Note: Descriptions are shown in the official language in which they were submitted.
METHODS AND EQUIPMENT FOR TREATING INDUSTRIAL GAS STREAMS
AND BIOLOGICAL FOULING
100011 This application is a continuation-in-part of prior Application No.
12/901,454, filed
October 8, 2010.
BACKGROUND
Background of the Invention
[0002] This invention relates to the treatment of industrial gas streams. More
specifically,
the invention relates to the treatment of industrial gas streams, such as a
gas stream produced
in a rendering process, to remove odorous and noxious components through the
use of a gas
scrubber system and to reduce biological fouling through the use of a biocide
in the gas
scrubber system.
Description of Related Art
[0003] In the processing of poultry, beef, fish, or other food, as well as in
secondary
processing (e.g., rendering), a large volume of organic material is processed
that can generate
large quantities of odiferous and noxious gases including organic sulfides,
thiols, amines,
alcohols, inorganic sulfides, ammonia, and simple carboxylic acids. These
compounds are
usually the result of biological action on the organic materials being
processed. The odors
produced are offensive and can travel significant distances to surrounding
real estate. In
other industries, such as chemical processing, paint production, wastewater
treatment, etc.,
noxious compounds, such as volatile organic compounds (VOCs), are produced and
are
subject to environmental air quality regulations.
[0004] These gases are usually collected and sent to a scrubber system where
they are
removed from the gas phase. In such a scrubber system, the collected gases
from the process
are evacuated into a gas/liquid contactor where they are contacted by a liquid
stream or
scrubbing solution that is recirculated in the scrubber to absorb the
odiferous and noxious gas
compounds.
100051 During operation of these scrubbing systems, the scrubbing solution
will quickly
saturate with the offensive gases and lose its absorbing potential. For
example, as the
scrubbing solution saturates with gases, particularly nitrogen-bearing gases
(e.g., ammonia),
1
Date recue/Date received 2023-05-24
the pH of the scrubbing solution will rise proportionally. This marked
increase in pH reduces
the solubility of the gases in the scrubbing solution and may cause them to
flash to the
atmosphere or off-gas. Further, at this point, the scrubbing solution has an
intense
disagreeable odor. Accordingly, additives may be added to the scrubbing
solution to reduce
its odor content. Ultimately, the scrubbing solution is either dumped to a
wastewater
treatment facility, or a portion of the scrubbing solution is sent to a
wastewater facility and
fresh makeup water is added to account for the difference.
[0006] In addition, as the water media recirculates in the system, there is an
increase in the
concentration of bacteria and protein and, accordingly, an increase in various
types of
biological growth, including the growth of bacteria, fungus, or yeast. This
biological growth
is typically referred to as biological fouling or biofouling and can cause
problems within the
system. For example, biofouling in the scrubber may begin to plug any packing
used in the
scrubber resulting in the obstruction of the flow of both the gas and liquid
through the
packing. This increases the pressure drop in the scrubber, and increases the
gas flow rate
through the scrubber thereby reducing the overall gas/liquid contact
efficiency and removal
efficiency of odorous and noxious components from the gas stream. Further, in
those
systems that utilize oxidizers to remove odorous and noxious components from
the gas
stream, the presence of biological activity and biofouling in the liquid
streams will reduce the
concentration of such oxidizers, thereby making less available for removal of
the odorous and
noxious components.
[0007] Accordingly, there exists a need in the art for a treatment process
that has a
sufficiently high electronegative potential to reduce substantially all odor
and/or noxious
compounds to simple, soluble, reduced-odor/noxious, or odor/noxious-free
compounds and
that reduces or prevents biofouling in the system. This treatment process
would offer even
greater advance in the art if the process could also eliminate or greatly
reduce the high cost of
treating the scrubber water effluent in the wastewater treatment process.
SUMMARY OF THE INVENTION
[0008] In general, the present invention relates to chemical compositions and
systems,
including processes and equipment for removing odorous and/or noxious
components from
an atmospheric effluent. In one embodiment, the chemical composition includes
an oxidizer
capable of oxidizing the odorous and/or noxious components. In another
embodiment, the
chemical composition includes an aqueous hydrogen peroxide composition of
hydrogen
peroxide, an additive that catalyzes the decomposition of hydrogen peroxide
into hydroxyl
CA 2997487 2018-03-06 2
radicals, and a biocide that treats biological fouling. When contacted with
the atmospheric
effluent, the oxidizer or aqueous hydrogen peroxide composition oxidizes the
odor and/or
noxious components to produce an atmospheric effluent having reduced amounts
of the odor
component and/or noxious component and, in some embodiments, a non-odor
offensive,
environmentally acceptable byproduct. In one embodiment, the addition of the
biocide to the
chemical composition prevents biological fouling. In other embodiments, the
addition of the
biocide to the chemical composition removes existing biological fouling.
100091 A method is described for removing at least one of an odor component
and a
noxious component from an atmospheric effluent. In one embodiment, the
atmospheric
effluent is contacted with a solution comprising an oxidizer. In another
embodiment, the
atmospheric effluent is contacted with an aqueous hydrogen peroxide
composition including
hydrogen peroxide and at least one additive that catalyzes the decomposition
of the hydrogen
peroxide to produce hydroxyl free radicals. The odorous and/or noxious
component in the
atmospheric effluent is absorbed by the oxidizer solution or the aqueous
hydrogen peroxide
composition and oxidized. In another embodiment, the method further comprises
contacting
the gas and liquid in a counter-current fashion. In another embodiment, the
oxidizer solution
or the aqueous hydrogen peroxide composition can be collected after contacting
the gas in a
tank and recycled via a recycle stream to again contact the gas. In this
embodiment,
additional oxidizer or additional hydrogen peroxide and decomposition additive
may be
added to the recycle stream as required or based upon measurement of a given
solution
parameter that is used to indicate whether additional oxidizer or additional
hydrogen peroxide
or decomposition additive is required. In some embodiments, the measurement of
the
solution parameter may be done continuously, periodically, or manually. In
some
embodiments, the addition of the oxidizer or other additives may be done
automatically using
a flow control valve based upon the measured value of the solution parameter
to provide a
more precise addition rate of these components and better control of the
solution composition
compared to a simple on/off valve.
[0010] In some embodiments, the decomposition additive comprises a metal-based
compound, such as a ferrous or ferric salt, such as ferrous sulfate or ferric
sulfate. In other
embodiments, the decomposition additive comprises ozone, which may be added
concurrently with the hydrogen peroxide to the liquid stream to improve
contacting between
the ozone gas and the hydrogen peroxide in the liquid stream.
[0011] In one embodiment, the method for removing an odorous or noxious
component
from a gas stream comprises adding hydrogen peroxide, a hydrogen peroxide
decomposition
CA 2997487 2018-03-06 3
additive, and a chelating agent to a liquid stream; contacting a gas stream
comprising at least
one odorous or noxious component with the liquid stream; and absorbing at
least a portion of
said odorous or noxious component in the gas stream into the liquid stream.
The chelating
agent is added to increase the solubility of the hydrogen peroxide
decomposition additive. In
some embodiments, the chelating agent allows the p1-1 of the liquid stream to
be controlled at
a higher value than the liquid stream would otherwise have under similar
operating
conditions without the chelating agent. This may improve removal of certain
odorous or
noxious components. In some embodiments, the decomposition additive comprises
a ferrous
salt, such as ferrous sulfate, and the chelating agent comprises
aminopolycarboxylates, such
as nitrilotriacetic acid and hydroxyethyliminodiacetic acid; N-heteroxcyclic
carboxylates,
such as picolinic acid; polyhydroxy aromatics, such as gallic acid; or other
compounds, such
as rhodizonic acid, tetrahydroxy-1,4-quinone, and hexaketocyclohexane. In
other
embodiments, the chelating agent comprises methylglycinediacetate or trisodium
methylglycinediacetate (available as TRILON M from BASF Corporation). In other
embodiments, methylglycinediacetate or trisodium methylglycinediacetate can be
mixed with
a source of ferric ion, such as a ferric salt solution, to produce a ferric
chelate, ferric
methylglycinediacetate, as described in U.S. Pat. No. 6,960,330 to Cox.
1001211 In some embodiments the pH of chemical composition or the liquid
stream may be
controlled at a select pH by adding acid or base directly to the liquid stream
or to a tank that
collects the liquid stream after contacting the gas. In other embodiments, the
acid or base
may be mixed with the decomposition additive before addition to the chemical
composition
or the liquid stream or the tank that collects the liquid stream after
contacting the gas.
100131 Other advantages of the present invention will become apparent from the
following
detailed description taken in conjunction with the accompanying drawings that
illustrate, by
way of example, the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
100141 Figure 1 shows a process flow diagram of one embodiment of a process
for
removing an odor and/or noxious component from a gas stream and for reducing
biological
fouling in the process;
100151 Figure 2 shows a process flow diagram of another embodiment of a
process for
removing an odor and/or noxious component from a gas stream and for reducing
biological
fouling in the process;
4
Date recue/Date received 2023-05-24
[0016] Figure 3 illustrates a control system for the system of Figures 1 or 2;
[0017] Figure 4 illustrates a flow diagram for a system for adding additives,
such as the
decomposition additive and other additives described above, including a
biocide, and acid or
base for pH control to one or more gas/liquid contactors or scrubbers;
[0018] Figure 5 illustrates a flow diagram for a system for adding an oxidizer
to one or
more gas/liquid contactors or scrubbers; and
[0019] Figure 6 illustrates a flow diagram for the connection between a
scrubber system
and a wastewater treatment system.
