EPA-650/2-74-009-J
September 1975
Environmental Protection Technology Series
IN
^^^^^J
CONY
8, I
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EPA-650/2-74-009-J
EVALUATION OF POLLUTION CONTROL
IN FOSSIL FUEL CONVERSION
PROCESSES
GASIFICATION: SECTION 8. WINKLER PROCESS
by
C. E. Jahnig
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
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EPA REVIEW NOTICE
This report has been reviewed by the U.S. Environmental Protection
Agency and approved for publication. Approval does not signify that
the contents necessarily reflect the views and policies of the Environ-
mental Protection Agency, nor does mention of 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. EPA-650/2-74-009-J
11
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TABLE OF CONTENTS
Page
1. SUMMARY .................. • ...... .... 1
2
2. INTRODUCTION
3. SELECTION OF BASIS
4. PROCESS DESCRIPTION. . ...... ............... 5
4.1 Coal Preparation ................. ..... 5
4.2 Gasification ......... ...'..• ..... ...... 5
4.3 Gas Cooling and Dust Removal. .... ........... «
4.4 Sulfur Removal ............ ........... ®
4.5 Auxiliary Facilities .............. ...... B
5. PROCESS STREAMS AND EMISSIONS .................. 10
5.1 Coal Preparation.. ........ ...... ....... 10
5.2 Gasification ......... ........ ....... 18
5.3 Gas Cooling and Dust Removal ................ 18
5.4 Sulfur Removal. . ............ ......... 19
5.5 Auxiliary Facilities .................... zo
6. SULFUR BALANCE . ................ • ..... -• ' 23
7. THERMAL EFFICIENCY ..... ............ ..... • 25
8. TRACE ELEMENTS .... ............. • ....... 27
9. TECHNOLOGY NEEDS . . ...................... 30
10. PROCESS DETAILS. ...... .................. 32
11. QUALIFICATIONS ......................... 40
\
12. BIBLIOGRAPHY ... ...... .......... ....... 41
iii
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LIST OF TABLES
1. WINKLER GASIFICATION PROCESS
PLANT STREAMS AND EFFLUENTS. 12
2. SULFUR BALANCE—WINKLER PROCESS 24
3. THERMAL EFFICIENCY—WINKLER PROCESS 26
4. TRACE ELEMENTS—ESTIMATED VOLATILITY 28
5. MAJOR INPUTS TO PLANT—WINKLER PROCESS . 33
6. MAJOR OUTPUTS FROM PLANT—
WINKLER PROCESS. 34
7. STEAM BALANCE—WINKLER PROCESS 35
8. ELECTRIC POWER REQUIRED--
WINKLER PROCESS. • 36
9. WATER BALANCE—WINKLER PROCESS 37
10. MAKE UP CHEMICALS—
WINKLER PROCESS. 38
iv
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LIST OF FIGURES
1. FLOWPLAN FOR WINKLER PROCESS WITH
AUXILIARY FACILITIES 6
2. WINKLER GASIFICATION SYSTEM '.' 7
3. WINKLER GASIFICATION PROCESS. H
4. WINKLER GASIFIER USING OXYGEN • . . 39
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TABLE OF CONVERSION UNITS
To Convert From
Btu
Btu/pound
Cubic feet/day
Feet
GalIons/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
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- 1 -
1. SUMMARY
effiliency are discussed, and technology needs are pointed out.
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- 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 programs are extensive and will cost millions of dollars, but this
is warranted by the projected high cost for commercial gasification plants
and the wide application expected in order to meet national needs. Coal
conversion is faced with potential pollution problems that are common to
coal-burning electric utility power plants in addition to pollution problems
peculiar to the conversion process. It is thus important to examine the
various conversion processes from the standpoint of pollution and thermal
efficiencies and these should be compared with direct coal utilization
when applicable. This type of examination is needed well before plans
are initiated for commercial applications. Therefore, the Environmental
Protection Agency arranged for such a study to be made by Exxon Research &
Engineering Company under Contract No. EPA-68-02-0629, using all available
non-proprietary information.
The present study under the contract involves preliminary design
work to assure that conversion processes are free from pollution where
pollution abatement techniques are available, to determine the overall
efficiency of the processes and to point out areas where present technology
or information is inadequate to assure that the processes are non-polluting.
All signficant 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 objectives. Thermal efficiency
is also calculated, since it indicates 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. Alternatively,
it is a way of estimating the amount of raw fuel resources that are consumed
in making the relatively pollution-free fuel. At this time of energy
shortage this is an important consideration. Suggestions are included
concerning technology gaps that exist for techniques to control pollution
or conserve energy. Maximum use was made of the literature and information
available from developers. Contacts were made with developers to up-date
published information. Not included in this study are such areas as cost,
economics, operability, etc. Coal mining and general offsite facilities
are not within the scope of this study.
Other previous studies in this program to examine environmental
aspects of fossil-fuel conversion processes covered various methods for
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gasifying coal to make synthetic natural gas or low Btu gas. Reports
have been issued on the Koppers, Synthane, Lurgi, C02 Acceptor, BIGAS,
HYGAS, and U-Gas processes (1,2,3,4,5,6,7).
In the area of coal liquefaction, reports have been issued on
the COED process of FMC (8) to make gas, tar, and char, as well as on the
SRC process of Pittsburg & Midway Coal Mining Company to make a heavy
liquid clean boiler fuel (9).
The present report presents our environmental evaluation of the
Winkler process to gasify coal with steam and oxygen to make medium Btu gas,
The study is based largely on literature references 10, 11, 12, 13, and 14
describing commercial plant operations. Acknowledgement is made to
Mr. John M. Ferraro who made initial calculations to define the material
balances for a Winkler gasifier.
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3. SELECTION OF BASIS
During the period 1926-1960, a large number of commercial plants
were built outside of the U.S. using the Winkler process to gasify coal.
In most cases high purity oxygen is used rather than air, therefore this
basis was selected for studying and evaluation. Although present units
operate at about atmospheric pressure, designs at 6 atmospheres pressure
are available and demonstration at higher pressure is planned. The present
study is based on operating at 2 atmospheres.
A wide range of raw materials can be processed, including lignite,
bituminous coal, anthracite, and heavy oil. However, to maximize carbon
conversion, high reactivity is desirable, as is characteristic of lignites
and younger coals. Our study is based on Leuna plant data for operation
on a German brown coal (10), since the results may be pertinent to pro-
cessing U.S. western coals. Operating conditions and oxygen consumption
are based on this literature reference and are consistent with thermo-
dynamic and heat balance calculation. The developer has since indicated
that oxygen consumption may be decreased somewhat for new designs,
together with a decrease in the amount of low level heat that must be
rejected to air or water.
In order to define environmental aspects, scrubbing to remove
sulfur was added, as well as a sulfur plant, oxygen plant, and other facilities
needed to make the plant complete and self-sufficient. Plant size was set
to provide net clean gas at the rate of 250 X 109 Btu/day, after supplying
process requirements. The gas might be used as fuel or reducing gas, or
it could be converted to ammonia, chemicals, SNG, or oil.'
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4. PROCESS DESCRIPTION
Lignite type coal is gasified at about 1700°F and 2 atmospheres
in a turbulent bed of particles using oxygen and steam, to make medium
Btu gas for fuel or synthesis. Some of the residual char is withdrawn
from the bottom of the gasification reactor, but most of it is blown
overhead as a result of the high gas velocity of S-lflft/sec. Most of the
entrained char is collected in cyclones for disposal, and the gas is then
cooled and cleaned up to remove residual dust and sulfur.
An overall flowplan of the process is shown in Figure 1. The
process can be subdivided into a sequence of steps, each of which willJ>e
described in the following sub-sections: (1) coal preparation, (2) gasi-
fication, (3) cooling and scrubbing, (4) sulfur removal, and (5) auxiliary
facilities.
