United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S7-84-007 Mar. 1984
vvEPA Project Summary
Process Gas Chromatography
Study of a Selexol Acid Gas
Removal System
W. A. Williams
This report gives results of continuous
compositional monitoring by process
gas chromatography (GC) for three gas
streams associated with the Selexol
acid gas removal system at the Bi-Gas
pilot plant in Homer City, PA. Data were
obtained from the inlet and outlet
streams of the Selexol system during
tests in April and May 1982. During the
two tests, product gas composition data
were logged for 55 hours of plant
operation.
The Bi-Gas pilot plant, utilizing a two-
stage, entrained-bed, high-pressure
slagging gasifier, produces a product
gas that is low in tars and heavy oils.
This gas stream required very little
cleanup prior to instrumental analysis.
However, some problems were encoun-
tered in the analysis of the Selexol acid
gas stream due to the presence of high
levels of naphthalene. The process gas
chromatographs (GCs) performed well
and remained very stable during the
tests. Material balances based on GC
analyses and process flow rate data
show a high degree of material account-
ability. The H2S removal efficiency of
the Selexol absorber was about 99
percent during the tests.
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 infor-
mation at back).
Introduction
As part of Radian Corporation's con-
tract, "Environmental Assessment of
Low- and Medium-Btu Gasification Pro-
cesses," with the U.S. Environmental
Protection Agency (EPA), two sets of
process gas chromatographs were oper-
ated at the Bi-Gas coal gasification pilot
plant in Homer City, PA, during April 21 -
22 (Run 19A) and May 18-19 (Run 19B),
1982. The process GCs provided semi-
continuous monitoring (continuous data
logging) of two streams simultaneously.
The GCs were used to:
acquire gas compositional data for the
Selexol acid gas removal process,
evaluate the potential for the use of
this technique for monitoring gas
streams in coal gasification facilities,
and
provide a means of "tracking" process
operation in order to assess the condi-
tions at which samples were collected.
Concurrent with the data acquisition
aspect of EPA's low-Btu program, an
Electric Power Research Institute (EPRI)
program and a Department of Energy
(DOE) program were implemented. The
EPRI test program focused on emissions
measurement from a coal gasification
facility. The DOE program addressed the
environmental, health, and safety aspects
of coal gasification. This report focuses
on EPA's data acquisition results and
summarizes the plant operation and the
instrument operation for the process gas
chromatographs over the two test periods.
Reports being prepared by EPRI and DOE
will present detailed data and results for
the overall program.
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Process Description and
Test Schedule
Radian conducted sampling and analy-
sis of process streams at the Bi-Gas pilot
plant in Homer City, PA, during three run
episodes (Plant Runs 19, 19A, and 19B)
during a 2-month period, April and May
1982. The Br-Gas pilot plant was funded
by the DOE and operated by Steams-
Roger Engineering Corporation. The coal
used in the tests was Pittsburgh No. 8.
During the tests, the nominal coal feed
and product gas generation rates were
2000 and 6000 kg/hr, respectively.
The first test of this series. Run 19, was
conducted in early April and lasted 12
hours. No process GC data were obtained
during this time. During the next test
(19A)from 0800 hours on April 21 until
1600 hours on April 22,1982, the process
GCs were used to collect compositional
data from the Selexol absorber inlet and
outlet gas streams. The next test, 19B,
was conducted May 18-19, 1982. During
this test period, the process GCs were
used to monitor the Selexol inlet and
Selexol acid gas streams. Two sets of
instruments, each containing three gas
chromatographs, were used to monitor
hydrocarbons (Ci-C4+), sulfur species
(H2S, COS, S02, CS2), and major gases
(CO2, N2, 02, H2, CO, CH<). In addition to
the EPA-funded process GC monitoring,
liquid- and gas-phase samples and oper-
ating data were collected from the Selexol
unit. Samples for analysis were collected
from all influent and effluent gas streams
including the high- and low-pressure
flash vents. Figure 1 is a schematic of the
Selexol module, including the sample
collection points.
Instrumentation
Instrument Description
Two sets of process GCs were used
during'-the test program: an Applied
Automation (AA) Model 7170, and a
Bendix Model 7000.
Both GC systems are housed in a 2.4 by
3.6 m trailer-mounted portable building.
The insulated enclosure is heated and air
conditioned to provide a stable atmos-
phere for the instruments and the data
acquisition system. All necessary electri-
cal wiring, instrument air filtration, and
drying systems are contained in the
enclosure.
Each process GC system provides the
following detectors: flame ionization (FID)
for Ci-C4+ hydrocarbons; flame photo-
metric for H2S, COS, SO2, and CS2; and
thermal conductivity for CO2, CO, H2, N2,
Selexol
Absorber Outlet
(To Thermal Oxidizer)
Absorber
Legend
Gas Sample
Liquid Sample
I # | Sample Point
Acid Gas
To Sulfur
Recovery
Selexol
Absorber /n/ei, , __,
(From HP (*"
Gas Washer)
Recycle
Condensate
Solvent
Stripper
Figure 1. Selexol acid gas removal system.
