EPA-650/2-74-009-J

September 1975
Environmental Protection Technology Series
    EVALUATION  OF POLLUTION CONTROL
             IN  FOSSIL  FUEL CONVERSION
                                 PROCESSES
             GASIFICATION:  SECTION 7. U-GAS PROCESS
                             U.S. f

-------
                                      EPA-650/2-74-009-i
EVALUATION  OF  POLLUTION  CONTROL
      IN FOSSIL  FUEL  CONVERSION
                  PROCESSES
       GASIFICATION:  SECTION 7.  U-GAS PROCESS
                         by

                      C. E. J ah nig

            Exxon Research and Engineering Company
                      P.O. Box 8
                 Linden , New Jersey 07036
                  Contract No. 68-02-0629
                   ROAP No. 21ADD-023
                 Program Element No. 1AB013
             EPA Project Officer: William J. Rhodes

           Industrial Environmental Research Laboratory
            Office of Energy, Minerals, and Industry
           Research Triangle Park, North Carolina 27711
                      Prepared for

           U.S. ENVIRONMENTAL PROTECTION AGENCY
              Office of Research and Development
                  Washington, D. C. 20460

                     September 1975

-------
                      EPA REVIEW NOTICE

This report has boon i-c-viewed by the U.S. Environmental Protection
Agency and approved for publication.  Approval does not signify that
the contents necessarJly reflect the views and policies of the Environ-
mental Protection Agency, nor does mention oi' trade names or commer-
cial products constitute endorsement or recommendation for use.
                  RESEARCH REPORTING SERIES

Research reports of the Office of Research and Development, U.S. Environ-
mental Protection Agency, have been grouped into series. These broad
categories were established to facilitate further development and applica-
tion of environmental technology.  Elimination of traditional grouping was
consciously planned to foster technology transfer and maximum interface
in related fields.  These series  are:

          1.  ENVIRONMENTAL HEALTH EFFECTS RESEARCH-

          2.  ENVIRONMENTAL PROTECTION TECHNOLOGY

          3.  ECOLOGICAL RESEARCH

          4.  ENVIRONMENTAL MONITORING

          5.  SOCIOECONOMIC  ENVIRONMENTAL STUDIES

          6.  SCIENTIFIC AND TECHNICAL ASSESSMENT REPORTS
          9.  MISCELLANEOUS

This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed to
develop and demonstrate instrumentation,  equipment and methodology
to repair or prevent environmental degradation from point and non-
point sources of pollution.  This work provides the new  or improved
technology  required for the control  and treatment of pollution sources
to meet environmental quality standards.
This document is available to the public for sale through the National
Technical Information Service, Springfield, Virginia 22161.
                 Publication No.  EFA-650/2-74-009~i
                               11

-------
                              TABLE OF CONTENTS






                                                                     Page




 1.  SUMMARY	  .  .      1




 2.  INTRODUCTION	      2




 3.  BASIS AND BACKGROUND	      3




 4.  PROCESS DESCRIPTION 	      4




 5.  EMISSIONS TO THE ENVIRONMENT	     11




     5.1  Coal Preparation and Drying  .  .	     11




     5.2  Pretreatment and Gasification  	     17




     5.3  Gas Cooling and Dust Removal	     18




     5.4  Sulfur Removal	     18




     5.5  Auxiliary Facilities	     18




 6.  SULFUR BALANCE	     21




 7.  THERMAL EFFICIENCY	     23




 8.  TRACE ELEMENTS	     25




 9.  TECHNOLOGY NEEDS  	     28




10.  PROCESS DETAILS	     31




11.  QUALIFICATIONS	     37




12.  BIBLIOGRAPHY	     38
                                   iii

-------
                                LIST  OF  TABLES


No«                                                                  Page

  1      RAW MATERIALS USED                                             7

  2      STREAMS LEAVING PLANT                                          8

  3      STREAMS ENTERING AND LEAVING SPECIFIC UNITS                   13

  4      SULFUR BALANCE                                                22

  5      THERMAL EFFICIENCY                                            24

  6      EXAMPLE OF TRACE ELEMENTS THAT MAY APPEAR IN                  26
          GAS CLEANING SECTION

  7      STREAM COMPOSITIONS                                           32

  8      STEAM BALANCE                                                 33

  9      ELECTRIC POWER CONSUMED                                       34

10      WATER BALANCE                                                 34

11      MAKE UP CHEMICALS AND CATALYST REQUIREMENTS                   35

12      POTENTIAL ODOR EMISSIONS                                      35

13      POTENTIAL NOISE PROBLEMS                                      35
                                     IV

-------
                               LIST OF FIGURES







No.                                                                  Page




 1      U-GAS PROCESS FLOWPLAN                                         5




 2      U-GAS PROCESS WITH COMBINED CYCLE FOR POWER GENERATION         6




 3      U-GAS PROCESS EFFLUENTS                                       12

-------
                         TABLE OF  CONVERSION UNITS
  To  Convert From




Btu




Btu/pound




Cubic feet/day




Feet




Gallons/minute




Inches




Pounds




Pounds/Btu




Pounds/hour




Pounds/square inch




Tons




Tons/day
               To
Calories  kg:




Calories, kg./kilogram




Cubic meters/day




Meters




Cubic meters/minute




Centimeters




Kilograms




Kilograms/calorie, kg




Kilograms/hour




Kilograms/square centimeter




Metric tons




Metric tons/day
Multiply By




0.25198




0.55552




0.028317




0.30480




0.0037854




2.5400




0.45359




1.8001




0.45359




0.070307




0.90719




0.90719
                                    VI

-------
                                     -  1  -
                               1.  SUMMARY
          The U-Gas Process being developed by the Institute of Gas Technology
has been reviewed from the standpoint of its effect on the environment.  The
quantities of solid, liquid and gaseous effluents have been estimated,
where possible,  as well as thermal efficiency of the process.  For the
purpose of reducing environmental impact, a number of possible alternatives
are discussed, and technology needs are pointed out.

-------
                                    - 2 -
                             2.  INTRODUCTION


           Along with improved control of air and water pollution, the
 country is faced with urgent needs for energy sources.  To improve the
 energy situation, intensive efforts are under way to upgrade coal, the
 most plentiful domestic fuel,  to liquid and gaseous fuels which give less
 pollution.  Other processes are intended to convert liquid fuels to gas.
 A few of the coal gasification processes are already commercially proven,
 and several others are being developed in large pilot plants.  These pro-
 grams are extensive and will cost millions of dollars, but this is war-
 ranted by the projected high cost for commercial gasification plants and
 the wide application expected  in order to meet national needs.  Coal con-
 version is faced with potential pollution problems that are common to
 coal-burning electric utility  power plants in addition to pollution prob-
 lems peculiar to the conversion process.  It is thus important to examine
 alternative conversion processes from the standpoint of pollution and
 thermal efficiencies,  and these should be compared with direct coal utili-
 zation when applicable.   This  type of examination is needed well before
 plans are initiated for commercial applications.   Therefore,  the Environ-
 mental Protection Agency arranged for such a study to be made by Exxon
 Research and Engineering Company under Contract No.  EPA-68-02-0629,
 using all available nonproprietary information.

           The present  study under the contract involves preliminary design
 work to assure that the  processes are free from pollution where pollution
 abatement techniques  are available,  to determine  the overall  efficiency of
 the  processes,  and to  identify   areas where present  technology and informa-
 tion are insufficient   to  assure that the processes  are nonpolluting.   This
 is  one of a series of  reports  on different fuel  conversion processes.

           All significant  input  streams  to the  processes  must be defined,
 as well as  all effluents and their compositions.   This  requires complete
 mass  and energy balances to  define all gas,  liquid,  and solid streams.
 With  this  information,  facilities  for control  of  pollution can be examined
 and modified  as  required to meet  Environmental  Protection Agency objectives.
 Thermal efficiency is  also  calculated,  since it gives  an  indication  of
 the  amount  of waste heat that must  be  rejected to  ambient  air and water
 and  is  related to  the  total  pollution  caused by the  production of a  given
 quantity of clean  fuel.

          Suggestions  are included for filling technology gaps that exist
 for techniques  to  control pollution or conserve energy.  Maximum use was
made of  the literature and information available  from developers.  Visits
 and/or  contacts were made with the developers to update published informa-
 tion.  Not  included in the studies are such areas  as cost, economics,
 operability,  etc.  Also coal mining and general offsite facilities are not
within  the  scope of this work.

          A number of reports have been issued on  individual processes
evaluated to date  in the program  (1,2,3,4,5,6).  We wish to acknowledge
 the information and help provided by EPA in making this study.

