United States Office of Research and EPA/625/R-97/002
Environmental Protection Development December 1997
Agency Washington DC 20460
Technology Transfer
x>EPA Capsule Report
Sources and Air Emission
Control Technologies at
Waste Management
Facilities
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Technology Transfer EPA/625/R-97/002
Capsule Report
Sources and Air Emission
Control Technologies at Waste
Management Facilities
December 1997
U.S. Environmental Protection Agency
Off ice of Research and Development
Cincinnati, Ohio 45268
Printed on Recycled Paper
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Disclaimer
The information in this capsule report has been funded by the U.S. Environmental
Protection Agency and the U.S. Department of Energy. It has been subjected to
the EPA's peer and administrative review, and it has been approved for
publication as an EPA document. Mention of trade names or commercial
products does not constitute endorsement or recommendation for use by EPA.
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Foreword
The U.S. Environmental Protection Agency is charged by Congress with
protecting the Nation's land, air, and water resources. Under a mandate of
national environmental laws, the Agency strives to formulate and implement
actions leading toacompatible 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 andtechnical support for solving environmental
problems today and building a science knowledge base necessary to manage
our ecological resources wisely, understand how pollutants affect our health,
and prevent 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 ground
water; and prevention and control of indoor air pollution. Thegoal 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 information 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
Research and Development to assist the user community and to link researchers
with their clients.
E. Timothy Oppelt, Director
National Risk Management Research Laboratory
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Contents
Figures vi
Acknowledgments v'i'
introduction 1
Sources and Control Technologies 1
Sources of Air Emissions 1
Surface Impoundments 1
Tanks -2
Fixed Roof Tanks 3
Floating Roof Tanks 4
Pressure Tanks -^
Containers 7
' Treatment Devices 10
Distillation 1°
Solvent Extraction 11
Air Stripping 11
Steam Stripping 11
Thin-Film Evaporation 12
Waste Incineration 13
Control Devices 13
Adsorption 13
Condensation 15
Absorption 15
Combustion Equipment 15
Thermal Incineration 16
Catalytic Incineration 17
Existing Boilers and Process Heaters 17
Unconventional Technologies 17
References 20
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Figures
1. Emissions from impoundments and other open
liquid surfaces 1
2. Major factors affecting emissions .2
3. Fate of organics in a surface impoundment:
emissions, effluent, biodegradation, sludge .2
4. Typical fixed roof tank .3
5. Tankworking losses .3
6. Covered tanks (working losses) .3
7. Tank breathing losses 4
a. Covered tanks (breathing losses) .4
9. Closed-vent system and control device .4
10. Floating roof -4
11. Internal floating roof .5
12. External floating roof .5
13. External floating roof tank -6
14. IFR mechanical shoe seal .6
15. IFR liquid-mounted seal. .7
16. IFR vapor-mounted seal with secondary seal .7
17. IFR fittings that require controls -8
18. EFR mechanical shoe seal with secondary seal 8
19. EFR liquid-mounted seal with secondary seal .9
20. EFR fittings that require controls -9
21. Splash loading method 9
22. Submerged fill pipe 9
23. Bottom loading reduces liquid turbulence and
vapor and/or liquid contact 10
24. Typical bottom loading system with vapor collection 10
VI
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Figures (continued)
25. Emission sources for distillation 11
26. Emissions from solvent extraction 11
27. Schematic diagram of an air stripping system 12
26. Steam stripper for ethylene dichloride (EDC)/vinyl chloride 12
29. Preliminary treatment prior to stripping 12
30. Flow path of thin-film evaporator 13
31. Carbon canisters 13
32. General process flow diagram of an adsorption process for
organic recovery 14
33. Fixed-bed regenerative carbon adsorption system process
flow diagram and potential emission sources 14
34. Schematic diagram of a contact condenser 15
35. Schematic diagram of a shell-and-tube surface condenser 15
/ 36. Packed tower for gas absorption 16
37. Steam-assisted elevated flare system 16
36. Thermal vapor incinerator 17
39. Schematic diagram of a catalytic incinerator system 18
40. Fluid-bed catalytic incinerator 18
41. Typical rotary carousel system 18
42. Carousel system with incinerator 19
43. Schematic of an open single-bed biofilter system 19
VII
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Acknowledgments
Thiscapsule reportwasdeveloped from technical material prepared by Research
Triangle Institute (RTI) for a seminar publication on air emissions control at
waste management facilities. The original seminar publication was prepared
under contract to the U.S. EPA Office of Research and Development (ORD),
through Eastern Research Group, Inc., and the Office of Air Quality Planning and
Standards (OAQPS).
Justice A. Manning, Center for Environmental Research Information, ORD,
coordinated the original seminars with assistance from ERG, Inc. Peer reviewers
who provided the final review of this capsule report are Michele Aston, OAQPS,
and John 0. Burckle and Scott R. Hedges, ORD, National Risk Management
Research Laboratory. The tireless efforts of Robert. A. Zerbonia of RTI were
greatly appreciated.
VIII
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Introduction
The chemicals processed during waste management
operations can volatilize into the atmosphere and cause
carcinogenic or other toxic effects or contribute to ozone
formation. Regulations have been developed to control air
emissions from these operations. The EPA has promul-
gated standards under the authority of Section 3004(n) of
the Hazardous and Solid Waste Amendments to the Re-
source Conservation and Recovery Act (RCRA) that limit
organic air emissions from waste management units at
hazardous waste treatment, storage, and disposal facilities
(TSDF); the rules also apply to 90-day accumulation units
at hazardous waste generator facilities. In June 1990, EPA
promulgated standards for process vents and equipment
leaks; additional RCRA standards were promulgated on
December 6, 1994, (effective December 6, 1996) and
amended on November 25, 1996, to limit air emission from
tanks, surface impoundments, and containers used in man-
aging hazardous wastes. Implementation of air emission
controls on many types of waste management operations
are required by these RCRA air rules.
This capsule report focuses on the major sources and
controls of air emissions at waste management facilities,
how these emissions occur, and how they can be con-
trolled. The major sources that are discussed in detail
include surface impoundments, the very broad and diverse
category of tanks and ancillary equipment, containers, and
treatment devices. As each source is described, controls
that are inherent to that source or commonly found on that
particular source are presented. In addition, details are
provided on the basic mechanisms by which emissions
occur and the major factors that affect the emissions.
