United States
Environmental Protection
Agency
Office of General Enforcement
Washington DC 20460
EPA-340/1-80-011
April 1980
Stationary Source Enforcement Series
Techniques to Detect
Failure in Carbon
Adsorption Systems
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TECHNICAL REPORT DATA .
(Please read Instructions on the reverse before completing)
REPORT NO.
340/1-80-011
3. RECIPIEr
. TITLE AND SUBTITLE
Techniques to detect failure in carbon adsorption
systems.
5. REPORT DATE
April 1980
6. PERFORMING ORGANIZATION CODE
. AUTHOR(S)
Theodore B. Michaelis, P.E.
8. PERF
PERFORMING ORGANIZATION NAME AND ADDRESS
Engineering-Science
7903 Westpark Drive
McLean, Virginia 22102
10. PROGf
11. CONTRACT/GRANT NO.
EPA 68-01-4146
Task Order 70
2 SPONSORING AGENCY NAME AND ADDRESS
U.S. E.P.A.
D.S.S.E.
401 M Street S.W.
Washington, D.C. .20460
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
5. SUPPLEMENTARY NOTES
Robert L. King, Task Manager
6. ABSTRACT
The study was originated to determine if simple techniques, or equipment inspec-
tion could determine that a given carbon adsorption system was operating at satis-
factory adsorbtion efficiency.
The study determined that no visual inspection would be adequate, but that two
other techniques are feasible. The first technique, utilizes portable, concentration-
sensitive, continuous-measuring equipment which can detect break-through. Break-
through is indication that a carbon adsorbtion system is not operating properly. This
technique is suitable for field inspections.
Maintenance of overall solvent material balances, subject to inspection, is an
alternate technique. A form for a material balance is presented.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
COSATI Field/Group
Air Pollution
Adsorbtion Inspection
Carbon Adsorbtion
Volatile Organic
Compounds
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (ThisReport!
Unclassified
21. NO. OF PAGES
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
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EPA-340/1 -80-011
Techniques to Detect Failure
in Carbon Adsorption Systems
by
Theodore B. Michaelis, P. E.
Engineering-Science
7903 Westpark Drive
McLean, Virginia 22102
Contract No. 68-01-4146
Task No. 70
EPA Project Officer: Robert L. King
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of General Enforcement
Division of Stationary Source Enforcement
Washington, DC 20460
April 1980 "' '" ' ~ '" "* 7"onm3n~tal Protection Agency
, - L • -rary (5PL-16) 'J~
--•• - K. xi?orn Street, Room 167Q
Chicago, IL 60604
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NOTICE
Mention of trade names or commercial products does not constitute endorse-
ment or recommendation for use by the D. S. Environmental Protection Agency.
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TABLE OF CONTENTS
Section
I
II
III
IV
APPENDIX A
APPENDIX B
SUMMARY
INTRODUCTION
Monitoring Techniques
Material Balance
MONITORING TECHNIQUES
Catalytic Oxidation Systems
Chromatography Systems
Diffusion Sensors
Flame-Ionization Systems
Nondispersive Infrared Systems
Ultra-Violet Systems
MATERIAL BALANCES
ORGANIZATIONS CONTACTED OR VISITED
MATERIAL BALANCE FOR DETERMINING OVERALL SOLVENT RECOVERY
EFFICIENCY
I"1
II~1
II- 3
H-5
III-l
III-l
III-2
III-2
III-2
III-2
III-2
IV-1
LIST OF ILLUSTRATIONS
Figure Title
H-1 Carbon-Bed Adsorption System Simplified Flow Diagram
II-2 Typical Discharge Concentration Vs. Time for a Carbon
Bed Vapor Adsorption System
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SECTION I
SUMMARY
For many industries the Control Technology Guidelines, published by OAQPS,
define overall efficiencies for the affected facility. The documents also
define control-device efficiencies which may be expected to achieve these re-
quired overall efficiencies. Enforcement of the guidelines will result in
installation of many volatile organic compound (VOC) control devices in the
near future.
Carbon-adsorption is the most widely-used technique for controlling VOC
discharges which can show a return on investment. Therefore, it is reason-
able to expect that many new carbon-adsorption installations will join the
many existing installations. Techniques exist for determining the exact con-
centration of solvent in inlet and discharge gas streams. These techniques
require high technology to perform, and are beyond the scope of what might
be considered feasible for continued surveillance.
