United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S7-83-052 Feb. 1984
&ERA Project Summary
Coal Gasification/Gas Cleanup
Test Facility: Volume V.
Preliminary Environmental
Assessment of the
Gasification and Gas Cleaning of
North Carolina Peat
J.K. Ferrell, R.M. Felder, R.W. Rousseau, M.J. Purdy, S. Ganesan, and A.A.
Bradley
Results are reported for five test
runs at a small pilot-scale coal gasifica-
tion and gas purification facility using
North Carolina peat. Results from the
peat gasification are compared with
results obtained previously with a New
Mexico subbituminous coal. The peat
gas produced had slightly more CO and
CC-2, while the coal gas had slightly
more methane. Production of gaseous
sulfur species was much less for peat
due largely to the lower sulfur content
of the peat itself. Wastewater analyses
showed higher concentrations of phenols
and other acidic compounds and lower
concentrations of PNAs in the peat-
derived wastewater than in the coal-
derived wastewater. Peat char remaining
after gasification was depleted of As,
Pb, and Hg to a greater extent than
was the coal char. The peat itself
contained a substantially higher Hg
content than did the coal.
This Project Summary was developed
by EPA's Industrial Environmental Re-
search Laboratory. Research Triangle
Park, NC. to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title {see Project Report ordering
information at back).
Introduction
As a part of continuing research on the
environmental aspects of solid fuel
conversion, the Department of Chemical
Engineering at North Carolina State
University tested the steam/oxygen
gasification of North Carolina peat and
subsequent gas cleaning during the
spring and summer of 1981.
The work was sponsored jointly by the
North Carolina Energy Institute, the
Carolina Power and Light Company, and
the U.S. Environmental Protection Agency.
The facility, constructed in 1977-78
under the sponsorship of the EPA, is a
small coal-gasification/gas-cleaning
pilot plant.
The plant, described in detail in Volume
I of this report series (1), consists of: a
fluidized-bed reactor; a cyclone and
venturi scrubber for particulates, conden-
sables, and solubles removal (PCS
system); and absorption and stripping
columns for acid gas removal and solvent
regeneration. The plant has a nominal
capacity of 23 kg/hr (50 Ib/hr) of feed for
steady state operation. A schematic
diagram of the gasifier, the PCS system,
the acid gas removal system (AGRS), and
other major components is shown in
Figure 1.
The primary objective of this investi-
gation was to characterize all feed and
effluent streams in the integrated gasifi-
er/gas-cleaning facility in order to
evaluate the effectiveness of a methanol-
based acid gas removal system for peat
gasification. Secondary objectives were
-------
Sweet
NX Purge
Acid Gas
Cyclone
1 6
Plant Water"
Solvent Pump
Circulation
Pump
S = Sample Port
Figure 1. Pilot plant facility.
to test the feasibility of steam/oxygen
gasification of North Carolina peat in a
fluidized/bed gasifier and to evaluate the
quality of the resultant raw product gas.
Prior to this study, detailed investigations
were performed of the removal of acid
gases by the gas cleaning system and the
fate of minor and trace contaminants
throughout the integrated facility when
gasifying a pretreated Western Kentucky
No. 11 coal and a New Mexico subbitumin-
ous coal. Full reports on these studies
have been issued (2,3).
This report concerns the steam/oxygen
gasification of North Carolina peat using
refrigerated methanol as the AGRS
solvent. The milled (shredded) peat was
obtained from First Colony Farms, Inc. in
Washington County, N.C. It was screened
to pass through a 1/4-in. (0.635 cm)
screen, air-dried, and gasified without
further treatment. Table 1 shows an
average analysis of the char, the subbi-
tuminous coal, and the peat used in the
studies.
Results and Discussion
Five gasifier test runs were completed
successfully using North Carolina peat.
