United States
Environmental
Protection Agency
Energy Minerals and industry
Office of Research
and Development
Washington, D.C. 20460
EPA 600/9-79-019
May 1979
<& EPA Decision Series
sulfur
emission:
control
technology
& waste
management
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sulfur
emission:
control
technology
6c waste
management
contents
sulfur oxide pollution 3
emission control technologies 7
waste management 15
status and outlook 29
for further reading 32
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The world's industrialized societies are responsible
for massive amounts of sulfur oxide pollutants
being discharged into the atmosphere each year—
about 65 million tons. Three quarters of that
amount comes from one percent of the global
surface area, namely, from central and northeastern
United States, southern Canada, and northern
Europe. Another 35 million tons come from natural
sources, such as volcanoes, which are generally
remote from human habitation. Increasing
worldwide demand for energy, derived mainly from
the burning of fossil fuels, will make this situation
even worse by the year 2000.
Most of this pollution comes from the
combustion of coal that contains sulfur as a natural
contaminant. The U. S. will be burning more coal
in the future in order to decrease its dependency
on foreign oil. Consequently, the nation will be
faced with more severe air pollution problems in
the years ahead.
Sulfur dioxide (SO2), which is the main pollutant,
has been found to irritate the respiratory tract and
can cause permanent injury to the lungs. People
with chronic pulmonary disease or cardiac
disorders, the young, and the elderly are most
susceptible to SO2 pollution. During an air pollution
episode in Donora, Pennsylvania, in 1948, high
levels of SO2 in combination with other pollutants
resulted in a significant increase in the death rate.
Sulfur dioxide and its related pollution have also
been implicated in loss of labor productivity. For
example, a recent estimate is that the reduction of
urban air pollution by 60 percent over the 1970
levels would result in an economic savings of
between 16 and 34 billion dollars.
Small sulfate particles are the major cause of
reduction in visibility in the eastern United
States. On an average summer day, visibility has
decreased from 15 to 8 miles over the last 25 years.
Much of this sulfur dioxide, when exposed to
moisture in the atmosphere, oxidizes into acidic
sulfates (H2SO4), which are then deposited in the
form of acid rain. The acid rain problem was first
recognized in Scandinavia. Swedish scientists
found steady increases of sulfur and nitrogen
componds in rain and snowfall, along with a
closely correlated increase in acidity. Since World
War II, the average acidity of precipitation in
Scandinavia and in the northeastern U. S. has
increased significantly—from about 10 to almost
100 times the acidity of normal rainwater.
The acid rain impact is not necessarily confined
to the locality where the sulfur dioxide is emitted.
Only about one-third of the total acid rainfall in
Scandinavia can be attributed to local emissic .B.
About one-half comes from other European sources,
and there is the possibility that at least a part of
the rest originates in North America.
Although the impacts of acid precipitation have
not been fully evaluated, studies in Europe,
Canada, the U.S.S.R., and the northeastern United
States have shown a number of adverse effects.
Acid rain is believed to be the cause of declines in
present forest and agricultural productivity.
Acid conditions in lakes or streams often cause
failure in fish spawning, particularly for trout and
salmon species. The most strongly affected areas
tend to be high altitude forest streams and lakes,
such as the acidified lakes in the Adirondack
Mountains. This suggests a serious long-range
threat to many of our national parks.
Depletion of nutrients from soils and streams is
another problem caused by acid rain. This problem
involves subtle but important mechanisms by
which the ecosystems are damaged. Research is
now being done to determine effects on
agriculture.
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/
the environmental Impact of uncontrolled sulfur emissions
materials «^^B ecology mm^mm health «^^^» economy
• metal oorroslon
• erosion of limestone,
marble & other similar
materials
• deterioration of
buildings & statuary
• reduced agricultural ft
forsst production
• adverse effects to fresh
water food chains
• extensive soil damags
• harmful to marine Ufa
• reduced visibility
respiratory Irritation;
aggravation of aathma
and emphysema
t potential for permanent
lung damage
In addition to these ecological impacts, acidic
sulfates corrode and deteriorate materials such as
metals, limestone, marble, roofing slate and mortar.
Some of civilization's greatest art and
archaeological treasures have resisted deterioration
for thousands of years. However, in recent years
they have become severe casualties of society's
sulfur dioxide emissions. One example is the
once gleaming, white-marble Taj Mahal, which
has been stained and damaged by industrial
pollution. Sulfur oxide fumes from a giant refinery
being built 60 miles north of the Taj Mahal could
be an increased threat to this architectural wonder.
sources and growth
Most industrial sulfur pollution comes from
coal-burning, electric-power generating plants.
These power utilities account for nearly 70 percent
of the society generated sulfur dioxide emissions
in the U. S., with the rest coming from industrial
sources and from residential/commercial heating
systems.
Increases in S02 emissions are thus closely tied
to the rapidly expanding electric power industry,
which since 1950, has doubled its electrical output
every 10 years. An indication of the potential
pollution problem can be seen in the massive
growth projected in electricity generation in the
TJ. S. Approximately 300 new fossil-fuel-fired power
plants are expected to begin operation within the
next 10 years. Associated with this growth is the
continued long-term increase in utility coal
consumption from 405 million tons per year in 1975
to between 800 and 1,300 million tons per year in
1995. This power growth is expected to increase
power plant SO2 emissions from 18.6 million tons
per year in 1975 to 20.6 million tons per year in 1995.
The present control strategy for new and
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existing power plants will only slow down the rate
of growth in SO2 emissions; it will not necessarily
decrease the total emissions below their current
level. Although controls are expected to limit
emissions from electric utilities, increases are
expected as a result of growth in other industrial
combustion sources, as new and existing facilities
increasingly turn to coal for their primary fuel.
While all of these projections are subject to a
number of assumptions — expected growth rate of
new sources, degree of control required for these
sources, degree of compliance with control
requirements for existing sources, and changes in
regulatory requirements — they nevertheless
illustrate the growing stress on our environment
from sulfur dioxide pollution. Civilization's growing
appetite for more energy will continue to require
greater amounts of fossil fuels to be burned.
Worldwide use of coal during the brief 30 year
period from 1940 to 1970 was approximately equal
to that consumed in all preceding history. In the
U. S., increased usage of coal is called for in the
future under the National Energy Plan. Increased
combustion of coal and the associated generation
of sulfur oxide pollutants will impose a continuing
need to ensure protection of public health and the
quality of our environment.
control requirements
The major national driving force for sulfur oxide
control is the Clean Air Act originally enacted in
1970. Under this Act, the Environmental Protection
Agency (EPA) established New Source
Performance Standards (NSPS) for new facilities
and for any major modification to existing facilities.
The present NSPS limits SO2 emissions
from coal-fired plants to 1.2 pounds per
million British Thermal Units (BTUs) of heat
generated. This limit requires about a 75 percent
reduction in SO2 emissions for combustion of coal
with a 3 percent sulfur content.
Revised NSPS, promulgated in June, 1979,
require a specific percentage of sulfur reduction
and a maximum ceiling amount of sulfur per
million BTUs. This means that some form of sulfur
oxide control technology will be required for all
types of coal, regardless of sulfur content.
1b meet the present air quality standards, some
form of S02 emission control technology may be
necessary on an estimated 25 percent of the
coal-fired plants in the U. S. In the future, all new
plants must install sulfur oxide pollution control
systems.
What emission control systems are there
currently available? What is the state of
development of alternative control technologies?
sources of society generated
sulfur pollution
residential/commercial
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inl
:t HI
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"today, flue gas desulfurization (FGD) technology is
playing a critical role in sulfur oxide pollution
control. It is the only control technology
commercially available that can be used to reduce
sulfur oxide emissions to comply with the Clean
Air Act. Being an "add-on" or post-combustion
type of system, it can be retrofitted with minimum
modification to existing boiler combustors. Over
the next five years or so, the only other available
options that can provide some degree of sulfur
oxide control are the use of low-sulfur coal and
physical coal cleaning.
