude oil costs less than $ 25/bbl.

7. Estimated costs to commercialize BIG/GTCCThe attractive long-term prospects for BIG/GTCC cogen-eration to compete commercially at sugar factories orsugar/ethanol factories must be considered against the factthat the technology today is still at a commercial demon-stration phase, where capital and O&M costs are relativelyhigh. How much time and how many BIG/GTCC unitswill need building before the costs can be expected toreach competitive levels? What is likely to be the totalincremental cost during this period, i.e., the cost aboveand beyond commercially competitive costs? We addressthese questions next. In our analysis we focus on estimat-ing capital investment requirements for BIG/GTCC plantsdesigned to generate electricity only, since mostBIG/GTCC cost estimates to date have been for stand-alone electricity generating systems.

Capital cost for a first-of-a-kind commercial stand-alone BIG/GTCC system installed in Brazil today is anestimated $ 2450/kW for a 30 MW unit.[14] This compareswith the estimate of $ 1400/kW for a 60 MW unit thatwas the basis for the cost analysis in the previous section.At $ 1400/kW, a BIG/GTCC system could produce elec-tricity at a cost less than 5 ¢/kWh,[15] which would makeit competitive with other sources of power in rural areasin many developing countries, including Cuba. Reachingthe level of $ 1400/kW appears feasible considering sev-eral cost reduction opportunities. These include eliminat-ing specialized engineering services needed for a

Figure 9. Cost of electricity production as a function of the trash cost to cogenerator. Bagasse is provided by the sugar producer in exchange forprocess steam and electricity. (See Table 10 for detailed inputs to this analysis.)

Table 14. Production costs for sugar and electricity, with trash priceto cogenerator equal to $ 19.6 per dry t ($ 1.15/GJHHV)[1]

Sugar($/t)

Electricity ($/kWh)BIG/GTCC CEST

Capital charges[2] 0 0.0471 0.0450O&M 53 0.0066 0.0062Sugarcane costs 92 0 0Trash 0 0.0069 0.0112Total 145 0.0606 0.0625Carbon credit[3] 0 -0.0044 -0.0044Total with C credit 145 0.0562 0.0581

Notes

1. A 20 %/year capital charge rate is assumed. See Table 10 for additional input assump-tions.

2. Charges for capital replacement are included as part of the O&M costs for sugar pro-duction. Capital charges for electricity include the cost for investments to reduce steamconsumption in the sugar or sugar and ethanol factories.

3. Assuming a carbon credit of $ 20/tC saved. Also, electricity generated from sugarcanebiomass (assuming zero net CO2 emissions) replaces electricity generated from oil(saving 0.22 kgC/kWh).


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first-of-a-kind plant, making technological improvements,and reducing contingency costs. We estimate that thesecost reduction opportunities would reduce the total in-stalled capital cost from $ 2450/kW to $ 1780/kW (Table16). A further cost reduction would arise as a result ofscaling up the plant to a larger size. Applying a scaling

exponent of 0.65 (derived for natural gas-fired gas turbinecombined cycle technology[16]) gives an installed capitalcost of $ 1400/kW for a 60 MWe BIG/GTCC (Table 16).If a global market for BIG/GTCC systems develops, com-petition in BIG/GTCC systems is likely to drive invest-ment costs down still further in the long term. Forexample, one study indicates a capital cost for a systembased on an intercooled steam-injected gas turbine (a tech-nology that is not yet commercially established) of around$ 900/kW in 1989 $ [Williams and Larson, 1996], orabout $ 1200/kW in year-2000 $.

How soon might a cost level of $ 1400/kW beachieved? All new energy technologies that can be mass-produced and that ultimately become established in com-mercial markets experience reductions in cost withcumulative production. For example, Figure 10 showscost reduction curves for several energy technologies atthe early stages of commercial introduction. Several fac-tors typically contribute to the observed cost reductions,including technology improvements, technology scale-up,and “learning by doing”. Each of the curves in Figure 10has associated with it a “progress ratio”, defined as onehundred minus the percentage reduction in cost for eachdoubling in cumulative production. For example, for atechnology characterized by an 80 % progress ratio therewould be a 20 % reduction in cost for each doubling incumulative production. The progress ratios for the initialcost reduction period for the technologies in Figure 10are all between 75 % and 85 %. Limited experience withcoal integrated-gasifier combined cycle (IGCC) technolo-gies, which have many similarities with BIG/GTCC

Table 15. Production costs for sugar, ethanol, and electricity, withtrash price to cogenerator equal to $ 19.6 per dry tonne

($ 1.15/GJHHV)[1]

Sugar($/t)

Ethanol($/l)