After the discussion of sources and their inherent con-
trols, air pollution control devices that may be generally
applicable to any enclosed or vented source (i.e., add-on
controls) are described. The discussion of control devices
focuses on their applicability, control performance, and the
major factors affecting performance. Organic removal (i.e.,
pretreatment) and destruction processes are also discussed
as a means of controlling air emissions and reducing or
eliminating the emission potential. This discussion de-
scribes processes that remove or destroy the organics in
the waste, which may eliminate the need to control subse-
quent waste processing steps.
Sources and Control Technologies
The types of sources found at waste management facili-
ties, inherent controls that are typically part of the con-
struction and operation of the sources, and emission
mechanisms are discussed in this chapter. As each source
is discussed, covers and enclosures that are specifically
applicable to the source are described, as well as simple
work practices that reduce emissions. Other emission con-
trols that are broadly applicable to many of the individual
sources are discussed collectively in the last part of the
chapter. These controls include traditional air pollution
control devices, processes that remove the organics be-
fore the waste is placed in units with a high emission
potential, and waste incineration.
Sources of Air Emissions
The discussion of emission sources is divided into four
categories: surface impoundments, the very broad and
diverse group of tanks and ancillary equipment, contain-
ers, and treatment devices. The major focus is on the first
three categories because they are the most directly im-
pacted by the RCRA air emission regulations.
Surface Impoundments
A surface impoundment is defined under RCRA as
"a natural topographical depression, man-made excava-
tion, or diked area formed primarily of earthen materials
(although it may be lined with man-made materials) which
is designed to hold an accumulation of liquid wastes or
wastes containing free liquids and which is not an injection
well. Examples of surface impoundments are holding, stor-
age, settling, and aeration pits, ponds, and lagoons."
Impoundments are simply ponds and lagoons that are
used primarily for managing aqueous wastes and sludges.
Specific uses include storage, equalization, neutralization,
evaporation, solids settling, and biodegradation.
A surface impoundment is below grade, usually has
berms with sloping sides to contain wastes, and has a
liquid surface that is exposed to the atmosphere. It may be
operated as a flowthrough system with liquid flowing in at
one point and out at the same time at another point, or the
liquid may be pumped out or evaporated, leaving behind a
sludge. Figure 1 illustrates emissions from impoundments
and other open liquid surfaces as caused by diffusion and
wind flow across the surface.
Figure 2 lists several of the factors that affect emissions
from impoundments. These same factors are applicable to
emissions from open tanks. The constituent's volatility has
a direct effect on emissions from impoundments and other
sources with exposed liquid surfaces. Highly volatile com-
pounds such as benzene are readily emitted from open
sources, whereas relatively nonvolatile compounds such
as phenol tend to stay in the water.
The residence time in the impoundment has an obvious
effect on emissions: longer residence times result in higher
emissions. If the waste is in the impoundment long enough,
even relatively nonvolatile compounds are evaporated. For
impoundments with relatively short residence times, a higher
percentage of the organics may be removed with the
effluent and emitted later in other units in the treatment
sequence.
From surface to air
Wind
Flow
in
Diffusion through liquid
Flow
Out -
Figure 1. Emissions from impoundments and other open
liquid surfaces.
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Constituent volatility
Residence time
Surface area
Turbulence (aeration, agitation)
Windspeed and temperature
Extent of competing mechanisms (such as biodegradation)
Figure 2. Major factors affecting emissions.
Many impoundments and tanks are agitated for mixing,
air stripping, or biodegradation. Agitation and aeration in-
crease emissions by creating turbulent zones and increase
contact between the waste and air. There are a highly
turbulent area and water spray around the agitators used
in mechanically aerated units. Essentially all of the highly
volatile compounds can be emitted when the impound-
ment is mechanically agitated.
Approximately half of the impoundments used to treat
hazardous waste are aerated or agitated.
As Figure 3 illustrates, organic removal from impound-
ments also occur from mechanisms other than air emis-
sions resulting from wind blowing across the exposed
surface of the waste. Organics can also be removed by
biodegradation, adsorption onto sludge, or removed with
the effluent. Emission models have been developed to
estimate the extent of each of these different removal
mechanisms.
The models developed for open liquid surfaces are
applicable to impoundments and open tanks. These mod-
els can account for the emissions from relatively calm
surfaces or from the turbulence created by aeration or
agitation. The emissions are modeled as two mass trans-
fer steps in series: (1) diffusion through the liquid, and (2)
mass transfer from the surface of the liquid to the air. The
approach can account for removal in flowthrough systems
and removal in units designed for disposal or evaporation.
The extent of biodegradation, if any, can also be esti-
mated.
One of the controls demonstrated for impoundments is
an air-supported structure, which uses fans to maintain a
positive pressure to inflate the structure. For effective
control, the air vented from the structure must be sent to a
control device, such as a carbon adsorber. Air-supported
Emissions
Wind
Flow-
in
Biodegradation
Sludge
Flow
in
Sludge
out
Figure 3.
Fate of organics in a surface impoundment:
emissions, effluent, biodegradation, sludge.
structures have been used as enclosures for conveyors,
open top tanks, and storage piles, as well as impound-
ments.
An air-supported structure and control device has been
installed on a l-acre aerated lagoon that is used for
biodegradation at a pharmaceutical manufacturing facility.
The cover material is PVC-coated polyester with a Tedlar
backing. An agitator system in the structure provides oxy
gen and keeps carbon and biomass suspended. In this
application, the exhaust from the structure is vented to a
carbon adsorber. Very few leaks were found around the
structure; consequently, the control efficiency is deter-
mined primarily by how well the control device works; it
may exceed 95 percent. This plant's experience with the
air-supported structure has found that corrosion can be
accelerated inside the structure, condensation may occur,
temperatures may be high, and special worker safety pre-
cautions are needed.
Floating membrane covers are another control option
and have been demonstrated on various types of im-
poundments, including water reservoirs in the western
parts of the United States. For proper operation as a
control technique for organic compounds, the membrane
must provide a seal at the edge of the impoundment and
provisions made to remove rainwater. If gas is generated
under the cover, vents and a control device may be needed.
