Working Group III: Mitigation

Other reports in this collection Biomass Conversion

Globally, biomass has an annual primary production of 220 billion oven-dry tonnes (odt) or 4,500 EJ (Hall and Rosillo-Calle, 1998a). Of this, 270 EJ/yr might become available for bioenergy on a sustainable basis (Hall and Rosillo-Calle, 1998a) depending on the economics of production and use as well as the availability of suitable land. In addition to energy crops (Section, biomass resources include agricultural and forestry residues, landfill gas and municipal solid wastes. Since biomass is widely distributed it has good potential to provide rural areas with a renewable source of energy (Goldemberg, 2000). The challenge is to provide the sustainable management, conversion and delivery of bioenergy to the market place in the form of modern and competitive energy services (Hall and Rao, 1994).

At the domestic scale in developing countries, the use of firewood in cooking stoves is often inefficient and can lead to health problems. Use of appropriate technology to reduce firewood demand, avoid emissions, and improve health is a no-regrets reduction opportunity (see Section

Agricultural and forest residues such as bagasse, rice husks, and sawdust often have a disposal cost. Therefore, waste-to-energy conversion for heat and power generation and transport fuel production often has good economic and market potential, particularly in rural community applications, and is used widely in countries such as Sweden, the USA, Canada, Austria, and Finland (Hall and Rosillo-Calle, 1998b; Moomaw et al., 1999b; Svebio, 1998). Energy crops have less potential because of higher delivered costs in terms of US$/GJ of available energy.

Harvesting operations, transport methods, and distances to the conversion plant significantly impact on the energy balance of the overall biomass system (CEC, 1999; Moreira and Goldemberg, 1999). The generating plant or biorefinery must be located to minimize transport costs of the low energy density biomass as well as to minimize impacts on air and water use. However, economies of scale of the plant are often more significant than the additional transport costs involved (Dornburg and Faaij, 2000). The sugar cane industry has experience of harvesting and handling large volumes of biomass (up to 3Mt/yr at any one plant) with the bagasse residues often used for cogeneration on site to improve the efficiency of fuel utilization (Cogen, 1997; Korhonen et al., 1999). Excess power is exported. In Denmark about 40% of electricity generated is from biomass cogeneration plants using wood waste and straw. In Finland, about 10% of electricity generated is from biomass cogeneration plants using sawdust, forest residues, and pulp liquors (Pingoud et al., 1999; Savolainen, 2000). In other countries biomass cogeneration is utilized to a lesser degree as a result of unfavourable regulatory practices and structures within the electricity industry (Grohnheit, 1999; Lehtilä et al., 1997).

Land used for biomass production will have an opportunity cost attributed to it for the production of food or fibre, the value being a valid cost which can then be used in economic analyses. Table 3.31 shows the technical potential for energy crop production in 2050 to be 396EJ/yr from 1.28Gha of available land27. By 2100 the global land requirement for agriculture is estimated to reach about 1.7Gha, whereas 0.69-1.35Gha would then be needed to support future biomass energy requirements in order to meet a high-growth energy scenario (Goldemberg, 2000). Hence, land-use conflicts could then arise.

Several developing countries in Africa (e.g., Kenya) and Asia (e.g., Nepal) derive over 90% of their primary energy supply from traditional biomass. In India it currently provides 45% and in China 30%. Modern bioenergy applications at the village scale are gradually being implemented, leading to better and more efficient utilization which, in many instances, complement the use of the traditional fuels (FAO, 1997) and provide rural development (Hall and Rosillo-Cale, 1998b). For example, production of liquids for cooking, from biomass grown in small-scale plantations, using the Fischer-Tropsch process (modified to co-produce electricity by passing unconverted syngas through a small CCGT), is being evaluated for China using corn husks (Larson and Jin, 1999). Biomass and biofuel were identified by a US Department of Energy study (Interlaboratory Working Group, 1997) as critical technologies for minimizing the costs of reducing carbon emissions. Co-firing in coal-fired boilers, biomass-fuelled integrated gasification combined-cycle units (BIGCC) for the forest industry, and ethanol from the hydrolysis of lignocellulosics were the three areas specifically recognized as having most potential. Estimates of annual carbon offsets from the uptake of these technologies in the USA alone ranged from 16-24Mt, 4.8Mt, and 12.6-16.8Mt, respectively, by 2010. The near term energy savings from use of each of these technologies should cover the associated costs (Moore, 1998), with co-firing giving the lowest cost and technical risk.

Woody biomass blended with pulverized coal at up to 10%–15% of the fuel mix is being implemented, for example, in Denmark and the USA, but may be uneconomic as a consequence of coal being cheaper than biomass together with the costs of combustion plant conversion (Sulilatu, 1998). However, major environmental benefits can result including the reduction of SO2 and NOx emissions (van Doorn et al., 1996).