-------
                        3.  BASIS AND BACKGROUND
          The U-Gas Process for making clean gas fuel is based on gasifying
coal with air plus steam,, and has been referred to in the literature.  Some
information is given in Reference 7 on application to electric power
generation using a combined cycle in which the gas is first burned for use
in a gas turbine, and then goes to a boiler where additional power is
generated using a steam cycle.  Pretreating of coal feed is incorporated
into the design to allow using caking type coal feed by first destroying
the caking properties in a pretreating zone.  Air is added to the pre-
treater to give partial oxidation at about 800°F.  Composition of the com-
bined gas, including that from pretreating, is given in Reference 8, while
a general description of the system is given in Reference 9.  More complete
information is given in Reference 10 for a combined cycle application to
generate electric power.  Environmental controls are provided, together
with a breakdown of the overall energy balance.  Our environmental evaluation
is based mainly on Reference 10, the others being used to arrive at a better
understanding of the process in order to estimate utilities and auxiliary
facilities where necessary, and to assess environmental and energy aspects
of the process.

-------
                                    - 4 -
                          4.   PROCESS DESCRIPTION

           Coal feed amounts  to 7346 tons/day containing 6% moisture.   It is
 dried,  then crushed, and sent to a pretreater where caking properties are
 destroyed by partial oxidation in the presence of air.   The pretreated coal
 is  gasified with steam and air in a fluidized solids system,  at 1900°F and
 300 psia to make low Btu clean gas fuel suitable for use in a combined cycle
 power  plant.

           As shown in Figure 1,  dry coal crushed to 1/4 inch  and smaller is
 fed to  the pretreater by means of lock hoppers.   Gases  from the pretreater
 flow into the gasifier at a  point above the  fluid bed  for the purpose of
 reacting and destroying all  tar and oil vapors that are evolved in pre-
 treating.   A residence time  of 10-15 seconds is  provided on the vapors (8).
 Figure  2 shows  the pretreater-gasifier system.  Table 1 gives inputs  to the
 plant,  while Table 2 shows outputs.  Additional  process details are given
 in  Section 10 of this report.

           In the fluid bed gasifier operating at about  2 ft/sec,  char is
 reacted to give  a carbon level of about 20%  in the ash.   Agglomeration of
 ash particles is accomplished  in a "spouting" zone or venturi throat  at
 the bottom of the gasifier maintained at sintering temperature by adding
 air and steam.   Ash agglomerates of perhaps  1/8  inch diameter pass  down
 through this throat,  to be quenched and removed  from the system.   Dust
 recovered  by cyclones from the raw gas  product is  also  passed through the
 agglomerating zone.   Further description of  this type of agglomeration is
 given in Reference (11).

           Raw gas  is  cooled  in a waste  heat  boiler to make high pressure
 steam,   following by additional heat recovery to  preheat  boiler feed water.
 Air cooling  is then used to  bring the  gas down to  scrubbing temperature.
 The water  scrubber removes dust  and ammonia  primarily,  together with
 unreacted  steam.   Gas  liquor from the  scrubber is  processed in a sour water
 stripper to  recover ammonia  and  remove  I^S (12).   The treated water is
 recycled to  the  cooling tower  or used  to  slurry  the  ash  being returned
 to  the  mine  for  disposal.

           In this  particular design, water is  indicated  to  be recycled to
 extinction within  the  process,  in which case  there would  be no net water
 discharge  that might  cause environmental  concern.  However, there will  be
 soluble  salts (e.g.,  sodium  chloride  and  sulfate)  introduced  with the  makeup
water,   plus  volatile  elements  from  gasification  (chlorine,  fluorine,  boron,
 etc.) that will  accumulate and must  be  purged  from the  system.   It  is
 obvious  that  some water must be  discharged.

          Sulfur  is removed  from the cooled  gas  using the Selexol process  (13)
based on a glycol  type  solvent, which can remove H2S  and  COS  from the  gas.
About 607» of  the C02  is  left in  the  gas, but  the solvent  does  dehydrate  the
gas.

-------
                                                                                           FIGURE 1

                                                                                         U-GAS PROCESS
                                                                          Flowplan and Flourates for Plant Processing
                                                                    7346 Tons/Day of Pittsburgh Type Coal  (6.C7. Moisture)
   Cons/day
670  Moisture
                                            Pretreater
                                           (X  Offgas
                  Fuel Gas
                  and Air
                  to Coal
                    Dryer
   Solids transferred from pretreater
   to U-Gas reactor is 6304 tons/day
                                    Low  Btu  Clean
                                                      Char
                                                      1037  (dry)
                                                      (20.37. Carbon)
                                                    Y
   Note:  Numbers are tons/day except as noted.
          (See Table 7 for details on stream compositions.)



Generation
and
Superheat











I
Steam









Hot Gas
275'F


Air
Cooler


Cooled

Gas
150°F '
CXD







Scrubber








Cooling Water System
A
Her Feed W-iter



\
Makeuu
Wateu-
Treati:i
tekeup


8

Air
t
•*?t 	

Cooling

^ ^


1
1

Gas to
Selexol



Sulfur
Removal
(Selexol)

1
Steam
^
Gas Liquor H s stream
Slurry 2178
2769 (16.67. H2S)
^-»-



V
— •?•
Waste
Water
Treating
»Z(_

Product Ga
124 X 109 I
(158 Btu^CI
Ne
Ga
25

V
Plan
coal dryer
tail gas i
air. compr
elec. gene


'
Clans
Plant
Tall Gas
Cleanup

Tail Gas

                                                                                                                                                                                   Net Product
                                                       478
                                                       224
                                                       733
                                                       413
                                                      1848
                                                                                       Makeup  U.ater
                                                                                                                   Air
                                                                                                                                         r
Ammonia Water
        Discharge
                                                                                                                                                                  Sulfur
                                                                                                                                                                   283

-------
                               - 6 -
                              FIGURE  2

                     U-GAS PROCESS WITH  COMBINED
                     CYCLE FOR  POWER  GENERATION

                          (From  Reference 8)
         Gasifier
1
f&

Dus
Rem
                                               Heat
                                             Recovery
Pretreater
                                                          Sulfur
                                                         Removal
                                                           800°F
                  Agglomerated
                      Ash
                                                                         Gas
                                                                        Turbine

-------
TABLE 1
RAW MATERIALS USED, U-GAS PROCESS
Coal: Pittsburgh Seam (Cleaned!
6% Mois ture 	
Analysis, Wt. % (dry basis)
C
H
0
N
S
Ash
Pi o-V| "Hpaf- V^lllP d*rv COal - .


Coal
71.5
5.0
6.5
1.2
4.4
11.4
100.0

	 	 7346
Pretreated Coa
71.25
4.02
7.50
1.00
3.74
12.49
100.00
13,178 Btu/lb
	 2122
tons /day
.1
gpm

-------
                            -  8  -
                           TABLE 2
            STREAMS LEAVING PLANT, U-GAS PROCESS
Net Product Gas
     Composition, Vol. %

               CO           20.16
               C02           6.72
               H2           13.75
               CH4           4.89
               N2           54.47
               H2S            .005
               COS            .01
                           100.00

High Heating Value :  158 Btu/SCF

Char from gasifier (dry basis)
     Composition
Wt.%
c
H
N
S
Ash
20.33
1.43
1.78
0.58
75.88
                    100.00
Waste water discharge

Sulfur byproduct

Ammonia byproduct
                   25,726 tons/day
                   (784 MM SCFD)
                   1037 tons/day
                  (plus 156 tons/day of water)
                   tons/day

                   2000 (334 gpm)

                    283
                      2

-------
                                    - 9 -
          If it were possible to remove sulfur and particulates at high
temperature, the gas cleanup system might be simplified and overall efficiency
improved.   However,  the potential NOX emissions would then have to be evaluated
carefully,  since the raw gas will contain ammonia which if not removed increases
the NOX formation in subsequent combustion.  By way of illustration, a modifi-
cation of the U-Gas Process has been proposed (8), in which sulfur is removed
by contact with a suitable metal at 800°F.  A practical process for removing
large amounts of sulfur at high temperature is not yet commercially available,
although trace amounts can be removed using guard beds of zinc oxide for
example.  Exploratory work has been done on using iron or nickel base materials
which can be regenerated (14), making it practical to remove large amounts
of sulfur from a gas stream.

          The sulfur acceptor may be regenerated by contacting it with air
to form S02, which is sent to a Glaus unit and reacted with H2S from other
sources for sulfur recovery.  Instead of using a metal as the sulfur acceptor,
half calcined dolomite might be used as has been mentioned in the literature  (4)
The sulfur acceptor is then regenerated by reacting with CC>2 and water at
about 200°F to form H2S which can be converted to free sulfur via a liquid
phase Glaus type operation.

          Returning to a discussion of acid gas treatment, clean low Btu gas
from the Selexol unit is available to use as fuel, in conventional  systems
or in a combined cycle system.  The H2S stream from solvent regeneration is
indicated to contain 16.6% H2S and is sent to a Glaus unit for sulfur recovery.
Tail gas cleanup by the We1Iman-Lord process  (15) is included to give 250 ppm
S02 in the  final gas released to the atmosphere.

          High heating value  of  the total  gas produced is 5533 MM Btu/hr,
but part of the gas is needed to supply requirements of  the process.  Net
gas available from  the process is  5162 MM  Btu/hr, equivalent  to a potential
power generation of 600,000 KW at  a nominal 40% efficiency.   Of the total
gas produced, 6.7%  is consumed in  the process  to  supply  fuel  to the coal
dryer and tail gas  incinerator, on  the sulfur  plant, plus  a combined cycle
system  supplying plant electricty  and power for air compression.  In  addition,
steam is  generated  from waste heat in the  process, but all of this  is used
within  the  plant,  partly  to drive  the air  compressor.