02, CH«, and H2S. The FID of the Bendix
Model 7000 was not operational during
the tests due to an undelivered factory
back order for parts.
Three process streams were monitored
during the tests. The sample acquisition
system for the Selexol inlet and outlet gas
streams was the same. The gas sample
was taken from a valve tao, filtered, and
the pressure reduced from 5250 to 440
kPa using a stainless steel two-stage gas
regulator. The sample was then trans-
ported to the analytical instruments via
heat-traced 0.64 cm Teflon tubing that
was maintained at 394 K.
The acquisition system for the Selexol
acid gas sampler was similar except this
gas stream was not under pressure.
Therefore, after filtration, a Teflon-lined
pump was used to move the sample
through the heat-traced transport line.
A separate gas conditioning system for
each GC system was used to further filter,
dry, and deliver sample gas to each
analyzer. Each analyzer was equipped
with a sample loop/valve injection system
through which the sample was continu-
ously purged. All the instruments utilize
multiple columns and automatic valve
sequencing for component speciation. A
Spectra-Physics Model 4000 Integrator
was used to record and integrate the
chromatographic output. The Integrator
also controlled the recycle time for the
five operating GCs.
Instrument Operation
The process GCs performed well and
remained very stable during the tests.
Limitations in the data obtained with the
GCs were caused either by (1) mechanical
problems with plant operation, or (2)
stream compositions beyond the analyt-
ical capability of the instrumentation as it
was configured during the tests. The
impact of mechanical problems with plant
operation on data collection is a reality
during any source test. The impact on the
process GCs can be minimized or elim-
inated by early reports of these problems
to the process GC operator. For item (2),
above, the sample preparation techniques
can easily be modified for subsequent
tests with the process GCs.
Results
During the two tests, the analyses
conducted (with the process GCs) on the
individual gas streams were:
Run 19A,
April 21-22,
1982
Selexol
Absorber Inlet
Selexol
Absorber
Outlet
Volatile
Major sulfur
species species
V
V V
Light
hydro-
carbons
v/
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Run19B,
May 18- 19, 1982
Selexol
Absorber Inlet
Selexol
Acid Gas
V
N/
V
N/
70
Samples of the gas streams were col-
lected and analyzed approximately every
10 minutes using the process GCs. In
addition, grab samples (gas bombs) were
collected three to five times at each
location. Graphs depicting hourly aver-
ages of the analyses for major gas
components are shown in Figures 2 and
3. Corresponding grab sample data are
also plotted for comparative purposes.
The discontinuity for the Selexol inlet
data in Figure 2 is due to a temporary loss
of instrument carrier gas flow. The large
excursion around midnight during Test
19A reflects the shutdown of the coal
feed which occurred following the slag
burner shutdown at 2310 hours. As
shown in the figures, the process GC data
are generally in good agreement with the
grab sample data.
Average gas compositions for Tests
19A and 19B are shown in Table 1. The
sulfur species data indicate about 99
percent removal of HaS from the inlet gas
stream during Test 19A. There also
appears to be some removal of COS;
however, the inlet analysis for COS for
both test periods was near the detection
50
45
40
1^ ^"S^^ > >»
H2=38.0%
30
Q.
§25
§70
5
\ ,-.'-.* CO = 31.5%
\ / *
\ / NOTE: Data points
\> are grab samples.
CO2 = 15.1%
NOTE: Data points
are grab samples.
50
40
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Table 1. Average Gas Composition for the Bi-Gas Pilot Plant, Runs 19A and 19B
Run 19A
Run 19B
Species
H2
C02
N2
CHt
CO
HtS
COS
C*He
Ct+
Selexol
Absorber
Inlet
38.0%
15.1%
6.9%
8.6%
31.5%
0.41%
200 ppm"
36 ppm
1100 ppm
Selexol
Absorber
Outlet
41.4%
14.1%
6.6%
7.9%
29.9%
<4 ppm
76 ppm
NA"
NA
Selexol
Absorber
Inlet
37.2%
20.1%
4.9%
9.2%
30.0%
0.38%
WOppm"
NA
NA
Selexol
Acid Gas
ND"
51.5%
23.1%
ND
ND
12.9%
c
c
c
"Not detected.
^Estimated value.
"Unable to quantify; detector overloaded.
aNot analyzed.
W. A. Williams is with Radian Corporation, Austin, TX 78766.
William J. Rhodes is the EPA Project Officer (see below).
The complete report, entitled "Process Gas Chromatography Study of a Selexol
Acid Gas Removal System," (Order No. PB 84-158 336; Cost: $11.50, subjectto
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
U S. GOVERNMENT PRINTING OFFICE. 1984 759-015/7635
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
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