Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS AND METHOD FOR THE TREATMENT OF ODOR AND VOLATILE
ORGANIC COMPOUND CONTAMINANTS IN AIR EMISSIONS
BACKGROUND OF THE INVENTION
[0001] Field: The invention is in the field of treating emission gases from
commercial
and industrial processing wherein the gases used for such activity contain
odors and/or volatile
organic compound contaminants and/or hydrocarbon compounds, some of which are
considered to
be pollutants, and need to be removed from the gas before release of the gas
to the atmosphere, and
wherein the removal systems include non-thermal plasma (NTP) generation cells.
(0002] State of the Art: Odorous compounds, which could be organic or
inorganic,
herein called odors, and/or volatile organic compound (VOC) contaminants
andlor hydrocarbon
compounds herein called VOCs, emitted into the environment from a range of
sources and processes
can fill the air in and about residential neighborhoods. Such odors and/or
VOCs can range from
mildly offensive to intolerable levels. This is a common problem in areas that
are in proximity to
such sources. Examples of odorous sources include industries that process
organic materials such as
those that process and produce food for human consumption and industries that
produce animal feed
for the pet, fish, poultry and hog industry, and general agricultural
applications. Other industries that
process organic materials and release odors are those that process animal
products including meat
processing and rendering plants. Other organic odor sources include composting
facilities, sewage
treatment centers, garbage transfer stations and other industrial organic
processing facilities.
Generally, these industrial operations exhaust gases from cooking, grinding,
drying, cooling,
manufacturing, or reduction processes. These exhausts contain low-level
concentrations of amines,
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aldehydes, fatty acids, and volatile organic compounds (VOCs) inherent in the
materials processed
and those are driven into the exhausted gas stream by the processing activity.
These industries
typically have large gas flow volumes, ranging from 1,000 to 250,000 actual
cubic feet of gas per
minute (ACFM) and above.
[0003] Agricultural activities that raise animals for food production, such as
hog, poultry
and dairy farms also emit strong and offensive odors into the environment from
manure and barn
ventilation odors and these can release offensive odors in sufficient quantity
to fill many square
kilometers under certain weather conditions.
[0004] Additional sources of environmental emissions exist that expel VOCs
from non-
organic processing, such as solvent evaporation from painting, cleaning, and
other general industrial
and commercial activities. Some VOCs may have little or no odor, but are
considered atmospheric
pollutants and/or carcinogens and need treatment to reduce them to harmless
compounds. In the case
where odors and VOCs are very potent, even concentrations in the parts per
billion ranges can be
offensive or exceed environmental emission limits and these also need
treatment.
[0005] There are various systems designed to oxidize and/or reduce odorous and
VOC
emissions in commercial and/or industrial process gas that is to be emitted
into the environment so
that the emitted exhaust gas stream is within environmental regulatory limits.
Some of these systems
use non-thermal plasma (NTP) which is formed in dielectric barrier discharge
(DBD) cells to create a
wide range of activated species such as activated or Reactive Oxygen Species
(ROS) that are then
mixed with the gas to be treated so that the organic compounds that humans
normally detect as odor,
andlor V OCs, are oxidized andlor reduced, typically to carbon dioxide and
water vapor, though other
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products are possible depending on the chemical characteristics of the
pollutants, by the energetic
ions in the ROS.
[0006] Activated species, as described herein, are chemical entities that are
created in
useful concentrations by the application of sufficient energy, such as through
dielectric barrier
discharge, to drive the molecules of interest from the ground state into the
active state required, with
the ground state being the normal state of these molecules typically at a
nominal one-atmosphere
pressure and 20 degrees C (or whatever atmospheric and temperature conditions
occur at the place of
the odor, VOC, and/or organic compound emissions). Activated species are
typically designated in
literature by "~" as in O~ for active oxygen (atomic oxygen in this case).
Activation occurs through
a number of mechanisms including direct electron collisions or secondary
collisions, light
absorption, molecular processes involving ionization, or internal excitation.
[0007] Dielectric Barrier Discharge (DBD) technology has been used to create
the NTP
that generates the activated species required for the purposes of this
invention, and as such
technology inherently limits the eV that can be applied to the gasses passing
through the barrier, it is
mainly the Reactive Oxygen Species (ROS) which include a range of hydroxyl
radicals, that are
involved in this case, though other electron activity assists in the process.