DETAILED DESCRIPTION OF THE INVENTION
[0020] Various embodiments of the present invention are described below with
reference
to the accompanying drawings. To facilitate explanation, the various
embodiments will be
described primarily in the context of a particular embodiment, namely, a wet
scrubber system
comprising a packed column as the gas/liquid contactor. However, it should be
understood
that the invention can be applied to a wide variety of applications, and it is
intended to cover
alternatives, modifications, and equivalents as may be included within the
spirit and scope of
the invention as defined by the appended claims. Accordingly, the following
description is
exemplary in that several embodiments are described (e.g., by use of the terms
"preferably"
or "for example"), but this description should not be viewed as limiting or as
setting forth the
only embodiments of the invention, as the invention encompasses other
embodiments not
specifically recited in this description. Further, the use of the term
"invention" throughout
this description is used broadly and is not intended to mean that any
particular portion of the
description is the only manner in which the invention may be made or used.
[0021] In general, the present invention uses a liquid stream or scrubbing
solution
comprising at least one chemical component that is an oxidizer to oxidize
odorous and/or
noxious components that have been absorbed from a gas stream into the
scrubbing solution.
In some embodiments, additives may also be added to the scrubbing solution,
including, for
example, acid or base to control the pH of the scrubbing solution, additives
to enhance the
effectiveness of the oxidizer (e.g., when using hydrogen peroxide as the
oxidizer the additive
may be a hydrogen peroxide decomposition additive that catalyzes the
decomposition of
hydrogen peroxide to hydroxyl free radicals; chelating agents that, for
example, increase the
solubility of the hydrogen peroxide decomposition additive; wetting agents;
and dispersants)
and a biocide to reduce or eliminate biofouling in the gas/liquid contactor,
including, for
CA 2997487 2018-03-06 5
example, the packing. It should be appreciated that any chemical added to the
scrubbing
solution may be referred to as an additive.
[0022] In one embodiment, the scrubbing solution comprises an aqueous hydrogen
peroxide composition of hydrogen peroxide, at least one additive that serves
to catalyze the
rapid decomposition of the hydrogen peroxide into hydroxyl radicals, and a
biocide. When
contacted with a gas stream containing odorous and/or noxious components, the
hydroxyl
radicals oxidize the odorous and noxious components to a non-odor offensive,
environmentally acceptable byproduct. The byproduct in combination with the
aqueous
hydrogen peroxide composition forms a liquid effluent that provides charge
neutralizing and
adsorption species that, in addition, aids in treatment of wastewater
effluents.
[0023] As can be seen in Table 1 below, the hydroxyl radical is known in the
art as the
second most electronegative species, second only to fluorine, and is
significantly higher in
oxidation potential than other compounds known in the art. The highly
electronegative
hydroxyl radical is, therefore, capable of a much greater decomposition of
odor-causing
molecules than any composition known in the art. As such, in some embodiments,
the
hydroxyl radical is used to oxidize the absorbed odorous and/or noxious
components, as
opposed to, or in addition to, hydrogen peroxide itself. Accordingly, in one
embodiment, at
least a portion of the hydrogen peroxide in the scrubbing solution used to
contact a gas stream
containing odorous and/or noxious components is decomposed to produce hydroxyl
radical,
which, in turn, oxidizes the absorbed odorous and/or noxious components.
TABLE 1
Oxidizer Oxidation Potential (Volts)
fluorine 3.0
hydroxyl radical 2.8
ozone 2.1
hydrogen peroxide 1.8
potassium permanganate 1.7
hypobromous acid 1.6
chlorine dioxide 1.5
chlorine 1.4
[0024] Therefore, in some embodiments, although not necessary, it is desirable
to drive the
hydrogen peroxide decomposition reaction to produce predominantly hydroxyl
radicals to act
CA 2997487 2018-03-06 6
in the oxidation of the odorous and/or noxious components in the gaseous
effluent. It should
be appreciated that neither all of the hydrogen peroxide needs to be
decomposed to hydroxyl
radicals nor does the decomposition need to result in only the production of
hydroxyl
radicals. In some embodiments, it is sufficient that a portion of the hydrogen
peroxide
decomposes to produce at least some quantity of hydroxyl radicals. Moreover,
in some
embodiments, the decomposition of hydrogen peroxide may produce some diatomic
oxygen,
which also has an oxidation potential.
[0025] As noted above, in another embodiment, one additive that may be used in
the
scrubbing solution is a biocide to reduce or prevent biofouling and related
operating
problems. Biofouling in the scrubber may begin to plug any packing used in the
scrubber
resulting in the obstruction of the flow of both the gas and the scrubbing
solution through the
packing. This increases the pressure drop in the scrubber, and increases the
gas flow rate
through the scrubber thereby reducing the overall gas/liquid contact
efficiency and removal
efficiency of odorous and noxious components from the gas stream. In other
scrubbers that
do not utilize packing, such as spray towers or AC cross flow scrubbers, a
biocide can be
used to keep the surfaces of the scrubber and spray nozzles free of biofilms
that can slough-
off the surfaces and impede spray nozzle and scrubber performance. Further, in
those
embodiments that utilize oxidizers to remove odorous and noxious components
from the gas
stream, the presence of biological activity and biofouling in the scrubbing
solution will
reduce the concentration of such oxidizers, thereby making less available for
removal of the
odorous and noxious components. The use of a biocide in the scrubbing solution
may reduce
or prevent biofouling by reducing or stopping biological growth of, for
example, bacteria,
fungus, or yeast.
[0026] Figure 1 shows a diagram of one embodiment of a process for removing an
odorous
and/or noxious component from a gas stream and for treating biofouling in the
process. In
this embodiment, a wet scrubber system 100 is used to contact a gas stream 102
comprising
an odorous and/or noxious component with a scrubbing solution 104 comprising
an aqueous
solution of hydrogen peroxide, at least one additive that catalyzes the
decomposition of the
hydrogen peroxide to hydroxyl radicals, and a biocide to remove certain
odorous and/or
noxious components from the gas stream 102.
[0027] In this embodiment, the gas stream 102 (as represented by the arrows)
comprising
at least one or more odorous and/or noxious component enters a wet scrubber
106. The gas
stream 102 may be from a food processing process, rendering process, or other
industrial
process that produces gaseous odoriferous and/or noxious components that can
be collected
CA 2997487 2018-03-06 7
and fed to a scrubber. In this embodiment, the wet scrubber comprises packing
108, although
it should be appreciated that any type of gas/liquid contactor may be used,
including a spray
tower with or without packing. The gas stream 102 enters the wet scrubber 106
and passes
through the packing 108 and eventually through a stack or outlet duct 110
where the gas
stream 102 is discharged to the atmosphere.
[0028] The wet scrubber 106 also comprises a sump 112 that holds the scrubbing
solution
104. In some embodiments, the sump 112 is integral to the scrubber 106;
however, the sump
112 may also be separate from the scrubber 106. The scrubbing solution 104 is
pumped by a
pump 114 from the sump 112 through a recycle line 116 to a bank of spray
nozzles 118
where is it discharged into the packing 108. It should be appreciated that a
wide variety of
pumps may be used. The pump should be chosen to provide sufficient power to
move fluid at
the mass flow rate required by the particular scrubber. It should also resist
chemical attach
by the scrubbing solution 104 and any additives present in the scrubbing
solution 104. For
certain applications, it may be desirable to use specific types of pumps. For
example, when
using the pump to introduce ozone or other gaseous catalysts, a pump capable
of introducing
a gas into a liquid stream could be used, such as a regenerative turbine pump.
It should also
be appreciated that the scrubbing solution 104 can be discharged onto the
packing in any
manner known in the art.
[0029] Once discharged onto the packing 108, the scrubbing solution 104 flows
in a
counter-current fashion to the direction of the gas stream 102. The packing
108 acts to
facilitate contact between the gas stream 102 and the scrubbing solution 104
to allow for the
absorption of one or more odorous and/or noxious components from the gas
stream 102 into
the scrubbing solution 104. Accordingly, the gas stream 102 that exits through
the stack or
outlet duct 110 has a reduced concentration of odorous and/nor noxious
components.
[0030] After passing through the packing 108, the scrubbing solution 104 is
collected in
the sump 112 and recycled back to the top of the packing 108. The sump 112
also has a
discharge line 120 that allows either the entire scrubbing solution 104 or a
portion thereof to
be discharged, for example, to a wastewater treatment system (not shown). One
of skill in
the art will appreciate that water may be added to the sump 112 depending upon
the amount
of scrubbing solution 104 discharged to maintain the water balance in the
process and a
desired level in the sump 112.
[0031] The scrubbing solution 104 comprises hydrogen peroxide, at least one
additive that
catalyzes the decomposition of at least a portion of the hydrogen peroxide to
hydroxyl
radicals, and a biocide. In one embodiment, the additive that catalyzes the
decomposition of
CA 2997487 2018-03-06 8
hydrogen peroxide is used to produce predominantly hydroxyl free radicals such
that the
scrubbing solution 104 has a relatively high concentration of hydroxyl
radicals compared to a
hydrogen peroxide solution upon discharge from the spray nozzles 118.
[0032] In the scrubber 106, and particularly in the packing 108, the gas
stream 102 and the
scrubbing solution 104 comprising hydroxyl free radicals contact each other.