In the past, the utilities and other industrial
sources relied on several approaches to reduce SO2
emissions. They used low-sulfur coal when it
was readily available and economically
advantageous to do so. Converting facilities to
burn oil and gas — both cleaner burning fuels —
was also a feasible approach before the oil crisis of
1974. In other cases, modernization of "dirty"
combustion equipment provided sufficient
improvement to meet emission standards. Such
approaches to SO2 emission reduction, however,
have gone about as far as possible; further
improvements in SO2 reduction are not expected
without the application of control technology.
low-sulfur coal
While naturally occurring low-sulfur coal is the
most straightforward control option, projected
production capacity for such coal is limited. It has
been estimated that production of low-sulfur coal
will satisfy less then 44 percent of the anticipated
demand for this type of coal in 1980. Also, most of
the low-sulfur coal reserves are in the west. Using
the western low-sulfur coal to meet mid-western
and eastern requirements would involve
substantial transportation costs. Because of these
additional costs, it is economically feasible to use
local high-sulfur coal and clean up the resulting
pollution by applying S02 control technologies.
Furthermore, recent tightening of the emission
standards eliminates the low-sulfur coal option for
new sources.
physical coal cleaning
Another option for reducing SO2 emissions is
physical coal cleaning, which has been used for
many years. In the past, its principal purpose was
to reduce ash-forming impurities. Tbday, this
technology is commercially available, relatively
simple, and low in both capital and annual costs.
Up to 80 percent of the inorganic sulfur can be
removed by physical removal techniques. Its use is
limited, however, to removing inorganic sulfur
(pyritic sulfur) in coal. Sulfur also exists in coal in
the form of organic sulfur, which is chemically
bound to the coal and cannot be removed by
physical means. The extent to which inorganic
sulfur can be removed economically is also limited,
because it depends on the size and distribution of
this form of sulfur in a particular coal. It has been
estimated that less than 14 percent of U. S. coal
reserves is of the type that can be physically
cleaned to meet the present NSPS standards.
Thus, although both of these options —
low-sulfur coal and physical coal cleaning—are
currently available, their application is limited.
flue gas desulfurization
Flue gas desulfurization technology is the SO2
emission control approach that is most common
today. Although there is a great deal of activity
and interest in these FGD control systems,
commonly called "stack gas scrubbers," they are
not new. The first commercial use of FGD to
control sulfur oxide pollution from a power plant
was in the United Kingdom in the early 1930s. Flue
gases were washed with alkaline water from the
Thames River at the Battersea A power plant of the
London Power Company The spent alkaline water
was discharged back into the Thames after settling
and oxidation. This FGD system operated
successfully for over 40 years, at up to 95 percent
SO2 removal efficiency, until the power plant closed
in 1975.
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Coal cleaning
PRE-COMBUSTION
Fluidized Bed Combustion (FBC)
DURING COMBUSTION
Flue Gas Desulfurization (FGD)
During the 1950s and '60s, the new FGD
processes were being developed and pilot tested.
During the '50s, the Tennessee Valley Authority
(TVA) investigated both wet and dry lime/
limestone scrubbing systems and dilute acid
processes. At the same time the Germans
developed the first major carbon absorption
processes. During the '60s, magnesium oxide,
copper oxide, and sulfite scrubbing processes were
investigated.
Over the past 10 years, the EPA and TVA have
sponsored extensive research, development, and
demonstration programs designed to develop FGD
as a practical SO2 control approach. As a result,
several types of FGD systems have been developed
and applied to operating power plants. These
systems have demonstrated, over several years of
operation, increasing reliability and performance in
removing up to 90 percent of the SO2 emissions.
Recent pilot-plant experience indicates that new
FGD systems can be expected to exceed 95
percent removal.
The number of FGD systems installed annually
in the United States has steadily increased since
1968. As of early 1978, there were 29 units in
operation, with an additional 51 units in design or
under construction. Nearly 25,000 megawatts
(MW) of FGD capacity were installed or under
construction on both new and existing utility
boilers; approximately 30,000 MW of FGD capacity
were in the planning stage. This total utility
commitment of 55,000 MW FGD capacity
represents over 25 percent of the current total U.S.
coal-fired capacity of 200,000 MW.
FGD systems can be classified into two general
types:
• non-regenerable or throwaway systems,
in which the sulfur material generated
through scrubbing or absorption is disposed
of as a waste product, and
• regenerable or recovery systems, in which
sulfur materials, such as elemental sulfur,
licfuid SO2, and sulfuric acid, are marketed as
saleable products.
POST-COMBUSTION
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Gasification
Liquefaction
About 90 percent of FGD systems currently
operational, under construction, or in planning are
lime or limestone scrubbers of the throwaway type.
Although over 50 FGD processes have been tested
at bench scale or larger, the number of
commercially significant processes is considerably
smaller. The following throwaway FGD systems are
considered the most important for near-term
(through 1985) SO2 control:
• direct lime scrubbing and direct
limestone scrubbing — the lime and
limestone scrubbing systems are
commercially available technologies. These
systems use a slurry of lime or limestone to
absorb SO2 from combustion gases, thereby
producing a waste product in the form of a
slurry or sludge.
• double alkali scrubbing — the double alkali
scrubbing is a second generation technology
Double alkali systems use scrubbing solutions
of soluble alkali salts, e.g., sodium, for SO2
removal. The spent scrubbing lic^uor is then
reacted with lime outside the scrubber system
thereby forming a slurry which, after drying,
produces a caked waste product.
Of the types of recovery FGD systems, the
following are considered most important for the
same near-term period:
• magnesium oxide scrubbing — magnesium
oxide (magnesia) is used to remove the SO2,
forming magnesium sulfite. Solids of
magnesium sulfite are separated by
centrifugation and dried. The magnesium
sulfite is then calcined (oxidized by heating)
to regenerate magnesium oxide which is
reused, and the SO2 gas is converted into
sulfuric acid.
• Wellman-Lord process — sodium sulfite is
used as the absorbent to obtain sodium
bisulfite, which is heated to regenerate sodium
sulfite and SO2 in a concentrated form. The
recovered SO2 is used to by-produce either
sulfuric acid or elemental sulfur.
• citrate, carbon adsorption and copper
oxide adsorption are some other potentially
important systems which have operated at or
near commercial scale.
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projected availability of alternate control technologies
1950
1960
1970
1980
1990
2000
2010
flue gas
desulfurlzatlon
(FGD)
fluidized
bed
combustion
(FBC)
coal
gasification &
liquefaction
research & development
full scale demonstration
commercially acceptable | ~\
fluidized bed combustion
An emerging technology that shows significant
potential for a clean-burning process is fluidized
bed combustion (FBC). Fluidized bed combustion
involves the combustion of pulverized coal in a bed
of granular limestone or dolomite. The combustion
takes place in a closed vessel containing a porous
plate that supports a bed of pulverized coal and
limestone/dolomite sorbent. Air is passed through
the plate, "fluidizing" the bed of coal and sorbent.
As the coal burns, the SO2 is absorbed by reaction
with the limestone. Coal and sorbent are fed
continuously to the bed, while spent sorbent and
ash are continually removed.
There are two types of FBC processes:
atmospheric fluidized bed combustion (AFBC) and
"pressurized fluidized bed combustion (PFBC). The
AFBC process operates with the combustion
chamber at close to atmospheric pressure.
Pressurized fluidized-bed combustion operates at
pressures from 6 to 16 times atmospheric pressure.
In the AFBC system, steam is produced inside
tubes that are built into the combustion chamber.
Electricity is generated in a conventional steam
turbine. In the PFBC system, steam is produced in
similar tubes, but more importantly, the hot gases
from the combustion chamber are used to drive a
gas turbine generator. Additional energy efficiency
can be obtained by using the waste turbine heat
to produce steam.