Electricity ($/kWh)

BIG/GTCC

CEST

Capital charges[2] 0 0.023 0.0485 0.0473

O&M 53 0.094 0.0066 0.0062

Sugarcane costs 92 0.141 0 0

Trash 0 0 0.0069 0.0112

Total 145 0.258 0.0620 0.0648

Carbon credit[3] 0 -0.014 -0.0044 -0.0044

Total with C credit 139 0.244 0.0576 0.0604

Notes

1. A 20 %/year capital charge rate is assumed. See Table 10 for additional input assump-tions.

2. Charges for capital replacement are included as part of the O&M costs for sugar pro-duction. Capital charges for electricity include the cost for investments to reduce steamconsumption in the sugar or sugar and ethanol factories.

3. Assuming a carbon credit of $ 20/tC saved. Also, electricity generated from sugarcanebiomass (assuming zero net CO2 emissions) replaces electricity generated from oil(saving 0.22 kgC/kWh). Ethanol from cane (assuming zero net lifecycle CO2 emissions)replaces gasoline (saving 0.72 kgC/l).

Table 16. Cost reductions from first-of-a-kind BIG/GTCC to commercially-competitive BIG/GTCC

Cost reduction area % costreduction

Installed cost$/kW

Notes[1]

First-of-a-kind, 30 MWBIG/GTCC

2450 Estimated cost for a first-of-a-kind unit built in Brazil.

Eliminate specialengineering

5 % 2200 In the Brazilian demonstration project, engineering services (substantiallybeyond normal engineering services for a commercial plant) will beprovided by the gas turbine supplier, the gasifier supplier, and the firmresponsible for overall engineering of the plant.

Technology improvements 15 % 1870 Advances (cost reductions) can be expected as a result of “learning bydoing”, especially for plant components that have relatively little history ofcommercial use, including the gasifier, gas cooling system, and gas cleanupsystem. Also, equipment redundancies can be eliminated. For example, theBahia, Brazil, plant design includes two biomass feeders of 100 % capacityeach, six baghouse filters (only four of which are used), and a number ofredundant pumps, heat exchangers and associated piping and valves.

Eliminate non-routinecontingencies

5 % 1780 Contingencies typically account for uncertainties in component costestimates and for unforeseen costs that arise for various reasons(site-specific requirements, currency exchange rate fluctuations, etc.).Uncertainty in the cost of components is higher in a first-of-a-kind plantthan in an “Nth” plant, but unforeseen costs may not be.

60 MW module size 21 % 1400 Based on cost quotes from Anonymous [1999] for turnkey natural gas-firedcombined cycles built around an LM2500 gas turbine (31.2 MW output, $809/kW) and around an LM6000 gas turbine (56.4 MW, $ 658/kW), ascaling exponent of 0.6511 is derived. For doubling of capacity from 30 to60 MW, this gives a 21.5 % reduction in unit cost.

Note

1. Where not otherwise indicated, the estimates are based on discussions with TPS engineers and other experts.


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Figure 10. Cost learning curves for several energy technologies [Nakicenovic et al., 1998].

Table 17. Capital cost reduction scenarios for two different progress ratios for BIG/GTCC systems in sugarcane applications. The right-mostcolumn shows the capital investments that would be required to install CEST systems with equivalent capacity to the indicated BIG/GTCC

systems in the 87 % progress ratio scenario

Unitsbuilt

Installed MWInstalled capital cost – BIG/GTCC

Capital (106 $) to installCEST (same MW as 87

% PR case)[3]

82 % progress ratio 87 % progress ratio

Unit Cumulative $/kW[1] 106 $ Incremental106 $[2]

$/kW[1] 106 $ Incremental106 $[2]

1 30 30 2450 73.5 31.4 2450 73.5 31.9 45

2 30 60 2010 60.2 18.2 2130 63.9 22.3 45

3 30 90 1790 53.6 11.6 1960 58.9 17.3 45

4 30 120 1650 49.4 7.3 1850 55.6 14.0 45

5 30 150 1550 46.3 4.3 1770 53.2 11.6 45

6 60 210 1400 84.2 0.0 1660 99.4 16.2 90

7 60 270 - - - 1580 94.5 11.3 90

8 60 330 - - - 1510 90.8 7.6 90

9 60 390 - - - 1460 87.8 4.6 90

10 60 450 - - - 1420 85.3 2.1 90

11 60 510 - - - 1390 83.2 0.0 90

367 73 846 139 765

Notes

1. The first unit in the buy-down program is assumed to cost $ 2450/kW (from Table 16).

2. The incremental capital cost is calculated as kWi×[($/kW)i - ($/kW)N], where kWi is the capacity of the ith plant and ($/kW)i and ($/kW)N are the unit installed costs for plant numberi (=1, 2, 3 …) and for the Nth (commercially mature) plant, respectively. For progress ratios of 82 % and 87 %, N is 6 and 11, respectively.