4.1 Coal Preparation . .
This section of the plant includes storage and handling, drying,
and crushing. It is assumed that coal cleaning is not required, or that
it is carried out elsewhere. Storage requirements will depend upon the
specific situation but may provide for example 30 days reserve.
Drying may not always be needed, since it is only necessary to
avoid surface moisture which would cause problems in handling and crushing.
Rotating tray dryers are used, and for this study a moisture removal of 5/0
en feed has been taken. Cool stack gas is recycled to control gas ^let
temperature so as not to drive off volatiles. Stack temperature is 350-400 F,
resulting in good fuel efficiency. Coal can be used as fuel if flue gas
desulfurization is provided, but instead of this we have used part of the
clean product gas as fuel to the dryer, with bag filters on the vent gas
to control dust emissions. Coal is crushed to 0-8mms and sent to the
gasifier feed hopper.
4.2 Gasification .
Coal from the feed hopper is fed to the gasifier by means of
screw feeders which give the necessary pressure seal. As shown in Figure 2,
steam and oxygen are added near the bottom of the reactor, maintaining the
particles in a turbulent bed where reaction takes place without reaching
temperatures that would fuse the ash. Typically, the bed may be at about
1700°F so that tar and heavy hydrocarbons are destroyed by gasification
reactions.
Considerable fines are entrained from the bed, consequently
supplemental oxygen and steam are added just above the bed to help consume
them. Heat exchange surface in the dilute phase above the bed removes heat
to protect refractories and for temperature control, generating useful
steam. The raw gas is cooled to about 1300°F before the gas leaves the
reactor, in order to prevent fused deposits in the downstream waste heat
boiler. Condensate can also be injected into the gas for temperature
control and also provides backup or emergency cooling.
With high reactivity coal, conversion of carbon in the coal feed
may be about 90%. The unconverted carbon is in the char by-product, and
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Vent Gas
C02 575
H20 1267
N2 1212
02 34
3089 Dried Coal
. B.7X Moiature
0 3.3Z Sulfur
[ HHV 9320 Btu/lb
Coal Feed COAL K WIN
> PREP. ;> GASI
21,158 20,100
(13.17. moisture)
t t f
Air Fuel Gas I
1574 457 steam
9849
Oxygen
11,536
Nitrogen
37,976
J_
Condensate
Quench
3417
1 Cyclone to PUnt p^ ,?9
4 j ~ , ^MH ^ . A
Raw Cooled f 1 Scrubbed Duat-free 1 Net
KLER Gas HEAT • Gas 11 Sfflimnvit ti*a KlJiUTRO- Gas SULFUR | Product Gas
43,978 40,432 PRECIP. 29,291 ,„ 9
Y (includes 25° K 10 Btu/day
I 'l moisture) ~i CO2 jl'l^
\f Ctvar Gas Liquor ni,130 «. V »2 994
}ihar 3546 uua,. 10 DU3t H2S strean to Cm, 371
„,, ^ j -j/,0 1 aulCur_platvt My 395
' H2S 615 COS 58
COS 60 Molat. 629
Returned to: CC>2 4768 22,920 '
.1 I^B^^^H^^^ tooling tower "7713 molnt. 149 °*
"" V TAIL rAS ^K 5«i? gas if ier quench 3417 5592 Dry 886 MMSCFD '
CL&wSp -** ^2 1QS7 A """^ 2S "W801"5
Fuel <;ae ft ,^™F ^2 19f7 ^ ^T7 HMsr.n
322 ^^ 21 U2 50
S°2 7B60 Drift loss p?> °°8t (274 Btu/CF wet gas)
To Cooling Boiler
Sulfur Moist Air Touer feed
605 963,400 t 4243 water
I .11 i1'936 K^"8 T I
•&-S-
OTILITIES COOLING clrcl. C.W. WASTE MAKEUP
OXYGEN SULFUR FOR TOWER 378,000 MATER WATER
PLANT PLANT SlARt (63,000 TREAT TREAT
UP gpm)
„ ,. ,. ,_ ., _ , , . — re**
f- ^Tt ' ' j Jf J~^ If
-19.512 559.2 ' 1439 "' „„„ ' ° (Z392 gpn)
FIGURE 1
Flowplaa for tfinkler TtoceBa with Auxiliary Facilities
Numbers are flowratea In tons/day except as noted.,
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FIGURE 2
Quench
Water
Gasifier
steam
Coal Feed
Coooool i
luuvjuu f
WINKLER GASIFICATION SYSTEM
(from reference 13)
steam
superheater
ipgooor
oxygen
steam
char
discharge
AV
5Z
char
hopper
Water
Scrubber
Electrostatic
Precipitator
Clean
Gas
waste
water
Settler
1
Char
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represents a significant loss of heating value unless it is used. Part of
the rejected char is withdrawn from the bottom of the gasifier, and the
remainder is recovered by a cyclone separator on the exit gases,
Steam fed to the gasifier amounts to about 0.5 pound per pound
of coal feed, while steam conversion including moisture in the coal feed
is 27%. Oxygen consumed is 0.57 pounds per pound of coal feed for this
specific design basis that does not use preheating on the streams fed to
gasification.
4.3 Gas Cooling and Dust Removal
Hot raw gas leaving the reactor at about 1300°F passes through
an exchanger to superheat steam, followed by a waste heat boiler and a cyclone
to remove entrained char. The gas then goes to a scrubbing tower where it
is cooled by direct contact with recirculated water.
Most of the particulates are removed by scrubbing and are separated
from the water in a settler. They are included with the char for disposal.
Clarified water is cooled by indirect exchange with cooling water before
it is recirculated to the scrubber. Net production of this water or gas
liquor constitutes sour water containing H2S, ammonia, cyanides, etc.,
present in the raw gas. The sour water is processed in waste water treating
so that it can be reused.
Since the scrubbed gas will still contain a small amount of dust,
it is passed through an electrostatic precipitator for final cleanup. It
can then be compressed, further processed, or used as desired. Traces
of containinants may remain in the gas after scrubbing, such as ammonia,
sulfur, oil, etc,, especially during upsets or start up. Depending on the
intended use, further cleanup may be necessary. In some applications the
'electrostatic precipitation may not be needed.
4.4 Sulfur Removal
The next processing step on the gas is sulfur removal by
scrubbing with a suitable solution, such as amine, hot carbonate, or a glycol
type solvent. These can be regenerated by stripping to give a concentrated
H2S stream that is sent to sulfur recovery. For this study scrubbing with
hot carbonate is assumed, since it will remove perhaps half of the carbonyl
sulfide present in the gas, and some 107. of the total sulfur will be in
this form which is not reaoved effectively by amines.
As an alternative, I^S in the gas might be converted directly
to free sulfur by using an absorption/oxidation type process such as is
offered by Stretford, Takahax, or IFF. In effect, this route would combine
the sulfur recovery plant with scrubbing to remove H2S. Sulfur compounds
other than H2§ are not usually removed by such systems.
4. 5 Auxiliary Facilitieo
In order to make a realistic and thorough evaluation of environ-
mental impacts, a complete and self-sufficient plant must be considered,
including items such as oxygen plant, sulfur recovery, water treating, and
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utilities generation. Oxygen is supplied from a conventional air lique-
faction plant. The amount is large, equal to 11,536 tons/day. For sulfur
recovery, a Glaus plant is included with tail gas cleanup using one of the
many processes offered for this service. Details and alternatives are
discussed more fully in previous reports of this series. Gas sent to the
Claus plant from acid gas treatment contains about 15 vol. % sulfur
compounds (mainly H~S) and 85 vol. % C02, on a dry basis. A small amount
of clean product gas is used as fuel to incinerate tail gas on the sulfur
plant.