          Auxiliary facilities are required in  addition  to the  basic  process,
such as coal handling  and  storage.  Coal  preparation will include drying  and
crushing, as well  as  coal  cleaning unless  this  is provided elsewhere.   Ash
handling  and disposal  are  also needed,  with means to drain the  ash  slurry,
recover the water  for  reuse,  and transport the  drained ash to the mine  or  to
a  landfill  area.   The Glaus plant  for sulfur  recovery  includes tail  gas
cleanup by  scrubbing with  sodium sulfite  using  the Wellman-Lord process,  but
sulfur  storage  and  shipping  facilities  are also needed.

          Waste water  treatment  employs  the Chevron  process  to  recover
by-product  ammonia, and makes it feasible  to  reuse  the water  (12).   While
not  included  in  the original  design,  a  biological oxidation  system  (biox)
is needed to  give  adequate  cleanup of the water for  return to the  cooling
water circuit.   In addition,  to  prevent buildup of  sodium salts etc.,  some
water will  have  to  be  discharged from the plant,  although no  net water
discharge was  shown in the  original design (10).

-------
                                   - 10 -
          The plant may be self sufficient in steam  and power during
normal operation, but in order to start it up a  furnace or other method
for heating is required, together with startup steam and power.  Fuel  for
startup probably should be oil rather than gas or coal, so as to avoid the
storage problem with gas, or the environmental problems with coal due  to
sulfur and ash.

          Makeup water must be brought in and treated to make it suitable
for use in the cooling water circuit, while further  treatment and demineral-
ization are required to supply boiler feedwater makeup.  Cooling towers are
used  and are a major area of environmental concern.

          Other facilities required are maintenance  shops, fire protection,
warehouses,  control laboratory, offices, cafeteria,  roads, trucks, .etc.,
all of which must be taken into account in assessing total environmental
impact.

-------
                                - 11 -
                    5.  EMISSIONS TO THE ENVIRONMENT
          Overall flow rates for the process were shown in Figure 1.
Figure 3 and Table 3 show all of the streams entering and leaving specific
units, some of which are returned to other units within the plant.  All
streams which are actually discharged to the environment are indicated
by heavy dashed lines in Figure 3 and by asterisks in Table 3.  Emissions
to the environment are discussed in the following subsections, in the
order of process sequence shown in Figure 1.

5. 1  Coal Preparation and Drying

          The first effluent is to the air  from  the coal handling and
preparation area.  Coal is delivered and crushed to 1/4 inch and smaller.
Such operations will normally have a dust problem, and careful considera-
tion and planning is required for control.  Covered conveyers should be
provided wherever possible; even so, there may be vent streams or leaks
that could release dust.  A dust collection system should be used
operating at slightly below atmospheric pressure to collect vent gas and
pass it through bag filters.  Since spills  from conveyers and leaks can
also create dust, facilities such as clean-up equipment and water sprays
may be needed.

          The coal storage pile is also of  concern in that wind can pick
up and disperse fine particles.  Evaluation is needed for each specific
situation in order to provide proper control measures.  Proposals for
dust control have been made such as spraying oil or asphalt on the sur-
face of the pile, or convering it with plastic.  The amount of coal
handled is so large that a loss of even a small  fraction of a percent
could be excessive.

          A further consideration on any coal storage pile is the
possibility of fires and spontaneous combustion which would result in
evolution of odors, fumes, and volatiles.   One control measure is to
compact the pile  in layers as it is being formed.  In any event, plans
and facilities should be available for extinguishing fires if they occur .

          The coal storage and preparation  area may also contribute to water
pollution.  If 30 days' storage is provided, it  amounts to over 200,000 tons;
so the coal storage pile will cover a large area.  Rain runoff can lead to
undesirable effluents.  A  large part of the rain can run off quickly and
carry suspended particles, while the remainder will have a long contact
time with the coal and can pick up acids and organics.  Therefore, rain
runoff from the storage area should be collected in storm sewers and sent
to a  separate storm pond.  With a certain amount of treatment, this water
can then be used as makeup for the process.  Control of seepage may be
desirable on the pond, and particularly on  the coal storage area, using
for example, a layer of concrete, plastic or clay.

-------
                                                                                    FIGURE  3

                                                                                 U-GAS PROCESS
                                                                     Block  Diagram Showing Streams  In  and
                                                                        Out  of  Specific  Sections  of  Plant
        2345
        M     A
        II   1   0  'f
       ji   *   n   1
Raw Gas
                                                      32
                                          Settler
                                            133
                                                               Cyclone
1
Coal Feed,,

Coal
Prep,
Dry
Crushed
Coal

1
1
Pre- 1
treat 1
1
ft ft I \
15 16 17 18 J 20
U-Gas
\
f
Quench
-^Y

<
1 -«

-------
                                       - 13 -
                                        TABLE 3
          Identification
Stream  	
    I   Coal Feed

   *2   Wind


   *3   Rain
   *4   Dryer vent gas
        Dust
    6   Steam
   *9   Air
   10   Gas liquor
11
            stream
  *12   Chemicals


   13   Condensate


   14   Net product gas
   15   Wind

   16   Rain
   17   Flue gas
                        Flow Rate  t'ons/day
                        7346
                        e.g.  6" in 24 hrs,
                        1700
                        (51.4 MM SCFD)
                                    Comments
                        7.752
    7   Superheated steam  4,052
    8   Steam              6,190
227,000

2,769

2.178
   18
   19
     Air
     Air
                        6,190
                        25,015
e.g. 6" in 24 hrs.
480

779
7,205
67» moisture, cleaned
Wind may blow dust from coal storage
and handling area.
Rain can wash fines from coal prepara-
tion and storage area, and leach
organics, sulfur, iron, trace elements
etc.
Combustion gases from coal dryer -
contain dust.  Part of product gas is
burned with 10% excess air.
Coal fines entrained in drying gas,
recovered in bag filters and returned
to gasifier.

High pressure steam made from waste heat
on process.
Superheated steam fed to gasifier.

Low pressure steam made from waste heat
used for Selexol unit and sour water
stripping.
Air cooling on raw gas before Selexol
unit.
Water layer condensed from raw gas and
sent to waste water treating.
Sulfur compounds removed by Selexol unit
and sent to sulfur plant.
Makeup glycol and chemicals are added to
Selexol unit and will appear in
effluents.
Recovered from steam used for heating -
return to boiler  feed water.

Clean fuel  gas,  produced by process

Wind action on coal storage and
preparation area.

Rain onto coal storage  pile
Part of  clean product  gas use as  fuel
in  coal  dryer.
Combustion  air  to coal  dryer
Process  air used in pretreater

-------
                                       - 14 -
                                   TABLE 3 (Cont'd)
Stream
  Identification
   20   Air
   21   Char

   22   Steam

   23   Steam
   24   Boiler feed water

   25   Steam
   26   Boiler feed water

   27   Air
   28   Chemicals

   29   Steam
   30
   31
   32
  *33
Water
Slurry
Water
Char
   34   Makeup water
   35   Boiler feed water
  *36   Sludge
  *37   Chemicals
  *38   Air

  *39   Drift loss

   40   Cooling water

  *41   Blow down

   42   Treated water
Flow Rate tons/day
14,987
1,037 (dry)

408

4,052
7,752

4,052
6,190

227,000
6,190

564
2,074
881
1,193

10,692
4,244
See Table 11
See Table 11
600.000
                                                               Comments
                   300,240
                   (50,000 gpm)
                   2,004
                   564
Process air added to gasifier
Char rejected from gasifier (20.3 wt. %
carbon).
Steam formed in quenching hot char -
returned to gasifier.
Steam to gasifier
To make high pressure steam from waste
heat.
Superheating of steam fed to gasifier.
To make low pressure steam from waste
heat.
Air cooling on raw gas.
Glycol and other chemicals.used in
Selexol unit.
Low pressure steam used for heating in
Selexol unit.
Makeup to char quench.
Slurry of char (50% water) to settler.
Water recovered in settler.
Char returned to mine (15% moisture on
dry char).
Makeup to cooling water circuit.
Makeup to boiler feed water supply.
From treating makeup water.
Waste chemicals from water treating.
Air from cooling tower (plus 8688
tons/day of evaporated water).
Loss of water mist from cooling tower -
not included in water balance.  May
provide blowdown (see stream 41).
Circulating cooling water

Blowdown from cooling water system td
control buildup of dissolved solids,  etc,
From waste water treating.  Returned
to ash quench.