For the activated species
generated in the NTP field, those ROS species that have the highest reduction
potential (between
about 2.4 and 5.2 eV) have the shortest availability with half life
concentrations of less than about
100 milliseconds. These react with the odorous molecules that need high
reduction potential
oxidizers for decomposition. These high reduction potential radicals, and the
reactions between
these particles and the odorous molecules reacting with them, occur only in
the NTP field, as these
radicals quickly decay to less active species outside the NTP field. These
radicals react with the
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odorous molecules by oxidation and reduction transformations so that the
odorous molecules are
transformed to simpler molecular forms that are no longer detectable as odor.
Additional activity
occurring within the NTP is that of electron collisions, bombardment and
direct ionization, which
acts on all molecules within the field, including the compounds of concern.
This electron action, as
well as creating the ROS of interest, also results in the disruption of the
molecular bonds of the odor
and/or VOC compounds, which also aids in the ROS activity of oxidation and/or
reduction of the
odor and/or VOC compounds. The NTP field also creates, within the ROS, a range
of lower
reduction potential radicals (between about 1.4 and 2.4 eV), and these are
longer lived with half lives
from about 100 milliseconds to several minutes. These radicals react with the
odorous molecules
that respond to this level of reduction potential and oxidation for
decomposition. These reactions
occur both in the NTP field and in the air stream outside the NTP field, as
those radicals are active
longer and are carried outside the NTP field by the airflow through the DBD.
These longer-lived
radicals also effect their changes on the odorous and/or VOC compounds by
oxidation and reduction
transformations, so that the compounds of concern are transformed to simpler
molecular forms that
are no longer detectable as odor. Such transformations also ultimately convert
the complex organic
molecules and hydrocarbon molecules into the most simplified oxides, such as
carbon dioxide,
hydrogen dioxide (water), nitrogen (N2) and other simplified oxide forms of
the elements that were
in the original complex compounds.
[0008] Four oxidation states of molecular dioxygen are known: [02]" , where n
= 0, +1, -
1, and -2, respectively, for dioxygen, dioxygen cation, superoxide anion, and
peroxide dianion
(symbolically expressed as 302, 302 +, 302 ~ , and 3O2 Z ). In addition,
"common" oxygen in air, 302 ,
is in a "ground" (not energetically excited) state. It is a free "diradical"
having two unpaired
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electrons. The two outermost pair of electrons in oxygen have parallel spins
indicating the "triplet"
state (the preceding superscript "3", is usually omitted for simplicity).
Oxygen itself is a common
terminal electron acceptor in biochemical processes. It is not particularly
reactive, and by itself does
not cause much oxidative damage to biological systems. It is a precursor,
however, to other oxygen
species that can be toxic, including: superoxide anion radical, hydroxyl
radical, peroxy radical,
alkoxy radical, and hydrogen peroxide. Other highly reactive molecules include
singlet oxygen, l0,
and ozone, 03.
[0009] Ordinary oxygen does not react well with most molecules, but it can be
"activated" by the addition of energy (naturally or artificially derived;
electrical, thermal,
photochemical or nuclear), and transformed into reactive oxygen species (ROS).
Transformation of
oxygen into a reactive state from the addition of a single electron is called
reduction (Eqn. 1 ). The
donor molecule that gave up the electron is oxidized. The result of this
monovalent reduction of
triplet oxygen is superoxide, 02 ' '. It is both a radical ( ' , dot sign) and
an anion (charge of -1).
Other reactive oxygen species known to be created with NTP, are noted below:
(On the Ionization of
Air for Removal of Noxious Effluvia [Air Ionization of Indoor Environments for
Control of Volatile
and Particulate Contaminants with Nonthermal Plasmas Generated by Dielectric-
Barner Discharge]
Dr. Stacy L. Daniels, IEEE Transactions on Plasma Science, Vol. 30, No. 4,
August 2002):
02 + e~ OZ~ - (Eqn 1 )
2 OZv + 2I-I + -~ H20z + 02~ (Eqn 2)
OZ._ + HZOa ~ OZ + OH . + OH_ (Eqn 3)
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02~' + 2 H20 ~ 02 + H OZ~ -+ OH-' (Eqn 4)
2 O2~' + 02 + H20 -~ 2 02 + OH-+ OH~ (Eqn 5)
[0010] For any given reactive oxygen species (ROS), there exists some
confirmed or
postulated reaction scheme for inter conversion to any of the other species.
In any event, several of
the above reactive oxygen species may be generated in the NTP and react with
odorous molecules to
transform them into simpler molecules that are no longer detected as odorous.
