Note: Descriptions are shown in the official language in which they were submitted.
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VAPOR RECOVERY SYSTEM UTILIZING COMPRESSION-
CONDENSATION PROCESSES AND RELATED METHODS
BACKGROUND
[000i] This disclosure relates to devices and methods for removing
contaminated
soil vapor.
SUMMARY
[0002] A vapor recovery system provides superior results to other systems for
removing volatile organic compounds and petroleum hydrocarbons from common
sources of such pollutants, such as above ground or underground storage tanks
and
transportable storage tanks. A vapor stream is extracted from a selected
source.
Depending on the parameters of the selected source and the constituents of
concern
to be treated, an appropriate technique or combination of techniques including
compression, chilling, reheating, condensation, and regeneration, and final
treatment are selected. The selected technique or combination of techniques
produce
liquid condensates and a final vapor stream that is either recirculated back
into a
source, treated with carbon, thermally or otherwise destroyed, or expelled
into the
atmosphere. Methods of accomplishing the same are similarly provided,
including
business methods for efficiently characterizing sources of volatile or semi-
volatile
vapors, optimizing target vapor stream treatment technique selection and
processing
of the same to achieve cost effective compliance with changing environmental
regulations.
[0003] According to a feature of this disclosure, a system for extracting
pollutants
from a vapor stream is disclosed comprising, in combination: a vapor
extraction
source, a compressor, a first heat exchanger to condense fluid from off gas
and reheat
the exhausted off gas, a second heat exchange system to condense fluid from
off gas,
a regenerative adsorbing unit having at least one regenerative adsorber, and a
final
treatment step.
[0004] According to another feature, one or many of the first heat exchanger,
regenerative adsorber, and final treatment step may be eliminated or bypassed
based
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on many factors disclosed herein, including the parameters of the selected
source,
the constituents of concern to be treated, and the jurisdiction's
environmental
regulations.
[0005] According to another feature, the compressor may act in any combination
of
the following: apply vacuum upon the off gas source, compress the off gas
stream,
and force the off gas stream through the vapor recovery system. The vacuum
applied
on the off gas source, the level of compression of the off gas stream, the
temperature
of compression, the temperature of the compressed off gas exiting the
compressor,
and the flow rate of the off gas stream through the vapor extraction system
can be
adjusted to optimize the recovery of contaminants from different sources of
vapor
and off gas to be treated as known by artisans.
[0006] According to another feature, novel techniques to prevent the
accumulation
of frozen condensate in the vapor extraction system are disclosed. A method of
reheating compressed off gas as it exits a first heat exchange system in order
to
optimize the functionality of the second heat exchange system is disclosed.
[0001 According to another feature, a regenerative adsorber is disclosed
comprising, in combination: at least one chamber containing activated alumina,
where each chamber has at least one inlet and at least one outlet. The
activated
alumina is charged with a pollutant at high pressure and the pollutant is
unloaded
from the activated alumina at low pressure.
[0008] Moreover, further features of this disclosure are disclosed including a
method of extracting pollutant from a vapor stream comprising, in combination:
selecting optimum flow, compression, condensation, regeneration, and final
treatment parameters for the vapor stream to be treated, extracting a vapor
stream,
compressing the vapor stream to the selected level and temperature of
compression,
achieving the desired flow rate of the compressed vapor stream, condensing the
vapor stream through a series of heat exchangers to form at least one
liquefied
contaminant in each heat exchanger, reheating the vapor stream prior to at
least one
heat exchanger in order to optimize the efficiency of that heat exchanger,
adsorbing
any residual pollutants from the compressed condensed vapor stream with at
least
one regenerative adsorber to produce a substantially pollutant-free off gas,
scrubbing
the substantially pollutant-free off gas with a final treatment selected from
the list of
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activated carbon, thermal oxidation, chemical oxidation, reintroduction into
the
source area, and determining compliance with applicable regulatory
requirements.
[0009] Further features of this disclosure are disclosed including a method of
extracting pollutant from a vapor stream comprising, in combination: selecting
optimum flow, compression, condensation, and recirculation parameters for the
vapor stream to be treated, extracting a vapor stream, compressing the vapor
stream
to the selected level and temperature of compression, achieving the desired
flow rate
of the compressed vapor stream, condensing the vapor stream through a series
of
heat exchangers to form at least one liquefied contaminant in each heat
exchanger,
reheating the vapor stream prior to at least one heat exchanger in order to
optimize
the efficiency of that heat exchanger, recirculating the substantially
pollutant-free off
gas to the off gas source, and determining compliance with applicable
regulatory
requirements.
[oolo] Still more features of this disclosure are disclosed including a method
for
optimizing extraction of pollutant from a vapor stream comprising, in
combination:
initiating testing to determine contaminants to be addressed at the selected
source,
determining the optimum flow, compression, condensation, regeneration, and
final
treatment parameters to treat the source vapor stream so that the vapor
extraction
flow and chemical recovery rates are optimized, determining the optimum flow,
compression, condensation, regeneration, and final treatment parameters to
treat
the source vapor stream so that the final treatment selected is the most cost
effective,
cross referencing this preliminary plan to a database of recovery parameters
defined
by a regulatory authority, executing the plan with a vapor extraction system
to
recover the contaminants, verifying the nature and quantities of the species
of
recovered contaminants to form a set of data, and confirming that the data
satisfy
regulations imposed by a regulatory body.
[ooli] Finally according to a feature of this disclosure, there is disclosed a
method
comprising: determining a source of at least one vapor stream, recovering at
least
one contaminant from at least one vapor stream, separating recovered
contaminants
into at least one subset of contaminants, and recycling the separated
recovered
contaminants for reuse.
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DRAWINGS
[0012] The above-mentioned features and objects of the present disclosure will
become more apparent with reference to the following description taken in
conjunction with the accompanying drawings wherein like reference numerals
denote like elements and in which:
[00131 Fig. i is a block diagram of embodiments of an off gas treatment
system;
[0014] Fig. 2 is a block diagram of embodiments an off gas treatment system
including a regenerative adsorber unit;
[oo15] Fig. 3 and Fig. 4 are block diagrams of embodiments of an off gas
treatment
system with the addition of programmable logistics controller module;
[0016] Fig. 5 is a block diagram of embodiments of vacuum, compression, and
flow
module;
[4:3017] Fig. 6 is a block diagram of embodiments of vapor dryer module 400;
[oo18] Fig. 7 is a block diagram of embodiments of a condensation module;
[43019] Fig. 8 is a block diagram of embodiments of a vapor elimination
module;
[0020] Fig. 9 is a block diagram of embodiments of refrigeration units; and
[0021] Fig. 10 is a block diagram of a regenerative adsorber module 610.
DETAILED DESCRIPTION
[0022] In the following detailed description of embodiments of this
disclosure,
reference is made to the accompanying drawings in which like references
indicate
similar elements, and in which is shown by way of illustration specific
embodiments
in which this disclosure may be practiced. These embodiments are described in
sufficient detail to enable those skilled in the art to practice this
disclosure, and it is
to be understood that other embodiments may be utilized and that logical,
mechanical, electrical, functional, and other changes may be made without
departing
from the scope of this disclosure. The following detailed description is,
therefore, not
to be taken in a limiting sense, and the scope of this disclosure is defined
only by the
appended claims. As used in this disclosure, the term "or" shall be understood
to be
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defined as a logical disjunction and shall not indicate an exclusive
disjunction unless
expressly indicated as such or notated as "xor."