During this
contact, odorous and/or noxious components in the gas stream 102 are absorbed
by the
scrubbing solution 104 and are oxidized to produce a substantially non-odor-
offensive,
environmentally acceptable byproduct. The oxidation of these components
enhances the
absorption capacity of the scrubbing solution 104 to allow additional odorous
and/or noxious
components to be absorbed. Dependent on the oxidation of the odorous and/or
noxious
component, the scrubbing solution 104 may contain byproduct that is soluble in
the scrubbing
solution 104 or that may adsorb onto semi-colloidal particles formed in the
scrubbing
solution 104.
[0033] It should be appreciated that at the start of the process the contents
of the sump 112
may be essentially makeup water until the process has completed several cycles
in which the
scrubbing solution 104 has been contacted by the gas stream 102. However,
during steady-
state operation, various components are added to the scrubbing solution to
maintain its
absorption capacity. Specifically, as the scrubbing solution 104 is pumped
from the sump
112 to the spray nozzles 118, various chemical components are added to the
scrubbing
solution 104.
[0034] Aqueous hydrogen peroxide and any other additives, including the
biocide, are
added to the scrubbing solution 104 in the recycle line 116. The hydrogen
peroxide 122 is
delivered from a source container 124 through a feed line 126 into the recycle
line 116 using
a pump 128. It should be appreciated that the hydrogen peroxide 122 is added
upstream of
the recycle pump 114, although, as discussed below, the hydrogen peroxide 122
may be
added downstream of the recycle pump 114. In some embodiments in which the
hydrogen
peroxide is added downstream of the recycle pump 114, any decomposition
additive can be
added downstream of the point where the hydrogen peroxide 122 is added.
Although it
should be appreciated that the decomposition additive can be added upstream or
downstream
of the hydrogen peroxide.
[0035] The concentration of hydrogen peroxide 122 in the source container 124
should be
chosen to allow safe handling given the equipment in use and to provide
sufficient
concentration for the needs of the scrubber. Although the concentration of
hydrogen
peroxide in the source container 124 may be selected within a wide range,
specific
CA 2997487 2018-03-06 9
embodiments will range between about 35% to about 50% by weight in an aqueous
solution
as these ranges are currently industrially available and legally
transportable. In a preferred
embodiment, the concentration is about 50% by weight in aqueous solution. In
other
embodiments, the concentration is about 70% by weight in aqueous solution.
100361 The decomposition additive 130, or a mixture of multiple decomposition
additives,
is delivered from a source container 132 through a feed line 134 into the
recycle line 116
using a pump 136. Upon the addition of the decomposition additive 130 to the
recycle line
116 and its inherent mixing with the scrubbing solution 104 in the recycle
line 116, the
decomposition of at least a portion of the hydrogen peroxide to hydroxyl
radicals is catalyzed
and occurs within the recycle line 116. The scrubbing solution 104 comprising
the hydroxyl
radicals is then delivered to the scrubber 106 and the packing 108 through the
spray nozzles
118. In one embodiment, the decomposition additive produces predominantly
hydroxyl
radicals; however, as noted above, it is not necessary that all of the
hydrogen peroxide
decompose to hydroxyl radicals or that the decomposition itself only produce
hydroxyl
radicals. Depending upon the amount of hydroxyl radicals produced, which can
be
determined based upon the removal efficiency of the odorous and/or noxious
components
from the gas stream 102, the rate and amount of decomposition additive
delivered to the
recycle line 116 can be adjusted.
100371 Since the decomposition of at least a portion of the hydrogen peroxide
to hydroxyl
radicals occurs upon the addition of the decomposition additive 130, it is
preferable to add the
decomposition additive 130 downstream of the recycle pump 114. This reduces
wear on the
recycle pump 114 from the decomposition product of hydrogen peroxide, e.g.,
the hydroxyl
radicals. However, it should be appreciated that the decomposition additive
130 may be
added upstream of the recycle pump 114.
[0038] In some embodiments, the decomposition additive is a catalyst that
catalyzes the
decomposition of hydrogen peroxide to hydroxyl free radicals. Generally, the
catalyst is
selected relative to the gas stream being treated and the specific gaseous
components to be
removed so as to generate an aqueous hydrogen peroxide composition having an
optimal
concentration of hydroxyl free radicals. The catalyst is also selected with a
view toward
safety and effectiveness. Obviously, the concentration of the catalyst used
will vary
depending upon the particular catalyst chosen. Typically, the catalyst will be
delivered using
an aqueous solution as described above, although for some catalysts, such as
ozone and
certain of the group VII elements (discussed further below), a direct gaseous
addition will be
necessary.
CA 2997487 2018-03-06 10
[0039] In one embodiment, the decomposition additive used is ferrous sulfate.
In aqueous
media, ferrous ion decomposes hydrogen peroxide in the following manner:
Fe2+ + H202 Fe3+ +OW + OH*
[0040] It should be appreciated that the solubility limit of the catalyst
presents an upper
bound on concentration of the catalyst in the source container 132. In the
case of ferrous
sulfate, the concentration may be selected within a wide range with specific
embodiments
within the range between about 20% to about 38% by weight in aqueous solution.
In a
preferred embodiment the concentration of ferrous sulfate is about 38% by
weight in aqueous
solution. In this embodiment, the aqueous hydrogen peroxide composition may be
added as a
50% by weight hydrogen peroxide solution in its source container.
[0041] The ratio by weight of the hydrogen peroxide solution to the ferrous
sulfate, based
on a 50% by weight hydrogen peroxide solution and a 38% by weight ferrous
sulfate solution
should be within the range between about 1:1 to about 100:1, within the range
between about
2:1 to about 50:1, or within the range between about 5:1 to about 15:1. The
higher the
ferrous sulfate ratio the more the decomposition reaction is driven to
producing hydroxyl free
radicals. The ratio can be as high as one part 50% by weight hydrogen peroxide
solution to
ten parts 38% ferrous sulfate solution, but an extreme amount of heat is
generated. While this
amount of heat may be acceptable in some settings, it may not be desirable in
others.
[0042] It should be appreciated that the use of highly electronegative
hydroxyl radicals is
capable of a much greater decomposition of odor-causing molecules than any
composition
known in the art. Further, the use of some of the decomposition additives,
particularly,
ferrous sulfate, not only reduces the hydrogen peroxide into the hydroxyl
radicals but also
introduces a semi-colloidal substrate into the aqueous media that is capable
of effectively
adsorbing odorous and/or noxious compounds.
[0043] Other additives that act as catalysts, other than ferrous sulfate, may
be used alone or
in combination with ferrous sulfate. In one embodiment, the catalytic additive
may be any
element chosen from elements in groups 3B, 4B, 5B, 6B, 7B, 8B, 1B, and 2B of
the Periodic
Table of Elements and may include combinations thereof. It will be readily
apparent to one
of normal skill in the art that the additive(s) selected from these elements
would be chosen
based upon cost, speed of reaction, and environmental impact. Among these
elements, iron
and its conjugates are the cheapest, most readily available, and of the lowest
environmental
impact.
CA 2997487 2018-03-06 11
[0044] The "d" block transition elements, characterized by the "d" electrons
in their
valence shell, and combinations thereof, may also be used. For example, the
additive may be
cobalt. In one embodiment, the aqueous hydrogen peroxide composition may be
formed
using an amount of cobalt within the range between about 0.5% wt/wt% to about
1% wt/wt%
of the total aqueous hydrogen peroxide composition. Or, the amount of cobalt
may be
between about 0.5% wt/we/0 to about 1% wt/wt% of a solution comprised of
cobalt and a
50% by weight hydrogen peroxide solution. In another embodiment, the additive
may be any
element selected from elements in Group 7A of the Periodic Table of Elements
and
combinations thereof, for example, fluorine.
[0045] In one embodiment, the decomposition additive may be ozone. Using ozone
as the
additive to catalyze the decomposition of the hydrogen peroxide provides
numerous
advantages. In particular, using ozone allows for operation at higher pH
because the ozone is
not as solubility limited at higher pH compared to the decomposition additives
that comprise
metals. As discussed below, the solubility of a metal-based decomposition
additive typically
decreases at higher pH, but a chelating agent may be used to enhance its
solubility. The use
of ozone, however, may displace the need to use a chelating agent in
combination with a
metal-based decomposition, thereby allowing operation at higher pHs. As noted
above,
operation at higher pH provides the aqueous hydrogen peroxide composition with
a greater
capacity to absorb acidic odorous and noxious components in the gas stream to
be treated,
thereby increasing the removal efficiency of the process. Accordingly, when
using ozone,
because solubility of a metal-based catalytic additive is not an issue, the pH
of the aqueous
hydrogen peroxide composition may be increased. The particular pH used in
operation can
be determined as discussed above and is based upon factors such as the type
and
concentration of the odorous and/or noxious components in the gas stream and
the operating
conditions of the scrubber. Generally, it should be appreciated that virtually
any pH above,
for example, 5.0, may be used.
