EPA-600/R-96-030
March 1996
REVIEW OF CONTROL OPTIONS
FOR METHYL BROMIDE
IN COMMODITY TREATMENT
By:
Glenn B. DeWolf and Jim L. Phillips
Radian Corporation
P.O. Box 201088
Austin, Texas 78720-1088
EPA Purchase Order No. 4D2817NALX
EPA Project Officer: Robert V. Hendriks
National Risk Management Research Laboratory
Research Triangle Park, North Carolina 27711
Prepared for:
U.S. Environmental Protection Agency
Office of Research and Development
Washington, D.C. 20460
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TECHNICAL REPORT DATA
. _ , (Please read Instructions on the reverse before complei
1. REPORT NO. 2.
EPA-600/R-96-030
3.'
4. TITLE AND SUBTITLE
Review of Control Options for Methyl Bromide in
Commodity Treatment
5. REPORT DATE
March 1996
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Glenn B. DeWolf and .Tim L. Phillips
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING OR0ANIZATION NAME AND ADDRESS
Radian Corporation
P.O. Box 201088
Austin, Texas 78720-1088
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
EPA P.O. 4D2817NALX
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Air Pollution Prevention and Control Division
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final; 9/94 - 8/95
14. SPONSORING AGENCY CODE
EPA/600/13
15.supplementary notes APPCD project officer is Robert V. Hendriks, Mail Drop 62B,
919/541-3928.
V
i6. abstract kg rep0ri; describes recent developments in the control of methyl bromide
(MeBrj 'and discusses technical considerations and requirements for and economic
feasibility of recovery: (NOTE: MeBr, a fumigant for agricultural commodities, is
an ozone depleting chemical. The U.S. EPA has banned its use beginning in 2001. In
some applications,' a suitable substitute forjMeBr has not been found, so the report
discusses an exempted use of MeBr with capture and recovery or recycle for some
applications.) -The primary focus of the report is on quarantine applications using
MeBr. Two of the most promising approaches to recovery, recycle, -and reuse con-
tinue to be physical adsorption on a solid sorbent and cryogenic condensation. In
addition to discussing these technologies, the report identifies some of the critical
considerations for process economics and remaining information gaps. The review
concludes that recovery, recycle, and reuse appear to be feasible, have not been un-
equivivocally proven to be so, and there is little current incentive to pursue such <
technologies unless there is hope of exemptions to or recision of the MeBr ban-T.'" r
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
b. IDENTIFIERS/OPEN ENDED TERMS
c. COSATl Field/Group
Pollution Quarantine
Bromohydrocarbons Sorption
Fumigation Cryogenics
Agricultural Products
Ozone
Climate Changes
Pollution Prevention
Stationary Sources
Methyl Bromide
13B 06E
07C 07D
06F 20M
02D
07B
04R
13. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)'
Unclassified
21. NO. OF PAGES
34
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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FOREWORD
The U. S. Environmental Protection Agency is charged by Congress with pro-
tecting the Nation's land, air, and water resources. Under a mandate of national
environmental laws, the Agency strives to formulate and implement actions lead-
ing to a compatible balance between human activities and the ability of natural
systems to support and nurture life. To meet this mandate, EPA's research
program is providing data and technical support for solving environmental pro-
blems today and building a science knowledge base necessary to manage our eco-
logical resources wisely, understand how pollutants affect our health, and pre-
vent or reduce environmental risks in the future.
The National Risk Management Research Laboratory is the Agency's center for
investigation of technological and management approaches for reducing risks
from threats to human health and the environment. The focus of the Laboratory's
research program is on methods for the prevention and control of pollution to air,
land, water, and subsurface resources; protection of water quality in public water
systems; remediation of contaminated sites and groundwater; and prevention and
control of indoor air pollution. The goal of this research effort is to catalyze
development and implementation of innovative, cost-effective environmental
technologies; develop scientific and engineering information needed by EPA to
support regulatory and policy decisions; and provide technical support and infor-
mation transfer to ensure effective implementation of environmental regulations
and strategies.
This publication has been produced as part of the Laboratory's strategic long-
term research plan. It is published and made available by EPA's Office of Re-
search and Development to assist the user community and to link researchers
with their clients.
E. Timothy Oppelt, Director
National Risk Management Research Laboratory
EPA REVIEW NOTICE
This report has been peer and administratively reviewed by the U.S. Environmenlal
Protection Agency, and approved for publication. Mention of trade names or
commercial products does not constitute endorsement or recommendation for use.
This document is available to the public through the National Technical Information
Service, Springfield, Virginia 22161.
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ABSTRACT
Methyl bromide (MeBr), a significant fumigant for agricultural commodities, is
listed by the Montreal Protocol as an ozone depleting chemical. The U.S. Environmental
Protection Agency has banned methyl bromide use beginning in 2001. In some applications, a
suitable substitute for methyl bromide has not been found. Therefore, in 1994, a brief study was
undertaken to characterize fumigation processes for one important type of commodity
fumigation, space fumigation, and to identify potential methods for control, recovery, and
recycle. EPA issued a report in 1994. Since that time, there have been additional developments
in finding appropriate technologies for this purpose. Continuing interest in the subject has been
reflected in two prominent forums for disseminating information related to methyl bromide. The
first was a conference held in Orlando, Florida in November, 1994. The second was in the
contents of a report issued by the United Nations Methyl Bromide Technical Options Committee,
in 1995. Also an important development was the installation and testing of methyl bromide
treatment and reuse system at the Port of San Diego in 1995. Because of these advances, and
additional study, the present report was prepared to communicate information on these
developments and to discuss further technical considerations and requirements for technical and
economic feasibility of recovery. The primary focus of the present report is on methyl bromide
treatment in quarantine applications.
