A Review Of Biomass Igcc Technology - Application To Sugarcane Industries

Reproduced with permission from Energy for Sustainable Development Articles

A review of biomass integrated-gasifier/gas turbine combined cycle technology and its application in sugarcane industries, with an analysis for Cuba Eric D. Larson and Robert H. Williams Center for Energy & Environmental Studies, Princeton University, Princeton, NJ, USA M. Regis L.V. Leal Centro de Tecnologia Copersucar, CP 162, Piracicaba, SP – Brazil – 13400-970

Biomass integrated-gasifier/gas turbine combined cycle (BIG/GTCC) systems will be capable of producing up to twice as much electricity per unit of biomass consumed and are expected to have lower 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 potentially attractive application for BIG/GTCC systems. We review BIG/GTCC designs and ongoing demonstration and commercial projects and present estimates of the performance of two different BIG/GTCC plant configurations integrated into sugar or sugar-and-ethanol factories. Because of the importance of operating a cogeneration facility the year round in order to achieve attractive economics, we present estimates of the availability of and collection cost for sugarcane trash (tops and leaves) as a fuel supplementary to bagasse. We present estimated costs for electricity generated by commercially mature BIG/GTCC systems using sugarcane-biomass for fuel in a Southeast Brazilian 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 potential impacts on the Cuban energy sector of the introduction of BIG/GTCC cogeneration systems in that country’s sugarcane industry. Cuba’s high per-capita production of sugarcane and its heavy dependence on oil for energy provide attractive conditions for a large-scale energy-from-sugarcane program. 1. Introduction The biomass integrated-gasifier/gas turbine combined cycle (BIG/GTCC) technology was first identified over a decade ago as an advanced technology with the potential to be cost-competitive with conventional condensing-extraction steam-turbine (CEST) technology using biomass by-products of sugarcane-processing as fuel, while dramatically increasing the electricity generated per unit of sugarcane 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 and leaves of the sugarcane plant (Figure 1), is another substantial energy resource. Bagasse and trash each account for about one-third of the above-ground energy stored by sugarcane, with the remaining one-third stored as sugar. The raw energy value of bagasse and trash associated with the year-2000 global sugarcane harvest (1.3 billion tonnes of sugarcane spread across more than 100 countries) is an estimated 8 EJ/year (or a continuous average

250 GWfuel), equivalent to 17 % of today’s total coal consumption in developing countries.[1] During the past decade, there have been substantial efforts undertaken worldwide to develop BIG/GTCC technology and carry out pilot, demonstration, and commercial projects. This paper briefly reviews alternative BIG/ GTCC system designs and technology commercialization efforts ongoing worldwide. We then present performance estimates for BIG/GTCC designs integrated with sugar or sugar/ethanol factories. We also review estimates of the availability and costs of sugarcane trash as a supplementary cogeneration fuel in Brazil, Cuba, and some other Caribbean countries. We estimate the prospective costs of electricity from BIG/GTCC systems under the assumption that the technology becomes commercially mature, and we also estimate how many BIG/GTCC units would need building before capital and operating costs can be expected to reach commercially mature levels. Finally, we present an analysis of the potential energy

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sector impacts of the widespread application of BIG/GTCC systems at sugarcane-processing facilities in a major sugarcane-producing country, Cuba. Cuba is currently the world’s 6th largest sugarcane producer, even with cane production levels less than half its peak production levels of the late 1980s. The relatively high percapita sugarcane production in Cuba provides the potential for sugarcane-derived electricity (and ethanol) to substantially reduce that country’s high fossil-fuel dependence. 2. BIG/GTCC technology 2.1. Design concepts The basic elements of a BIG/GTCC power plant include a biomass dryer (ideally fueled by waste heat), a gasifier for converting the biomass into a combustible fuel gas, a gas cleanup system, a gas turbine-generator fueled by combustion of the biomass-derived gas, a heat recovery steam generator (HRSG) to raise steam from the hot exhaust of the gas turbine, and a steam turbine-generator to produce additional electricity (Figure 2). Three variations of this basic configuration are under commercial development. Table 1 summarizes the main relative advantages and disadvantages of the three variants. The principal differences among the variants arise from the design of the gasifier. Variant 1 involves a fluidized-bed reactor operating at atmospheric pressure using air for partial oxidation of the biomass. One of the leading atmospheric-pressure gasifier developers, TPS (Sweden), uses a second gasification stage with a catalyst (dolomite) to reduce the content of heavy hydrocarbon products (“tars”) that are part of the gas produced in the first reactor. The elimination of tars is required to prevent downstream operating difficulties

Figure 1. The sugarcane plant

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

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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)

-

-

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

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

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, using Ahlstrom (now Foster Wheeler) pressurized gasifier and ceramic hot gas filters for gas cleanup. Plant commissioning was 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, North Yorkshire, UK

First fully-integrated commercial BIG/GTCC. Shakedown testing began in late 2000. The plant will produce 8 MWe from 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 (ABB Alstom “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 to begin in 2001. A General Electric LM2500 gas turbine modified for biomass-derived gas will be used. Fuel will be eucalyptus wood chips from dedicated plantations and from purchased plantation harvesting residues. Gasifier and gas turbine 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 is to evaluate and develop technology to enable BIG/GTCC to be used at sugarcane-processing facilities with bagasse and trash as fuels. Work has included evaluating availability and quality of trash, agronomic routes to green cane harvesting with trash recovery, gasification tests (at 2 MWth TPS pilot plant) of bagasse and trash, design integration of BIG/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. Testing started in 1998, with gas burned in existing boiler of a conventional wood-fired power plant. Plans are to install a gas turbine 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.

that can arise from tar condensation. The product gas from the tar “cracker” is cooled from about 900ºC to near-ambient temperature, cleaned, and compressed to the pressure needed for injection into the gas turbine combustor. Variant 2 involves operating the gasifier near atmospheric pressure and using some form of indirect heating of the biomass, rather than partial combustion. In one leading design (Battelle Columbus Laboratory, USA), hot sand carries heat to gasify most of the biomass, leaving behind some solid carbon (char). The char and sand are circulated to a second reactor, where air is introduced to burn the char and thereby reheat the sand. The product gas passes through a tar cracking unit and is then cooled, cleaned and compressed to fuel the gas turbine. The heat in the combustion products leaving the char-burning reactor is recovered to raise steam, to dry biomass fuel, or

for other useful purposes. Variant 3 involves operating a fluidized-bed gasifier under elevated pressure using air for the partial oxidation. In this configuration, the gasifier product gas is cooled only modestly, cleaned at elevated temperature using a ceramic or sintered metal filter, and then passed to the gas turbine combustor. Leading developers of the pressurized gasifier concept include Foster-Wheeler (USA) and Carbona (Finland). 2.2. Demonstration and commercial projects Since the early 1990s, there have been considerable technology development and demonstration efforts relating to BIG/GTCC commercialization, as summarized in Table 2. The first commercial BIG/GTCC project will produce 8 MWe from wood chips grown on short-rotation plantations in the UK. Shakedown testing of the plant began at

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the end of 2000. Additionally, construction of a 32 MWe BIG/GTCC system is expected to begin in 2001 in Bahia, Brazil. Both of these projects will utilize a design based on the TPS atmopsheric-pressure gasifier (Design Variant 1 in Table 1). The pilot-plant project in Varnamo, Sweden (Table 2), has demonstrated the feasibility of BIG/GTCC systems based on pressurized gasifiers (Design Variant 3). The project in Burlington, USA is demonstrating a system based on indirectly-heated gasification (Design Variant 2). No demonstration projects are ongoing today involving BIG/GTCC systems operating on sugarcane biomass. However, in preparation for a pilot demonstration project, extensive testing and analysis is being conducted at the Copersucar Technology Center (CTC) in the state of São Paulo, Brazil. Pilot scale atmospheric-pressure gasification tests with bagasse and trash are being carried out under this program by TPS in Sweden. The objective of the CTC work is to understand in detail the key technical and cost issues associated with introducing BIG/GTCC technology into sugarcane-processing facilities with the intention of designing and installing a pilot demonstration unit in the next phase of the program. 3. The sugarcane-processing industries Understanding how BIG/GTCC systems might be introduced into sugarcane-processing facilities requires an understanding of present sugarcane-processing practices. The discussion here is based on current Brazilian practices. The conversion of sugarcane into sugar or ethanol begins with the crushing and washing of crushed cane stalks, which results in separate streams of cane juice and bagasse containing about 50 % moisture. The bagasse is sent to the mill’s cogeneration system, where current practice is to burn it to generate the steam and electricity needed to run the factory. Existing cogeneration facilities have typically been designed to be relatively inefficient in order to ensure that little or no bagasse disposal costs are incurred. The amount of bagasse available for fuel is actually far greater than the amount needed to meet all process energy demands. With efficient cogeneration systems, a mill could generate electricity considerably in excess of factory needs, while still meeting all process energy demands (as discussed in Section 4). The option of selling electricity to the grid was generally not available when the factories were built, however, so there was little incentive to have efficient cogeneration systems. Furthermore, rather than the current industry practice of shutting down the cogeneration system during the time of the year when sugarcane is not being harvested (5 to 6 months of the year), a cogeneration system selling power to the grid could continue to operate during the off-season if a supplementary fuel were available. Sugarcane “trash”, the tops and leaves of the sugarcane plant that are not used for fuel today, is a potentially attractive supplementary fuel (as discussed in Section 5). 3.1. Making sugar or sugar and ethanol In sugar production, steam is used throughout the facility in a sequence of processing steps to convert clarified cane juice into final sugar. The steps include juice concentraEnergy for Sustainable Development

