SEPA
United States
Environmental Protection
Agency
Office of Environmental
Engineering and Technology
Washington DC 20460
Research and Development
EPA-600/S7-80-173 Mar. 1981
Project Summary
Environmental, Operational
and Economic Aspects of
Thirteen Selected Energy
Technologies
L. Hoffman, S. E. Noren, and E. C. Hole
In an era of increases in the cost and
scarcity of fuels as well as continuing
concerns for a clean environment, it is
important to consider the various
options for the generation of steam
and electric power and the conversion
of fossil fuels into alternative forms of
energy.
About 19 percent of the current
U.S. energy production comes from
coal; 26 percent from natural gas; 46
percent from oil; and 9 percent from
other sources. However, the recover-
able resources of these fuels are sig-
nificantly different from our current
consumption patterns and are
estimated as follows: coal, 71
percent; natural gas, 12 percent; oil,
14 percent; other sources (nuclear,
assuming only light water reactors,
and hydropower), ? percent. Natural
gas and oil lack the price stability and
consistent availability for which a
reliable generating industry e.g.,
electric power, should be based.
Moreover, these scarce fuels are
needed for heating, industrial process-
ing and transportation. Therefore,
current technologies must be environ-
mentally enhanced and new technol-
ogies developed to use the nation's
abundant coal reserves. A number of
such technologies, now under devel-
opment and testing, could prove
successful and allow for the increased
use Of fossil fuel resources, such as
coal, heavy crudes and oil shale.
A better understanding of major
energy processes, their environmental
impacts, efficiencies, applications and
economics as described in this
publication will be a valuable guide to
enable the U.S. to make intelligent
decisions on the course of actions to
be taken in the energy-limited future.
This Project Summary was develop-
ed by EPA's Office of Environmental
Engineering and Technology,
Washington, DC, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
The report provides a review of 13
processes for generating energy or
converting fuel from one form to a more
useful form. These processes are either
already in commercial use or believed to
be commercially available and are
undergoing intensive research and
development. The processes are:
• conventional boiler (with steam
turbine)
• diesel generator
• fluidized-bed combustion
• combined cycle systems
• low/medium-Btu gasification
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• chemically active fluid bed (CAFB)
• indirect coal liquefaction
• high-Btu gasification
• surface oil shale processing
• in situ oil shale processing
• direct coal liquefaction
• fuel cells
• magnetohydrodynamics (MHD)
For each process discussed in this
report, there are six major sections:
overview; process description; applica-
tions; environmental considerations;
performance; and economics. The
material is based on information
obtained from available technical litera-
ture as well as from government and
industry sources (see Table 1).
Overview of Technologies
Conventional coal-fired steam
electric power plant efficiencies range
from about 31 to 38 percent. Newer
plants of this type will also have
efficiency values below 40 percent, and
it is unlikely that values exceeding 40
percent from conventional plants will be
realized in the foreseeable future. With-
out pollution control measures, coal
fired steam-electric plants cause un-
desirable environmental impacts.
Current state-of-the-art environmental
controls are capable of mitigating
known, undesirable pollution and other
environmental effects. Continuing
environmental regulatory activities are
expected to control the near-term un-
desirable effects resulting from the
increasing use of coal for steam-electric
plants.
Diesels have been used commercially
for more than 80 years. They are used
extensively to power moderate-sized,
stationary electric generators for a
variety of services. Although the output
of a large diesel generator is small com-
pared to a typical utility fossil-fuel
steam-electric generator, the attainable
efficiency is generally the same.
Recently, concern has developed over
the potential carcinogenic aspects of
diesel exhaust. Future use of stationary
diesel generators may well depend on
diesel emission control standards as
well as cost. Department of Energy
(DOE) experience indicates that diesel
energy is at least twice as expensive as
that from an electric utility (per kwh
electric energy). Diesel generators are
appropriate for selected applications,
however.
Fluidized-bed combustion technology
is currently in the research, develop-
ment, and demonstration stages. Some
manufacturers have begun to advertise
the availability of atmospheric com-
mercial/industrial scale units. The
attainable boiler efficiency is limited by
the same general loss components as
for a conventional boiler. Boiler effi-
ciency values equal to those attainable
by conventional boilers will depend on
the ability to achieve complete carbon
burn-up. The environmental effects of a
fluidized-bed boiler are similar to those
of an equivalent capacity conventional
boiler with flue gas desulfunzation
(FGD) burning the same coal. A major
difference, however, is the relatively
low NOx emissions and the amount and
nature ot the spent bed material
compared to the effluent from the FGD
system. Yet, for fluidized-bed combus-
tion with the same SO* removal, almost
three times as much limestone is
required. Spent bed material from a
fluidized-bed boiler contains apprecia-
ble CaO (i.e., quicklime) that may pre-
sent handling and disposal problems.