A major item is waste water treating on the gas liquor condensed
in the scrubber. Flow rate is 11,140 tons/day, and cleanup is required
to remove particulates, contaminants such as compounds containing sulfur,
nitrogen, or oxygen, as well as arsenic, cadmimum, lead, chlorine, fluorine,
and other trace elements that are known to be volatile at conditions in
the gasifier. This water stream must be thoroughly cleaned up in any
case, and then represents a very desirable makeup water for the plant.
Facilities include sour water stripping, biological oxidation (biox),
and sand filtration prior to using it as cooling tower makeup. Production
of phenols is expected to be relatively low at the conditions used in the
gasifier (170Q°F) so that solvent extraction to remove large amounts of
phenols is not included. Definitive information should be obtained on
the nature of the gas liquor resulting from the Winkler operation.
Other auxiliary facilities include treatment of makeup water for
the cooling water system and for boiler feed water, plus plant utilities
such as steam and electric power. It appears from the balances that the
plant should be self-sufficient in steam and power during normal operation,
although provision must also be made for startup. As far as energy balances
and thermal efficiency are concerned, no coal or clean product gas need be
consumed to generate plant utilities.
The cooling tower has a very important potential environmental
impact in that the air flow through it is by far the largest stream in the
whole plant. Any potential contamination of the air is a major concern,
such as may result from leaks that could contaminate the circulating
cooling water. Moreover, evaporation in the cooling tower is the primary
factor determining net water makeup required by the process.
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5. PROCESS STREAMS and EMISSIONS
A block diagram is given in Figure 3 indicating the various streams
for the plant, with a description of these in Table lo Process streams are
shown as well as those streams actually released to the environment. The
latter are indicated in Figure 3 by heavy dashed lines and in Table 1 by
asterisks, while the other streams are returned to the process. Environ-
mental aspects and control techniques will now be discussed for the various
gas, liquids and solid streams, in the order of processing steps as
indicated in the preceding section on process description.
5.1 Coal Preparation
A first consideration is the handling and storage of large amounts
of coal feed. Delivered coal must be loaded on conveyors, with transfer
to and from storage piles. Such operations necessarily tend to create
problems due to noise, dust nuisance, and spillSo These facilities should
be enclosed as much as possible, with plans and equipment provided for
cleanup. A dust collector system is desirable, operating at below atmo.-
spheric pressure to collect vent gas and pass it through bag filters.
Storage piles are an additional concern since wind can disperse
fine particles. In some cases consideration has been given to covering
the coal pile, or coating it, for' example with heavy tar. The pile is very
large, over 600,000 tons for 30 days storage, requiring an area of about
10 acres. Coal piles are also liable to spontaneous combustion, calling
for special attention and plans for control, together with provision for
extinguishing fires if they occur (15). The obnoxious fumes, sulfur, and
odor from this type of fire is well known. Previous reports in this series
include further discussion of the general subject (e.g. 5) but for any
specific project, a very careful and thorough evaluation and definition
of facilities is needed.
Noise control should be carefully considered since it is often
a serious problem in solids handling and size reduction. If the crushing
equipment is withiii a building, the process area may be shielded from undue
noise but additional precautions are needed from the standpoint of person-
nel inside the building. Other sources of noise include compressors or
other rotating equipment, furnaces, vents, valves, flares, etc.
The present design is based on processing run of mine lignite.
If the process were used on bituminous coal then some cleaning or washing
operation would normally be used» It should be pointed out that coal
cleaning and washing results in rejection of a large amount of refuse and
fines, often 25% of the mined coal, with major environmental impacts as
discussed in previous reports in this series.
Coal is crushed through 4 mesh and fed to a dryer where surface
moisture is removed. The dryer is designed to avoid overheating coal
particlesj which would release volatileso To maximize fuel efficiency,
combustion is carried out with only 10% excess air, and dryer offgas is
recycled to temper the hot gas to about 700°F before it enters the dryer.
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TGURB 3
WD1KLEH. GaSIFICATIOH PROCESS
Coal
Feed
TTTT
15 16 17 18
Plant Streams and Effluents
(See Table
6 7
' t
a '
Gastfier
1 t f
19 20 21
26 27
t I
Oxygen
Plant
f
42
!
22
8
i
f
Heat
Recovery
1 for details on numbered streams)
Cyclone
T
23
28
g
29
1
Sulfur
Plant
43 44
46
r1-!
J I
4 1
V
*
24
X
1
ft
UtllltlC!
Eor
Start up
f |
4*8 49
9 10 11 12
f ]_ JLJL"
Electro-
static
Preclp .
Removal Product
Gas
I
35 37
3A A 33i f A ?f A A8 3$ *& A
! ! i 111!! IT!
Cooling
Tower
Waste
Water
Treat
Make Up
Water
Treat.
nn ti n
50 51 52 53 34 53 58 57
45 47
Note: Streams actually released to the environment
are shown by heavy dashed lines, other
streams are returned to process.
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- 12 -
TABLE 1
WINKLER GASIFICATION PROCESS
PLANT STREAMS AND EFFLUENTS (see Figure 3)
Stream No0 Identification Flow, tons/day
1
Coal feed
Wind
Rain
219158
e.g. 6" in
24 hr.
Vent Gas
Oust
3089
*6
Char
924
Steam
9045
8
Steam
6030
Comments
Cleaned coal feed with
13o3% moisture (see
Table 5 for specifications)
Action of wind on
storage pile may cause
dusting or fires0
Rain action on storage
pile can wash out fines,
cause leaching of sulfur,
metals, and organics—
similar to acid mine
water, should be
collected and sent to
pond for use as make upc
Flue gases from coal
dryer—see Figure 1 for
composition,,
Recovered from vent gas
on coal dryer and
included in feed to
gasifier.
Withdrawn from bottom of
gasifier. Contains 42%
carbon and should be
burned using environmental
controls so that heating
value is recovered.
High pressure steam (600
psig) generated in gasi-
fication section, (see
Table 7).
125 psig generated from
waste heat in raw gas
(see Table 7).
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- 13 -
Table 1 (con't.)
Stream No8 Identification
Gas Liquor
*10
11
*12
13
14
15
16
17
18
Dust
H_S Stream
Chemical
Purge
Plant Fuel
Gas
Product Gas
Wind
Rain
Fuel Gas
Air
Flow, tons/day
11,140
Comments
5592
779
229920
e0go 6" in 24
he's.
457
1574
Water condensed from
scrubbing raw gas—
contains ammonia, sulfur
compounds, and dust, etc.,
and is sent to waste water
treating to clean up for
reuseo
Minor amount of dust
removed by electrostatic
precipitator to make clean
product gas.
Sulfur compounds together
with C02 from sulfur
removal on gas—sent to
sulfur plant,. See
Figure 1 for composition.
Some of chemical scrubbing
solution used in sulfur
removal is lost or purged
to maintain capacity and
constitutes an effluent
from the plant.
Part of clean product
gas is used as fuel in
coal dryer and Glaus tail
gas incineratoro
Net clean product gas«
See Table 6 for details„
Wind action on Storage
pile0
Rain onto storage pile0
Part of product gas used
as fuel in coal dryer0
Air for combustion of
fuel gas in coal dryer„
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- 14 -
Table 1 (con't,)
Stream No. Identification
19
20
21
22
23
24
25
26
*27
*28
*29
*30
Steam
Oxygen
Boiler feed
water
Quench Water
Boiler Feed
Water
Char
Chemical
Makeup
Oxygen
Nitrogen
Sulfur
Tail Gas
Flue Gas
Flow, tons/day
9849
11,536 .
9045
3417
Comments
6030
3546
119536
379976
605
7860
Steam added to gasifier.
Oxygen added to gasifier„
To generate steam on
gasifier. See item 70
Treated sour water—added
at outlet of gasifier to
temper gas and prevent
slag deposits on waste
heat boiler.