In addition, if sludge accumulates, some means for peri-
odic sludge removal may be required, such as a sludge
pump.
Emission control depends primarily on the type of mem-
brane, its thickness, and the individual organic compounds
in the waste. Theoretical estimates based on diffusion
through the membrane indicate worst-case control effi-
ciencies of 50 to over 95 percent. Laboratory studies indi-
cate that the cover is an efficient control for some organic
compounds, but, for specific compounds that permeate
the membrane, the control efficiency is lower.
The floating membrane cover has been demonstrated
on an impoundment that is used as an anaerobic digester.
The impoundment is about 7 acres in size with a depth of
approximately 14 feet. The membrane material is 100-mil
high-density polyethylene. The cover is anchored over a
concrete ring wall that extends above grade level around
the perimeter of the impoundment. The membrane ex-
tends over the concrete wall and is covered with backfill to
anchor and seal it. Punctures or tears in the membrane
can be patched. This installation has been in operation for
over 4 years, and the company supplying the membrane
offered a 20-year warranty on the life of the material.
Tanks
The most diverse group of waste management sources
falls into the category of tanks, which is broadly defined
under RCRA. If the unit is not a land disposal source, it is
probably a tank. A tank is defined as "a stationary device,
designed to contain an accumulation of hazardous waste,
which is constructed primarily of nonearthen materials
(e.g., wood, concrete, steel, plastic) that provide structural
support." A tank system is defined as a tank and its
ancillary equipment, where ancillary equipment includes
such devices as piping, fittings, flanges, pumps, and valves.
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The category of tanks and tank systems includes two
broad classes, open top tanks and covered tanks. The
latter class is divided into fixed roof tanks, floating roof
tanks, and pressure tanks. Fixed roof tanks are the most
common type of storage tank found at hazardous waste
facilities. Emissions occur through the tank's vent, which
may be open to the atmosphere, equipped with a pres-
sure-vacuum relief valve, or vented to a pollution control
device.
Fixed Roof Tanks
The fixed roof may have several openings in addition to
the vent, such as a manhole for tank entry, a hatch used
for measuring the liquid level, or an overflow pipe (Fig-
ure 4). The pressure-vacuum relief valve is also called a
conservation vent, which permits small changes in the
liquid level without expelling the tank's vapors. If the tank
has a conservation vent or is vented to a control device, it
is important that the other openings on the tank be kept
closed and sealed for the emission controls to be effective.
As an emission control option, fixed roofs can be retrofit-
ted to open tanks, or a fixed roof tank can be used to
replace an open tank or impoundment. Compared to an
open tank, a fixed roof tank can provide additional control
of 66 to 99 percent, depending on the waste volatility and
the operating characteristics of the tank openings. If the
fixed roof tank is constructed to withstand pressures of
2.5 psig, an additional control of 20 to 45 percent can be
obtained. (Most tanks are not designed and constructed to
withstand this^pressure.)
Emissions from fixed roof tanks occur primarily from
working! (loading) losses and, to a lesser extent, from
breathing losses. The quantity emitted is most directly
affected by the rate at which vapors are expelled from the
tank and the volatility of the tank's contents. These emis-
sions are increased by heating or aeration. Working losses
occur when waste is pumped into the tank and vapors are
expelled by the rising level of liquid (Figures 5 and 6).
Breathing losses occur when the volume of vapor in the
tank is increased because of changes in temperature or
pressure (Figures 7 and 8).
Equations developed by the American Petroleum Insti-
tute (API) are used to estimate emissions for organic
liquids. The basic form of the equation, which can be used
for other types of wastes, estimates the volume of vapor
Pressure/vacuumvalve
(for venting)
Manhole
H Nozzle
(for submerged
H fill or drainage)
Figure 5. Tank working losses.
Working losses ,
due to loading J
Volume of
displaced -
vapors
Vapor space
: Liquid waste :
New
liquid
. level
Original
liquid
level
>* £3- Liquid in
Figure 4. Typical fixed roof tank.
Figure 6. Covered tanks (working losses).
expelled from the tank based on the amount of liquid
pumped in and on the vapor concentration. The concen-
tration of constituents in the vapor can be measured or
estimated from volatility data. One error in using the API
tank equations for aqueous wastes is to estimate the
concentration in the vapor from the mole fraction of the
compound in the liquid, which significantly underestimates
concentration. Henry's law constant should be used for
dilute aqueous wastes. Breathing losses are usually very
low compared to working losses. Note that if the tank is
operated at a constant liquid level, as some separators
and collection tanks are, very little vapor is displaced and
working losses are small.
Two primary emission control approaches exist for fixed
roof tanks. The vapor space above the liquid can be
eliminated by keeping the liquid level at the roof line (or
vice versa), or the vapor space can be vented to a control
device. An alternative to keeping the tank at a constant
liquid level is to install a floating roof, as discussed as
follows. Figures 9 and 10 illustrate the .application of a
closed vent system with control device and two arrange-
ments of floating roof tanks.
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Figure 7. Tank breathing losses.
Breathing losses due
to ambient pressure
and temperature
fluctuations
Vapor phase concentration
in equilibrium with
waste liquid
Liquid waste
Head space
- volume
decreases as
temperature
increases
Figure 9. Closed-vent system and control device.
Figure 10. Floating roof.
Figure 8. Covered tanks (breathing losses).
Floating Roof Tanks
Floating roof tanks are common at petroleum refineries
and gasoline marketing facilities for the storage of volatile
liquids. The floating roof can be installed internally in a
fixed roof tank or externally without a fixed roof. Figures 11
and 12 show internal floating roof and external floating
roof tanks in cross-section. The roof floats on the liquid
and moves with changes in the liquid level, thus reducing
vapor displacement and controlling working losses. The
major requirement for a floating roof is an effective seal
between the roof and the tank walls. Emissions from a
properly maintained floating roof are very low and occur
from standing losses and withdrawal losses.
Figure 13 shows the equipment associated with an ex-
ternal floating roof. Standing losses occur at the deck
seals and at openings for fittings in the floating roof.
