EPA
Decision
Jnited States
nvironmental
'rotection Agency
Office of
Research and
Development
Energy,
Minerals and
Industry
EPA-600/9-77-013
June 1977
Advanced
Fossil Fuels
and the
Environment
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ADVANCED
FOSSIL FUEL
AND THE
ENVIRONMENT:
An Executive Report
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CONTENTS
Introduction 1
Chemical Coal Cleaning 3
Synthetic Fuels 7
Chemically Active Fluid Bed 13
Oil Shale 16
Liquid Fuels Cleaning 19
Prospect 22
Further Reading 23
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CHEMICAL
COAL
CLEANING
Process
Chemical coal cleaning is used to remove sulfur and other
pollutants from coal before it is burned. Sulfur is found in
coal in two general forms: organic and pyritic. Organic
sulfur is part of the molecular structure of coal, while
pyritic sulfur, or iron sulfide, is part of the mineral portion
of coal. The sulfur content of coal, both organic and
pyritic, ranges from less than 1% to over 8%, depending
on the coal type. Pyritic sulfur accounts for about half of
the total sulfur in a given type of coal. When coal is
burned, the pyritic sulfur, along with some of the organic
sulfur, is transformed to sulfur dioxide and becomes a
major source of air pollution. Chemical cleaning, which
involves leaching to wash out pyritic sulfur and heating to
break the bonds that bind the organic sulfur to coal, is
potentially more effective in ridding coal of its pollutants
than conventional physical cleaning methods.
Four chemical coal cleaning methods are currently being
evaluated by EPA. These are:
Meyers process
Hydrothermal process
Flash desulfurization process
Microwave process.
Meyers Process In the Meyers process, a heated
liquid iron sulfate leaching solution is reacted with ground
coal. This leaching action releases pyritic sulfur as well as
iron, alkaline ash, and other impurities. Following the
leaching, the coal is washed to remove these
contaminants and the leaching solution is then processed
for reuse. No organically bound sulfur is removed
because the leaching solution does not penetrate the
carbon-coal matrix. The Meyers process is 95% effective
in removing pyritic sulfur in pilot plant tests (7 metric tons
per day).
Hydrothermal Process The hydrothermal process
adds a leaching solution of sodium hydroxide, calcium
hydroxide, or their combination, to a mixture of crushed
coal and water at moderate temperatures. This heating/
leaching transforms the solid sulfur compounds and ash
to a solution, which can then be separated from the coal.
This process removes up to 95% of the pyritic sulfur
and 40% of the organic sulfur in pilot plant tests (1A ton
per day).
Flash Desulfurization Process This process exposes
coal to hydrogen at low pressure and high temperature. In
this reaction, the sulfur in the coal is released into the gas
stream where it is purified. Flash desulfurization removes
over 90% of the total sulfur content of coal in laboratory
tests.
Microwave Process The microwave process heats
coal to high temperatures so that the volatile parts of the
pyritic sulfur are vaporized for separate recovery. This
process is being evaluated to determine how much of the
sulfur can be removed.
Rationale
The successful development of chemical coal cleaning
and its adoption by the public and private sectors could
potentially:
Assure removal of pyritic and organic sulfur
from coal, while at the same time maintain a high
level of energy content in the cleaned coal.
Physical coal cleaning methods in industrial use
today remove some of the pyritic sulfur but do not
remove organic sulfur. The amount of pyritic sulfur
removed by physical methods ranges from 50% to
70%. In removing this pyritic sulfur, however,
physical cleaning methods also significantly reduce
the energy content of coal.
Offer a viable alternative to smaller users of coal
for control of air pollution from combustion.
Some industrial users of coal may not be able to use
flue gas desulfurization equipment because its size
may be incompatible with installed combustion
equipment, or the cost of adding stack gas
scrubbers may preclude economical operation of
the industrial plant.
Provide an economic advantage to coal users.
Initial cost/benefit analyses of cleaning coal using
both chemical and physical methods plus flue gas
desulfurization indicate a net cost saving to coal
users compared with the use of flue gas scrubbers
alone. Although some of the coal is inevitably lost in
the cleaning process, thereby reducing the total
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coal cleaned and its pyritic sulfur content. If the Meyers
process proves to be efficient and economical, this could
be an advantage to small industrial users of coal who may
not be able to afford stack-gas contaminant removal
technologies.