3. Assuming $ 1500/kW installed cost for CEST units.


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technologies, suggest a progress ratio of 82 % [MacGre-gor et al., 1991]. A more general analysis of learningcurves of power generating technologies suggests an av-erage progress ratio of 87 % for smaller-scale technolo-gies [Neij, 1997].

If one assumes that the first BIG/GTCC built at a su-garcane processing facility will cost $ 2450/kW, that theNth plant will cost $ 1400/kW, and that the cost reductioncurve against cumulative MW installed will be charac-terized by a progress ratio of 82 %, then the $ 1400/kWcost level could be reached with construction of the sixthplant[16] (Table 17). The cumulative investment requiredfor the six plants would be $ 370 million. Of this total,$ 75 million is the incremental cost, i.e., the investmentrequired in excess of the projected cost for commerciallymature technology (Table 17).

If progress in cost reductions is more accurately char-acterized by a progress ratio of 87 %, then a cost of$ 1400/kW would be reached with construction of the11th plant. The total and incremental capital investmentrequirements for building the 11 plants would be $ 850million and $160 million, respectively (Table 17). Table17 also shows that an investment of $ 765 million wouldbe required to install CEST units with capacity equivalentto the 11 BIG/GTCC units considered in the 87 % pro-gress-ratio cost reduction scenario. There would be higherinvestment risk involved with early BIG/GTCC units thanwith CEST units, but the actual investment required tocommercialize BIG/GTCC technology is only 11 %higher than the cost of installing an equivalent number ofMW of conventional CEST technology.

8. The potential impact of BIG/GTCC in CubaCuba’s current level of sugarcane production is 35 to 40Mt/yr (about 3 % of world production), which is down bymore than half from the level in the late 1980s (Figure 11).The per-capita production of sugarcane today, 3.2 tc/per-son/year, is the highest by far among all sugarcane-pro-ducing countries, which suggests that there is a moresubstantial opportunity in Cuba than elsewhere for sugar-cane-derived energy to reduce dependence on other en-ergy sources. In Cuba, over 90 % of conventional primaryenergy consumed is oil – some 8.6 Mt in 1998. Electricityproduction and vehicles account for nearly 70 % of theoil consumed, and over 80 % of Cuban oil is imported.[17]

Cuba’s sugarcane processing industry includes 156 fac-tories, with cane-crushing capacities ranging from lessthan 2000 tc/day to over 10,000 tc/day. Many of thesefactories provide small amounts of electricity to the na-tional grid on an intermittent basis today [Egusquiza andGonzalez, 2000]. The Hector Molina factory (milling ca-pacity 7000 tc/day) will be the first one to export a sub-stantial amount of electricity (109 kWh/tc) to the grid. Inaggregate, Cuba’s sugar factories have the crushing ca-pacity to support about 2.8 GW of CEST cogenerationcapacity or nearly 5.6 GW of BIG/GTCC capacity (Figure12). For comparison, the total installed electric utility gen-erating capacity in Cuba today is 4.3 GW. Although onlyabout half of the factories have sufficient capacity to sup-

port BIG/GTCC systems larger than 25 or 30 MW each,the extensive cane transportation system that exists inCuba provides the possibility of aggregating (with lowtransport costs) cane trash and bagasse from smaller fac-tories to enable installing of additional larger capacity co-generation systems. Larger systems are desirable tocapture scale economy benefits.

In the long term, if Cuba were to install BIG/GTCCsystems throughout its sugarcane processing industry,electricity exports could total 12 to 23 TWh/yr (for har-vest levels of 40 to 80 Mtc/yr). The potential with CESTsystems would be 40 % lower than this, but still signifi-cant. For comparison, the 1999 level of oil-fired electricitygeneration in Cuba was about 12 TWh/yr. If cane-basedpower were to displace oil-generated utility electricity,savings in expenditure on oil (at $ 25/bbl) would be upto $ 1.2 billion/year with BIG/GTCC and $ 0.7 bil-lion/year with CEST (Table 18). The high efficiency ofthe BIG/GTCC relative to the CEST results in a higheroil cost savings per t of sugarcane processed: theBIG/GTCC system would save $ 15/tc, compared with$ 9/tc for the CEST (Table 18). Carbon dioxide emissionswould also be reduced more substantially withBIG/GTCC than with CEST. If BIG/GTCC electricitywere to displace oil-generated power, up to 5 MtC emis-sions might be avoided (Table 18), which represents about70 % of the 7.3 MtC released by oil-burning in Cuba in1997.

