Biomedical Engineering Reference
In-Depth Information
dioxide (a major GHG) to the atmosphere. Biomass could, on the other hand,
substitute fossil hydrocarbons either as a fuel or as a chemical feedstock.
Gasification of biomass into CO and H 2 provides a good base for produc-
tion of liquid transportation fuels, such as gasoline, and synthetic chemicals,
such as methanol. It also produces methane, which can be burned directly
for energy production.
1.2.2.5 Liquefaction
Liquefaction of solid biomass into liquid fuel can be done through pyrolysis,
gasification, and through hydrothermal process. In the latter process, biomass
is converted into an oily liquid by contacting the biomass with water at ele-
vated temperatures (300
350 C) and high pressure (12
20 MPa) for a
period of time. There are several other means including the supercritical
water process (Chapter 9) for direct liquefaction of biomass. Behrendt et al.
(2008) presented a review of these processes.
1.3 MOTIVATION FOR BIOMASS CONVERSION
Biomass conversion especially into heat and light is as ancient as human civ-
ilization. Discovery of fire from wood started the scientific development of
human race that set it apart from other creatures. Its use waned due to the
availability of more energy dense and convenient fossil fuels like coal and
oil. However, there has been a recent surge of interest in conversion of
biomass into gas or liquid. It is motivated mainly by following three factors:
1. Renewability benefits
2. Environmental benefits
3. Sociopolitical benefits.
A brief description of these benefits is given in the following sections.
1.3.1 Renewability Benefits
Fossil fuels like coal, oil, and gas are practical convenient sources of energy,
and they meet the energy demands of society very effectively. However, there is
one major problem: fossil fuel resources are finite and not renewable. Biomass,
on the other hand, grows and is hence renewable. A crop cut this year could
grow again next year; a tree cut today may grow up within a decade through
fresh growth. Unlike fossil fuels, the biomass is not likely to be depleted with
consumption. For this reason, its use is sustainable, and this feature is contribut-
ing to the growing interest in biomass use especially for energy production.
We may argue against cutting trees for energy supply because they serve
as a CO 2 sink. This is true, but a tree stops absorbing CO 2 after it stops
growing or dies. On the other hand, if left alone on the forest floor it can
release CO 2 through natural degradation or in a forest fire. Furthermore, a
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