[0023] As used in this disclosure, the term "fluid" shall be understood to
mean
materials that flow, i.e, gasses, liquids, or plasmas.
[0(324] As used in this disclosure, the term "off gas" shall be defined as
fluids
extracted from contaminated sources and includes soil vapors, previously
collected
soil vapors, vapors from enclosed sources including tanks, and collected
vapors from
the production or use of volatile organic compounds, petroleum hydrocarbons,
and
other volatile vapors. The term vapor is sometimes used herein to be
synonymous
with the term "off gas" that contains chemical vapors to be recovered.
[0025] In the context of a vapor elimination device, the term "recovery" or
"recover" refers to thawing or rewarming a heat exchange module that has been
cooled in a prior cycle.
[0026] The industrial revolution marked a radical change to many aspects of
society. Industrialized nations became increasingly productive and urbanized.
Gasoline and oil production became centralized. Increased pollution resulted.
Soil,
air, and water carried unprecedented levels of pollutants over the last 200
years.
[00271 Nevertheless, during the middle of the 20th century, social conscience
and
government sought to eliminate or reduce pollution where possible. The United
States government passed strict environmental laws and set aside funds for
cleaning
polluted natural resources and limiting the emission of carbon dioxide,
methane, and
volatile vapors into the atmosphere. Similarly, corporations and companies are
taking steps to improve the nature and quality of pollutants and to address
polluted
natural resources.
[0028] The venting of explosive vapors from petroleum and gasoline storage
tanks
is necessary prior to de-sludging and other maintenance events such as
repairing
floating deck roofs. Traditionally, pollutants and pollutant vapor trapped in
the
storage tanks have been vented in order to reduce the concentration of vapors
to
below lower explosive limits. Venting of these vapors releases large amounts
of
methane and other green house gasses into the environment. Flaming of these
vented vapors reduces the detrimental effect on the environment by reducing
the
amount of methane introduced into the atmosphere, but is not sustainable when
CA 02752163 2011-08-16
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vapor BTU levels begin to decline. Thermal destruction via oxidation, using
supplemental fuel supplies to bolster a threshold BTU level and maintain
burning,
was introduced to remedy this problem. However, vast quantities of carbon
dioxide
and other damaging emissions are emitted by this process. Moreover, this
process
uses additional fuels to maintain thermal destruction of volatile vapors.
[0029] Furthermore, storage tanks and other sources contaminated with high
levels
of predominately petroleum hydrocarbons present a different problem. Common
petroleum hydrocarbons such as jet fuels, Stoddard solvent, gasoline, fuel
oils,
benzene, toluene, ethylbenzene, xylenes, naphthalene, methyl t-butyl ether,
aromatic
hydrocarbons, and hexane cannot be compressed in a traditional manner due to
their
explosive properties. In the presence of detectable concentrations of
petroleum
hydrocarbons, a traditional compression cycle with compression temperatures
below
200 Fahrenheit will cause a portion of the petroleum hydrocarbon vapors to
turn
from gas to liquid phase inside the compression stage of the compressor when
the
pressure is rapidly increased. The introduction of liquid phase hydrocarbons
in the
presence of oil will degrade the oil used by the compressor for lubrication
and
cooling. This disclosure addresses the problem by providing a novel method of
preventing the liquefaction of gasses containing petroleum hydrocarbons during
compression.
[oceo] Because common petroleum hydrocarbons have comparatively lower
saturation temperatures and pressures than common chlorinated solvents, the
utilization of a vapor extraction system using the high compression levels
necessary
to process and recover chlorinated solvents may result in unnecessary
compression
and power consumption when the off gas stream contains predominately petroleum
hydrocarbons. This disclosure addresses this problem by providing a novel
method of
regulating the minimum necessary compression parameters of the off gas
necessary
to maintain a certain desired flow rate through a determined plurality of heat
exchangers, regenerative adsorbers, and final treatment steps.
[0031] The ideal gas law confirms that the state of a gas is determined by its
pressure and temperature. Therefore, the ideal gas law holds that as the
pressure of
an off gas stream increases, the temperature necessary to reach a given
saturation
rate decreases. When one or more compression devices increase the pressure
level of
an off gas stream, pollutants in the compressed off gas stream will condense
at a
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higher temperature compared to the same pollutants in an uncompressed off gas
stream. This disclosure addresses this problem by providing a novel method of
regulating the pressure of the off gas stream through one or more heat
exchangers,
regenerative adsorbers, and final treatment steps in order to decrease the
cryogenic
capacity, complexity, and overall size of condensation system used to recover
the
entrained pollutants.
[0032] As flow rates through the vapor extraction system increase, the rate of
chemical recovery through each heat exchanger will increase. At a certain
level of
increased flow, a given set of heat exchangers will become overloaded with
chemical
transitioning from gas phase to liquid phase and from liquid phase to solid
phase,
thus causing blockages in the system, even if it is cycled between
refrigeration and
thawing cycles. Conversely, if too little a flow of off gas vapors enters
through a given
set of heat exchangers, the rapid clogging of those heat exchangers with
pollutants
cooled too rapidly into a solid phase will occur. To overcome this dilemma,
this
disclosure teaches a novel method for regulating the flow of the vapor
extraction
system by utilizing different series of heat exchangers.
[00331 Turning now to embodiments illustrated in Fig. 1, vapor extraction and
recovery system too is shown. Vapor extraction and recovery system loo
generally
comprises a connection of off gas treatment system 200 to an off gas source
oto. In
Fig. 1, off gas treatment system 200 comprises a number of subsystems,
according to
embodiments, including vacuum, compression, and flow module 300, vapor dryer
module 400, vapor elimination module 500, and contaminant recovery module 800.
Vacuum, compression, and flow module 300 removes off gas from an off gas
source
ow, removes liquid constituents recovered in the off gas removal process,
compresses the off gas, and produces flow pressure to move the off gas through
vapor
extraction and recovery system loo. Vapor dryer module 400 cools the off gas,
removes liquid constituents and substantially all water from the off gas, and
reheats
the off gas. Vapor elimination module 500 further removes contaminated vapor
from
the gas and further cools the off gas, producing a substantially dry gas that
is free of
chemical vapors and routes this gas back to the off gas source 010.
Contaminant
recovery module 800 separates condensed and collected chemical constituents by
specific gravity, and stores the constituents in one or more storage units.
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[0034] According to embodiments illustrated in Fig. 2, vapor extraction and
recovery system wo comprises the same core features as vapor extraction and
recovery system 100 illustrated in Fig. 1 with the addition of regenerative
adsorber
unit 60o. According to these embodiments, vapor dryer module 400 cools the off
gas, removes liquid constituents and substantially all water from the off gas,
and
reheats the off gas. Vapor elimination module 500 further removes contaminated
vapor from the gas and further cools the off gas, producing a substantially
dry gas as
an intermediate result. Regenerative adsorber unit 600 further removes
contaminated vapors from the off gas, and routes contaminated gas back to
vacuum,
compression, and flow module 300. Also routed from regenerative adsorber unit
600
is an air stream that is substantially free of chemical vapors back to off gas
source
olo. This air stream that is substantially free of chemical vapors may be
expelled
into the atmosphere directly, further scrubbed with granular activated carbon,
or
directed to further processes.
