United States
Environmental Protection
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-87/024  Feb. 1988
Project Summary
Pollution  Control
Considerations  for  Low-  and
Medium-Btu  Coal Gasification

William E. Corbett, Lynn M. Erickson, and Nancy P. Meserole
  This report contains a summary and
an analysis of data collected by the U.S.
EPA from 1977 to 1981, which relate
to the characteristics of controlled and
uncontrolled waste streams from low-
and medium-Btu gasification pro-
cesses. This analysis focuses on the key
waste streams which are  likely to
require control in  a commercial coal
gasification facility and identifies the
pollutants which will have the greatest
impacts  on pollution control process
selection, design, and/or performance.
Key data gaps and areas of process/
performance uncertainty which should
be considered  by  permit writers and
reviewers of proposed environmental
monitoring plans are indicated.
  This Project Summary  was devel-
oped by EPA's Air and Energy Engi-
neering 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).

  In the past  decade, the  EPA  has
conducted numerous  environmental
data acquisition studies at coal gasifica-
tion facilities both in the U.S. and abroad.
Facilities employing moving-bed, fluid-
bed, and entrained-bed coal gasifiers
have been examined,  and data  on the
characteristics of key process and waste
streams have been obtained from these
sampling programs. These data  can be
used to define the general characteristics
of the waste streams produced in com-
mercial coal gasification facilities and to
evaluate  potentially  applicable  control
  The EPA is called upon periodically to
provide assistance to state and local
regulatory authorities who must issue
new facility construction and operating
permits. These authorities may  require
support in assessing the adequacy and
appropriateness of  proposed control
strategies and discharge limits.  The
EPA's environmental assessment data
base provides information to aid these
groups in:

• Identifing environmental and health
  issues requiring  further definition
  through data acquisition;

• Recognizing  process- or facility-
  specific waste stream characteristics
  which should be considered in control
  process selection design; and

• Identifying areas of control  process
  performance uncertainty.

  In order to  support this effort,  five
documents have been prepared which
address specific categories of environ-

mental  pollutant discharges. These
categories are: sulfur and nitrogen
species, organics, trace elements, waste-
water, and solid wastes. Each document
summarizes  the  environmental  data
gathered at a series of facilities employ-
ing   moving-bed,  fluid-bed,   and
entrained-bed gasification  processes.
These data  have been  evaluated to
identify  trends and/or develop correla-
tions  that can  be used to assess the
characteristics of discharge  streams
associated  with  different gasification
  This report summarizes the findings of
the five  reports from the standpoints of:
relative  waste  stream characteristics;
relative  potential  control  options;  and
data gaps which,  if filled, might resolve
some indicated areas of uncertainty.
  This presentation is organized accord-
ing to the  general class of  the waste
stream (gaseous, aqueous, or solid) being
  Note that many of the facilities where
EPA-sponsored tests were  conducted
were  either:  (1)  developmental units
which were  not equipped  with  fully
integrated pollution control systems, or
(2) commercial facilities which are not
designed to meet current U.S. environ-
mental standards. Thus, much of the data
which were acquired should be viewed
as being more representative of control
process  input streams than  discharges
from a modern, well controlled facility.

  The overall objective of this report is
to present a concise summary of publicly
available information related to the
characteristics of  controlled and uncon-
trolled waste streams from commercial
scale coal  gasification processes.  The
data  available  from  environmental
assessment  efforts, supplemented by
literature data, are compiled, summar-
ized, and evaluated to-

• Identify  trends in pollutant behavior
   across processes;

• Identify unique or specific waste
   stream  characteristics  of individual
   gasification processes;

• Compare control  process selection,
   design,  and performannce issues,
   revealing those common  to all  pro-
   cesses and those unique to individual
   processes; and
• Recommend ways to monitor future
   commercial scale systems to further
   define unresolved issues or to confirm
   trends in pollutant behavior.

This document provides those  involved
in assessing pollution controls for new
gasification  facilities,  both  facility
designers and  regulatory agencies, with
a consolidated source of information on
available performance data and current
commercial practices.

