United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-86/015c June 1986
&ERA Project Summary
Coal Gasification
Environmental Data
Summary: Solid Wastes and
By-Product Tars
A. Gwen Eklund
This report is one of several data
summary reports on environmental as-
pects and pollutants specific to coal
gasification. It addresses characteris-
tics of solid wastes (ash and cyclone
dust) and by-product tars and oils ana-
lyzed in nine EPA source tests and eval-
uation studies and limited other data.
The objectives of this report were to
compile and summarize solid waste
properties and identify behavioral
trends. The results of this data compila-
tion showed that gasifier ash and cy-
clone dust are nonhazardous under
RCRA and negative according to se-
lected bioassay tests. However, ash
compositions differed with different
processes, operating conditions, and
feedstocks. Tars and oils are more likely
to pose environmental problems due to
detectable concentrations of polynu-
clear aromatic compounds, other toxic
and carcinogenic organic compounds,
and entrained trace elements. How-
ever, high heating values of tars and
oils make them candidates for use as
fuels if the inorganic residues are
treated properly. Engineering and
leaching properties of gasifier solid
wastes are not sufficiently defined to
allow a good evaluation of disposal al-
ternatives.
This Project Summary was devel-
oped by EPA's Air and Energy Engineer-
ing Research Laboratory, Research Tri-
angle Park, NC, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
During the past decade, the EPA has
conducted many data acquisition stud-
ies at synthetic fuel facilities in order to
characterize the different processes and
discharge streams. These data have
been used to evaluate applicable con-
trol technologies and to estimate poten-
tial discharge characteristics from com-
mercial plants. Compilation of EPA's
Environmental Assessment data allows
identification of potential environmen-
tal problems and special monitoring
needs for specific synfuel processes.
Under the Energy Security Act, the EPA
will use these Environmental Assess-
ments to advise on the adequacy of pro-
posed Environmental Monitoring Plans
and participate in Monitoring Review
Committee activities for projects receiv-
ing financial assistance from the Syn-
thetic Fuels Corporation (SFC).
This report is one of several data sum-
mary reports on environmental aspects
and pollutants specific to coal gasifica-
tion. It addresses characteristics of solid
wastes (ash and cyclone dust) and by-
product tars and oils from synthetic fuel
facilities studied by the U.S. EPA and
others. The facilities discussed here
were selected on the basis of greater
availability of process, gas, liquid, and
solid phase data. These processes in-
clude: Chapman (low-Btu), two
Wellman-Galusha (low-Btu), Riley Gas
Producer (low-Btu), Foster-Wheeler/
STOIC (low-Btu), Lurgi-type (medium-
Btu), Kellogg-Rust/Westinghouse
(medium-Btu, funded by the Gas Re-
search Institute), two Koppers-Totzek
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(medium-Btu), and Texaco (medium-
Btu, funded jointly by EPA, TVA, and
EPRI).
The conversion of coal to gaseous
fuels results in the generation of large
quantities of solid waste that must be
used beneficially or disposed of in an
environmentally acceptable manner.
Commercial-scale coal conversion facil-
ities are uncommon in the U.S.; thus,
practical experience with, and research
on, coal conversion solid wastes has
been limited. Fundamental environ-
mental questions about these wastes
are related to elemental partitioning in
gasification systems and to the mobility
of components in gasification solid
wastes when contacted by aqueous so-
lutions during disposal. Differences in
feed coal and process conditions affect
the composition and teachability of
these wastes; therefore, proper dis-
posal cannot be dictated by the nature
of the conversion process alone or the
feedstock alone. Coal conversion solid
wastes that are demonstrably similar,
both physically and chemically, to well-
characterized combustion wastes will
probably be handled in the same man-
ner as combustion wastes.
Data from the source testing and eval-
uation studies for the solid waste by-
products include: elemental composi-
tion of components, radioactive
speciation, organic analysis, evaluation
of leaching potential, health and
ecology-based bioassays, and a limited
array of physical properties related to
handling and disposal characteristics.
These data are evaluated in this report
for general trends in behavior and pos-
sible correlations with processes.
Although composition and leaching po-
tentials differ for the conversion pro-
cesses, general trends will be useful in
determining disposal and monitoring
requirements.
Objectives
This report addressed the characteris-
tics of coal gasification solid wastes and
by-product tars and oils analyzed dur-
ing nine EPA source tests and evalua-
tion studies.
Major objectives of this report in-
clude: (1) compilation and summary of
characteristics of solid wastes and
streams—ash, cyclone dust, and by-
product tar and oil from gasifiers;
(2) evaluation of behavioral trends in
data with respect to processes; and
(3) identification of unresolved issues.
Results and Conclusions
The major solid waste streams from
gasification processes include coarse
ash or slag and cyclone dust. The major
solid process streams likely to be dis-
charged are by-product tar and oil.
The gasifier ash and cyclone dust
originate primarily from the inorganic
components in the coal. Data have
demonstrated that these materials are
non-hazardous under the criteria and
test procedures of the Resource Conser-
vation and Recovery Act (RCRA). How-
ever, the physical characteristics and
the composition of the waste can vary
widely as a function of process configu-
ration, operation, coal feed composi-
tion, and coal handling. In addition,
these solids do not exhibit a hazardous
biological response in bioassays.