At this time, two of the most promising approaches to recovery, recycle, and reuse
continue to be physical adsorption on a solid sorbent and cryogenic condensation.
A new adsorption system was installed and tested at the Port of San Diego. Based
on zeolite adsorption technology, the system achieved over 95% removal efficiency of methyl
bromide from the post-fumigation vent stream. This is consistent with expectations based on
other tests that have been reported in the past. In addition to zeolite adsorption, condensation at
cryogenic temperatures still appears to be a potentially feasible candidate for some applications.
However, like activated carbon, another candidate technology, little if any new activity in these
areas appears to have occurred recently. In addition to discussions on each of these technologies
iii.
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and their costs, this report identifies some of the critical considerations for process economics
and identifies remaining information gaps and further needs. The overall conclusion of this
review is that recovery, recycle, and reuse appears to be feasible, has not been unequivocally
proven to be so, and that there is little current incentive to pursue such technologies unless there
is hope of exemptions to or a rccision of the methyl bromide ban.
iv
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TABLE OF CONTENTS
Page
Abstract j "M i
List of Figures . v
Conversion Factors v i i
i.O INTRODUCTION 1
2.0 QUARANTINE APPLICATIONS 3
2.1 Overview 3
2.2 Definition of Quarantine Treatment 4
2.3 Characteristics of Fumigation Process 5
3.0 TECHNOLOGIES FOR RECOVERY AND RECYCLE 6
3.1 Overview 6
3.2 Adsorption Processes 8
3.2.1 The Bromosorb1M Process (Zeolite Adsorption) 9
3.2.2 Carbon Adsorption 13
3.3 Condensation Processes 15
3.4 Additional Considerations for Adsorption and Condensation 20
3.5 Effect of Impurities on Direct Recycle of Methyl Bromide 21
3.6 Other Technologies 22
4.0 INFORMATION GAPS AND FURTHER NEEDS 23
REFERENCES 27
V ;
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LIST OF FIGURES
Page
3-1 Overall Concept of Methyl Bromide Emissions Control, and Recycle from
Commodity Space Fumigations 7
3-2 Bromosorb™ Test Unit for Methyl Bromide Recovery and Reuse 11
3-3 Methyl Bromide Vapor Pressure 16
3-4 Methyl Bromide Condensation at -35°C Condenser Temperature 19
f
i vi
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CONVERSION FACTORS
Certain nonmetric units are used in this report for the reader's convenience.
Readers more familiar with metric units may use the following factors to convert to that system.
Nonmetric Multiplied bv Yields metric
atm 98.1 kPa
Btu/hr 0.293 W
cal 4.18 J
cfm 0.000472 mVs
°F 5/9 (°F-32) °C
ft 0.305 m
ft2 0.0929 m2
ft3 0.0283 nr
gal. 0.00379 nr
hp 0.746 kW
in 0.0254 m
in. WC 0.249 kPa
lb 0.454 kg
mil 0.0000254 m
psi 6.89 kPa
ton 907 kg
I
v i i
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SECTION 1.0
INTRODUCTION
Methyl bromide (methyl bromide), with the chemical formula CH3Br, also called
bromomethane, is listed by the 1991 Montreal Protocol as an ozone depleting chemical similar to
the other halogenated hydrocarbons such as the chlorofluorocarbons (CFCs). The U.S. Environ-
mental Protection Agency's (EPA's) regulations authorized by the Clean Air Act (CAA) call for a
phaseout of methyl bromide as of January 1,2001. This means an end to commodity fumigation
uses that emit methyl bromide to the atmosphere. In some applications, there is no apparent,
ready substitute for methyl bromide.
In 1994, a brief study was undertaken to identify potential methods for emissions
control, recovery, and reuse. A report was issued by EPA in July 1994 (1). The study discussed
possible means for methyl bromide recovery for reuse as well as for destruction to prevent
atmospheric emissions of any residual methyl bromide in vent streams. Since that time, there
have been additional developments on the subject. While developments have not radically
altered the findings and conclusions of the earlier report, some additional information is included
here.
Continuing interest in methyl bromide emission control has been reflected in two
forums for disseminating information on methyl bromide. The first was a conference, the 1994
International Research Conference on Methyl Bromide Alternatives and Emissions Reductions,
held in Orlando, Florida in November, 1994 (2). The second was in the contents of a report on
the 1994 International Research Conference on Methyl Bromide Alternatives and Emissions
Reduction, issued in 1995, by the United Nations Technical Options Committee for Methyl
Bromide (3).
Also a new methyl bromide recovery and recycle system, offered by Halozone
Recycling, Inc., was installed and tested at the Port of San Diego in 1995. Additional activities
1
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by this firm also include a test on shiphold and structural fumigations, and a commercial unit in
Chile. Because of these developments and additional study, the present report was prepared to
discuss these developments and further technical considerations on the technical and economic
feasibility requirements of recovery and recycle. The primary focus of the present report is on
methyl bromide treatment in quarantine applications.
This report was prepared as a brief update on recent activities and is not intended
as a complete compendium or research review. The study did not attempt to identify all possible
technologies that might be applied or programs underway. It does discuss key developments and
insights that have occurred since the earlier report was issued.
The remainder of the report discusses quarantine applications (Section 2),
technologies for recovery and recycle (Section 3), and information gaps and future needs (Section
4).
2
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SECTION 2.0
QUARANTINE APPLICATIONS OF METHYL BROMIDE
2.1 Overview
Treatment processes for commodities using methyl bromide can be classified
according to the commodities being treated and the reasons for the treatment. Regardless of
these classifications, however, there are many similarities with the overall procedure for the
fumigation. The primary differences between the various applications is in the way in which the
commodities are contained during fumigation and the dosages and duration of treatment.