To generate steam in
waste heat boiler after
gasifier0 See item 80
Residue left after gasi-
fication and entrained
with raw gas.
Chemicals are used in
sulfur removal (e0g0
amine, or carbonate) and
are lost or purged so
that a corresponding
chemical makeup is
requiredo
Produced in oxygen plant
and sent to gasifier,,
By product from oxygen
production and vented to
air0 Should be clean.
By product recovered in
sulfur plants to be sold.
From tail gas cleanup
after Claus sulfur
recovery plant. See
Figure 1 for composition.
From utility boiler. Not
used during normal
operation but is needed
for startup. Low sulfur
oil fuel may be used to
avoid pollution problems
at startup0
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- 15 -
Table 1 (con'to)
Stream No.
*31
Identification Flow9 tons/day
Air 963,400
Comments
*32
*33
Mist
Blowdown
756
1800
34
35
36
Quench Water 3417
Makeup Water 7713
Sour Gas
*37
Dust
10
*38
Sludge
39
40
Makeup Water 4243
Makeup Water 10,119
Moist air from cooling
tower—contains 9400
tons/day of evaporated
water.
Nominal drift loss of
cooling water lost by
entrainment in air,,
Purge from cooling water
circuit to control
buildup of dissolved solids-
will contain cooling water
additives such as chromate
and chlorine so may require
treatment before disposal„
Treated waste water used
as quench at gaslfier
outleto See item 22„
Treated waste water used
as makeup on cooling water„
NH
etC
-j, -S o stripped
from sour water and sent
to Glaus plant for
incineration and disposal.
Nominal amount of dust
in sour water from
scrubbing which is
recovered in settler and
can be included with char
for disposalo
Sludge produced in
biological oxidation
which may be burled or
incinerated o
Fresh water makeup
needed to balance cooling
water circuit,,
Net boiler feed water
makeup required after
crediting cendensate that
can be collected and reused c
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- 16 -
Stream No,
42
43
44
45
46
47
48
49
50
51
52
53
54
55
Table 1 (cont'd.)
Identification Flow0 tons/day
Sludge
Air
H.S Stream
Sour Gas
Air
Fuel Gas
Mr
Fuel Oil
Air
Air
Cooling Water
Makeup Water
Additives
Gas Liquor
Chemicals
- 49.512
5592
1439
322
1112
954,000
3789000
119956
11140
See Table 10
Comments
From chemical treating of
makeup water9 e.g0 lime
sludge0 See Table 10.
Air processed in oxygen
plant„
Sent to Claus unit from
sulfur removal section.
From sour water stripping—
sent to Claus unit for
incineration and disposal.
Air for incineration in
Claus unito
Part of clean product gas
used to incinerate tail
gas from Claus unit prior
to tail gas cleanup „
Used to burn fuel in item 46.
Low sulfur fuel oil used
for plant startup„ Not
needed during normal
operation.
Combustion air for item 48.
Air flow into cooling tower.
Circulating cooling water0
Makeup water to cooling
water circuit—the sum
of items 35 and 39„
Chemicals added to cooling
water system to control
corrosion (chromates) and
fouling (chlorine) etc0
Foul water from scrubber
fed to waste water treating,,
Chemicals used to treat
waste water, such as lime
for pH control and to
precipitate fluorides0
Nutrients may be needed
in bios unit,,
-------
- 17 -
Stream Noc
56
57
Table 1 (cont'd.)
Identification Flow9 tons/day
Makeup Water
Chemicals
14,362
See Table 10
Comments
Total makeup water to
plant„ See Table 90
Chemicals used to treat
makeup water, such as
lime, alum,, acid,
caustic, etc0
* These streams are actually released to the environments, other
streams are returned to the process,
-------
- 18 -
Low excess air also decreases the volume of vent gas compared to some other
drying systems that may use as much as 100% excess air in order to facilitate
drying.
To prevent sulfur emission in the dryer vent gas, part of the
clean product gas is used for fuel, rather than burning coal. This consumes
2% of the product gas. Dust control is also needed, therefore bag filters
are provided, with the fines being returned to the gasifier. As extensive
drying is not essential for process operability, consideration can be
given to ommiting the dryer and allowing for increased heat load on the
gasifier.
5.2 Gasification
Coal is fed to the gasifier from a feed hopper, using screw
conveyors or feeders. As this system is enclosed, dust and gas can be
contained to prevent emissions to the environment. Attention should be
given to potential leaks, operating procedures, and maintenance, to assure
that this is the case. Gas from purging and blanketing must be collected,
and can be sent to bag filters, for example on the coal dryer.
The major effluent from the gasification section is char that is
withdrawn from the bottom of the reactor. Screw conveyors transfer the char
to enclosed storage hoppers, from which it is withdrawn from disposal. While
this portion of the char consists of coarser particles due to elutriation in
the gasifier, there can still be a dusting problem associated with handling
and disposal. Dusting can be controlled by proper planning and design, pos-
sibly using water sprays and partial wetting of the char. Inadvertent spills
of char can also be a problem, so consideration of this is needed with pro-
vision for cleaning up spills if they occur. The same applies generally to
solids handling operations, such as coal storage, preparations and feeding.
Based on the literature reference used as a bases (10), rejected
char from the gasifier contains about 40% carbon, therefore it will be
desirable to consider ways to recover the heating value it represents.
One possibility is to burn it in a furnace, but environmental controls
would be needed to give acceptable sulfur and dust emissions. Flue gas
scrubbing would be one method for control. A second and much larger stream
of char is rejected from the gas cleaning section of the plant, which also
has a high carbon content. Aspects of char disposal will be discussed
further in the following section 5.3 relating to gas cleanup.
5.3 Gas Cooling and Dust Removal
A waste heat boiler recovers useful heat from the raw gas leaving
the gasifier. Steam superheating is also provided, and all plant steam
and power requirements can be supplied using by product steam from the
process. Considerable char is entrained from the gasifier and passes
through the heat recovery exchangers before being collected in cyclone
separators. The collected' char is relatively fine and contains a sub-
stantial amount of carbon, roughly 30% for this study case. It is
removed from the system to a storage hopper for ultimate disposal.
The char streams from a Winkler plant might be used as land
fill, although the resulting loss in carbon would represent 11.5% of the
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- 19 -
heating value in the coal feed. One possibility is to burn the combined
char streams left after gasification, as is done in the commercial Winkler
plant at Kutahya, Turkey (16) where the char is burned in a steam boiler.
•This same approach could be used in the United States except that stack
cleanup would be required in order to control emissions of dust and sulfur.
Spent char might also be used as fuel in cement manufacture, or it could be
considered and evaluated as an adsorbent for use in water treating.
The next step in the gas cleanup sequence is water scrubbing to
give additional dust removal and at the same time cool the gas. Water is
condensed from the gas, giving a gas liquor containing many contaminants
present in the raw gas, including ammonia, H2S, and probably small amounts
of phenols, cyanides, hydrocarbons, etc., and dust. In addition, it is
known that certain trace elements are at least partially volatile at gasifica-
tion conditions; consequently, they may be present in the raw gas and haves
to be removed. Some condensation and buildup of volatile materials on
entrained char or dust can be expected and the potential environmental
impacts need to be defined. Many of the volatile trace elements are very
toxic, such as; arsenic, cadmium, lead, and fluorine. The subject of trace
elements calls for special attention and is discussed in a separate section.
The gas liquor is not released directly to the environment, but goes to
waste water treating, and will be discussed in Section 5.5 on auxiliary
facilities.
In some applications additional dust removal may be needed to
prevent plugging of catalyst beds or to protect equipment such as compres-
sors, therefore an electrostatic precipitator is provided in the study
case. The small amount of dust recovered in it can be included with the
rejected char for disposal. In some situations the electrostatic precipita-
tor may not be needed, for example, dust removal might be achieved in the
subsequent sulfur removal operation which usually will involve efficient
scrubbing with liquid.