tion, sugar crystallization, centrifuging, and drying. Juice concentration is conducted in a continuous multiple-effect evaporator where the initial concentration of 14 to 16º Brix (% solids by weight) is increased to 65 to 70º Brix. In this system “live” steam is fed to the first evaporator effect, and the vapor that results from evaporating water in each effect is used as heating steam for the following effect and for other steps in the process. Normally four or five effects are used. The concentrated juice, now called syrup, is directed to the vacuum pans where it is further concentrated under vacuum to around 91-93º Brix in either a continuous or a batch process. This step produces a mixture called massecuite, consisting of around 50 % crystals surrounded by molasses (a sugar solution with remaining impurities). This massecuite, at a temperature of 65-75ºC, is discharged into crystallizers where a slow cooling takes place, usually aided by water or air cooling. The cooled massecuite is sent to the centrifuges where molasses and sugar crystals are separated. The process is completed by washing of the sugar crystals with pressurized water or steam inside the centrifuges to further remove the molasses film from the crystal surface. The sugar is discharged from the centrifuges at a temperature of 65-85ºC and moisture content of 0.5-1.5 % and directed to a dryer/cooler. The latter uses steam to heat the drying air, and it uses ambient air in the cooling section. The sugar leaving this unit is delivered for packaging or bulk storage. The molasses collected from the centrifuges can be returned to the vacuum pans for recovery of residual dissolved sugar. Depending on the degree of sucrose recovery desired, factories produce one, two or three massecuites (also referred to as one, two, or three strikes). The exhausted molasses, called final molasses, has several potential uses. At most sugar factories in Brazil, the final molasses is used as one of the feedstocks for production of fuel ethanol at a distillery annexed to the sugar factory. The final molasses is blended with part of the raw cane juice to constitute the fermentation feedstock. At a typical Brazilian sugar/ethanol production facility, 45-55 % of the sucrose entering the factory as cane is converted to sugar, with the balance being converted to ethanol. Such Brazilian factories use only one or two strikes for sugar, and divert the remaining molasses for blending with raw cane juice to be converted to ethanol. 3.2. Process energy demands A cogeneration facility serving a sugar or sugar/ethanol factory must always satisfy the demand for steam to run the factory during the cane-crushing season. Cogeneration technologies that convert a high fraction of the biomass fuel input into electricity, such as BIG/GTCC, correspondingly convert a smaller fraction of the fuel input into process steam and cannot satisfy process steam demand via cogeneration unless measures are taken to improve the efficiency with which steam is consumed during sugar or ethanol production. Factories producing sugar alone or co-producing sugar z

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Table 3. Alternative factory process energy demands and capital investments required to reduce energy demands to the indicated levels at a facility processing 7000 tc/day Sugar-only factory[1] Typical today Process steam consumption, kg/tc Process electricity consumption, kWh/tc Total capital investment (million US$)

Sugar factory with annexed ethanol distillery[2]

Steam saving I

Steam saving II

500

340

280

20

28

-

1.60

Typical today

Steam saving I

Steam saving II

500[3]

340[4]

280[5]

29

20

28

29

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), mechanical stirrers 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 bleeding from 5th effect for vacuum pans.

steam use and estimated the capital investments required to implement such modifications. Table 3 summarizes results from the CTC analyses.

and ethanol today consume similar levels of process steam per tonne (t) of sugarcane crushed. A typical level of process steam consumption almost anywhere in the world today is 400 to 500 kg steam/t of sugarcane crushed (kg/tc). As noted earlier, sugar factories have historically had little incentive to minimize process steam demands. In contrast, the process steam consumption in beet-sugar factories or corn-ethanol distilleries is far lower than in canebased factories, because in those factories process energy is provided using costlier fossil fuels. Adopting some of the technologies commonly used in the beet-sugar or cornethanol industries would lead to substantial reductions in process steam demand in cane-processing industries. This in turn would enable a cogeneration system at a mill to generate larger amounts of electricity. The possibility of exporting electricity to earn additional revenue provides an incentive for adopting process steam reductions at cane-processing facilities. The return on investment from added electricity sales would typically be attractive. Detailed studies have shown that there is a potential for reducing the process steam consumed in sugar and ethanol production by up to half levels typical for the industry today [Ogden et al., 1990; 1991]. As interest in the export of electricity from sugar mills has risen, an increasing number of feasibility studies of process steam use reductions have been undertaken at specific mills. One such study was carried out for the Hector Molina mill in Cuba, where a CEST cogeneration system will be installed as part of a project co-financed by the Global Environment Facility (GEF). The plan for the Hector Molina project includes a 32 % reduction in process steam consumption, from 500 kg/tc to 340 kg/tc [Guzman and Valdes, 2000]. Engineers at the CTC have assessed the potential for reducing process steam demand in typical Brazilian caneprocessing facilities [CTC, 1998]. They developed detailed designs for modifications required to reduce process

Engineers at the CTC have also developed detailed performance calculations for alternative cogeneration systems operating on bagasse and trash and integrated into a sugarcane-processing facility. On the basis of the CTC’s calculations, we illustrate the key differences between steam turbine-based and gas turbine-based cogeneration. In all cases, we consider a cogeneration facility at a factory with a maximum crushing rate of 7000 tc/day and a capacity factor of 87 %. Most of our analysis assumes a crushing season lasting 214 days (as in Southeast Brazil), but we also examine the impact of a 150-day season (as in Cuba). A uniform mixture of bagasse and trash is assumed to be the fuel throughout the year in all cases. A uniform fuel composition simplifies the design and operation of the gasifier or boiler to which it is fed.[2] It also facilitates seasonal fuel storage by increasing the average moisture content of the stored fuel. (The low moisture content of trash by itself increases fire risks.) 4.1. Partial BIG/GTCC design Until sufficient confidence in the reliability of BIG/GTCC technology is developed, it is unlikely that a sugar or sugar/ethanol producer will be willing to rely entirely on a BIG/GTCC cogeneration system to meet its process energy demands. In this context, a “partial” BIG/GTCC design can be envisioned that would utilize some of the existing cogeneration equipment at a typical existing factory to provide process steam requirements. The particular design considered here assumes that the process steam demand is fully met by an existing 22-bar bagasse-burning boiler.[3] The steam from this boiler is expanded to 2.5 bar in back-pressure steam turbines that run mechanical equipment in the factory (cane knives,

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

shredders, and crushers) and generate a small amount of electricity. The process steam consumption in the factory is assumed to be reduced to 340 kg/tc from the typical present-day level of 500 kg/tc, as a result of steam conservation investments in the factory. In parallel to the 22bar boiler, the design includes a gasifier supplying fuel to a gas turbine-generator, the hot exhaust from which is used in a heat recovery steam generator to produce 82-bar steam that drives a steam turbine-generator. Also, a small amount of bagasse is burned in a furnace for drying the gasifier fuel to an average of 10 % moisture content (Figure 3).[4] The performance estimates for the gasifier, gas turbine, and heat recovery steam generator portion of the plant were provided to the CTC by TPS, the Swedish gasifier supplier and system integrator. The TPS design includes an atmopheric-pressure gasifier coupled with a raw-gas tar cracker and followed by a wet scrubber for gas cleaning and cooling. An intercooled fuel gas compressor is used to bring the gas to the pressure needed for injection into a General Electric LM2500 gas turbine modified for biomass-derived gas [Neilson et al., 1999]. The TPS design is based on the design of the BIG/GTCC commercial demonstration plant planned for Bahia, Brazil [Waldheim and Carpentieri, 2001]. For comparison purposes, CTC engineers also developed performance calculations for a high-pressure steam turbine cogeneration system (Figure 4). The CTC design for this system includes a boiler producing 82-bar steam that is expanded through a condensing extraction steam Energy for Sustainable Development