However, these differences do not fundamentally alter the applicability of possible emissions
control technologies that might be applied for recovery and recycle; only the volumes involved
and, therefore, the potential economics of treatment.
Some classifications of treatment are as follows:
• Durables fumigation;
• Perishables fumigation;
• Structural fumigation;
• Soil fumigation;
• Long-term storage fumigation; and
• Quarantine fumigation.
Of the various applications, quarantine treatment has been singled out for
closer examination in this study. Such treatment typically occurs in relatively small volumes at
port facilities where fumigation must accommodate irregular schedules, short durations, and
minimal technical resources. In this application, other pest control methods, as alternatives to
methyl bromide fumigations, might be more difficult to implement than in non-quarantine
applications.
3
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2.2
Definition of Quarantine Treatment
Quarantine treatment is the treatment of commodities just prior to shipment to
another jurisdiction or upon receipt from another jurisdiction, whether it be a state or another
country. In some cases quarantine treatment is a standing requirement for certain commodities
and certain jurisdictions; for others it is left to the discretion of a commodities inspector or other
authority that may call for its use in a given situation.
Most commonly, quarantine treatment takes place with tarpaulin covered
commodities in the open or in warehouses; in special buildings or rooms called fumigation
chambers; or in trucks or ships.
For those ports that have a specific building for commodity quarantine treatment,
a recovery and recycle system could be a permanent installation. For cases where the location
might vary or where the fumigation would to take place in a truck or ship, a portable unit,
perhaps on a flat-bed truck would be appropriate.
In either case, the basic technology would be the same. The process system would
be designed to accommodate the flow rate, temperature, pressure, and composition of the
fumigation vent stream being treated. The characteristics of that vent stream depend on the
manner in which the fumigation process is carried out.
At this time, it does not appear that there is a single, comprehensive listing of all
quarantine application sites in the country. In general, quarantine fumigation will take place at
major shipping ports, both seaports and overland shipping locations, such as between the United
States and Mexico.
4
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2.3 Characteristics of the Fumigation Process
The details of fumigation arc discussed in more detail elsewhere (1). Briefly, the
enclosed commodity, in bulk or in containers (boxes or bags) that are permeable to methyl
bromide gas, is exposed for a specified period of time to a specified concentration of methyl
bromide injected into the air space surrounding the commodity. The methyl bromide is
introduced for a specified time and rate into the enclosed fumigation space and the supply shut
off. After a specified holding time period, the space is then vented to remove the residual methyl
bromide. For enclosed spaces, the venting is accomplished by sweeping fresh air through the
space. The vent stream has been traditionally exhausted directly to the atmosphere. In the
traditional tarp configuration, the tarp was often merely removed from covering the commodity
and the methyl bromide allowed to escape to the atmosphere.
If methyl bromide recovery and recycle is to be practiced, there will have to be a
single location from under the tarp from which the venting would take place through a hose or
ducting, or the commodities would have to be fumigated within a building or room that would
then provide controlled venting through ducting to an emission control device and recovery
system. However, for the most effective control, it is advantageous to avoid any more dilution of
the vent stream than is absolutely necessary.
As an example of a typical treatment, methyl bromide might be fed into a
fumigation chamber at a dosage of 200 pounds or more and the commodity held in the methyl
bromide atmosphere for 1.5 to 2 hours. The feed to achieve this concentration would take place
over a period of 30 minutes. After fumigation, the venting period would be about 2 hours.
An obvious characteristic of the fumigation process that affects design of a
recovery and recycle system is that it is intermittent and yields a varying concentration of methyl
bromide in the vent stream. The process itself is applied irregularly according to shipping
schedules of specific commodities and it is applied seasonally according to the harvests.
Therefore, the economics of such a process suggests that portability, not only at a given port
facility, but perhaps between port facilities might be desirable.
5
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SECTION 3.0
TECHNOLOGIES FOR RECOVERY AND RECYCLE
3.1 Overview
In a 1994 report (1), various technology options were identified and discussed.
Since that time, it is apparent that the main thrust of this new work has focused on adsorption
processes, but the application of condensation processes should not be ignored. The overall level
of development activity for any technology appears to remain fairly low because the major focus
of responding to the stated ban on methyl bromide has been toward finding methyl bromide
substitutes and alternative methods of pest control, rather than methods for methyl bromide
recovery and recycle. This is logical considering that there is little economic incentive for
researching recovery and recycle if the use of methyl bromide is going to be banned. Should this
policy change, more interest in recovery and recycle could be expected to arise.
There are several features of the recovery and recycle concept that will be
common, regardless of the technology to be used. Figure 3-1 illustrates the overall concept
of a methyl bromide recovery and recycle process applied to commodity fumigation. The
commodity to be treated is held in an enclosed fumigation space. The fumigation stream
consisting of air and methyl bromide enters the fumigation space and is held for a specified
period as in the conventional process. The difference is that the fumigation stream contains
recycled methyl bromide in air from intermediate storage after recovery from the vent
removal process, or directly from the regeneration of an adsorption removal process run in a
recovery or regeneration mode. Some methyl bromide makeup would also be added to the
fumigation stream to compensate for losses. A makeup or regeneration air stream would
also enter the overall process loop. Some purge air and minor amounts of methyl bromide
6
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regeneration/make-up air stream
Commodity
Fumigation
Space
Methyl
Bromide
Recovery
System
i
purge air stream
Final
Destruction
or Capture
with
methyl bromide
Vent
methyl bromide make-up recycle fumigation stream
Figure 3-1. Overall Concept of Methyl Bromide Emission Control, Reuse, and Recycle
from Commodity Space Fumigations
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would also he vented to form the basic treatment and recover)' process. This stream would
either vent to the atmosphere or through a final destruction or capture device as shown in the
figure.