Program
The four chemical cleaning methods being sponsored by
the EPA Interagency Program are currently undergoing
careful evaluation:
Meyers Process Development is at the pilot-
plant stage and is receiving the major portion of
current Interagency Program funds allocated to
chemical coal cleaning because it appears to be the
most promising of the four technologies under study.
EPA is funding $4 million for a one-year demon-
stration of the process, scheduled to begin in the
spring of 1977. The reactor test unit was designed by
Procon, Inc., Los Angeles. Construction of the unit
began in November 1976, at a site near Capistrano,
California. TRW, Inc., Redondo Beach, California,
will operate the pilot plant. The unit, which will treat
about 7 metric tons of coal per day, performs only
leaching and regeneration operations. Dewatering,
drying, and sulfur removal will be done in the
laboratory using coal samples from the test unit.
Bench-scale support and applicability studies will be
carried out concurrent with the test of the pilot plant.
The actual operation of this pilot plant is expected to
demonstrate more effective coal cleaning process-
ing and lower costs than previously indicated in
laboratory and bench-scale tests. If these
expectations are realized, EPA may
recommend completion of the pilot plant
to add dewatering, drying, and sulfur
removal equipment. Further
testing will then define process
applicability, design, and cost data. Industrial and utility
support will be sought during the test to help identify
practical operating problems.
Flash desulfurization Experiments are under
way at the Institute of Gas Technology (IGT) in
Chicago to establish the potential of this process.
EPA is funding $370,000 for this 20-month project.
Chemical reactions to remove nitrogen as well as
sulfur are being evaluated as a part of this
EPA-sponsored program.
Hydrothermal coal cleaning This process was
investigated by Battelle Laboratories in Columbus,
Ohio. Although the process is technologically
feasible, it does not appear to be cost competitive
with other chemical coal cleaning methods.
Microwave treatment Research performed at
General Electric Company, Valley Forge,
Pennsylvania, is currently being reviewed by EPA to
determine the potential of microwave treatment to
release both the pyritic and the organic sulfur in
coal.
EPA also has a large ongoing program of environmental
assessment of chemical coal cleaning processes.
Process streams, compounds, and discharges that have
adverse health and ecological effects are being analyzed.
Results are used to establish permissible concentrations
of potentially hazardous substances. Environmental
guidelines for developers of coal cleaning processes will
be based on the permissible concentrations determined in
these studies.
As an adjunct to this chemical cleaning research, EPA and
the U.S. Bureau of Mines plan to use computer modeling
HYDROTHERMAL
MEYERS PROCESS
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SYNTHETIC
FUELS
Process
The federal government is giving priority to the develop-
ment of coal gasification and liquefaction processes. Such
processes, it is hoped, will produce an adequate supply of
synthetic gaseous and liquid fuels as sources of domestic
petroleum are exhausted and petroleum imports become
more expensive. The prime responsibility for the actual
development of these coal conversion processes belongs
to ERDA. The EPA responsibility is to ensure that these
processes do not create adverse health and ecological
effects. Major EPA concerns are the nature of pollutant
by-products, the locations in the process stream where
environmental control technologies should be integrated,
and the development of effective environmental control
techniques.
Synthetic fuel development research is concentrated on
producing substitute natural gas (SNG) and liquid fuels,
primarily for use as refinery feedstock and in electric
power generation. However, gasification units are already
being used by industry and more are scheduled to be
installed. Thus, it is logical to assume that industry, rather
than the electric utilities, will be the first to adopt advanced
gasification techniques as they become ready for
commercial use.
Coal gasification can produce iow-, medium-, and
high-Btu gas. The low-Btu gas has a heating value of 100
to 200 Btu per cubic foot and is used as a fuel feedstock
or to generate power in combined gas-steam turbine
power cycles. The medium-Btu gas has a heating value of
300 to 650 Btu per cubic foot and is usually used as a
feedstock in the production of high-Btu gas. This high-Btu
gas, with a heating value of 950 to 1,000 Btu per cubic
foot, can be substituted for natural gas in industrial and
residential consumption.
Coal liquefaction is used to produce an entire range of
liquid products from coal. These products include fuel oil,
gasoline, jet fuel, and diesel oil. Processes are being
developed and improved to increase the supply of
nonpolluting liquid fuels as well as to facilitate their
transport and use. Current emphasis is being placed on
the development of lower grade synthetic fuels suitable
for firing industrial and electric utility boilers and gas
turbines.