-------
                                   -  15  -
                               TABLE 3 (Cont'd)
Stream    Identification
   43   Treated water

  *44   Ammonia

   45   H2S

  *46   Oil

  *47   Sludge
  -'-48   Sludge

  *49   Solids

    50   Condensate

  *51   Sulfur
  *52   Tail  gas

  *53   Chemical  purge

    54   Makeup  water

    55   Chemicals
    56   Air
    57   Cooling water
    58   Chemicals

    59  Gas liquor
                       Flow Rate tons/day
                       2,205
                                                               Comments
                        830

                        283
                        3,171

                        See  Table 4

                        14,936

                        See  Table 11
                        600,000
                        308,928
                        See  Table 11

                        2.769
60
61
62
63
Chemicals
Steam
H2S stream
Air
--
830
2,17.8
1,075
64   Fuel gas

65   Chemicals
                            205
Treated waste water used as makeup
water.
Recovered from sour water stripping
system; may be sold or incinerated.
Sour  gas stripped from gas liquor  -
returned to' Glaus unit.
Some  oil, tar, phenols, etc. may be
removed from raw gas.
Cellular material from biox unit.
Sludge from chemical treatment of  waste
water, if used e.g., to precipitate  fluoride
Ash,  coal fines, etc. removed  from
raw gas in scrubber  - may  contain  trace
elements.
Condensed steam used on sour water
stripper - returned to boiler  feed water.
From  sulfur plant.
After incineration and tail gas
cleanup.
From  tail  gas  cleanup  system,  may  contain
2 ton/day  sulfur.
To makeup  water  treating  (includes 2205
 tons/day  from waste  water).
For  water  treating.
Air  to cooling tower.
 Cooling water to cooling tower
 Additives  to cooling water circuit to
 control fouling and corrosion.
 Water layer from scrubber sent to
 waste water treating.
 As may be used in waste water treatment.
 To reboiler on sour water stripper.
  Sulfur compounds from Selexol unit.
  For  oxidation of sulfur compounds in
  sulfur plant  (includes 382 tons/day to
  incinerate tail gas for cleanup).
  Part of product gas is used as fuel  on
  sulfur plant  incinerator.
           r
 Make  up sodium sulfite,etc,j   to replace
  chemicals purged on tail gas cleanup.

-------
                                - 16 -
          Cleaning and washing of run of mine coal is not included in the
present  design, assuming that this will be done elsewhere.  However, it
should be pointed out that some applications of the process tnay include
cleaning and washing, which employ large amounts of water, and generate large
volumes of solid refuse to dispose of.

          Noise control should be carefully considered since it is often a
serious problem-in solids handling and size reduction.  If the grinding
equipment is within a building, the process area may be shielded from
undue noise, but additional precautions are needed for personnel inside
the building.

          Crushed coal next goes to a dryer where essentially all of the
moisture is removed.  To make the plant complete and self-sufficient, we
have included coal preparation and drying in the balances.  Fuel for the
dryer is supplied by using part of the clean gas product, so that sulfur
removal is not needed on the vent gas.  However, dust recovery must be
provided, using for example bag filters, scrubbing, or electrostatic pre-
cipitation.  Recovered fines can be returned to the process, possibly to
the "agglomerating" zone of the gasifier to minimize entrainment.  One other
concern on the dryer vent gas is possible odors, -which calls for careful
evaluation with .specific coals and drying facilities that will be used.

          Regulations on coal dryers may call for a maximum dust loading in
the vent gas of  .07  to  .10 grains per standard  cubic foot of gas, as
legislated by the State of West Virginia (Chapter 16-20  Series V, 1968).
Smoke  emission must not be darker than No.  1 on the Ringelman Smoke Chart.

          In the drying operation a large volume of hot  gas is contacted
with the coal.  Oxygen content is normally  limited to about 10 Vol. 7.
by„safety considerations.  Also the maximum temperature  should be limited
to avoid heating the coal above 500°F,  so as not to release volatile matter.
It is  common practice to use a large  amount of  excess air,  such  as 100%,
in order to minimize moisture  content of the drying gas  and thereby
facilitate  drying.   In some cases effluent  gas  may be recycled or inert
gas added to control gas temperature  and oxygen content.

          With  the  present high price of fuel,  the design of drying
facilities  should be optimized to minimize  fuel consumption.  This subject
is discussed more fully in a previous study (4).  In brief, it is desirable
to operate  the  dryer with minimum excess air,  for example 10% excess,  and
to recycle  vent gas  as.needed  to control temperature of  the hot  gas.   This
gives  minimum  fuel  consumption as well  as minimum volume of vent gas to be
cleaned  up.  Of  course, the moisture  content of the drying  gas will  be
higher than when a  large amount of excess air is used, making it more
difficult to achieve the same  degree  of drying, although the moisture
content  of  the  dried coal could be allowed  to increase slightly.  Further
details  on  flue  gas  from the dryer are  given in Table 3.

          In general, it will  be desirable  to preserve the  sensible  heat in
the dried coal,  so  as to maximize heat  recovery on the pretreater.   Coal
preheat  temperatures as high as 500°F have  been used without substantial
evolution of volatile matter  from coal.  This temperature has also been
considered  practical from the  standpoint of using  lock hoppers.

-------
                                    - 17 -
          The coal feeding system for pressurizing the coal in this specific
design uses lock hoppers.  Vent gas from depressuring the lock hoppers should
be cleaned up and returned to the process.  Normally there will be no
effluent to the air from this system.  Coal feeding may involve pneumatic
transport of coal, in which case recovery and cleanup of the conveying
gas is needed.

5.2  Pretreatment, and Gasification

          In the pretreatment reactor, coal is contacted with air and
partially decomposed, releasing tar as well as lighter hydrocarbons.  Gases
from pretreating pass to the upper zone of the gasifier above the fluidized
bed,  with the intention of completely destroying all tar and hydrocarbons.
However, the temperature in this zone varies from 1900°F leaving the bed, to
1550°F outlet temperature on the combined gas stream, and it is unlikely
that  refractory aromatic type compounds will be destroyed completely.  There
is also a possibility that some soot may be formed by cracking at high
temperature.  If these problems occur, they would complicate considerably
the cleanup and waste disposal facilities for the plant, beyond the simple
system shown.

          Pretreated coal,  amounting  to 91.3 wt. % on dry coal, is trans-
ferred to the gasification reactor  as a separate stream, to be reacted
with air and steam.  All overhead gases are contained and processed for
cleanup.  The only direct effluent to the environment from this section
of the plant is the char or ash removed from the bottom of the gasifier.
It is dropped into an enclosed hopper filled with water - the resulting
steam flowing back up into the gasifier - and the ash slurry is depressured
for removal via a settler.  Water recovered in the settler is returned to
the quench hopper.  Wet ash is then disposed of as landfill, or returned
to the mine.

          A desirable feature  in this design is the  agglomeration of  ash
provided by a sintering  zone in the bottom of the gasifier.  Benefits
obtained are:

          o Lower carbon in ash

          o Large ash particles,  and less dust

          o Higher  density particles

          Sintering to give increased ash density may be particularly desirable
so as to minimize disposal problems.  If there is no sintering, particle
density of  the ash may be very low, for example 5^10 Ib./cu. ft.  As previ-
ously pointed out (6), when coal is gasified without change in particle
size, density of  the char or ash must decrease correspondingly.  The particles
also become much more friable  tending.to aggravate problems of dust separa-
tion on the raw gas,  and in disposing of the ash.

          A potential problem  is leaching of chemicals'or  toxic elements
 from the ash.  Thus,  potential contamination of natural water'must  be
evaluated,  and data  needed  for this purpose  should be obtained when
developing  the process.

-------
                                - 18 -
          Hopefully,  the sintered nature of the ash will minimize  ash
disposal problems such  as leaching.  It should be recognized that  makeup
water  supplied to quenching will normally contain dissolved solids,  and
that these have no way  to leave except with the ash.  Consequently,  a
thorough evaluation of  potential leaching will be needed.

5.3  Gas Cooling and  Dust Removal

          Raw gas leaving the gasifier passes through a cyclone to recover
dust, which is returned to the gasifier agglomerating zone.  Next  the  gas
goes to waste heat boilers and a steam superheating exchanger to recover
useful heat.  Air cooling is then used to bring the gas down to scrubbing
temperature.  Normally  all process streams are confined within the equip-
ment and there are no intentional emissions to the environment.  However,
leaks are common, especially on exchangers, and if leaks occur on  air
coolers ,  the emissions will be dispersed in the large volume of air used
for cooling.  Consideration of this problem is needed in design, possibly
with some monitoring  of operations.

          Water scrubbing removes dust, soluble compounds such as  ammonia,
and phenol that may also be present.  This scrubber water will be  saturated
with H2S and other gases.  It is sent to waste water treating to clean it
for reuse in the process,  as will be discussed further in Subsection 5.5
on Auxiliary Facilities.  This gas liquor is expected to contain fine dust,
as well as tar, cyanides, phenols and other oxygenated compounds^  etc. to
be removed in the waste water treating operations.