The purpose of this study was to determine if simple techniques were
available for assuring that large carbon-bed solvent-vapor adsorption sys-
tems operated properly, and were maintaining the design adsorption effici-
ency. Large systems were defined as multi-bed (two- or more-bed) systems
equipped with automatic-cycle control. In the process of investigating
these issues, ES made telephone contacts and field visits to the following:
o Existing installations;
o Organizations which design and construct adsorption systems; and
o Trade associations.
The study determined that no visual inspection technique could reliably
predict or define loss of adsorption efficiency. However, it did identify
two techniques which could determine the loss in system efficiency. These
were the measurement of solvent concentration in the discharge, and the pre-
paration of a material balance.
Portable instruments are available for measuring low-level solvent con-
centrations in a gas stream. Although the instruments may not be calibrated
for the gas stream being measured, they do indicate the increase in solvent
1-1
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adsorption system is not functioning properly. This technique is recommended
for inspection of existing systems. Those jurisdictions which encompass seve-
ral carbon adsorption systems should be equipped with a suitable solvent-con-
centration meter, and recorder, and have personnel trained in their use. Such
training is not difficult. Alternatively, a consultant familiar with carbon-
adsorption systems might be called in to make the tests when they are required.
Preparation of an overall solvent material balance can determine solvent
recovery efficiency for an entire facility. Inasmuch as the Industry Guide-
lines define overall recovery as their primary goal, this might be the better
technique. The overall material balance would not be difficult for a faci-
lity to maintain, or for an inspector to review. Many existing facilities
are equipped to maintain the necessary records, and many others could be so
equipped by the addition of one or more totalizing flow meters to measure re-
covered solvent flow.
Existing systems should be inspected periodically by either of the above-
mentioned techniques. New systems should be equipped with instrumentation to
continuously record discharge solvent concentrations, as well as with equipment
to measure the quantity of solvents recovered. EPA may also require that each
facility prepare monthly reports similar to those prepared for opacity-monitor-
ing installations.
1-2
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SECTION II
INTRODUCTION
This project was originated.to determine if visual inspection could as-
sure that large carbon-bed solvent vapor recovery systems retained the recov-
ery efficiency for which they were originally designed. A large system is
defined as a two- (or more) bed system which is regenerated by automatic con-
trol.
A list of typical failure modes was drawn up following discussions, and
visits with trade organizations, design and construction corporations, and
operating corporations. These are listed in Appendix A. The failure modes
identified were:
o Steam valves leak;
o Air discharge valves leak;
o Insufficient steam flow during regeneration;
o Insufficient time for steamout;
o Collapse of carbon bed;
o Loss of carbon activity;
o Bed blockage due to buildup of lint, dust, polymers, or other materi-
als;
o Uneven bed distribution; and
o Improper setting of system controls.
Based on inspections at six plants, it was determined that an expert might
detect several of these failures in some systems, but it would be impossible to
detect most of the failure modes by physical inspection. Two alternate techni-
ques were then identified for determining the effectiveness of operating carbon-
adsorption systems. These were:
o Monitoring the discharge to determine if breakthrough occurs; and
o Preparation of a material balance to determine overall system effici-
ency.
A discussion of the operation of a carbon-bed adsorption system may pro-
vide an understanding of how these techniques may be applied. Figure II-4--is
a simple operating flow diagram of a typical carbon-adsorption unit. Bed A
is "on-stream". Solvent flows through the blower, up through carbon Bed A.
II-l
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FIGURE II-l
STEAM
CARBON BED ADSORPTION SYSTEM
SIMPLIFIED FLOW DIAGRAM
VESSEL A
I
VESSEL B
SOLVENT
LADEN
AIR
COOLING
WATER
TO ATMOSPHERE
CONDENSER
RECOVERED
SOLVENT
II-2
ENGINEERING-SCIENCE
-------
Solvent is adsorbed by the carbon, and the purified air flows to atmosphere.
Bed B is being regenerated. Steam flows down through the bed, heating the
carbon, driving off previously-adsorbed solvents, and carrying them to the
condenser. Condensed water and solvent flow from the condenser to whatever
treatment is required to make the solvent reusable. Steam flow rate, and
steam-out time are adjusted to provide adequate regeneration of Bed B before
Bed A is loaded. Usually, Bed B is placed on stream when regeneration is com-
pleted, and Bed A is regenerated. In a properly operating system, the bed being
regenerated is placed onstreaca before the other bed is fully loaded with solvent.