[0011] Commercial and industrial volumes of contaminated gases to be treated
normally
have contaminants such as condensing water or other vapors and liquids,
particles of some kind, or
mixtures of both condensing fluids and particles. A problem arising from the
use of dielectric barrier
discharge (DBD) cells, generating the NTP for treating industrial scale flows
of contaminated gases,
is that after a period of use, sometimes only a matter of minutes, the
contaminants inherent in these
gases build up in the cells and cause electrical short circuits in the cells
from hot electrodes, across
the insulation and support frames, to the ground electrodes. Of course, this
interferes with the
designed electrical properties of the DBD cell and immediately destroys any
ability for the DBD cell
to generate the NTP. In this case, it is very likely DBD cell component damage
has occurred as
electrical arcs have very high temperatures and parts are usually damaged that
have been in contact
with the arc, and at the very least, cleaning of the DBD cell is necessary to
restore the electrical
dielectric integrity of the DBD cell, and damaged parts must be replaced.
SUMMARY OF THE INVENTION
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[0012] According to the invention, a dielectric barrier discharge (DBD) cell
used to create
non-thermal plasma (NTP) particularly useful as part of apparatus for treating
odorous gases and
gases containing volatile organic compounds (VOCs) includes electrodes
positioned within the cell
to confine the area of NTP generation to keep the NTP away from the support
frames and terminals
for the electrodes so the frames do not suffer damage from the NTP and the
terminals do not short
out. Further, at least the portions of at least the hot electrodes in the cell
where the contaminated
gases to be treated pass over or along such electrodes are hermetically sealed
so contaminants in the
gases do not contact and build up on the "hot" electrodes. Further, the gas
treating apparatus of the
invention may be configured so that with gases that can be treated
satisfactorily with relative low
energy activated species, atmospheric air is passed through the NTP to
generate the activated species
and that air is then mixed with the gas to be treated where the longer lasting
activated species react
with the odorous molecules in the gas to treat the odor. With harder to treat
gases, some or all of the
gas to be treated passes through the NTP where the electron activity in the
NTP field and the shorter
lived, stronger energy activated species both act on the gas molecules to be
treated. Generally larger
capacity cells for generating NTP are necessary when all gas to be treated is
passed through the cells.
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'The NTP Generation Cells
[0013] The DBD cells that generate the NTP, hereinafter referred to as DBD
Plasma
Generation Cells (PGC), or as DBDPGC, are planar in design and utilize two
types of stainless steel
electrodes or other conductor, where the thickness of the conductor ranges
from a few microns up to
8 mm or even more, the height ranges from 10 mm up to 1000 mm or more, and the
length ranges
from 200 mm up to 2000 mm or more. There are two types of electrodes within
the DBDPGC's,
namely the "hot" electrodes, which have the high voltage connected to them and
the "ground"
electrodes, which are at ground potential, but can also be insulated and at a
different phase for extra
potential. The "hot" electrodes and the "ground" electrodes are shaped
differently so that the NTP is
isolated in the center and can only form in the area away from the electrode-
supporting frame.
1. The "hot" electrodes are totally enclosed in a high dielectric, chemically
resistant and high
thermal resistance material, typically a ceramic material, such as
borosilicate glass and must
be sealed to ensure electrical isolation of the electrically conductive part
within the "hot"
electrode from the external environment of the ceramic surface and maintain
the dielectric
barrier. The seal of the "hot" electrodes within the dielectric isolation
plates can be either
high dielectric strength silicone, or the entire plate can be totally enclosed
in a ceramic
bonded directly to the conductor (except for the electrical connection to the
conductor).
2. The ground electrodes are polished smooth and without burrs or high points
that might
concentrate the NTP and are usually uninsulated. In some cases, they are
insulated almost
exactly the same as the "hot" electrodes.
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3. Each "hot" electrode has a ground plate facing it, spaced so that the
surface of the electrode
has a distance anywhere from 2 mm up to 25 mm or more, from the dielectric
surface of the
"hot" electrode. It is within this space where the NTP forms when the power is
applied to the
electrodes. The shaping of the "hot" and "ground" electrodes is such that no
NTP can form
near the support frame, while the spacing between plates is dictated by the
airflow through
the DBD and the differential pressure across the DBDPGC permitted.
The Electrical Activation of the DBDPGC's
[0014] The NTP within the DBDPGC forms with the application of high voltage
alternating current between the "hot" and ground electrodes. This AC voltage
needs to be anywhere
from about 4,000 volts up to and above about 100,000 volts and at medium
frequency, anywhere
from about 50 Hz up to about 50,000 Hz depending on the application, cell
geometry, and spacing.
[0015] The DBDPGC's are housed in a Plasma Containment Cabinet, which is
usually
stainless steel, but can be any other steel that can be securely grounded. All
high voltage
components are totally enclosed in this grounded cabinet to meet standard
industrial safety codes.