Coal Gasification Process
Coal is gasified by applying heat and pressure or a
catalyst to break down the components of coal to form a
synthesis gas containing mainly carbon monoxide, hydro-
gen, and some methane. The gas formed in this way may
also contain carbon dioxide, nitrogen, water vapor, and
contaminants such as hydrogen sulfide and ash.
In simple gasification, a synthetic gas is produced by
reacting coal with steam or hydrogen and air or oxygen. If
air is used, a low-Btu, nitrogen-rich gas is produced. The
nitrogen limits the heating value of the synthesis gas and
could cause release of environmentally hazardous
nitrogen oxides (NOx) if the gas were burned as fuel. The
gas also will contain sulfur oxides and other pollutants
that have to be removed.
Alternatively, if oxygen is used, medium-Btu gas is
produced. This product gas contains some sulfur oxides
but no nitrogen. It is usually intermediate to the production
of high-Btu gas.
Other gasification reactions use hydrogen instead of
steam. This produces more methane directly in the
synthesis gas than is produced in simple gasification.
Consequently, the medium-Btu gas produced by hydro-
gasification requires less additional processing to be trans-
formed to a high-Btu gas. Moreover, higher overall con-
version efficiencies can be realized with hydrogasification
than with simple gasification.
High-Btu gas is made from low- and medium-Btu gases
by adjusting the ratio of hydrogen to carbon monoxide in
these gases. This ratio adjustment is called the water-gas
shift reaction. The gas is also purified by removing the
acid gases produced in the reaction, chiefly hydrogen
sulfide and carbon dioxide. The remaining hydrogen and
carbon monoxide are then combined to form methane
and water a methanation reaction. The water is then
removed leaving a methane-rich product with the
essential characteristics of natural high-Btu gas.
Gasification is carried out in either a fixed bed reactor,
fluidized bed reactor, or entrained bed reactor.
In the fixed bed reactor crushed coal is fed to the reactor to
form a bed. Air or oxygen and steam are blown upward
through the bed at a relatively low velocity to gasify the
coal. The raw synthetic gas exits from the top of the reactor
and is quenched to remove tars, oils, and particulates. The
gas is then cooled for further processing.
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DIRECT CATALYTIC
HYDROGENATION
processing.
The data developed on the
types and quantities of
pollutants and the levels at
which they become toxic are used to
develop criteria for controlling such pollution.
A synthetic fuel industry will grow rapidly when
production processes are proven technically and
economically viable. Environmental control technologies
developed concurrent with the processes themselves will
avoid costly delays which would be necessitated by
attempts to add environmental controls after processes
are perfected. Environmental controls integrated into
processing systems are also likely to be more efficient
than add-on methods.
lack of information on individual devices hinders their
environmental control evaluation. Moreover, the United
States has only a few advanced processing pilot plants on
which to test control technologies. Some information is
being collected on gasification processes in foreign
countries. However, the results obtained from monitoring
the operation of foreign plants may not be applicable to
U.S. plants because of the differences in foreign and U.S.
coal and the consequent variations in effluents.
Other technical problems involve the removal of individual
pollutants, such as solid waste in the form of particulates,
at the high temperatures and high pressures in some of
the gasification processes. Large particulates, over a few
microns in size, can cause erosion of power plant turbine
blades, while the smaller particulates are environmentally
undesirable. It is not clear at what stage in the fuel
conversion stream these particulates can be most
effectively and economically removed. Their effective
removal, in any event, will be a benefit both to process
technology and to environmental control technology. The
current alternatives for removal are during or after
gasification. The tradeoffs between these alternatives
Factors
Technological Most process technology developed for
gasification/liquefaction
is proprietary. The
consequent
PURIFICATION
SOLVENT
EXTRACTION
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will produce 90,000 cubic meters per hour {cu M/H) of raw
generated gas and 60,000 cu M/H of clean gas. It also
produces appreciable amounts of tar; heavy, medium-
heavy, and light oil; raw phenol; and ammonia water. The
Kosovo plant is equipped with only minimal environmental
controls. It does not have a sulfur recovery unit or an
operational waste water treatment facility.