[0035] According to embodiments and as illustrated in Fig. 5, contaminated
vapor
is removed from off gas source ow and transferred via inlet conduit 302 into
vacuum, compression, and flow module 300. According to embodiments, liquid
(e.g.,
water) and gas are separated using gas/liquid separator 310 to prevent liquid
from
entering compressor 330. Separated liquid is routed from gas/liquid separator
310
via liquid outlet 370, while gas separated in gas/liquid separator is muted to
compressor 330 via gas outlet 303. According to embodiments, gas/liquid
separator
310 may be, for example, a 120 gallon Manchester vertical tank (Manchester
Tank,
Franklin, TN).
[0036] Gas outlet 303 routes separated gas from gas/liquid separator 310 to
compressor 330 (e.g., Quincy model QSI 300 air compressor, 255 cfin at 15" Hg
and
155 psi, loo horsepower, 3 phase, air cooled 460 volt electric motor).
Compressor
330 creates a vacuum that pulls an off gas stream from off gas source oio.
Compressor 330 may be any number of commercially available air compressor
systems known to artisans (e.g., Quincy model QSI 370i air compressor, 300 cfm
at
15" Hg and 155 psi, um horsepower, 3 phase, air cooled cooled 460 volt
electric
motor). A person of ordinary skill in the art will know and understand the
applicable
rotary screw, reciprocating, oil-less, and other compressors to use based on
the
relevant parameters in the system. Other similar vacuum creation devices may
be
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used depending on the desired gas flow rate, etc., as known and understood by
a
person of ordinary skill in the art.
[0037] Liquid is moved through liquid outlet 370 with transfer pump 360, which
pumps liquid from gas/liquid separator 310 into initial contaminant recovery
tank
810 via liquid conduit 361. Depending on the source of the off gas stream and
prior
separation of liquid before entry into inlet conduit 302, little water will be
extracted
from off gas source oio. However, in air sparging or dual phase soil vapor
extraction
applications, liquid (e.g., water) flow by may occur, necessitating gas/liquid
separator 310 to separate the liquid from the gas.
[0038] Transfer pump 360 removes liquid from gas/liquid separator 310.
Transfer
pump 360 may be, for example, a centrifugal 120/230 volt 1/2 horsepower motor
pump capable of moving 20 gallons per minute, according to embodiments.
Naturally, off gas source 010 that produce large volumes of liquid may require
transfer pump 360 that is capable of pumping liquid at a more rapid rate.
Similarly,
off gas sources oio producing only nominal amounts of water may be fitted with
transfer pump 360 that moves fewer gallons per minute. The exact choice of
transfer
pump 360 will be known and understood by artisans.
[0039] Initial contaminant recovery tank 810 may be any tank suitable for the
purpose of collecting contaminated liquids. As described below, a specific
gravity
separator may be disposed between transfer pump 360 and initial contaminant
recovery tank 810 along liquid conduit 361 to separate each specific
contaminant
from the other contaminants, according to embodiments.
[0040] As illustrated according to embodiments shown in Fig. 5, vacuum created
by
compressor 330 moves contaminated off gas from gas/liquid separator 310 to
compressor 330. According to embodiments, compressor 330 receives information
from programmable logic controller 910 (see Figs. 3 and 4), including: optimum
off
gas pressure settings for compressor 330, optimum temperature for compressor
330
to heat off gas during compression, optimum vacuum pressure for compressor 330
to
apply to off gas source oio, and optimum resulting flow rate from exhaust of
compressor 330. According to embodiments, compressor 330 compresses
contaminated off gas to a pressure range between about approximately 75 and
175
psi. According to embodiments, compressor 330 heats compressed off gas to
temperature range between about approximately 120 and 235 degrees Fahrenheit.
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According to embodiments, compressor 330 applies a vacuum on the off gas
stream
to be extracted from off gas source mo of between approximately o and 20 in.
Hg.
According to embodiments and depending upon the desired pressure, heat, and
vacuum levels, compressor 330 attains an off gas exhaust stream of between
approximately o and 380 dm when compressor 330 is a Quincy model QSI 370i air
compressor. Compressing off gas containing contaminated vapor concentrates the
contaminated vapor for later removal in vapor dryer module 400, vapor
elimination
module 500, and optionally, regenerative adsorber unit 600.
[00411 After off gas is compressed with compressor 330, compressed
contaminated
off gas is routed to aftercooler 350 via conduit 331, which commences a first
round of
cooling for the compressed contaminated off gas. According to embodiments,
aftercooler 350 is comprised of one or more of an Arrow model AFC 120-1 air to
air
cooler systems (at 150 psi and 180 scfm), or a similar arrangement with
different
flow and temperature ratings. As the contaminated off gas is compressed,
temperature of gas increases substantially according to the ideal gas law.
Aftercooler
350 provides the initial cooling of the compressed contaminated off gas prior
to
condensation in vapor dryer module 400 and vapor elimination module 500.
According to embodiments, aftercooler 350 cools compressed off gas from
approximately 185 degrees Fahrenheit to approximately 90 degrees Fahrenheit.
According to other embodiments, programmable logistics controller 910 engages
and
disengages the cooling fan motor of aftercooler 350 so that the off gas
exiting the
aftercooler 350 to maintain a constant temperature, for example ioo degrees
Fahrenheit. As the compressed contaminated off gas cools inside aftercooler
350,
initial condensation may occur and contaminated vapor may condense to a
liquid.
The condensate is transferred from aftercooler 350 via aftercooler conduit 355
to
initial contaminant recovery tank 810. According to embodiments, aftercooler
conduit 355 may connect into liquid conduit 361 or liquid outlet 370.
[0042] Turning again to Figs. 1-4 and according to embodiments, exhaust from
vacuum, compression, and flow module 300 is directed via control valve 402
(Fig. 1)
to either vapor dryer module 400 via vapor dryer inlet conduit 403 or to vapor
elimination module 500. Programmable logistics controller 910 operates control
valve 402 and determines the direction of the compressed off gas flow. When
control
valve 402 directs compressed off gas flow to vapor dryer module 400, the
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programmable logistics controller 910 will also open control valve 405,
allowing off
gas exiting vapor dryer module 400 to enter vapor elimination module 500.
[00431 According to embodiments, vapor dryer module 400 comprises
condensation module 410 and control valves 402, 404. According to embodiments
and as illustrated in Fig. 6, condensation module 410 is a modified air dryer,
such as
a ERF-500A-236 refrigerant air dryer rated at 230 psi for a 35-39 F pressure
dew
point, or a similar unit with different flow and temperature ratings.
According to
embodiments, vapor is first directed to condensation module 410.
[0044] According to embodiments, condensation module 410 is comprised of
air/air heat exchanger 416, gross water separator 418, air/refrigerant heat
exchanger
420, and refrigerant unit 450. In condensation module 410, the compressed
vapor
stream is cooled (e.g., from approximately 85 F to approximately 39 F) causing
condensation of pollutants and water. Condensed liquid pollutant and water
from the
now-cooled vapor stream is directed to initial contaminant recovery tank 810
via
conduit 422, and the vapor stream is heated to (e.g., to about approximately
75 F) as
it exits condensation module 410.
