.V
United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/S2-85/012 May 1985
Project Summary
Full-Scale Carbon Adsorption
Applications Study
T. P. Nelson, J. R. Blacksmith, and J. L. Randall
The full report presents the results
of theoretical and field test investiga-
tions of full-scale carbon adsorption
applications. The program focused on
the performance testing of several
fixed-bed, steam-regenerated carbon
adsorption systems used in the rub-
berized fabric, magnetic tape, and
flexible packaging industries. The test
results showed that a 96 percent
volatile organic compound (VOC)
reduction can be expected for most
common industrial solvents when ex-
haust gases are processed through a
properly designed and operated ac-
tivated carbon bed. The test program
was also designed to measure the ef-
fective carbon life for each of the test
facilities. Carbon life was found to
vary from plant to plant and ranged
from as low as 9 months at a
magnetic tape facility to over 5 years
at a rubberized fabric coating opera-
tion. The full report also includes a
brief discussion on the theory of car-
bon adsorption and on computer
simulations of carbon bed systems.
This Project Summary was
developed by EPA's Hazardous Waste
Engineering Research Laboratory, Cin-
cinnati, OH, to announce key findings
of the research project that is fully
documented in a separate report of
the same title (see Project Report
ordering information at back).
Introduction
The U.S. Environmental Protection
Agency (EPA) is currently evaluating the
environmental and health impacts of
volatile organic compound (VOC) emis-
sions from a variety of industrial sources.
As part of this effort, Radian Corporation
has contracted a program (EPA Contract
No. 68-03-3038) to evaluate the perform-
ance of full-scale vapor-phase carbon ad-
sorption VOC control systems for solvent
recovery. Inherent in any cost-
effectiveness evaluation of a carbon ad-
sorber installation is some decision on the
effective life of the carbon. The Agency
was unable to find substantive data to
reflect the effect of irreversible fouling
that may take place as a result of im-
purities or byproducts of some industrial
operations. This study was initiated to in-
vestigate the change, if any, in efficiency
of the carbon bed with time.
Carbon adsorption-based solvent
recovery is a commonly used VOC control
technology in the surface coating in-
dustry. Economic and/or regulatory incen-
tives contribute to its wide application.
Limited data are available on
measurements of carbon service life and
VOC removal efficiencies for full-scale, ex-
isting carbon bed systems. Therefore, to
evaluate the VOC control performance,
the following program objectives were
established: (1) to determine the effects
of carbon service life on long-term system
performance and (2) to compare the per-
formance of the tested systems and the
major factors affecting performance.
Summary of Results
Six full-scale activated carbon systems
were tested at various locations across
the United States. The test sites included
two plants from each of the following sur-
face coating industries: rubberized fabric,
magnetic tape, and flexible packaging.
These categories were selected because
they represented a variety of coating
solvents and control system sizes. The
coating solvents examined in the study in-
clude hexane, toluene, tetrahydrofuran
(THF), isopropyl acetate, n-propyl
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acetate, and methyl ethyl ketone (MEK).
The volumetric flow rate of the gas
streams treated ranged from 3.7 to 32
NmVsec (7800 to 68,000 scfm). The ad-
sorption systems at the rubberized fabric
and flexible packaging plants feature
horizontal carbon beds, although SLA
flow direction through the beds differs
(downward for the rubberized fabric
plants and upward for the flexible packag-
ing plants). Conversely, the magnetic tape
plants feature adsorption systems with an-
nular carbon beds, although again, SLA
flow direction through the bed differs (in-
ward for one plant and outward for the
other). The number of carbon beds per
system also varied from two to six,
depending on the volume of gas being
treated.
The relative SLA flow rates, as com-
pared to the bed carbon capacity, average
approximately 0.0015 Nm3/sec-kg carbon
(1.5 scfm/lb carbon) for the six tested
systems with the rates ranging from a
relatively conservative 0.00069 Nm3/sec-
kg carbon (0.65 scfm/lb carbon) to a high
of 0.0026 Nm3/sec-kg carbon (2.5
scfm/1b carbon). Also, the horizontal bed
systems generally feature average design
superficial bed velocities of 0.45 m/sec
(89 fpm), while the thin-bed designs of
the annular bed systems feature lower
velocities, nominally 0.33 m/sec (65 fpm).
The six designs are characterized by
significant differences in inlet solvent
loadings, with average inlet concentra-
tions ranging from less than 1000 ppmv to
over 4000 ppmv. On a carbon basis,
design solvent loadings vary over an order
of magnitude, from 0.0066 to 0.097 kg
solvent/kg carbon (0.0066 to 0.097 Ib sol-
vent /Ib carbon).
Cost data were also developed for each
of the tested facilities based on plant in-
formation. In 1983 dollars, the total capital
costs for the activated carbon systems
range from $267,000 to $2,685,000. The
capital cost normalized to the SLA flow
rate ranges from $51,000 to $173,000 per
Mm3 ($24 to $82 per scfm). The normal-
ized annual costs range from 0.19 to 0.66
$/kg (0.09 to 0.30 $/lb) of recovered sol-
vent.