The discussions that follow describe key features of the various technologies that
could be applied in the methyl bromide recovery system and the final destruction or capture
system of the process. This follows from earlier reporting on the general characteristics of these
technologies and their potential applicability to this problem. The technologies discussed
include:
1) Adsorption;
2) Condensation; and
3) Other technologies, some of which would apply to final destruction of
methyl bromide residuals in the vent stream rather than recovery, recycle,
and reuse.
3.2 Adsorption Processes
Recovery of methyl bromide by adsorption was described in EPA's July
1994 report (1). In a typical adsorption process, the exhaust air from a fumigation chamber is
passed through a vessel containing a fixed bed of a solid sorbent material that has an affinity for
methyl bromide. The methyl bromide vapor is transferred to the sorbent and the cleaned exhaust
air is either discharged or recirculated to the chamber. The sorbent containing the adsorbed
methyl bromide is then either regenerated or disposed of. If the sorbent is regenerated, the
methyl bromide may either be recycled directly to the chamber for reuse, recovered for
intermediate storage, or fed to a destruction process. For a methyl bromide adsorption system,
the most practical method of regeneration appears to be by heating the bed in hot air. This causes
the methyl bromide to desorb from the sorbent into the hot air stream.
8
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The extent of methyl bromide recovery in an adsorption
process depends on the following factors:
• The equilibrium relationship between the vapor-phase and adsorbed-phase
concentrations of the methyl bromide. The equilibrium relationship is also
referred to as the adsorption isotherm because it is a function of
temperature.
• The rate of adsorption or transfer of the methyl bromide from the exhaust
air to the sorbent. This rate is a complex function of the rates of several
individual steps that occur in series in the overall adsorption process.
• The arrangement and operating conditions of the adsorption process
equipment. This includes such factors as the dimensions of the sorbent
bed and the volumetric flow rate of exhaust air through the sorbent bed as
well as the conditions of the regeneration step, if employed.
Recently published information regarding the use and performance of two
different adsorption processes for recovery of methyl bromide is discussed below. One process
uses a synthetic solid adsorbent. The other process uses activated carbon.
3.2.1 The Bromosorb™ Process (Zeolite Adsorption)
The Bromosorb™ Process is an adsorption process that uses a proprietary
synthetic zeolite, or "molecular sieve", as the sorbent. The process is offered by Halozone
Technologies, Inc. of Mississauga, Ontario, Canada. The synthetic zeolite sorbent is reported to
selectively adsorb methyl bromide from humid air without adsorbing a significant amount of
moisture.
Results of demonstration tests using the Bromosorb process were reported by
Halozone at the 1994 International Research Conference on Methyl Bromide Alternatives and
Emissions Reduction in Orlando, Florida (4). The process was tested on a 1,640-m3 (cubic
meters) fumigation chamber at Stemilt Growers in Wenatchee, Washington during July 1994.
9
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Figure 3-2 shows the process configuration for these tests. The process equipment
consists of two fixed-bed adsorbers operated in parallel. In the adsorption part of the operation,
during the post fumigation venting, exhaust air containing nominally 55-60 g/m3 (grams/cubic
meter)(1.4-1.5% vol) methyl bromide is evacuated from the chamber by a circulation fan and
passes through each of the two beds containing the zeolite. Effluent air from the adsorbers
containing a reduced concentration of methyl bromide is recirculated to the chamber. After three
to four air changes have been processed (about 1.5 to 2 hours), the concentration of methyl
bromide in the chamber exhaust air is reduced to that of the effluent air from the adsorption beds,
and the adsorption part of the recovery cycle is completed. The unit is then isolated from the
chamber. Residual methyl bromide in the chamber air is then vented to the atmosphere.
However, the quantity of vented methyl bromide has been reduced to about 5% of what would
have been vented without the treatment device. The chamber is then shut down and the
fumigated commodity removed.
Following the adsorption step and chamber venting, when the chamber is ready
for the next fumigation cycle, the regeneration and reuse part of the process is initiated. Exhaust
air from the chamber is again recirculated through the adsorbers, but only after the air is heated to
about 121 °C by a gas-fired indirect heat exchanger. This increase in temperature is sufficient to
desorb the methyl bromide, circulating it back into the fumigation chamber for reuse. The
desorption part of the process requires less time: about 30 to 45 minutes.
Reported performance results for the Bromosorb demonstration at Stemilt
Growers showed that an average of slightly more than 95% of the available methyl bromide
following fumigation could be captured by the process, and more than 99% of the captured
methyl bromide could be recovered for reuse in the chamber. A sample of the recovered
methyl bromide was collected by condensation for subsequent chemical analyses. Independent
analytical results by the U.S. Department of Agriculture (U.S.D.A.) showed no significant
difference in composition between the recovered methyl bromide and virgin methyl bromide
supplied by Great Lakes Chemical Company.
10
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ilalo/itc
Adsorber A
V-101A
Halo/.ile
Adsorber B
v-ioin
Sampling Ports:
1. Bed Inlet
2. Bed A Outlet
3. Bed B Outlet
4. Chamber
( '
\
Fumigation Cliamher
¦ I • ). .•
- • . - '¦ ' •' ' !• } • li-.i
i • '¦
w*. J
F.xhausl
&
Fan F-10I
Heat lixchanger
li 101
-x-
Heaier
H-101
4 Q*~Air
Fan F-102
Figure 3-2.
Bromosorb™ Test
Unit for Methyl Bromide Recovery and Reuse
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Following the successful results of the above demonstration program, a
commercial installation of the Bromosorb process was designed and constructed for a
2,000-m3 fumigation chamber operated by the San Diego Unified Port District of San Diego,
California. Test results obtained during February of 1995 for this unit have also been recently
reported (5).