The first three made use of the gasif ier-
PCS system only, and were used to
determine optimum operating conditions
for the gasifier. The last two integrated
Tablet. Coal, Char, and Peat Analysis
Coal
Char
Wt%
Proximate Analysis
Fixed Carbon
Volatile Matter
Moisture
Ash
86.0
2.4
0.9
10.7
New Mexico
Coal
Wt%
North Carolina
Peat
Wt%
35.2
31.7
10.S
22.6
26.3
46.3
22.8
4.6
Ultimate Analysis
Carbon
Hydrogen
Oxygen
Nitrogen
Sulfur
Ash
83.8
0.6
2.2
0.1
2.6
10.7
52.6
4.8
18.3
1.2
0.6
22.6
45.9
4.3
44.1
0.9
0.2
4.6
the gasifier and AGRS by using the
gasif iej make-gas as feed to the acid-gas
removal system. The milled peat feed was
a mixture of fibrous material, small pieces
of wood, particles of solid peat, and a
fairly large amount of finely divided
material (< 100 mesh). The moisture
content of the peat as received was
approximately 50%. The peat was prepared
for gasification by screening through
1 /4-in. wire mesh and air-drying at room
temperature to a moisture content of
about 25%. The peat was fed to the
gasifier without further preparation.
For most of the runs the fluidized-bed
gasifier worked very well. With the top
feed arrangement, most of the gas
production took place by devolatilization
in the zone above the fluidized bed. The
gasifier acted as a two-stage gasifier with
a small fluidized bed of peat char in the
lower zone and a devolatilization zone in
the region above the bed. As a result of
the first two runs, optimum gasifier
operating conditions were determined to
be a feed rate of about 30 kg/hr (65 Ib/hr)
and a fluidized-bed temperature of 900°C
(165p°F). Under these conditions the
gasifier produced a make-gas flow of
about 0.5 std mVmin (18 scfm)of dry gas.
Comparisons of North Carolina peat
and New Mexico coal runs are rendered
-------
difficult due to the different operating
conditions used in most cases; however,
coal run GO-78 does compare reasonably
well with peat run GOP-4B (GO-78 and
GOP-4B have significance only as test
run identifiers). Gasifier conditions for
peat run GOP-4B and New Mexico
subbituminous coal run GO-78 are
summarized in Table 2. Except for the
lower steam rate and corresponding
lower steam-to-carbon ratio for the peat
run, necessitated by the higher moisture
content of the peat, the conditions of the
two runs were quite similar and thus form
an excellent basis for comparison of
results.
Though not evident in Table 2, lower
operating temperatures were generally
required for peat gasification than for
New Mexico coal; however, the product-
gas yields obtained from both were of
similar magnitude. The higher feed rates
Table 2. Summary of Gasifier Conditions for GOP-4B and GO-78
Table 3. Comparison of Gas Analyses for
GOP-4B and GO-78
From Sample Point Following Cyclone (Figure
11
Species
Hi
CO
CH4
COt
/Va
HuS
COS
Thiophene
CHaSH
Ethylene
Ethane
Propylene
Propane
Butane
Benzene
Toluene
GOP-4B
Peat Ftun
Mole%
28.40
15.56
5.65
23.17
25.94
0.04
0.002
0.001
0.002
0.44
0.65
0.53
0.14
0.07
0.11
0.04
GO-78
Coal Run
Mole%
27.49
11.94
8.46
21.88
30.21
0.24
0.007
0.003
0.005
0.33
0.46
0.12
0.05
0.02
0.02
0.04
Pressure, psig
Temperature, "F
Coal/Peat Feed, Ib/hr
Moisture Content of Feed, %
Coal/Peat Feed, Dry Basis, Ib/hr
Steam Feed, Ib/hr
Steam/Carbon Ratio
Dry Make-Gas Flow, scfm
GOP-4B
(Peat)
104.7
1607
57.9
22.3
45
33
0.83
17.1
GO-78
(Coal)
103.9
1606
41.1
9.6
37
57
1.71
15.9
used in the peat runs were probably a
major factor in this result but the similar
product rates at lower temperatures may
also reflect a greater reactivity of the peat
relative to the coal.