10
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For several years, a considerable effort has been
expended in the development of FBC, with DOE
and EPA supporting the experimental work in both
the U. S. and England. The culmination of the effort
has been the construction of a 30-MW AFBC plant
at Rivesville, West Virginia. This plant is currently
the largest FBC unit in the world. Other small
industrial AFBC units are planned, but none is
expected to be operating until 1979. On a larger
scale, TVA has preliminary designs for a AFBC
steam generator under development and is
studying the construction of a 200-MW
demonstration unit.
The AFBC systems are in a more advanced
stage of development than PFBC systems. This is
principally because the pressurized systems
require the development of high pressure gas
cleaning technology. Both systems require a
considerable flow of sorbent material through the
combustion chamber. In the AFBC system, the
spent sorbent is discarded producing a significant
solid waste disposal problem.
The amount of sorbent required and the
associated spent sorbent disposal problems can be
greatly minimized by employing a regeneration
process.
Research is in progress on the PFBC system to
regenerate the spent sorbent. Added benefits from
this process may be the production of by-product
chemicals such as elemental sulfur and sulfuric
acid.
This during-combustion control technology
may eventually surpass other conventional
post-combustion control processes in its potential
for air pollution control and economy. It is a way of
burning coal (as well as other fuels) in a clean
and economic manner. Because of the higher heat
transfer characteristics inherent in the process, the
combustors are more compact than conventional
coal combustors and the system more energy
efficient. While the combustion temperature is
sufficiently high for efficient combustion, it is low
enough to produce a decrease in nitrous oxide
emissions and allows the formation of calcium
sulfate as a by-product of burning sulfur-bearing
fuels.
The fluidized-bed combustion system is viewed
as a potentially energy-efficient technology that
could have some useful economic and
environmental advantages. Preliminary data from
Rivesville indicate that the SO2 reduction is in the
range of 85 to 89 percent with the limestone feed
that is presently being used there.
control of
sulfur emissions in U. S.
generating
capacity in
thousands
of MW
600
1500
1400
300
200
100
1975 1985 1995
1975 1985 1995
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TECHNOLOGY
PHYSICAL
COAL CLEANING
FLUE GAS
DESULFURIZATION
FLUIDIZED BED
COMBUSTION
LIQUEFACTION
GASIFICATION
DESCRIPTION
CURRENT STATUS
ADVANTAGES
• removes Inorganic sulfur by
using difference In specific
gravity of sulfur & coal
• commercially used
• future limited as emission
standards become more
stringent
• can be used In conjunction wltl
FGD to reduce costs
• Inexpensive process
• does not require boiler
modifications (normally)
• remove SOs from combustion
gases after burning through
absorption In an alkaline
solution
commercially used
offers most efficient and
economical method of SOa
control now available on a
widespread basis
• can be retrofitted to existing
boilers
• efficient
combustion of pulverized coal
In a bed of limestone or
dolomite
fluldlzed by air, SOs absorbed
by absorbent
• emerging technology In pilot
plant testing
• commercial availability
for atmospheric FBC In mld-
1980's; In early 1990'8 for
pressurized FBC
• SOa removal: 80-90%
• lower combustor
capital costs
• wide fuel flexibility
• lower operating temperatures
reaction with hydrogen, heat &
pressure, In presence of
catalysts or chemical solvents
to produce liquid fuels
• 4 processes In pilot stage:
-direct catalytic hydrogenatloh
-solvent extraction
-pyro lysis
-liquid hydrocarbon synthesis
• commercialization: 1990's
• wide variety of coals
• produces clean burning fuels
• SOa removal; > 95%
• reaction with steam or
hydrogen & air/oxygen at high
temperature to produce high or
low BTU gas
• low BTU commercialization: mid
1980's
• current low BTU demonstration
(small scale Industrial)
• high BTU commercialization:
1990
• can be used In conventional
gas fired power plants
• SO: removal: > 95%
other emerging control technologies
Other pre-combustion coal technologies under
development that would reduce SOe emissions, as
well as provide additional domestic supplies of
rapidly depleting fuel resources, include coal
gasification and coal liquefaction.
Low BTU gasification is currently in the
demonstration phase of development and is
expected to make a commercial impact in the
mid-1980's. High BTU gasification and liquefaction
are currently in the pilot plant stage of
development and are expected to be
commercialized in the post 1990 period.
These technologies will produce relatively clean
burning fuels to replace natural gas for residential
heating and fuels for boiler and transportation
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DISADVANTAGES ECONOMIC FEASIBILITY WASTE PRODUCT
Bonly 14% of U. S. coals can be
cleaned enough to meet NSPS
large quantities of high sulfur
refuse/ash
§ relatively inexpensive but
-Standards
f-rhay require large electrostatic
limited in application
* provides an effective and
efficient means of meeting
NSPS emission standards
without modifying or replacing
existing boilers
^generates large quantities of
sulfur laden sludge
> generates large quantities of
spent absorbent
.larger precipitators required
• appears to have economic
advantage over FGD operating
& capital costs
• dry spent sorbent
» unidentified pollution problems
f potential for toxic by-products
I nigh particu late control needed
9 high overall development costs
* same as liquefaction
I -same as liquefaction
applications. At present, however, their
environmental impacts have not been adequately
determined. The Environmental Protection Agency
has initiated a comprehensive environmental
assessment program to develop and evaluate
pollution control technology associated with these
processes in an effort to reduce their effluents and
emissions.
All of these control technologies reduce
emissions of air pollutants; however, they generate
other pollutants — solid and liquid byproducts.
Thus, there are two environmental problems
associated with sulfur oxide pollution: first, the
SO2 control problem; and second, the waste
management problem resulting from the
application of SO2 controls.
What is the size and scope of this waste
management problem? What are our options
for disposal and/or utilization of SO2 control
wastes?
13
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waste
management
The management of solid wastes is a major
problem for electric power producers and industrial
boiler operators using throwaway FGD control
systems. Because the waste must be disposed of
within the constraints of land and water quality
regulations, EPA is funding an extensive research
and development program to evaluate, develop,
and demonstrate environmentally accepable
methods for disposal and treatment of FGD waste.
Studies are also being sponsored on the economics
of current and conceptual disposal technologies.!
Extensive field investigations are being conducted
on a process (forced oxidation) for converting FGD
waste into gypsum, the basic ingredient of plaster.
The Tennessee Valley Authority (TVA) also has
been active for several years in developing and
evaluating FGD scrubber systems and FGD waste
treatment and disposal methods. Over the next
five years the Electric Power Research Institute
(EPRI) will be funding an extensive research and
development program related to FGD waste
treatment and disposal.
scope
Waste management associated with emission
control systems is of environmental concern be-
cause of the large amount of solids and liquids
generated by those systems. For the FGD process,
which will be the primary emission control tech-
nology in use for the near term, the total amount of
FGD waste produced in a typical 1,000 MW plant,
burning coal with a 3.5 percent sulfur content, is
about 225,000 tons annually. This is comparable,
on a dry basis, to the amount of coal ash produced.
(When burning low-sulfur, western coal, the
amount of FGD waste produced is only 30 to 40
percent of the ash generated.)
15 place FGD scrubber waste in perspective, the
amounts of FGD wastes generated annually can be
compared with other kinds of utility, industrial,
mining, and municipal wastes that our society has
been dealing with for many years. For example,
during 1980, the amount of coal ash generated by
utilities alone will be nearly six times the amount
of FGD waste generated from utility applications.
The amount of solid waste from mining coal is
about fifteen times greater than FGD waste and
about the same as the amount of municipal refuse
generated annually Industrial wastes are almost
forty times the amount of FGD waste. Municipal
sewage sludge projected for 1980 will be about half
the amount of FGD sludge generated from utilities.
Many of these types of solid wastes contain
potentially hazardous constituents, for which tech-
niques have been developed to reduce their en-
vironmental, public safety and health impacts.