turbine (CEST). Some steam is extracted at 22 bar to drive the existing back-pressure mechanical steam turbine drives and turbine-generator, after which the expanded steam is delivered for process use. The CEST was designed with the same process steam demand and same total biomass consumption as the BIG/GTCC design. As detailed in Table 4, the partial BIG/GTCC system designed by CTC engineers generates 28 MW of exportable electricity (i.e., electricity in excess of process electricity needs) during the milling season and 29 MW in the off-season. The CEST generates 22 MW of exportable electricity throughout the year. All of the bagasse generated during the crushing season (140 kg dry matter/tc) is consumed over the course of the year, and additionally about 58 kg (dry matter) of trash is required as fuel/tc.[5] 4.2. Pure BIG/GTCC design Once sufficient confidence has developed in the reliability of the BIG/GTCC technology, “pure” BIG/GTCC cogeneration systems would likely be introduced. The performance of such a system (Figure 5) has been estimated by CTC engineers. In contrast to the “partial” BIG/GTCC design, there is no bagasse-burning boiler in this system. Additional fuel is then available for the gasifier, enabling a larger gas turbine to be utilized. For simplicity, CTC engineers modeled this design assuming it includes two BIG/GTCC modules identical to the one used in the “partial” BIG/GTCC configuration. Steam at 82 bar pressure from the heat recovery steam generator is expanded through a condensing extraction steam turbine, with one z

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Figure 4. Schematic diagram for a condensing-extraction steam turbine (CEST) cogeneration system. The design shown here is the same for the CEST systems 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 turbine drives. The electrical output of the condensing steam turbine augments the process mechanical and electrical power provided by the back-pressure drives. Remaining electricity is available for export to the grid. Table 4. Energy balances for “partial” BIG/GTCC and for CEST cogeneration at a mill processing 7000 tc/day during a crushing season length characteristic 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) On-season Off-season Annual Electricity generation Gas turbine, kW Condensing steam turbine, kW Back-pressure steam turbine, electricity, kW Back-pressure steam turbine mech. power, kW Total, kW Total, GWh Total, kWh/tc On-season process energy consumption Steam (130ºC, 2.5 bar), kg/tc kg/hr Electrical & mechanical power, kW kWh/tc Exported electricity, kW GWh kWh/tc Hourly biomass fuel consumption[1] Bagasse, t50/hr Trash, t15/hr Total biomass fuel consumption[1] Bagasse, thousand t50 per year Trash, thousand t15 per year Biomass dry matter consumed/tc[1] Bagasse, t0/tc Trash, t0/tc Cogeneration efficiencies (%, HHV basis) Electricity generation Process steam generation Electricity plus steam Cogeneration efficiencies (%, LHV basis) Electricity generation Process steam generation Electricity plus steam

23,910 2,260 4,045 30,215 135 104

21,976 21,976 69 57

340 99,200 8,239 28 21,976 98 75

-

Partial BIG/GT On-season Off-Season Annual

204 157

16,800 13,033 2,483 4,045 36,361 162 125

16,800 12,432 29,232 92 71

255 196

21,976 69 53

167 129

340 99,200 8,239 28 28,122 126 96

29,232 92 71

218 167

55.6 14.4

31.1 8.0

-

63.0 11.7

20.5 11.8

-

261 64

103 25

365 90

296 52

68 37

365 89

0.100 0.042

0.040 0.017

0.140 0.059

0.114 0.034

0.026 0.024

0.140 0.058

14.3 31.8 46.1

18.6 18.6

15.5 22.8 38.3

16.5 30.4 46.9

28.1 28.1

19.4 22.8 42.2

17.3 38.5 55.8

22.6 22.6

18.8 27.6 46.4

20.1 37.1 57.1

33.3 33.3

23.5 27.6 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).

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Table 5. Energy balances for “pure” BIG/GTCC and for CEST cogeneration at a mill processing 7000 tc/day during a crushing season length characteristic 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) On-season

Off-season

“Pure” BIG/GTCC

Annual

On-season

Off-season

Annual

Electricity generation Gas turbine Condensing steam turbine Back-pressure steam turbine, electricity Back-pressure steam turbine, mech. power

-

-

-

33,600

33,600

-

33,651

30,638

-

12,270

24,877

-

2,850

-

-

3,250

-

-

2,567

-

-

2,567

-

-

39,068

30,638

-

51,687

58,477

-

174

97

271

230

185

415

Total, kWh/tc

134

75

209

177

142

320

On-season process energy consumption

280

-

-

280

-

-

81,700

-

-

81,700

-

-

Total, kW Total, GWh

Steam (130ºC, 2.5 bar), kg/tc kg/hr Electrical & mechanical power, kW

8,403

-

-

8,403

-

-

29

-

-

29

-

-

30,665

30,638

-

43,284

58,477

-

GWh

137

97

234

193

185

378

kWh/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

365

Trash, thousand t15 per year

107

50

158

92

65

158

Bagasse, t0/tc

0.095

0.045

0.140

0.082

0.058

0.140

Trash, t0/tc

0.070

0.033

0.103

0.060

0.043

0.103

Electricity generation

16.1

19.1

17.1

24.8

28.1

26.2

Process steam generation

22.8

-

15.5

26.5

-

15.5

Electricity plus steam

38.9

19.1

32.6

51.3

28.1

41.7

Electricity generation

19.2

22.8

20.4

29.6

33.5

31.2

Process steam generation

27.2

-

18.5

31.7

-

18.5

Electricity plus steam

46.5

22.8

38.9

61.3

33.5

49.8

kWh/tc Exported electricity, kW

Hourly biomass fuel consumption[1]

Total biomass fuel consumption[1]

Biomass dry matter consumed/tc[1]

Cogeneration efficiencies (%, HHV basis)

Cogeneration efficiencies (%, LHV basis)

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).

extraction at 22 bar. The extracted steam is expanded in back-pressure mechanical turbine drives and a small turbine-generator. The exhaust steam from these back-pressure units is used as process steam. The process steam demand in this case was assumed to be reduced to 280 kg/tc through capital investments in steam conservation. For comparison purposes, CTC engineers also calculated the performance of a high-pressure steam turbine system with the same process steam demands and biomass consumption as for the pure BIG/GTCC case. As detailed in Table 5, the pure BIG/GTCC system produces about 43 MW of exportable electricity during the milling season and 58 MW during the off-season. The main reason for the higher off-season production of exportEnergy for Sustainable Development

able electricity in this case is that process steam is not needed during the off-season. As a result, a much larger amount of steam is expanded fully through the steam turbine in the off-season. In this configuration, all of the bagasse generated during the crushing season is consumed over the course of the year, and additionally about 103 kg (dry matter) of trash are required per tc. The CEST system consumes the same amount of fuel annually as the BIG/GTCC system and produces about 31 MW of exportable power the year round. Figure 6 summarizes the power export potential in terms 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 z

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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 of the back-pressure turbine drives. The electrical output of the combined gas turbine/steam turbine cycle augments the process mechanical and electrical power 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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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.

electricity on an annual basis, or 29 % more than the 129 kWh/tc produced by its counterpart CEST system. The pure BIG/GTCC produces 62 % more exportable power than its counterpart CEST system (291 kWh/tc versus 180 kWh/tc). 4.3. Cogeneration performance in the Cuban context The performance results in Figure 6 would be different for cogeneration systems integrated into Cuban sugar factories, primarily because of the shorter crushing season in Cuba. The requirement for fuel to supplement bagasse at a sugar factory with a processing capacity of 7000 tc/day would be greater in Cuba than in Brazil. If an adequate amount of supplementary fuel were available, however, a cogeneration facility associated with a factory crushing for 150 days would generate larger amounts of electricity (on an annual basis) per tc than with the same factory crushing for 214 days (Figure 7 and Table 6). The trash requirement in this case (220 dry kg/tc for the “pure BIG/GTCC” case) is more than double the trash required with the longer crushing season. 4.4. Performance estimates for the long term The BIG/GTCC performance shown in Table 5 is used as the basis for subsequent analysis in this paper. It represents a conservative system design that could be the basis for initial introduction of BIG/GTCC systems into the sugar industry. Once a commercial BIG/GTCC industry is established, however, performance could improve considerably over the levels shown in Table 5 as a result of component and system optimization. For example, the strategy for drying the biomass feed to the gasifier in the Energy for Sustainable Development

design of Table 5 requires about 4 % of the fuel consumed at the plant to be burned to generate hot gas for drying. A more integrated system design would recover waste heat from the HRSG and other sources to dry the biomass.[6] Other design changes, such as optimizing the steam pressure from the HRSG and better overall thermal integration, could further improve efficiency. The potential for increasing electricity generating efficiency through such improvements can be assessed from a detailed calculation presented by Consonni and Larson [1996] for an optimized BIG/GTCC system using the same gasifier design considered for Table 5. The electric generating efficiency of a 26 MW stand-alone BIG/GTCC system in that case was 34 % (higher heating value basis). For comparison, the electric efficiency in Table 5 (for a 59 MW system) for the off-season operating period, which would be equivalent to a stand-alone power generating efficiency, is 28 % (HHV basis).[7] In the longer term, additional technological innovations will further improve performance. An indication of the possibilities in this regard is the calculated electrical efficiency of 40 % (HHV) for a 76 MW electric BIG/GTCC system utilizing a pressurized gasifier (instead of the nonpressurized gasifier in Table 5) and an advanced gas turbine.[8] 5. Biomass fuels for cogeneration at a sugar or ethanol factory This section examines whether there would be sufficient sugarcane biomass available at a facility to fuel z