[0046] When using ozone very poor gas transfer to liquid media has been
observed in the
art. As part of the present invention, use of a regenerative turbine pump, for
example, a
Burks regenerative turbine pump manufactured by Burks Manufacturing, can be
used as the
recycle pump to provide sufficient to excellent mixing of the ozone with the
scrubbing
solution in the recycle line. Referring back to Figure 1, such a regenerative
turbine pump can
be used as the recycle pump 114 in the recycle line 116. In this case, the
hydrogen peroxide
is added as shown in Figure 1 upstream of, or on the vacuum side, of the
regenerative turbine
pump. An ozone/air mixture can then be added to an inlet port pre-built on the
vacuum side
12
CA 2997487 2018-03-06
of the regenerative turbine pump. The resulting liquid discharged from the
regenerative
turbine pump provides a well mixed stream. In particular, pressurizing the
discharge side of
the pump to a minimum of 100 psi by using a pinch valve (not shown) gives
excellent gas
transfer of the ozone to the liquid media in the recycle line. It will be
appreciated that this
pinch valve may also be controlled using the same control system that
regulates the addition
of the other additives shown in Figure 1. It should be appreciated that in
some embodiments,
the ozone may be added either upstream or downstream of the recycle pump or in
any other
manner to maximize the transfer of the ozone into the liquid phase and the
decomposition of
the hydrogen peroxide.
[0047] More particularly, as the scrubbing solution, enriched with hydrogen
peroxide (due
to the addition of hydrogen peroxide from the hydrogen peroxide source
container 124),
enters the vacuum side of the regenerative turbine pump, the air/ozone mixture
is introduced
through a pre-machined air port. Intense shear is developed inside the
regenerative turbine
pump that breaks the ozone/air mixture into microbubbles entrained in the
scrubbing solution.
The discharge from the regenerative turbine pump is pressurized to
approximately 100 psi
through a pinch valve assembly, ensuring solubilization of the ozone into the
scrubbing
solution enriched with hydrogen peroxide, but noting that lower pressures may
be used. This
allows for the efficient decomposition of the hydrogen peroxide by the ozone
into hydroxyl
radicals.
[0048] The system and process of the embodiment of Figure 1 may also include a
pH
control loop to measure the pH of the scrubbing solution 104 in the recycle
line 116 and, in
response, to regulate the addition of an acid or base 138 into the recycle
line 116 to maintain
the pH of the scrubbing solution 104 within a preferred pH range.
[0049] In such an embodiment, a sidestream 140 of scrubbing solution 104 is
taken from
the recycle line 116 and passed by a pH probe 142 and then returned to the
scrubber 106.
The pH probe 142 measures the pH of this sidestream 140 and communicates the
measured
pH to a pH controller 144. The pH controller 144 then regulates, as needed,
the addition of
an acid or base 138 from an acid or base source container 150 into the recycle
line 116
through feed line 146 using a pump 148. In one embodiment, the acid or base
138 is added
upstream of the recycle pump 114. However, it may also be added to the
sidestream 140 or
downstream of the recycle pump 114. In another embodiment, the acid or base
138 can be
added directly to the sump 112.
[0050] Through the addition of acid or base using the pH control loop, the pH
of the
scrubbing solution 104 in the recycle line 116 can be maintained at a level
that maximizes the
13
CA 2997487 2018-03-06
decomposition of the hydrogen peroxide by the decomposition additive that
catalyze such
decomposition. This, in turn, allows the removal of the odorous and/or noxious
component
from the gas stream to be optimized. One of skill in the art will appreciate
that the optimal
pH to be used will be dependent upon the particular gaseous components to be
removed and
oxidized and their respective properties and concentration in the gas stream
102, as well as
the composition of the scrubbing solution 104 and operating conditions of the
scrubber 106.
For example, in removing hydrogen sulfide, its solubility is pH dependent and
increases with
increasing pH above about pH 5 to about pH 9.5. In some embodiments, hydrogen
sulfide is
completely soluble at a pH of 9.2 and above. In some embodiments, the
solubility of amines
can be easily changed by changing the pH of the scrubbing solution. For
example, aromatic
amines are water-soluble (protonated) below pH 4, and aliphatic amines are
water-soluble
(protonated) below pH 9. Accordingly, the solubility property of the compound
being
removed needs to be taken into account in selecting an operating pH of the
scrubbing
solution. Additionally, the solubility of the decomposition additive,
particularly a metal-
based additive (discussed below), relative to the pH of the scrubbing solution
needs to be
taken into account. Typically, metal-based additives are less soluble at
higher pH, so that the
pH may need to be controlled at a lower level to maintain an adequate
concentration of such
an additive in solution to catalyze the decomposition of the hydrogen
peroxide.
[0051] In some embodiments, the scrubbing solution 104 may include additional
additives,
including wetting agents, dispersant polymers, and/or chelating agents
(discussed further
below). Addition of these additives would be made similar to the addition of
the additive for
catalyzing the decomposition of the hydrogen peroxide discussed above. Thus,
there may be
separate source containers to enable the regulated delivery of these
additional additives in
aqueous form to the recycle line 116. Preferably, these additional additives
are added on the
downstream side of the recycle pump 114; however, these additives could be
added at other
locations, including, for example, anywhere along the recycle line 116 or
directly to the sump
112. Additionally, some or all of these other additives may be mixed together
and delivered
from a single source container. Alternatively, any one or more of these
additives may be
provided together with one or more other additives. For example, the hydrogen
peroxide in
its source container 124 may contain any one or more chemically compatible
(e.g., resistant
to oxidation) additives such as certain chelating agents and/or wetting
agents. Of course, the
additives may also be provided with the decomposition additive 130 from its
source container
132 and/or from a source container 150 containing acid or base 138.
14
CA 2997487 2018-03-06
[0052] In one embodiment, a nonionic wetting agent may be added to the
scrubber or to the
scrubbing solution to enhance its activity by allowing further penetration of
the oxidizing
agent into crevices of bacterial forms of odorous and/or noxious components.
While the
exact mechanism is not known, it is believed that certain nonionic
surfactants, i.e., wetting
agents, assist in the degradation of bacterial cell walls allowing the
scrubbing solution to
more readily kill the bacteria in the medium.
[0053] Preferred wetting agents are octylphenols, ethylene oxide block
copolymers,
propylene oxide block copolymers, and combinations thereof The determining
factors for
wetting agent choice is organic loading of the effluent, i.e., the level of
proteins or starches in
the effluent, cleanliness of the system being treated, i.e., the amount of
deposits and slime on
the surfaces of the scrubber tank and packing, as well as need for defoaming
capabilities.
[0054] In one embodiment, the wetting agent, as 100% active material, is
present in an
amount up to about 10% by weight of the scrubbing solution (in the scrubber or
as additives
to recycle line), an amount up to about 5% by weight of the scrubbing
solution, or an amount
up to about 1% by weight of the scrubbing solution.
[0055] In another embodiment, a low molecular weight dispersant polymer may be
added
to the scrubber or to the scrubbing solution in order to prevent iron and
other particle
agglomeration in the aqueous media as well as to prevent iron and organic
deposition in
lower liquid flow areas. In one embodiment, the average molecular weight of
these low
molecular weight dispersants is within the range between about 1,000 to about
22,000 or
within the range between about 1,000 to about 9,000. These low molecular
weight
dispersants may be, but are not limited to, homopolymers of acrylic acid,
methacrylic acid,
acrylamide, copolymers and terpolymers acrylates, methacrylates, acrylamide,
AMPS (2-
acrylamido-2-methyl propane sulfonic acid), and combinations thereof. For
example, a
dispersant resistant to oxidation may be desirable in situations where sulfur-
based compounds
that are formed as a result of operation at higher pHs and interaction with a
metal-based
decomposition additive in which insoluble agglomerations, such as zinc
sulfate, are formed.
[0056] The low molecular weight dispersant polymer is added on a weight
percent basis
(i.e., wt/wt% on the total composition weight of the aqueous hydrogen peroxide
composition
in the scrubber or as additives to a scrubber sidestream). In one embodiment,
the percentage
of the low molecular weight dispersant in the scrubbing solution is within the
range between
about 0.5% active wt/wt% to about 10% active wt/wt% of the total scrubbing
solution, within
the range between about 0.5% active wt/wt% to about 5% active wt/wt% of the
total
CA 2997487 2018-03-06 15
scrubbing solution, or within the range between about 0.5% active wt/wt% to
about 2% active
wt/wt% of the total scrubbing solution.
100571 In another embodiment, a chelating agent may be added to the scrubbing
solution.
As earlier discussed, a semi-colloidal metal complex may form during the
oxidation process,
and in some instances, the development of this colloidal metal complex is
undesirable. A
chelating agent may be added to prevent the formation of metal hydroxides or
other insoluble
metal complexes. In one embodiment, the chelating agents may be organic acids
such as
gluconic acids, glycolic acids, lactic acids, and combinations thereof. It
will be appreciated
that a large number of chelating agents may also be used and their selection
readily apparent
to those of skill in the art; however, the chelating agent should not be of
such potent chelating
ability as to prevent the availability of the metal complex for decomposition
purposes.
100581 A chelating agent may also be added to enhance the solubility of the
decomposition
additive or catalyst. This may, in some embodiments, allows for operation at
higher pH. As
noted above, higher pH increases removal of the odorous and/or noxious
components in the
gas compared to lower pH operation. It should be appreciated, however, that a
chelating
agent may be used to enhance the solubility of the decomposition additive in
some
embodiments where increasing the pH may not be necessary.