If retrofitted to a hazardous waste tank, the floating roof
materials must be compatible with the waste; also floating
roofs cannot be used in hazardous waste treatment tanks
with surface mixers or aeration equipment. The emission
reductions achieved by a floating roof relative to a fixed
roof have been evaluated for volatile organic liquids by
using empirical models. Depending on the type of deck
and seal system selected, emission reductions of 93 to 97
percent can be obtained. For the smaller size tanks and
varieties of wastes found at hazardous waste facilities,
reductions of 74 to 82 percent can be obtained relative to
a fixed roof. Convening an open top tank to a floating roof
tank is estimated to reduce emissions by 96 to 99 percent.
Internal and external floating roofs have different design
and operating requirements. Typical EPA requirements
relating to roof seals and fittings for floating roof tanks are
discussed as follows.
An internal floating roof must be equipped with either a
mechanical shoe seal, or a continuous liquid-mounted
seal, or double-seal system. Figures 14, 15, and 16 illus-
trate the different kinds of seals. Mechanical shoe seals
(Figure 14} operate through a scissors design with a
weighted leg to maintain pressure between the seal and
the tank wall. A flexible envelope covers the area between
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Gauge
float system
F i g . 1 1 . Internal floating roof.
Gauge float
system
Mechanics*
shoe
seal
Automatic
Aleeder
vent
Emergency
roof drain
Figure 12. External floating roof.
the roof deck and the seal. Liquid-mounted seals (Figure
15) maintain pressure between the roof and the tank wall
by means of a liquid-filled tube that rides between the two.
The term "liquid-mounted" refers to the fact that the seal in
this case contacts the liquid directly. A scuff band, sealed
to the roof, protects the tube from abrasion against the
wall. A variation of this seal uses a resilient foam ring
instead of a liquid-filled tube. Double-seal systems are
illustrated by a vapor-mounted seal with secondary seal
(Figure 16). This seal is similar to the liquid-mounted seal
with two exceptions. The liquid is replaced by foam and a
flexible rim-mounted seal is added to the top of the floating
deck. The term "vapor-mounted" refers to the fact that the
seal does not come into direct contact with the liquid.
Fittings that typically require controls to achieve emis-
sion reductions are shown in Figure 17. A seal is required
around each of these vents, wells, or hatches. Further,
each opening must project below the liquid surface. Ac-
cess openings and gauge wells must be equipped with
gasketed covers equipped with bolts, and the cover must
be closed and bolted except when in use. Ladder wells
must have a gasketed sliding cover. Other requirements
include a gasketed sliding cover or flexible fabric seal for
column wells and slitted fabric covers that cover at least
90 percent of the opening for sample wells. Automatic
bleeder vents must be gasketed and must be closed
except when the internal floating roof is floated off or
landed. Rim space vents must be gasketed, and open only
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Main drain
Pontoon manhole
Seal envelope
Figure 13. External floating roof tank
' Tank wall
Envelope
Figure 14. IFR mechanical shoe seal.
when the roof is floated off or as directed by the manufac-
turers for proper and safe operation.
External floating roof (EFR) requirements are similar in
that the EFRs must use a primary seal with continuous,
roof rim-mounted secondary seal. This specification means
that the EFR must have a primary and a secondary seal.
The primary seal can be either liquid-mounted or equipped
with a mechanical shoe seal.
Figure 18 is an illustration of the EFR mechanical shoe
seal with secondary seal. This seal is identical to the
internal floating roof seal except for the addition of a
flexible secondary seal mounted to the top of the deck rim.
Figure 19 shows EFR liquid-mounted seals with added
secondary seals at the deck rim. These seals also are
identical to their internal floating roof counterparts except
for the added secondary seals.
The EPA rules that apply to storage tanks have very
specific requirements for the EFR fittings. The EFR fittings
requiring controls are shown in Figure 20. Access open-
ings, sampling wells, and gauge wells must project below
the liquid surface, their covers must be gasketed, and the
cover must be closed and sealed except when in use.
Emergency roof drains, must be equipped with a slotted
membrane fabric cover that covers at least 90 percent of
the opening. Automatic bleeder vents must be gasketed
and closed except when the EFR is floated off or landed.
The rim space vents must be gasketed and may be open
only when the roof is floated off.
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Tank wall
/IT
Tank wall
Floating roof
Seal fabric
Figure 15. IFR liquid-mounted seal.
-Tank wall
L
Rim-mounted
secondary seal
Floating roof
Scuff band
Foam filled tube
Vapor space
-A
Figure 16. IFR vapor-mounted seal with secondary seal.
Pressure Tanks
Pressure tanks are designed to operate safely at inter-
nal pressures above atmospheric pressure. Consequently,
these tanks can often be operated as closed systems and
do not have emissions at normal storage conditions or
during routine loading and withdrawal. Pressure-relief valves
on the tanks open only in the event of improper operation
or an emergency to relieve excess pressure. These tanks
are most common for the storage of gases; however, they
can also be used to store liquids.
Low pressure tanks can be defined as those operating
at up to 2 atm, and high-pressure tanks are those operat-
ing at more than 2 atm. However, these values are not
specified in the RCRA air rules; pressure tanks are de-
fined in the rules as designed not to vent to the atmo-
sphere as a result of compression of the vapor headspace
in the tank during filling of the tank to its design capacity.
In summary, tank emissions primarily occur due to am-
bient temperature changes and tank filling operations. Con-
trol of tank emissions is accomplished by reducing vapor
displacement or by venting vapors to closed systems.
Tank controls include use of floating roofs with specific
seal types and fittings or installation of leak-tight closed-
vent systems and control devices that achieve 95 percent
or more control.
Containers
Containers are defined under RCRA as, "any portable
device in which a material is stored, transported, treated,
disposed of, or otherwise handled." Examples of typical
containers are drums, dumpsters or roll-off bins, and tank
trucks. Emissions occur from loading these containers,
from uncovered containers during storage or transport,
from treatment operation losses, and from spills.
Sources of emissions associated with drums include air
emissions from the evaporation of leaks and spills; and
poor housekeeping practices that can make spill detection
and cleanup difficult. If the drums are well maintained on a
diked pad, emissions from spills or ruptures can be identi-
fied by routine inspection procedures and promptly cleaned
up. Dumpsters or roll-off bins can be a source of emis-
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Gauge
float system
Ladder
well
ff
Access
hatch
Bleeder
vent
s^_MM
Column
/well
Sample
well
Figure 17. IFR fittings that require controls.