Results and Conclusions
  Comments  on the characteristics of
key  gasification  process discharge
streams, potential control options for the
pollutants which may be present in those
streams, and  additional  data  require-
ments are summarized in Tables  1, 2,
and  3. These  comments were derived
from an analysis of the data gathered in
the  EPA-sponsored source  test and
evaluation programs  which  are the
subject of this  report.
  In the design of most new  coal gas-
ification facilities, the high volume waste
streams  listed in Tables 1 through 3
generally receive the most attention from
the standpoint of control strategy devel-
opment and detailed design review. The
comments offered in the tables related
to the availability of data  are consistent
with this level of interest. Most of the
high  volume   discharge streams listed
have been  studied extensively, and
representative characterization data are
available for  a wide  range of gasifier
types and operating modes. Most of the
low volume discharge streams, however,
have not received as much attention m
past test programs. Generally, control
processes for  these streams are not as
well defined or demonstrated  as those
which apply to the high volume streams.
As noted, characterization of some of the
low volume   discharge  streams and
evaluations of control  processes which
may be applicable to them should be a
primary goal  of future data acquisition
  Of the gaseous  discharge  streams
listed in Table 1, combustion flue gases
and acid gases/tail gases from acid gas
removal/sulfur recovery systems are the
two highest  volume  waste   streams.
Because these streams are common to
many existing and   most proposed
commercial-scale coal gasification facil-
ities, applicable control techniques  for
these streams are well established, and
several types are commercially available.
Many of the  remaining gaseous dis-
charge streams listed are the result of"
venting losses.  Coal feeder vent gases,
flash gases, by-product storage tank vent
gases,  and fugitive losses all  contain
varying amounts of the pollutant species
found in raw product gas. Because of this
characteristic, these streams are usually
either recycled or incinerated. Other vent
gases and offgases have highly varying
flow rates and  compositions, and con-
trols for those  streams  must take into
account their  unique  sources  and
  The  two  aqueous discharge streams
which result directly from the quenching
and cleaning  of the raw product gas are
raw gas liquor/process condensate and
acid gas removal (AGR) condensate.
These  streams  generally have  similar
compositions  and  may be  blended
together for  treatment.  Another high
volume discharge stream  is  cooling
tower blowdown. Although generated in
large quantities, this stream is usually
of little concern because it should not
contain materials unique to coal gasifi-
cation  facilities unless treated  process
wastewater is  used as  cooling tower
makeup. The other aqueous discharge
streams will  have varying  types and
amounts of contaminants depending on
their source. Environmentally acceptable
and cost effective treatment and disposal
techniques for  these streams will  like-
wise be unique  to each application.
  Many of the solid discharges generated
in the quenching  and cleaning of the
gasification process still  retain good fue
qualities and  can be recycled or used as
fuel in boilers or incinerators. Coal fines
char/ash fines in  product gas,  and by
product tars  and oils generally do no
pose a waste disposal problem because
they are among the by-products/waste;
that can be used as fuel. Available dat<
on  ashes from combustion processes
particularly gasifiers and steam/powe
boilers, suggest that these residues cai
be disposed of as non-hazardous wastes
Testing of specific  ashes/residues  i
needed to confirm  this characteristic
  By-product sulfur is usually assume*
to be of saleable quality. Disposal option
for contaminated or off-spec sulfur hav
not been addressed publicly. Likewise
very limited  data  are available whic
describe the  characteristics,  treatmer
methods, or disposal options for most c
the low volume solid discharges fror
coal gasification  facilities. Generall
these streams are specific to the dowr
stream treatment processes  chosei

Although these  streams are of  low
volume, they may contain pollutants at
high  enough  levels  to require special
treatment or disposal.
Table 1.    Caseous Discharge Streams: Characteristics. Control Options, and Data Base Status
        Waste Stream
       Characteristics and
      Determining Factors
     Typical and/or Possible
        Control Options
         Status of Data
High Volume Wastes

flaw or Quenched Gasifier
Product Gas"
Combustion Flue Gas
Acid Gases
Low Volume Wastes
Coal Feeder Vent Gases
Flash Gases from Liquid
Product/Waste Stream
Vent Gases from By-Product
Storage Tanks
Low-Btu (air blown) gasifiers
produce a high N2, low CO2
product gas. Oxygen-blown
gasifiers produce a low-Nz, high
COz product gas. A diverse array
of reduced sulfur- and nitrogen-
containing species are also
normally found in this stream with
the distribution determined by the
coal type and gasifier operating