The long-term potential for producing ethanol as agasoline substitute in Cuba is also substantial. Ethanolmay be an especially important option if future sugarcaneproduction levels in Cuba return toward the high levelsthat existed in the late 1980s, because export of additionalsugar into the free market will be increasingly difficult.[18]

If Cuban sugarcane production were to rise to the 80Mtc/yr level, and the incremental sucrose production(above today’s 40 Mtc/yr level) were to be converted intoethanol, Cuba would produce 3.4 billion l of ethanol peryear, which would be more than sufficient to entirely re-place all petroleum-derived motor vehicle fuels presentlyused in Cuba (about 15 million bbl/yr)[19]. The savings inoil expenditures would be about $ 400 million per year(Table 18).

Recognizing the potential for sugarcane-derived energy,the Cuban government has made the development of thisenergy source a major focus of its energy policy[Comision Nacional de Energia, 1993]. The governmenthas also stated a commitment to reduce greenhouse gasemissions. Additionally, Cuba provides an attractive con-text for early introduction of BIG/GTCC technology be-cause (1) Cuba’s electricity sector is almost whollydependent on petroleum, which increases the potential forattractive economics for sugarcane electricity due to highlong-run marginal costs of utility power (well in excessof 5 ¢/kWh); (2) the close relationship between the sugarindustry, the electricity utility industry and other key gov-ernment institutions in Cuba could greatly facilitate theintroduction of a new technology like the BIG/GTCC; (3)there is a high level of engineering and technical capacity


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Figure 11. Cuban sugarcane production, sugarcane yield, sugarcane harvested area, and sugar production, 1960-1998. Source: www.fao.org.

Figure 12. Sugarcane-biomass electricity generating capacity that could be supported at individual sugar mills in Cuba. Cumulative capacity is alsoshown.


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in Cuba that could be trained to support such new tech-nology; and (4) Cuba’s unique sugarcane harvesting sys-tem already involves some collection of sugarcane trash.

9. ConclusionsThe biomass integrated-gasifier/gas turbine combined cy-cle technology promises high efficiencies and lower elec-tricity costs than conventional biomass-fired condensingsteam turbine technology. Efforts are going on worldwideto commercialize BIG/GTCC systems. Construction of thefirst revenue-earning unit was completed in 2000 (in theUK) and that unit is undergoing start-up testing. The costsfor such early commercial units will be high, but ouranalysis suggests that competitive costs will be achievedby the time six to eleven units have been built. The su-garcane processing industry provides an attractive contextfor early commercial applications. Because of its high per-capita production of sugarcane and its high dependenceon imported oil today, Cuba is an especially attractivecountry for early introduction of BIG/GTCC systems.Eric Larson and Robert Williams can be contacted at:Ph: 609-258-5445; Fax: 609-258-3661E-mail: [email protected] Leal can be contacted at:Ph: 55-19-429-8217; Fax: 55-19-429-8108E-mail: [email protected]

This paper is based on a presentation given by one of the authors (Larson) at the Interna-tional Workshop on Energy from Sugarcane, hosted by the Cuban Sugar Ministry in Havana,7-9 November 2000. The analysis in the paper was financed by the Norwegian Ministry ofForeign Affairs. For helpful contributions to the paper, the authors thank Suleiman JoseHassuani, Helcio Martins Lamonica, Francisco A.B. Linero, Isaias de Carvalho Macedo, andJose Perez Rodrigues Filho at the Copersucar Technology Center; Andrew Ellis, OlavKjorven, and Haakon Vennemo at ECON, Oslo, Norway; and Felix J. Perez Egusquiza andPaulino Lopez Guzman at the Ministry of Sugar, Havana, Cuba.

Notes

1. In this paper, the energy content of a fuel is expressed on a higher heating value (HHV)basis. The HHV of bagasse is 18.8 GJ/dry t. For bagasse with 50 % moisture content

(as is commonly found at sugar mills), the HHV is 9.4 GJ/t. The lower heating value(LHV) for 50 % moisture content bagasse is 7.5 GJ/t. The HHV of sugarcane trash (asmeasured in SE Brazil) is 17.0 GJ/dry t. For trash with 15 % moisture content (asdelivered in SE Brazil), the HHV is 14.5 GJ/t. The LHV for trash with 15 % moisturecontent is 13.0 GJ/t.