5.4  Sulfur Removal

          The final step in cleaning up the raw gas is sulfur removal.  The
product gas is then suitable for use in a gas turbine, without requiring
stack gas cleanup to  remove sulfur or particulates.  It is not necessary to
remove C02 for this use, therefore the base design uses the Selexol process
which scrubs the gas with a glycol type solvent.  A concentrated H2S stream
is sent to the sulfur plant,  along with moisture removed by the dehydrating
effect of the solvent.  Steam used to regenerate the solvent is supplied
from waste heat recovery on the hot raw gas.   Some makeup of glycol, and
possibly other chemicals such as inhibitors,  may be added to the system,
in which case they must also appear in one of the efficient streams and
should be considered  in any detailed specific design. ' If any such materials
are carried out in the product gas,  they could affect operation of turbines
etc.                                                                       '

5.5  Auxiliary Facilities

          In addition to the basic plant, auxiliary facilities are needed
to make the plant self-sufficient, including sulfur recovery, cooling water,
water treating, and electric power.  A Glaus plant is used to recover sulfur.
In a typical Claus plant the acid gas is first burned with air to  form free
sulfur which is condensed and recovered.  This is followed by additional
stages using a catalyst to allow operating at lower temperature so as to give
more complete reaction between H2S aild- S02> au(* increase tne sulfur recovery.
In this case having a Claus plant feed containing 16.6 vol. % F^S,  sulfur
recovery may be about 95% in a 3 stage operation.  Since the resulting
15 tons/day sulfur emission would be excessive, -tail gas cleanup is provided
using the Wellman-Lord  process based on incineration plus scrubbing with a
sodium sulfite solution.

-------
                                  - 19 -
          A modification of the U-Gas process was mentioned earlier based on
removing sulfur from the raw gas at high temperature, for example with
molten metal.  The sulfur acceptor would then be regenerated with air to
form S02.  With this modification, a conventional Glaus plant could not be
used for sulfur recovery.  Instead, it would be necessary to reduce S02 to
sulfur, for example using carbon as the reducing agent.  Of course if
sufficient H,S were available from some other source, it could be reacted
with the S02 in a Glaus plant, in which case the environmental effects of
sulfur would be similar to the present study case.  However, high temper-
ature cleanup of the gas may not remove ammonia, in which case the contribu-
tion of ammonia to NO  formation in subsequent combustion would have to be
carefully evaluated.

          One other consideration  on the sulfur plant is to control odor
emissions due to leaks or associated with handling the product sulfur.  There
is an  appreciable solubility of H2S in molten sulfur, and it may escape
during handling or  storage; however, there  are well  established techniques
for controlling this and other possible sources of contamination such  as
sulfur dust.

          The utility cooling tower, which  has by far the largest emission
to the atmosphere of any part of  the plant,  is of particular concern  regarding
environmental considerations.  Since a very large volume of air is  contacted
efficiently  with cooling water, any contaminants  in  it  such as ammonia,
H2S, phenol,  cyanide, etc. can be  stripped  out.   It  might be thought  that the
cooling water is perfectly clean,  however,  experience  shows that there will
be leaks  in  exchangers  such  as those in sour water service  and on acid gas
treatment.   Since the process operates at elevated pressure, any leakage
is into  the  cooling water circuit. This source  of contamination has  been of
concern  in petroleum refineries and on chemical  plants.  If the problem  is
severe, monitoring  for  leaks  may  be warranted.

          The volume of air  passing  through the  cooling tower  is so large
that every precaution  should be taken  to see that it does  not  inadvertently
become contaminated.   On any cooling  tower  there are also  potential problems
associated with  drift  loss or mist  and the formation of a plume or fog.
If  the cooling  tower  is near public highways,  these  may be  of  concern,
especially  in the winter when icing  may occur  and condensation to  form
a plume  is  likely.   In designing  the  plant, careful  consideration  should be
given  to this in placing equipment,  in  order to minimize or avoid  potential
problems.

           Some  blowdown is needed from the  cooling water system to  purge
soluble  salts that  become concentrated  by  evaporation,  and chemicals that
 are  added to control  algae  and corrosion.   The blowdown goes  to  waste water
 treating before  leaving the  plant as  an effluent.

           Waste  water  to be  treated  includes the cooling tower blowdown,
 gas  liquor from scrubbing the raw gas,  and  chemical  purge from tail gas
 cleanup on the sulfur  plant.  Boiler blowdown is relatively clean so it  is
used as  makeup to the  cooling water  system.  The gas liquor may contain
 considerable ammonia,  as 60-70% of the nitrogen in the coal feed often
 shows  up in this form on gasification operations.  It is also saturated with
 H2S  and other gases from contacting in the scrubber at elevated pressure.
When the sour water is depressured,  gases  which flash off must be collected
 and returned to the system,  for example to the Claus plant.  As in other

-------
                                 - 20 -
 gasification processes,  the gas liquor is expected to contain various other
 contaminants,  such as cyanides, thiocyanates,  phenols,  fatty acids,  oil,
 possibly some  tar,  and particulates.   In any event,  there will be startup
 conditions and plant upsets that produce a full range of contaminants,  so
 provision to handle them should be provided,  including such facilities  as
 oil separators,  settlers or filters for solids,  and  biological oxidation
 (biox)  for cleanup.

           In addition to the above, trace elements are of concern in that
 some of them are known to be partly or highly volatile at gasification
 conditions,  and  will be  removed in the gas cleanup system.   Consequently
 they can appear  in the gas liquor. Many of these trace elements are known
 to  be toxic,  and the amounts involved are large,  giving cause for real
 concern on their satisfactory disposal.   Considerable volatility has been
 shown for arsenic,  lead,  cadmium,  mercury,  fluorine,  chlorine,  etc.   The
 particular subject  of trace elements  is  discussed more  completely in
 Section 8.

           Solid  residue  will be separated from the gas  liquor,  representing
 fines  and ash  that  remain in the raw  gas and  are  separated  in the scrubber.
 Depending upon the  amount and the  combustible  content,  it may be desirable
 to  return them to the gasifier,  or they  might  be  included with  the ash  stream
 for  disposal.  Again,  the question of trace elements  appears,  since  some of
 these may be recovered as particulates and  present special  disposal  problems.

           Other  solid residues  will include sludge from biox treatment,
 where contaminants  are removed  by  incorporating into  cellular material.
 This  sludge can  be  an odor problem and might be incinerated,  buried,  or  sent
 to  the  gasifier.  There may also be solid wastes  from treating  waste  water
 with  lime  for  example, to release  ammonia,  or  to  deactivate fluorides,  etc.
 In  any  case, there- will be sludge  from treating makeup  water, which  is
 innocuous  and  can be  disposed of along with ash from  the  gasifier.

          While  not shown in the original design,  there will  have to  be  a
 significant discharge  of  water  from the  process in order  to purge soluble
 salts and maintain  an  operable  system.   Such salts enter  in the plant makeup
water and become  concentrated by evaporation in the cooling tower.
Additional amounts  are contributed  by  chemicals used  in water treating,
demineralization  to prepare  boiler  feed water, cooling  water  additives,   etc.
In addition, sodium sulfate  is purged  from  the tail gas cleanup  system,
while chlorides  in  the coal  feed appear  to  be volatile  in which  case  they
will appear in the  gas liquor.   Depending upon these  factors  and  the quality
of makeup water,   the minimum amount of waste water may  amount to  20-2570  of
the net makeup water used.   The  latter is set primarily by  the  amount
evaporated in the cooling  tower.

-------
                                 - 21 -
                           6.   SULFUR BALANCE
          Sulfur in the coal feed is mostly removed by gasification,
appearing as H2S in the raw gas.  Some 10% of it may be-as carbonyl
sulfide rather than H2S,  due to reaction with carbon monoxide.  A small
amount of sulfur remains in the ash leaving the bottom of the gasifier.

          Raw gas treatment in the Selexol unit separates 99% of the I^
entering, and about one-half of the COS, into a stream which is sent to
the Glaus plant.  With tail gas cleanup, the sulfur plant gives 99+%
removal of sulfur, leaving 1 ton/day of sulfur or 250 ppm of SC>2 in the
tail gas.  Details on sulfur balance are shown in Table 4.

-------
                          -  22  -
                          TABLE 4
               SULFUR BALANCE. U-GAS PROCESS
Sulfur in Coal

Sulfur in ash
Sulfur in product gas
Sulfur to Glaus plant
Balance on sulfur plant

  Sulfur in acid gas feed

  Sulfur product
  Sulfur in chemical purge
  Sulfur in tail gas
tons/day


   303

     6
     7
   290
   290

   287
     2 (est.)
   	1
   290
Wt. %

100

  2.0
  2.3
 95.7

100.0
 95.7

 94.7
  0.7
  0.3
 95.7

-------
                                  - 23 -
                         7.  THERMAL EFFICIENCY


          Thermal efficiency relates the useful heating value of the net
clean product gas from the process to the heating value of coal consumed,
after making full allowance for all process requirements such as fuel  for
coal drying, power  for compressors, and utilities such as steam, electric
power, and water.   Literature values for thermal efficiency do not always
include these effects, but to be realistic, our studies give thermal
efficiency for a complete plant that is self-sufficient.  On this basis,
the heating value of net available product gas from  the U-Gas process  is
68.1% of the heating value of coal consumed.

          Details on thermal efficiency are given in Table 5, showing
that part of the clean gas product is needed within  the process to supply
fuel for coal drying, for part of  the power on air compression, and as
fuel in the Glaus plant incinerator prior  to tail gas cleanup.  Combined,
these use 6.7% of the total gas made.