Researchers hope to find commercial
uses for the spent bed material. In the
near-term fluidized-bed boilers are
projected to compete with industrial/
commercial scale conventional boilers
with SO" emission control. Such units,
when developed, will permit coal to be
burned more conveniently at such
locations as schools, hospitals, shop-
ping centers, office buildings, and small
industrial parks.
Gas turbine-steam combined-cycle
power plants currently in operation
achieve overall efficiencies of around
40 percent. However, these systems
rely on gas or oil. Major emphasis
should then be on making today's
turbines run more efficiently on these
scarce fuels and on developing
improved turbines that will operate
efficiently on synthetic fuels.
Combined-cycle power plants using
gas-turbine and steam-turbine technol-
ogy have a number of key features
which could make them particularly
appealing to the utility industry. These
include quickstart capabilities, low
capital investment per kilowatt of
electric generation, relatively low
operating costs, and the capability for
use as a base-load or peaking power.
Another promising aspect is their
projected ability to use low-energy gas
from coal Since this low-Btu gas can be
clean burning, environmental control
problems and expense associated with
conventional coal-fired steam genera-
ting plants would be avoided. A
variation- of the combined gas-turbine
and steam-turbine system features the
direct combustion of coal in a pressur-
ized fluidized-bed (PFB). Although
internal particulate control is still re-
quired , the PFB offers the potential for
direct combustion of high-sulfur coal
without stack gas cleanup.
Low/medium-Btu gasification of coal
is currently used in Europe, South
Africa, and, to a limited extent, the U.S.
Coal is gasified by any of several pro-
cesses1 synthesis, pyrolysis, or hydro-
gasification. In synthesis, coal or char is
reacted with steam and oxygen or air.
This produces the heat for a reaction
that produces a mixture of hydrogen and
carbon monoxide. In pyrolysis, coal is
heated in a starved air atmosphere;
some gas and liquids result, the major
product being a coke residue. In hydro-
gasification, coal, coke, or char is
reacted with hydrogen to form methane.
Pipeline gas is produced by upgrading a
medium-Btu gas (see Figure 1).
Environmental problems common to
coal associated energy generating
systems will generally also apply to coal
gasification facilities. Additional
adverse environmental aspects of
proven and pilot-plant processes are
difficult to assess because of limited
data. The conversion efficiency, as
based on total energy input, is some-
what process and site-specific, and is
estimated to be in the 70 to 80 percent
range, including raw gas cleanup. The
value without gas cleanup (i.e., raw hot
gas output) is estimated to be as high as
90+ percent, when sensible heat for the
gas is included. The efficiencies of this
technology are not expected to improve
significantly. The cost is estimated at
$2.50 to $4.00 per million Btu.
The chemically active fluid bed (CAFB)
process uses a shallow fluidized-bed of
lime or lime-like material to produce a
clean, hot gaseous fuel from high sulfur
feedstock (e.g., residual oil). Solid fuel
feedstocks, such as coal are also
feasible. A 10 Mw demonstration plant,
constructed by Foster Wheeler at the La
Palma Power Station (Central Power
and Light Company) in San Benito,
Texas, is being sponsored by EPA. The
size of the particles in the product gas
stream, the vanadium (bound in a
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'able 1 . Summary of Representative Current and Projected Efficiencies of the Thirteen Energy Technologies
Process Efficiency (%)
Input Principal Current Projected
Technology Status Fuel(s) Output(s) (1980) (1990's) Comments
1 . Conventional Steam
Electric Plant
2. Diesel Generator
3. a) Atmospheric
•Fluidized-Bed
Combustion
b) Pressurized
Fluidized-Bed
Combustion
4. Combined Cycle
5. a) Low-Btu
Gasification
b) Medium-Btu
Gasification
6. Chemically Active
Fluid Bed (CAFB)
7. Indirect Coal
Liquefaction
8. High-Btu Gasification
9. Surface Oil Shale
Processing
10. Modified in situ Oil
Shale Processing
11. Direct Coal Liquefaction
12. Fuel Cells
13. Magnetohydrodynamics
(MHD)
Commercial
Commercial
Commercial
and R&D,
R&D
Commercial
and R&D
Commercial
and R&D
Commercial
and R&D
R&D
Commercial
and R&D
R&D
R&D
R&D
R&D
R&D
R&D
Coal
Diesel Oil
Coal
Coal
Gas or Oil
(or Coal)
Coal
Coal
Heavy
Residual
Oil or Coal
Coal
Coal
Oil Shale
Oil Shale
Coal
Fossil Fuel
(e.g., gas
obtained
from coal)
Coal
Electricity 34
Electricity 33
Steam (a)
Electricity (a)
Electricity 38
Low-Btu 86
Gas
Medium- 80
Btu Gas
Gas (a)
Hydrocarbon fa)
Products
High-Btu (a)
Gas
Oil and Gas (a)
Oil and Gas (a)
Hydrocar- (a)
don Products
Electricity (a)
Electricity (a)
38 Values for plants with flue
gas desulfurization (FGD).