MONITORING TECHNIQUES
Continuous discharge monitoring can demonstrate that breakthrough does, or
does not ccur. Although not an exact test, it is probable that a system which
goes through several cycles of full-load operation, without reaching breakthrough,
is operating at adsorption efficiencies approaching the original adsorption effi-
ciency for the VOC inlet loads during the test. Instruments suitable for these
tests are discussed in Section III. Figure II-2 presents typical discharge sol-
vent concentration plotted against time. The diagram is a representative example
example of the general shape of such a curve. Actual time, and discharge concen-
tration will vary from system to system. Initially, discharge concentration will
be high because the bed remains hot from regeneration, and because the vessel is
full of steam and solvent vapor. The bed cools rapidly, due to the evaporation
of water which condenses on the carbon, and the discharge solvent concentration
falls rapidly (1 to 2 minutes) to low levels (50 to 250 ppm). Discharge concen-
tration then rises slowly. The beds are usually switched at the point marked
"A" on graph. If a bed is kept on stream, the discharge concentration continues
to rise slowly until it reaches point "B", where it begins to rise rapidly. This
point is known as breakthrough. It can occur because bed changeover is delayed,
because bed capacity is reduced, or because steamout is incomplete so that the
time to breakthrough is reduced to less than the cycle time.
A measure of total solvent capacity can be determined by interrupting
the normal operating cycle and delaying regeneration until breakthrough has
occurred. This can be express as:
Time to Breakthrough x Solvent Loading at Time of Test - Actual
Normal On-Stream Time Capacity
II-3
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FIGURE 11-2
800
700
^ 600-
i500
Ul
o
o 400
(9
oc
«c
300-
200-
100-
50-
TYPICAL DISCHARGE CONCENTRATION VS, TIME
FOR A CARBON-BED VAPOR ADSORPTION SYSTEM
i i i i r r
12345
25 30 35 40 50
ON-STREAM TIME (minutes)
NOTE: This curve is an example. Actual time will vary for each application.
n-4
ENGINEERING-SCIENCE
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This is not an exact measure of adsorption system capacity, but it can indicate
significant deterioration.
MATERIAL BALANCE
An overall system material balance is the best technique for determining
the overall system efficiency addressed in the OAQPS Guideline Series. Data
to prepare a material balance could be assembled in many existing facilities.
Other facilities could be modified simply by addition of totalizing flow me-
ters to the recovered solvent lines. This is discussed in more detail in
Section IV.
II-5
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SECTION III
MONITORING TECHNIQUES
Determination of time to breakthrough requires that solvent concentrations
in the 50-500 ppm range be continuously measured. Several types of instruments
are available for measuring solvents at these low levels.
o Catalytic oxidation;
o Chromatography;
o Diffusion sensor;
o Flame ionization;
o Instantaneous sampling;
o Nondispersive infrared; and
o Ultra-violet ionization.
These systems each have some advantages and disadvantages. They require cali-
bration for the solvent being measured if exact measurements are required, but
can also be used without calibration to indicate relative concentration levels.
If the output of a suitable detector is connected to a recorder, the adsorber-
discharge concentration could be monitored over several cycles to demonstrate
the absence of breakthrough. For a facility operating at normal production
rates, the absence of breakthrough may be taken as evidence that the adsorp-
tion system is operating satisfactorily. A brief description of each of the
available instruments follows. Costs for VOC instruments are contained in a
report "Summary of Available Portable VOC Detection Instruments" prepared by
PEDCO Environmental, Inc. under Task No. 120 of EPA Contract 68-01-4147. It
would not be difficult to train inspectors in use of the instrumentation, and
in their application to carbon-adsorption systems.
CATALYTIC OXIDATION SYSTEMS
Catalytic oxidation systems measure the heat evolved when the organic va-
pors in a gas stream are oxidized by a platinum-black catalyst. These units
are light, and easy to use. System response varies with the heat of combus-
tion of the organic vapor, but most hydrocarbons, including most chlorinated
hydrocarbons can be detected. At low vapor concentrations, catalytic oxida-
tion units must be zeroed every few minutes. They are not suitable for con-
tinuous low-level measurement.
III-l
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CHROMATOGRAPHY SYSTEMS
Chrornatography systems require considerable operator training if reliable
results are desired. They are not suitable for this service.