2. One key issue with the use of trash as a boiler or gasifier fuel is its relatively highalkali content compared with bagasse. Combustion or gasification of high-alkali fuelscan cause deposition problems in boilers, heat exchangers, and other downstreamequipment. Bagasse has much lower ash and alkali fractions than trash [CTC, 1999].Thus, mixing bagasse with trash should enable the average alkali content of the fuelto be maintained at adequately low levels.

3. Steam pressures in this paper are given as absolute pressures.

4. A more efficient plant design might utilize waste heat to dry the biomass, but a directly-fired dryer is simpler to integrate into the overall plant and would be less capital-inten-sive if it enables higher-temperature drying.

5. Gas turbines are sold in a limited set of discrete sizes, and thus the choice of gasturbine for a BIG/GTCC system determines the amount of fuel (trash in this case) thatmust be supplied to the system. This is in contrast to boiler/steam turbine systems,which can typically be designed to match a specified quantity of fuel supply.

6. For the system shown in Table 5, the HRSG waste heat is vented to the atmosphereand there is no heat recovery during cooling of the gasifier product gas.

7. The average moisture content of the biomass input to the system described in Table5 is 40 %. The moisture content of the fuel in the calculations of Consonni and Larsonwas 50 %. If a fuel moisture content of 40 % were used instead, the electrical efficiencycalculated by Consonni and Larson would be higher than 34 %.

8. For input fuel moisture content of 50 %. The gas turbine used in this design is onewith an intercooled compressor. See Consonni and Larson [1996].

9. In this paper, the subscript on kg refers to the moisture content of the biomass (weightbasis). Thus kg0 is zero moisture content.

10. All costs in the this paper are given in year-2000 US$.

11. See Table 3.1 and 3.2 in Alexander [1985].

12. See http://www.prototypecarbonfund.org.

13. As a blend-stock, one l of ethanol replaces one l of gasoline [Macedo, 2000].

14. As of several years ago, one published estimate of the capital cost for the 32 MWe

BIG/GTCC commercial demonstration project in Bahia, Brazil (see Table 2) was $2600/kW [CHESF et al., 1998]. Since that estimate was made, considerable advancesin understanding of costs have occurred, in part as a result of the construction of thefirst commercial BIG/GTCC plant in the UK (see Table 2). On the basis of discussionswith knowledgeable experts, we estimate that the cost for a BIG/GTCC today would be$ 2450/kW for a 30-MW system.

15. With an installed capital cost of $ 1400/kW, a capital charge rate of 15 %/yr, an 85 %capacity factor, and O&M costs of $ 0.006/kWh, the capital and O&M costs would be$ 0.034/kWh. Assuming an efficiency of 34 % for a commercially mature system (see

Table 18. Potential long-term impact on Cuban oil consumption of electricity and ethanol production from sugarcane

Caneharvest,

million tc/yr

ElectricityOil saved

EthanolOil saved

Output[1]

TWh/yrMillionbbl/yr[2]

Million$/yr[3]

$/tc[4] Carbonsaved

106 tC/yr

Output[5]

106 l/year106 bbl per

yr[6]106 $ per

yr[3]Carbon

saved 106

tC/yr

BIG/GTCC

40 11.6 23.8 595 15 2.5

80 23.2 47.6 1190 5.1 3395 16.4 410 1.8

CEST

40 7.10 14.7 370 9 1.5

80 14.4 29.4 735 3.1 3395 16.4 410 1.8

Notes

1. Table 5 gives values assumed here for kWh output per tonne of cane harvested.

2. Electricity is assumed to displace utility-generated electricity, which today consumes 279 t of oil/GWh (2045 bbl/GWh).

3. Oil at $ 25/bbl.

4. Saved oil expenditures per tonne of sugarcane harvested. Oil at $ 25/bbl.

5. Half of sugarcane sucrose is assumed to be converted to ethanol at a rate of 85 l/t of cane.

6. This assumes that ethanol would be used as a neat fuel, in which case one l ethanol replaces 0.75 l of petroleum.


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Section 4.4), the fuel cost would be $ 0.016/kWh for a biomass price of $ 1.5/GJ, whichmight be representative of the average price of sugarcane biomass (trash plus bagasse)sold to an independent power generator.

16. This assumes the first five units are 30 MWe plants, and subsequent ones are 60 MWe

plants.

17. http://www.eia.doe.gov/emeu/international/cuba.html

18. Only about one-quarter of global sugar production is traded on the free market, andCuban sugar already accounts for about 10 % of all sugar traded in this market.

19. At such high levels of ethanol production, it is likely that ethanol would be used as aneat fuel, in which case 1.3 l of ethanol would be needed to give the same vehicledistance travelled as one l of gasoline [Macedo, 2000].

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A Review of Biomass IGCC Technology - Application to Sugarcane Industries