The Lurgi process is to be used in three industry-
sponsored commercial U.S. coal gasification plants. The
three are sponsored by the Western Gasification
Company (WESCO), the El Paso Natural Gas Company,
and the Michigan-Wisconsin Pipeline Company. The
results of research at the Kosovo plant will provide a basis
for establishing environmental control technologies to be
incorporated into the design of U.S. plants, an
economically and operationally superior alternative to
retrofit controls. Recommendations for municipal
regulations on disposal of solid waste from coal
gasification plants also will be made on the basis
of the study.
The Kosovo project was approved by the U.S. and
Yugoslavian governments in June 1976. EPA has
allocated $290,000 for the three-year program.
Yugoslavia is providing matching funding.
Gas and water treatment A gas treatment test facility
is being constructed at North Carolina State University to
treat raw gas that contains large amounts of acids. The
facility is being designed and installed by the Aerotherm
Division of Acurex Corporation, Mountain View, California.
Research on treating waste water is being performed by
the University of North Carolina under a grant from EPA.
High temperature/high pressure particulate re-
moval To develop the technology necessary to remove
solid waste particles from fluidized bed reactors used in
gasification, HTP particulate removal programs, mainly at
the bench-scale level, have been funded. Additionally,
some demonstration tests of electrostatic precipitators
have also received agency support. An HTP electrostatic
precipitator (1700°F) is being developed by Research-
Cottrell, Inc., Bound Brook, New Jersey, under a
$130,000 contract from EPA. Standard electrostatic
precipitators operate at 600° to 800°R
Filter concepts for HTP control are under study by several
contractors. A contract for assessment of granular bed
filtering is currently being negotiated. Westinghouse is
evaluating the use of ceramics and other materials as
filters. Aerotherm is comparing the collection perfor-
mance of metallic, ceramic, and fabric filters against the
performance of electrostatic precipitators.
Air Pollution Technology Corporation, San Diego, has a
contract to develop a bench-scale dry scrubber for HTP
particulate removal.
Economically viable techniques to remove large and small
particulate matter at gasifier exit temperatures are being
sought. The cost tradeoffs between high-temperature and
low-temperature particuiate removal are also being studied.
Pollutant sampling and emission standards
Additional research on identifying pollutants from synthetic
fuels processing is expected to begin by early 1977.
EPA is reviewing preliminary new source performance
standards for atmospheric emission of sulfur and
hydrocarbons from coal gasification plants. These
standards will be published in 1977. But no new standards
on water pollution are planned because the demands of
environmental control technologies on plant water use are
not yet known.
Agency Interaction
EPA, under the auspices of the Interagency Program, is
working closely with ERDA to collect data on environ-
mental effects of coal gasification/liquefaction in a
number of projects.
EPA is evaluating data on process effluents from
ERDA gasification and liquefaction pilot plants
HYGAS in Chicago, Solvent Refined Coal (SRC) in
Tacoma, Washington. Joint agency environmental
testing is planned. SRC is the liquefaction process
that is closest to commercialization. In addition, EPA
has entered into an agreement with ERDA to
characterize effluents and to provide guidance for
ERDA's comprehensive industrial gasification
program including the startup and operation of pilot
plant gasifiers at Morgantown, West Virginia, and
Grand Forks, North Dakota.
EPA and ERDA are
coordinating work on
particulate removal
concepts. The most
effective devices will
be recommended
for future analysis.
LIQUID HYDROCARBON SYNTHESIS
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CHEMICALLY
ACTIVE
FLUID BED
Process
The chemically active fluid bed (CAFB) process is
designed to convert heavy, high-sulfur residual oil to
clean, low-sulfur gas. The process also may be applicable
to making clean gas from high-sulfur coal.
In applying the process to residual oil, the oil is first heated
and then fed to a reactor that contains a fluidized bed of
fine particles of limestone. The oil is vaporized in the
reactor through a series of catalytic cracking and oxida-
tion reactions. Hydrogen sulfide and some organic
sulfur are released from the vaporized oil to be absorbed
by the lime in the "boiling" limestone. The remaining hot,
low-sulfur fuel gas produced in the process can be piped
directly to steam boilers or gas turbines for combustion.