Characteristics depend on
combustor feed stream properties
and combustor design/operating
characteristics. Generally, /V0«,
SOX, and particulates are the
main flue gas contaminants
present. Trace elements and toxic
organics may be present at low
but still environmentally
significant levels.
All acid gas removal systems
produce HzS-rich streams; some
also produce COz-rich streams if
the A GR system is operated in a
selective mode. Hydrocarbons,
reduced nitrogen species, and
non-HiS reduced sulfur species
may also be present at significant
Composition similar to raw
product gas unless inert
pressurants or seal fluids
employed. Amount produced
depends on gasifier operating
pressure and feeder system
design features.

Composed of volatile and semi-
volatile components of raw
product gas with specific
composition determined by
Composed of VOCs and reduced
sulfur/nitrogen species present in
Paniculate removal followed by
processes to remove reduced
sulfur/nitrogen species and
possibly COi and hydrocarbons
depending on product gas end use
A combination ofNO*. SO«,
paniculate, and/or toxic
substances controls. Monitoring
and control of combustion process
variables can be used to achieve
acceptable combustion
efficiencies while minimizing NO,
formation. Add-on controls
generally used to achieve
acceptable paniculate and/or SOi
emissions control.

All AGFt systems remove HiS. A
wide range of sulfur recovery
systems are available to process
the HzS-rich gas stream. Process
selection decisions are usually
dictated by waste stream
properties (minor and trace
species are important) and also
control requirements/emission
Some streams may require
reduced sulfur in addition to
hydrocarbon/paniculate emission
controls; this stream would
normally be recycled or
incinerated after scrubbing for
paniculate removal.

Depending on source, these
streams may require reduced
sulfur/nitrogen or VOC controls;
these streams would normally be
collected and recycled or

Depending on source, these
streams may require reduced
sulfur/nitrogen or VOC controls,
these streams would normally be
collected and recycled or
The raw or quenched product gas
stream was sampled and analyzed
at all of the facilities tested This
stream is well characterized
Considerable data on emissions
from boilers and incinerators
exist. However, very little of this
data base deals with coal
gasification product and/or waste
stream combustion.
Some of these streams were not
available for sampling in the EPA
Source Test Program Also,
limited data have been collected
on specific components within
these streams such as
hydrocarbons and non-H2S
reduced sulfur species which may
impact control system selection,
design, and performance
Few facilities have measured
these emissions. Although some
product gas species are usually
present, extensive data on
emission rates for different types
of feeders in both pressurized and
atmospheric systems are scarce

Only limited opportunities to
characterize these streams were
available in the EPA  Source Test
While limited characterization
data on these streams are
available, needs and options for
control of streams are relatively
well established.

Table 1.     Continued

       Waste Stream
      Characteristics and
     Determining Factors
    Typical and/or Possible
        Control Options
        Status of Data
Fugitive Losses
Vent Gases from Coal, Ash,
and Other Solids Handling
Vent Gases from Pollution
Control Equipment and
Catalyst Regeneration
Composed of any of the species
found in the process.
Amounts and characteristics of
these emissions are highly
process- and equipment-
dependent. Particulates are
always the major concern with
these streams unless other
fugitive gases (e.g.. raw product
gas) are present.

Highly variable depending on
characteristics of inlet waste
streams and control process
design and operating features.
Similar to combustion flue gas
characteristics with higher
probability of VOC arid trace metal
Depending on source, these
streams are normally controlled
through a periodic inspection
(source screening)/'follow-up
maintenance program.
Some streams may require VOC
or reduced sulfur controls in
addition to those for particulates,
this stream would normally be
vented to the atmosphere after
the removal of particulates or
incinerated if residual pollutant
levels high.

Highly variable depending on
stream characteristics.
Some streams may require VOC,
sulfur, or paniculate control.
Fugitive emission rates were
determined in only one of the
facilities tested in the EPA Source
Test Program. Needs and options
for control of these streams are
relatively well established.

Limited data on the characteristics
of these streams were gathered in
the EPA Source Test Program.
This is not considered to be  an
area of great deficiency.
Limited opportunities to gather
data on the characteristics of
these streams were available in
the EPA Source Test Program
because most of the facilities
tested were essentially

No opportunities to characterize
these streams were available in
the EPA Source Test Program.
'A/though product gas is not a waste stream itself, an evaluation of its composition provides insight into the components which may be present in
 discharges from downstream processing operations.