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Table 6. Energy balances for “pure” BIG/GTCC and for CEST cogeneration at a mill processing 7000 tc/day during a crushing season length characteristic 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) On-season

Off-season

“Pure” BIG/GTCC

Annual

On-season

Off-season

Annual

Electricity generation Gas turbine Condensing steam turbine

-

-

-

33,600

33,600

-

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

-

-

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

Total, kW

On-season process energy consumption Steam (130ºC, 2.5 bar), kg/tc kg/hr Electrical & mechanical power, kW kWh/tc

280

-

-

280

-

-

81,700

-

-

81,700

-

-

8,403

-

-

8,403

-

-

29

-

-

29

-

-

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

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

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

44.0

Exported electricity, kW

Hourly biomass fuel consumption[1]

Total biomass fuel consumption[2]

Biomass dry matter consumed/tc[1]

Cogeneration efficiencies (%, HHV basis)

Cogeneration efficiencies (%, LHV basis)

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).

the cogeneration systems described in the previous section. 5.1. Bagasse The percentage of the bare cane stalk that is bagasse varies with the cane variety. A typical level in Brazil is 140 dry kg of bagasse per tonne of milled cane stalk (140 kg0/tc).[9] After milling, the bagasse contains about 50 % water, so bagasse availability is often quoted in terms of bagasse with 50 % moisture content. In this case, the Brazilian figure is 280 kg50/tc. This level of bagasse is fairly typical for sugarcane worldwide. 5.2. Trash The practice in most countries where sugarcane is grown

is to burn off the trash just before the harvest to facilitate harvesting of the stalks. Pollution from burning of cane fields is leading to restrictions on this practice in some parts of the world. For example, in Brazil a 1998 law established a timetable for eliminating pre-harvest burning: for areas with a grade under 12 % (considered harvestable by machine), all burning must end by 2006; for areas with a grade above 12 %, all burning must end by 2013. Such restrictions are likely to be introduced in many countries in the future. Motivated by the growing awareness of the negative environmental impacts of cane-burning and, especially, by the recognition of the potential energy value of sugarcane

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trash, efforts have been made over the past 15 years to develop the capability for recovering and using trash as a fuel for electricity generation in a number of countries, including Australia [Schembri and Carson, 1997], Brazil [Leal, 1995], Colombia [Cock et al., 2000], the Dominican Republic [Lopez, 1987], India [Anonymous, 2000], the Philippines [Varua, 1987], Puerto Rico [Phillips, 1987; Allison, 1987], Thailand [Winrock, 1991], and elsewhere. 5.2.1. Brazil One of the most intensive efforts to understand and design trash recovery and transport systems is the program being carried out at the CTC. Measurements there indicate that the total amount of trash produced by sugarcane varieties commonly grown in Southeast Brazil ranges from 110 to 170 kg0/tc, with an average of 140 kg0/tc [Macedo et al., 2001]. The CTC has analyzed a number of concepts for machine harvesting and delivering of trash to a mill’s cogeneration facility. It estimates that the maximum amount of trash that can physically be recovered and delivered to a cogeneration facility is about 89 % of the total trash produced [Macedo et al., 2001]. This corresponds to about 125 kg0/tc on average, which is well above the level required to fuel the cogeneration systems described in Tables 4 or 5, but below that required with the shorter crushing season (as in Table 6). The CTC estimates the direct cost of collecting trash from the field, baling it, and transporting the bales to the mill to be $ 10.9/dry t ($ 10.9/t0), or $ 0.64/GJHHV [Macedo et al., 2001].[10] The total net cost of delivered trash must also account for the substantial agronomic impacts of removing trash, including loss of recycled nutrients. The largest component of the agronomic cost is additional herbicide used to replace the weed-suppressing trash blanket that remains on the field after conventional machine harvesting. Agronomic costs add an additional 80 % to the direct recovery costs, resulting in a total net cost of delivered trash bales of $ 1.2/GJHHV (Table 7). 5.2.2. Cuba The sugarcane harvesting system in Cuba is unique among cane-producing countries in two important respects. First, an estimated 70 % of the sugarcane crop is harvested by machine without prior burning, which is far higher than for any other country. For example, only 20 % of Brazil’s sugarcane is machine harvested at present. The second unique feature of Cuban harvesting practice is the longstanding commercial use of “dry cleaning stations” to remove trash from the cane stalks before the stalks are transported to the crushing mills. Cuba has over 900 cleaning stations to serve its 156 sugar mills. The cleaning stations are generally not adjacent to the mills, but are connected 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 manually cut cane. Trash is removed from the stalk and blown out into a storage area. The stalks travel along a conveyor to waiting rail cars. The predominant practice today is to incinerate the trash at the cleaning station to reduce the “waste” volume. Energy for Sustainable Development

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

Cost, US$ Per dry t

Per GJ

Fraction of total cost, %

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

cost2

8.66

0.510

44

19.55

1.150

100

Agronomic

Total net cost Source: Macedo et al., 2001. Notes

1. Rectangular bales (0.8×0.87×1.90 meters) with an average weight of 306 kg and with 15 % 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 herbicide required when there is an insufficient trash blanket on the field. Other costs include a reduction in cane productivity due to compaction, and a lower degree of field terracing that can be done. One positive agronomic impact (resulting in a cost reduction) is that soil preparation is easier without a trash blanket present.

Detailed estimates developed by the Cuban Ministry of Sugar [Egusquiza, 1994; Egusquiza and Gonzalez, 2000] indicate that the total trash production of Cuban sugarcane varieties is considerably higher per tc than those found in Brazil. The estimated trash production in Cuba is nearly 200 kg0/tc (Table 8), compared with 140 kg0/tc in Brazil. In Cuba today, about half of the trash (97 kg0/tc in the case of machine-harvested cane) is left on the field after harvest, about one-quarter (47 kg0/tc) is concentrated at the cleaning stations, and an additional one-quarter (46 kg0/tc) is delivered to the mill with the cane (Table 8). If a trash recovery level similar to that achieved in Brazil (89 %) could be realized in Cuba, the total trash that could be delivered to a cogeneration facility would be some 174 kg0/tc on average. Such a level is still shy of the level needed to operate the cogeneration systems described in Table 6, where the crushing season lasts only 150 days. The costs for recovering and delivering trash to a mill site in Cuba are likely to be considerably lower than the costs estimated in Table 7 for Brazil since some trash is already concentrated at cleaning stations and since rail transport of trash to the mill site is feasible. Our “guesstimate” is that direct costs per t of trash delivered to a mill can be reduced by 50 % relative to the $ 10.9/t0 estimated for Brazil. Assuming the costs of agronomic impacts are the same as in Brazil, the total cost of delivered bales in Cuba would then be $ 14.1/t0, or $ 0.83/GJHHV. 5.2.3. Other Caribbean countries Measurement of trash production by cane species typically grown in some other Caribbean countries show ratios of trash-to-millable stalk that are even higher than z

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Table 8. Mass balance of sugarcane biomass in Cuba. This table shows the disposition of sugarcane stalks and cane trash throughout the harvesting, 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 additional 24-30 % is left at the cane cleaning stations, and 17 % to 24 % is crushed in the mills with the cane. Machine harvested fields Cane stalks (%)

Trash (%)

Manually harvested fields

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.

those reported for Cuba. Phillips [1987] cites a study done in the Dominican Republic for the Dominican Electric Corporation which indicated, on the basis of measurements, “a rather consistent correlation between cane tonnage and barbojo (trash) tonnage per hectare. On the average, for each ton of cane there is 0.66 ton of barbojo at a field moisture content of 50 % (by weight) when harvested,” i.e., 330 kg0/tc. Phillips also presents results Table 9. Trash production per tonne of millable cane for different cane varieties and locations, as measured in Puerto Rico Location

Barahona

Quisqueya

Consuelo

Average[2]

Cane Millable variety[1] cane (t/ha)

Trash (dry t/ha)

Ratio of trash to millable cane (dry t/tc)

PR 980

123.1

44.8

0.36

PR 980

71.3

25.4

0.35

PR 980

34.7

29.1

0.84

PR 1028

86.2

23.5

0.27

PR 1028

33.3

14.6

0.44

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 0.34

Source: Phillipps, 1987. Notes 1. The same cane varieties give a wide range of production per hectare, depending on cultivation practices. For example the PR 980 variety at Barahona yielding 123 t/ha is with irrigation. 2. This is the average of all values in the table, excluding the anomalous 0.84 value.