100591 Generally, chelating agents can be selected based upon the particular
decomposition
additive being used. For example, chelating agents known in the art may be
used to increase
the solubility of metal-based decomposition additives, such as ferrous ion and
other metal
complexes. In addition, ferric (Fe3+) ion may be used as the decomposition
additive to
decompose hydrogen peroxide to produce hydroxyl radicals, and chelating agents
may be
added to increase the solubility of the ferric ion, thereby increasing the
production of
hydroxyl free radicals and allowing for operation at a higher pH. Chemical
Treatment of
Pesticide Wastes--Evaluation of Fe(III) Chelates for Catalytic Hydrogen
Peroxide Oxidation
of 2,4-D at Circumneutral pH, Sun et al., J. Agric. Food Chem., 1992, 40, 322-
327, describes
several chelating agents that may be used to solubilize ferric ion. Such
chelating agents that
showed "high" catalytic activity and that may be used in the present invention
include:
aminopolycarboxylates, such as nitrilotriacetic acid and
hydroxyethyliminodiacetic acid; N-
heteroxcyclic carboxylates, such as picolinic acid; polyhydroxy aromatics,
such as gallic acid;
and other compounds, such as rhodizonic acid, tetrahydroxy-1,4-quinone, and
hexaketocyclohexane. These chelating agents may be used separately. However,
it may be
possible to use mixtures of these chelating agents as well. In other
embodiments, the
chelating agent comprises methylglycinediacetate or trisodium
16
Date recue/Date received 2023-05-24
methylglycinediacetate (available as TRILON M from BASF Corporation) or
methylglycinediacetic acid.
[0060] It should be appreciated that the chelating agent and the decomposition
additive,
such as ferrous ion or ferric ion (which may be added, for example, as ferric
sulfate) may be
mixed before use to allow for chelation. For example, referring to Figure 1,
the chelating
agent and the ferric ion may be chelated prior to placing such a mixture in
the source
container 132 for the decomposition additive. In this case, the selection of
the decomposition
additive and chelating agent can be based upon the specific application or
particular gaseous
components to be removed and the desired operating pH. By mixing the
decomposition
additive and the chelating agent prior to use, this mixture is essentially
"tailor-made" and is
ready for immediate use in the particular application at issue. In fact, this
mixture can be
prepared remote from the facility where it will be used and shipped to that
facility for
immediate use. In some embodiments, methylglycinediacetate or trisodium
methylglycinediacetate can be mixed with a source of ferric ion, such as a
ferric salt solution,
to produce a ferric chelate, ferric methylglycinediacetate, as described in
U.S. Pat. No. 6,960,
330 to Cox.
100611 Alternatively, the decomposition additive and the chelating agent may
be added
separately to the decomposition additive source container 132, thereby
allowing for in-situ
chelation in the source container 132. In this case, consideration must be
given to the rate at
which this solution is added to the recycle line 116 to provide sufficient
time for chelation to
occur. One of skill in the art will appreciate the conditions necessary to
chelate, including
use of the proper pH, which may be, for example, pH 6. Alternatively still,
the chelating
agent may be added through the use of a separate source container (not shown)
in a manner
similar to that of the decomposition additive source container 132. Further,
the use of a
separate source container for the chelating agent may be used to dispense the
chelating agent
into the recycle line 116 either upstream or downstream of the recycle pump
114; however, it
is preferable to dispense the chelating agent into the recycle line 116 as
closely as possible to
the point where the decomposition additive is added to the recycle line 116.
[0062] As noted above, use of a chelating agent to increase the solubility of
the
decomposition additive (for example metal-based additives and, in particular,
ferrous or ferric
ions) allows for operation at a higher pH in the aqueous hydrogen peroxide
composition that
is fed to the scrubber. Operation at higher pH increases the capacity of the
aqueous hydrogen
peroxide composition to absorb additional acidic gases, thereby increasing the
removal
efficiency of the process. It should be appreciated that the specific pH used
will be
17
Date recue/Date received 2023-05-24
dependent upon the particular gaseous components to be removed from the gas
stream and,
correspondingly, may include a wide range of pHs. In some embodiments, it may
be
desirable to not change the operating pH significantly or at all upon the
addition of a
chelating agent.
[0063] The system and process of the embodiment of Figure 1 also includes a
source
container 152 that delivers the biocide 154 into the scrubber 106. In one
embodiment, the
biocide 154 is added to the scrubber 106 through a feed line 156 to the
recycle line 116 using
a pump 158. In this case, the biocide 154 may be added upstream or downstream
of the
recycle pump 114. In either case, the biocide 154 will enter the scrubber 106
with the
scrubbing solution 104. The biocide can be added continuously or semi-
continuously or a
designated intervals as necessary. In another embodiment, the biocide can be
added batch-
wise to shock-treat the system and thereafter added as described herein from
its source
container 152. In some embodiments in which a given system, such as the
scrubber 106 or
the packing 108 already contains biological fouling or growth, the biocide can
be added in an
amount to reduce or eliminate the existing biological fouling or growth and
thereafter added
to maintain a given or reduced level of biological fouling or growth or to
maintain no
biological fouling or growth or to maintain no biological activity in the
scrubbing solution
104 at all. The amount of biocide to be added will depend upon the levels or
concentrations
of biocide necessary to become toxic to the organism being treated. However,
it should be
appreciated that higher concentrations of biocide, for example, concentrations
above the
amount that would be toxic to the organism being treated, can accelerate the
removal of any
existing bio-films or biological fouling. In other embodiments, the biocide is
used at the start
of the process to avoid biological growth or fouling in the scrubber 106.
[0064] According to another embodiment, the biocide may be combined with the
aqueous
hydrogen peroxide 122 in its source container 124 and added to the recycle
line 116 with the
aqueous hydrogen peroxide composition 122. In yet another embodiment, the
biocide may
be combined with the acid or base 138 in its source container 150 and added to
the recycle
line 116 with the acid or base 138. In another embodiment, the biocide may be
combined
with the decomposition additive 130 in its source container 132 and added to
the recycle line
116 with the decomposition additive 130. Additional details describing the
process of adding
the biocide are discussed in below. The biocide may also be added directly to
the sump 112.
The biocide is added in the various methods described above as an aqueous
solution. In other
embodiments, a tablet foul' of a biocide, such as bromide, is used and can be
added directly
to the sump 112. It should be appreciated that in those embodiments in which
the biocide is
CA 2997487 2018-03-06 18
combined with another material before being added to the recycle line 116 the
biocide may
be added directly to the respective source container of the other material or
added to its own
source container 152 and from there added through its feed line 156 to the
appropriate other
source container through separate feed lines 160, 162, 164.
[0065] Figure 2 shows a process flow diagram of another embodiment of a
process for
removing an odor and/or noxious component from a gas stream and for reducing
biological
fouling in the process. This process 200 is similar to that shown in Figure 1;
however, in this
case the decomposition additive, acid or base, and the biocide are combined
202 in one
source container 204. The additive, acid or base, and biocide are delivered to
the recycle line
116 through a feed line 146 using a pump 148. In this case, these materials
202 are delivered
upstream of the recycle pump 114 and the hydrogen peroxide 122 is delivered
downstream of
the point where these materials 202 are added to the recycle line 116 but also
upstream of the
recycle pump. It should be appreciated, however, that the hydrogen peroxide
122 may also
be added downstream of the recycle pump 114.
[0066] As described above in connection with Figures 1 and 2, a biocide is
added to the
scrubber 106 to treat biofouling that may occur in the scrubber 106,
particularly in the
packing 108 or in the sump 112. According to one embodiment, the amount of
biocide added
is the amount necessary to maintain a residual concentration in the scrubbing
solution 104.
Depending upon the biocide used, manufacturer's recommendations for the amount
of
biocide necessary may also be used. Further, certain operating parameters can
be measured
to determine whether the amount of biocide added or the concentration of
biocide needs to be
altered. For example, one technique for determining whether an accumulation of
biofouling
exists in the scrubber 106 is by monitoring the gas pressure differential
across the packing
108. A drop in the gas pressure across the packing 108, or an increase in the
gas differential,
may be used to indicate an increase in biofouling in the packing 108 that
increases the
pressure drop across the packing 108. In this case, additional biocide may be
added or the
residual biocide concentration may be increased. In some embodiments, the
amount of
biocide added to achieve or maintain a given residual concentration of biocide
in the
scrubbing solution 104 is that amount necessary to maintain a given pressure
drop across the
scrubber 106 or packing 108 without a significant increase during operation.
The given
pressure drop may be a starting pressure drop obtained when the system is
first started, or it
may be a particular, predetermined pressure drop set point. Alternatively, the
amount of
biocide may be that amount necessary to maintain no biological fouling or
growth or any
surfaces within the scrubber 106, the packing 108, or any other surfaces in
contact with the
CA 2997487 2018-03-06 19
scrubbing solution 104. In other embodiments, the amount of biocide may be
that amount
necessary to eliminate or prevent any biological activity within the scrubbing
solution 104.
[0067] Generally, any biocide may be used. In one embodiment, the biocide is
quatemary
ammonium. In some embodiments, the residual concentration of quaternary
ammonium in
the scrubbing solution is about 6 to about 7 parts per billion (ppb). In other
embodiments, the
concentration of quaternary ammonium for maintaining the desired lack of
biological activity
or lack of formation of biological fouling is from about 6 ppm to about 15 ppm
and up to
about 50 ppm to provide aggressive cleaning, for example, in situations where
bio-films or
biological fouling is already present. In another embodiment, the biocide is
not an oxidizer.
Such non-oxidizers include dibromo nitrilopropionamide (DBNPA), 2,2 Dibromo-3-
nitrilopropionamide, gluteraldehyde, a carbamate, mercaptobenzothiazole (MBT),
or
isothiazolinone. In some embodiments, the biocide is a mixture of alkyl
dimethylbenzyl ammonium chloride and alkyl dimethylethylbenzyl-ammonium
chloride,
including, in some embodiments, a mixture of these two compounds at 25% by
weight. In
another embodiment, the biocide is peracetic acid. In some embodiments, the
concentration
of peracetic acid is from about 5 ppm to about 50 ppm in the scrubbing
solution. In some
embodiments, the concentration of peracetic acid is from about 10 ppm to about
25 ppm in
the scrubbing solution.