The process configuration of the San Diego unit is similar to that shown in Figure
3-2, except that a cooling heat exchanger is also supplied on the effluent side of the adsorbers.
This enables more rapid desorption without overheating the recirculated air in the chamber. Test
results for this unit showed an average capture of 95.4% of the methyl bromide from chamber air
containing nominally 50-60 g/m3 methyl bromide. Again, no residual impurities were detected in
the recovered methyl bromide after a number of adsorption/regeneration cycles. Cycle times for
this unit were less than 30 minutes for adsorption and 15 minutes for regeneration and recycle.
The residual methyl bromide concentration in the exhaust air vented to the atmosphere was about
670 ppmv.
The capital cost for the San Diego Bromosorb unit is reported to be about
$960,000, including the cost of performance tests (1,6). Assuming that the equipment capital
cost is about $900,000, after deducting for the performance tests, the annualized capital charge
for this process is about $150,000 (amortized over 10 years at 10.6% interest). The primary
operating costs include heat for the desorption cycle and power for the recirculation fans.
Assuming that two chamber volumes of air are heated in the desorption step and that an
equivalent amount of heat is needed to heat the process equipment and sorbent, then the total
heat energy consumed per cycle is about 1 million kJ (kilojoules). If natural gas is burned to
supply this heat at a cost of $3/106 kJ, the fuel costs amount to about $3.00 per cycle. The
circulating fan sizes are not reported, but assuming that two 20-hp fans are used (one for
circulating; one for heating or cooling), the total fan power per 45-minute cycle is about $0.50.
The cost for sorbent replacement has not been reported, but sorbent life is estimated at 10 years.
12
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For each fumigation cycle, about 100 kg (kilograms) of methyl bromide that
would otherwise have been vented is recovered and reused. The facility at San Diego is used
only part of the year. Assuming 40 fumigation days per year, and 4 cycles per day, the number of
cycles per year is 160. Then the total annualized cost per cycle is about $938 (exclusive of
sorbent replacement), nearly all of which is capital charges. Assuming that nominally 100 kg of
methyl bromide is recovered per cycle, the recover)' cost is about S9.38/kg, which is considerably
more than the reported cost for makeup methyl bromide of S1.70/kg (7). Obviously, as the on-
stream time or number of cycles per year increases, the cost of recovered methyl bromide will
decrease.
The design, recovery-efficiency of an adsorption process such as Bromosorb can
be increased (with a constant cycle time) by increasing the depth and/or cross-sectional area of
the adsorber bed. For example, Nagji and Veljovic estimate that a system could be designed for
99% capture at a cost of two to three times that of the 95%-system (4). For the same cost and on-
stream time assumptions used above, the marginal cost per unit of additional methyl bromide
captured in going from a 95%-efficient to a 99%-efficient system would be $35 to $70/kg, and
the overall average recovery cost would increase to $3 to S6/kg methyl bromide. Thus, the
economics also depends highly on the level of any allowable emissions from recovery and reuse
process venting.
Additional work with this type of unit in 1995 includes testing on shiphold and
large structural fumigations (200,000 ft? and mure) and sale of a commercial unit in Chile.
The latter application is for a 10.000 ft3 chamber quarantine fumigation. The capital cost of
the system has been reported as $ 250.000 (8). Further details were not available for this
report.
3.2.2 Carbon Adsorption
Another adsorption process for methyl bromide is carbon adsorption. Progress
in the use of carbon adsorption for methyl bromide recover}' and recycle has also been
13
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reported since EPA's previous report. In that report, bench-scale and pilot-scale tests completed
by Australian investigators during the late 1970's were described. More recently, the UN Methyl
Bromide Technical Options Committee reports several applications of activated carbon for
methyl bromide capture (3).
Five small (30 nr) chambers in the Netherlands are using once-through activated
carbon beds for capturing methyl bromide from chamber exhaust air. Each adsorber has a 70-kg
carbon bed that is reported to recover 40 to 50% of the methyl bromide following fumigation at
an inlet loading of 30 g/m1. This particular installation is only for emissions reduction, however.
Recovery and recycle is not practiced. After about 40 fumigation cycles, the spent carbon is
incinerated in a regulated facility. Based on the above operational description, the average
methyl bromide loading on the spent carbon would be about 16 to 20%, assuming that 80% of
the 30 g/nv initial charge is available for capture. This loading agrees approximately with the
bench-scale data in Radian's previous report (1).
For this type of once-through application, equipment costs should be relatively
low and the cost of the carbon sorbent replacement and spent carbon disposal will be the
major costs. For example, if carbon can be loaded to an average of 16% by weight before
disposal, then the carbon consumption will be 6.25 kg carbon/kg methyl bromide. Small
quantities of activated carbon cost about S6/kg, so that the equivalent carbon cost will be about
S37/kg methyl bromide. Disposal of small volumes of the spent carbon as a hazardous waste in
the U.S. is expected to cost as much as $2/kg based on Radian's in-house experience. This brings
the total cost for 40 to 50% methyl bromide capture by a once-through carbon system to about
$50/kg methyl bromide.
The above example (40 to 50% capture) results in a relatively high
concentration of methyl bromide in the exhaust air from the chamber to the atmosphere. As
with the synthetic zeolite, lower concentrations of methyl bromide can be adsorbed with
carbon, but at reduced loading. For example, at a residual methyl bromide concentration of
100 pprriv (99%+ capture for a typical chamber concentration of 1.5%), the equilibrium
14
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loading on the carbon will be only 0.4% at 30°C. For this case with 99% capture, the average
loading on the carbon might be only one-fourth that in the above example at 40 to 50% capture,
increasing the average cost to about $100/kg methyl bromide captured.