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of measurements made for several Puerto Rican cane varieties that show an average of 340 kg0/tc (Table 9). In some of the first work published about the potential for utilizing trash for energy, Alexander [1985] indicates an average trash production associated with typical Puerto Rican sugarcane in the early 1980s to be 280 kg0/tc.[11] 5.3. Energy cane Alexander also indicates that there is a potential for even larger trash production via breeding of “high-tonnage cane”, which he refers to as “energy cane”. He observes that energy cane can yield more trash and more sugar per hectare than conventional sugarcane, even though sugar content per tc would be lower than with conventional cane. The high yields of both components result from a combination of denser spacing of cane plants and selective breeding for high fiber production. On the basis of mean yield values of energy-cane trials over five crop years and using four varieties and two row spacings, Alexander shows that total dry matter per ha with energy cane could be 3 to 4 times as large as with conventional Puerto Rican sugarcanes, while the total fermentable solids (sugar) production per ha will more than double. [See Figures 3-7 in Alexander, 1985]. Alexander points out that sugar producers historically have dismissed the idea of milling high-fiber cane, despite higher sugar production per ha, because much more tonnage must be milled than with conventional sugarcane to extract a comparable amount of sugar. The possibility of revenues from increased sale of electricity with higherfiber sugarcanes have not been considered in such thinking. For certain market conditions (prices of electricity and sugar and/or ethanol), the added revenue from electricity sales may make the high-fiber cane option attractive. 6. Cogeneration economics Here we assess the prospective economics associated with electricity production from sugarcane biomass in association z

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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] Ethanol yield from cane, liters per

0.13

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] Cost of sugarcane delivered to crushing mill, $ per tonne

72.3

cane[8]

12

Cogeneration capital costs, O&M costs, and fuel consumption

CEST

Installed generating capacity, MW[9]

BIG/GTCC

33.7

58.5

50.4

86.8

2.20

2.20

4.86

4.86

Capital investments charged to cogeneration plant Cogeneration plant, million $ For process steam reductions at sugar-only

factory,[10]

million $

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

Bagasse

126

126

Trash

194

194

168994

168994

234

378

Sugar, tonnes per year

84497

84497

Ethanol, m3 per year

55248

55248

234

378

Operating and maintenance costs, million $ per

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

Products sold for revenue, sugar-only factory Sugar, tonnes per year Export electricity, GWh per year[13] Products sold for revenue, sugar-ethanol factory

Export electricity GWh per

year[13]

Notes 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 crushed that 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 most advanced 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&M costs. 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 other half 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 are achieved 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 within the 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 gate with 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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Table 11. Operating labor costs for cogeneration systems, based on Brazilian wage rates[1] Job description

Monthly rate ($)[2]

CEST [3]

BIG/GTCC [3]

Jobs

$/yr

Jobs

$/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

36

343368

42

381672

Totals 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.

with sugar production. We also consider electricity production in conjunction with combined sugar and ethanol production, when half of the sucrose in the cane is converted to sugar and half to ethanol. We compare the overall economics for BIG/GTCC cogeneration with that for CEST cogeneration. Our assessment uses capital and operating cost estimates for commercially mature BIG/ GTCC technology, i.e., costs that are projected for BIG/GTCC technology after several systems have been installed. (BIG/GTCC cost reduction trajectories are dis-

cussed in Section 7.) Table 10 summarizes key inputs to our cost analyses. The notes in Table 10 refer to additional detailed breakdowns of investment costs to achieve process steam use reductions (Table 3), cogeneration operating labor and consumables costs (Tables 11 and 12, respectively), and ethanol distillery investment costs (Table 13). Total installed capital costs for the CEST and BIG/GTCC facilities are especially important inputs. The total investment for the CEST system, $ 1500/kW, is based on the estimate in a feasibility study for a 33 MW CEST project planned for the Hector Molina sugar mill in Cuba [MINAZ, 1999]. The capital cost for the BIG/GTCC plant is based on estimates by engineers at the CTC and on the analysis in Section 7 of the likely costs for commercially mature stand-alone electric-power BIG/GTCC systems. In Section 7 the cost for such systems are estimated to be $ 1400/kW at a scale of 60 MW. This estimate is consistent (within the accuracy range of preliminary cost estimation) with cost estimates that have been made by several others for commercially mature plants [Carpentieri and Macedo, 2000; Craig and Mann, 1996; Elliott and Booth, 1993; Faaij et al., 1998; Weyerhaeuser et al., 1995]. For the same electric output capacity, a BIG/GTCC cogeneration system will have a higher cost per kW than a stand-alone system due to added costs associated with process steam production. The cost estimate shown in Table 10 for the BIG/GTCC cogeneration system is $ 1480/kW. Our cost analysis considers a 7000 tc/day capacity facility operating in a Southeast Brazil context, i.e., with a 214-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 producer pays the cost of delivered sugarcane. The cogenerator pays for collection and delivery of trash. Bagasse is delivered from the cane-crushing mills to the cogenerator in

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Table 12. Cost of consumables for cogeneration systems Unit Annual quantity quantity

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

8

8

1014

8100

13

99177

0.18

17900

Lube oil, m3/hr Treated water, m3/hr Total

360600 CEST

Treated water, m3/hr

[1]

13

99177

0.18

17900

8

8

1014

8100

Diesel fuel (baler), l/hr

15

66929

0.35

23600

Diesel fuel (tractor), l/hr

21

160630

0.35

56700

Lube oil, m3/hr

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 consumables

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Table 13. Capital investment required to add an ethanol distillery to an existing sugar factory.[1] The capacity of the distillery is 300 to 350 m3 anhydrous ethanol per day, which is approximately the capacity 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 Cooling water system Total

15 100 6388

Note 1. Estimated by CTC engineers. The estimate is consistent with an independent quote from 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 and ethanol storage tanks.

Figure 8. Cost model for electricity production in conjunction with sugar production. The sugar producer buys sugarcane and sells sugar. The cogenerator buys trash and sells electricity. The sugar producer and cogenerator exchange bagasse for process steam and electricity.

exchange for process steam and electricity, which is effectively the arrangement at most sugar or sugar/ethanol factories today. We use a capital charge rate of 20 % per year in all calculations. Investments to reduce process steam consumption are charged to the cogenerator, since the benefit arising from such investments is an increased level of electricity generation. 6.1. Production costs for electricity and sugar Figure 9 shows the busbar production cost for electricity cogenerated at a BIG/GTCC facility and at a CEST facility as a function of the cost of trash to the cogenerator in the case where the factory is one that makes sugar only. The BIG/GTCC yields a lower busbar cost over the entire Energy for Sustainable Development