5.4 Sulfur Removal
There are a number of alternative processes that could be used
to recover H2S from the gas such as scrubbing with amine or modified
amines, hot carbonate, glycol type solvent, or refrigerated methanol.
Carbonyl sulfide is also present in the gas, equivalent to perhaps 10%
of the total sulfur, and should be removed. Although conventional amine
scrubbing is not effective for removing carbonyl sulfide, part or most
of it can be taken out by scrubbing with hot carbonate, glycol, or
refrigerated methanol. Our study assumes that hot carbonate or glycol
scrubbing will be used, giving COS removal with moderate utilities con-
sumption. It may be desirable to include a hydrolysis step to convert
COS to H2S plus C02 prior to scrubbing for acid gas removal.
The H2S stream is sent to a Glaus type sulfur plant with tail
gas clenaup. No specific attempt is made to remove C02 from the gas,
assuming that the primary need is to remove sulfur. However, considerable
C02 is removed along with the l^S, such that the stream to sulfur recovery
contains about 15% l^S and 85% C02s) on a dry basis.
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- 20 -
A possible arrangement to consider for sulfur removal would
combine H2S removal with conversion to by product sulfur in one operation,
using an absorption/oxidation type process. Such processes are offered by
Stretford, Takahax9 and IFF. They use a catalytic scrubbing solution
to absorb H2S, which is then oxidized to free sulfur using combined oxygen
which is held by the solution. In effect, the absorption of I^S and its
conversion to free sulfur are combined into a single operation. An
advantage of this route is that very efficient removal of H2S is practical
at low pressure. Also, C02 is not removed9 which may or may not be an
advantage. A disadvantage Is that these processes are not usually
effective for removing other forms of sulfur such as carbonyl sulfide;
however9 it may be possible to hydrolyze these other sulfur compounds to
H2S prior to sulfur removal by incorporating a bed of alumina or bauxite
catalyst in the gas cooling system at an appropriate point to give the
proper temperature of 500-700°F. (17).
In general, the scrubbing solutions used for sulfur removal
will degrade due to side reactions or accumulation of inert materials.
A small amount of solution Is usually purged to maintain capacity or
activity. This constitutes a chemical effluent from the plant that must
be disposed of. To the extent that it is combustible, Incineration may
offer a means of disposal, but for materials such as potassium carbonate
or metals such as vanadium, other methods of disposal will have to be
defined.
5.5 Auxiliary Facilities
These include the oxygen and sulfur plants, plus utilities
supply and water treating. The oxygen plant is a large consumer of utilities,
but has no objectionable effluents. The waste nitrogen stream is clean,
and the only other effluent is some water condensed from the air, which
can be used as boiler feed water.
In addition to byproduct sulfur, the sulfur plant releases
treated tail gas which is comparable to flue gas from combustion of low
sulfur fuel, A typical sulfur recovery is 99% for a Glaus plant with tail
gas cleanup, giving about 1600 wt. ppm of sulfur dioxide in the stack
gas emitted to the atmosphere. This would be comparable to the flue gas
from burning a char of about 1»0% sulfur. Some clean product gas is
burned with air to provide incineration required for tail gas cleanup.
In some cases tail gas cleanup is carried out by reducing sulfur
compounds in the Glaus plant tail gas to I^S, which is then removed by
scrubbing, for example with amine. In other cases the tail gas may be
incinerated to form S02 which is then scrubbed out. From an envlron-
sental control standpoint, either approach should be satisfactory and
the choice saay teflect other considerations. Chemical solutions are
nonamlly used for scrubbing in tail gas cleanup, and undergo some degred-
ation such that a small amount must be purged. Disposal of this purge
solution can be handled as discussed in the preceding section 5.4 on
sulfur removal.
-------
- 21 -
The sulfur plant will, of course, be a likely source of odors,
which must be carefully controlled. Suitable designs and operating
techniques have been established for clean operation of sulfur plants,
and for handlings, storing, and shipping sulfur.
Other auxiliary facilities include supply and distribution of
steam and electric power. As mentioned, these can be supplied as by-
products from waste heat recovered in the process, so that no utility
boiler is needed during normal operation. Provision will be needed for
startup, etc. Potential pollution from furnace flue gas on the utility
boiler is, therefore, not a problem, nor is it necessary to consider
burning part of the clean product gas in order to supply utilities. For
startup conditions it would be reasonable to depend on storage of low
sulfur oil, rather than use coal which would require additional pollution
control facilities.
A moderate size cooling tower is required to supply cooling
water used in the process. It has by far the largest emission from the
plant, namely 954,000 tons/day of air plus 9,400 tons/day of evaporated
water. As discussed in previous reports, it is imperative to keep
contaminants out of the cooling water circuit, so that they can not then
be stripped out into the air passing through the cooling tower. There
are also the usual questions of drift loss and potential plume or fog
formation which must be considered and evaluated. Proper design and
placement of the cooling tower can aleviate or avoid potential problems
such as effect on public highways.
A further effluent from the cooling water circuit is blowdown of
purge water to control buildup of dissolved solids in the cooling water.
Additives used 'in the cooling water circuit will necessarily appear in
the blowdown stream, together with dissolved solids that accumulate and
buildup. Chlorine is often added to cooling water to inhibit algae
growth and the fouling of heat exchanger surfaces, while chromates or
other chemicals are usually added to combat corrosion. These additives
will then be in the blowdown water, which may also include products of
corrosion such as copper, etc. from extensive heat transfer surfaces.
As is usually the case, the only point where soluble salts can
leave the plant is in the cooling tower blowdown. Thus, dissolved solids
in the plant makeup water, such as sodium sulfate and chloride, become
concentrated due to evaporation of water in the cooling tower. If the
makeup water contains 500 ppm of such salts, they will then buildup
to 2500 ppm in the blowdown water for the purge rate used in this eval-
uation. Such water would be considered brackish, and unsuitable even for
irrigation, and at Inland locations may present a disposal problem. In
one proposed plant it is sent to an evaporation pond, where the dried salts
are stored. It would be desirable to have better ways of handling the
blowdown water, for example recovering the water content for reuse in
an indirect evaporator using waste heat.
-------
- 22 -
Additional auxiliary facilities provide treatment of waste
water and plant makeup water. The rates are shown in Figure 1 and Table 1.
Waste water cleanup will include sour water stripping to remove ammonia
and I^S. The ammonia may be sufficient to warrant recovery, but the small
amount of t^S dissolved at this low pressure can be sent to the sulfur
plant for disposal. The amount of phenols, HCN, and oil or other hydro-
carbons is expected to be minor at the gasification conditions of 1700°F.
and low pressure. These can probably be removed adequately by biological
oxidation (biox) with 7-10 days retention time, before the sour water
is used as cooling tower makeup. It may be necessary to also use filtration
and treatment with activated carbon to clean up the sour water. In fact,
the spent char may be useful for this purpose. Effluents to the environ-
ment from waste water treating are: byproduct ammonia, ash and solids
removed by the settler, oil or other contaminants removed during cleanup,
together with sludge from the biox unit. If chemical treatments are used,
such as lime, these will also contribute effluents. In addition, there
will be trace elements that vaporize in the gasifier and accumulate in
the sour water. These must be removed and recovered as byproducts, or
deactivated for disposal in a safe and satisfactory manner. The subject
will be discussed in more detail in Section 8 on Trace Elements.
Finally, facilities are needed to treat the makeup water needed
by the plant. This usually includes treatment with lime, alum, etc.,
as well as demineralization to prepare boiler feed water. The latter
may use water softeners, and ion exchange resins that are regenerated
by back washing with acid or caustic. Obviously, all chemicals used and
consumed in treating will appear in plant effluents at some point, together
with materials removed from the makeup water. Further definition is needed
for each specific case, but the sludge from water treating can probably
be disposed of along with the char, or separately as land fill.