Processes for methyl bromide capture and recycle with activated carbon are also
being developed. A mill in Germany reportedly has been equipped with a full-scale activated
carbon system for methyl bromide capture and recycle (3). This process is said to include a
concentration and condensation step as part of the desorption cycle. Details of the total process
design are not available, but pilot-scale test results for the desorption method (direct electrical
heating under vacuum) have been published (9). In these tests, the total energy used for
desorption was about 14,000 kJ/kg, which is equivalent to an energy cost of only S0.20/kg at
$0.05/kWhr. The investigators pointed out that the desorption temperature must be limited to
less than about 120°C to avoid decomposition of the methyl bromide and production of hydrogen
bromide due to the reaction of methyl bromide with water on the carbon surface.
Costs for an integrated recovery, recycle, and reuse system using activated carbon
have not been reported, but are expected to be the same order of magnitude as those for the
Halozone system described above, because of similarities in the types of equipment for
adsorption systems in general.
3.3 Condensation Processes
Methyl Bromide is a relatively volatile gas and therefore is difficult to
condense. Figure 3-3 is a vapor pressure curve for methyl bromide, based on technical
literature information (10),plotted as In P (atm) versus 1/T (K) to yield a straight line. For
convenience, a few points for temperatures in °C and vapor pressures in atmospheres are
also shown. For example, at the normal chamber concentration of 1.5% methyl bromide in
air, condensation of methyl bromide (at atmospheric pressure) would begin at a temperature
of -71 °C, which is well below temperatures that,can be produced by normal mechanical
15
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cooling systems. Recovery of 95% of the methyl bromide from the exhaust air (as with the
adsorption processes), leaving a residual concentration of 750 ppmv, would require cooling to
about -101 °C.
A condensation process using liquid nitrogen was reported as recovering 98% of
the available methyl bromide from two vacuum fumigation chambers at Pacific Coast
Fumigation, Inc., Terminal Island, CA (3,11). This process condenses methyl bromide from a
single volume of chamber air, and the residual methyl bromide is then captured by
activated carbon. No details of the process design or equipment costs are available. Because
liquid nitrogen boils at -196°C, there is ample temperature difference for cooling the air stream.
The facility is no longer in use due to high electricity costs.
The heats of vaporization of nitrogen and methyl bromide are 19.9 and 30.7 kJ/kg,
respectively. Therefore, about 1.5 kg.N2/kg methyl bromide will be required at a minimum to
remove the latent heat of condensation. Assuming that one chamber volume of air is cooled to -
101 °C, and the initial air/methyl bromide weight ratio is 20:1 (for 1.5% methyl bromide by
volume), then the heat duty for air cooling (from 25°C to -101 °C) will be about 2,500 kJ/kg
methyl bromide, and the liquid nitrogen demand for air cooling will be about 125 kg/kg methyl
bromide. Allowing for heat losses, the actual quantity might be as high as 150 kg NVkg methyl
bromide. Liquid nitrogen is available at a cost of about 50.05/kg. At this cost, the operating cost
for a condensation process using liquid nitrogen to cool one chamber volume of air plus methyl
bromide would be a minimum of $7.50/kg methyl bromide (not including annualized equipment
costs). This cost compares favorably with the once-through carbon system described above for
the 30-m3 chambers, even if the annualized equipment charges are significant for the
condensation system.
Methyl bromide condensation can be conducted at higher temperatures if the
concentration and/or total pressure can be increased. Therefore, condensation can be applied
downstream of an adsorption process to condense the methyl bromide following the
desorption cycle. If the desorption is conducted under partial vacuum and by direct heating,
17
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high concentrations of methyl bromide can be obtained. Suppose, for example, that a stream of
25% methyl bromide in air can be obtained from the desorption cycle. A brine cooler can obtain
a temperature of about -35 rC, at which the partial pressure of methyl bromide is about 0.17 atm.
At atmospheric pressure, only about 30% of the methyl bromide could be condensed at this
temperature, but if the total pressure in the condenser were raised to 5 atm, the recovery would
increase to about 86%. Similarly, at 10 atm, about 93% condensation could be obtained.
A two-stage high-pressure condensation system with intcrcooling was one of the
designs proposed for the San Diego Port District (1). This system was to be operated at 70 atm.
No details of this process design are available. However, at this pressure, good methyl bromide
condensation can be obtained even with low inlet concentrations without an intermediate
adsorption/desorption step. For example, assuming that the methyl bromide concentration in the
chamber exhaust air is 1.5%, then the partial pressure of methyl bromide after compression to 70
atm is about 1 atm. With a condenser temperature of -35 °C at 70 atm, a recovery of about 80%
would be obtained.
Figure 3-4 summarizes the above discussion. The percentage of inlet methyl
bromide that can be condensed at -35 :C is plotted versus the condenser operating pressure. Two
curves are shown. The lower curve represents direct condensation, with no intermediate
adsorption/desorption cycle, assuming that the condenser inlet methyl bromide concentration is
1.5% in air. The upper curve represents condensation of 25% methyl bromide in air. produced
during a desorption cycle. These results are only approximate, especially at high pressure,
because ideal gas behavior was assumed.
To reuse the methyl bromide, condensation processes will require that water
vapor be separated from the air before methyl bromide is condensed. Technically this should
not be difficult, because the vapor pressure of water is much lower than that of methyl
bromide at equivalent temperature, but it would require a two-stage process with intermediate
removal of condensed water. The condensed water, which might contain methyl bromide
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100
25% McBr in Air
90
80
70
1.5% MeBr in Air
60
50
40
30
20
10
0
0
10
20
30
90
100
Condenser Pressure (atm)
Figure 3-4. Methyl Bromide Condensation at -35° C Condenser Temperature
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and other contaminants, would require proper disposal methods to be for the process to be
commercially viable.