Proximate and ultimate analyses of the
feed peat, the solid samples collected
from the cyclone, and the spent char were
as expected. The spent char was found to
have a relatively high carbon content as a
result of the very low ash content of the
peat. Overall carbon conversion was
satisfactory for our purposes (56 - 65%),
and very little spent char was formed.
The gas analyses for peat are compared
with those for New Mexico coal in Table
3. These data indicate no major differences
in gas composition, except for the sulfur
species. This is undoubtedly due to the
difference in the sulfur content of the
feed materials, since the ratio of total
sulfur in the two product gases is the
same as the ratio of sulfur in the feed
materials. The peat gas contained slightly
more CO and CO2, while the coal
contained slightly more methane. The
higher concentration of methane from
the New Mexico coal, compared to peat, is
consistent with the results of a series of
independent devolatilization studies (4,5)
of these materials.
Gaseous production rates, calculated
as grams produced per kilogram of peat or
coal fed, are shown in Table 4 and
indicate that, in general, hydrocarbons
produced are of similar magnitude in both
coal and peat gasification, while the
sulfur-gas production is much less for
peat. The peat gas had a greater benzene
production rate than the coal, while the
methane production rate was greater for
the coal.
As shown in Table 5, except for
dissolved carbon (indicated by total
carbon, chemical oxygen demand (COD),
total organic carbon (TOC), and total
volatile carbon (TVQ), the wastewater
analyses for coal and peat are nearly the
same. These analyses represent the
composition of aqueous condensate
collected in a side stream sampling train
located immediately after the cyclone
shown in Figure 1 .The condensate at this
point contains no contribution from the
recirculating gas quench water. The
dissolved carbon content for the peat runs
was quite high and was mostly in the
form of phenols. This is consistent with
other results which indicate that the
gasification of peat produces relatively
greater amounts of phenols and other
acidic compounds than the gasification of
coal. An analysis of the peat-derived
wastewater by gas chromatography/mass
spectrometry (GC/MS) also showed a
greater amount of acidic compounds and
a smaller amount of base/neutral com-
pounds than did the coal-derived waste-
water. Compared to previous results from
coal gasification, the wastewater from
peat gasification contained a lower
concentration of polynuclear aromatic
compounds (PNA's), and very few PNAs
of high molecular weight (greater than
250).
A GC/MS analysis of the liquid
condensed from the gas downstream
from the sour gas compressor and heat
exchanger is shown in Figure 2 and
indicates the presence of only the organic
compounds of intermediate volatility:
Peak
No.
Compound
1 Hexene or methyl-substituted
pentene
2 Benzene
3 Heptene or other C? hydrocarbon
4 Toluene
5 Octene or other Ca hydrocarbon
6 Octane
7 Ethylbenzene
8 Xylene
9 Substituted benzene
10 Nonene
11 Nonane
12 Methyl-ethyl-substituted
benzene
13 Decene
Table 4.
Comparison of Gaseous Production from Gasification of New Mexico Coal and
North Carolina Peat
Grams Produced per Kilogram of Feed
N.M. Coal
N.C. Peat
Species
HiS
COS
CHaSH
Thiophene
CH4
Ethane
Ethylene
Benzene
Avg for
All Runs
6.4
0.35
0.10
0.17
75
15
9.1
5.0
GO-78
5.4
0.29
0.17
0.16
88
7.8
6.0
0.9
Avg for
All Runs
0.9
0.07
0.08
0.07
52
10.0
7.6
3.5
GOP-4B
O.7
O.O6
0.05
O.O5
45
9.3
5.8
4.1
-------
Table 5. • Sample- Train Cold- Trap Water Analyses for Coal and Peat
From Sample Point Following Cyclone (Figure 1) Concentrations mg/l except pH
Average Value or Range
for All Runs
GOP-4B GO-78
Ammonia
Carbon
Chloride
COD
Cyanate
Cyanide
Fluoride
Nitrogen
PH
Phenolics
Sulfate
Sulfite
Thiocyanate
TOC
TVC
Peat
6.580
13,720
115
36,460
600-1.770
55
20-120
4.700-9,800
8.5
1,370
14
37
330
11.200
3,800
Coal
6,000
3.200
40
6.000-10,000
2,000-5,000
25-200
10
6.000
8.5
600-1,100
40-300
40
250
2.600
1,500
Peat
7,919
11,400
50
34,200
870
64
20
9,840
8.2
1,493
20
60
NA
10,600
4,450
Coal
6,065
3,380
38
9,350
1,749
167
10
NA'
8.5
772
28
55
233
2,760
1.630
* Not analyzed.