[0045] According to embodiments, hot saturated compressed vapor stream from
vacuum, compression, and flow module 300 entering condensation module 410
first
enters air/air heat exchanger 416, which cools the air, and gross water
separator 418
removes the condensed liquid. The compressed vapor stream enters air/air heat
exchanger 416 via vapor elimination conduit 403 where it is pre-cooled by the
air
discharged from air/refrigerant heat exchanger 420 exiting the condensation
module
via conduit 421. Cooled vapor is routed from gross water separator 418 to
air/refrigerant heat exchanger 420 via conduit 419, which further cools the
compressed vapor stream. In air/refrigerant heat exchanger 420, the compressed
vapor stream is further cooled (e.g., to about approximately 39 F), and
additional
condensed liquid is separated from the vapor stream. Conduit 421 transfers the
vapor
stream to air/air heat exchanger 416 where it acts as the cooling medium for
the
previous pre-cooling stage. Air/air heat exchanger 416 also reheats the
discharge gas
to optimize the temperature of the vapor stream for entry into vapor
elimination
module 500. Discharge gas exiting air/air heat exchanger 416 exits
condensation
module 410 and vapor dryer module 400 via vapor dryer module outlet 404 and to
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control vale 405, where the vapor stream is directed to vapor elimination
module
500.
[0046] According to embodiments, when control valve 402 directs compressed off
gas flow to vapor elimination module 500, programmable logistics controller
910
keeps control valve 405 closed, preventing the reversal of flow through
condensation
module 410. According to embodiments, vapor elimination module 500 comprises
condensation module 510 and control valve 502, as illustrated in Figs. 1-4.
[0047] According to an embodiment shown in Fig. 7, further differentiation of
other
systems is schematically illustrated, whereby, for example condensation module
510
comprises a heat exchange system for reducing the temperature of the off gas
containing contaminated vapor. This module responds to ongoing challenges
others
have had in dealing with certain volatiles which are not easily converted into
the
liquid phase. The process causes many chemicals to condense into a liquid,
which is
subsequently routed to contaminant recovery module 800.
[00481 According to embodiments, condensation module 510 comprises a plurality
of heat exchangers 512a, 512b, 516a, and 516b. Air/air heat exchanger 512
accomplishes initial cooling of compressed contaminated gas. Air/air heat
exchanger
512 removes virtually all of the residual water and water vapor in the
compressed
gas. After initial cooling has occurred in air/air heat exchanger 512, the
compressed
contaminated gas is transferred to air/refrigerant heat exchanger 516 via warm
vapor
conduit 514. Further cooling of the compressed contaminated vapor occurs in
air/refrigerant heat exchanger 516, causing condensation of the compressed
contaminated vapor as the temperature of the gas containing the contaminated
vapor
drops below condensation point depending on the chemical being condensed. At
this
stage the compressed gas is virtually dry and free of water and water vapor,
according to embodiments.
[0049] Air/air heat exchanger 512 and air/refrigerant heat exchanger 516 work
in
tandem to heat and cool their respective input and output gasses. The cold
output
gas from air/refrigerant heat exchanger 516 is routed through air/air heat
exchanger
512 via cold vapor conduit 518. Warm gas incoming to air/air heat exchanger
512
from either aftercooler 350 via control valve 402 or condensation module 410
via
control valve 405 is therefore cooled by the cold gas routed into air/air heat
exchanger 512 and the cold gas in cold vapor conduit 518 is likewise warmed by
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warm gas incoming from either aftercooler 350 via control valve 402 or
condensation
module 410 via control valve 405.
[0050] According to embodiments shown in Fig. 8, air/air heat exchanger 512
and
air/refrigerant heat exchanger 516 are disposed in condensation module 510 in
a
series of two pairs, each pair comprising one air/air heat exchanger 512 and
one
air/refrigerant heat exchanger 516. Other configurations with additional
air/air
exchangers 512 or air/refrigerant heat exchangers 516 are also contemplated.
According to embodiments, two Quincy type QSI 370i compressors are used in
vacuum, compression, and flow module 300 to apply a vacuum (e.g., 15 in. Hg)
on
the off gas source olo and a compression level of (e.g., 155 psi) on the off
gas stream
causing a resultant flow of compressed off gas sufficient for the pairs of
heat
exchangers 512,516 (e.g., approximately 500 cfm).
[oosi] The compressed off gas flows through vapor condensation module 510 when
control valve 402 directs the off gas to condensation module 510, according to
embodiments. Accordingly, the programmable logistics controller 910 activates
both
heat exchanger pairs 512, 516 to work in cydes. During a primary cooling
cycle,
valves 521, 524, 526 are open and valves 522, 523, 525 are closed and
refrigerant is
delivered to air/refrigerant heat exchanger 516b. Compressed off gas delivered
through either valve 402 or control valve 405 enters module 500 through inlet
conduit 452, and is directed through valve 521, conduit 452a, heat exchanger
512a,
conduit 514a, collection can 561a, heat exchanger 516a, conduit 518a,
collection can
562a, heat exchanger 512aconduit 552a, conduit 553, conduit 452b, heat
exchanger
512b, conduit 514b, collection can 561b, heat exchanger 516b, conduit 518b,
collection can 562b, heat exchanger 512b, conduit 552b, valve 524, and conduit
552
when the primary cooling cycle is initiated. Coolant flows from refrigeration
units
530, 54o into heat exchanger 516b via valve 526 when the primary cooling cycle
is
initiated. Compressed off gas passing through heat exchangers 512a, 516a is
preliminarily cooled to about approximately 15 Fahrenheit by the residual
cold
temperature of prior cooling cycles. Any frozen condensate in heat exchangers
512a,
516a from the prior cooling cycle is heated by the comparatively warmer
compressed
off gas entering said heat exchangers. Initial condensate of the compression
off gas
forms in heat exchangers 512a, 516a. Condensate is collected in collection
cans 561a,
562a and transported to contaminant recovery module 800. The preliminarily
cooled
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Off gas flows through conduits 552a, 553, and 552b and enters heat exchangers
512b,
516b. Compressed off gas passing through heat exchanger 516b is cooled to
about
approximately -45 Fahrenheit as refrigerant flows through heat exchanger
516b.
This cold gas is directed at the return side of heat exchanger 512b, where it
is warmed
to approximately -20 Fahrenheit by the gas flowing through the off gas side
of heat
exchanger 512b. Similarly, the approximately 15 Fahrenheit gas flowing
through the
off gas side of heat exchanger 512b is pre-cooled to about approximately 5
Fahrenheit by the cold gas flowing through the return side of heat exchanger
512b.
Cold gas exiting the return side of heat exchanger 512b flows through conduits
552b,
552 into module 530, 540.
[0052] Condensate will continue to form as long as refrigerant remains in
air/refrigerant heat exchanger 516b. To remove all condensate, the
air/refrigerant
heat exchanger pair 512b, 516b must undergo a thawing cycle to completely
liquefy
the condensate and remove it, which requires the refrigerant level to be
reduced from
air/refrigerant heat exchanger 516b by closing valve 526.