When values for elemental concentra-
tions in ashes from this series of source
tests are generally compared to ele-
mental compositions found in other
gasifier ashes, ranges of elements in the
waste residues are generally similar.
Available physical properties data, such
as densities and particle size distribu-
tions, for gasifier ashes are closer to
conventional combustion bottom ash
than fly ash properties. Other studies
have shown that slags produced from
gasification and conventional combus-
tion are also similar. These results sug-
gest that gasifier slags may not require
solid waste management practices sub-
stantially different from those currently
used for coal combustion solid wastes
solely based on the elemental composi-
tional data for the slags. Until unre-
solved issues are better defined, testing
should be on a case by case basis.
Elemental concentration ranges in cy-
clone dusts from these source tests are
comparable to ranges found in other
gasifier wastes analyzed in other stud-
ies. The cyclone dust is also similar in
composition to the gasifier ash. Ele-
ments enriched in the cyclone dusts in-
cluded lead, tin, zinc, antimony, and ar-
senic for most of the EPA Source
Testing of gasifiers.
The cyclone dust, the finest fraction of
the gasifier solid waste, resembles con-
ventional fly ash. These wastes have
also been shown to be morphologically
similar based on scanning electron mi-
crographs. This similarity extends to
major oxide constituents: SiO2, AI2O3,
and CaO. Proximate/ultimate analyses
of cyclone dusts generally had high
heating values (as high as > 10,900 Btu/
Ib), indicating that recycle as a fuel may
be a viable alternative to disposal. Alter-
natively, since they have high heating
values, they might be used as fuels.
Polynuclear aromatic compounds
(PNAs) contribute greatly to possible
environmental problems of discharge
streams containing tar and oil. These
streams include heavy tar solid wastes
and gaseous discharges from areas
where tar makes up a large portion of
paniculate matter discharged. Ben-
zo(a)pyrene is one of the most poten-
tially hazardous PNAs identified in gasi-
fier tars. Besides containing toxic or
carcinogenic organic compounds, tars
also contain many trace elements.
Therefore, tar and oil streams are poten-
tially hazardous and may require careful
disposal. Alternatively, since they have
high heating values, they might be used
as fuels.
Proximate/ultimate analyses of the
gasifier by-product tars indicate high
heating values which may encourage
use of these wastes as a combustion
fuel rather than codisposal with other
solid wastes. However, metals could be
an environmental concern with inciner-
ation due to concentration enhance-
ment in the final residue. High carbon
and volatiles may indicate a possibility
of a hazardous waste classification ac-
cording to the ignitability characteristic.
Engineering properties of gasifier
slag, cyclone dusts, tars, and oils have
not been well defined; however, slag
and dust appear similar to conventional
coal combustion wastes and are likely
to be landfilled using current technol-
ogy. Tars and oils could be codisposed
with solid wastes, although this might
affect their RCRA classification. (Under
RCRA, tars and some oils probably will
be evaluated as solid wastes.) Obvi-
ously, utilization of these streams is
preferable to disposal.
Detailed characterization and leach-
ing data are needed to relate waste
properties to process types and vari-
ables. In evaluating possible environ-
mental problems from leaching of these
wastes, the RCRA Extraction Procedure
Extracts and the ASTM Extracts did not
exceed the established criteria. Al-
though ash-slags would be classified as
"nonhazardous" under currently pro-
posed RCRA criteria, soil attenuation
experiments would permit a better as-
sessment of actual impacts to affected
ground and surface water systems.
Some studies of this type are already
underway at Oak Ridge National Labo-
ratory. In general, leaching studies of
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gasifier ashes have shown that both in-
organic elements and polynuclear aro-
matic hydrocarbons in the leachates are
relatively low and at this time appear
not to be of significant environmental
concern. The major environmental im-
pact associated with disposal of these
wastes may be the sulfate dissolution
and potential acidification of ground-
water. However, studies of soil attenua-
tion of soluble constituents leached
from coal conversion solid wastes have
shown that soil properties control the
degree of attenuation to a greater extent
than the chemical composition of the
waste leachates.
To better assess disposal constraints,
engineering and physical properties
(e.g., permeability, load bearing capac-
ity, strength, and flow properties) would
have to be evaluated. To determine the
effects on the environment of these
wastes in a given disposal site, bench
scale and field studies may be required.
These field data, in conjunction with
comprehensive characterizations of
wastes and their leaching properties,
may be used to predict leaching and at-
tenuation behavior of mobile pollu-
tants. Design and operation guidelines
for coal gasification waste disposal sites
should consider the chemical and phys-
ical characteristics of the waste, and
their behavior in the environment.
A. G. Eklundis with Radian Corporation. Austin, TX 78766.
William J. Rhodes is the EPA Project Officer (see below).
The complete report, entitled "Coal Gasification Environmental Data Summary:
Solid Wastes and By-Product Jars.." (Order No. PB 86-192 283/AS; Cost:
$16.95, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
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