range of trash costs shown. The gap in generating cost between the two systems grows as the trash price increases due to the higher efficiency of the BIG/GTCC system. As a reference, the shaded vertical bar on the left in Figure 9 indicates the range in required electricity sale price for the Hector Molina CEST project: 5.8 to 7.5 ¢/kWh [MINAZ, 1999]. The generating costs calculated for the BIG/GTCC and CEST systems both fall within this range for the trash prices shown. Table 14 shows sub-components of the cost of electricity when the trash price is $ 1.2/GJHHV, the average cost estimated for Southeast Brazil (Table 7). The busbar cost is dominated by capital charges, which are slightly higher for the BIG/GTCC than for the CEST. Total generating cost is lower for the BIG/GTCC than for the CEST, however, due to the much lower cost per kWh for trash arising from the higher efficiency of the BIG/GTCC. The cost of sugar production shown in Table 14 is representative of current average production costs in Southeast Brazil. Busbar electricity costs would be reduced if carbon dioxide emission reductions were credited against generating costs. Electricity from sugarcane biomass would have relatively low levels of associated net emissions of carbon dioxide: on average, the CO2 emitted at the cogeneration facility would be completely reabsorbed in subsequent regrowth of the sugarcane, and the only net CO2 emissions to the atmosphere would be the relatively small amounts arising from use of fossil fuel-based fertilizers and agricultural machinery operations [Moreira, 2000]. If the sugarcane-derived electricity were to displace electricity generated from fossil fuels, there would be net savings in CO2 emissions per kWh generated. If the net CO2 emission reductions correspond to those avoided by not burning oil to generate electricity, a scenario appropriate for Cuba, then the saved CO2 would be 0.22 kgC/kWh generated. If a carbon credit of $ 20/tC displaced were available – a value currently offered by the Prototype Carbon Fund of the World Bank[12] – cost of electricity shown in Figure 9 would be reduced by 44 mills/kWh ($ 0.0044/kWh). The impact of such a carbon credit is also shown in Table 14. 6.2. Production costs for electricity, sugar, and ethanol In conjunction with a factory producing both sugar and ethanol from sugarcane, the cost of cogenerated electricity would be slightly higher than with a sugar-only factory, because steam conservation investments, which are charged against electricity production, are higher for a sugar/ethanol factory than for a sugar-only factory. (See Table 3.) Also, the difference between the cost of BIG/GTCC and CEST electricity would be slightly greater, because the same steam conservation investments would be spread over a higher number of kWh with the BIG/GTCC. Table 15 gives a breakdown of sugar/ethanol/electricity costs when sugarcane trash costs $ 1.2/GJ. The ethanol cost shown there ($ 0.26/liter (l), without carbon credit), would enable ethanol to compete as a gasoline blendstock when the crude oil price is close to $ 30 per barrel (bbl).[13] This ethanol cost is representative of current z

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Figure 9. Cost of electricity production as a function of the trash cost to cogenerator. Bagasse is provided by the sugar producer in exchange for process steam and electricity. (See Table 10 for detailed inputs to this analysis.) Table 14. Production costs for sugar and electricity, with trash price to cogenerator equal to $ 19.6 per dry t ($ 1.15/GJHHV)[1] Sugar ($/t)

Electricity ($/kWh)

when crude oil costs less than $ 25/bbl. 7. Estimated costs to commercialize BIG/GTCC

average production costs in Southeast Brazil. Many producers in Brazil can make ethanol at lower cost. The key variable is the cost of the sugarcane. At $ 12/tc, cane accounts for over half the cost of the ethanol in Table 15. Cane costs as low as $ 8/tc are achieved in some parts of SE Brazil and should be achievable elsewhere over time. A cane cost of $ 8/tc would lower the cost of ethanol by $ 0.05/l compared with the cost in Table 15. Under this condition, ethanol would be competitive with gasoline

The attractive long-term prospects for BIG/GTCC cogeneration to compete commercially at sugar factories or sugar/ethanol factories must be considered against the fact that the technology today is still at a commercial demonstration phase, where capital and O&M costs are relatively high. How much time and how many BIG/GTCC units will need building before the costs can be expected to reach competitive levels? What is likely to be the total incremental cost during this period, i.e., the cost above and beyond commercially competitive costs? We address these questions next. In our analysis we focus on estimating capital investment requirements for BIG/GTCC plants designed to generate electricity only, since most BIG/GTCC cost estimates to date have been for standalone electricity generating systems. Capital cost for a first-of-a-kind commercial standalone BIG/GTCC system installed in Brazil today is an estimated $ 2450/kW for a 30 MW unit.[14] This compares with the estimate of $ 1400/kW for a 60 MW unit that was the basis for the cost analysis in the previous section. At $ 1400/kW, a BIG/GTCC system could produce electricity at a cost less than 5 ¢/kWh,[15] which would make it competitive with other sources of power in rural areas in many developing countries, including Cuba. Reaching the level of $ 1400/kW appears feasible considering several cost reduction opportunities. These include eliminating specialized engineering services needed for a

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Capital charges[2]

BIG/GTCC

CEST

0

0.0471

0.0450

O&M

53

0.0066

0.0062

Sugarcane costs

92

0

0

0

0.0069

0.0112

145

0.0606

0.0625

0

-0.0044

-0.0044

145

0.0562

0.0581

Trash Total Carbon

credit[3]

Total with C credit Notes

1. A 20 %/year capital charge rate is assumed. See Table 10 for additional input assumptions. 2. Charges for capital replacement are included as part of the O&M costs for sugar production. Capital charges for electricity include the cost for investments to reduce steam consumption in the sugar or sugar and ethanol factories. 3. Assuming a carbon credit of $ 20/tC saved. Also, electricity generated from sugarcane biomass (assuming zero net CO2 emissions) replaces electricity generated from oil (saving 0.22 kgC/kWh).

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Table 15. Production costs for sugar, ethanol, and electricity, with trash price to cogenerator equal to $ 19.6 per dry tonne ($ 1.15/GJHHV)[1] Sugar ($/t)

Capital charges[2]

Ethanol ($/l)

Electricity ($/kWh) BIG/ GTCC

CEST

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

0

-0.014

-0.0044

-0.0044

139

0.244

0.0576

0.0604

Carbon credit[3] Total with C credit Notes

1. A 20 %/year capital charge rate is assumed. See Table 10 for additional input assumptions. 2. Charges for capital replacement are included as part of the O&M costs for sugar production. Capital charges for electricity include the cost for investments to reduce steam consumption in the sugar or sugar and ethanol factories. 3. Assuming a carbon credit of $ 20/tC saved. Also, electricity generated from sugarcane biomass (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).

first-of-a-kind plant, making technological improvements, and reducing contingency costs. We estimate that these cost reduction opportunities would reduce the total installed capital cost from $ 2450/kW to $ 1780/kW (Table 16). A further cost reduction would arise as a result of scaling up the plant to a larger size. Applying a scaling

exponent of 0.65 (derived for natural gas-fired gas turbine combined cycle technology[16]) gives an installed capital cost of $ 1400/kW for a 60 MWe BIG/GTCC (Table 16). If a global market for BIG/GTCC systems develops, competition in BIG/GTCC systems is likely to drive investment costs down still further in the long term. For example, one study indicates a capital cost for a system based on an intercooled steam-injected gas turbine (a technology that is not yet commercially established) of around $ 900/kW in 1989 $ [Williams and Larson, 1996], or about $ 1200/kW in year-2000 $. How soon might a cost level of $ 1400/kW be achieved? All new energy technologies that can be massproduced and that ultimately become established in commercial markets experience reductions in cost with cumulative production. For example, Figure 10 shows cost reduction curves for several energy technologies at the early stages of commercial introduction. Several factors typically contribute to the observed cost reductions, including technology improvements, technology scale-up, and “learning by doing”. Each of the curves in Figure 10 has associated with it a “progress ratio”, defined as one hundred minus the percentage reduction in cost for each doubling in cumulative production. For example, for a technology characterized by an 80 % progress ratio there would be a 20 % reduction in cost for each doubling in cumulative production. The progress ratios for the initial cost reduction period for the technologies in Figure 10 are all between 75 % and 85 %. Limited experience with coal integrated-gasifier combined cycle (IGCC) technologies, which have many similarities with BIG/GTCC

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

% cost reduction

First-of-a-kind, 30 MW BIG/GTCC

Notes[1]

Installed cost $/kW 2450

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

Eliminate special engineering

5%

2200

In the Brazilian demonstration project, engineering services (substantially beyond normal engineering services for a commercial plant) will be provided by the gas turbine supplier, the gasifier supplier, and the firm responsible for overall engineering of the plant.

Technology improvements

15 %

1870

Advances (cost reductions) can be expected as a result of “learning by doing”, especially for plant components that have relatively little history of commercial use, including the gasifier, gas cooling system, and gas cleanup system. Also, equipment redundancies can be eliminated. For example, the Bahia, Brazil, plant design includes two biomass feeders of 100 % capacity each, six baghouse filters (only four of which are used), and a number of redundant pumps, heat exchangers and associated piping and valves.