The DBDPGC's are normally grouped in sets of three and are powered by a three
phase power
supply.
Electrical Design
[0016] The three phase, high voltage, medium frequency power required by the
BDBPGC's to create the NTP is provided by step up transformers, installed
inside the cabinet where
the BDBPGC's are. Normally the transformers have a primary voltage near that
used by a typical
industrial motor (480 volts, 3 phase).
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[0017] An industrial invertor or mid frequency SCR power supply or other
suitable AC
power supply that can deliver the required frequencies, waveforms, voltage,
and current, located in a
separate control cabinet, powers the DBDPGC transformers. The voltage and
frequency applied to
the DBD, which controls the power level developed in the DBD, is varied by the
width and
frequency of the pulses in the case of a simple IGBT invertor, or by phase
angle or duty cycle control
in the case of an SCR supply, or by a changing frequency in the case of a
swept frequency IGBT
supply that seeks the resonance or off resonance of the DBD capacitance and
high voltage
transformer inductance, or by other means, and this voltage frequency
combination is delivered to the
high voltage transformer primary windings and this in turn adjusts the voltage
produced by the high
voltage transformer secondary windings, which is then applied to the DBDPGC,
which has the
effect of adjusting the level of the NTP produced in the DBD. Typically, a
closed PID control loop
that monitors the actual power output of the invertor is measured and
controlled to a power level
setpoint that can be cascaded from another control loop from an ozone sensor,
or the setpoint can be
manually entered.
[0018] Small units are usually single phase devices. These are, typically, but
not limited
to, 2 kilo volt amps (kva) and under. Larger units, up to and exceeding 250
kva, are typically three
phase systems, though they can also be three phase input and single phase
output. On a three phase
system, the power supply used can be a modified three phase Variable Frequency
Drive (VFD) motor
inverter power section (three phase bridge rectifier, capacitor, and IGBT), if
the VFD chosen can run
a transformer load in unbalanced mode and can attain the wave shape and
frequency required. In the
case where a three phase inverter output is used, it is connected to three
inductor/transformer groups
with the primary side of the transformers wired in delta arrangement. The
transformer high voltage
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secondary connections are wired in a center grounded wye configuration. The
ground electrodes are
connected to the center ground in most cases. In the case where other power
alternatives are used
and those have a three phase power input and a single phase power output,
usually a single high
voltage transformer is used, with one side of the high voltage secondary tied
to ground potential and
the ground electrode of the DBDPGC, while the high voltage side is connected
to the "hot"
electrodes of the DBDPGC.
THE DRAWINGS
[0019] In the accompanying drawings, which show the best mode currently
contemplated
for carrying out the invention:
[0020] Fig. 1 is a side elevation of an apparatus of the invention with the
upper side wall
removed to show interior parts;
[0021] Fig. 2, a vertical section taken on the line 2-2 of Fig. 1;
[0022] Fig. 3, a vertical section taken on the line 3-3 of Fig. 2 through the
side opposite
that shown in Fig. 1;
[0023] Fig. 4, a horizontal section taken on the line 4-4 of Fig. l;
[0024] Fig. 5, an exploded perspective view of a dielectric barrier discharge
NTP
generation cell (DBDPGC) housing showing how two of the electrodes would be
positioned in the
housing;
[0025] Fig. 6, a top plan view of a DBDPGC;
[0026] Fig. 7, a vertical section through the DBDPGC housing showing an
electrode in
elevation and a second electrode in broken lines; and
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[0027] Fig. 8, a fragmentary vertical section taken on the line 8-$ of Fig. 7,
but showing
only a few of the adjacent electrodes.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
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[0(128] A preferred apparatus of the invention includes a housing that forms
at least one
gas flow passage therethrough and a dielectric barrier discharge NTP
generation cell (DBDPGC)
through which at least a portion of gas flows. The apparatus can be configured
so that all of the
contaminated gas to be treated flows through the DBDPGC, only a portion of the
contaminated gas
to be treated flows through the DBDPGC, or none of the contaminated gas to be
treated flows
directly through the DBDPGC, but atmospheric air flows as the gas through the
DBDPGC and is
then mixed with the contaminated gas to be treated to treat that gas. The gas
passing through the
DBDPGC is activated so that the activated gas from the DBDPGC, when mixed with
gas that has not
passed through the DBDPGC, treats the gas that has not passed through the
DBDPGC. In instances
where less than all of the contaminated gas to be treated flows through the
DBDPGC, a mixing
chamber is included in the apparatus to mix the gas that flows through the
DBDPGC with the
contaminated gas that does not flow through the DBDPGC. Figs. 1-4 show a
preferred apparatus
wherein all of the contaminated gas to be treated, only a portion of the
contaminated gas to be
treated, or atmospheric air is passed through the DBDPGC and, if less than all
gas to be treated is
passed through the DBDPGC, the gas passing through the DBDPGC is then mixed
with the
contaminated gas to be treated that has not passed through the DBDPGC to treat
that gas. As
specifically configured and shown in Figs. 1-4, the apparatus passes
atmospheric air through the
DBDPGC and then mixes such treated atmospheric air with the contaminated gas
to be treated. The
advantage of treating either atmospheric air or only a portion of the
contaminated gas in the
DBDPGC is that less gas flows through the DBDPGC and is treated directly in
the DBDPGC
meaning that the size and air flow capacity of the DBDPGC does not need to be
as great as when all
gas to be treated flows directly through the DBDPGC. This is the usual
configuration when the
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contaminants are of a low concentration in a large gas flow stream, so that
the system component
sizing is determined by the amount and type of contaminant needing to be
treated, rather than the
total gas flow involved. In the case where the contaminant is more
concentrated, or needing higher
eV energy to oxidize and/or reduce the components of concern, or of a
sufficiently low volume, then
all gas can pass through the NTP field to take advantage of the higher
electrical efficiency realized
when all gas passes through the NTP field.