[0053] Thus, according to embodiments when two 512, 516 heat exchanger pairs
are operated in a cycle, air/refrigerant heat exchanger pair 512b, 516b cools
during
the primary cooling cycle while the heat exchanger pair 512a, 516a thaws
(i.e.,
recovers). Once the primary cooling cycle is complete, the respective
functions are
reversed in what is referred to as the secondary cooling cycle wherein
refrigerant is
reduced from heat exchanger 516b by closing valve 526, refrigerant is
introduced into
heat exchanger 516a by opening valve 525, and the heat exchanger pair 512b,
516b
begins to thaw while the heat exchanger pair 512a, 516a begins to cool. During
the
secondary cooling cycle, valves 521, 524, 526 are closed and valves 522, 523,
525 are
open and refrigerant is delivered to air/refrigerant heat exchanger 516a.
Compressed
off gas from either control valve 402 or control valve 405 enters module 500
through
inlet conduit 452 or inlet conduit 351 and is directed through valve 523,
conduit
452b, heat exchanger 512b, conduit 514b, collection can 561b, heat exchanger
516b,
conduit 518b, collection can 562b, heat exchanger 512b, conduit 552b, conduit
554,
conduit 452a, heat exchanger 512a, conduit 514a, collection can 561a, heat
exchanger
516a, conduit 518a, collection can 562a, heat exchanger 512a, conduit 552a,
valve
522, and conduit 552 during the secondary cooling cycle. Coolant flows from
refrigeration units 531, 541 into heat exchanger 516a via valve 525 when
during the
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secondary cooling cycle. Compressed off gas passing through heat exchangers
512b,
516b is preliminarily cooled (e.g., to about approximately 15 F) by the
residual cold
temperature of prior cooling cycles. Any frozen condensate in heat exchangers
512b,
516b from the prior cooling cycle is heated by the comparatively warmer
compressed
off gas entering the heat exchangers 512b, 516b, thereby thawing the frozen
condensate and preparing the heat exchangers for the next cooling cycle.
Initial
condensate of the compression off gas forms in heat exchangers 512b, 516b.
Condensate is collected in collection cans 561b, 562b and transported to
contaminant
recovery module 800 via conduit 520. The preliminarily cooled off gas flows
through
conduits 552b, 554, and 55= and enters heat exchangers 512a, 516a. Compressed
off
gas passing through heat exchanger 516a is cooled (e.g., to about
approximately -45
F) as refrigerant flows through heat exchanger 516a. This cold gas is directed
at the
return side of heat exchanger 512a, where it is warmed (e.g., to approximately
-20 F)
by the gas flowing through the off gas side of heat exchanger 512a. During
each
cooling, condensate forms and is collected in collection cans 561a, 562a,
561b, 562b
and moved to contaminant recovery module 800. Similarly, the cooled (e.g., the
15
F gas referenced above) gas flowing through the off gas side of heat exchanger
512a is
pre-cooled (e.g., to about approximately 5 F) by the cold gas flowing through
the
return side of heat exchanger 512a. Cold gas exiting the return side of heat
exchanger
512a flows through conduits 552a, 552 into module 53o, 540.
[0054] According to embodiments, refrigerant and warm gas to be cooled by
refrigerant are input at the same location and experience parallel flow rather
than
cross flow. In other words, during one cycle the input of off gas is at one
Embodiments employing parallel flow are more rapidly cooled, allowing for
shorter
cycle times and improving the overall efficiency of the system. According to
embodiments, cross flow configurations and parallel flow configurations may be
chosen on a case by case basis as would be known to a person of ordinary skill
in the
art. As used herein, the term parallel flow refers to recovering one heat
exchange
module while using another heat exchange module for final cooling and
condensing,
until the heat exchange module either experiences a reduce efficient in air
flow,
condensation, or temperature, etc., or after a given time period has elapsed.
Then the
flow of incoming off gas is adjusted for the recovery of the heat exchange
module (or
another heat exchange module in need of recovery) by using another heat
exchange
module to do the final cooling.
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[0055] Air/refrigerant heat exchanger 516 exchanges heat as would be known to
a
person of ordinary skill in the art. That is, the refrigerant provides the
cooling for the
gas. The final temperature range of the gas depends on the coolant used,
airflow, and
other factors. According to embodiments, if a majority of contaminant
condenses in
air/air heat exchanger 512, then gas flow may be increased or cycle time may
be
decreased as a matter of efficiency. Similarly, where contaminated vapor fails
to
condense at an efficient rate, gas flow may be decreased or cycle time may be
increased to expose gas to refrigerant for a longer period. According to
embodiments,
the programmable logistics controller 910 selects the proper temperature range
and
cycle time based on the constituents of concern in the off gas, concentration
of those
constituents in the off gas, position of control valves 402, 404, pressure of
the off gas,
and other user-defined parameters.
[0056] According to embodiments, when the heat exchangers cycle, gas flow rate
remains constant, but the duration the gas is exposed to the heat exchangers
is
varied. Thus, according to embodiments, the programmable logistics controller
910
sets a fixed cycle time, for example 30 minutes per pair, when two heat exe
anger
pairs 512, 516 are operated. When the programmable logistics controller 910
detects
any decrease in flow rate as measured from a point that is after either of the
then-
actively-cooling air/refrigerant heat exchangers 516, the programmable
logistics
controller 910 will instruct the affected air/refrigerant heat exchanger 516
to cycle
into a thawing cycle with its associated air/air heat exchanger 512 while the
remaining heat exchanger pair 512, 516 continues its cooling cycle, and the
programmable logistics controller 910 will simultaneously reset the fixed
cycle time.
Thus, the flow rate of compressed off gas flowing through any given set of
heat
exchangers remains constant.
[0057] According to embodiments, programmable logistics controller 910
monitors
and controls aftercooler 350 and condensation module 410 so that the
compressed
contaminated gas exiting aftercooler 350 and condensation module 410 for
delivery
to condensation module 410 or condensation module 510 is within an optimal
temperature range for the chosen condensation cycling. Compressed contaminated
gas that is too cold will not effectively warm cold exhaust from
air/refrigerant heat
exchanger 516 and compressed contaminate gas that is too warm will be
inefficiently
cooled in condensation module 510 requiring cycle times to be increased to
remove a
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substantial portion of contaminated vapors. Thus, the programmable logistics
controller 910 controls the temperature of off gas exiting aftercooler 350 and
regulates the flow of that off gas through or around condensation module 410
to
provide an optimal compressed contaminated gas temperature to increase
efficiency
of the system and serves as an optimization step for off gas exiting
condensation
module 510.
[0058] For example, condensed off gas leaves compressor 330 at approximately
220 F and approximately 155 PSI. Aftercooler 350 reduces the temperature from
approximately 220 F to approximately 85 F. As previously described, an initial
condensate will be formed as the gas is initially cooled in aftercooler 350.
The initial
condensate is transferred to an initial contaminant recovery tank or,
according to
embodiments, to contaminant recovery module 800.
[0059] The off gas is transferred from aftercooler 350 to air/air heat
exchanger 512
via vapor elimination inlet conduit 351 and a series defined by either control
valve
402, vapor elimination conduit 403, condensation module 410, control valve
405,
and vapor elimination conduit 402. According to embodiments, off gas entering
air/air heat exchanger 512 via control valve 402 is cooled from approximately
85 F to
approximately 20 F, as the heat exchange occurs between the gas from
aftercooler
350 and the cold gas from air/refrigerant heat exchanger 516. Further
condensate is
formed as the gas further cools to approximately 20 F. It is transferred to
initial
contaminant recovery tank 810 in contaminant recovery module 800 via
contaminant recovery module conduit 520, according to embodiments. Specific
gravity separator 808 may be included to separate contaminants by specific
gravity
and store separated chemical contaminants in multiple contaminant recovery
tanks
in contaminant recovery module 800.