          The air compressor requires 132,000 BHP most of which can be
supplied by using byproduct steam.  In  addition, about 10,000 KW of
electric power is needed in coal preparation, for cooling tower pumps  and
fans, etc.  Incremental power beyond that  available  from byproduct steam
is supplied by a combined cycle consuming  part of the product gas, at  a
nominal 40% efficiency based on heating value of the gas.  Thermal efficiency
from coal to electric power is less, of course.

                                 j
          The losses that occur are itemized in the  lower part of the  table.
Unused carbon in the ash accounts  for 4.4% of the heating value in the coal'
feed.  Perhaps this could be consumed in a final "cleanup zone" to improve
thermal efficiency.  The Selexol unit and  sour water stripper consume
considerable steam  for stripping.  If this requirement could be decreased
possibly by using some .type of sulfur removal at high temperature, thermal
efficiency would be improved.  Heat dissipated to the atmosphere is 13.1%
of the input,  representing waste heat that is at too low a temperature  level
for eonomical recovery.

oon       It: should be recognized that the product gas is available at  about
280 psig,  so credit should be allowed for the compression power that would
have been required  if the gas were produced at lower pressure.  This com-
pression power is 130,000 theoretical horsepower from atmospheric pressure
corresponding  to 6.0% on thermal  efficiency.                               '

-------
                              - 24 -
                             TABLE 5
                THERMAL EFFICIENCY,  U-GAS  PROCESS
                                            MM  Btu/hr
 Coal feed

 Net  available  clean  product  gas

 Plant  fuel  gas

  To coal  dryer
  For air  compression
  To make  electric power  consumed
  To tail  gas  incinerator
Losses

  Sulfur byproduct
  Ammonia byproduct
  Ash from gasifier
  Steam to Selexol and
    sour water stripper
  Air cooling
  Cooling tower and other
                                       7,583

                                       5,162
                                          96
                                         147
                                          83
                                          45
                                         371
                                         96
                                          2
                                        335

                                        620
                                        237
                                        760

                                      2,050
100
 68.1
  1.3
  1.9
  1.1
  0.6
  4.9
  1.3

  4.4

  8.2
  3.1
 10.0

 27.0
Note:
Expansion energy available from product gas at 280 psig
corresponds to a credit of 6.0% on thermal efficiency.
Although this effect should be recognized, it may not be
a realistic credit and has not been included in previous
reports of this series.

-------
                                _ 25 -
                           8.   TRACE ELEMENTS


          Coal contains many trace elements present in less than 1%
concentration that need to be carefully considered from the standpoint
of potential impact on the environment.  Many of these may volatilize
to a small or large extent during processing, and many of the volatile
components can be highly toxic.  This is especially true for mercury,
selenium, arsenic, molybdenum, lead, cadmium, beryllium and fluorine.
The fate of trace elements in coal conversion operations, such as gasi-
fication or liquefaction, can be very different than experienced in
conventional coal fired furnaces.  One reason is that the conversion
operations take place in a reducing atmosphere, whereas in combustion
the conditions are always oxidizing.  This maintains the trace elements
in an oxidized condition such that  they may have more tendency to com-
bine or dissolve  in the major ash components such as silica and alumina.
On the other hand, the reducing atmosphere present in coal conversion
may form compounds such as hydrides, carbonyls or sulfides which may be
more volatile.  Studies on coal fired furnaces have indicated that smaller
particles in fly  ash contain  a higher concentration of  trace elements,
presumably due to volatilization of  these elements in the combustion zone
and their subsequent condensation and collection on the  fly ash particles
(16).  Other studies on coal  fired  furnaces  are pertinent  (17, IB, 19) and
some of  these report mass balances  on  trace  elements around the furnaces
(20).

          Considerable  information  is  available  on  the  analyses of coal,
including trace constituents,  and  these  data have been  assembled  and
evaluated (21,22,23).  A few  studies have been made to  determine what happens.
to various  trace  elements  during  gasification  (24,25).   As  expected,  these
show a very  appreciable  amount  of volatilization on certain elements.  As
an order of  magnitude,  using  these  factors  for this specific U-Gas design
would result in  147  Ibs.  per  day  carryover  for each 10  ppm of  trace  element
in  the coal  that  is  volatilized.

          In order to  make the  picture  on  trace  metals  more meaningful,
the approximate degree of  volatilization shown for various  elementshas
been combined with their  corresponding  concentration  in a hypothetical
coal  (as typical), giving  an  estimate  of the pounds per day of  each  element
that might  be carried  out  with  the  hot gases leaving  the gasifier.   Results
are shown in Table 6 in the order  of decreasing  volatility.  Looking at  the
estimated amounts that may be carried  overhead,  it  becomes immediately
apparent that there  can be a very real problem.   For  each element an
evaluation  must be made  to determine the net amount carried overhead and the
potential problem.   Where  a problem exists,  the  constituent must  be  collected,
removed  from the  system,  and  disposed  of in an acceptable manner.   In the
case of  zinc, boron  and fluorine  the degree of volatilization  has not yet
been determined,  but they  would be  expected to be rather volatile.   Even
if  only  101 of  the total amount is  volatile, there  will be large  quantities
to  remove in the  gas cleaning operation and to dispose of.

-------
                         - 26 -
                         TABLE 6
EXAMPLE OF TRACE ELEMENTS THAT
MAY APPEAR IN RAW GAS FROM GASIFIER


Element
Cl
Hg
Se
As
Pb
Cd
Sb
V
Ni
Be
Zn
B
F
Ti
Cr

Possible
ppm in Coal (a) %
1,500
0.2
2.2
31
7.7
0.14
0.15
35
14
2
44
165
85
340
22

Possible
Volatile (b)
90+
90+
74
65
63
62
33
30
24
18
(10)
(10)
(10)
(10)
nil
Estimated
In Gas
Ib/day
<19,800
3
24
296
71
1
1
154
49
5
65
243
125
500
nil
(a)  Mainly based on Pittsburgh Seam Coal (2).

(b)  Mainly based on reference 24, and indicated at
     107» for Zn,  B,  and F, in absence of data.

-------
                                 -  27  -
          The preceding discussion has been directed primarily at trace
elements that are partially volatilized during gasification and that may
have to be recovered and diposed of in the gas cleaning section.  Con-
sideration must also be given to trace elements that are not volatilized
and leave in the solid effluents from the plant,  particularly the char
from gasification.  Undesirable elements might be leached out of this char,
since it is slurried in water and handled as a wet solid, and will
ultimately be exposed to leaching by ground water when it is disposed of
As land fill or to the mine.

          Sufficient information is not now available to adequately evaluate
the potential problems of trace elements,  and the necessary information
needs to be developed in future programs so as to assure environmentally
sound planning on large scale operations.

-------
                                - 28 -
                          9.   TECHNOLOGY NEEDS


          From this review and examination of environmental aspects of
the U-Gas process,  a number of areas have been defined where further
information is needed in order to evaluate the situation,  or where
additional studies  or experimental work could lead to a significant
improvement from the standpoint of environmental controls,  energy
consumption,  or thermal efficiency of the process.  Items of this
nature will be discussed in this section of the report.

          Any coal conversion operation has solid refuse to be disposed
of.  Although not included in this specific design, coal cleaning must
be provided at some location.  The cleaning operation will generate
solid refuse that could amount to over 2000 tons/day, for example.  In
addition char is rejected from gasification at a rate of over 1000 tons/day.
Other solid residues include fines removed during gas cleanup, plus sludges
from biox and water treating.  More work is needed in order to define
methods of disposal that do not create problems due to leaching of acids,metals,
organics, or sulfur which could contaminate natural water.  In addition,
adequate controls are needed with regard to the potential dust nuisance
and washing away of particulates.  In many cases the material may be
suitable for land fill with revegetation.  Although there is- already a
lot of background on this subject, specific information is needed on each
coal and for each specific location in order to allow thorough planning
to be sure that the disposal will be environmentally* sound.

          Coal drying is used on most coal conversion processes;  con-
sequently, considerable effort is warranted to optimize the operation
from  the standpoints of fuel consumption, dust recovery, and volume of
vent  gas to be handled.  It will  often be attractive to burn high sulfur
coal  rather than clean gas fuel for inplant use,  and to include facilities
for cleaning up the vent gas.

          The  need  for a simple,  efficienct means  of feeding  coal  to  the
high  pressure  gasifier has been apparent and  has  received  considerable
study.   For pressure levels  of  300-500  psig,  lock  hoppers have been used
satisfactorily although  they  are expensive.

           One  potential  improvement would be  to  develop  a  way  to efficiently
remove  dust  from gas at high temperature.  An important  advantage is  that
particulates  are  then  kept  out  of the  sour water stream,  and  consequently
 it is easier  to  clean  up.   Sand bed  filters  are  promising  for  dust removal
 from hot gases  although  they have not  been  fully demonstrated  commercially.

