Page 237 - Synthetic Fuels Handbook

FUELS FROM BIOMASS 223

Biomass feedstocks and fuels exhibit a wide range of physical, chemical, and agricultural/
process-engineering properties. Despite their wide range of possible sources, biomass feed-
stocks are remarkably uniform in many of their fuel properties, compared with competing
feedstocks such as coal or petroleum.
For example, there are many types of coal and the gross heating value of these types
varies from 8600 to 12,900 Btu/lb (20–30 GJ/t). However, nearly all kinds of biomass feed-
stocks destined for combustion fall in the range 6450 to 8200 Btu/lb (15–19 GJ/t) (Wright
et al., 2006). For most agricultural residues, the heating values are even more uniform—
approximately 6450 to 7300 Btu/lb (15–17 GJ/t); the values for most woody materials are
7750 to 8200 Btu/lb (8–19 GJ/t). Moisture content is probably the most important deter-
minant of heating value. Air-dried biomass typically has about 15 to 20 percent moisture,
whereas the moisture content for oven-dried biomass is around 0 percent. Moisture content
is also an important characteristic of coals, varying in the range of 2 to 30 percent. However,
the bulk density (and hence energy density) of most biomass feedstocks is generally low,
even after densification, about 10 and 40 percent of the bulk density of most fossil fuels.
Liquid biofuels have comparable bulk densities to fossil fuels.

8.1 BIOMASS FUELS

Solid biofuels such as wood (Chap. 9) or dried dung have been used since man learned to
control fire.
On the other hand, liquid biofuels for industrial applications was used since the early
days of the car industry. Nikolaus August Otto, the inventor of the combustion engine, con-
ceived his invention to run on ethanol while Rudolf Diesel, the inventor of the diesel engine,
conceived it to run on peanut oil. Henry Ford originally had designed the Ford Model T,
a car produced between 1903 and 1926, to run completely on ethanol. Ford’s desires to
mass produce electric cars did not come to fruition. However, when crude oil began being
cheaply extracted from deeper in the soil (thanks to oil reserves discovered in Pennsylvania
and Texas), cars began using fuels from oil.
Nevertheless, before World War II, biofuels were seen as providing an alternative to
imported oil in countries such as Germany, which sold a blend of gasoline with alcohol
fermented from potatoes under the name Reichskraftsprit. In Britain, grain alcohol was
blended with petrol by the Distillers Company Ltd. under the name Discol and marketed
through Esso’s affiliate Cleveland.
After the war, cheap Middle Eastern oil lessened interest in biofuels. Then, with the oil
shocks of 1973 and 1979, there was an increase in interests from governments and academ-
ics in biofuels. However, interest decreased with the counter-shock of 1986 that made oil
prices cheaper again. But since about 2000 with rising oil prices, concerns over the poten-
tial oil peak, greenhouse gas emissions (global warming), and instability in the Middle East
are pushing renewed interest in biofuels. Government officials have made statements and
given fiscal aid in favor of biofuels, which can play a major role in the future.
The supply of crude oil, the basic feedstock for refineries and for the petrochemical
industry, is finite and its dominant position will become unsustainable as supply/demand
issues erode its economic advantage over other alternative feedstocks. This situation will
be mitigated to some extent by the exploitation of more technically challenging fossil
resources and the introduction of new technologies for fuels and chemicals production
from natural gas and coal.
However, the use of fossil resources at current rates will have serious and irreversible
consequences for the global climate. Consequently, there is a renewed interest in the utili-
zation of plant-based matter as a raw material feedstock for the chemicals industry. Plants