Without FGD, values are 35.4
and 39.5 respectively.
36 Established technology.
85 Insufficient operating history
to establish efficiency value.
39 A combined cycle concept.
43 Currently fueled by gas or oil.
Projected efficiency is based
on an integrated coal, fed
gasifier.
90 The efficiency values include
the sensible heat component
and export power.
83 The efficiency values include
the sensible heat component.
87(b) The efficiency value includes
the sensible heat component.
58 Commercial in South Africa.
all U.S. activities R&D.
Efficiency value very depen-
dent on product mix.
75 The efficiency value includes
credit for export electric
power.
68 Substantial variation in ob-
tainable value depending on
very site-specific conditions.
68 Substantial variation in ob-
tainable value depending on
very site-specific conditions.
63 Value for EDS process.
Includes credit for by-products.
50 The efficiency value is for a
coal fueled (via gasifier) plant
with a steam-turbine bottom-
ing cycle.
48 The efficiency value is for an
open-cycle MHD/ steam plant
la) No U.S. commercial plants in existence or with an operating history.
Ibj Protected overall efficiency to produce electricity (via steam generator) is 31 percent
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• 100%
Energy input from coal
4.21%
Losses from ash, sulphur
product and latent heat
of gas
3~26%4 *
Gasifier radiation loss and
Stretford misc. losses
0.69% r r
Losses via coal pulverizer,
misc., less heat recapture
8.01%*-*
Product gas
sensible heat
°roduct gas heating value
12.22%
Various
condenser
losses
(latent heat)
3.75%
Export power*
(based on 3413 Btu/kwh)
75.87%
Product gas available heat
"If export power is calculated on the basis of 9000 Btu/kwh (the energy required to generate the equivalent
output), the system efficiency is 85.75% /vs. 79.62%) (i e., for product gas heating and sensible heat values
plus electrical energy based on Btu's required to produce equivalent electrical energy)
Figure 1. Heat flow diagram for low-Btu gasification plant.
mixture of oxides) emission level, and
the disposal of spent, sulfided limestone
are areas of concern. Since all activities
are research and development, no
actual full-scale performance data are
available and environmental data are
limited. The total gasification efficiency
is estimated to be about 87 percent.
Similarly, economic values are also
projections. EPA estimates that a retro-
fit CAFB plant to fuel a 500 Mw plant
would cost $172 per kw of installed
capacity. The operating cost is esti-
mated at 2-3 mills per kwh (1977
dollars).
Coal liquefaction produces liquid fuels
from coal. In indirect liquefaction, the
coal is gasified to make a synthesis gas
and then passed over a catalyst to pro-
duce alcohols (methanol) or paraffinic
hydrocarbons. In direct liquefaction, the
coal is liquefied without a gasification
intermediate step. Specific processes
are generally directed toward convert-
ing coal to liquid fuels with minimal
production of gases and organic solid
residues. The liquid products produced
vary with the type of process and the
type of coal used. Currently, only South
Africa is producing liquids from coal.
Commercial demonstration of coal
liquefaction has never been accom-
plished in the U.S. and current U.S.
activities are limited to research and
development and pilot-plant programs.
Environmental problems common to
fossil energy facilities will also apply to
coal liquefaction facilities. Liquefaction
processes also present some unique
problems, such as the need for charac-
terizing materials with carcinogenic
effects, characterizing and treating
wastes, fugitive emissions and efflu-
ents, and disposing of sludges and solid
wastes. These problems are generally
common to all liquefaction processes.
However, since no large-scale plants
are operating in the U.S., the only avail-
able data on emissions and effluents are
estimated from pilot-plant studies and
cannot be completely quantified for a
commercial operation. Projected effi-
ciencies for coal liquefaction facilities
are in the 55 to 70 percent range.
Accurate values for coal conversion
efficiencies will not be available until
commercial demonstration takes place.
Estimated costs for indirect coal lique-
faction plants are in the $7-10 p
million Btu range (1980 dollar
Generally, the estimated cost for dirt
coal liquefaction plants is less than t
cost for indirect liquefaction.
