Over the next decades, a much larger fraction of fuels, chemicals, and materials will be produced from renewable plant materials. These biobased industrial products offer the potential for a much more sustainable economy based on environmentally superior products. This section briefly describes the associated costs of producing electricity, fuels, and chemicals from various feedstocks using biorenewable resources.
Table 7.13 Availability and cost of potential feedstocks.
Source: Crop data from Polman (1994) and Waste and residue data from Lynd (1996).
| Feedstocks | Production (106 T/Y) | Price (194 $/kg) |
| Corn | 191 | 0.09 |
| Potato | 17 | 0.16 |
| Sorgham | 16 | 0.09 |
| Beet molasses | 1 | 0.09 |
| Cane molasses | 1 | 0.03 |
| Sugar cane | 25 | 0.03 |
| Agricultural residues | ||
| Low cost | 4 | 12.9 |
| Mid cost | 36 | 38.8 |
| High cost | 50 | 47.4 |
| Forest residue‐logging | ||
| Low cost | 3 | 12.9 |
| Mid cost | 3 | 25.9 |
| High cost | 3 | 43.1 |
| Forest residue mill | 3 | 17.2 |
| Municipal solid waste | ||
| Mixed paper | 26 | 0–19 |
| Packaging | 14 | 0–5.2 |
| Urban wood | 3.5 | 12.9–25.9 |
| Yard waste | 11 | 0.12.9 |
Electricity from Combustion of Biomass
The capital and operating costs for steam power plants fired with biomass are relatively well known because of significant operating experience with these systems. The capital cost for a new plant ranges between $1400 and $1800/kW capacity. Accordingly, a 50‐MW biomass plant based on direct‐combustion would cost approximately $80 million. On the basis of a target price of $41.90/GJ for biomass, the cost of production for direct‐fired biomass power is about $0.06/kWh (Environmental Law & Policy Center 2001).
Electricity from Gasification of Biomass
The capital cost for a gasification plant, including fuel feeding and gas cleanup, is dependent on both the size and the operating pressure of the system. In the United States, an atmospheric‐pressure gasifier producing 50 MW thermal energy would cost about $15 million. A gasification/gas‐turbine power plant producing 50 MW of electricity would have total capital cost of between $75 and $138 million (between $1500 and $2750/kW), the smaller number reflecting improved technical know‐how after building at least ten plants. Electricity production costs would range from $0.05 to $0.09/kWh if fuel is available at an optimistic price range of $1.00–$1.50/GJ.
Capital costs for high‐temperature fuel cells suitable for integrated gasification/fuel cell power plants currently cost $3000/kW. Molten carbonate fuel cells are expected to be $1500/kW at the time of market entry, decreasing to about $1000/kW for a commercially mature unit. The cost of electricity from a mature unit operating on natural gas is projected to be between $0.049 and $0.085/kWh. More attractive economics result if less expensive fuel is available. The cost of electricity generated from landfill gas using mature fuel‐cell technology is expected to be comparable to that for an internal combustion engine/electric generator set, i.e., about $0.05/kWh (Bridgewater 1995; Hirschenhoofer et al. 1994; William and Larson 1993).
Biogas from Anaerobic Digestion
Anaerobic digestion is commercially developed for the purpose of treating wastewater. Power production from anaerobic digestion is in its infancy. The methane generated is often fired in internal combustion engines to produce electricity in an effort to help offset costs of waste treatment, but there are no immediate prospects for it to replace natural gas. Capital costs for anaerobic digestion facilities processing more than 200 T/day of volatile solids are estimated to be between $44 000 and $132 000 for each T/day of volatile solids processed. Methane yields will be approximately 0.38 m3/kg of volatile solids. Thus, a 200 T/day anaerobic digestion plant could produce 28 million m3 of methane per year, representing almost 2900 GJ/day of chemical energy. Projected operating costs for producing methane from dedicated energy crops were in the range of $5–6/GJ in 1986 dollars. In comparison, the cost of natural gas in the United States, which shows large seasonal and geographical variations, ranges between $1.90 and $4/GJ. In niche markets, where the feedstock is inexpensive and natural gas is not available, biogas can be a viable alternative energy source (Benson et al. 1986). A similar biogas manufacturing using poultry WtE by catalytic steam gasification process is described in Chapter 10.
Ethanol from Biomass
The cost of producing ethanol from biomass varies tremendously depending on the feedstock employed, the size and management of the facility and the market value of coproducts generated as part of some conversion processes. Cost information for ethanol plants to be built in the United States is most reliable for those using cornstarch, the basis of the US ethanol industry. A 5000 barrel/day plant (about 265 million l/day) built from the ground up will have a capital cost of about $140 million in 1987 dollars, or $0.53/l of annual capacity. Smaller facilities can have capital costs as high as $0.79/l of annual capacity, and poorly designed facilities of any size may cost $1.06/l of annual capacity. On the other hand, ethanol plants that are built from existing facilities, such as refineries or chemical plants, or ethanol plants integrated into a larger industrial facility, can have substantially lower capital costs, often in the range of $0.26–0.40/l of annual capacity.