3.4 Additional Considerations for Adsorption and Condensation
Based on the information presented above, technology for capture and
recycle of methyl bromide is advancing at the demonstration level. For large and/or frequently
used chambers where high capital investment is justified, an adsorption/desorption process with
direct recovery, recycle, and reuse may be the most cost-effective method if purity of the recycled
methyl bromide is not a significant issue. The cost of recycled methyl bromide for reuse depends
heavily on the number of fumigation cycles per year for a given facility. These systems appear to
have the capability of capturing and recycling/ reusing methyl bromide at a cost that is roughly
equivalent to purchasing virgin methyl bromide. However, more long-term performance data
will be needed to completely characterize the suitability of these processes for direct reuse of
methyl bromide in the fumigation chamber.
The issue of methyl bromide purity may become more important as operating
experience is gained with adsorption processes. If captured methyl bromide is not suitable
for direct reuse, a condensation step must be added to the process to produce liquid methyl
bromide for reclaiming by the manufacturer or other party. This will add to equipment costs,
and may also eliminate the economic credit for avoided purchase of virgin methyl bromide.
Facilities that use this recovery method may be required to become US EPA regulated pesticide
facilities.
The cost trade-offs between different approaches depends primarily on the
chamber size and frequency of use, which fix the total amount of methyl bromide that must be
captured.
Activated carbon may also be used to capture residual methyl bromide that
cannot be economically recovered by an adsorption/desorption process. Very low
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concentrations of methyl bromide may be captured, but at correspondingly low carbon loading
and therefore high cost. Again, the cost trade-off between adsorption/desorption recover)'
efficiency and residual methyl bromide capture on once-through carbon will be site-specific.
The most significant economic factor is the annual quantity of commodities
treated. The greater the quantity the lower the unit cost of the system applied to each batch
of commodities treated. Approximate values of treatment cost with and without recycle/reuse
and recovery related to total volume treated can easily be estimated.
For a given capital investment and the operating and maintenance costs for the
emission control, recovery/reuse, and treatment system, the economics of treatment will depend
on the following variables:
1) Total treatment volume per batch of commodity;
2) Methyl bromide requirement per treatment;
3) Methyl bromide recovery efficiency for recycle/reuse; and
4) Number of fumigations per year.
3.5 Effect of Impurities on Direct Recycle/Reuse of Methyl Bromide
In adsorption systems where capture and direct recycle/reuse of methyl bromide is
intended, the potential effect of impurities in the methyl bromide must be considered. For
example, natural odorant compounds from agricultural products or other compounds such as
wood preservatives from pallets or off-gases from synthetic packaging materials might
contaminate the recovered methyl bromide, making direct reuse impractical. In this case, the
captured methyl bromide must be condensed and recovered as a liquid to be purified before
reuse.
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3.6
Other Technologies
So far we have discussed adsorption and condensation which appear to be the
most promising technological approaches, to date, for recovery' and recycle of methyl bromide for
on-site reuse. One other technology that has shown promise in other applications for separations
of organic substances from air streams is membrane separation (12). This technique compresses
a gas stream to a suitable pressure, typically in the range of 45 to 200 psig, passes it through a
condenser, and then a separation element containing a porous semipermeable membrane of a
composite material. The organic compound passes through, while the air is retained on the high
pressure side. The recovered organic, now much more concentrated than it was before, is more
readily condensed for recovery. It is not known whether any attempt has been made to use this
for methyl bromide or not. The suitability of this technology for methyl bromide recovery would
have to be tried before data were available to make a realistic comparison between it and the
other techniques already discussed. One reference states that membranes can be used with
methyl bromide (13).
For final destruction of residual methyl bromide in any final vent stream, several
methods were previously discussed (1). Methods include incineration, either direct or of spent
activated carbon, chemical reagent scrubbing, and ultraviolet irradiation. We have not delved
into the details of the latter method for this report, however, this technology has seen increasing
application in recent years and might offer potential for methyl bromide destruction.
Our overall conclusion at this time is that adsorption techniques show genuine
promise for methyl bromide recovery and reuse. However, the economics are very dependent on
the total on-stream time in a year. Further, there still are some questions regarding sustained long
term effects of recuse because of the possibility over time for the build up of contaminants, either
from the commodities or from decomposition or reaction product with the methyl bromide. The
incentive for more work in developing and testing recovery, recycle, and reuse techniques
depends very much on the prospect for a change in the statutory ban on methyl bromide for 2001.
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SECTION 4.0
INFORMATION GAPS AND FUTURE NEEDS
Research efforts at control appear to have been very limited. Although there have
been many conferences on methyl bromide phase-out, they have all centered on finding an
alternative replacement for methyl bromide, rather than on recovery and emissions control.
Examples of these technical meetings are:
• UNEP Methyl Bromide Technical Options Committee meetings (held
around the world);
• Methyl Bromide Alternatives Conference, Sponsored by Alliance for
Responsible CFC Policy, and the U.S. Environmental Protection Agency.
March 8-9, 1993, Fresno, CA.
• USDA Workshop on Alternatives for Methyl Bromide. June 29 -
July 1, 1993, Crystal City, VA; and
• 1994 International Research Conference on Methyl Bromide Alternatives
and Emissions Reductions, Orlando, FL., November 1994.