100681 It should be appreciated that the addition rates of any of the
foregoing materials to
the recycle line 116, the sump 112, or to the scrubbing solution 104 in
general can be
regulated to achieve the desired feed rate and concentration in the scrubbing
solution 104 by
any means known in the art, such as control valves, flow meters, or variable
speed pumps.
Further, the equipment for feeding these components may by stand-alone or
independent or
be incorporated as part of a larger control system, particularly in the case
where the system
includes more than one scrubber. It will be appreciated that other embodiments
may be
utilized in which the components of the scrubbing solution 104 are added at
different
locations within the system, including different locations along the recycle
line 116 or
directly to the sump 112.
[0069] One of skill in the art will appreciate that the actual composition of
the scrubbing
solution in the recycle line and, specifically, the concentration of hydrogen
peroxide, the
decomposition additive, and hydroxyl free radicals therein, is determined
based upon the
composition of the gas stream entering the scrubber and the specific gaseous
components to
be removed, as well as the scrubber operating conditions. At a given set of
scrubber
operating conditions (such as the gas flow rate and concentration of odorous
and/or noxious
CA 2997487 2018-03-06 20
components and the scrubbing solution flow rate through the scrubber), the
addition rate of
either or both of the hydrogen peroxide and the decomposition additive may be
adjusted to
provide the necessary production of hydroxyl free radicals to achieve the
desired removal rate
of odorous and/or noxious components. Of course, the concentration of the
hydrogen
peroxide and the decomposition additive in their respective source containers
may be
adjusted to achieve the desired rate of addition of each to the system taking
into account
overall water balance considerations.
[0070] The various embodiments described above have been primarily with
reference to
removal of odorous and/or noxious components from a gas stream in which the
odorous
and/or noxious components are absorbed and oxidized during contact with a
scrubbing
solution comprising hydrogen peroxide and hydroxyl radicals to produce a
substantially non-
odor offensive, environmentally acceptable byproduct. It should be
appreciated, however,
that various oxidizers or solutions containing oxidizers may be used. For
example, oxidizing
compounds such as chlorine gas, sodium hypochlorite, hypobromous acid,
chlorine dioxide,
hydrogen peroxide, peroxy acids, ozone, and permanganate may be used.
[0071] In addition, various embodiments have been described above in the
context of the
use of a wet scrubber system using a single packed column with a single
integrated sump. It
should be appreciated that other gas/liquid contactors may be used in the wet
scrubber
system. For example, spray towers, venturi spray condensers, or a combination
of spray
towers and packed columns may be used. Further, counter-current scrubbers,
where the
direction of the gas flow is opposite the direction of the liquid flow; co-
current scrubbers,
where the direction of the gas flow is in the same direction as the liquid
flow; and cross-flow
scrubbers, where the direction of the gas flow is at an angle to the direction
of the liquid flow;
may be used. In addition, it should be appreciated that more than one sump may
be used for
a single scrubber or, alternatively, one sump may be used for more than one
scrubber.
Further, it should be appreciated that the sump does not necessarily need to
be integral to the
gas/liquid contactor and may be a separate tank, provided that appropriate gas
seals are in
place.
[0072] It should also be appreciated that more than one gas/liquid contactor
may be used in
a single system. Such gas/liquid contactors may be of the same or various
types and may be
configured to operate in series or in parallel. Each gas/liquid contactor
could also have its
own reservoir or multiple gas/liquid contactors may share the same sump. In
using more than
one gas/liquid contactor with one or more sumps, it is possible to utilize one
set of source
containers for hydrogen peroxide, additives, and any acid or base required for
pH control.
21
CA 2997487 2018-03-06
[0073] Figure 3 illustrates a control system for the systems of Figures 1 and
2. As noted
above, the addition of the hydrogen peroxide and the decomposition additive,
as well as other
additives, is regulated to provide the desired composition in the scrubbing
solution in the
scrubber. Similar to the pH control loop discussed above in connection with
Figure 1, Figure
3 illustrates a probe 302 that is designed to measure a given solution
parameter or measurable
parameter that can be used to control the addition rate of the hydrogen
peroxide, the other
additives, or both. For example, the probe 302 may measure the oxidation-
reduction
potential of the solution or a particular chemical species, such as a given
additive, a species
that is indicative of the concentration of the additive, the concentration of
gaseous species
absorbed by the scrubber, or a combination of these. This probe 302 may be
placed in a
sidestream 304 similar to the one described above in connection with the pH
probe 142. A
controller 306 may be used to receive the output from the probe 302 and in
response
automatically control the addition rate of either the hydrogen peroxide 122 in
source
container 124, the decomposition additive 130 in source container 132, or the
biocide 154 in
source container 152 or the addition rate of all of these by controlling their
respective feed
pumps 128, 136, 158. In one embodiment, the hydrogen peroxide addition rate
may be set at
a given, constant value, and the probe 302 and controller 306 would be used to
control the
addition rate of the decomposition additive 130. Alternatively, the rate of
addition of the
decomposition additive 130 may be set at a given, constant value, and the
probe 302 and
controller 306 would be used to control the addition rate of the hydrogen
peroxide 122.
Similarly, the biocide addition rate may be set at a given, constant value,
and the probe 302
and controller 306 would be used to control the addition rate of the
decomposition additive
130. It should be appreciated, that separate control loops may be used for the
hydrogen
peroxide 122 and the decomposition additive 130, respectively, depending upon
the type of
probe used and the solution parameter that is being measured. It should also
be appreciated
that the above described controls may be used in combination with the pH
control loop
previously described in connection with Figure 1 for the addition of an acid
or base 138.
100741 Figure 4 illustrates a flow diagram for a system for adding additives,
such as the
decomposition additive and other additives described above, including a
biocide, and acid or
base for pH control to one or more gas/liquid contactors or scrubbers. As
noted above, a
system for treating a gas stream containing odorous and/or noxious components
may include
more than one scrubber/sump combination. In the configuration shown in Figure
4, each
source container for each additive 402 and for acid or base 404 (e.g., a
ferrous sulfate source
container and a source container for acid or base for pH control) is fluidly
connected to a
CA 2997487 2018-03-06 22
single feed tank 406. The feed tank 406 may have a level controller 408 that
is used to
control the addition rate of the additive(s), the acid or base, make-up water
410, or a
combination of these to the feed tank 406. Of course, the concentration of the
additive(s) and
acid or base in their respective source containers 402, 404 will need to be
accounted for in
determining their addition rate to the feed tank 406 or vice versa. It should
be appreciated
that while Figure 4 is shown for use in adding additives and acid or base to
multiple
scrubbers, the use of a single tank 406 for mixing additives and acid or base
may be used for
systems having only one scrubber! sump as well.
[0075] The feed tank 406, accordingly, comprises a solution 412 of the various
additives
fed to it and any desired acid or base for pH control of the scrubbing
solution for each
scrubber. Depending upon the additive or combination of additives used, the
chemical effect
of the addition of acid or base to the feed tank 406 on any such additives
needs to be
considered to ensure that the desired chemical effect of the additives would
not be adversely
altered before its addition to the scrubbers.
[0076] The feed tank 406 is fluidly connected to a distribution pump 414 that
is fluidly
connected to each scrubber's recycle line at the desired location along each
recycle line. One
desired location for distributing the solution 412 from the feed tank 406 to
each recycle line
of each scrubber may be downstream of each scrubber's recycle pump. It should
be
appreciated, however, that the point of addition to each scrubber may vary
from scrubber to
scrubber and may include points other than the recycle line or other locations
along the
recycle line. In other words, the solution 412 may be added to different
locations along each
scrubber's recycle line or at different points for each scrubber, such as each
scrubber's sump.
[0077] It should be appreciated that flow control valves 416 may be used to
control the
flow rate of the solution 412 in the feed tank 406 to each scrubber. Any flow
control valve,
including a valve having precise control over the flow rate that passes
through it, such as an
analog valve, or, alternatively, an on/off valve may be used depending upon
the method and
amount of control desired. In either case, the flow control valves 416 may be
controlled
based upon a certain solution parameter measured, either on a continuous, semi-
continuous or
periodic, or manual basis, in each scrubber's recycle line or in each
scrubber's sump. The
solution parameter measured may be the concentration of any chemical species
or solution
specific measurement that provides information that can be used to determine
whether to add
additional additive(s). The solution parameter may include such parameters as
pH, oxidation
reduction potential, the concentration of the decomposition additive or a
particular chemical
species indicative of the concentration of the additive, the concentration of
gaseous species
CA 2997487 2018-03-06 23
absorbed by the scrubber, or a combination of these as further described
below. In some
embodiments, the measurement of the solution parameter is done automatically
either on a
continuous, semi-continuous or periodic basis, and the results of such
measurement are used
to automatically control the flow control valve 416. Of course, the required
feed rate of the
solution 412 in the feed tank 406 to each scrubber will be based upon each
particular
application, including, for example, the particular noxious components to be
removed, the
amount of gas being treated, and the operating conditions of each scrubber
(e.g., the
recirculation rate of the scrubbing solution through the scrubber) and the
concentration of the
various components in the solution 412 in the feed tank 406.
