Page 176 - Synthetic Fuels Handbook

162 CHAPTER FIVE

of petroleum (Dooley et al., 1978; Speight, 2007), but because of the difference between coal
liquids and petroleum, some modification of the basic procedure is usually required to make
the procedure applicable to coal liquids (Ruberto et al., 1976; Bartle, 1989).
The composition of coal liquids produced from coal depends very much on the character
of the coal and on the process conditions and, particularly, on the degree of hydrogen addi-
tion to the coal (Aczel et al., 1978; Schiller, 1978; Schwager et al., 1978; Wooton et al.,
1978; Whitehurst et al., 1980; Kershaw, 1989).
Current concepts for refining the products of coal liquefaction processes rely for the
most part on the already existing petroleum refineries, although it must be recognized
that the acidity (i.e., phenol content) of the coal liquids and their potential incompatibility
with conventional petroleum (including heavy oil) may pose new issues within the refinery
system (Speight, 1994, 2007).

5.6.4 The Future
With the continuing violence in the Middle East and (at the time of writing) oil prices in
excess of $90 per barrel, the issue of energy security is again of prime importance. Part of
this energy security can come by the production of liquid fuels from coal. As always, the
real question relates to economics—that is tied to the price of oil.
The Sasol technology, a third-generation Fischer-Tropsch process, was developed in
Germany and used in World War II, and later in South Africa. In the process, steam and
oxygen are passed over coke at high temperatures and pressures. Synthesis gas (a mixture
of carbon monoxide and hydrogen) is produced and then reassembled into liquid fuels
through the agency of the Fischer-Tropsch reaction (Chap. 7).
Although considered too expensive to compete with the production of liquid fuels
from petroleum, the liquid fuels produced from coal (by gasification and the conver-
sion of the synthesis gas) have been environmentally friendly insofar as they have no
sulfur and, therefore, are more in keeping with the recent laws regarding ultra-low
sulfur fuels.
The coal-to-liquid technology would complement the expanding tar-sands technology
(Chap. 4) allowing the long-predicted decline in petroleum production to be delayed for
decades and the geopolitics of energy would be rewritten.
Overall, the coal-to-liquids technology is one element of an integrated program that is
necessary to deal with energy fuel security and assurance of supply.
In fact, the technologies required to produce large-scale supplies of clean liquid
fuels from coal are not on the drawing boards or in laboratories. They are in use around
the world today, from countries such as South Africa, which has long relied on coal
liquefaction to provide a substantial percentage of its transportation fuels, to China,
India, Indonesia, and the Philippines.
The production of liquid fuels from coal begins with coal as a raw material or feedstock.
Both indirect and direct liquefaction processes have been proven.
In indirect coal liquefaction, coal is subjected to intense heat and pressure to cre-
ate a synthesis gas comprised of hydrogen and carbon monoxide. The synthetic gas
is treated to remove impurities and unwanted compounds such as mercury and sulfur.
This clean gas enters a second stage (Fischer-Tropsch process) which converts the
synthesis gas into clean liquid fuels and other chemical products. Diesel fuel pro-
duced by Fischer-Tropsch synthesis is virtually sulfur-free with low aromatics and a
high cetane value and is cleaner than conventional diesel. It burns more completely
and emissions are significantly lower than low-sulfur diesel. Most of the CO is
2
already concentrated and ready for capture and possible sequestration or for use in
enhanced oil or gas recovery.