           In the  area  of  acid gas removal,  conventional  systems  based on
 amine or hot  carbonate leave room for  improvement.  Amine scrubbing is
 not effective on carbonyl  sulfide,  while contaminants  such as  cyanide
 interfere with regeneration of the scrubbing liquid.   Hot carbonate systems

-------
                                     - 29 -
partially remove carbonyl sulfide, but it is often difficult to provide a
highly -concentrated stream of H2S to send to the sulfur plant.
Adsorption/oxidation systems are often not effective on carbonyl sulfide.,
and its presence may require increase liquid circulation.  The Selexol process
is used in the U-Gas case.  The design indicates a reasonably high H2S con-
centration in the stream to the Glaus plant,  although steam requirement
and pumping rates for the operation are sizeable.

          Available systems for acid gas removal have high utility
requirements, causing a significant loss in thermal efficiency for con-
version of coal to clean fuel products.  In addition there is often a
waste stream of chemical scrubbing medium which may be difficult and
expensive to dispose of.

          Desirable objectives for an acid gas removal process can be
summarized as follows:  (a) good clean up of all forms of sulfur to
give a stream high in sulfur concentration for processing in a Glaus
sulfur plant, (b) low utility and energy consumption, (c) no waste
streams that present a disposal problem.

          The need for a process to remove sulfur at high temperature
was mentioned earlier.  Systems based on half calcined dolomite or iron appear
promising; however, they may give less complete sulfur removal than conven-
tional scrubbing systems and do not remove ammonia or other nitrogen compounds.
If filtering techniques could be incorporated to remove particulates at the
same time that sulfur is removed, such systems could be quite attractive.
A further need is to destroy or remove undesirable contaminants such as
carbonyl sulfide, cyanides, and possibly phenol and ammonia.  This function
might also be provided by a high temperature gas cleanup system.

          The need for a simple, effective method to clean up sour water
for reuse is another item that is commonfJto most fossil fuel conversion
operations.  Sour water generally contains sulfur compounds, ammonia, H2S,
phenol, thicyanates, cyanides, traces of oil, etc.  These are generally
present in too high a concentration to allow going directly to biological
oxidation, but their concentration is often too low to make recovery
attractive.  Particulates, if present, further complicate the processing
of sour water.  Usual techniques for clean up include sour water stripping
to remove H2S and ammonia, and in addition, extraction may be required
to remove phenols and similar compounds.  Such operations are large con-
sumers of utilities and have a large effect on overall thermal efficiency.

          One possible approach is to vaporize sour water to make steam
which can be used in the gasifier.  In this case, compounds such as
phenol should be destroyed and reach equilibrium concentration in the
circulating sour water.  It may not be practical to vaporize sour water
in conventional equipment such as exchangers, due to severe fouling and
corrosion problems.  Therefore, new techniques may be required,  and one
possibility would be to vaporize the sour water by injecting it into a
hot bed of fluidized solids.

-------
                                  - 30 -
          In a large scale application there will be a water effluent
from the plant,, therefore, detailed study of the facilities for clean up
will be needed.  In any event, the water make-up that is brought to the plant
will contain dissolved solids including sodium and calcium salts.  Calcium
                      l)
salts may be precipitated during the water treating operation to form a
sludge which can be disposed  of with the other waste solids, but the
fate of the sodium salts  in the make-up water calls for further study.
These will leave with the blowdown from the cooling tower.  If the con-
centration of  dissolved solids is too high in this blowdown water to allow
discharging it to the river,  then some suitable method of disposal will
have to be worked out.  On one proposed commercial plant, this has been
handled by using an evaporation pond where the water is evaporated to
dryness.  The  salts accumulate and will ultimately have to be disposed of.
If  they cannot be used or sold then it would seem logical to dispose of
them in the ocean.

          On trace elements   information is needed on  the amount vaporized
in  the  gasifies?, what happens to them, where they separate out and in
what form, so  that techniques can be worked out for recovering or disposing
of  the materials.  Again  specific information is needed for each coal and
for each coal  conversion  process since operating conditions differ.  In
many cases, the  trace elements may tend to recycle within the system and
build up in concentration.  This offers an interesting opportunity to
perhaps recover  some of them  as useful by-products.  The  toxic nature of
many of the volatile elements should be given careful  consideration from
the standpoint of emissions  to the environment, as well as protection of
personnel during operation and maintenance of the plant.  Carcinogenicity
of  coal tar and  other compounds present in trace amounts  or formed during
start up or upsets must also  be evaluated.

          Protection of personnel, especially during maintenance operations
should  be given  careful attention, which will require  that additional
information be obtained.  Thus,  toxic  elements  that vaporize  in  the gasifier
may condense in  equipment such as piping and exchangers where  they could
create  hazards during cleaning operations.

-------
                                 - 31 -
                          10.   PROCESS DETAILS
          Additional details on the process and information on potential
problems are given in Tables 7 through 13.

-------
                                    -  32  -
                                   TABLE  7
STREAM COMPOSITIONS
, U-GAS PROCESS
(See Figure 1 for identification)
Pretreater
Ib mol/hr Offgas
CO 735
C02 2,011
H2
H20 5,806
PTJ 11C
Ui^ 115
N2 16,311
H2S
COS
S02 176
C2H6 63
Tar 8
Raw Gas
18,595
9,609
12,686
13,148
4,516
50,246
750
24
—
—
—
Gas to
Selexol
18,593
9,601
•12,681
328
4,514
50,246
748
24
—
—
—
Selexol
Effluent
18,593
6,198
12,681
—
4,513
50,246
5
12
—
—
—
H2S to
Glaus
—
3,403
—
328
1
—
743
12
—
—
—
                 25,225       109,574      96,735      92,248       4,487
Note:  Value reported for COS is based on calculation in absence of data -
       data for some other processes show much higher proportion of sulfur
       in form of COS, for example, 10% of the total sulfur in the gas may
       be as COS.  Amount of ammonia in raw gas is unknown but some processes
       show 60-70% of the nitrogen in coal appears as ammonia in the raw
       gas.

-------
                                 -  33  -



                                 TABLE 8

                      STEAM BALANCE, U-GAS PROCESS


                                                                 Ib/hr

High Pressure Steam, 600 psig

     From waste heat on pretreater and raw gas9
     preheated to 800°F.  Used in gasifier	 . 338,000


     From waste heat on pretreater, raw gas, and
     intercooler on air compressor, preheated to
     900°F.  Used to supply 108,000 shaft HP on
     air compressor	646,000


Low Pressure Steam, 125 psig and 15 psig.

     From waste heat on cooling raw gas.  Used
     in Selexol unit and sour water stripper 	 516,000


Ash Quenching

     Steam from quenching ash - returned to
     gasifier. . 	  34,000


Sulfur Plant

     By product steam from waste heat recovery.
     Used to supply utility requirements of
     Glaus plant and tail gas cleanup	50,000

-------
                      - 34 -

                     TABLE  9
     ELECTRIC POWER CONSUMED, U-GAS PROCESS
                    TABLE 10
          WATER BALANCE. U-GAS PROCESS
                                           KW
  Coal preparation and handling           4,000
  Cooling water pumps                     1,500
  Cooling tower fans                      1,000
  Air cooler fans                           500
  Other plant uses                        3,000
                                         10,000
Net consumed in gasifier                     202
In wet ash to mine                            26
Evaporated in cooling tower                1,448
Waste water discharged from plant            334
In H2S stream to Claus plant                  12
Losses on steam and condensate               100
Total water makeup required                2,122

-------
                       - 35 -



                      TABLE 11

     MAKE UP  CHEMICALS AND CATALYST REQUIREMENTS


Chemicals

  Acid Gas Removal;

     - scrubbing solution
     - additives

  Sulfur Plant tail gas cleanup


  Cooling Tower Additives

     Anticorrosion, e.g., chromate
     Antifouling, e.g., chlorine


  Water Treating

     Lime
     Alum
     Caustic
     Sulfuric acid



Catalysts,  etc.

  Sulfur plant catalyst

  Ion exchange resin for water treating

-------
           - 36 -
           TABLE 12
   POTENTIAL ODOR EMISSIONS
Coal storage and handling.
Coal drying - vent gas.
Vent gas from lock hoppers.
Wet ash handling and disposal.
Sour water stripping and handling,
Sulfur plant and tail gas.
Biox pond and other ponds.
Leaks: ammonia, H2S, phenols, etc
           TABLE 13
   POTENTIAL NOISE PROBLEMS
 Coal handling and conveyors.
 Coal crushing, drying and  grinding,
 Air compressor.

 In utilities area:
  Burners  on furnaces.
  Stacks  emitting flue  gases.,
  Turbo-generator etc.

-------
                                  - 37 -
                           11.  QUALIFICATIONS


          As pointed out, this study does not consider costs or economics.
Also, areas such as coal mining and general offsites are excluded, as well
as miscellaneous small utility consumers such as instruments, lighting
etc.  These will be similar and common to all coal conversion operations.

