Page 37 - Synthetic Fuels Handbook

FUEL SOURCES 25

With respect to coal, there are several processes for the conversion of coal to gas. One
in particular, the Karrick process, is a low temperature carbonization process in which coal
is heated at 360 to 749°C (680 to 1380°F) in the absence of air to produce oil and gas. For
example, Karrick processing of 1 ton (2000 lb) of coal yields up to 1 bbl of coal tar
(12 percent by weight, rich in lower molecular weight hydrocarbons suitable for processing
3
into fuels), 3000 ft of fuel gas (a mixture of hydrogen, carbon monoxide, methane, and
other volatile hydrocarbons), and 1500 lb of solid smokeless char or semicoke. Smokeless
char can be used for utility boilers and cooking coal in steel smelters, yields more heat than
raw coal, and can be converted to water gas which, in turn, can be converted to hydrocarbon
fuel by the Fischer-Tropsch process.

1.4.4 Bioprocesses

A bioprocess is any process that uses complete living cells or organisms or their compo-
nents (e.g., bacteria, enzymes) to effect a desired physical and/or chemical change in the
feedstock. Transport of energy and mass is fundamental to many biological and environ-
mental processes.
Modern bioprocess technology used this principle and is actually an extension of older
methods for developing useful products by taking advantage of natural biologic activities.
Although more sophisticated, modern bioprocess technology is based on the same prin-
ciple; combining living matter (whole organisms or enzymes) with nutrients under the
conditions necessary to make the desired end product. Bioprocesses have become widely
used in several fields of commercial biotechnology, such as production of enzymes (used,
e.g., in food processing and waste management) and antibiotics.
Since bioprocesses use living material, they offer several advantages over conventional
chemical methods of production. Bioprocesses usually require lower temperature, pressure,
and pH (the measure of acidity) and can use renewable resources (biomass) as raw materials.
In addition, greater quantities can be produced with less energy consumption.
In most bioprocesses, enzymes are used to catalyze the biochemic reactions of whole
microorganisms or their cellular components. The biologic catalyst causes the reactions to
occur but is not changed. After a series of such reactions which take place in large vessels
(fermenters or fermentation tanks), the initial raw materials are chemically changed to form
the desired end product. Nevertheless, there are challenges to the use of bioprocesses in the
production of synthetic fuels.
First, the conditions under which the reactions occur must be rigidly maintained.
Temperature, pressure, pH, oxygen content, and flow rate are some of the process param-
eters that must be kept at very specific levels. With the development of automated and
computerized equipment, it is becoming much easier to accurately monitor reaction condi-
tions and thus increase production efficiency.
Second, the reactions can result in the formation of many unwanted by-products. The
presence of contaminating waste material often poses a twofold problem related to (a) the
means to recover (or separate) the end product in a way that leaves as little residue as pos-
sible in the catalytic system, and (b) the means by which the desired product can be isolated
in pure form.

1.5 REFERENCES

American Coalition for Ethanol: “Benefits of Ethanol,” 2004, http://www.ethanol.org.
Bartis, J. T., T. LaTourrette, L. Dixon, D. J. Peterson, and G. Cecchine: “Oil Shale Development in
the United States Prospects and Policy Issues,” Report No. MG-414-NETL, RAND Corporation,
Santa Monica, Calif., 2005.