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- 23 -
6. SULFUR BALANCE
Nearly all of the sulfur In the coal appears in the raw gas
leaving the gasifier, from which it can be separated and sent to a Glaus
plant for sulfur recovery. The latter gives 99% sulfur recovery with tail
gas cleanup. Of the total sulfur in the raw gas, 10% of it may be in the form
of carbonyl sulfide plus small amounts of CS2 and other sulfur compounds,
half of which is recovered and sent to the sulfur plant. For this particular
study, byproduct sulfur accounts for 91.2% of the sulfur entering with the
coal feed. An overall sulfur balance is shown in Table 2.
In calculating sulfur content of the product gas, it was assumed
that .half of the carbonyl sulfide in the raw gas would be removed and sent
to sulfur recovery, while the remainder would appear in the product gas.
This could change depending on the technique used for gas cleanup, and it
would be desirable to have methods giving more complete sulfur removal
from the gas with low energy consumption.
The rejected char may possibly have a relatively low sulfur
content compared to the feed coal, such that it might be burned without
requiring special provision to decrease sulfur emission. Detailed plant
data to confirm this are not readily available in the literature but should
be examined where possible. Other background (8,18) suggests that gas-
ification conditions may tend to desulfurize the char sufficiently so that
the byproduct char might be marketed as a low sulfur solid fuel, at least
in some cases. If this is true, it could turn the problem of char disposal
into a potential advantage. In effect there would be a credit for desulfur-
izing part of the coal feed, and there would be less incentive to operate
at high carbon conversion in the gasifier.
-------
- 24 -
TABLE 2
SULFUR BALANCE—WINKLER PROCESS
tons/day %
Sulfur in coal feed 663 100
Sulfur In net product gas 31 407
Sulfur in plant fuel gas 1 Oe2
By product sulfur from Claus plant 605 9102
Sulfur in tail gas of sulfur plant 6 009
Sulfur in char and ash (esto) _2Q^ 300
663 lOOoO
-------
- 25 -
7. THERMAL EFFICIENCY
Heating value of the net clean product gas from the process is
66.8% of that for the coal consumed as shown in Table 3. This is for the
complete plant including auxiliaries such as oxygen plant, sulfur plant,
and utilities. It does not include any credit for the char byproduct,
which would bring the total heating value of products to 78.3% of that for
the coal feed. Clearly there is a large incentive to recover the heating
value contained in the char. If it is low enough in sulfur, it can be
burned as fuel using proper dust recovery. If the char is high in sulfur,
the emphasis should be placed on efficient gasification to minimize the
residual carbon content of the char.
Distribution of losses that decrease thermal efficiency are shown
in Table 3. Most of the loss is rejected to cooling water or in air coolers,
representing low level heat that is impractical to recover and use with present
conventional technology.
Thermal efficiency will of course depend upon the specific coal
used, particularly the ash and moisture content, and the coal reactivity
which affects carbon level in the rejected char.
-------
- 26 -
TABLE 3
THERMAL EFFICIENCY—WINKLER PROCESS
109 Btu/day
Coal feed @ 9320 Btu/lb HHV 374 100
Net product gas (wet) 912 MM SCFD @ 274 ^- 250 66 08
CF
Losses:
Fuel gas to coal dryer 5 io3
Fuel gas to Claus incinerator 4 101
Carbon in withdrawn char 43 11.5
In E,S to sulfur recovery 10 207
Power consumers 5 103
To air cooling 18 408
To cooling water* 27 702
Heat losses and miscellaneous 12 303
124 33o2
9
* Approximately 20 x 10 Btu/day goes to evaporate water, and the rest
goes to sensible heat of the air flowing through the cooling tower0
-------
- 27 -
8. TRACE ELEMENTS
Coal contains many trace elements present in less than 1% con-
centration 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 processings, 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 gasification 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 con-
dition such that they may have more tendency to combine 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 (19). Other studies on coal fired
furnaces are pertinent (20,21,22) and some of these report mass balances
on trace elements around the furnaces (23).
Considerable information is available on the analyses of coal,
including trace constituents, and these data have been assembled and evaluated
C24,25,26). A few experimental studies have been made to determine what happens
to various trace elements during gasification (27,28). As expected, these
show a very appreciable amount of volatilization on certain elements. As
an order of magnitude, in this specific Winkler design, each 10 ppm of element
volatilized would amount to about 400 pounds per day.
In order to make the picture on trace metals more meaningful„
the approximate degree of volatilization shown for various elements has
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 A in the order of decreasing volatility. Looking at the
estimated amounts that may be carried overhead, it becoaes immediately
apparent that there can be a very real problem. For each element the net
amount carried out in the gas leaving the gasifier may have to be collected,
removed from the system, and disposed of in an acceptable manner„ In the
case of zinc, boron and fluorise the degree of volatilization has not ysfc
been determined, but they would be expected to be rathor volatile,, Ewa
if only 10% of the total amount io volatile, there tfill &G lasgo-quaatitiGO
to remove in the gas cleaning operation and to dispooG of.
-------
- 28 -
TABLE 4
TRACE ELEMENTS— ESTIMATED VOLATILITY
Cl
Hg
Se
As
Pb
Cd
Sb
V
Ni
Be
Zn
B
F
Ti
Cr
Hypothetical
Coal ppm
1500
0,3
Io7
906
509
008
002
33
12
Oo9
44
165
85
340
15
% Volatile*
90+
90+
74
65
63
62
33
30
24
18
e, g. 10
e. go 10
e0 go 10
e. g. 10
nil
lb/day**
54000
10
50
250
148
20
3
397
115
7
177
660
340
1360
nil
* Volatility based mainly on gasification experiments (27)
but chlorine is taken from combustion tests9 while zinc9
borons and fluorine were taken at 10% for illustration
in absence of data0
* Estimated volatility for 20,000 tons/day of coal to
gas if i cation c,
-------
- 29 -
A complication that has not generally been recognized, occurs in
the gas cleanup section due to the volatility of trace elements. These are
carried out with the raw gas, and will be removed in the gas cleanup
facilities when the gas is cooled and scrubbed. In any event, they do not
remain in the product gas, and it follows that they must leave the system
at some point. Compounds such as cyanides might be destroyed by recycling
to the process (e.g., the gasifier), but this can not be the case for
elements such as arsenic, lead, chlorine, etc. Neither will they disappear
in the biox unit. Therefore provision will be needed to separate and recover
them, or to deactivate them for disposal in a satisfactory manner. As can
be seen from Table 4, the combined amounts of all volatile portions of
trace elements can present a formidable disposal problem.
The preceeding discussion has been directed primarily at trace
elements that are partially volatilized during gasification and that there-
fore must be recovered and disposed of in the gas cleaning section. Con-
sideration must also be given to trace metals that are not volatilized
and leave in the solid effluents from the plant, one of which is the char
from gasification. Undesirable elements might be leached out of this char
if it is handled as a water slurry, and it 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 evaluate the potential
problems and the situation may be quite different from the ash rejected
from coal fired furnaces, since the char is produced in a reducing atmosphere
rather than an oxidizing one. Background information on slag from blast
furnaces used in the steel industry may be pertinent from this standpoint,
since the blast furnace operates with a reducing atmosphere. However, a
large amount of limestone is also added to the blast furnace, consequently
the nature of the slag will be different.
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- 30 -
9. TECHNOLOGY NEEDS
This review and examination of environmental aspects of the Winkler
process has defined a number of areas where further information is needed
to evaluate the situation, or where additional work could lead to significant
improvement with regard to environmental Impact, energy consumption, or
thermal efficiency. Items of this nature will now be discussed, taken in
the order of processing steps shown on the flowplan in Figure 1, and used
in previous sections.