Eliminate non-routine contingencies

5%

1780

Contingencies typically account for uncertainties in component cost estimates 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 plant than 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-fired combined cycles built around an LM2500 gas turbine (31.2 MW output, $ 809/kW) and around an LM6000 gas turbine (56.4 MW, $ 658/kW), a scaling exponent of 0.6511 is derived. For doubling of capacity from 30 to 60 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-most column 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 Installed capital cost – BIG/GTCC Units built

Installed MW Unit

Cumulative

82 % progress ratio $/kW[1]

106 $

87 % progress ratio $/kW[1]

Incremental 106 $[2]

106 $

Incremental 106 $[2]

Capital (106 $) to install CEST (same MW as 87 % PR case)[3]

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 number i (=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 % [MacGregor et al., 1991]. A more general analysis of learning curves of power generating technologies suggests an average progress ratio of 87 % for smaller-scale technologies [Neij, 1997]. If one assumes that the first BIG/GTCC built at a sugarcane processing facility will cost $ 2450/kW, that the Nth plant will cost $ 1400/kW, and that the cost reduction curve against cumulative MW installed will be characterized by a progress ratio of 82 %, then the $ 1400/kW cost level could be reached with construction of the sixth plant[16] (Table 17). The cumulative investment required for the six plants would be $ 370 million. Of this total, $ 75 million is the incremental cost, i.e., the investment required in excess of the projected cost for commercially mature technology (Table 17). If progress in cost reductions is more accurately characterized by a progress ratio of 87 %, then a cost of $ 1400/kW would be reached with construction of the 11th plant. The total and incremental capital investment requirements for building the 11 plants would be $ 850 million and $160 million, respectively (Table 17). Table 17 also shows that an investment of $ 765 million would be required to install CEST units with capacity equivalent to the 11 BIG/GTCC units considered in the 87 % progress-ratio cost reduction scenario. There would be higher investment risk involved with early BIG/GTCC units than with CEST units, but the actual investment required to commercialize BIG/GTCC technology is only 11 % higher than the cost of installing an equivalent number of MW of conventional CEST technology. 8. The potential impact of BIG/GTCC in Cuba Cuba’s current level of sugarcane production is 35 to 40 Mt/yr (about 3 % of world production), which is down by more than half from the level in the late 1980s (Figure 11). The per-capita production of sugarcane today, 3.2 tc/person/year, is the highest by far among all sugarcane-producing countries, which suggests that there is a more substantial opportunity in Cuba than elsewhere for sugarcane-derived energy to reduce dependence on other energy sources. In Cuba, over 90 % of conventional primary energy consumed is oil – some 8.6 Mt in 1998. Electricity production and vehicles account for nearly 70 % of the oil consumed, and over 80 % of Cuban oil is imported.[17] Cuba’s sugarcane processing industry includes 156 factories, with cane-crushing capacities ranging from less than 2000 tc/day to over 10,000 tc/day. Many of these factories provide small amounts of electricity to the national grid on an intermittent basis today [Egusquiza and Gonzalez, 2000]. The Hector Molina factory (milling capacity 7000 tc/day) will be the first one to export a substantial amount of electricity (109 kWh/tc) to the grid. In aggregate, Cuba’s sugar factories have the crushing capacity to support about 2.8 GW of CEST cogeneration capacity or nearly 5.6 GW of BIG/GTCC capacity (Figure 12). For comparison, the total installed electric utility generating capacity in Cuba today is 4.3 GW. Although only about half of the factories have sufficient capacity to supEnergy for Sustainable Development

port BIG/GTCC systems larger than 25 or 30 MW each, the extensive cane transportation system that exists in Cuba provides the possibility of aggregating (with low transport costs) cane trash and bagasse from smaller factories to enable installing of additional larger capacity cogeneration systems. Larger systems are desirable to capture scale economy benefits. In the long term, if Cuba were to install BIG/GTCC systems throughout its sugarcane processing industry, electricity exports could total 12 to 23 TWh/yr (for harvest levels of 40 to 80 Mtc/yr). The potential with CEST systems would be 40 % lower than this, but still significant. For comparison, the 1999 level of oil-fired electricity generation in Cuba was about 12 TWh/yr. If cane-based power were to displace oil-generated utility electricity, savings in expenditure on oil (at $ 25/bbl) would be up to $ 1.2 billion/year with BIG/GTCC and $ 0.7 billion/year with CEST (Table 18). The high efficiency of the BIG/GTCC relative to the CEST results in a higher oil cost savings per t of sugarcane processed: the BIG/GTCC system would save $ 15/tc, compared with $ 9/tc for the CEST (Table 18). Carbon dioxide emissions would also be reduced more substantially with BIG/GTCC than with CEST. If BIG/GTCC electricity were to displace oil-generated power, up to 5 MtC emissions might be avoided (Table 18), which represents about 70 % of the 7.3 MtC released by oil-burning in Cuba in 1997. The long-term potential for producing ethanol as a gasoline substitute in Cuba is also substantial. Ethanol may be an especially important option if future sugarcane production levels in Cuba return toward the high levels that existed in the late 1980s, because export of additional sugar into the free market will be increasingly difficult.[18] If Cuban sugarcane production were to rise to the 80 Mtc/yr level, and the incremental sucrose production (above today’s 40 Mtc/yr level) were to be converted into ethanol, Cuba would produce 3.4 billion l of ethanol per year, which would be more than sufficient to entirely replace all petroleum-derived motor vehicle fuels presently used in Cuba (about 15 million bbl/yr)[19]. The savings in oil 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 this energy source a major focus of its energy policy [Comision Nacional de Energia, 1993]. The government has also stated a commitment to reduce greenhouse gas emissions. Additionally, Cuba provides an attractive context for early introduction of BIG/GTCC technology because (1) Cuba’s electricity sector is almost wholly dependent on petroleum, which increases the potential for attractive economics for sugarcane electricity due to high long-run marginal costs of utility power (well in excess of 5 ¢/kWh); (2) the close relationship between the sugar industry, the electricity utility industry and other key government institutions in Cuba could greatly facilitate the introduction of a new technology like the BIG/GTCC; (3) there is a high level of engineering and technical capacity z

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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 also shown.

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Table 18. Potential long-term impact on Cuban oil consumption of electricity and ethanol production from sugarcane Cane harvest, million tc/yr

Electricity Oil saved Output[1] TWh/yr

Million bbl/yr[2]

Million $/yr[3]

Ethanol Oil saved $/tc[4]

Carbon saved 106 tC/yr

Output[5] 106 l/year

106 bbl per yr[6]

106 $ per yr[3]

Carbon saved 106 tC/yr

3395

16.4

410

1.8

3395

16.4

410

1.8

BIG/GTCC 40

11.6

23.8

595

80

23.2

47.6

1190

15

2.5 5.1 CEST

40

7.10

14.7

370

80

14.4

29.4

735

9

1.5 3.1

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. (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 (as measured in SE Brazil) is 17.0 GJ/dry t. For trash with 15 % moisture content (as delivered in SE Brazil), the HHV is 14.5 GJ/t. The LHV for trash with 15 % moisture content is 13.0 GJ/t.

in Cuba that could be trained to support such new technology; and (4) Cuba’s unique sugarcane harvesting system already involves some collection of sugarcane trash. 9. Conclusions The biomass integrated-gasifier/gas turbine combined cycle technology promises high efficiencies and lower electricity costs than conventional biomass-fired condensing steam turbine technology. Efforts are going on worldwide to commercialize BIG/GTCC systems. Construction of the first revenue-earning unit was completed in 2000 (in the UK) and that unit is undergoing start-up testing. The costs for such early commercial units will be high, but our analysis suggests that competitive costs will be achieved by the time six to eleven units have been built. The sugarcane processing industry provides an attractive context for early commercial applications. Because of its high percapita production of sugarcane and its high dependence on imported oil today, Cuba is an especially attractive country for early introduction of BIG/GTCC systems. Eric Larson and Robert Williams can be contacted at: Ph: 609-258-5445; Fax: 609-258-3661 E-mail: [email protected] Regis Leal can be contacted at: Ph: 55-19-429-8217; Fax: 55-19-429-8108 E-mail: [email protected] Acknowledgements This paper is based on a presentation given by one of the authors (Larson) at the International 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 of Foreign Affairs. For helpful contributions to the paper, the authors thank Suleiman Jose Hassuani, Helcio Martins Lamonica, Francisco A.B. Linero, Isaias de Carvalho Macedo, and Jose Perez Rodrigues Filho at the Copersucar Technology Center; Andrew Ellis, Olav Kjorven, and Haakon Vennemo at ECON, Oslo, Norway; and Felix J. Perez Egusquiza and Paulino 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

Energy for Sustainable Development

2. One key issue with the use of trash as a boiler or gasifier fuel is its relatively high alkali content compared with bagasse. Combustion or gasification of high-alkali fuels can cause deposition problems in boilers, heat exchangers, and other downstream equipment. 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 fuel to 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 directlyfired dryer is simpler to integrate into the overall plant and would be less capital-intensive if it enables higher-temperature drying. 5. Gas turbines are sold in a limited set of discrete sizes, and thus the choice of gas turbine for a BIG/GTCC system determines the amount of fuel (trash in this case) that must 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 atmosphere and 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 Table 5 is 40 %. The moisture content of the fuel in the calculations of Consonni and Larson was 50 %. If a fuel moisture content of 40 % were used instead, the electrical efficiency calculated 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 one with an intercooled compressor. See Consonni and Larson [1996]. 9. In this paper, the subscript on kg refers to the moisture content of the biomass (weight basis). 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 advances in understanding of costs have occurred, in part as a result of the construction of the first commercial BIG/GTCC plant in the UK (see Table 2). On the basis of discussions with 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 z