Table 3.31: Projection of technical energy potential from biomass by 2050
Derived from Fischer and Heilig, 1998; D�Apote, 1998; IIASA/WEC, 1998)
Region Population in 2050
Total land with crop production potential
Cultivated Land in 1990
Additional cultivated land required in 2050
Available area for biomass production in 2050
Max. Additional amount of energy from biomassa
Developedb   0.820 0.670 0.050 0.100 30
Latin America            
   Central & Caribbean 0.286 0.087 0.037 0.015 0.035 11
   South America 0.524 0.865 0.153 0.082 0.630 189
   Eastern 0.698 0.251 0.063 0.068 0.120 36
   Middle 0.284 0.383 0.043 0.052 0.288 86
   Northern 0.317 0.104 0.04 0.014 0.050 15
   Southern 0.106 0.044 0.016 0.012 0.016 5
   Western 0.639 0.196 0.090 0.096 0.010 3
Chinac           2
Rest of Asia            
   Western 0.387 0.042 0.037 0.010 -0.005 0
   South –Central 2.521 0.200 0.205 0.021 -0.026 0
   Eastern 1.722 0.175 0.131 0.008 0.036 11
   South –East 0.812 0.148 0.082 0.038 0.028 8
Total for regions above 8.296 2.495 0.897 0.416 1.28 396
Total biomass energy potential, EJ/yr 441d
a Assumed 15 odt/ha/yr and 20GJ/odt
b Here, OECD and Economies in Transition
c For China, the numbers are projected values from D�Apote (1998) and not maximum estimates.
d Includes 45 EJ/yr of current traditional biomass.

Gasification of biomass

Biofuels are generally easier to gasify than coal (see Section, and development of efficient BIGCC systems is nearing commercial realization. Several pilot and demonstration projects have been evaluated with varying degrees of success (Stahl and Neergaard, 1998; Irving, 1999; Pitcher and Lundberg, 1998). Capital investment for a high pressure, direct gasification combined-cycle plant of this scale is estimated to fall from over US$2,000/kW at present to around US$1,100/kW by 2030, with operating costs, including fuel supply, declining from 3.98c/kWh to 3.12c/kWh (EPRI/DOE, 1997). By way of comparison, capital costs for traditional combustion boiler/steam turbine technology were predicted to fall from the present US$1,965/kW to US$1,100/kW in the same period with current operating costs of 5.50c/kWh (reflecting the poor fuel efficiency compared with gasification) lowering to 3.87c/kWh.

A life cycle assessment of the production of electricity in a BIGCC plant showed 95% of carbon delivered was recycled (Mann and Spath, 1997). From the energy ratio analysis, one unit of fossil fuel input produced approximately 16 units of carbon neutral electricity exported to the grid.

Liquid biofuels

Ethanol production using fermentation techniques is commercially undertaken in Brazil from sugar cane (Moreira and Goldemberg, 1999), and in the USA from maize and other cereals. It is used as a straight fuel and/or as an oxygenate with gasoline at 5%-22% blends. Enzymatic hydrolysis of lignocellulosic feedstocks such as bagasse, rice husks, municipal green waste, wood and straw (EPRI/DOE, 1997) is being evaluated in a 1t/day pilot plant at the National Renewable Energy Laboratory and is nearing the commercial scale-up phase (Overend and Costello, 1998). Research into methanol from woody biomass continues with successful conversion of around 50% of the energy content of the biomass at a cost estimate of around US$0.90/litre (US$34/GJ) (Saller et al., 1998). In Sweden production of biofuels from woody biomass (short rotation forests or forest residues) was estimated to cost US$0.22/litre for methanol and US$0.54/litre for ethanol (Elam et al., 1994). However, the energy density (MJ/l) of methanol is around only 50% that of petrol and 65% for ethanol. Using the available feedstock for heat and power generation might be a preferable alternative (Rosa and Ribeiro, 1998).

Commercial processing plants for the medium scale production of biodiesel from the inter-esterification of triglycerides have been developed in France, Germany, Italy, Austria, Slovakia, and the USA (Austrian Biofuels Institute, 1997). Around 1.5 million tonnes is produced each year, with the largest plant having a capacity of 120,000 tonnes. Environmental benefits include low sulphur and particulate emissions. A positive energy ratio is claimed with 1 energy unit from fossil fuel inputs giving 3.2 energy units in the biodiesel (Korbitz, 1998). Conversely, other older studies suggest more energy is consumed than produced (Ulgiati et al., 1994).

Biodiesel production costs exceed fossil diesel refinery costs by a factor of three to four because of high feedstock costs even when grown on set-aside land (Veenendal et al., 1997), and they are unlikely to become more cost effective before 2010 (Scharmer, 1998). Commercial biodiesel has therefore only been implemented in countries where government incentives exist. Biofuels can only become competitive with cheap oil if significant government support is provided by way of fuel tax exemptions, subsidies (such as for use of set-aside surplus land), or if a value is placed on the environmental benefits resulting.

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