The first item to consider is coal drying. While thorough drying
may not be needed or warranted, it is usually necessary to at least remove
surface moisture in order to have reliable coal handling and feeding systems.
Conventional dryers burn high value fuel and have a large volume of vent
gas that must be cleaned up. An alternative to consider is using indirect
heating, for example in a fluidized bed containing heating coils. Air
might be recirculated through the bed and through condensers which would
recover water that could be used as makeup. Heat might be supplied by low
pressure steam if it is readily available from waste heat recovery. In
other cases it may be possible to use waste heat that would otherwise
be rejected to the atmosphere via air cooling. The advantage to be gained
is that heat which must be rejected anyway is put to use. It also adds
preheat to the coal feed, thereby decreasing heat load on the gasifier and
oxygen consumption.
On gasification, if there were a way to make low purity oxygen
at much lower energy consumption, the applications to provide clean fuel
gas might then be more efficient. The oxygen plant is one of the largest
consumers of utilities in the plant. Operating the gasifier at higher pres-
sure will also save energy, particularly when the product gas is to be
used at high pressure, as in a combined cycle. Even if the gas is burned
in a low pressure furnace, an expander could be used to recover energy
if the gas is generated at high pressure. In other cases, the expander
could be used to provide final cooling of the gas so as to save cooling
water, or even to provide refrigeration.
As mentioned earlier, the char may be desulfurized during gas-
ification to give a^ valuable low sulfur solid fuel. If so, it may be
desirable to purposely maximize the yield of byproduct char. Techniques
for augmenting desulfurization in the gasifier or by auxiliary facilities
should be considered and evaluated as one approach. An alternative is to
develop ways to obtain a high overall carbon conversion, so that the char
contains little or no combustibles. Otherwise an effective way to recover
the heating value in spent char is needed so as to avoid a large debit
in thermal efficiency. One possibility is "clean combustion" in a fluid
bed of limestone which serves as a sulfur acceptor.
On gas cleanup, a more effective way to remove dust would be
uaeful. Even Hater scrubbing is not considered adequate in some commercial
designs, and electrostatic precipitation is added. A dust removal system
that can operate at elevated temperature would be desirable when using
expanders or with a combined cycle application,, Sand bed filters have
been progooed for such service. A general discussion of alternatives for
gco cleoaup aad sour water handling is given in reference 9.
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- 31 -
The sulfur removal system often represents the largest single
consumer of steam in a process for reboiling or stripping the solution
used to absorb H2S. A solvent having higher capacity may be helpful,
possibly with operation at a higher pressure level. When making clean gas
for fuel uses, it is not necessary to remove C02 and it is preferable
to leave it in the gas when used in combined cycles. For such applications,
more selective removal of sulfur would help and might save utilities in
the regeneration step. Metals such as iron have been explored for desulfur-
ization of gases, and should have the advantage of removing most forms of
sulfur to a low level. These systems may be particularly useful when the
operating pressure is low.
Cleanup of waste water for reuse consumes considerable energy,
and is a difficult, complicated operation. Simpler, more effective and
dependable systems would be useful. One possiblity is to use the adsorptive
properties of the char, which would then be burned or circulated through
the gasifier. A further discussion of considerations in waste water
cleanup is given in reference 5.
Trace elements will also accumulate in the waste water. More
information is needed on what happens to trace elements in the coal feed,
where they appear, and in what form, so that satisfactory methods can be
worked out for their recovery or disposal.
Water consumption by the plant is set largely by evaporation in
the cooling tower. Therefore ways to minimize use of cooling water are
of interest. Heat exchange and heat recovery should be maximized, while air
cooling can then be used to decrease the amount of heat finally rejected
to cooling water. In general, improvements in thermal efficiency and
reduced utilities consumption will tend to save water. Practical ways
to recover water from blowdown streams would also be desirable.
Additional discussion of technology needs will be found in
earlier reports in this series.
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10. PROCESS DETAILS
Further details on the basis used for this evaluation are given
in Tables 5-10. A simplified flow diagram for the gasification section
is shown in Figure 4.
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TABLE 5
MAJOR INPUTS TO PLANT—WINKLER PROCESS
Coal to dryer (1303% moisture) 21,158 tons/day
Coal from dryer ( 807% moisture) 20,100 tons/day
Coal Composition* Wt %
Moisture 8,7
Carbon 5401
Hydrogen 4»1
Oxygen 13„9
Nitrogen 006
Sulfur 303
Ash 15.3
100 00
High heating value 9320 Btu/lb.
Plant makeup water - 14,362 tons/day
* German dry brown coal. From reference 10, Table IV.
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TABLE 6
MAJOR OUTPUTS FROM PLANT—WINKLER PROCESS
Net product gas 22,920 tons/day
(incl. 629 tons/day moisture) (912 MM, scf)
Gas Composition (wet)
moisture
H2
CO
co2
ffl4
N
2
H_S + COS
2.9
41.4
37.8
14.7
1.9
1.2
0.1
100.0
High heating value (wet) 274 Btu/scf
Char
from gasifier (42% carbon) 924 tons/day
from cyclone (29% carbon) 3546 tons/day
Sulfur from sulfur plant 605 tons/day
Waste Water discharged from plant 1800 tons/day
Other; sludges and solids from treating waste and makeup water, dust
from electrostatic precipitator, nitrogen (37,976 tons/day)
from oxygen plant, plus gases from coal dryer, sulfur plant9
and cooling tower„
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TABLE 7
STEAM BALANCE— WINKLER PROCESS
tons /day
team
Generated in gasifier 9045
Used in bleeder turbine exhausting at 35 psig0
to supply all power needed in oxygen plant and
to generate electricity for process „ Exhaust
steam at 35 psigc provides gasifier steam0
125 psig steam
Generated in waste heat boiler on raw gas 6030
Used in gasifier, acid gas removal s sour water
stripping, etce
Note: plant is self-sufficient in utilities, so auxiliary steam
and power generation are only needed for startup.
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TABLE 8
ELECTRIC POWER REQUIRED—WINKLER PROCESS
KW
Coal preparation 12,800
Gas scrubbing 600
Acid gas treatment 100
Gasifier 100
Sulfur plant 400
Cooling water pumps 3,000
Cooling tower fans 2,000
Oxygen plant and misc0 1,000
20,000
This power is supplied by bleeder turbine on part of
gasifier steam supply0
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TABLE 9
WATER BALANCE—WINKLER PROCESS
tons/day
Cooling Tower
Evaporation 9,400
Drift loss 756
Blowdown 1,800
11,956
From waste water treating 7,713
Fresh water makeup 4,243
Boiler Feed Water
Steam to gasifier 9,849
Steam and condensate losses 270
Total BFW required 10,119
Fresh Water Makeup
To cooling tower 4,243
To boiler feed water 10,119
14,362
Net plant discharge of waste water 1,800
(cooling tower blowdown)
Note: 3417 tons/day of treated sour water is used as quench at outlet
of gasifier.
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TABLE 10
MAKE UP CHEMICALS—WINKLER PROCESS
Chemicals
Acid Gas Removal;
- scrubbing solution
- additives
Sulfur Plant tail gas cleanup
Cooling Tower Additives
Anticorrosion, e» gc chromate
Antffouling, e, g0 chlorine
Water Treating
Lime
Alum
Caustic
Sulfuric Acid
Ion exchange resin
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Coal;
Moisture
C
H
0
N
S
Ash
8.7
54.1
4.1
13.9
0.6
3.3
15.3
100.0
FIGURE 4
WINKLER GASIFIER USING OXYGEN
Numbers are pounds except as indicated
Reference: (10)
High Heating Value
9320 Btu/lb
Steam 49
Oxygen 57.4
WINKLER
GASIFIER
1700°F
15 psig
Gas 184.1
(includes 42.3 moisture)
Composition (dry) Vol.