The carbon adsorption systems were
tested using EPA and ASTM methods. In-
let and outlet VOC concentrations were
measured semicontinuously with flame
ionization detector (FID) total hydrocar-
bon (THC) instrumentation as described in
EPA Method 25A. Volumetric flow rates
were measured according to EPA
Methods 1 and 2. All test results were
verified by EPA-specified quality
assurance/quality control procedures.
Other process information, including
steam rate, steam temperature, SLA
temperature, and carbon weight, was
determined from process instrumentation
or design specifications.
All six plants were originally tested in
early 1982. During these tests, data were
taken to characterize the VOC removal ef-
ficiency of the carbon bed systems and to
characterize the conditions of the carbon.
Four of the six plants were retested using
the same test methods approximately 18
to 22 months later. A comparison of the
changes in performance was made in an
attempt to define the effects of long-term
carbon degradation. In general, the data
indicate significant differences in perform-
ance from plant to plant and from test
period to test period. However, these dif-
ferences were not always attributable to
carbon degradation. A summary of the
test results for all six plants is shown in
Table 1.
The average VOC control efficiency
data indicate that, with the exception of
one plant, 'all tested adsorption systems
were capable of achieving efficiencies of
95 percent or greater. (Mechanical prob-
lems at two plants caused considerable
decreases in the VOC control performance
during the repeat testing.) Average
removal efficiencies exceeding 99 percent
were measured for two of the systems
during the original testing.
The useful carbon life of the activated
carbon systems examined in this study
ranged from a few months to over 6
years. During the repeat testing at four of
the original six test sites, carbon degrada-
tion was definitely detected at only one of
the facilities. The other three facilities
either did not indicate any substantial
reductions in VOC removal performance
or were experiencing reductions in per-
formance not related to carbon degrada-
tion. It was concluded that the test
methods currently used for measuring car-
bon bed performance cannot be used to
predict useful carbon life.
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Table 1. Comparison of Test Results—Plants 1-6
Rubberized Fabric
Magnetic Tape
Flexible Packaging
PLANT 1 5
Original Original
Test Test
Solvent Type MEK toluene
Adsorption mode 95* 150
length, min
SLA flow rate. 5.4 4.3
Nrrf/seclscfm) (11,400) (9,100)
Inlet solvent concen- 2, 190 1,940
tration, ppmv
VOC control 84.9 97.6
efficiency, %
Desorption mode 55 50
length, min
Steam/ recovered sol- 20120) 8.218.2)
vent, kg/kg (Ib/lb)
Carbon age, years 0.4 5.0
Cost Information
(1983 dollars)
Total Capital, tlO> 622 267
Relative Capital. $ 10*/ 110(56) 51(24)
Nrrf/sec (f/scfm)
Total Annualized 262 125
Cost, $10>
Relative Annualized 0.53 (0.24) 0. 19 (0.09)
Cost, S/kg
Recovered solvent
2 3
Repeat Original Repeat Original
Test Test Test Test
toluene THF/to/uene3 THF/toluene* THF/toluane/
MEK/MIBK/
cycfohaxanone
200 64 65 47
3.7 4.6 4.5 9.4*
17,8001 (9.800) (9.500) (19.800)
896 1.470 1,140 3,220
80.5 99.7 ' 95.2 94.7
40 32 32 35
15115) 5.2(5.2) 6.5(6.5) 6.0(6.0)
6.5 2.0 3.8 0.4
650 1,800
108(51) 173182)
325 1,430
0.61(0.28) 0.66(0.30)
4 6
Original Repeat Original Repeat
Test Test Test Test
hexane hexane toluene/ If AC toluene IIP AC
120 90 470* 580"
8.3 10.7 15.8* 16.0^
(17,700) (22.600) (33,400) (33.900)
1,260s 940* S04 847
99.0s 4S.7e-i 97.5 97.9
25 25 30 30
4.6(4.6) 11(11) 1.0(1.01 0.8(0.8)
3.0 4.5 0.2 1.6
1,334 2,685
129 161) 72 (34)
494 839
0.51 (0.23) 0.28 (0. 13)
^Original THF/ toluene percentages were 50/50: repeat test percentages were 75/25.
^Cycle timing controlled by exhaust gas (breakthrough) hydrocarbon analyzer.
cFlow rate measured when 4 of the 6 beds were in service (2 beds were on permanent standby).
^Process Train 1 conditions (total system capacity was twice that of Process Train 1).
^Measurements made at common inlet/common outlet.
' Removal efficiency is low due to steam valve leakage (99 percent efficiency was measured after repair of the valves).
T. P. Nelson, J. R. Blacksmith, andJ. L. Randall are with Radian Corp., Austin, TX
78766.
Ronald J. Turner is the EPA Project Officer (see below).
The complete report, entitled "Full-Scale Carbon A dsorption Applications Study, "
(Order No. PB 85- 1 72 906/AS; Cost $20.50, subject to change) will be available
only from:
National Technical Information Service
5285 Port Royal Road
Springfield, V A 221 61
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
ft U.S. GOVERNMENT PRINTING OFFICE: 1985-559-016/27054
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Environmental Protection
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