United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-86/015e July 1986
v°/EPA Project Summary
Coal Gasification Environmental
Data Summary: Trace Elements
Larry J. Holconbe, Ronald D. Achord,
Robert A. Magse, and Robert M. Mann
This report summarizes trace element
measurements made at several coal gas-
ification facilities. Most of the measure-
ments were madu as part of EPA's source
testing and evaluation program on low-
and medium-Btu gasification. The behavior
of trace element:: is discussed in light of
their distribution from feed coal to various
discharge, product and by-product streams.
This summary piovides a basis for deci-
sions concerning monitoring needs at coal
gasification facilities.
The stream flow data and trace element
concentration measurements were typi-
cally not precise or accurate enough to
make quantitative conclusions concerning
trace element behaviors in the gasifiers.
However, some general trends in element
distribution are apparent. Elements that
consistently had more than 70 percent of
their total inlet mass partition to the bot-
tom ash or slag included aluminum, bar-
ium, cobalt, potassium, uranium, tungsten,
and zirconium. Other elements consistently
had less than 70 percent of their mass par-
tition to the bottom ash, and had signifi-
cant mass flow in the overhead gas and
aerosols. They included antimony, arsenic,
bromine, cadmium, chlorine, germanium,
iodine, lead, mercury, selenium, and thal-
lium. Other elements measured in the
gasifier output streams had varying be-
haviors depending on the gasifier. Un-
known controlling factors and the varia-
bility of the processes precluded com-
parisons between the trace element be-
haviors in the different gasifiers.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Triangle
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
This summary report presents and dis-
cusses trace element and other selected
minor and major element distributions at
the coal gasification facilities tested dur-
ing eight EPA studies, and from the Kel-
logg-Rust/Westinghouse (KRW) PDU, Syn-
thane, and Lurgi (SASOL) process char-
acterizations. The U.S. EPA data acquisi-
tion studies were conducted at the follow-
ing synthetic fuel facilities.
• Chapman low-Btu gasifiers at King-
port, TN;
• Wellman-Galusha low-Btu gasifiers at
the Bureau of Mines Twin Cities Met-
allurgy Research Center, Fort Snell-
ing, MN, and Glen Gery Brick Com-
pany, York, PA;
• Riley Gas Producer low-Btu gasifier at
Worcester, MA;
• Foster-Wheeler/STOIC low-Btu gasi-
fier at the University of Minnesota,
Duluth;
• Koppers-Totzek medium-Btu gasifiers
at Modderfontein, South Africa;
• Lurgi-type medium-Btu gasifiers at
Kosovo, Yugoslavia; and
• Texaco medium-Btu gasifier at the
Ruhrkohle/Ruhrchemie facility in
Oberhausen-Holten, Federal Republic
of Germany.
Considerable research has been con-
ducted to define trace element distribution
and emissions from coal combustion faci-
lities. A number of groups have researched
the volatility and distribution of elements
in specific ash fractions and other dis-
charge streams at coal combustion plants.
The data from seven of the source test
and evaluation studies and results from the
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KRW, Synthane, and Lurgi (SASOL) pro-
cess characterizations were evaluated,
and general behavior trends are presented
in this report. Wide variations may exist
between trace element behavior in the
various processes; however, the general
trends reported here will serve as a
guideline for further source testing or
discharge stream monitoring.
Objectives
The purpose of this report is to char-
acterize the partitioning of trace elements
between the various gasification process
streams and to compare that partitioning
among gasifier processes. This summary
is based on data obtained from source
testing at several coal gasification facili-
ties. In some cases, enough data were
obtained to close the material balance on
all discharge streams and by-products.
This entails having trace element concen-
tration and flow data on the product gas,
major cleanup streams (typically cyclone
dust), solid ash, and ash sluice water.
However, in most of the source tests the
product gas trace element data were not
available. In these cases, the trace element
distributions in the discharge and by-pro-
duct streams are expressed as a percent
of the total trace element input in the coal.
This is the same as assuming that the total
trace element flow from discharge streams
is equal to the total input (coal) trace ele-
ment flow. This assumption is not entirely
accurate due to large imprecisions in flow
and concentration measurements. How-
ever, in most cases the results are ade-
quate to identify general trends of trace
elements in the gasification processes.
Conclusions
Data from seven gasification processes
were evaluated for trace element distribu-
tions: Chapman, Wellman-Galusha (Glen-
Gery), Wellman-Galusha (Ft. Snelling),
Riley, Foster Wheeler/STOIC, Lurgi-type,
and Texaco.
In addition, data collected at the Syn-
thane Pilot Plant, Lurgi (SASOL), and
Kellogg-Rust/Westinghouse (KRW) PDU
were included for comparison.
Trace Element Distributions
Trace elements enter the gasification
process in the coal feed. In the gasifier the
fraction of coal that does not combust
moves to the bottom of the gasifier as ash
or slag. The gas produced contains vapor-
ous trace elements as well as dust and
aerosols containing trace elements.
The flow measurements and concentra-
tion (mass) measurements made in these
gasification tests had inherent impreci-
sions. Comparisons between the total
mass flow of individual elements entering
the gasifier in the coal and the sum of the
mass flows exiting the gasifier confirmed
this imprecision in many trace element
measurements. A ratio of mass flow in/
mass flow out should be unity for a perfect
mass balance. Actual ratios were often
much greater or less than unity, depending
on the element or analytical method. De-
spite these imprecisions, which include
more than just analytical imprecision,
general trends in trace element distribution
and behavior were apparent. These trends
are noted below:
• Seven elements consistently had
more than 70 percent of their total
inlet mass partition to the bottom ash
or slag (for all gasifiers evaluated):
aluminum, barium, cobalt, potassium,
uranium, tungsten, and zirconium.