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Section 4.4), the fuel cost would be $ 0.016/kWh for a biomass price of $ 1.5/GJ, which might 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, and Cuban 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 a neat fuel, in which case 1.3 l of ethanol would be needed to give the same vehicle distance travelled as one l of gasoline [Macedo, 2000]. References Alexander, A.G., 1985. The Energy Cane Alternative, Elsevier, Amsterdam. Allison, W.F., 1987. “Alternative uses of sugarcane for Puerto Rico”, in Cane Energy Utilization Symposium – a Report from the 2nd Pacific Basin Biofuels Workshop, Volume II: Presented Papers, Report No. 88-04, Office of Energy, Bureau of Science and Technology, US Agency for International Development, Washington, DC, April. Anonymous, 1999. 1999-2000 Gas Turbine World Handbook, Volume 20. Anonymous, 2000. “Alternative biomass fuel for sugar mills: trials with cane trash”, Cane Cogen India: A Quarterly Newsletter of the GEP Project, Winrock International India, New Delhi, January. Carpentieri, E., and Macedo, N., 2000. “The introduction of BIG-GT technology – possible future uses in Northeast Brazil”, Energy for Sustainable Development, IV(3), October. CHESF, CIENTEC, CVRD, Eletrobras, and Shell, Brazilian Wood BIG-GT Demonstration Integrated Wood Gasification System Project – WBP: Final Report on Phase II, Brazil Ministry of Science and Technology and United Nations Development Program, Brasilia, 1998. Cock, J., Briceno, C.O., and Torres, J., 2000. “Energy from cane trash in Colombia”, International Cane Energy News, Winrock International, Arlington, Virginia, USA, April. Comision Nacional de Energia, 1993. Programa de Desarrollo de las Fuentes Nacionales de Energia, Havana, June. Consonni, S., and Larson, E.D., 1996. “Biomass-gasifier/aeroderivative gas turbine combined cycles: Part B – Performance calculations and economic assessment”, Journal of Engineering for Gas Turbines and Power, 118, pp. 516-525, July. Craig K.R., and Mann, M.K., 1996. Cost and Performance Analysis of Biomass-Based Integrated Gasification Combined-Cycle (BIGCC) Power Systems, NREL/TP-430-21657, National Renewable Energy Laboratory, Golden, Colorado, October. Copersucar Technology Center (CTC), 1998. Steam Economy in Sugar Mills, Project BRA/96/G31 Newsletter of the Centro de Tecnologia Copersucar, Piracicaba, Brazil, June. Copersucar Technology Center (CTC), 1999. Biomass Power Generation, Sugarcane Bagasse and Trash, Project BRA/96/G31 Newsletter No. 5, Copersucar Technology Center, Piracicaba, SP, Brazil, January. Elliott, P., and Booth, R., Brazilian Biomass Power Demonstration Project”, Special Project Brief, Shell International Petroleum Company, Shell Centre, London, UK, 1993. Egusquiza, F.J. Perez, 1994. Balanco Nacional de Paja de Cana, Ministry of Sugar, Havana, Cuba, 20 June. Egusquiza, F.J. Perez, and Gonzalez, A. Rubio, 2000. “Realities about the use of the cane straw (C.A.W.) as combustible in the Cuban sugar cane industry in the last twenty years”, presented at the 1st World Conference on Biomass Energy, Seville, Spain, June. Faaij, A., Meuleman, B., and van Ree, R., 1998. Long Term Perspectives of Biomass Integrated Gasification with Combined Cycle Technology: Costs and Efficiency and a Comparison with Combustion, Report 9840, Netherlands Agency for Energy and the Environment, December.

Larson, E.D., Williams, R.H., Ogden, J.M., and Hylton, M.G., 1990. “Biomass gas turbine cogeneration for the cane sugar industry”, International Sugar Journal, March/April. Leal, M.R.L.V., 1995. “Brazilian mill burns cane trash”, International Cane Energy News, Winrock International, Arlington, Virginia, USA, August. Lopez, P., 1987. “Field experience in the collection and transport of cane trash (barbojo) at central Romana”, in Cane Energy Utilization Symposium – a Report from the 2nd Pacific Basin Biofuels Workshop, Volume II: Presented Papers, Report No. 88-04, Office of Energy, Bureau of Science and Technology, US Agency for International Development, Washington, DC, April. Macedo, I.C., 2000. “Commercial perspectives of bioalcohol in Brazil”, presented at the 1st World Biomass Energy Conference, Seville, Spain, June. Macedo, I.C., Leal, M.R.L.V., and Hassuani, S.J., 2001. “Sugar cane residues for power generation in the sugar/ethanol mills in Brazil”, Energy for Sustainable Development, V(1) (this issue). MacGregor, P.R., Maslak, C.E., and Stoll, H.G., 1991. “The market outlook for integrated gasification combined cycle technology”, Proceedings of the 4th International Exhibition and Conference for the Power Generation Industries, published by Power-Gen, Houston, Texas. Ministerio de la Industria Azucarera (Ministry of Sugar) (MINAZ), 1999. CUB.G41/45 Project, C.A.I. Hector Molina Feasibility Study, Final Report, Ministry of Sugar, Havana, March. J.R. Moreira, 2000. “Sugarcane for energy – recent results and progress in Brazil”, Energy for Sustainable Development, IV(3), pp. 43-54. Nakicenovic, N., Grubler, A., and McDonald, A., (eds.), 1998: Global Energy Perspectives, International Institute for Applied Systems Analysis and the World Energy Council, Cambridge University Press, Cambridge, UK. Neij, L., 1997. “Use of experience curves to analyse the prospect for diffusion and adoption of renewable energy technology”, Energy Policy, 23(13), pp. 1099-1107, November. Neilson, C.E., Shafer, D.G., and Carpentieri, E., 1999. “LM2500 gas turbine fuel nozzle design and combustion test evaluation and emission results with simulated gasified wood product fuels”, ASME Journal of Engineering for Gas Turbines and Power, pp. 600-606, October. Ogden, J.M., Hochgreb, S., and Hylton, M., 1990. “Steam economy and cogeneration in cane sugar factories”, International Sugar Journal, 92(1099), pp. 131-143. Ogden, J.M., Williams, R.H., and Fulmer, M.E., 1991. “Cogeneration applications of biomass gasifier/gas turbine technologies in the cane sugar and alcohol industries”, Energy and the Environment in the 21st Century, the MIT Press, Cambridge, Massachusetts, pp. 311-346. Phillips, A., 1987. “Harvest and preparation technology for biofuels”, in Cane Energy Utilization Symposium – a Report from the 2nd Pacific Basin Biofuels Workshop, Volume II: Presented Papers, Report No. 88-04, Office of Energy, Bureau of Science and Technology, US Agency for International Development, Washington, DC, April. Schembri, M., and Carson, C.A., 1997. “The challenge of harvesting green cane”, International Cane Energy News, Winrock International, Arlington, Virginia, USA, July. Varua, V.F., 1987. “Trash for fuel: a Luisita project”, in Cane Energy Utilization Symposium – a Report from the 2nd Pacific Basin Biofuels Workshop, Volume II: Presented Papers, Report No. 88-04, Office of Energy, Bureau of Science and Technology, US Agency for International Development, Washington, DC, April. Waldheim, L., and Carpentieri, E., 2001. “Update on the progress of the Brazilian wood BIG-GT demonstration project”, Paper No. 98-GT-472, ASME Journal of Engineering for Gas Turbines and Power (forthcoming). Weyerhaeuser Company, Stone & Webster Engineering, Amoco, and Carolina Power & Light, 1995. New Bern Biomass to Energy Project: Phase I Feasibility Study, report to the National Renewable Energy Laboratory (Golden, Colorado) and Electric Power Research Institute (Palo Alto, California), June. Williams, R.H., and Larson, E.D., “Biomass gasifier gas turbine power generating technology”, Biomass and Bioenergy, 10(2-3), pp. 149-166, 1996.

Guzman, P.L., and Valdes, A., 2000. “Heat and power cogeneration at a Cuban sugar mill based on bagasse and trash as fuel: the ‘Hector Molina’ Project”, Energy for Sustainable Development, IV(3), October.

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