Page 255 - Synthetic Fuels Handbook

FUELS FROM BIOMASS 241

only about 10 percent of the caloric content of the grain. When looked at in this light, it
does not seem to be so unreasonable to use some fertile land to grow fuel. Marginal land
and underutilized agricultural land can also be used to grow biomass for fuel.
Acid rain, which can damage lakes and forests, is a by-product of the combustion of
fossil fuels, particularly coal and oil. The high-sulfur content of these fuels together with
hot combustion temperatures result in the formation of sulfur dioxide (SO ) and nitrous
2
oxides (NO ), when they are burned to provide energy. The replacement of fossil fuels
x
with biomass can reduce the potential for acid rain. Biomass generally contains less than
0.1 percent sulfur by weight compared to low-sulfur coal with 0.5 to 4 percent sulfur.
Lower combustion temperatures and pollution control devices such as wet scrubbers and
electrostatic precipitators can also keep emissions of NO to a minimum when biomass
x
is burned to produce energy.
The final major environmental impact of biomass energy may be that of loss of biodi-
versity. Transforming natural ecosystems into energy plantations with a very small number
of crops, as few as one, can drastically reduce the biodiversity of a region. Such “monocul-
tures” lack the balance achieved by a diverse ecosystem, and are susceptible to widespread
damage by pests or disease.

8.4 FUELS FROM BIOMASS

The production of biofuels to replace oil and natural gas is in active development, focusing
on the use of cheap organic matter (usually cellulose, agricultural, and sewage waste) in the
efficient production of liquid and gas biofuels which yield high net energy gain. The carbon
in biofuels was recently extracted from atmospheric carbon dioxide by growing plants, so
burning it does not result in a net increase of carbon dioxide in the Earth’s atmosphere. As a
result, biofuels are seen by many as a way to reduce the amount of carbon dioxide released
into the atmosphere by using them to replace nonrenewable sources of energy.
Gasoline is a blend of hydrocarbons with some contaminants, including sulfur, nitrogen,
oxygen, and certain metals. Ethanol and methanol are biofuels that provide alternative to
gasoline (Table 8.1). Bioethanol is a fuel produced by processing familiar and renewable
crops such as cereals, sugar beet, and maize using natural fermentation. Blended with petrol
at 10 percent, bioethanol can be used in vehicles without the need to change fuel or engine
specifications.
Biofuels are important because they replace petroleum fuels and can be used to fuel
vehicles, but can also fuel engines or fuel cells for electricity generation (Kavalov and

TABLE 8.1 Current and Alternate Motor Fuels
Fuel type Available motor fuel

Traditional fuels Diesel and gasoline
Oxygenated fuels Ethanol, methanol, methyl tertiary butyl ether (MTBE), ethyl
tertiary butyl ether (ETBE), tertiary butyl alcohol (TBA), and
tertiary amyl methyl ether (TAME)
Alternative fuels Liquefied petroleum gases (LPG), ethanol, 85% (E85);
ethanol, 95% (E95); methanol, 85% (M85); methanol, neat
(M100); compressed natural gas (CNG); liquefied natural gas
(LNG); biodiesel (BD); hydrogen; and electricity
Source: AFDC, 1997.