[0o6o] According to the example, off gas entering air/air heat exchanger 512
via
control valve 402, vapor elimination conduit 403, condensation module 410, and
control valve 405 is cooled from approximately 75 F to approximately 20 F, as
the
heat exchange occurs between the gas from aftercooler 350 and the cold gas
from
air/refrigerant heat exchanger 516. Further condensate is formed as the gas
further
cools to approximately 20 F. It is transferred to initial contaminant recovery
tank
810 in contaminant recovery module 800 via contaminant recovery module conduit
520, according to embodiments. Specific gravity separator 8o8 may be included
to
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separate contaminants by specific gravity and store separated chemical
contaminants
in multiple contaminant recovery tanks in contaminant recovery module 800.
[0061] The gas cooled to 20 F then transfers to air/refrigerant heat exchanger
516
for further cooling to a cold gas from approximately 20 F to approximately (-
50) F
due to the heat exchange between gas and refrigerant, as known to artisans. As
depicted in Figs. 8 and 9, refrigeration unit 531 and refrigeration unit 541
provide
refrigerant via refrigerant inlet conduit 532 and refrigerant inlet conduit
542 to
air/refrigerant heat exchanger 516 for cooling of the cold gas. To prevent
blockages of
frozen condensate, gas/gas heat exchanger 512 may be cycled with
gas/refrigerant
heat exchanger 516, as would be known to artisans. Thus, prior to freezing up,
warmer gas from heat exchanger 512 is used to warm the cold gas in heat
exchanger
516. After cooling, the refrigerant returns to refrigeration unit 531 and
refrigeration
unit 541 via refrigerant outlet conduit 534a, 524b and refrigerant outlet
conduit
544a, 544b, according to embodiments. At this point in the process, virtually
all
water vapor has been removed from the off gas, but chemical vapors may remain
due
to varying dew points and vapor pressures.
[0062] According to another example, the gas cooled to 20 F then transfers to
air/refrigerant heat exchanger 516 for further cooling to a cold gas from
approximately 20 F to approximately (-3o) F due to the heat exchange between
gas
and refrigerant, as known to artisans. As depicted in Figs. 8 and 9,
refrigeration unit
530 is turned on and refrigeration unit 54o is turned off. In this embodiment
refrigeration unit 530 provides refrigerant via refrigerant inlet conduit 532
to
air/refrigerant heat exchanger 516 for cooling of the cold gas. To prevent
freezing up
problems, gas/gas heat exchanger 512 may be cycled with gas/refrigerant heat
exchanger 516, as would be known to artisans. Thus, prior to freezing up,
warmer gas
from gas/gas heat exchanger 512 is used to warm the cold gas in
gas/refrigerant heat
exchanger 516. After cooling, the refrigerant returns to refrigeration unit
530 via and
refrigerant outlet conduit 544, according to embodiments. At this point in the
process, virtually all water vapor has been removed from the gas, but chemical
vapors may remain due to varying dew points and vapor pressures.
[0063] If the temperature of the off gas exiting the vapor elimination module
via
conduit 552 must is below about approximately 20 Fahrenheit, the efficiency
of
regenerative adsorber unit 600 may be degraded. Optimally, the temperature of
the
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off gas entering regenerative adsorber unit 600 is about approximately 60 F.
Similarly, when treated off gas exiting vapor elimination module 500 is routed
directly back to the off gas source olo, a this warmer temperature is desired
to assist
in the volitization of pollutants to be extracted via vacuum, compression, and
flow
module 300. As viewed in Figs. 8 and 9, when one or both refrigeration units
530,
540 are turned on, off gas exiting the return side of heat exchanger 512 is
routed
through conduit 552. Conduit 552 travels through refrigeration units 531, 541.
In
refrigeration unit 531, 541, off gas from conduit 552 enters heat exchanger
560.
According to embodiments, heat exchanger 560 is a turbo heat exchanger made by
Packless Industries. Off gas enters heat exchanger 560 at approximately -20 F,
where it is exposed to coils containing warm air of approximately 110 F from
refrigeration condenser 530 or 540 that has entered heat exchanger 560 via
conduit
536a or 536b. The off gas is warmed to approximately 643 F in heat exchanger
560,
and then exits via conduit 552.
[0064] According to embodiments, in air/refrigerant heat exchanger 516 final
condensation occurs and the condensate is collected after thawing and
transferred to
contaminant recovery module 800 via contaminant recovery module conduit 520.
The dry cold gas is then transferred to air/air heat exchanger to cool
incoming warm
gas from aftercooler 350 or vapor chiller module 400 and warm the dry cold gas
from air/refrigerant heat exchanger 516 to prepare it for final treatment.
According
to embodiments, the gas treated by air/refrigerant heat exchanger 516 and
routed
through air/air heat exchanger 512 is then routed to regenerative adsorber
unit 600
to remove residual chemical vapors via regenerative adsorber inlet conduit
652.
[0065] According to embodiments, multiple condensation modules 510 may be
used in parallel or in series to improve efficiency of the condensation
process. A
person of ordinary skill in the art will understand that each remediation site
may
require optimization dependant on the particular contaminants at the site,
their
relative abundance, their vapor pressures, their dew points, and their
specific heat of
phase conversion.
[oo66] This invention's optimizing improves it from existing systems, with
condensation modules 510 used in parallel to provide for greater gas flow
through
the system. Conversely, condensation modules 510 may be used in series to
expose
contaminated vapor to subsequent condensation steps in an attempt to remove
19
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greater percentages of total contaminants during the condensation step,
according to
embodiments.
[0067] After the condensation step, residual contaminated vapor typically
remains
in the gas due to incomplete condensation or chemicals that are not cooled
enough or
for long enough for condensation to occur. According to embodiments
illustrated in
Fig. 10, high-pressure gas containing residual contaminated vapor is routed to
regenerative adsorber module 610 via regenerative adsorber inlet conduit 652.
As
shown, two adsorption chambers 66oa, 66ob work in tandem to adsorb residual
contaminated vapor. During operation, one adsorption chamber 66oa, 66ob
adsorbs
residual contaminated vapor while the other adsorption chamber 66ob, 66oa
deadsorbs contaminated vapor. The process of desorption regenerates adsorption
material 662a, 662b for re-adsorption of contaminated vapor.
[0068] According to an embodiment, an adsorption material 662a, 662b is
activated alumina. A person of ordinary skill in the art will readily know and
appreciate that other, similar materials may be used in adsorption module
depending
on the nature of the remediation site, the chemicals involved, and goals of
each
remediation project. Adsorption by adsorption materials, such as activated
alumina,
carbon, or resins, occurs at high pressure; desorption occurs at low pressure.
Other
similar materials and materials specifically suited to adsorption of specific
chemicals
are expressly contemplated as would be known to a person of ordinary skill in
the art.
Both adsorption and desorption are relatively temperature insensitive
processes,
which makes the present system superior for many types of remediation, such as
with halogenated chemicals due to the lack of necessity to introduce heat and
form
strongly acidic byproducts as a result in the desorption process.