• Eleven elements had consistently
less than 70 percent of their mass
partition to the bottom ash. Where
overhead stream measurements were
made, these elements had greater
than 20 to 30 percent mass flow in
the overhead gas and the dust and
aerosols entrained with the gas: an-
timony, arsenic, bromine, cadmium,
chlorine, germanium, iodine, lead,
mercury, selenium, and thallium.
Data were neither precise enough nor con-
sistent enough to be able to make any con-
clusions comparing the differences in
trace element behavior between different
gasifiers.
Overhead gas streams are routed
through control devices to remove unde-
sirable constituents such as dust, heavy
tar, acid gases, and organic gases. By-
products, such as tar, oil, and naphtha,
may also be removed.
The tendency for trace elements to dis-
tribute in the dust captured in cyclones
was evaluated by examining data from
four fixed-bed gasifier tests. The follow-
ing elements were highly enriched (relative
to the coal ash) in the cyclone dust: anti-
mony, arsenic, bismuth, cadmium, gallium,
germanium, lead, mercury, and tin. (NOTE:
The enrichment factor is the ratio of the
concentration of the element in the stream
to that of ash in the stream, divided by the
ratio of the concentration of the element
in the coal to that of ash in the coal.) Ad-
ditionally, thallium and zinc were enriched
in the cyclone dust from the four fixed-bed
gasifiers, and nickel was enriched in the
gas particulate matter from KRW.
Trace element concentrations were mon-
itored in several gas cleanup waste and by-
product streams at the Lurgi-type (Kosovo)
gasifier. The gas cleanup streams moni-
tored, in order of successive downstream
location, were heavy tar, light tar, and
medium oil. Six of the elements measured
during a test at the Lurgi-type (Kosovo)
gasifier showed slight depletion in the
gasifier ash and a generally increasing
enrichment factor in the cleanup streams
successively downstream. In other words,
these elements (lead, chromium, stron-
tium, arsenic, selenium, and copper) were
more highly enriched in the medium oil
than in either the light or heavy tar.
Environmental Issues
Solid Waste
The gasifier ash or slag carries the
greatest mass of trace elements from the
process. Cyclone dust, also a solid waste
stream, is another vehicle for discharge of
trace elements from the gasifier. The ulti-
mate fate of trace elements carried from
the process in the solid waste streams is
a function of the method of disposal. Trace
elements in the gasifier ash/slag or cyclone
dust may enter the environment as a result
of leaching by run-off waters from surface
disposal sites or by leaching from landfills
into ground water. Trace element concen-
trations in mild acidic teachings (RCRA EP
Toxicity Test) of gasifier ash and cyclone
dust were compared to RCRA maximum
permissible concentrations. All solids
tested were nontoxic by the EP Toxicity
criteria.
Aqueous Discharges
Water that is used to quench or trans-
port the ash or cyclone dust is another
vehicle for discharge of trace elements
from the gasifier. The concentration of
trace elements in the ash water depends
on the form of the element in the ash, the
length of time the ash is in contact with
the water, and the physical characteristics
of the ash. Concentrations of trace ele-
ments in ash or cyclone dust sluice waters
were compared to the strictest drinking
and irrigation water quality criteria. Under
normal procedures these criteria would not
be used in a direct comparison to assess
environmental risk. Some consideration
for dilution or the eventual discharge of the
water would be made prior to establishing
pollutant discharge limits. However, the
criteria provide a relative basis to identify
elements which may be of environmental
concern in the ash waters. Trace elements
that exceeded the strictest criteria at one
or more of the plants were barium, boron,
chromium, mercury, manganese, and
molybdenum.
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Gaseous Discharges
Gaseous discharges with trace element
concentrations of possible environmental
concern are fugitive emissions (pokehole
gases, coal hopper vent gases, and other
vent gases). Only a few fugitive emissions
were measured directly. However, it can be
assumed that fugitive emissions will be
similar in chemical composition to the pro-
duct gas, except for different particle
loading. Product gas concentrations of
trace elements from four fixed-bed gasi-
fiers were compared to work place TLVs
(Threshold Limit Values) to indicate poten-
tial environmental and health concerns. In
this direct comparison of product gas con-
centrations to TLVs, dilution by work place
air or loss, through settling, of entrained
particulate matter has not been consi-
dered. Elements which exceeded the TLV
in at least one stream included aluminum,
arsenic, barium, beryllium, cadmium, cop-
per, iron, lead, mercury, selenium, silver,
and tellurium. All but arsenic, copper, lead,
silver, and tellurium exceed the TLV, due
solely to their particulate matter
contribution.
Vaporous trace element concentrations
were measured in the gas phase only at
the KRW PDU. Considerably fewer ele-
ments were analyzed at KRW than at the
four fixed-bed gasifiers. Only nickel in the
subbituminous coal test exceeded the TLV.
L. Holcombe, R. Achord. R. Magee. andR. Mann are with Radian Corp.. Austin, TX
78766.
William J. Rhodes is the EPA Project Officer (see below).
The complete report, entitled "Coal Gasification Environmental Data Summary:
Trace Elements," (Order No. PB 86-195 278/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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