These techniques include disposition by ponding
and landfill. Although some problems associated
with non-FGD wastes have not been completely
resolved, work is continuing to improve treatment
and disposal methods. It is expected that continu-
ing research and development will lead to im-
proved methods for managing and disposing of
SOi control technology wastes, as well.
millions of tons
annually
400
estimated
solid wastes:
1980
15
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land use
With the increasing application of emission control
systems will come additional requirements for land
for disposal of generated wastes. For example, a
typical 1,000-MW utility plant will retire 400 to
700 acres for disposal of ash and FGD waste over a
lifetime of 30 years depending upon the type of
coal and the regional locations. This acreage
includes only the excavated area (landfill or
impoundment). The actual disposal area may be
larger, since land would be required for access
roads, truck parking and unloading areas, and
buffer zones. It is anticipated that public concern
about buffer zones to lessen the adverse aesthetic
impacts of disposal areas will further increase land
requirements.
Preliminary estimates of maximum national land
requirements for the waste disposal area are
18,000 acres by 1985 and 63,000 acres by the year
2000. These estimates are the upper limits for the
disposal area if all FGD waste is disposed of on
land, i.e., with no product utilization or other
disposal method. Actual land taken for this use —
which would include access roads and buffer zones
—would be higher.
disposal regulations
The disposal of FGD waste is subject to regulations
at both the Federal and state levels. At present,
FGD waste is disposed of exclusively on land.
Four major issues impacting land disposal are:
• Waste stability/consolidation
• Groundwater contamination
• Surface water contamination
• Fugitive emissions
The issues are regulated under a number of
Federal legislative acts. One of the most significant
of these is the Resource Conservation and
Recovery Act of 1976, which regulates the disposal
of all types of wastes in mines, landfills, and
impoundments. It requires the development of
criteria that classify disposal areas as either open
dumps or sanitary landfills. These criteria address
all forms of land disposal, including
impoundments, land spreading, and surface mine
disposal. After the criteria are issued, the states
must develop plans which require that existing
open dumps be upgraded or closed. Future land
disposal operations will be required to meet the
criteria established for sanitary landfills. The
criteria are expected to prohibit any contamination
of the groundwater that would result in requiring
additional purification steps before using.
disposal alternatives
Ponding and landfill are the two primary methods
currently in use for disposing of FGD sludge. In
addition to these, EPA, through its Office of Water
and Waste Management, is developing methods to
improve the existing disposal technology and is
also examining alternative disposal options. Two of
these alternatives are mine disposal and ocean
disposal.
Ponding of Untreated Sludge—At present, FGD
scrubber waste is primarily disposed of without
additional physical or chemical treatment,
although the waste is sometimes thickened prior
to discharge. Historically, the disposal method
most frequently used by utilities has been
ponding. In most ponding operations, the slurried
solids are pumped directly from the scrubber or
from the bottom outlet of a thickener to a disposal
pond usually located within a mile of the power
plant. Ponded waste settles to a semi- solid
toothpaste-like material, and excess water is
returned to the scrubber, Some utilities do not line
the disposal pond, while others install a clay lining.
16
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total: 68
Two environmental issues arise from the ponding
of FGD waste:
• Water pollution potential of soluble
materials in the waste
• Land-degradation potential of nonsettling
or physically unstable waste.
In all ponding operations, local surface and
groundwater must be monitored for possible
contamination by leachate from the disposal pond.
Because of the physical properties of untreated
FGD waste, the settled waste is not structurally
stable. Even after extended settling, the waste
possesses thixotropic properties, that is, if
physically disturbed, it becomes fluid. This creates
handling problems during transport and landfill
disposal, and impedes future reclamation of the
ponds. In addition, if the pond is not reclaimed and
an appreciable level of water is permitted to
remain indefinitely on top of the waste, soluble
constituents can be forced into the groundwater.
With regard to ponding of untreated sludge, it is
EPA's position that permanent land disposal of raw
(unfixed) FGD waste is environmentally unsound
because it indefinitely degrades large quantities of
land (Federal Register, Volume 40, No. 176, Sep-
tember 1, 1975). By fixing or chemically treating
FGD waste, it sets up into hard, clay-like form that
permits it to be disposed of in a more environmen-
tally acceptable manner. Several such treatment
methods have been developed and are commer-
cially available.
millions of tons
annually
601
SO
40 i
20 i
10 i
projected FGD
waste generation
1980
1990
2000
Landfill Disposal—Where ponding has been
impractical, landfilling has been used for many
years by utilities as a means for disposing of coal
ash. FGD waste has also been disposed of as
landfill in some areas, in order to avoid the land
deterioration and water pollution associated with
ponding.
17
-------
comparative waste output: FGD/FBC
•- olHBlng it 88% ttfionnfly
For landfill disposal, the FGD sludge must be
dewatered or chemically treated before being
hauled to the disposal site. In some cases,
untreated slurries are pumped to the disposal site
for dewatering or treatment. The dewatered
wastes are then placed and compacted. Although
sanitary landfill procedures (daily covering) are not
necessary, the soil may be periodically layered to
minimize exposure to rainfall. This practice
reduces leaching and possible reslurrying in the
case of untreated wastes. FGD sludge must have
enough physical stability to be handled by
earthmoving equipment for landfill disposal. This
means the material must be dewatered to at least
50 percent solids and possibly to as high as 65 to
70 percent solids by mechanical, thermal, chemical
or a combination of these methods.
Mine Disposal — Disposal of FGD waste in coal
mines has interested utility engineers and EPA
scientists for many years. The transportation
system for moving the waste from the plant to the
mines already exists in the form of the railroads
used for bringing coal to the plant. In addition,
many plants have inadecjuate land area for on-site
disposal. This potential has led EPA to support
several studies to examine the potential of this
disposal option.
In one study, an initial technical/environmental
screening identified four general categories of
mines as the most promising candidates for FGD
sludge disposal: (1) active surface coal mines, (2)
active underground coal mines, (3) inactive or
mined-out portions of lead/zinc mines, and (4)
inactive or mined-out portions of active
underground limestone mines.
Midwestern surface mines appear to be the most
promising area for surface mine disposal. The
waste would have to be dewatered to 65 to 70
percent solids so that it could be dumped into a
mined-out strip, adjacent to one being mined, and
then covered over. Both midwestern and western
surface mines were considered to be much more
promising than eastern surface contour mines,
because of the latter's low capacity for FGD waste
and the greater difficulty in placing the waste in
the contour mines. However, a disadvantage of the
western surface mines is their greater potential
for ground water contamination.
Disposal of FGD waste in surface mines is
currently planned by several utilities. An
18
-------
evaluation of their experience will enable the
suitability of this disposal option to be fully
determined.
Finally, the study concluded that for
underground mine disposal, the placement of
either treated or untreated FGD waste would tend
to neutralize and reduce acid mine drainage. This
would result in improving both groundwater and
nearby stream water quality fri addition to this
benefit, disposal of chemically treated FGD wastes
could minimize long-term mine subsidence by
providing lateral pillar and roof support. Untreated
wastes would not be expected to provide sufficient
strength for subsidence control unless substantial
settling of the waste solids occurred after
placement.
Contamination of groundwater in the mine
would most likely occur if untreated FGD waste
were used. Contamination of public supply
aquifers is not expected, although the water
quality of nearby streams would be affected.
Ocean Disposal— Ocean disposal of wastes has
occurred for many years. However, in view of the
increasing awareness of the adverse effects of
much of this activity, recent efforts have been
undertaken to reverse the degradation of the ocean
environment. The Marine Protection Research and
Sanctuaries Act of 1972, the major Federal
legislation in this area, states, "The Congress
declares that it is the policy of the United States to
regulate the dumping of all types of materials into
ocean waters and to prevent or strictly limit the
dumping into ocean waters of any material that
would adversely affect human health, welfare, or
amenities, or the marine environment, ecological
systems, or economic potentialities."