The CAFB reactor contains two sections, one for
gasification of the oil and one for regeneration of the
sulfur-absorbing lime. In the regeneration step, air reacts
with the limestone, freeing it from the sulfur, which is
released into the air stream as sulfur dioxide. The sulfur
dioxide is removed from the regeneration gas and may be
converted to a nonpolluting solid. The cleansed limestone
is then recycled through the reactor continuously until it
loses its efficiency as an absorbent.
Rationale
Many utilities are required to burn only low-sulfur fuel in
order to meet federal and state emissions regulations.
This means that large supplies of heavy residual oils
remain untapped as sources of fuel for power plants. In
the face of the growing shortage of domestic oil supplies,
it is important that maximum use be made of all grades of
petroleum. By efficiently converting high-sulfur residual oil
to clean gaseous fuel, the CAFB process offers an
environmentally sound means of freeing this resource for
the production of energy.
The process has particular importance as a retrofit
mechanism for the numerous gas-fired power plant
boilers in the southwest. These boilers cannot be readily
converted to the use of high-sulfur heavy oil or coal. Most
of the existing gas-fired boilers in Texas, for instance,
have a remaining life of 20 to 30 years, but the sources of
natural gas to fuel them are expected to be unavailable in
just a few years. These boilers are in power plants that
currently produce approximately 120,000 megawatts of
power. Use of the CAFB process could permit this level of
energy production to be maintained throughout the useful
life of these boilers.
In addition, the CAFB process offers a technological
advantage over other methods of contaminant removal by
avoiding the necessity of cooling and scrubbing the gas.
These methods lower the heating value of the product gas
and the efficiency of the gasification process.
Factors
Technological Individual power plants may present
engineering problems in retrofitting the CAFB process.
The age and condition of boilers and the size of burners
will have to be considered in designing retrofit equipment.
The adequacy of existing pipelines to handle liquid fuels
will be another design consideration. But these problems
are expected to be readily solved on a case-by-case basis
using good engineering practice.
Environmental The release of large amounts of sulfur
in the gasification step of the CAFB process is a basic
environmental concern. The efficiency of the fluidized bed
of limestone will determine how much of this sulfur, in the
form of highly toxic hydrogen sulfide gas, reaches the
atmosphere. Efficient removal of the sulfur dioxide gas
released from the limestone in the regeneration step is
also necessary to maintain air quality.
Another environmental concern is the release of con-
taminant metals such as vanadium, nickel, sodium, and
some alkali metals during gasification. These metals pose
a health hazard because of their high toxicity. There is
concern that these toxic metallic substances, which may
have been present only in trace amounts in the original
fuel, will be concentrated as a result of the fuel conversion
process in amounts that intensify their pollution potential.
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Approximately $1.3 million is allocated for studies of the
process in FY77.
Outlook
Preliminary calculations indicate that the CAFB process
can be as much as three times more efficient in pollutant
removal than initial estimates suggested. However,
demonstration tests under a range of operating conditions
and grades of fuel are necessary to confirm these
indications. The full capability of the process also has
yet to be determined. To confidently predict the efficiency
of the process over years of operation, it will be important
to determine early in the demonstration tests how
effectively contaminants are removed.
With the capabilities of the process determined, standards
of practice and recommendations for control technologies
can be formulated to meet environmental requirements.
For these purposes, long-term monitoring of emissions
and waste streams will be necessary.
The economics of the process in terms of retrofit,
operation, maintenance, and costs added to the fuel
product will have to be determined. How well the process
competes with the cost of alternative technologies such
as flue gas desulfurization also will require analysis.
Work on the CAFB concept to date suggests that it has
significant potential as a means of producing clean fuel.
The next step in the development of the process is the
demonstration at La Palma Station to determine the
technical, environmental, and economic realities of plant
operation.
Chemically Active Fluid Bed Facts
Process: Heating high-sulfur coal or residual oil in the
presence of a fluidized bed of limestone to
convert the coal or oil to gas and transfer sulfur
and other contaminants to the limestone.
Purpose: Make high-sulfur oil and coal available as a
boiler fuel.
Problems: Retrofit of boilers to use the CAFB process.
Transport of liquid fuels to the boilers.
Hydrogen sulfide and sulfur dioxide emissions.
Heavy metals release from spent limestone.
Inadequate information on installation and
operating costs.
Potential: CAFB may be more efficient than
expected. Fuels produced by CAFB
will be clean and air pollution will be
reduced. Techniques to handle
CAFB solid wastes already exist.
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