8
56
64
72
16 24 32 40 48
Time, minutes
Figure 2. GC/MS analysis of compressor knockout liquid (from combined peat runs GPO-1
through -6).
primarily benzene, toluene, xylene, and
other substituted benzenes. While sub-
stantial amounts of these compounds
had persisted in the gas stream up to this
point in the process, only traces of
compounds heavier than Cio-compounds
were found, indicating that most of the
PNAs and other heavy hydrocarbons
were effectively removed by the scrubbing,
cooling, and filtering operations of the
PCS system.
Samples of tar collected from the
sample-train cold trap, located at the
sampling point following the cyclone.
were partitioned into acid, base, and
neutral fractions. The neutral fraction
was further partitioned into nonpolar
neutrals, polar neutrals, PNAs, and
compounds insoluble in cyclohexane. Tar
partition results are given in Table 6.
Generally, the tar from the peat
gasification contained more acidic com-
pounds and fewer of the higher molecular
weight PNA compounds, although the
differences were not great. The peat-
derived tar contained very few organic
sulfur compounds in contrast to the coal-
derived tar. Concentrations of most sulfur
compounds in the peat tar were below
detection limits. Results of the tar
analyses are shown in Table 7.
Detailed trace element analyses for As,
Pb, and Hg were performed on samples of
peat feed, gasifier char, cyclone dust, and
the tar, particulates, and condensate
collected in the side stream sample train
for run GOP-4B. Mass balance closures
for Pb and Hg were well below 100%,
indicating that substantial amounts of
these volatile metals remained in the gas
stream at this point in the system. The
gasifier char from peat gasification was
depleted of these elements to a greater
extent than the coal char. One possible
explanation is that these elements are not
as strongly bound to the organic matrix in
peat as they are in coal, and hence are
more easily devolatilized. A somewhat
surprising result was the relatively high
concentration of Hg in the peat feed
material; about 10 times that in the New
Mexico coal.
A major purpose of this study was to
evaluate the potential environmental
consequences of the use of methanol as a
acid-gas removal solvent for gases
generated by peat gasification. In this
study, the AGRS operated well and, for
both AGRS runs, the overall mass
balances and the balances for the major
compounds were excellent (overall mass
balance closures were 101.7 and 102.2%).
Under the absorber conditions used, the
principal acid gases, CO2 and H2S, were
removed to very low levels in the sweet
gas (see Table 8), with a combination of
lower solvent inlet temperature, higher
solvent flow rate, and higher absorber
pressure giving somewhat higher removal
efficiencies. Table 8 shows a complete
set of gas analyses for one AGRS run.
A feature of gases produced from coal or
peat is the relatively high levels of COS
produced with the H2S. The conversion of
COS to H2S before it enters the acid-gas
removal system is necessary in many
processes proposed for treating these
gases because of the difficulty of remov-
ing COS to levels required for downstream
catalytic processes. From the data
collected, both in this study and from
previous studies on coal, refrigerated
methanol appears to remove COS effec-
tively, and no unusual solubility charac-
teristics are evident.
Conclusions
The fluidized-bed steam/oxygen gasifi-
cation of North Carolina peat produces a
gas similar in composition to that
produced from New Mexico subbitumin-
ous coal, except for lower concentrations
-------
Table 6. Tar Partition Results
Tar Sample from Sample-Train Cold Trap
Acids
Bases
TOTAL NEUTRALS
Nonpolar
Polynuclear Aromatics
Polar Neutrals
Cyclohexane Insolubles
GO-78
Wt%
17.29
6.05
76.66
11.53
26.85
16.45
21.83
GOP-4B
Wt%
22.5
4.4
a
76.6
75.8
20.8
2.6
'Analytical difficulties with the cyclohexane insoluble species precluded a material balance for the
neutral fraction of the peat derived tar.