100781 In operation, the addition rate of the solution 412 from the feed tank
406 to each
recycle line of each scrubber may be controlled in various manners. In some
embodiments,
the addition of this solution 412 is controlled by the pH control loop on each
recycle line as
described above in connection with Figure 1. In this case, a separate pH
controller would be
used for each scrubber and would control a respective flow control valve 416
to determine
the flow rate of solution 412 from the feed tank 406 to that scrubber's
recycle line. In other
embodiments, different solution parameters could be monitored and used to
control the
addition rate of the solution 412 from the feed tank 406 by each flow control
valve 416. As
noted above, oxidation reduction potential, the concentration of the
decomposition additive or
a particular chemical species indicative of the concentration of the additive,
the concentration
of gaseous species absorbed by the scrubber, or a combination of these could
be monitored
and used to control the addition rate of the solution 412 to each scrubber.
100791 As described above, depending upon the specific application, the
concentrations of
the additive(s), including any biocide, and the acid or base in the solution
412 can be adjusted
so that the appropriate amount of each is fed to each scrubber. In addition,
the relative
concentrations in the solution 412 in the feed tank 406 may need to be
adjusted for each
specific application so that the appropriate amount of each additive and acid
or base can be
fed to each scrubber. This can be accomplished by adjusted the concentration
of the additives
and the acid or base in their respective source containers 402, 404. Further,
these
concentrations must be adjusted to be consistent with each scrubber's and the
overall system
water balance.
[0080] It should be appreciated that using a flow control valve 416 allows for
more precise
control of the flow rate to each scrubber, as opposed to a simple on/off
valve, in combination
with monitoring either pH or another solution parameter provides for better
control of the
solution chemistry and removal of the noxious and odorous components.
Particularly by
CA 2997487 2018-03-06 24
monitoring the pH or another solution parameter in the recycle stream, as
shown in Figures 1
and 3, the composition of the solution that is contacting the gas stream is
better known than,
for example, monitoring the solution in the sump. Further, by adding the
additive and/or acid
or base directly to the recycle line based upon the results of monitoring of
the solution in the
recycle line allows the recycle line chemistry to be properly controlled or
adjusted just prior
to entering the scrubber. This allows for more optimal control of the removal
of the odorous
and/or noxious components.
[0081] Optionally, any make-up water 410 required for each reservoir may also
be added
to the feed tank 406. In this case, the dilution effect of any water added to
the feed tank 406
must be taken into account so that the desired amount of each additives and
acid or base are
ultimately added to each recycle line. In addition, the water make-up needs of
each reservoir,
to the extent that they are different, must be taken into account. In other
words, a water
balance must be achieved for the overall system, which will also impact the
amount of water
in the feed tank 406, as discussed above. Alternatively, make-up water 410 may
be added
directly to each scrubber's sump.
[0082] It should be appreciated as an alternative to Figure 4 that the
hydrogen peroxide can
be added from separate source containers directly to the recycle line of each
scrubber, or a
single source container can be used with a distribution system to each recycle
line of each
scrubber. Preferably, the hydrogen peroxide would be added upstream of each
scrubber's
recycle pump. In all cases, a control valve would be used to monitor and
regulate the flow of
hydrogen peroxide to each scrubber. The control of such a control valve could
be based upon
the removal efficiency of each scrubber or it could be based upon the relative
addition rate of
the decomposition additive to the recycle line of each scrubber.
[0083] Further, it should be appreciated as an alternative to Figure 4, each
source container
of additive or acid or base may be separately connected to a separate
corresponding main
header line that is fluidly connected to each recycle line of each scrubber at
the desired
location along the recycle line. In other words, the source container for each
additive would
be separately connected to each scrubber via its own main header line. As
described above,
one desired location for the addition of additives that catalyze the
decomposition of hydrogen
peroxide to each scrubber may be downstream of each scrubber's recycle pump.
It should be
appreciated, however, that the desired location for the addition of other
additives may vary
according to the particular additive used. For example, as described above, in
using ozone as
the catalyst, an air/ozone mixture may be added directly to a regenerative
turbine pump in the
recycle line of each scrubber. Alternatively, a regenerative turbine pump may
be used to
CA 2997487 2018-03-06 25
pump hydrogen peroxide from its source container to a main header line that is
fluidly
connected to each scrubber, wherein an air/ozone mixture is added to that
regenerative
turbine pump rather than to each pump in each recycle line.
[0084] Desired locations for the addition of acid or base for pH control in
this alternative
embodiment include upstream of each scrubber's recycle pump and in some
embodiments
upstream of the addition point for the hydrogen peroxide. In this alternative,
the hydrogen
peroxide may be added, for example, in the same manner as described above in
connection
with Figure 4.
[0085] Generally, it should be appreciated that the addition of the various
components
comprising the aqueous hydrogen peroxide composition may be added at various
locations
throughout the scrubber system and are not limited to those described in the
above
embodiments. For example, the hydrogen peroxide and other additives may be
added at other
locations in the recycle line or directly to each scrubber's sump, although
some of these
locations are more desirable than others, as discussed in the embodiments
above.
[0086] Figure 5 illustrates a flow diagram for a system for adding an oxidizer
to one or
more gas/liquid contactors or scrubbers. A feed tank 502 is used to hold the
oxidizer, which
may include hydrogen peroxide or another oxidizer such as chlorine gas, sodium
hypochlorite, hypobromous acid, chlorine dioxide, hydrogen peroxide, peroxy
acids, ozone,
and permanganate. The feed tank 502 may also have a level controller 504 that
functions to
provide an alert when the tank level is low and additional hydrogen peroxide
and/or water is
required. It should be appreciated that certain additives, including any of
the additives
described such as a biocide (with the exception of a decomposition additive if
hydrogen
peroxide is used as the oxidizer) may also be added to the feed tank 502
provided they are
chemically compatible with an oxidizer, such as hydrogen peroxide, so that
their chemical
activity is not lost prior to being added to the scrubber. It should also be
appreciated that the
system of Figure 5 can be used in conjunction with the system of Figure 4 and
further in
conjunction with a pH control loop.
[0087] The feed tank 502 is fluidly connected to a distribution pump 506 that
is fluidly
connected to each scrubber's recycle line via a flow control valve 508 at the
desired location
along each recycle line. One desired location for distributing the oxidizer
from the feed tank
502 to each recycle line may be upstream of each scrubber's recycle pump. It
should be
appreciated, however, that the point of addition to each scrubber may vary
from scrubber to
scrubber and may include points other than the recycle line or other or
additional points along
26
CA 2997487 2018-03-06
the recycle line. In other words, the oxidizer may be added to different
locations along each
scrubber's recycle line or at different points for each scrubber, such as each
scrubber's sump.
[0088] In operation, the addition rate of the oxidizer from the feed tank 502
to each recycle
line of each scrubber may be controlled in various manners. In some
embodiments, the
addition of the oxidizer is simply set a given feed rate for each scrubber
using the flow
control valve 508. In other embodiments, different solution parameters could
be monitored
and used to control the addition rate of the oxidizer from the feed tank 502
by the flow
control valve 508. As noted above, oxidation reduction potential, the
concentration of the
decomposition additive or a particular chemical species indicative of the
concentration of the
additive, the concentration of gaseous species absorbed by the scrubber, or a
combination of
these could be monitored and used to control the addition rate of the oxidizer
from the feed
tank 502. Of course, the concentration of the oxidizer will need to be
accounted for in
determining its addition rate to each scrubber or vice versa.
[00891 It should be appreciated that using a flow control valve 508 allows for
more precise
control of the flow rate to each scrubber, as opposed to a simple on/off
valve. Particularly, by
monitoring a given solution parameter in the recycle line the composition of
the solution that
is contacting the gas stream is better known than, for example, monitoring the
solution in the
sump. Further, by adding the oxidizer directly to the recycle line based upon
the results of
monitoring of the solution in the recycle line allows the recycle line
chemistry to be properly
controlled or adjusted just prior to entering the scrubber. This allows for
more optimal
control of the removal of the odorous and/or noxious components. However, it
should be
appreciated that in one embodiment it is desirable to simply set the addition
rate of the
oxidizer to a given, constant value and to adjust the addition rate of any
additives (e.g., a
decomposition additive in the case of using hydrogen peroxide as the oxidizer)
accordingly.
[0090] Optionally, any make-up water required for each reservoir may also be
added to the
feed tank 502 (not shown). In this case, the dilution effect of any water
added to the feed
tank 502 must be taken into account so that the desired amount of each
additives and acid or
base are ultimately added to each recycle line. In addition, the water make-up
needs of each
sump, to the extent that they are different, must be taken into account. In
other words, a
water balance must be achieved for the overall system, which will also impact
the amount of
water in the feed tank 502, as discussed above. Alternatively, make-up water
may be added
directly to each scrubber's sump.
[0091] As mentioned above, liquid discharged from each scrubber's sump, as
shown, for
example, in Figure 1 by the discharge line 120, also offers advantages as in
influent to the
CA 2997487 2018-03-06 27
wastewater treatment process. For example, when using ferrous sulfate as the
additive to
catalyze the decomposition of the hydrogen peroxide, the discharge from each
scrubber's
sump can be passed to a wastewater treatment facility, for example, by dumping
the entire
liquid content of the sump or by continuous overflow from the sump or recycle
line, and this
stream will have been effectively "pretreated" by cationic ferric hydroxide
complexes that
offer effective colloidal charge neutralization as well as the ability to
adsorb wastewater
constituents into its floc matrix. The addition of a charge
neutralizing/adsorption species is
always an added cost at the wastewater treatment plant, which may be
accordingly be
eliminated or greatly reduced.