Based on these criteria, studies have been
undertaken to determine if ocean disposal is an
environmentally acceptable alternative. Several
preliminary conclusions were drawn:
• Until more definitive data are available, it
would appear that disposal of untreated FGD
waste on the Continental Shelf or in the deep
ocean is not advisable.
• It appears that all soil-like FGD wastes —
sulfite or sulfate, treated or untreated —
should not be disposed via quick dumping
surface craft or pipeline (outfall) on the
Continental Shelf.
• The following option (using surface craft) may
have potential, but requires further study:
—Concentrated disposal of treated, brick-like
waste on the Continental Shelf. In this
regard, a pilot demonstration of the con-
cept of artificial reefs of this material is
being sponsored by EPA, DOE, EPRI,
Power Authority of the State of New York,
and the New York State Energy Research
& Development Authority.
treatment alternatives
Forced Oxidation—Under EPA's FGD and Water
and Waste Management Programs, forced
oxidation technology is being investigated as an
alternative treatment option. The process consists
of forcing air into the slurry of calcium sulfite
waste to oxidize it into calcium sulfate, which is
gypsum. The gypsum can then be easily
dewatered to greater than 80 percent solids.
Beginning in 1976, studies conducted by EPA
with the 0.1 MW pilot plant at the Industrial
Environmental Research Laboratory located at
Research Triangle Park, North Carolina (IERL-RTP),
have shown that calcium sulfate can be readily
oxidized to gypsum by simple air/slurry contact in
a hold tank to the scrubber recirculation loop.
Based on the findings at the IERL-RTP pilot
plant, a program was initiated at the Shawnee Test
Facility located at the TVA Shawnee Steam Plant
near Paducah, Kentucky, to develop operational
procedures for forced oxidation. Forced oxidation
testing was initiated in January 1977 on the 10 MW
EPA prototype scrubbers and has continued
as a major part of the Shawnee Advanced Test
Program. These tests are designed to determine
the optimum operational parameters and long-term
reliability of the process equipment. Runs of a
month or more in duration, using lime/limestone
scrubbing with forced oxidation, have been
19
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FGD waste
treatment/disposal
alternatives
CHEMICAL
BY PRODUCTS
CONSTRUCTION
MATERIALS
NONBUILDABLE
LANDFILL
successfully demonstrated on prototype process
equipment. Scale-up of these results to commercial
scrubbing equipment appears quite feasible.
Leachate from land disposed gypsum will be
similar to that from untreated FGD waste and
therefore should be prevented from entering water
supplies, Because gypsum tends to form a
protective surface scale capable of shedding
rainwater, tests are currently being conducted at
the Shawnee test site to determine if land disposal
of gypsum is feasible without the use of ground
liners or impoundment dikes. Limited results have
shown that gypsum sludges crack badly under
freeze-thaw conditions, thereby allowing rainwater
to enter into the material. Also, gypsum sludge has
been found to slump in its freshly deposited
condition when exposed to rainfall. This results in
runoff containing potentially high concentrations of
dissolved solids from the sludge. These preliminary
results indicate that considerable site maintenance
may be required on an operational scale to
reconfigure the disposal pile after weathering
(freeze-thaw and erosion) and to control the runoff.
Tests are continuing to determine what controls
should be exercised at the site during and after
disposal.
Commercial Fixation—Several utilities presently
stabilize or "fix" the sludge through chemical
treatment. These fixation processes result in a
solidification or hardening of the sludge to a
clay-like material, This material can then be left in
an impoundment or hauled to a landfill,
One process developed by Dravo Lime Company
involves the addition of Calcilox®, a cement-like
product derived from basic, glassy blast furnace
slag, to FGD sludges. Dravo's "full impoundment"
disposal process produces a stronger, more stable,
less permeable material than simple ponding.
Principal advantages of the stabilized product are:
the volume of leachate is reduced and the leachate
quality is improved, the final site is more suitable
for other development, and there is less danger
from dam or dike failures.
Another process, developed by IU Conversion
Systems, Inc. (IUCS), involves vacuum-filter
dewatering of FGD waste followed by the addition
20
-------
of lime, dry fly ash, and other additives to produce
a dry product called Poz-O-Tec which can be
landfilled. When Poz-0-Tec is properly placed and
compacted in a landfill, it has a lower permeability,
higher density and greater strength than untreated
wastes. Leachate concerns are reduced, and
possibilities for ultimate land reclamation and
usage are increased. The Poz-O-Tec process
generates a dry material, allowing for greater
flexibility in the utilization of disposal areas and
increasing the possibility for by-product utilization
in applications such as roadway pavement.
The Dravo and IUCS processes have been in
operation at several full-scale plants for nearly two
years. Additional data are now being collected to
determine their long-term operational
characteristics.
Fly Ash Blending— One of the easiest ways to
dewater FGD wastes is by adding dry solids such
as fly ash. Without fly ash blending, a maximum of
only 50 to 60 percent solids can be obtained
through gravity settling followed by vacuum
filtration. However, if an equivalent amount of dry
fly ash is added to a 55 percent solids material, an
increase to about 70 percent solids is obtained.
Some power plants have developed their own
blending formulas such as mixing sludge with fly
ash and lime {similar to the IUCS process) or
adding dry fly ash to sludge prior to landfilling.
Treatment Overview—Overall, it appears that
chemical treatment or other stabilization processes
are desirable to improve the FGD waste disposal
operation. Additional cost for these processes are
environmental concerns of
waste disposal alternatives
groundwater
contamination
surface water
contamination
21
-------
minimal, and they greatly enhance the
opportunities for long-term use of the affected site,
commercial utilization
As an alternative to disposal, FGD waste, after
treatment, can be utilized as a raw material
component in the production of various
commercial products. In addition to the utilization
of recovered gypsum, technology has been
developed to use chemically treated FGD waste in
products and applications such as mineral wool,
bricks, concrete products, soil amendment, mineral
recovery, road base materials, parking lot materials,
and aerated concrete. However, in spite of efforts
to promote some of these products, little or no
commercial utilization is occurring in the United
States at present. This situation could change if
these raw materials become more economically
competitive with their presently available
counterparts.
Several recent EPA and utility-funded studies
have been conducted on the potential for
by-product recovery from FGD waste. In one study,
gypsum was used in the manufacture of standard
wallboard, The study identified some potential
problems associated with this utilization of FGD
waste. For example, it was found that the gypsum
containing fly ash can cause wallboard bonding
problems, due to the presence of iron and various
salts in the fly ash. This problem, however, is
characteristic of only certain types of coal. There
are coals that burn with a fly ash that does not
contain sufficient quantities of contaminants to
cause such problems. Fly ash and other impurities
also were found to cause tinting of the wallboard.
However, this may not preclude sale of such
wallboard in some markets.
EPA has also funded two TVA computer model
studies on the potential market for FGD
by-products; one on the feasibility of gypsum
production and marketing for use in wallboard and
cement, and the other on the potential for
production and marketing of by-product sulfuric
acid in the U. S. The pertinent conclusions from
these studies are:
• Cement plants offer the greatest market outlet
for by-product gypsum.
• The wallboard industry, as presently
structured, would provide an extremely
limited market. Use of FGD gypsum in
wallboard could be feasible, however, if new
wallboard plants were built nearby to power
plants, so that savings could be realized in
transportation costs for gypsum,
• At the present price level of elemental sulfur,
the market for by-product sulfuric acid from
power plants would be saturated at
approximately 15 percent of the total market.
International Experience — In contrast to the
U. S., both Japan and the Federal Repubic of
Germany have considerable experience with
nonregenerable FGD and have emphasized the
recovery of usable by-products from the FGD
waste.
In the Federal Republic of Germany, FGD
processes and by-product utilization were under
intensive study, as of late 1977, although there
were no large-scale operational applications of
FGD. Because limited space is available for
disposing of FGD waste, emphasis is being placed
on the development of FGD systems that produce
marketable by-products. One system under
development will produce high grade gypsum for
use in the construction and mining industries and
in the manufacture of cement.
