Page 30 - Synthetic Fuels Handbook

18 CHAPTER ONE

Ethanol is the most common biofuel, and over the years many engines have been
designed to run on it. Many of these could not run on regular gasoline, so it is debatable
whether ethanol is a replacement in them. In the late 1990s, engines started appearing that
by design can use either fuel. Ethanol is a direct replacement in these engines, but it is
debatable if these engines are unmodified, or factory modified for ethanol.
In reality, small amounts of biofuel are often blended with traditional fuels. The biofuel
portion of these fuels is a direct replacement for the fuel they offset, but the total offset is
small. For biodiesel, 5 percent or 20 percent are commonly approved by various engine
manufacturers.
Using waste biomass to produce energy can reduce the use of fossil fuels, reduce green-
house gas emissions, and reduce pollution and waste management problems. A recent pub-
lication by the European Union highlighted the potential for waste-derived bioenergy to
contribute to the reduction of global warming. The report concluded that 140 million barrels
of oil equivalent will be available from biomass by 2020, 46 percent from bio-wastes:
municipal solid waste (MSW), agricultural residues, farm waste, and other biodegradable
waste streams (European Environment Agency, 2006; Marshall, 2007).
Landfill sites generate gases as the waste buried in them undergoes anaerobic digestion.
These gases are known collectively as landfill gas (LFG); this can be burned and is a source
of renewable energy. Landfill gas (Chap. 12) contains approximately 50 percent methane
(the same gas that is found in some types of natural gas) and can be burned either directly
for heat or to generate electricity for public consumption. If LFG is not harvested, it escapes
into the atmosphere; this is not desirable because methane is a greenhouse gas (GHG), and
is more harmful than carbon dioxide. Methane has a global warming potential of 23 rela-
tive to carbon dioxide (i.e., 1 ton of methane produces the same GHG effect as 23 tons of
carbon dioxide).
Anaerobic digestion can be used as a distinct waste management strategy to reduce the
amount of waste sent to landfill and generate methane, or biogas. Any form of biomass
can be used in anaerobic digestion and will break down to produce methane, which can be
harvested and burned to generate heat, power, or to power certain automobiles.

1.2.7 Bioalcohol
Alcohol fuels are usually of biologic rather than petroleum sources. When obtained from
biologic sources, they are referred to bioalcohols (e.g., bioethanol). It is important to note
that there is no chemical difference between biologically produced alcohols and those
obtained from other sources. However, ethanol that is derived from petroleum should not
be considered safe for consumption as this alcohol contains about 5 percent methanol and
may cause blindness or death. This mixture may also not be purified by simple distillation,
as it forms an azeotropic mixture.
Bioalcohols are still in developmental and research stages. Use of optimized crops with
higher yields of energy (Chaps. 8 and 9), elimination of pesticides and fertilizers based
on petroleum, and a more rigorous accounting process will help improve the feasibility of
bioalcohols as fuels.
Alcohols are a useful type of liquid fuel because they combust rapidly and are often
cheap to produce. However, their acceptance is hampered by the fact that their production
often requires as much or even more fossil fuel than they replaced since they are typically
not primary sources of energy; however, they are a convenient way to store the energy for
transportation. No type of fuel production is 100 percent energy-efficient, thus some energy
is always lost in the conversion. This energy can be supplied by the original source, or from
other sources like fossil fuel reserves, solar radiation (either through photosynthesis or
photovoltaic panels), or hydro, wind, or nuclear energy.