[0092] Figure 6 illustrates a flow diagram for the connection between a
scrubber system
and a wastewater treatment system. Figure 6 illustrates a scrubber system 602
according to
any of the embodiments described above. Liquid discharge 604 from the scrubber
system
602, such as liquid discharge 120 shown in Figure 1, is passed by a common
wastewater line
606 to a wastewater treatment facility 608. As earlier described, the liquid
discharge from
the scrubber system 602 may include an entire dump of the scrubber sump or may
be a
continuous overflow of liquid from the scrubber sump, depending upon operating
conditions.
[0093] Wastewater 610, 612 from other process areas 614, 616 of the plant,
such as wash
and rinse waters, chicken feather processing waters, rendering cooker waters,
etc., may also
be added to the common wastewater line 606. All of the wastewaters added to
the common
wastewater line 606 are sent to the wastewater treatment facility 608 where
the wastewaters
are treated as necessary.
[0094] When the wastewater enters the wastewater treatment facility 608,
however, the
wastewater is effectively "pre-treated" as the discharge from the scrubber
sump may contain
metal hydroxide complexes, for example, cationic ferric hydroxide complexes,
that offer
effective colloidal charge neutralization, as well as provide for adsorption
of wastewater
constituents into its floc matrix. While some of the complexes are utilized by
the components
of the discharge from the scrubber system 604, a residual amount of these
complexes are also
available to react with components in other wastewaters 610, 612 combined with
the
discharge from the scrubber 604. As wastewater treatment facilities typically
purchase
additives to accomplish these results, the addition of these charge
neutralizing and adsorption
species eliminates or greatly reduces any costs incurred by the waste
treatment facility 608.
[0095] The present invention has been described above with reference to
removal of odor
and/or noxious components from an atmospheric effluent in which the oxidized
odor and/or
noxious components are oxidized during contact with an aqueous hydrogen
peroxide
CA 2997487 2018-03-06 28
composition to produce a substantially non-odor offensive, environmentally
acceptable
byproduct that is solubilized in or adsorbed onto the aqueous hydrogen
peroxide composition
to form a liquid effluent, and the advantages of such a system provided to
wastewater
treatment processes. The present invention also has application in other areas
of processing
plants as an effective biocide, especially in areas related to aqueous food
transport flumes.
[0096] Food primary and secondary processing involves the handling of large
amounts of
organic materials. As a result of the amount of organics being processed,
biological activity
is inevitable. In fruit and vegetable processing, large amounts of water are
used to wash and
transport food through the various processing steps. Because of the buildup of
organic
matter, the transport and wash waters are very prone to biological growth, as
well as
accumulation of toxic organic materials such as herbicides and pesticides. A
need exists to
provide microbial control of these waters without imparting further toxic
products to the
aqueous food contact streams. Also needed is an economical method for
eliminating or
reducing the buildup of toxic herbicides and pesticides in the food transport
system.
[0097] Attempts in the art have been made utilizing oxidizing compounds such
as chlorine
gas, sodium hypochlorite, hypobromous acid, chlorine dioxide, hydrogen
peroxide, peroxy
acids, ozone, and permanganate. While some are effective in limiting microbial
growth,
either toxic byproducts, cost, or inefficiencies are limiting factors.
[0098] Particularly, the use of chlorine and chlorine dioxide, while effective
antimicrobial
agents, has come under environmental scrutiny due to the toxic byproducts it
produces.
When contacted with amines, toxic chloramines are formed, as well as
trihalomethane
compounds, which are now prevalent in most ground waters in the United States.
Chlorine-
based technologies also use large quantities of these materials, as they are
rapidly consumed
by the high organic loading of the aqueous media before they can impart
antimicrobial
properties. Hypobromous acid produced by the decomposition of sodium bromide
by
chlorine has been used with some success, but it too is affected by high
organic loading and
the chlorine substrates, which, while reduced, still impart the same
toxicities as hypochlorous
acid.
[0099] Hydrogen peroxide has been used with limited success. Hydrogen peroxide
is a
slow reacting compound with known antimicrobial properties. The reaction rates
are too
slow for effective, cost advantageous microbial control. Peroxy acids such as
peracetic acid
have proven to be effective antimicrobial compounds in aqueous systems.
Peracids are
usually manufactured by the combination of hydrogen peroxide, acetic acid, and
inorganic
acid catalyst, and various wetting and sequestering agents. Peracetic acid is
normally
CA 2997487 2018-03-06 29
provided in 5 to 15% peracetic acid concentrations. These peracid compounds
contain large
amounts of the manufacturing precursors, such as hydrogen peroxide, and acetic
acid. These
peroxy acid materials have a strong pungent odor and residual acetic acids are
toxic by
ingestion or exposure at 1 Oppm in misted form. Peroxy acids are also limited
in use by the
high costs that are associated with it. Ozone has found limited use in aqueous
food transport
and processing streams. Ozone is an effective biocide and its high
electronegativity is
capable of breaking down selected organic compounds. Ozone is associated with
extremely
high capital investments cost, and the efficiency is limited by poor transfer
coefficients from
the generated ozone gas phase to the liquid media being treated.
[00100] Use of the present invention, however, in which an aqueous hydrogen
peroxide
composition of hydrogen peroxide decomposed by ozone is contacted with the
transport
waters, results in an effective biocide. This allows sterilization of food
transport waters with
no toxic byproducts. Further, in food transport flumes, regulation of the
ozone can also break
down accumulated pesticide and herbicide compounds from fruit and vegetable
washing into
simple non-toxic carboxylic acids. Accordingly, this technology offers
significant cost and
efficiency advantages over current technologies.
EXAMPLES
[00101] The following examples describe specific aspects of the present
invention to
illustrate the invention and aid those of skill in the art in understanding
and practicing the
invention. The examples should not be construed as limiting the present
invention in any
manner.
Example #1
[00102] A 1000 ml sample of chicken feather processing scrubber water having a
pH of 5.5
due to sulfuric acid addition in the scrubber reservoir was evaluated. The
sample had an
intense odor after treatment with chlorine dioxide. The sample was treated
concurrently with
300 ppm of hydrogen peroxide (50% solution) and 100 ppm ferrous sulfate (38%
solution).
The reaction was instantaneous, and there was no detectable odor, other than a
slight chlorine
smell.
Example #2
[00103] A 1000 ml sample from a rendering cooker was adjusted to pH 5.5 with
sulfuric
acid. The sample had a very intense odor. The sample was treated concurrently
with 300
ppm of hydrogen peroxide (50% solution) and 100 ppm ferrous sulfate (38%
solution). The
CA 2997487 2018-03-06 30
reaction was instantaneous, and the odor was eliminated within 15 seconds. The
sample was
then undisturbed for 48 hours, and there was no re-occurrence of any odor.
Example #3
[00104] A five gallon sample from a rendering cooker was adjusted to p1-1 5.5.
The sample
was recirculated at 10 gpm through a Burks regenerative turbine pump throttled
by pinch
valve assembly to 100 psi. Hydrogen peroxide was introduced into the suction
line at 300
ppm. Ozone as a 6% gas stream generated by a corona discharge type ozonater on
dried air
was added into the air inlet for the Burks pump (suction side). The ozone dose
was 10 ppm
as ozone. The sample was recirculated for 2 minutes, and odors were completely
neutralized.
The sample was then un-aerated and undisturbed for 48 hours, and there was no
re-
occurrence of any odor.
Example #4
[0100] A trial was performed at a mixed proteins rendering plant that used
chlorine dioxide
in a scrubber to reduce VOC emissions by 88%. In this system, the pH was
reduced to pH
5.5 with sulfuric acid. 300 ppm of hydrogen peroxide (50% solution) and 100
ppm ferrous
sulfate (38% solution) were added concurrently. As a result, VOC emissions
were reduced
by 96%.
[0101] In the above examples, odor reduction was measured using the sense of
smell and
VOC emission measurements using standard emission detectors. It will be
appreciated that
various other devices and measurement techniques may also be used that conform
to standard
practices as may be required for a particular processing industry.
Example #5
[0102] A pilot plant test using hydrogen peroxide decomposed by ozone was
conducted to
evaluate microbiological control. The test or run was performed using 100
gallons and a
Pennsylvania apple wash/transport flume with the following characteristics:
BOD = 900
ppm, COD = 2100 ppm, and a significant amount of large organic matter. The
material was
recirculated for 36 hours and the following data was collected: bio count via
dip slide = 109,
filtered BOD (0.45 micron) = 685 ppm, filtered COD (0.45 micron) = 1725 ppm.
[0103] 300 ppm hydrogen peroxide (50% solution) was added, and ozone was added
at 10
ppm into a regenerative turbine pump used to recirculate solution. When the
addition of
hydrogen peroxide and ozone was completed the addition was stopped. The
following bio
count in colonies was observed: @ t=4 min bio count = 102, @ t= 10 min bio
count = none
detected, @ t = 8 hours bio count = none detected, @ t= 12 hours bio count =
10, and @ t=
CA 2997487 2018-03-06 31
18 hours bio count = 102. Additional data included: filtered BOD = 210 ppm and
filtered
COD = 720 ppm.
[0104] As can be seen by this test, microbial control was excellent with good
sustained kill
of biopopulation. The lowering of the COD showed decomposition of organic
material in the
sample water. Analysis for toxicity indicated a sharp drop.
CA 2997487 2018-03-06 32