22
-------
economics
"estimates based on 500 MW generating plant and 3.5% sulfur coal
Proceedings: Symposium on FGD, Hollywood, Florida
November, 1977.
In Japan, about 1,000 FGD plants, having a
combined capacity of about 31,000 MW, were
operational at the beginning of 1978.
Approximately half of the total capacity represents
utility boiler applications (primarily oil fired), while
the remainder includes industrial boilers, sintering
plants, smelters, and sulfuric acid plants.
Because natural gypsum is not available in
Japan, forced oxidation in FGD scrubbers has been
employed extensively to produce high-quality
gypsum raw material for the cement and wallboard
industries. Gypsum is by-produced by plants
comprising about 65 percent of the total Japanese
FGD capacity. The remaining FGD plants utilize
waste to by-produce sulfuric acid, elemental sulfur,
ammonium sulfate, and sodium suln'te or sulfate.
Japanese FGD practice has been the subject of
intensive study by U. S. government agencies. An
interagency task force recently completed a study
on the status of FGD in Japan.
economics
The economics of waste treatment, disposal, and
utilization should be considered in selecting SO2
control technologies for utilities and industrial
facilities. This is because the costs associated with
waste management are an important element in
the total costs of installing and operating any
control technology.
FGD technologies are, of course, the primary
methods in use today for SO2 control. There is
sufficient experience with and data available on
FGD control systems in operation on which to base
specific design applications. Further, FGD
technologies are widely applicable to both new
and existing coal and oil-fired boilers.
In searching for the most cost-effective approach
to meeting environmental standards, the use of
some form of coal cleaning in conjunction with
FGD controls should be carefully considered. Users
may find that coal cleaning can be used to reduce
the size of the FGD control system needed. Thus,
physically cleaned coal in combination with stack
gas scrubbing may provide a definite overall cost
advantage. (For more information, see Coal
Cleaning with Scrubbing for Sulfur Control—An
Engineering/Economic Summary, EPA-600/9-77-017.)
Under EPA sponsorship, TVA has been
evaluating costs associated with six alternative
sludge treatment/disposal systems:
Untreated ponding
Dravo process (two variations)
IUCS process
Chemfix process
Untreated sludge-fly ash blending
Landfill disposal of gypsum produced by
forced oxidation of waste
23
-------
The primary emphasis of the TVA work was not
on the feasibility of the disposal technology, but
rather on evaluating the relative economics of the
disposal alternatives.
Results indicate that on a relative basis, the
sludge treatment alternative involving forced
oxidation of the sludge to gypsum requires the
lowest capital investment and lowest total annual
operating cost. This alternative requires a smaDer
capital investment than any other alternative
except untreated ponding where the only major
expense is the disposal pond. The selection of the
forced oxidation alternative would require that a
typical lime/limestone FGD system be modified (at
some additional cost for capital equipment) to
convert the raw FGD waste to gypsum. The
studies also concluded that the alternatives
involving pond disposal require higher capital
investment than all landfill disposal alternatives.
The TVA-derived costs for the alternative FGD
waste treatment processes do not take into account
site-specific waste disposal conditions that a utility
may encounter when selecting a system for
installation. Results discussed here are based only
on a set of pre-determined design and economic
premises and should not be interpreted to
represent a site-specific disposal situation. In the
case of gypsum disposal, they are also based on a
conceptual design only; there is little commercial
experience.
The TVA-derived costs for FGD waste disposal
range from $5 to $9/ton for direct ponding or
landfilling operations. This estimate is well within
the range for disposal of other solid wastes, such
as sanitary landfill of municipal wastes or
sanitary/chemical landfill of industrial wastes.
FBC waste
In the post-1985 period, as utilities invest in
construction of new power plants, FBC technology
may begin to displace the current dominance of
FGD for SO2 control. Although FBC shows promise
for a cleaner-burning process, waste management
will continue to be of concern because of the
potentially large quantities of spent sorbent
generated by the process. Preliminary estimates
indicate that a typical 1000 megawatt FBC plant
may generate as much as 730,000 tons of dry
spent sorbent per year. That is over twice the
amount of ash (300,000 tons) that would also be
generated when burning coal containing about 3.5
percent sulfur and 12 percent ash. The amounts of
spent sorbent generated by AFBC and PFBC
systems are about the same.
The physical characteristics of FBC waste are
quite different from the ash generated in
conventional combustion processes, FBC waste
consists primarily of the dry spent and unspent
sorbent as well as the coal ashes from the bottom
of the combustor. In addition, there is also some fly
ash, which is removed from the flue gas by
participate control equipment. FBC waste is
sometimes described as "soft ash" because it is
only partially in the vitrified or glassy state. It is
made up of soft granular particles, and, after being
cured for several weeks, can be compacted and
used for landfill.
The landfilling disposal option is being actively
investigated to determine its environmental
impact. It appears, at present, that FBC wastes
may be disposed of in a sanitary type landfill
operation with a minimum of environmental
impact. Leaching tests have been carried out on
FBC wastes and the results compared with
standards for drinking water, because water
standards for FBC waste have not yet been
established. These results indicate that the
leachate contains concentrations of calcium,
sulfates, total dissolved solids and alkaline levels
that exceed the standards. The concentration of
trace metals in the leachate is below the standards.
24
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FBC waste
disposal
alternatives
® REGENERATION
CYCLE
(2) NONREGENERATION
PROCESS OR CYCLE
At this point, however, there is no
experience with FBC waste from any
full-scale operational plant and
considerable additional research is
necessary to determine the actual
environmental impact.
Commercial uses for FBC waste
material are also being investigated —
mostly under funding by DOE. The major
obstacles to using the waste are the large
volumes generated, transportation costs,
and availability of competitive raw materials. Fly
ash and bottom ash from conventional coal-fired
power plants have been used in a number of
products for years, but presently only about 20
percent of the total production is utilized. A
summary of areas of potential FBC waste usage is
presented in the accompanying table.
Because of the potentially large c/uantities of
FBC waste material, one of the most likely markets
is in the construction industry for use as road
subbase, synthetic aggregate, or cement.
Preliminary tests have been carried out to
demonstrate the technical feasibility of making
stable solid compacts and to determine the
environmental impact. These tests show that FBC
fly ash and waste sorbent can be substituted for
small amounts of Portland cement in concrete,
while maintaining the same or greater compressive
strength as standard concrete. The FBC residues
may replace up to 100 percent of the aggregate in
asphalt and still maintain its strength. Process
design and economics for these options are being
developed.
Other possible new uses include autoclaved
products such as bricks, hot press sintering-pipes
and metal coatings; gypsum products including
wallboard and plaster; and mineral recovery.
Treatment of acid mine drainage is another
potential use for FBC waste. A program is
presently underway to evaluate the potential use of
FBC waste as an FGD scrubbing reagent and as a
stabilizing medium for FGD sludge. There are also
programs currently at TVA and the U. S.
Department of Agriculture on agricultural
utilization of FBC wastes.