Tank wall
Rim-mounted
secondary seal
Envelope
Floating roof
Shoe
Figure 18. EFR mechanical shoe seal with secondary
seal.
sions if they are left uncovered with the surface of the
waste exposed to the atmosphere.
Emissions from containers also occur when they are
loaded, and emissions are greatest when splash filling
(shown in Figure 21) is used. When splash filling, the
vapors displaced from the container by loading can quickly
become saturated with volatiles caused by the splashing.
Submerged filling (shown in Figure 22) uses an influent
pipe that is below the liquid surface, which reduces splash-
ing and the degree of saturation of the displaced vapors. A
study of submerged filling of tank trucks indicates that
emissions are reduced by about 65 percent relative to
splash filling.
A third method of filling containers, bottom loading, is
shown in Figure 23. In this case, a tight connection is
made between the fill pipe or hose and the container.
Also, the container hatches remain closed and all vapors
vented from the container can be routed to a control
device. A typical bottom loading system with vapor collec-
tion is shown in Figure 24. Advantages for bottom loading
include improved safety, faster loading, reduced labor costs,
and lower emissions.
Other basic controls for containers include using simple
covers during storage, placing containers used for treat-
ment operations in an enclosure vented to a control device
during treatment, or ensuring that appropriate transport
and routine housekeeping practices are followed, with daily
inspections and prompt cleanup of spills. For enclosures
vented to a control device, EPA has provided criteria for
design and operation of the enclosure (40 CFR 52.571,
Appendix B). Efficiency of the system depends on the type
and operation of both the control device and the enclo-
sure.
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- Tank wall
Rim-mounted
secondary seal
-Tank Wall
Rim-mounted
secondary seal
Figure 19. EFR liquid-mounted seal with secondary seal.
Automatic
bleeder
vent
Emergency
roof drain
Guide-pole well
Figure 20. EFR fittings that require controls.
Gauge float
svstem
1
Fill pipe
Organic vapor emissions
Fill pipe
Hatch
cover
Cargo
tank
Organic vapor emissions
Hatch
cover
Cargo
tank
Figure 21. Splash loading method.
Figure 22. Submerged fill pipe.
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Vapor vent
to recovery
or atmosphere
Hatch closed
Waste
Cargo
tank
Figure 23.
Fill pipe
Bottom loading reduces liquid turbulence and
vapor and/or liquid contact.
Treatment Devices
Several treatment technologies may be used to remove
organic compounds from waste. The most common of
these treatments include steam stripping, air stripping,
thin-film evaporation, solvent extraction, distillation, and
waste incineration.
Features common to all the technologies include avoid-
ing the need for controls on subsequent processes (hence
pretreatment), removal efficiency dependant on waste con-
stituents and process design, removal of essentially 100
percent of highly volatile compounds, and applicability to
many wastes and compounds.
The control efficiency achieved by waste treatment de-
pends on several factors including the following: percent
removed from waste and emissions from removal process,
e.g., emissions from a steam stripping operation. Overall,
a 98 to 99 percent removal efficiency can be obtained. For
example, benzene being steam stripped from wastewater
would typically achieve a 98 to 99 percent removal.
Distillation
One of the most commonly used treatment process for
organic liquids is distillation. This separation process is
based on the differences in volatility of components, and
can be performed as continuous or batch operations at
atmospheric pressure, under vacuum, or at greater than
atmospheric pressure. Batch distillation is the most com-
mon of the three for TSDF sites. For each type of distilla-
Level sensor
Island wiring
\
Figure 24. Typical bottom loading system with vapor collection.
Product
supply
To vapor
processor
10
-------
Vapors
Waste
in
sun
Vent
t
Condenser
Residual
out
Vent
t
Receiver
Figure 25. Emission sources for distillation.
tion operation, the organics are transferred from the liquid
waste to the vapor phase, then condensed and collected
as a separate liquid.
Emissions from distillation typically occur from the over-
head venting system, the collection tank vents, or the
vacuum system. The primary condenser is an inherent
control for these emissions, but pollution control devices
can be added to the still vents to provide additional con-
trol. Examples include a second condenser or an activated
carbon canister. Figure 25 is a schematic showing emis-
sion sources for the distillation process.
Solvent Extraction
Solvent extraction is another type of separation process
used for organic liquids. In this process, the constituent to
be removed preferentially dissolves in a solvent chosen for
its high capacity for dissolving the constituent combined
with easy physical separation from the remainder of the
treated waste. The solvent in the extract is typically recov-
ered by distillation, while the still bottoms containing the
constituent are decanted for reclamation or disposal. How-
ever, this solvent recovery stage is associated with emis-
sions as shown in Figure 26 at the still vent. Any collection
tanks associated with the unit may also have emission
points. Although 80 to 100 percent .of the target organics
can be removed from the waste by the solvent, the overall
control efficiency is probably less. Also, waste residuals
usually require further treatment.
In common industrial applications, solvent extraction is
used to remove phenols, acetic acid, hydroxy aromatic
acids, and petroleum oils. Extraction is also applicable for
organic sludges such as benzene from petroleum refinery
sludge.
Air Stripping
Air stripping is a common treatment process used for
aqueous wastes. The stripper may be a spray tower, a
packed column, or simply an aerated tank used to provide
contact between the waste and air. Strippers are most
commonly used to remove parts per million or lower levels
of volatiles from dilute aqueous wastes. Many strippers are
simply vented directly to the atmosphere, while others are
controlled by carbon adsorption or incineration. Condens-
ers on air strippers are uncommon and are generally inef-
fective because of low vapor phase concentrations and
high volumetric flow rates. Figure 27 is a schematic dia-
gram of an air stripping system and shows the system
elements and vents that are emission points.
Steam Stripping
Steam stripping is another method used to treat aque-
ous wastes with concentrations on the order of hundreds
of parts per million or higher. Steam is injected directly into
the wastewater, the overhead vapors are condensed, or-
ganics are separated from the condensed water, and the
decanted water is returned to the feed stream. Emissions
occur from the vent on the condenser/decanter and from
collection tank vents. Continuous steam strippers operate
with either trays or packing and require a low solids con-
tent in the feed to prevent plugging and fouling.