[0069] Off gas with residual contamination is introduced to regenerative
adsorber
module 610 via regenerative adsorber inlet conduit 652. Disposed between
regenerative adsorber inlet conduit and each adsorption chamber 66oa, 66ob are
inlet valves 654. Inlet valve 654 control which adsorption chamber 66oa, 660b
is
adsorbing residual contaminated vapor and adsorption chamber 66oa, 66ob
desorbing contaminated vapor. During the adsorption process, inlet valve 654
is in
an open position allowing off gas containing residual contaminated vapor to
enter
adsorption chamber 66oa, 66ob and contact adsorption material 662a, 662b.
During
CA 02752163 2011-08-16
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the desorption process, inlet valve 654 is in a dosed position to prevent gas
from
entering adsorption chamber 66oa, 66ob.
[0070] During the adsorption process, gas containing residual contaminated
vapor
is forced through adsorption material 662a, 662b in adsorption chamber 66oa,
66ob.
Adsorption material 662a, 662b removes vapor from the gas, including
contaminated
vapor. As vapor is removed from the gas, adsorption material 662a, 662b
charges
with contaminated vapor. Gas leaving adsorption chamber 660a, 66ob is
therefore
substantially, about approximately 99.9%, free of VOCs. Artisans will
recognize that
one of flow rate of the gas containing contaminated vapor or cycle time will
vary from
remediation site to remediation site.
[0071] Depending on the types of chemicals being removed, the concentration of
the contaminants, the relative amount of contaminated vapor removed in
previous
remediation steps, for example compression/condensation, and the efficiency of
adsorption material 662a, 662b in removing particular vapors from the gas, the
parameters within which the system runs will differ. Adsorption material 662a,
662b,
surface area of adsorption material 662a, 662b, and other similar variables
known to
artisans will be evaluated and optimized on a per site basis. In some cases,
multiple
regenerative adsorption modules 6io will be used in series to accomplish a
desired
reduction in contaminated vapor passing through vapor elimination module 500.
[0072] According to embodiments where adsorption material 662a, 662b is
activated alumina, adsorption of vapor in gas occurs at high pressure. For
example
and according to embodiments, cold gas leaving condensation module 510 is at
approximately 150 PSI having been compressed prior to entering condensation
module 510. After leaving condensation module 510 and entering regenerative
adsorber module 61o, gas pressure is still at approximately 150 psi.
[0073] Referring again to Fig. 10, once gas has been exposed to and caused
adsorption material 662a, 662b to be charged with contaminated vapor, the
exhaust
is substantially clean. It escapes through clean exhaust conduit 672. Disposed
on
clean exhaust conduit 672 are clean exhaust valves 674, according to the
exemplary
embodiment. Generally, at least one clean exhaust valve 674 is disposed along
clean
exhaust conduit 672 per adsorption chamber 660a, 660b, although multiple clean
exhaust valves 674 are contemplated as would be known to artisans. Clean
exhaust
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conduit 672 releases substantially clean gas into vapor stream source 010,
according
to embodiments.
[0074] In one embodiment, back pressure regulator 681 is disposed along clean
exhaust conduit 672 to maintain a baseline of pressure range of about
approximately
130 to 15o psi throughout chemical recovery system 100.
[0075] According to embodiments, clean exhaust valves 674 shunts a portion of
substantially clean gas for the purpose of desorption. When clean exhaust
valve 674
is "closed," it allows a small flow of clean exhaust gas to flow to charged
adsorption
chamber 66oa, 66ob and through charged adsorption material 662a, 662b. This
low
pressure flow causes adsorption material 662a, 662b to release the
contaminated
vapors collected in the charging step. These vapors exit through exhaust
conduit 670
as inlet valve 654 is closed for charged adsorption chamber 66oa, 66ob as the
desorption step occurs.
[00761 To that end, dean exhaust valves 674 are configured to shunt a portion
of
the substantially clean gas into adsorption chamber 66oa, 66ob that is
desorbing
contaminated vapor. Because desorption occurs at lower pressure, a small
percentage of the total clean exhaust gas is diverted as a low pressure gas to
desorbing adsorption chamber 660a, 66ob, while the remaining substantially
clean
gas continues through clean exhaust conduit 672. The process of shunting a
small
percentage of substantially clean gas may be accomplished by partially opening
clean
exhaust valve 674 or through the use of a multiple valve system, as would be
known
to artisans. For example, clean exhaust valve 674 may comprise one valve that
allows
low-pressure substantially dean gas to pass during adsorption chamber's 66oa,
660b
desorption cycle and a separate valve that may be fully opened to allow high-
pressure
substantially clean gas to escape during the adsorption cycle. The
implementation of
such a system will be known and understood by a person of ordinary skill in
the art.
[0077] Consequently, as one adsorption chamber, e.g., 66oa, of regenerative
adsorber module 6io is being charged with contaminated vapors and exhausting
substantially clean exhaust gas, adsorption chamber, 66ob is being desorbed of
contaminated vapors previously collected and contained in adsorption material
662b. Desorption occurs as a percentage of the substantially clean gas forming
a low
pressure flow is shunted into adsorption chamber 66ob. After adsorption
chamber
66oa becomes fully charged, the system is reversed and adsorption chamber 66ob
is
22
CA 02752163 2011-08-16
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charged with contaminated vapors while adsorption chamber 66oa is desorbed of
the
previously collected contaminated vapors.
[0078] During the desorption cycle of adsorption chamber 66oa, 66ob,
adsorption
material 662a, 662b starts in a state wherein adsorption material 662a, 662b
is fully
charged with contaminated vapor. As low-pressure substantially clean air is
shunted
into adsorption chamber 66oa, 66ob, vapor contained in adsorption material
662a,
662b is released from adsorption material 662a, 662b into the low-pressure
substantially clean gas. The resultant gas comprises concentrated contaminated
vapor. The gas containing the concentrated contaminated vapor is then routed
through exhaust conduit 670 to vacuum and compression module 300 for
recompression and rerouting through the compression/condensation process.
[0079] Multiple regenerative adsorber modules 6io may be placed in series or
in
parallel as a matter of efficiency to ensure adequate removal of particularly
difficult
contaminants. Moreover, efficiencies of the present system may provide for
increased
gas flow rates, and thus more rapid remediation of a polluted remediation
site, due to
increased efficiency of remediation and chemical recovery system loo over
conventional SVE systems.
[oo8o] Thus, artisans will appreciate that nearly all contaminated vapor from
the
ground is eliminated by compression/condensation. Vapor that escapes
compression/condensation is captured by adsorption material 662a, 662b for
reconcentration during the desorption process. The reconcentrated contaminated
media will then be more readily condensed out during a second round of
compression/condensation owing to the increased concentration of the
contaminated vapor, where it would have originally escaped due to the fact
that the
concentration of contaminated vapor dropped below a critical point where no
additional contaminated vapor of a given chemical could be condensed out of
the gas.
The compression/condensation¨adsorption cycle is repeated until the measured
volumetric concentration output of contaminant being removed shows the
remediation site is substantially clean.
