3.8.4.3.2 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
3.6.4.3), 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 4.3.2.1).
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
Billion
|
Total land with crop production potential
Gha
|
Cultivated Land in 1990
Gha
|
Additional cultivated land required in 2050
Gha
|
Available area for biomass production in 2050
Gha
|
Max. Additional amount of energy from biomassa
EJ/yr
|
| |
| 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 |
| |
|
|
|
|
|
|
| Africa |
|
|
|
|
|
|
| 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 |
| |
| |
Gasification of biomass
Biofuels are generally easier to gasify than coal (see Section
3.8.4.1.3), 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.