Table 7. Capillary GC Tar Analyses
Tar Samples from Sample-Train Cold Trap
Compound
Phenol
Cresols
Xylenols
Naphthalene
Benzothiophene
Quinoline
2-Methylnaphthalene
1 -Methylnaphthalene
Biphenyl
Acenaphthylene
Acenaphthene
Dibenzofuran
Fluorene
Dibenzothiophene
Phenanthrene
Anthracene
Fluoranthene
Pyrene
Benzo(a)anthracene
Chrysene
Triphenylene
BenzofbJFIuoranthene
Benzo(k)Fiuoranthene
Benzo(e)Pyrene
Benzo(a)Pyrene
Perylene
Total Wt %
" Not analyzed
* Not detected
GO-78
Wt%
NA'
NA
NA
2.10
0.08
0.13
0.97
0.81
0.28
0.60
0.26
0.53
0.43
0.09
0.47
0.49
0.23
0.17
0.05
0.04
0.02
0.013}
0.007 \
0.007 >
0.075
0.07 J
7.802
GOP-4B
Wt%
4.93
6.14
4.40
6.06
0.02
0.20
3.17
1.22
0.74
0.80
1.83
2.58
1.74
ND"
1.70
0.56
0.53
0.14
0.07
0.04
0.02
0.50 Total of
5 Ring
Compounds
37.39
of sulfur compounds and higher concen-
trations of acidic organic species (such as
phenols) in the peat-derived gas.
The raw gas cleaning (PCS) system,
consisting of a cyclone separator, a
venturi scrubber, filters, coolers, and
demisters, removed nearly all of the
relatively nonvolatile compounds from
the gas stream. For all practical purposes,
no hydrocarbons with boiling points
greater than that of decane entered the
acid gas removal system (AGRS). Over
the range of conditions studied, an
important point to be made about the
distribution of aliphatic (Ci to €4) hydro-
carbons through the AGRS is their
presence in significant quantities in the
flash- and acid-gas streams. Since the
gasification of peat tends to produce more
of these compounds than coal, the point
may be of some importance for the design
of gas cleaning systems for peat gasifica-
tion.
Substantial amounts of aromatic
hydrocarbons are also produced during
peat gasification. In this study, these
species were observed to accumulate in
the recirculating methanol. A sample of
the methanol leaving the stripper was
analyzed by high performance liquid
chromatography (HPLC). The only com-
pounds identified were benzene, toluene,
xylenes, and other substituted benzenes;
no multi-ring aromatic compounds were
found. Those compounds which did
accumulate in the chilled methanol
solvent appear to be easily removed by
distillation.
The fluidized-bed gasification of peat
can also be expected to produce relatively
large quantities of heavy organic com-
pounds (which will condense as tars) and
significant quantities of water soluble
organic compounds such as phenols
(which will appear in the wastewater).
Both the tars and wastewater, while
presenting potential environmental prob-
lems, are also potential sources of
valuable chemical byproducts or fuels.
If the product gas from gasification of
North Carolina peat is to be used, in a
catalytic process such as the production
of substitute natural gas (SNG) or
methanol, an acid gas removal system of
some type will be necessary to prevent
sulfur species from poisoning the catalysts.
Alternatively, the product gas could be
burned as an industrial fuel gas on-site.
Either the incineration of the acid gas
from an AGRS or the direct combustion of
the raw product gas in an industrial boiler
would result in a maximum emission of
about 0.4 Ib S02/106 Btu (173 ng/J) of
heat input to the gasifier, assuming that
all the sulfur originally present in the peat
is converted ultimately to S02, a worst
case possibility.
References
1. Ferrell, J.K., R.M. Felder, R.W.
Rousseau, J.C. McCue, R.M. Kelly,
and W.E. Willis, Coal Gasification/
Gas Cleanup Test Facility: Volume 1.