FBC
WASTE
REGENERATED
SORBENT
CONSTRUCTION
MATERIALS
BUILDABLE
LANDFILL
AGRICULTURAL
& OTHER
APPLICATIONS
CHEMICAL
BY-PRODUCTS
25
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FGD waste treatment/disposal
DISPOSAL/TREATMENT
ALTERNATIVES
DESCRIPTION
CURRENT STATUS
ADVANTAGES
1 PONDING
I LANDFILL
I
I MINE
1 DISPOSAL
1
\
i OCEAN
1 DISPOSAL
|f
• • untreated slurried solids
• pumped directly to a
1 pond disposal
W • dewatered or chemically treated
I sludge is hauled to disposal site,
• or untreated slurries pumped
1 there for dewatering or treatment
• • dewatered material placed &
B compacted in excavated area
• • treated or untreated FGD
B wastes deposited In depleted
I underground mines or dumped
B into surface mines
W* bottom dump barge & slurry
• dispersion
• • pipeline outfall
1 • various chemical & physical
• forms (soil or bricklike forms)
B • outer continental shelf or ocean
• one of two primary FGD
disposal methods currently used
• same as ponding
• under development and testing
at controlled mine sites
• surface mine disposal being
planned by several utilities
• ocean dumping used for
many years
• legislation prevents /limits
dumping of harmful materials
• studies on environmental
impact have halted practice
• minimizes operational
processing and transportation
• minimum costs
• avoids land deterioration
and water pollution
associated with ponding
• transportation system already i
place linking power plant & mir
• substantial capacity available
• potential for reducing acid
drainage from mines
• minimizes subsidence (treated
• could alleviate land use limits
in converting plants to coal
• in chemically stabilized brick
form, potential for artificial ree
DEWATERING
• dry solids such as fly ash are
added to slurry after settling
and vacuum filtration, resulting
in 70% solids waste
• currently in commercial use
easy to use
formulas can be varied to
meet specific conditions
suitable for landfill
FORCED
OXIDATION
CHEMICAL
FIXATION
air is passed through slurry
oxidizing the calcium sulfite
waste into gypsum. Gypsum is
dewatered to over 60% solids
several pilot plants now in
operation
extensively used commercially
in Japan
upgrades waste for landfill
potential for saleable by produi
smaller volume than slurry
several commercial processes
that physically stabilize sludge
and chemically fix It to reduce
release of pollutants
several processes commercially
available and in use
improved landfill characteristic
decreased leaching potential
REGENERATION
several processes in which the
absorbed SO2 is removed as
useable sulfur products (sulfuric
acid or elemental sulfur) and the
absorbant is recycled for reuse
• current commercial usage is
extremely limited
• EPA considers Wellman-Lord
process a demonstrated
technology
reduced waste volume
reduced absorbent needed
useable by-product recovered
Potential Utilization of FBC Waste
construction
FBC ash residue for road-paving.
FBC ash and spent sorbent for cement and
concrete.
Bricks from ash residue plus sodium silicate.
Ash residue for cement additive.
Wallboard composition, e.g., FBC
ash-water-organic polymer.
Cement and concrete articles.
Filler on construction sites.
Soil stabilization.
Lightweight aggregate.
26
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DISADVANTAGES
ECONOMIC FEASIBILITY
BY-PRODUCT(S)
potential for ground water and
surface water contamination
degrades large quantities of
and; difficult to reclaim
currently offers low
cost disposal
long term land commitments
could make it a costly
approach in future
jnless treated, waste is
physically unstable and lacks
;ompressive strength
potential for leaching
contaminants into ground &
surface water
• lower capital investment
than ponding
• higher annual operating costs
than untreated ponding
DOtential for ground water
;ontam rnation
DOtential for surface water
contamination (surface mines)
degradation of ocean
snvironment for any untreated
waste on the continental shelf
sr deep ocean
lot as stable as chemical
:ixation
somewhat higher annual
operating costs than untreated
nonbuildable landfill
ligh fly ash content in
jy product
eachate potential similar to
intreated waste
• cement plants greatest
market in U.S.
• wall board market limited
• low capital investment
and operating costs
• gypsum
• buildable landfill
dditional cost
quid wastes require purging
higher annual operating costs
than untreated waste disposal
economic feasibility dependent
on local conditions, markets,
suppliers, etc.
• buildable landfill
sulfuricacid
elemental sulfur
gaseous sulfur dioxide
extraction/separation of ash components
Hydrated lime, calcium sulfate, and ash residue for
subsequent FBC reuse.
agriculture
Soil conditioning, calcium sulfate extract, sintered
FBC ash, fertilizer.
miscellaneous
Extraction of minor components, e.g., alumina as
catalysts or catalyst supports.
Ion-ex changers as catalysts or catalyst supports.
Ion-exchangers as water purifiers; gas adsorbents.
27
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-------
U.S. industry-—primarily the electrical utility
industry—faces many difficult problems and
decisions in complying with the SO2 emission
requirements of the Clean Air Act, as amended in
1977. The recently promulgated New Source
Performance Standards, based on the use of best
available technology for continuous emissions
control, will mandate the application of SO3 control
technology to boilers burning low as well as
high-sulfur coal. Because of the imminent increase
in the installation of SO2 control systems, much
attention is being focused on the problem of
managing the wastes generated by these systems.
The only commercially mature technology
capable of meeting these standards for the near
term is flue gas desulfurization. Choices will
need to be made among the numerous FGD control
processes currently available and among waste
treatment, disposal, and utilization options. Various
factors such as control effectiveness, operating
reliability, waste characteristics, and economics
must be considered in making a choice.
In the post-1985 period, FBC, an emerging
alternate control technology, may have some
advantages in terms of emissions control and
relative ease of waste disposal.
current status FGD
Of the approximately 30 utility power plants
currently {early 1978) using some type of lime or
limestone FGD control system, about two-thirds
pond FGD wastes and one-third dispose of wastes
by landfilling. About 90 percent of the plants
ponding wastes use unlined ponds. Over
two-thirds of all plants dispose of FGD wastes
without any pre-treatment. Although a total of
about 25,000 MW of FGD capacity was installed or
under construction in 1978, the FGD waste
disposal practices described here represent only
those of the nearly 13,000 MW FGD capacity plants
actually operating at that time. This operating FGD
capacity represents about 6 percent of the total
U.S. coal-fired capacity
By comparison, Japan currently has about twice
that percentage (11.5) of its steam electric capacity
under FGD controls. Japanese FGD power plants
under construction or planned, however, amount to
only an additional 5 percent. This reflects Japan's
rapid progress in application of FGD systems
during the early 1970s, and the more recent slow
down in their economy Their experience with FGD
operation and by-product utilization has been very
successful.
In terms of megawatts of FGD capacities, rather
than relative percentages of each country's steam
electric generating capacities, the U. S. of course
has a far greater total. This country's currently
installed, under construction, and planned total
FGD capacity amounts to about 55,000 MW. This
compares to a total of about 14,000 MW for Japan.
current FGD waste
disposal practices
%of
FGD plants
70*
60 •
50i
401
30'
20'
10
lined ponds
unlined ponds
pond
disposal
landfill
disposal
29
-------
current status:
utility FGD control & waste
millions of tons
annually
80
1979
power production
1979
waste production
FGD and FBC waste disposal Issues
As the FBC technology continues to develop,
waste management concerns of FBC vis-a-vis
conventional FGD practices are of growing
interest. The waste disposal issues associated with
FGD and FBC are similar in many respects. Of
course, the FGD process differs significantly from
FBC in design and operation, but a comparison
can be made between FGD and FBC waste
disposal issues. In making this comparison it must
be noted that as of 1978 FGD systems were used in
about 30 full-scale installations, while FBC systems
are still in the developmental stage; a full-scale,
integrated FBC unit waste disposal or regeneration
operation has not yet been tested.
Land Use Impact— Comparisons of the volume
of wastes and the land impact associated with
disposal of solid wastes from FGD and FBC
systems depend on several variable factors.
Among these are the amount of solids in the FGD
waste, the calcium and sulfur ratio and gas
velocity used in the FBC combustor, the amount of
sulfur in the coal burned, and the compaction
characteristics of the solid waste produced.
Depending on the assumptions made for such FBC
and FGD variables, one or the other technology
can be shown to produce more solid wastes. Based
on realistic assumptions, it can be concluded that
the Quantities of solid waste produced by FBC and
conventional FGD systems are of the same order of
magnitude.
The land impact, on the other hand, may be
considerably different if the current practice of
ponding of FGD waste is compared to direct
landfilling of FBC wastes. Ponding of the FGD
waste results in a commitment of this land for the
operating life of the plant, whereas disposal of the
dry FBC waste with successful reclamation of the
land would not involve such a commitment. Forced
oxidation, or other treatment of FGD waste, would
allow landfill disposal and would reduce the land
impact differences between FGD and FBC.
