&EFA
United States
Environmental Protection
Agency
Office of Environmental Engineering
and Technology
Washington DC 20460
Research and Development
EPA-600/S7-81-153 Oct. 1981
Project Summary
Environmental and Economic
Aspects of Indirect Coal
Liquefaction Processes:
A Report Emphasizing the
Relationship Between
Product Mix and Efficiency
L. Hoffman
Considerable activity is under way
in the U.S. to address intermediate
and longer range energy supply re-
quirements, in this regard, even
though petroleum reserves and, to a
lesser extent natural gas reserves, are
quite limited, the U.S. has plentiful
coal resources. Even so, our society
and supporting infrastructure depend
greatly on liquid and gaseous fuels.
We are forced at present to import
approximately 40 percent of our oil.
Thus, considerable efforts have and
are being directed to developing
technically sound and environmentally
acceptable technologies to convert
coal to gaseous and liquid fuels.
The full report addresses selected
indirect coal conversion technologies,
associated efficiencies, environmental
aspects and relative economics. The
intent is to provide insight into the
impact of liquid/gas product mixes on
process efficiency for a variety of
energy production scenarios incor-
porating indirect coal liquefaction
technologies.
This Project Summary was devel-
oped by EPA's Office of Environmental
Engineering and Technology, Wash-
ington. DC, to announce key findings
of a study that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
In September of 1980 the U.S.
Environmental Protection'Agency (EPA)
published: "Environmental, Operational
and Economic Aspects of Thirteen
Selected Energy Technologies" (EPA-
600/7-80-173, NTIS No. PB81 -153926),
a study that described selected fuel
utilization and conversion technologies.
Because the amounts of gaseous and
liquid products depend on process
conditions and because these conditions
can be altered to produce more or less of
a specific product, an analysis was
made to relate product mix to the
efficiency of a synthetic fuel process.
This analysis was based on the capability
of a process to (1 (produce the maximum
amount of liquid fuel, (2) recover a
useful product based on recovering the
maximum input energy, and (3) maximize
its efficiency to produce a preselected
output (i.e., a definite liquid-to-gas
ratio). Normally, a resultant reduction in
pollutant emissions and effluences will
occur per unit output if the efficiency of
a given process is maximized.
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Discussion
The demonstrated coal reserve base
of the U.S. on January 1, 1974 was
estimated at 475 billion tons. This
quantity is widely distributed geograph-
ically, with 45 percent in the states east
of the Mississippi River and the rest in
the western states, including Alaska.
However, quantities of different ranks
as well as the amounts amenable to
production by underground and surface
mining methods differ markedly in
different areas.
The Nation's substantial coal re-
sources can be used in two ways: 1)
directly as coal, or 2) as a feedstock for
conversion into an alternate fuel form
(e.g., oil). Because in any conversion
process some of the total energy is lost,
from an energy conservation consid-
eration, it is generally best to use coal
directly. However, there are numerous
applications that cannot use coal, such
as motor vehicle combustion engines.
Coal liquefaction processes can be
classified as either direct or indirect. In
indirect liquefaction, the coal is first
gasified to make a synthesis gas and
then passed over a catalyst to produce
alcohols (methanol) or parafinic hydro-
carbons. A major advantage of indirect
liquefaction is that essentially all of the
sulfur and nitrogen in the coal can be
separated in the gaseous phase and
thus eliminated from the liquid products.
With direct processes, however, these
materials are difficult and expensive to
remove.
The indirect liquefaction processes
receiving significant attention are the
Coal-to-Methanol, Fischer-Tropsch and
the Mobil M. A modified Fischer-
Tropsch process, capable of producing a
range of hydrocarbon products, is in
commercial use in South Africa. The
Mobil process, which produces gasoline
as its principal product is in the
demonstration stage.
The environmental problems common
to fossil energy facilities will also apply
to coal liquefaction facilities. However,
liquefaction facilities present some
unique environmental concerns due to
incomplete combustion of the process:
the presence of a wide variety of organic
compounds, H2S and other reduced
sulfur compounds, and spent catalyst.
Since no large-scale domestic plants
are in operation, the only available data
on emissions and effluences are esti-
mates based on bench-scale, pilot and
demonstration synfuel plants and
related industries.
There have been a number of esti-
mates and assessments of the obtainable
efficiencies from indirect liquefaction
processes. Some estimates have been
based on energy balance approaches
and/or the performance of process
elements comprising the overall con-
version system. Table 1 indicates the
estimated thermal efficiency for the co-
production of gasoline and synthetic
natural gas (SNG) using the Mobil
methanol-to-gasoline technology. The
reports show that as one moves away
from a gaseous product to gas and liquid
co-products towards nothing but liquids,
the efficiency decreases. Thus, as the
yields of gasoline and hydrocarbon
liquids are increased the amount of
energy loss increases. It is noted that
the Mobil process is inherently more
efficient than the Fischer-Tropsch
process.
The analysis estimates hpw the
overall efficiency would vary as the
liquid-gaseous product ratios are
changed. Figure 1 is the estimate for
product mix versus efficiency for the
Sasol type Fischer-Tropsch technology.