Figure 28 is a schematic of an actual steam stripping
system and illustrates the use of a heat exchanger to
preheat the feed (to recover energy) and to cool the bot-
toms stream from the stripper before additional wastewater
treatment. This particular system has a high level of or-
ganic recovery because both a primary and much colder
secondary condenser are used. Overall emission control
should be excellent because noncondensibles are vented
to an incinerator.
For continuous steam strippers, pretreatment as shown
in Figure 29 may sometimes be required to adjust pH or to
remove solids, which can foul the column packing or trays
and cause plugging problems. Any separate organic phase
that can be decanted from the wastewater is removed prior
to stripping.
Solvent
Waste in
1
idr^ ^b
Solvent
extractor
Emissions
Extracted
Extracted
organics
f
and solvent J \ _. .... .. \
Solvent
recycle
Figure 26. Emissions from solvent extraction.
11
-------
Overhead vapors
Liquid distributor
Vent
Control device > Vent air
I
Control device residue
(e.g., spent carbon)
Waste in
Figure 27. Schematic diagram of an air stripping system.
Feed
To incinerator
Water to feed tank
EDO
Bottoms
Figure 28. Steam stripper for ethylene dichloride (EDC)/vinyl chloride.
Additives Vent
1 t
Wastewater -
Decanter
Organics
Decanted
water
Sludge
Figure 29. Preliminary treatment prior to stripping.
Emissions from steam stripping come from the con-
denser/decanter vent and collection tanks. The primary
condenser provides an inherent control for this process,
but additional control may be obtained by installing control
devices on the equipment vents.
Thin-Film Evaporation
Thin-film evaporation typically is used for viscous liq-
uids, sludges, and slurries that often cannot be treated
with other technologies. A thin layer of waste is spread
over a moving or wiped surface that is heated to volatilize
organics. This configuration makes the technology adapt-
able to many physical forms and waste compositions.
The vertical thin-film evaporator (TFE) looks like a distil-
lation column. In the TFE, the vapors with volatile organics
are removed overhead to a condenser, and the treated
waste is discharged from the bottom as shown in Figure
30. As with distillation units, emissions occur from vents
on condensers, decanters, collection tanks, and vacuum
systems if used. The primary condenser is an inherent
control, but additional control may be obtained from con-
trol devices on the system vents.
12
-------
Drive
systemi
vapor \ To condenser/
outlet / decanter
Modular
heating
bodies
Adsorption
In the adsorption process, organics are selectively col-
lected on the surface of a porous solid adsorbent (acti-
vated carbon, silica gels, molecular sieves). Activated
carbon is the most commonly used adsorbent because it
has high internal surface area, low cost, and insensitivity
to water. One gram of activated carbon can have a sur-
face area equal to that of a football field and typically can
adsorb up to half its weight in organics. The adsorber will
remove essentially all of the target volatiles from the vented
vapors until breakthrough, which is when the volatiles are
first detected in the cleaned vapor leaving the adsorption
bed. Carbon adsorbers can achieve control efficiencies of
at least 95 percent, and control levels of 97 to 99 percent
have been demonstrated in many applications. The two
common types of adsorbers are carbon canisters and
regenerable fixed beds.
Carbon canisters, shown in Figure 31, are used for low
vent flows, usually less than 100 ft3/min, and are not
regenerated onsite. They are usually discarded or re-
turned to the supplier. The canisters are fairly compact
units and can be removed easily and fresh canisters in-
stalled. However, their compact size implies limited capac-
ity and a possible requirement for frequent changes.
Fixed-bed carbon adsorbers that can be regenerated
(shown as a general process flow diagram in Figure 32
and in more detail in Figure 33) are used for controlling
continuous vent streams, with flows exceeding 100,000 ft3/
min, and can handle a wide range of organic concentra-
Product outlet
Figure 30. Flow path of thin-film evaporator.
Waste Incineration
Waste incineration is also an emission control option
that can be used instead of processing the waste in units
with a high emission potential. Waste incineration is com-
monly used for wastes that were previously land-disposed.
The technology provides destruction of 99.9 percent or
higher as demonstrated in many units and is applicable to
organic wastes and sludges. This technology should not
be confused with vapor incineration, which is discussed in
a later section.
Control Devices
Conventional, or commonly used, air pollution control
technologies applicable to waste management operations
are discussed in this section. The conventional air pollu-
tion control devices are divided into two types: recovery
devices, e.g., adsorption, condensation, and absorption;
and combustion devices, e.g., flares, thermal incineration,
catalytic incineration, and boilers or process heaters. The
recovery devices recover organics for reuse when they are
of value, while the combustion devices oxidize the organ-
ics to destroy them.
. For vent flows less than 100 CFM
. Cannot be regenerated in canister
Activated
carbon
Figure 31. Carbon canisters.
13
-------
Organic-
containing
gas stream
On-line.
Sorbent
Clean gas
Organfci
,sensor
Regenerating
gas -
.Qff-jjne.
Sorbent
bed
Organic + regenerating
gas
Organic (liquid)
Byproducts
Figure 32. General process flow diagram of an adsorption process for organic recovery.
Exhaust vent
Vent
Filter Blower
tream /^ \ \
=>y>=i_r^ =n
f- j
leal exchanger rvmiinn
°P*>nal> dSng9
air
Ambient
air intake for
cooling/drying I"
L
Filter Blower
.^tnnm 1
E t*fl-
-j-
T
H>
I
Z]
;
L
i
*
^
1
absorber
Steam
Carbon
absorber
/
^St=
«-cSj-
N
l|
/\ <2>
Vent Vlnt
Condenser
~
\3/
Organ; phase-
o recovery
0
Aqueousphase
to disposal or
treatment
Figure 33. Fixed-bed regenerative carbon adsorption system process flow diagram and potential emission sources.
tions. A common procedure is to have dual beds with one
desorbing while the other is adsorbing. The carbon capac-
ity for organics is affected by the concentration of organics
in the vapor. Carbon manufacturers generally have equi-
librium data for specific compounds and specific carbons.
The bed design is important and must be deep enough to
prevent rapid breakthrough, yet not so deep as to cause
excessive pressure drop. Flow rate is important in the bed
design and in determining carbon capacity requirements.