[04381] According to embodiments of a method for the removal of pollutants
from a
stream of off gas, off gas vapor is processed through a vapor elimination
module, said
vapor elimination module containing at least one air-to-air heat exchanger and
at
least one air-to-refrigerant heat exchanger, working in tandem, wherein off
gas vapor
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is condensed in each heat exchanger and removed as a liquid from the vapor
elimination module. The off gas vapor stream exiting the vapor elimination
module
will contain less pollutants than it contained when it entered the vapor
elimination
module. The nature and concentration of the pollutants, pressurization rate of
the off
gas stream, refrigerant used, number and size of condensation units used,
cooling
cycle time, and other factors known to artisans will determine the precise
proportion
and quantity of pollutants removed as condensed liquid from the vapor
elimination
module.
[0082] According to embodiments of a method for the operation of a vapor
elimination module, the refrigerant flow is decreased to initiate a thawing
cycle. The
thawing cycle is needed to one or both prevent the freezing of condensate and
remove frozen condensate from within both the air-to-air and air-to-
refrigerant heat
exchangers, especially their inlets and outlets. The thawing cycle is unique
in that the
air-to-air and air-to-refrigerant heat exchangers work in tandem to warm each
other.
Warm air flowing into the air-to-air heat exchanger traverses that heat
exchanger
and enters the air-to-refrigerant heat exchanger, where it warms that heat
exchanger.
The air exiting the air-to-refrigerant heat exchanger is warm enough to help
thaw the
air-to-air heat exchanger as it flows through the return side of that heat
exchanger.
[0083] According to embodiments of a method for off gas extraction and
processing
shown in Figs. 1-4, off gas vapor is extracted from an off gas source. These
vapors, as
previously discussed, contain vapors contaminated with pollutant. The off gas
is
extracted by means of a vacuum pump, blower, compressor, ring pump, or other
device as known by artisans. For example, the off gas is compressed to about
approximately 150 psi. The pressurized off gas enters aftercooler 350, where
initial
water and pollutant condensate are collected. Thereafter, the pressurized off
gas
enters condensation module 410. Condensation module 410 cools the gas further,
causing contaminated vapors to condense into a liquid form that may be
captured.
Condensation module 410 then warms the cooled gas prior to its exit from the
drying
process. This warming function is integral to the functionality of the
condensation
process, especially the interaction between the air-to-air heat exchanging
condensers
and the air-to-refrigerant heat exchanging condensers in the vapor elimination
process 500. Vapor elimination process 500 further cools the gas and causes
much of
the contaminated vapors to condense into a liquid form that may be captured.
The
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CA 02752163 2011-08-16
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drying and vapor elimination process recovers a large percentage of
contaminated
vapors from the gas stream. According to embodiments, the gas stream is then:
CO
recirculated back to the off gas source, for example a storage tank, to create
a closed-
loop process; or (2) directed to a regenerative adsorber module 610, as shown
in Fig.
2, that further removes any remaining contaminants from the air stream, and
then
recirculated back to the off gas source, for example a storage tank, to create
a closed-
loop process.
[0084] Likewise disclosed is a method for optimizing the use of the systems of
this
disclosures. The optimization method ensures efficient flow. Initially, plans
are
generated to do this based on the contaminants to be removed and the source of
the
contaminants. These plans may be directed towards general remediation of a
site, to
specific contaminants, or according to the directive of a regulatory
authority, such as
the United States Environmental Protection Agency, or the South Coast Air
Quality
Management District. Generally, the plan will include use of a degassing
system,
such as the closed-loop degassing system disclosed herein. Depending on the
particular contaminants to be addressed and the source of those contaminants,
optimizations of the system will address the particular parameters of the
application.
[0085] For example, a railcar tank may be contaminated with difficult to
remove
contaminants such as vinyl chloride or freon that will be removed
inefficiently by a
drying and vapor elimination process alone. In these types of cases, for
example, the
flow of refrigerant through one or more heat exchangers in a vapor elimination
module may be increased in order decrease the temperature of the off gas
flowing
through the heat exchangers to optimize the recovery of liquid phase
condensate.
Additionally, the freezing and thawing cycles of the vapor elimination module
may be
varied and optimized based on the plan. Furthermore, a regenerative adsorber
module may be added after a vapor elimination module any residual pollutants
not
recovered as liquid phase condensate. Similarly, decisions may be made to use
systems with multiple compression and condensation modules and regenerative
adsorber modules in series or in parallel, depending on embodiments.
Similarly, the
adsorption and desorption of the regenerative adsorber module may be cycled to
adjust the system to site conditions, as necessary and according to
embodiments.
[oo86] In a different example, a degassing site containing a 150 foot diameter
above
ground storage tank with petroleum hydrocarbon vapors will be efficiently
degassed
CA 02752163 2011-08-16
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using a compression, vapor drying, and vapor elimination process. Some
residual
pollutants may still be present in the treated air stream that is returned to
the storage
tank, but after the degassing process is complete, the concentration of the
gasses
present in the storage tank will be below safe LEL levels.
EXAMPLES
Example 1
[0087] An above-ground storage tank at an active refinery site is selected for
remediation, wherein the system optimization is conducted to maximize the
efficiency of the vapor extraction system and expedite tank degassing. The
vapor
extraction system targets petroleum hydrocarbon-impacted vapors inside the
storage
tank
[oo88] One mobile vapor extraction system is installed at the site, adjacent
to the
storage tank to be treated. The vapor extraction system is rated at 300 scfm
capacity.
This system draws and processes off gas from the storage tank via a 6 inch
diameter
flex hose. One end of this flex hose is connected to an adaptation that
creates an
airtight seal around the open, front access cover of the storage tank. The
other end of
this flex hose is routed to the vapor extraction system's vacuum, compression,
and
flow module.
[0089] As depicted in Fig. 3, the vapor extraction and recovery system
comprises a
vacuum module, a vacuum, compression, and flow module 300, a vapor dryer
module 400, a vapor elimination module 500, a contaminant recovery module 800,
and a programmable logistics controller module 900. The vacuum, compression,
and
flow module consists of one Atlas Copco Model ZE 375 hp air compressor capable
of
compressing 310 scfm of off gas to so psi while delivering a vacuum of 2 in.
Hg. and
one specially fabricated stainless steel air-to-air heat exchanger with
condensation
drain capable of cooling 350 cfm flow at 5o psi. The vapor dryer module
consists of
one Great Lakes Model ERF-500A-236 refrigerant air dryer, rated for up to 230
psi
for a 35-39 F pressure dew point. The vapor elimination module consists of two
pairs
of air-to-air heat exchangers and air-to-air heat exchangers working in line.
[0090] The vapor extraction and recovery system delivers recovered, condensed
pollutants and water collected from the off gas stream to contaminant recovery
module 800, a series of two interconnected 750 gallon storage tanks. One inlet
is
26
CA 02752163 2013-08-19
Docket No. 38356-01020
present on the first storage tank of the interconnected series of storage
tanks. Water
delivered to the interconnected series of storage tanks accumulates in this
first
storage tank, with LNAPL and petroleum pollutants also collecting in this
first
storage tank and overflowing into the second storage tank of the
interconnected
series of storage tanks. LNAPL is collected from the second storage tank and
the
bottom of the first storage tank of the interconnected series of storage tanks
and,
after the tank degassing is complete, transferred back to the storage tank
that was the
original source of the off gas stream via a portable transfer pump. The
remaining
water and trace pollutant is removed for off site disposal.
[0091] While the apparatus and method have been described in terms of what are
presently considered to be the most practical and preferred embodiments, it is
to be
understood that the disclosure need not be limited to the disclosed
embodiments.
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