The products of coal liquefaction span
a broad range of chemical compounds,
depending on the specific liquefaction
processes and feedstocks used. Many
by-products of coal liquefaction and
associated discharges have been identi-
fied, but the full range of chemicals
created and their potential environ-
mental effects have not been completely
characterized. The report lists the
general environmental residuals from
the indirect liquefaction process. The
potential environmental and health
hazards posed by liquefaction processes
are uncertain. The chemical structure of
many species appears to indicate a
potential carcinogenic risk that is higher
than that of conventional petroleum
products.
Although it is difficult to provide
projections of the cost of synthetic fuels
from indirect liquefaction processes,
the analysis estimates the relative cost
of conversion in terms of cost per million
Btu of product output. Table 2 presents
this assessment of relative costs.
Conclusions
1. There is a significant difference in
the thermal efficiencies of the
coal-to-methanol, Mobil M, and
the Fischer-Tropsch processes
when compared on a similar basis.
In general, the thermal efficien-
cies are highest for coal-to-
methanol and lowest for Fischer-
Tropsch (F-T). When the liquid-
fuel component contains approx-
imately 25 percent of the Btu
output, the Mobil M process is
estimated to be approximately 15
percent more efficient than the
Fischer-Tropsch process.
2. The thermal efficiency for each of
the above processes decreases as
the percentage of the liquid pro-
ducts increases. Since thermal
efficiencies are higher with greater
percentages of gaseous outputs
and are reduced with additional
Tablet.
Estimated Thermal Efficiency for Co-production of Gasoline & SNG with
the Mobil M Process* (Subbituminous Coal, Lurgi Gasifier, Methanol
Process, Mobil M Process)
Input
W6 Btu/Hr
Percent of Input
(Btu Basis)
Coal
Coal Fines (Excess)
Net Input
Output*
19,383
(872)
18,511
SNG
CaLPG
CtLPG
10 RVP Gasoline
Power (Process Excess)
Total
6.067
247
385
4,689
18C
1 1.406
32.8
1.3
2.1
25.3
0.1
61.6°
81 Based on subbituminous coal with as-received heating value of 8500 Btu/lb.
bl In addition, there are small amounts of sulfur & ammonia with economic value.
c) Direct Thermal Equivalent Value.
"' Reference in full report indicates an efficiency of 61% with gasoline containing 24%
of the input Btu's.
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40-
o
I
3
10
co
15
30-
I
20-
10-
37 40 45
Overall Efficiency (Percent)
50
a Value based on a reference in the full report for the pro-
duction of gasoline and diesel fuel. Also provided as F-T
maximum liquid value.
b Values from full report. Also provided as F-T maximum
Btu values.
c Values (shown in full report) based on Mobil M liquid/gas
ratio with methane reforming as required to provide de-
sired liquid/gas ratio.
Figure 1. Estimate of obtainable efficiency with product mix for Sasol Type
Fischer-Tropsch Technology (using subbituminous coal and lurgi
gasifier).
Table 2. Synfuels-from-coal Projected Efficiencies & Relative Cost*
Product(s) of Interest
(With Btu percentages of input) Efficiency
Relative Cost
per Btu of Product
Methanol
Liquids-34%. Gas-32%
Liquids-53%
Methanol-Mobil M
Liquids-31%. Gas-30%
Liquids-49%
Fischer-Tropsch
Liquids-24%. Gas-29%
Liquids-37%
66%
53%
61%
49%
53%
37%
1.0 Reference
1.3
1.1
1.5
1.3
2.0
reforming of methane, it is desir-
able from resource conservation
and environmental standpoints to
increase the use of gaseous fuels
and minimize the demand for
liquid fuels.
3. The cost per Btu of product at
reasonable equivalent liquid/gas
ratios is greatest for Fischer-
Tropsch and lowest for the coal-to-
methanol process.
4. The reduction in environmental
impacts resulting from increased
efficiencies due to modifying the
product mix (i.e., by process
and/or output mix selection),
although not completely quanti-
fiable, appears to present a sig-
nificant opportunity for reducing
pollution.
5. In the national interest of maxi-
mizing conservation of energy
resources and minimizing envi-
ronmental impacts, energy planners
should consider applications that
will maximize the use of synthetic
gaseous-fuels.
"Based on reference in full report.
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L Hoffman is with Hoffman-Holt. Inc.. 750 Georgia Avenue, Suite El34, Silver
Spring, MD20910.
Morris Altschuler is the EPA Project Officer (see below).
The complete report, entitled "Environmental and Economic Aspects of Indirect
Coal Liquefaction Processes: A Report Emphasizing the Relationship Between
Product Mix and Efficiency." (Order No. PB 82- 103 581; Cost: $6.50, subject
to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Office of Environmental Engineering and Technology
U.S. Environmental Protection Agency
Washington, DC 20460
US GOVERNMENT PRINTING OFFICE; 1981—559-017/7417
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Environmental Protection
Agency
Center for Environmental Research
Information
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