Progress has been made and continues to be made concerning possible emissions
control and recycle, recovery, and reuse technologies. There are still some remaining questions
that must be answered and more experience is required before it can be stated unequivocally that
the recycle, recovery, and reuse of methyl bromide is generally feasible. The future application
of the required technologies appears to depend on expectations regarding the likelihood that
regulatory exemptions on methyl bromide use could occur as the deadline of 2001 for the methyl
bromide ban approaches. Only with the realistic prospect of such exemptions, or rescinding the
ban entirely, would one expect there to be a strong incentive for extensive further research,
development, and application of technology.
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In the July 1994 report (1), some key issues that were identified as significantly
influencing the progress of methyl bromide recovery, recycle, and reuse were the following:
1)
Regulatory issues;
2)
Stream characteristics;
3)
Fumigation commodity containment options;
4)
Achievable recovery from fumigation;
5)
Technology performance characteristics;
6)
Economic issues; and
7)
Availability of substitutes.
Since 1994. the regulatory issues remain the same, with the future ban on methyl
bromide still in effect. In spite of the most recent testing at the Port of San Diego, stream
characteristics are still not defined. The testing there was based solely on methyl bromide
removal and the quality of recycled methyl bromide, but did not examine other contents of the
vent stream.
Achievable recovery information has advanced based on the most recent testing,
and technology characteristics have been further clarified based on the recent tests. The
operation of this system has contributed to a further understanding of the technical information
needed for an economic evaluation, but such an evaluation still has not teen performed. The
availability of substitutes both in terms of substitute chemicals and new processes for pest control
has received extensive investigation and continues to do so.
The fundamental performance characteristics for each potential recovery
technology have not been established. Removal efficiency from the aeration stream has not been
established. This information has not been obtained for:
Specific commodities and commodity classes;
Different containment options and fumigation applications; and
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• Different control technologies.
The most critical needs appear to be for adsorption systems, especially with regard
to contaminant effects from organic substances picked up from the commodities themselves and
with regard to partial decomposition of the methyl bromide on the adsorbent. In addition to
activated carbon, data are not available for zeolites and other adsorbents that might be candidates
for adsorption applications.
Research on combustion and condensation would appear to be less critical,
although the destruction efficiency at different flame temperatures and other combustion
conditions is not available.
Additional considerations include:
• Performing tests on different commodities would be advisable to
determine if differences between commodities might result in different
levels and types of contamination in recycled/reused methyl bromide.
• Testing long-term operation through repeated removal and recovery cycles
would be needed to prove that no breakdown products such as hydrogen
bromide and other compounds nor accumulation of detrimental trace
chemical materials would occur, especially as the recycle/reuse ratio of
methyl bromide to makeup increased.
• Performing a detailed economic analysis between molecular sieve (zeolite)
adsorption, activated carbon adsorption, and condensation (and other
applicable technologies) should be made to determine the relative
advantages and disadvantages across a full range of applications.
• Evaluating the implications of and costs of achieving different total
emission limits for methyl bromide would have to be evaluated if methyl
bromide were permitted in limited applications. The relative effectiveness
and costs of greater removal efficiencies from the vent stream compared
with requirements for final destruction of methyl bromide residuals from a
recycle/reuse system would have to be compared.
• Establishing chemical purity specifications and standard analytical
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protocols for recycled/reused methyl bromide to ensure its suitability for
reuse.
Future needs in the development of methods for methyl bromide recovery,
recycle, and reuse basically would be to expand the applications and performance data to
establish the conditions under which the practice is feasible.
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REFERENCES
1. DeWolf, G.B., and M.R. Harrison. Evaluation of Containment and Control Options for
Methyl Bromide in Commodity Treatment. EPA-600/R-94-126, U.S.E.P.A., Research
Triangle Park, NC, July 1994. 109 pp, NTIS No. PB94-195070.
2. International Research Conference on Methyl Bromide Alternatives and Emissions
Reduction, Orlando, FL, November 1994.
3. United Nations Environment Program (UNEP). 1994 Report of the Methyl Bromide
Technical Options Committee - 1995 Assessment. EPA 430/K94/029. 301 pp.
4. Nagji, M., and V.M. Veljovic. Bromosorb™ Adsorption Technology for Capturing and
Recycling Methyl Bromide. Presented at the International Research Conference on Methyl
Bromide Alternatives and Emissions Reduction, Orlando, FL, November 1994.
5. Veljovic, V.M. Bromosorb™ Test Report - Methyl Bromide Recovery and Reuse Unit at
San Diego Unified Port District - San Diego, CA. Halozone Recycling, Inc, Mississauga,
Ontario, March 1995.
6. Telephone Conversation with Bob Walton of Halozone Recycling, Inc., Mississauga,
Ontario, May 1995.
7. Chemical Marketing Reporter, April 1995.
8. Letter from Vladan Veljovic, Halozone Recycling, Inc., Mississauga, Ontario, August
17,1995.
9. Stankiewicz, Z., and H. Schreiner. Temperature-Vacuum Process for the Desorption of
Activated Charcoal. Transactions of the Institute of Chemical Engineers, 71-Part B: 134-
140, May 1993.
10. Perry, R.H., C.H. Chilton, and S.D. Kirkpatrick. Perry's Chemical Engineers' Handbook.
McGraw-Hill, New York, 1963.
11. Internet Communication with Don Smith, Industrial Research Limited, New Zealand, May,-
1995.
12. Technical Sales Literature, Membrane Technology and Research, Inc., Menlo Park, CA,
1995.
13. Simmons, V. L., M. L. Jacobs, J. Kaschemekat, and H. Wijmams, Membrane Technology
and Research, Inc., "Membranes Provide New Alternative for VOC Recovery: Case Studies
from the Chemical Processing and Pharmaceutical Industries," Summary of Material
Presented at Hazmacon, 1994, San Jose, CA, March 30, 1994.
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