Description and Operation, EPA-
6QO/7-80-046a, March 1980(NTIS
PB80-188378).
2. Ferrell, J.K., R.M. Felder, R.W.
Rousseau, S. Ganesan, R.M. Kelly,
J.C. McCue, and MJ. Purdy, Coal
Gasification/Gas Cleanup Test
Facility: Volume II. Environmental
Assessment of Operation with
Devolatilized Bituminous Coal and
Chilled Methanol, EPA-600/7-82-
023, April 1982 (NTIS PB82-222936).
3. Ferrell, J. K., R. M. Felder, R. W.
Rousseau, R. M. Kelly, M. J. Purdy,
and S. Ganesan, Coal Gasification/
Gas Cleanup Test Facility: Volume
III. Environmental Assessment of
Operation with New Mexico Sub-
bituminous Coal and Chilled Meth-
anol, EPA-600/7-82-054, August
1982 (NTIS PB83-107417).
4. Agreda, V.H., R.M. Felder, and J.K.
Ferrell, Devolatilization Kinetics and
Elemental Release in the Pyrolysis
of Pulverized Coal, EPA-600/7-79-
241, November 1979 (NTIS PB80-
130222).
-------
Table 8. Gas Analysis Summary for GOP-4B, AMIP-2
Concentrations in Mole %
Species
H2
CO
CW4
C02
Nz
HiS
COS
Thiophene
CHaSH
CsHsSH
CS2
Ethylene
Ethane
Propylene
Propane
Butane
Benzene
Toluene
Methanol
Cyclone
Exit
28.40
15.57
5.65
23. J 7
25.95
0.0436
0.0021
0.0011
0.0020
0.0000
0.0000
0.4359
0.6512
0.5319
0. 1351
0.0706
0. 1072
0.0374
0.0000
PCS
Exit*
28.61
15.60
5.55
23.26
25.75
0.0480
0.0021
0.0023
0.0014
0.0000
0.0000
0.2863
0.4518
0.2994
0.1051
0.0389
0. 1074
0.0421
0.4532
AGRS
feed
28.61
15.60
5.55
23.26
25.75
0.0480
0.0021
0.0023
0.00/4
0.0000
0.0000
0.2563
0.4518
0.2994
0. 1051
0.0389
0. 1074
0.0421
0.0000
Sweet
Gas
38.47
20.42
6.31
0.32
34.37
0.0047
0.0019
O.OOOO
0.0000
O.OOOO
0.0000
0.0920
0.0833
0.0249
0.0728
0.0057
0.0000
O.OOOO
0.4385
Flash
Gas
16.45
18.94
9.82
23.68
28.65
0.0196
0.0019
O.OOOO
O.OOOO
O.OOOO
0.0003
0.6889
1.2203
0.2248
0. 1038
0.0256
0.0855
0.0000
3.5977
Acid
Gas
0.8882
1.3970
2.52
67.15
24.71
0.0771
0.003/
0.0000
0.0014
0.0000
0.0001
0.9867
1.5965
1. 1883
0.2703
0.0960
0.0217
O.OOOO
7.5832
*Due to sampling difficulty, sour gas sample was taken to be the same as PCS exit sample.
5. Felder, R.M., C.C. Kau, J.K. Ferrell,
and S. Ganesan, Rates and Equilibria
of Devolatilization and Trace Element
Evolution in Coal Pyrolysis, EPA-
600/7-82-027, September 1982
(NTIS PB82-260944).
J. K. Ferrell. R. M. Felder, R. W. Rousseau, M. J. Purdy, S. Ganesan, and A. A.
Bradley are with North Carolina State University, Raleigh, NC 27650.
N. Dean Smith is the EPA Project Officer (see below).
The complete report, entitled "Coat Gasification/Gas Cleanup Test Facility:
Volume V. Preliminary Environmental Assessment of the Gasification and Gas
Cleaning of North Carolina Peat," Order No. PB 84-113 091; Cost: $13.00
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
-------
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