High-Btu gasification of coal also c;
be accomplished by synthesi
pyrolysis, or hydrogasification.
produce a pipeline quality gas, mediui
Btu gas (e.g., from hydrogasification)
cleaned and further treated. This tree
ment could include a shift conversion
obtain the proper carbon monoxide-t
hydrogen ratio followed by a secoi
purification process, followed by
methanation process. Environment
concerns common to coal-fired boil
facilities will also apply to coal gasi
cation facilities to some extent. Adc
tional unique adverse environment
impacts are difficult to estimate, f
commercial plants are in operation an
where in the world and assessmen
must be based on limited informatic
from pilot-plant studies which may n
be representative of a commerci
operation. Projected overall eneri
efficiencies for coal gasification ha\
been estimated to be approximately "/
percent. The estimated at-gate-costs
high-Btu gas produced by a gasificatic
plant are $4 to. $6 per million Btu (191
dollars).
Oil shale resources can be processc
either by conventional mining follow*
by surface processing or by in situ (
place) processing. In situ processing ca
be accomplished by either true i
modified in situ methods to extract c
from shale. Oil shale resources in tr
U.S. are estimated to exceed two trillic
barrels of petroleum with 25 to 3
percent of that estimate projected £
commercial. The only commercial pr<
duction facilities are in Russia (Estoni
and China with a combined productic
of approximately 150,000 barrels p<
day. The conventional process (convei
tional mining and surface retorting) t
produce a crude consists of four maj<
steps: mining the shale; crushing it 1
the proper size for the retort vesse
retorting the shale to release the oil; an
refining the oil to a high-quality produc
True in situ processes involve fracturin
the shale bed via vertical well bores 1
create permeability without mining <
removing material followed by unde
ground retorting. Retorting can also b
done via wellbores 'using naturi
permeability where it may exist. Th
modified in situ process involves minin
or removing by other means (such a
leaching or underreaming) up to 40 pe
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cent of the shale (i.e., in the retorting
section) in order to increase the void
volume and allow rubblization before
retorting. In modified in situ, the mined
shale can be surface retorted.
The fuel cell can efficiently use fuels
without an intermediate mechanical
step by converting chemical energy
directly to electricity. This technology
also offers many advantages, such as
modular construction, low environ-
mental emissions, high efficiency and
rapid response to load demand fluctua-
tions. Because of the modular construc-
tion, fuel cells are easily transported
and installation times and costs
reduced. This concept is not new. What
is new is the effort to capitalize on the
fuel cell's inherent flexibility, safety,
and efficiency by putting together a
generator system that can use a variety
of fuels to meet today's utility-scale
power needs economically. Environ-
mental considerations like low water
requirements, limited emissions, and
quiet operation help make fuel cell
plants a practical power alternative. But
since fuel cells use hydrocarbon fuels,
they share with conventional
generating processes the environ-
mental problems associated with
extracting and processing fossil fuels.
The required hydrogen for the fuel cell
power section can be derived by coal
gasification which would be an integral
part of the plant. The Energy Conversion
Alternatives Study (EGAS) team esti-
mated an overall efficiency of 50
percent for its conceptual molten
carbonate fuel cell power plant.
Although still in the prototype stage, the
fuel cell offers a means to produce
electricity efficiently on both small- and
large-scales. These systems could be
used to complement existing facilities or
supply new generating capacity where
environmental considerations restrict
conventional combustion plants.
In magnetohydrodynamics (MHD)
electricity is generated directly from
thermal energy, thus eliminating the
conversion step of thermal-to-
mechanical energy encountered in
conventional steam-electric genera-
tors. However, due to the nature of the
process, it would be inefficient to apply
MHD by itself to the large-scale genera-
tion of electricity. Therefore, its
eventual implementation is being
planned around combining MHD with a
conventional steam plant to make use of
the waste heat from the MHD
generator. The efficiency of such a com-
bined MHD/steam plant is predicted to
be about 50 percent, compared to 38
percent projected for conventional coal-
fired power plants with flue gas desul-
furization systems. Much of this
increase inefficiency is attributed to the
fact that all the rigid structures in MHD
generators are stationary, thus permit-
ting operation • at temperatures
approaching 5000°F. These high
temperatures result in higher efficien-
cies through the entire thermal cycle.
Although much work remains before
the widespread application of the MHD
energy conversion process to electric
utility power generation, there is experi-
mental evidence that MHD can signifi-
cantly improve overall power-plant
efficiencies. Another promising aspect
of this technology is its ability to remove,
during the process, pollutants such as
SO«, NOx, and particulates generated
during combustion of coal, thereby
eliminating the need for external flue
gas scrubbing to meet environmental
standards.
L. Hoffman, S. E. Noren, and E. C. Hole are with The Hoffman-Munter Corp.,
Silver Spring, MD 20910.
W. N. McCarthy is the EPA Project Officer (see below).
The complete report, entitled "Environmental, Operational and Economic
Aspects of Thirteen Selected Energy Technologies," (Order No. PB 81-153 926;
Cost: $18.50, 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 (RD-681)
401 M Street, S.W.
Washington DC 20460
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