9
CO
CO
CH
+ COS
Dust 17.7
(29% Carbon)
100.0
Ash 4.6
(42% Carbon)
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11. QUALIFICATIONS
As pointed out, this study does not consider cost 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 study uses high sulfur,
lignite type coal for gasification. As mentioned earlier, the developer
has indicated that oxygen consumption may be decreased in new plant
designs. 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 are not on a completely comparable
basis.
The study is based on processing run of mine lignite. If bit-
uminous coal were used, then coal cleaning would normally be needed with
a considerable environmental impact as described in some other studies
in this series (5). Refuse from coal cleaning may be 20-25% of the coal
as mined, presenting a sizeable disposal problem.
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.
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12. BIBLIOGRAPHY
1 Magee, E. M., Jahnig, C. E. and Shaw, H.f "Evaluation of Pollution
Control in Fossil Fuel Conversion Processes, Gasification; Section
I- Koppers-Totzek Process," Report No. EPA-650/2-74-009a, January
1974. (Pb 231 675, NTIS, Springfield, VA 22151).
2 Kalfadelis, C. D., and Magee, E. M., "Evaluation of Pollution
Control in Fossil Fuel Conversion Processes, Gasification; Section
2: Synthane Process," Report No. EPA-650/2-74-009b, June 1974.
(PB 237 113, NTIS, Springfield, VA 22151).
3 Shaw, H.t and Magee, E. M. , "Evaluation of Pollution Control in
Fossil Fuel Conversion Processes, Gasification; Section 3: Lurgi
Process," Report No. EPA-650/2-74-009c, July 1974. (PB 237 694,
NTIS, Springfield, VA 22151).
4. Jahnig, C. E., and Magee, E. M., "Evaluation of Pollution Control
in Fossil Fuel Conversion Processes, Gasification; Section 4: CC>2
Acceptor Process," Report No. EPA-650/2-74-009d, December 1974.
(PB 241 141, NTIS, Springfield, VA 22151).
5. Jahnig, C. E., "Evaluation of Pollution Control in Fossil ^
Conversion Processes, Gasification; Section 5: BIGAS Process,
Report No. EPA-650/2-74-009g, May 1975. (PB 243 694, NTIS, Springfield,
VA 22151).
6 Jahnig, Co E,, "Evalution of Pollution Control in Fossil
Conversion, Gasification, Section 6s HYGAS Process,1 EPA 650/
2-74-009h, August, 1975.
7 Jahnig, C. E0 , "Evaluation of Pollution Control in Fossil Fuel
Conversion, Gasification, Section 7: U-Gas Process," EPA 650/
2_74_009i9 September, 1975.
8. Kalfadelis, C0 D0 , "Evaluation of Pollution Control in Fossil
Fuel Conversion Processes, Liquefaction: Section Is COED Process,
EPA-650/2-74-009e, January 1975. (PB 240 3719 NTIS, Springfield,
VA 22151).
9. Jahnig, C. E., "Evaluation of Pollution Control in Fossil Fuel
Conversion Processes, Liquefaction: Section 2: SRC Process,
EPA-650/2-74-009f, March 1975. (PB 241*792, NTIS, Springfield, VA
22151) .
10. Newman, L. L., "Oxygen in the Production of Hydrogen or Synthesis
Gas," Indust, and Engo Chem. 40 (4) p» 566 (April 1948) .
11. Flesch, W0 and Veiling, G., "Die Vergasung von Kohleim Winkle r-
Generator." ERdol und Kohle, ERdgaSo Petrochemie 15 (9) ,
pp= 710-713 (Sept0 1962) o
12. Davy Powergas Sales Brochure, "Winkler Generator Units," 21e/6/730
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- 42 -
13Q Banchik, M. N., "The Winkler Process for Production of Low Btu
gas from Coal," Clean Fuels from Coal Symposium (I. G. T0)
Chicago, Illo Septc 1973.
14o Winkler Process for Low Btu Fuel Gas, Pipeline & Gas Journal
March 19740 p» 34„
150 Colgate, J0 L0, efalo, "Gob Pile Stabilization, Reclamation, and
Utilization," Office of Coal Research R&D Report No. 75, 1973.
16 o Personal Communication from Davy Power gas gmBH.
170 Pearson, M0 Jo, Hydrocarbon Processing _529 (2), p0 810
18o Metrailer, W. J., et al., "Properties of Coke Produced in
Flexicoking Process„" presented at American Chemical Society
Meeting, Philadelphia, Pa. April 6-11, 19750
19„ LGO, S. E., et al., "Trace Metal Pollution in the Environment,"
Jouraal of Air Pollution Controlp 23,, (10), October 1973.
20. Schultz, H., Hattman, E. A., and Booker, W. B., ACS Div, of Fuel.
Chesa., Vol. 89 Ho. 4, p. 108, August 1973.
21. Billings, C. E., Sacco, A. M., Matson, W. R.t Griffin, R. M.,
Coniglio, Wo R., and Harleys R. A., "Mercury Balance on a Large
Pulverized Coal-Fired Furnace," J. Air Poll. Control Association,
Vol. 23S No. 9, September 1973, p. 773.
22. Schultz, Hyman et al.9 "The Fate of Some Trace Elements During Coal
Pretreatment and Combustion.," ACS Div. Fuel Chem. 8_, (4), p. 108,
August 1973.
23. Bolton, N. E., et al., "Trace Element Mass Balance Around a Coal-Fired
Plant/' NCS Div. Fuel ch*m'., 18, (4)p p. 114, August 1973.
24. M&gse, E. M., Halls H. J.. and Varga9 G. M., Jr., "Potential Pollutants
in Fossil Fuels/1 EPA-R2-73-249, June 1973.
2=;. Halls H. J., "Trace Elements and Potential Toxic Effects in Fossil
EPA Syapoaium "Environmental Aspects of Fuel Conversion Technology
St. Louis, Mo., May 1974. EPA 650/2-74-118
26. Ruch, R. R. et, al., "Occurence and Distribution of Potentially Volatile
Trace Elements in Coal." Illinois State Geological Survey. EPA &50/2-^
27. Afcfcari, A.B "The Fate of Trace Constituents of Coal During Gasification "
"""• Saport 650/2-73-004p August 1973. '
28. Ateari, A., et al., "Fate of Trace Constituents of Coal During
Gaoi£ieaei®a/' (Fasrt 11), Presented at Amercian Chemical Society
p Div. of Fuel Che®., Phil;, PA., April 6-11, 1975.
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-650/2-74-009-J
4. TITLE AND SUBTITLE E valuation of Pollution Control in
Fossil Fuel Conversion Processes; Gasification:
Section 8. Winkler Process
3. RECIPIENT'S ACCESSION NO.
5. REPORT DATE
September 1975
6. PERFORMING ORGANIZATION CODE
7. AUTMOH(S)
C. E. Jahnig
I. PERFORMING ORGANIZATION REPORT NO.
Exxon/GRU.14DJ.75
9. PERFORMING OR8ANIZATION 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 report gives results of a review of the Winkler coal gasification process, from
the standpoint of its potential for affecting the environment. 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 reduced environmental impact,
control systems, modifications , and alternatives which could facilitate pollution
control or increase thermal efficiency are discussed, and new technology needs are
pointed out.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. cos AT i Field/Group
Air Pollution
Coal Gasification
Fossil Fuels
Thermal Efficiency
Air Pollution Control
Stationary Sources
Clean Fuels
Winkler Process
Fuel Gas
Research Needs
13 B
13H
2 ID
20M
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (Thi3Report)
Unclassified
21. NO. OF PAGES
49
20. SECURITY CLASS fThtepage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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