Low‐end production costs are about $0.26/l. However, the volumetric heating value of ethanol is only 66% that of gasoline. This production cost, therefore, is equivalent to gasoline selling for $0.39/l before tax, transportation, or profit. In contrast, refinery price for gasoline in 1990 dollars was $0.20/l. Currently, the economics of fermentation are such the commercial viability of ethanol is entirely dependent on government incentives in the form of tax credit, currently $0.16 for each liter of ethanol used for fuel blending. Also, a strong market for fermentation by‐products is key factor in the economic viability of ethanol‐from‐corn.
Technology to convert lignocellulose to sugar is expected to reduce the cost of fuel ethanol, although dedicated economic information is not currently available. Capital cost for a 5000 barrel/day plant to produce ethanol from lignocellulose using simultaneous saccharification and fermentation is estimated to be $175 million (1994 dollars). Assuming wood costs $42/dry ton, ethanol can be produced for about $0.31/l. Combining economies of scale with advances in processing technology are projected to decrease production costs to 40.31/l. However, some reports have suggested that ethanol from cellulose will have to cost as little as $0.08–0.11/l to be competitive with the gasoline prices anticipated early in the twenty‐first century (Lynd et al. 1996; National Advisory Panel 1987).
Methanol from Biomass‐Derived Syngas
Capital investment for a 7500 barrel/day plant to produce methanol from biomass would be about $280 million in 1991 dollars. The cost of methanol from $40/dry ton of wood is projected to be about $0.27/l. Since the volumetric heating value of methanol is only 49% that of gasoline, the production cost from this plant is equivalent to gasoline selling for $0.55/l. Methanol from natural gas can be produced at significantly lower cost, but this assumes much larger plant capacities to capture economies of scale. Such large plants are not feasible for widely dispersed biomass feedstocks. New methanol‐synthesis technologies may be able to significantly reduce this price. The U.S. Department of Energy’s methanol from biomass program has a goal of $0.15/l ($7.90/GJ) based on feedstock cost of $1.90/GJ (Klass 1998).
Bio‐Oil from Fast Pyrolysis
Capital investment for a 5000 barrel/day plant to produce pyrolysis liquids would be $63 million in 1987 dollars. Assuming biomass feedstock was available at $1.70/GJ, this size plant could produce pyrolysis liquids for $0.18/l, which has an energy value of $6.70/GJ (Elliott et al. 1990).
Biodiesel from Vegetable Oils
Capital costs for a biodiesel facility are relatively modest, costing about $250 000 for a 50 barrel/day (3.2 million l/year). However, feedstock costs for production of biodiesel are relatively higher than feedstocks for production of other kinds of fuel, ranging from $0.16 to $0.26/l for waste fats to $0.53–0.79/l for vegetable oils. Under the best scenarios, a biodiesel plant might produce fuel for $0.44/l. Diesel fuel produced from petroleum typically sells for less than $0.25/l (Gavett et al. 1993).
Succinic Acid
Succinic acid is used in producing food and pharmaceutical products, surfactants and detergents, biodegradable solvents and plastics, and ingredients to stimulate animal and plant growth. Although it is a common metabolite formed by plants, animals, and microorganisms, its current commercial production of 15 000 T/Y is from petroleum. However, the recently discovered rumen organism Actinobacillus succinogenes produces succinic acid with yields as high as 110 g/l, offering prospects for producing this chemical from biorenewable resources. In contrast to most other commercial fermentations, the process consumes CO2 and, integrated with a process like ethanol fermentation, succinic acid production could contribute to reduction in greenhouse gas emissions.
Optimum yields occur under pH conditions where succinate salt rather than free acid is produced. Thus, recovery entails concentration of the salt, conversion back to free acid, and polishing of the acid to the desired purity. Downstream purification can account for 60–70% of the product cost.
Lactic Acid
Lactic acid, a three‐carbon molecule, is used in the production of polylactide resin, a biodegradable polymer expected to compete with polyethelene and polystyrene in the synthetic fibers and plastic markets. Lactic acid is currently produced by milling corn, separating the starch, hydrolyzing the starch to glucose, and anaerobically fermenting the glucose to lactic acid with Bacillus dextrolactius or Lactobacillus delbrueckii. Esterification with ethanol produces ethyl lactate, which can be polymerized to polylactate resin.
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