          The study is based on the specific process design and coal type
cited, with modifications as discussed.  Plant location is an important
item of the basis and is not always specified in detail.  It will affect
items such as the air and water conditions available, and the type of
pollution control needed.  For example, this U-Gas study uses high sulfur
Pittsburgh seam coal.  Because of variations in coal feed, moisture content,
and other basic items, great caution is needed in making comparisons
between coal gasification processes as they may not be on a completely
comparable basis.

          The design for this study did not include coal cleaning and
washing, which therefore must be provided elsewhere, together with
associated energy and water requirements.  Related environmental
impacts must be included to give a complete overall assessment.

          Other gasification processes may make large amounts of various
by-products such as tar, naphtha, phenols, and ammonia.  The disposition
and value of these must be taken into account relative to the increased
coal consumption that results and the corresponding improvement in overall
thermal efficiency.  Such variability further increases the difficulty of
making meaningful comparisons between processes.

          The U-Gas process as described in publications makes no appreciable
amounts of tar,  naphtha, or phenols; although there is a small yield of
ammonia, amounting to about 2 tons/day which might be disposed of by incinera-
tion.  It is possible, at least under some conditions such as startup or
plant upsets that ammonia yield might be very much higher, and that some
tar, oil,  and/or soot may be formed in the gasification system.  These
would complicate the gas cleanup facilities and require provision for
disposal,  therefore such possibilities should be evaluated thoroughly in
process development and in planning commercial applications.  Provision
will definitely be needed for separating trace elements and disposing
of them in a satisfactory manner, especially the portions volatilized
in gasification,  but additional information is needed in order to define
the problem and to develop suitable control systems.

-------
                                 _  38  -
                           12.  BIBLIOGRAPHY


1.  Magee, E. M., et. al., "Evaluation of Pollution Control in Fossil
    Fuel Conversion Processes, Gasification; Section 1:  Koppers-Totzek
    Process," Report No. EPA-650/2-74-009a, January 1974.

2.  Kalfadelis, C. D., et. al., "Evaluation of Pollution Control  in
    Fossil Fuel Conversion Processes, Gasification; Section 2:
    Synthane Process," Report No. EPA-650/2-74-009b, June  1974.

3.  Shaw, H.,  et. al., "Evaluation of Pollution Control  in Fossil  Fuel
    Conversion Processes, Gasification;  Section 3:  Lurgi  Process,"
    Report No.  EPA-650/2-74-009c, July 1974.

4.  Jahnig,  C.  E., et. al.,  "Evaluation  of  Pollution Control  in  Fossil
    Fuel  Conversion  Processes, Gasification;  Section 4:   C02  Acceptor
    Process,"  Report No.  EPA-650/2-74-009d, December 1974.

5.  Jahnig,  C.  E., et. al.,  "Evaluation  of  Pollution Control  in
    Fossil Fuel Conversion Processes, Gasification;  Section  5: BI-GAS
    Process,"  Report No.  EPA-650/2-74-009g, May  1975.

6.  Jahnig,  C. E., et.  al.,  "Evaluation  of  Pollution  Control  in  Fossil
    Fuel  Conversion  Processes,  Gasification;  Section  6:   HYGAS Process,"
    Report No. EPA-650/2-74-009h,  July  1975.

7.  .Bodle, W.  W.,  et. al.,  "Clean Fuels  from Coal," Oil  Gas  J. August
     26,  1974,  p. 85.

 8.   Loeding, J. W.,  et.  al., "The U-Gas  Process," Chemical Engineering
     Progress 71, 4:85-86 (1975).

9.  Loeding, J. W.,  et.  al., "IGT U-Gas  Process," Clean  Fuels from Coal
     Symposium at the Institute of Gas  Technology, Chicago Sept.  10-14,  1973

10.  Glaser,  F., et.  al.,  "Emissions  from Processes Producing Clean Fuels,"
     for Environmental Protection Agency.  Report BA9075-015 Section XIV
     (March  1974).               .

11.   Goldberger, W. M.,  "The Union Carbide Coal Gasification Process,"
     4th Synthetic Pipeline Gas Symposium, Chicago, Oct.  30-31, 1972.

12.   "Profit in Processing Foul Water," Oil and Gas J., June 17,  1968,
     p. 96 (see also US Patents 3,518,056 and 3,518,166).

13.   "Selexol Process," Hydrocarbon Processing, April  1973 p. 100.

14.   Bureau  of Mines, "Removal of Hydrogen  Sulfide from Hot Producer
     Gas by  Solid Adsorbents," RI 7947 (1974).

15.   Princiotta, F.  T., "Status of Flue Gas Desulfurization Technology,"
     EPA  Symposium on Environmental Aspects of Fuel Conversion Technology,
     St.  Louis, Mo.,  May  13-16, 1964. Report EPA  650/2-74-118.

-------
                               - 39 -
16.  Lee,  R. E., et. al., "Trace Metal Pollution in the Environment,"
     of Air Poll. Control, 23, (10), October 1973.

17.  Schultz,  H., Hattman, E. A., Booker, W. B., ACS Div. of Fuel.
     Chem., Vol. 8,  No. 4, p. 108, August 1973.

18.  Billings,  C. E., Sacco,  A.M., Matson,  W. R., Griffin, R. M.,
     Coniglio,  W. R., and Harley, R. A., "Mercury Balance on a Large
     Pulverized Coal-Fired Furnace," J. Air Poll. Cont. Association,
     Vol.  23,  No. 9, September 1973, p. 773.

19.  Schultz,  Hyman et. al.,  "The Fate of Some Trace Elements During
     Coal  Pre-Treatment and Combustion," ACS Div. Fuel Chem. ^,  (4),
     p. 108, August 1973.                                    ~

20.  Bolton, N. E.,  et. al.,  "Trace Element Mass Balance Around  a
     Coal-Fired Stream Plant," NCS Div. Fuel Chem., _1£, (4), p.  114,
     August 1973.

21.  Magee, E.  M., Hall, H. J., and Varga,  G. M., Jr., "Potential
     Pollutants in Fossil Fuels," EPA-R2-73-249, June, 1973.

22.  Trace Elements and Potential Toxic Effects in Fossil Fuels
     Hall, H.  J., EPA Symposium,  "Environmental Aspects of Fuel
     Conversion Technology," St.  Louis, MO., May 1974.

23.  Ruch, R.  R. et. al., "Occurence and Distribution of Potentially
     Volatile Trace Elements in Coal," EPA 650/2-74-054,  July 1974.

24.  Attari, A., "The Fate of Trace Constituents of Coal During
     Gasification," EPA Report 650/2-73-004, August 1973.

25.  Attari, A. et.  al., "Fate of Trace Constituents of Coal During
     Gasification (Part II)" presented at ACS Meeting, Philadelphia,
     Pa.,  April 6-11, 1975 (Division of Fuel Chemistry).

-------
                          	- 40  -	
                                 TECHNICAL REPORT DATA
                          (Please read Jaslructions on the reverse before completing)
 1. REPORT NO. .
 EPA-650/2-74-009-1
                            2.
                                                        3. RECIPIENT'S ACCESSION NO.
 4. TITLE AND SUBTITLE EvaiUation of Pollution Control in
 Fossil Fuel Conversion Processes; Gasification:
 Section 7.  U-Gas  Process
             5. REPORT DATE
             September 1975
             6. PERFORMING ORGANIZATION CODE
 7. AUTHOR(S)
 C.E.  Jahnig
             8. PERFORMING ORGANIZATION REPORT NO.


              Exxon/GRU.12DJ.75
9. PERFORMING OR9ANIZATION NAME AND ADDRESS
 Exxon Research and Engineering Company
 P.O.  Box 8
 Linden, NJ 07036
             10. PROGRAM ELEMENT NO.
             1AB013; ROAP 21ADD-023
             11. CONTRACT/GRANT NO.
             68-02-0629
 12. SPONSORING AGENCY NAME AND ADDRESS
 EPA, Office of Research and Development
 Industrial Environmental Research Laboratory
 Research Triangle Park, NC  27711
             13. TYPE OF REPORT AND PERIOD COVERED
             Final
             14. SPONSORING AGENCY CODE
 15. SUPPLEMENTARY NOTES
 16. ABSTRACT The repOr{. gives results of B. review of the U-Gas  Process being developed
 by the Institute of Gas Technology, from the standpoint of its effect on the environ-
 ment.  The quantities of solid, liquid, and gaseous  effluents have been estimated,
 where possible, as well as the thermal efficiency of the process.   For the purpose of
 reducing environmental impact, a number of possible alternatives  are discussed,
 and technology needs are pointed out.
 7.
                              KEY WORDS AND DOCUMENT ANALYSIS
                 DESCRIPTORS
                                           b.lDENTIFIERS/OPEN ENDED TERMS
                         c.  COSATI Field/Group
 Air Pollution
 Coal Gasification
 Fossil Fuels
 Thermal Efficiency
Air Pollution Control
Stationary Sources
U-Gas Process
Clean Fuels
Fuel Gas
Research Needs
 13B
 13H
 21D
 20M
 8. DISTRIBUTION STATEMENT

 Unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES

    46
                                           20. SECURITY CLASS (Thispage)
                                           Unclassified
                                                                    22. PRICE
EPA Form 2220-1 (9-73)

-------