Disposal Options —Disposal options for both
FBC and FGD are generally the same — mine,
ocean and land (landfill or ponding) disposal. It is
unlikely that the ocean disposal will be utilized,
except for research. Mine disposal is a possible
alternative, although it is sensitive to
transportation costs involved. Presently, ponding is
the major method for disposal of FGD sludge.
Landfilling after treatment by one of several
commercially available fixation methods is the
preferred option for new FGD systems. FBC waste
would also be disposed of in landfills.
By-Product Utilization — The projected uses of
FBC waste are considerably greater than for FGD
sludge. This is primarily due to the dry physical
nature of FBC waste, some of which contains a
high percentage of lime. The FGD sludge, on the
other hand, can only be utilized for other
applications after fixation treatment or oxidation.
In the long run, market forces will determine the
extent to which FBC waste and FGD sludge
will be utilized.
30 '
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Disposal Costs — Any cost comparison between
FBC and FGD may be subject to considerable
uncertainty, because there has not yet been a
full-scale FBC waste disposal operation. However,
based on estimates developed by TVA, it appears
that the capital and annual operating disposal
costs for FBC wastes will probably be similar to
those incurred for the FGD-gypsum landfill
operation.
outlook
It is clear that coal will have a key transitional role
in the changeover from fossil fuels to sustainable
or renewable energy sources. Improved
environmental control technology and cleaner
combustion processes will ameliorate the air
pollution problems associated with the increased
use of this fuel. FGD, coal cleaning, and FBC
technologies will increasingly be applied to new
coal-fired power plants and industrial boilers.
Of the small percentage of coal-fired power
plants that used FGD technology to control SO2
emissions in 1978, less than half (about 4,500 MW)
used any waste pre-treatment processing before
disposal. It is clear that the waste problems
associated with the expected increased use of
control technologies will require more extensive
waste disposal pre-treatment and more effective
waste utilization approaches in the future.
Experience so far, both in the U. S. and abroad,
has shown that environmental control techniques
can be reliable and effective, and that the
environmental impacts associated with
combustion and control wastes can be
maintained within acceptable limits.
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Advanced Fossil Fuels and the
Environment, EPA Decision Series,
EPA 600/9-77-013, Office of Energy,
Minerals and Industry, Office of
Research and Development, U. S.
Environmental Protection Agency
(June 1977).
This report reviews five major
advanced fossil fuel processes and the
control technologies being developed
for them.
Economics of Disposal of Lime/
Limestone Scrubbing Wastes:
Untreated and Chemically
Treated Wastes, EPA 600/7-78-023a,
Industrial Environmental Research
Laboratory, Office of Research and
Development, U. S. Environmental Pro-
tection Agency and the Tennessee
Valley Authority (February 1978).
A joint EPA-TVA study, conducted to
provide detailed comparative eco-
nomic evaluation of four alternatives
available to the utility industry for
disposal of waste produced from flue
gas desulfurization systems, using
limestone or lime slurry scrubbing.
The four alternatives evaluated were
untreated sludge and three different
commercial processes for treating
sludge. A 3.5 percent sulfur coal was
used for all cases.
Energy/Environment II, EPA
Decision Series, EPA 600/9-77-012,
Office of Energy, Minerals and
Industry, Office of Research and
Development, U.S. Environmental
Protection Agency (November 1977),
pp. 137-147.
A joint EPA-TVA report summarizing
the current program for the
environmental management of
effluents and solid wastes from
steam-electric generating plants.
Sulfur Oxide Throwaway Sludge
Evaluation Panel (SOTSEP),
Volume I: Final Report —
Executive Summary, EPA
650/2-75-010-a, Office of Research and
Development, National Environmental
Research Center, U.S. Environmental
Protection Agency {April 1975).
This report presents the results of an
intermedia evaluation of the
environmental and economic factors
associated with disposal or utilization
of sludge from nonregenerable flue gas
desulfurization processes. Although
the report is rather technical, it does
give one of the best overviews of the
FGD sludge disposal/utilization
problems.
Proceedings of the Symposia on
Flue Gas Desulfurization,
Sponsored by the Industrial
Environmental Research Laboratory,
Office of Research and Development,
U.S. Environmental Protection
Agency.
Symposia are held annually and
include a variety of technical papers
from industry and government
representatives which deal with the
status of FGD technology in the
United States and abroad. Subjects
covered include: regenerable,
nonregenerable, and advanced
processes; process costs; and
by-product disposal, utilization and
marketing.
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An Evaluation of the Disposal of
Flue Gas Desulfurization Wastes
in Mines and the Ocean: Initial
Assessment, EPA 600/7-77-051,
Industrial Environmental Research
Laboratory, Office of Research and
Development, U. S. Environmental
Protection Agency (May 1977).
An initial assessment of the
environmental, technical, regulatory,
and economic aspects of disposing
FGD sludge in mines and in the
ocean.
State-of-the-Art of FGD Sludge
Fixation, EPRIFP-671, Project 786-1,
Final Report, January 1978, prepared
by Michael Baker, Jr., Inc., Beaver,
Pennsylvania.
A comprehensive, up-to-date survey
of all of the available FGD sludge
fixation technology including details
of technologies in current use at U. S.
utilities.
Proceedings of the Fourth
International Conference on
Fluidized-Bed Combustion,
December 9-11, 1975, Sponsored by
the U. S. Energy Research and
Development Administration,
Washington, D.C., Coordinated and
Published by The Mitre Corporation,
McLean, VA (May 1976).
Includes 38 technical papers from 7
sessions on the state of FBC
technology. Areas covered include:
Bench and lab-scale studies, pilot and
demonstration plants, process
problems, SO2 absorption and
regeneration, emission and control
technology, and commercialization
prospects.
Controlling SO2 Emissions from
Coal-Fired Steam-Electric
Generators, Volume II: Technical
Discussion, EPA 600/7-78-044b
(NTIS No. PB281100) March 1978.
This study supports a review by the
EPA Office of Air Quality Planning and
Standards, Office of Research and
Development, Durham, North
Carolina, of proposed New Source
Performance Standards for sulfur
dioxide emissions from coal-fired
steam electric generators, considering
three alternate strategies for removal
of SO2. It provides an assessment of
technological, economic, and
environmental impacts, projected to
1998, of the increased solid wastes
resulting from the application of the
various more-stringent controls as well
as the current NSPS.
Effects of Setting New Source
Performance Standards for
Fluidized-Bed Combustion
Systems, Final Report, March 1978,
Energy Resources Company Inc.,
Cambridge, Massachusetts 02138.
This study was undertaken for the
U. S. Environmental Protection
Agency to examine the potential
consequences of revisions in New.
Source Performance Standards on
fluidized-bed combustor based steam
electric generators. It studied the
appropriateness of differential effects
of alternate regulatory approaches to
the standards-setting process. An
examination was made of the
potential benefits of fluidized-bed
systems relative to conventional
coal-fired systems equipped with FGD
scrubbers.
Proceedings of the Fluidized
Bed Combustion Technology
Exchange Workshop, April 13-15,
1977, Sponsored by the U. S. Energy
Research and Development
Administration and the Electric Power
Research Institute, The Mitre
Corporation/Metrek Division, McLean,
VA (August 1977}.
This two volume set contains the
technical papers from a six session
workshop covering all aspects of FBC.
Sulfur in the Atmosphere: Pro-
ceedings of the International
Symposium held in Dubrovnik,
Yugoslavia, 7-14 September 1977.
Pergamon Press, Elmsford, New York.
Visibility reduction, acid rain, possible
effects on human health, and weather
and climate modification are evidently
associated with the reaction products
rather than with SO2 itself. Since the
sulfate formation typically continues
over a period of a day or more, the
near field dispersion and maximum
ground level concentration of primary
pollutants were not considered in de-
tail. Several invited and contributed
papers focus on the size distribution
and chemical composition of aerosol
sulfur compounds, as well as on asso-
ciated measurement and monitoring
techniques.
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