DIFFUSION SENSORS
Diffusion sensors have been used^ for several years in carbon adsorption sys-
tems. According to the manufacturer, detection of gases is accomplished by em-
bedding a heater and collector in a metal oxide silica type material. At opera-
ting temperature, a very high resistance exists between the sensor elements.
Upon sensing gas, this resistance changes significantly producing several volts
output in relation to the gas concentration. These instruments, available in
portable sizes, can be set up to indicate concentration as low as 50 ppm full
scale, or up to several thousand ppm full scale. One type of instrument could,
therefore, be used to monitor both inlet and discharge solvent concentrations.
An instrument of this type would be an excellent tool to detect breakthrough
in working carbon-adsorption systems.
FLAME-IONIZATION SYSTEMS
Flame-ionization units are among the oldest of the low-level solvent-de-
tection systems. A sample of the gas flows continuously through a pure-hydro-
gen flame, and the resulting ions induce current flow to an electrode placed
adjacent to the flame. Current flow is proportional to solvent concentration.
Essentially, all hydrocarbons may be detected. These units are suitable for
the application.
INSTANTANEOUS SAMPLING
There are several techniques which might be used to withdraw samples
from the gas stream, and analyze them. The analysis may be rapid enough to
be considered instantaneous, but the time between samples is usually several
minutes. These techniques may be suitable for the application, but are
usually not as convenient to use as continuous measuring techniques, and they
cannot provide a continuous record.
III-2
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NONDISPERSIVE INFRARED SYSTEMS
Nondispersive infrared systems require that the system be set for each
hydrocarbon to be measured and that the measured sample be free from water.
Operation of these systems is relatively complex. The maximum absorption fre-
quency for each measured hydrocarbon must be known, and the instrument must
be set for that frequency. Less complex systems are available to detect break-
through, so the system is not considered desirable for this service.
ULTRA-VIOLET IONIZATION SYSTEMS
Ultra-villet ionization is a relatively new technique for detecting the
presence of organic-carbon molecules. High-energy ultra-violet light ionizes
the molecules, which induce current flow between two elecrodes. System re-
sponse varies with light-source energy, and with sensitivity of the organic
compound, but most commercial hydrocarbons, including chlorinated hydrocarbons,
can be detected. Commercially-available units are light, safe, easy to use,
and suitable for this application.
III-3
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SECTION IV
MATERIAL BALANCES
Material balances, taken over a reasonable time period (usually more than
one week) can provide demonstration that the entire facility is maintaining the
collection efficiency required by the facilities' operating permit. To be ef-
fective, the- operating plant must maintain accurate records of solvent-contain-
ing materials entering the process, and of the recovered solvent. Recovered
solvent returned to the process is considered as part of the solvent entering
the system. The solvent concentration of all materials entering the process
must be known. A .form for a material balance is presented in Appendix B.
Most of the information can be assembled by the source from shipping da-
ta, and from component data available from raw-material suppliers. The only
data which must be generated directly by the source is the quantity of recov-
ered solvent. This can be determined by use of totalizing flow meters measur-
ing solvent from the recovery systems. These meters are similar to residen-
tial water meters. Many installations have such flow meters installed. It
would not be difficult to install them in existing systems. All new systems
should be so equipped.
IV-1
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APPENDIX A
ORGANIZATIONS CONTACTED
OR VISITED
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TRADE ASSOCIATIONS
Flexible Packaging Association
Gravure Research Institute
Graphic Arts Technical Foundation
OPERATING FACILITIES
Meredith-Burda Corporation - Rotogravure
Technicolor Laboratories, Inc. - Film Processing
Adhesives Research, Inc. - Pressure Sensitive Tape
Kecoughtan Laundry - Central Dry Cleaning
SCM Corporation - Pressure Sensitive Tape
Wabash Tape Corporation - Magnetic Tape
Alco-Gravure Corporation - Rotogravure
ADSORPTION SYSTEM MANUFACTURING ORGANIZATIONS
NuCon Corporation
Oxy-Catalyst Division of Research-Cottrell Corporation
Vara International, Inc.
SENSOR MANUFACTURING CORPORATIONS
HNU Systems, Inc.
International Sensor Technology, Inc.
Bacharach Instrument Company
Mine Safety Appliance Corporation
Analytical Instrument Development Company
A-l
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APPENDIX B
MATERIAL BALANCE FOR DETERMINING
OVERALL SOLVENT RECOVERY EFFICIENCY
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