Humidity has an adverse effect when water occupies some
of the adsorption sites. For a relative humidity of 50 per-
cent or more, dehumidification or dilution may be neces-
sary to lower the relative humidity of the inlet stream. The
bed's operating temperature affects capacity, and some
compounds such as aldehydes and ketones may generate
heat in adsorbers. For these special cases, some means
of removing the excess heat may be necessary.
For effective emission control by adsorption, it is neces-
sary either to monitor for breakthrough or to replace the
carbon periodically before breakthrough occurs (based on
design and operating experience). In addition, any emis-
sions from the disposal or regeneration of the carbon
should be controlled. It is of little value to control emis-
sions from a vent stream only to emit the collected organ-
14
-------
ics later in the wastewater treatment associated with re-
generation.
Condensation
One of the most common devices for organics recovery
is the condenser. Condensers work by cooling the vented
vapors to the dew point and removing the organics as a
liquid. Typical coolants include cooling tower water, refrig-
erated water, brines, and glycols. The efficiency of a con-
denser is determined by the vapor phase concentration of
the specific organics and the condenser temperature. Two
common types of condensers are contact condensers and
surface condensers (also called non-contact or shell and
tube condensers).
The contact condenser (shown in Figure 34 ) is cheap
and efficient. However, the cooling liquid that directly con-
-vtet
Vapojt inlet »
"^ ^ Distribution tray
Liquid level
Liquid outlet (water and VOCs)
Figure 34. Schematic diagram of a contact condenser.
tacts the vented vapors can present a disposal problem.
For example, if the coolant is water that is sent to waste-
water treatment, the volatiles may be emitted in open
tanks.
The shell and tube condenser (Figure 35) does not
allow contact between the vented vapors and the cooling
medium. In this type of condenser, a concentrated organic
liquid can be recovered for recycle or other use.
Absorption
Absorption also is used as an air pollution control tech-
nology. In absorption, the organics in. the vent gas are
dissolved in a liquid by direct contact as shown for the
packed tower absorber in Figure 36. The contact between
the absorbing liquid and the vent gas is accomplished in
spray towers or packed or plate columns. Some common
solvents that may be useful for volatile organics include
water, mineral oils, or other nonvolatile petroleum oils.
Absorption efficiency is affected by temperature of the gas
and sorbent (higher temperatures give poorer absorption),
pressure (higher pressures increase solubility), solubility of
the constituent in the sorbent (higher solubilities require
less sorbent and allow higher efficiencies at equilibrium),
and reaction kinetics (for reactions that can effectively
remove the constituent from the surface of the absorbing
liquid). Absorption efficiencies of 60 to 96 percent have
been reported for organics. For example, methylene chlo-
ride removal from vented vapors has been measured at
87 percent using water as the absorbing liquid. Commonly,
absorbers also are used to remove inorganic gases such
as SO,, H2S, HCI, and NH,. When choosing a solvent, it
must be compatible with the target constituent at the
operating conditions of the absorber.
The material removed from the absorber may present a
disposal or separation problem. For example, organics
must be removed from the water or nonvolatile oil without
losing them as emissions during the solvent recovery or
treatment process.
Combustion Equipment
Vapor combustion is another control technique for vented
vapors. The destruction of organics can be accomplished
Coolant inlet
Cooling tower or
refrigeration unit
Coolant outlet
Vapor outlet
Vapor inlet
Condensed VOC
(to decanter or receiving tank)
Figure 35. Schematic diagram of a shell-and-tube surface condenser.
15
-------
3 c> Cleaned gas
to final control
device
Absorbing
liquid in
Organic
laden
gas in
Absorbing liquid with organics to disposal
or organic solvent recovery
in flares; thermal oxidizers, such as incinerators, boilers,
or process heaters; and in catalytic oxidizers.
Flares are an open combustion process in which oxygen
is supplied by the air surrounding the flame. Surrounding
the flame with steam improves combustion. Flares are
operated either at ground level (usually with enclosed
multiple burner heads) or are elevated. Elevated flares
often use steam injection to improve combustion by in-
creasing mixing or turbulence and by pulling in additional
combustion air. Properly operated flares can achieve de-
struction efficiencies of at least 98 percent. Figure 37 is a
schematic of the basic components of a flare system. The
EPA has developed regulations for the design and opera-
tion of flares that include tip exit velocities for different
types of flares and different gas stream heating values
(above 200 Btu/scf). These design and operating criteria
were established because of the difficulty and cost associ-
ated with measuring flare emissions.
Figure 36. Packed tower for gas absorption.
Thermal Incineration
Thermal incineration is a common air pollution control
technology used to destroy organic vapors. Thermal incin-
Steam
nozzles
Gas
barriers
Helps prevent flashback
Pilot
burners
Rare
stack'
Gas collection header
and
ollection header n^
I transfer line A
£3Il_r-"-i
I
Knock-out_w.
drum ^^
seal
Steam
line
f - Ignition
device
i f - - Air line
Gas line
Drain
Figure 37. Steam-assisted elevated flare system.
16
-------
eration requires high temperatures, good mixing, sufficient
oxygen, and adequate resident time for proper operation
and complete combustion of the organics. Auxiliary fuel is
needed if the heating value of the waste gas is less than
50 Btu/scf. Thermal vapor incinerators are available in a
wide range of sizes; capacity from 200 to 50,000 scfm are
available. Destruction efficiency of at least 98 percent is
achievable for an inlet concentration greater than
2,000 ppm. Below 2,000 ppm, EPA studies have found
that combustion or destruction efficiency decreases as
concentration decreases below 2,000 ppmv. A heat recov-
ery unit, such as a steam generator, may be used to
recover some of the energy from a thermal incinerator.
Figure 38 is a depiction of the major components of a
thermal vapor incinerator.
The two types of thermal incinerators are recuperative
and regenerative. Recuperative incinerators have an exte-
rior shell and tube type heat recovery system and process
gases with heats of combustion sufficiently high to sustain
high temperatures without auxiliary fuel. Regenerative in-
cinerators have internal heat recovery by means of two or
more, usually ceramic, gas paths through the incinerator.