Table 2.    Aqueous Discharge Streams: Characteristics, Control Options, and Data Base Status
        Waste Stream
       Characteristics and
      Determining Factors
     Typical and/or Possible
        Control Options
                                                                                                            Status of Data
High Volume Wastes

flaw Gas Liquor/Process
Acid Gas Removal System
Condensates and Slowdown
Coo/ing Tower Slowdown
Low Volume Wastes

Ash/Slag Quench/Sluice
Discharges from Auxiliary
Facilities and Air Pollution
Control Equipment
Storm and Area Runoff
Tar-producing gasifiers generate
condensate streams with high
organic loadings. Entrained and
fluidized-bed gasifiers produce
condensate streams with low
organic loadings. In all systems,
these streams will contain
dissolved inorganics find, trace
metals) and dissolved gas species
(e.g., CO,, W2S, HCN. NH3. HCL).

These streams are highly variable
in flow and composition
depending on process-specific

High volume but usually
contaminated mainly with
inorganic species from makeup
water and treatment chemical
residuals in concentrated form.
Contains mainly suspended and
dissolved inorganics derived from
contact with the ash as we/I as
makeup water species in
concentrated form.

Highly variable depending on
Highly variable and intermittent;
likely to contain oily wastes and
other contaminants resulting from
process spills.
Gravity separation and/or
filtration to remove suspended
tars, oils, and so/ids, so/vent
extraction, biological oxidation,
and/or carbon adsorption to
recover organics; and steam
stripping to remove volatile gases
are examples of controls which
are typically proposed for use with
these streams.

Blended and treated with process
condensate (if these streams have
compatible treatment needs) or
separately (if not).

Minimal treatment is usually
necessary; discharge standards
for conventional systems are
based on tight control of
treatment chemical use;  if
contaminated water source is
used as makeup, extensive
treatment may be required
Either co-disposed with ash or
discharged after suspended solids
removed (and pH ad/ustment if
Each of these wastes must be
evaluated individually; blending
with higher volume streams
having compatible treatment
requirements is attractive in many
situations; highly contaminated
streams may require unique
treatment approaches.

Discharged directly or to ho/ding
pond; generally treated in
combination with other similar
streams if highly contaminated.
These streams were sampled and
analyzed in all of the facilities in
which they were generated during
the EPA Source Test Program
Extensive characterization data
from other related studies are also
Only two facilities (both of which
employed the Rectisol process)
were available for sampling in the
EPA Source Test Program

"Conventional" waste streams of
this type were not studied in the
EPA Source Test Program.
Extensive data on the
characteristics of these types of
streams are available from other
Only limited data on the
characteristics of these streams
were obtained in the EPA Source
Test Program.
No characterization data on these
streams were obtained in the EPA
Source Test Program.
No characterization data needed
for these streams; good
engineering practice in facility
design and proper operating
guidelines needed to manage
these wastes.

Table 3.    Solid Waste: Characteristics, Control Options, and Data Base Status
        Waste Stream
       Characteristics and
       Determining Factors
     Typical and/or Possible
         Control Options
          Status of Data
High Volume Wastes

Coal Fines

Gasifier Ash/Slag
Char/Ash Fines in Product
Boiler/Incinerator Ash
By-Product Tars and Oils
By-Product Sulfur
Low Volume Wastes

Spent Catalysts, Sorbents.
and Filler Media
Sludges and Brines from
Pollution Control and Raw
Water Treatment Processes
Fines can represent up to 30%
Iwt) of the raw coal feed.

This stream can represent up to
     W. £. Corbett, L. M. Erickson. and N. P. Meserole are with Radian Corporation,
       Austin. TX 78766.
     William J. Rhodes is the EPA Project Officer (see below).
     The complete report, entitled "Pollution Control Considerations for Low- and
       Medium-Btu Coal Gasification Processes," (Order No.  PB 88-131 305/AS;
       Cost: $19.95) 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
United States
Environmental Protection
Center for Environmental Research
Cincinnati OH 45268
Official Business
Penalty for Private Use $300

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