While gases are burned and heating one side, the previ-
ously heated side is used to heat the incoming gas. The
two sides are switched to maintain an operating equilib-
rium. Regenerative incinerators are effective for waste
gases with low concentrations of the constituent to be
destroyed.
Catalytic Incineration
Catalytic incinerators provide oxidation at temperatures
lowe*1han those required by thermal incinerators (typically
350°C to 500°C versus 750°C to 1 ,000°C). Design consid-
erations are important because the catalyst may be ad-
versely affected by high temperatures, high concentrations
of organics, fouling from particulate matter or polymers,
and deactivation by halogens or certain metals. Destruc-
tion efficiencies in catalytic incinerators are on the order of
98 percent. The basic components of a catalytic oxidizer
are shown in Figure 39 and are similar to those of a
thermal unit except that a catalyst bed is used. Sizes of
catalytic incinerators range from large, high-volume units
to small, low-volume packaged units. A fluid-bed catalytic
incinerator is shown in Figure 40. The energy require-
ments (and therefore, operating costs) of a catalytic oxi-
dizer are lower than those of a thermal unit because of the
lower operating temperatures. However, capital costs are
higher.
Existing Boilers and Process Heaters
The organics in vented vapors can also be destroyed
with a high level of efficiency in existing boilers or process
heaters. In this case, no dedicated or new control equip
ment is required. In these devices, vapors with halogens
or sulfur are sometimes avoided because of potential cor-
rosion problems when acid gases are formed. These de-
vices recover the heating value of the vent stream and
also offer the advantage of using existing equipment to
control emissions. Vent streams are added as fuel, as
secondary combustion air, or as diluent. Other advantages
include recovery of the heating value of vent stream and
destruction efficiencies of 98 percent or higher.
Unconventional Technologies
New, unconventional technologies are being used more
frequently in the United States. One of these technologies,
a modified two-stage system, combines adsorption with
incineration or further adsorption. The first stage collects
the target constituent and concentrates it in a regenerated
gas from less than 100 ppm up to more than 2,000 ppm.
The second stage involves more conventional treatment
and depends on the concentration and chemical charac-
teristics of the constituent. For example, if the constituent
Waste gas
Auxiliary
fuel burner
(discrete)
Stack
Mixing
section
Combustion section
optional
Heat
Recovery
Figure 38. Thermal vapor incinerator.
17
-------
can be reused, fixed bed adsorption would be used to
collect it. Otherwise, the constituent would be thermally or
catalytically incinerated. The most common of the two-
stage systems with rotary carousels is shown in Figure 41.
In this system either activated carbon or zeolite is used as
the first-stage sorbent. While one segment of the wheel is
adsorbing, another segment is being desorbed. While the
second stage shows incineration or recovery in the figure,
the specific process that is chosen depends on site condi-
tions.
A carousel system in line with an incinerator is shown in
Figure 42. In this configuration, combustion gas is used to
produce hot desorption gas by means of a heat exchanger.
Many of these units are in operation in Japan and Europe,
and several have recently begun operation in the United
States. Their use is driven by air standards and air toxics
rules. These systems do not tolerate particulate loadings
well and may require filtration of the incoming gas stream.
Another nonconventional device that is finding increased
use for air pollution control is biofiltration. Vapors are
vented through biologically active material where organics
are digested to carbon dioxide and water by microorgan-
isms. This technology, similar to compost in a garden, has
been successfully applied in Europe to control odors, vola-
tile organic compounds, and air toxic emissions. However,
the process has not been used extensively in the United
States. One of the properties of biofiltration is a general
limitation to organic concentrations of 1,000 ppm or less,
although new systems are reportedly treating higher con-
centrations. Control efficiencies greater than 90 percent
are achieved in various applications, and the literature
indicates low operating costs that provide an economic
advantage over other technologies. Figure 43 is a sche-
matic of an open single-bed biofilter system. In practice,
industrial applications typically involve multiple closed or
covered beds.
Emission source
Supplementary
Tuei Catalytic incinerator
Preheater
Stack
- Catalyst bed1
Heat
exchanger
(optiona
Figure 39. Schematic diagram of a catalytic incinerator system.
t Outlet
Stack
Transition
H eatexchanger
r
Process
gas
inlet
Catalyst bed
,. Temperature
T indicating
controller
Process
air in
Concentrate
Blower
Desorptionflow
1(| Incinerator
Recovery
Preheat burner
» Return
to process
Solvent
Figure 40. Fluid-bed catalytic incinerator.
Figure 41. Typical rotary carousel system.
18
-------
Mist removal filters
Adsorption cylinder
Fan
Preheater
Catalytic combustion
Figure 42. Carousel system with incinerator.
Hot
desorbing
air
Ducting
Raw gas
Blower
Clean gas
tJ
Or o
Humidifier Drainage
Figure 43. Schematic of an open single-bed biofilter system.
Filter material
VVVVVSA*
xVVVVVVV
Air distribution system
Biofilter
19
-------
References
U.S. Environmental Protection Agency, CERI. "Handbook:
Control Technologies for Hazardous Air Pollutants." EPA/
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Leaks. EPA-45013-89-009, July 1990.
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89-023. (Will be available to the public upon proposal of
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as an Air Pollution Control Technique." EPA-600/2-86-
028. NTIS PB86-172095/AS. March 1986.
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U.S. Environmental Protection Agency. "Distillation Opera-
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Publication No. EPA-450/3-83-005a. December 1983.
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U.S. Environmental Protection Agency, Office of Air
Quality Planning and Standards. "Hazardous Waste
Treatment, Storage, and Disposal Facilities (TSDF)-
Background Information for Promulgated Organic
Emission Standards for Process Vents and Equip-
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U.S. Environmental Protection Agency, Office of Air Qual-
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U.S. Environmental Protection Agency, Office of Air Qual-
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U.S. Environmental Protection Agency, Office of Air Qual-
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Standards." EPA-450/3-86-009. October 1990.
U.S. Environmental Protection Agency, Office of Research
and Development, Hazardous Waste Engineering Re-
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88-153, NTIS PB88-239082. Cincinnati, OH. August
1988.
U.S. Environmental Protection Agency, Office of Research
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PB86-172095/AS. March 1986.
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Cincinnati, OH. Publication No. EPA-600/2-84-I 39. Au-
gust 1984.
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