[0029] As shown in Figs. 1-4, the apparatus includes a main flue 20, adapted
to be
connected at an inlet end 21 to the source of contaminated gas to be treated,
such as odorous exhaust
gas emanating from a pet food dryer. The flue 20 forms a mixing chamber 22 for
mixing gas that
passes through the DBDPGC with the gas to be treated flowing in flue 20. A
housing or cabinet 23
supports and completely encloses the high voltage and DBDPGC components of the
apparatus. The
low voltage electrical components and controls, including the power supply,
are housed in a separate
standard electrical cabinet. Atmospheric air enters the apparatus through
inlet 24, and flows as
shown by arrow 25 in Fig. 2 through filter 26 and DBDPGC's 27. During such
flow, the air passes
around transformers 30, supported by brackets 31, Fig. 2, secured to and
extending from wall 32, to
cool the transformers. Immediately after passing through DBDPGC's 27, the air
flows into mixing
chamber 22 where the air mixes with the contaminated gas flowing through the
chamber as
represented by arrow 35, Fig. 1. The air from mixing chamber 22, Fig. 2,
passes into an exhaust
flue, not shown, connected to outlet end 36 of flue 20, for discharge to the
atmosphere. Mixing of
the gases will continue through the exhaust flue. Generally a fan will be
provided in the exhaust flue
to draw the gases through the DBDPGC's and mixing chamber. The apparatus shown
includes three
DBDPGC's 27, Fig. 4, mounted side-by-side to handle the air flow through the
apparatus. Divider
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walls 37 form individual inlets for the respective DBDPGC's. Wall 32 has
openings 38 therethrough
so that the DBDPGC's 27 can be slid into place or removed, 27a, Fig. 2, for
maintenance. The front
of cover 23 is removable, and interlocked to disable power, to provide access
to the transformers and
allow removal of the DBDPGC's as shown in Fig. 2. DBDPGC 27a is a DBDPGC 27
during
removal. Wall filler 39 blocks opening 38 above DBDPGC 27.
[0030] T'he housing or cabinet 23 may be made of various materials, to be
compatible
with the process gas, but preferably of electrically conductive material such
as stainless steel or other
steel that can be securely grounded. All high voltage components are totally
enclosed in this
grounded cabinet to meet applicable industrial safety codes.
[0031] Flow of air through inlet 24 and through DBDPGC's 27 is controlled by a
pair of
slatted plates 40 and 41, Figs. 2 and 4, which slide over one another to open
or close the passageway
from inlet 24. As shown in Fig. 4, the slats 41 are positioned directly over
slates 40 so that slats 40
are not visible under slats 41, and the maximum flow openings 42 are created
for maximum air flow.
Sliding slats 41 over slats 40 will close flow openings 42 to any desired
degree to adjust the air flow
through the DBDPGC's.
[0032] To ensure substantially equal air flow through each of the DBDPGC's and
to
provide for good mixing of air from the DBDPGC's with the contaminated gases
to be treated,
baffles 45, 46, and 47, Fig. 3, are adjustably secured in mixing chamber 22 by
brackets 48. The
baffles are pivotally secured at their mounting ends by pins 49 and can be
rotated about the pivot to
the extent allowed by bracket slots 50. A pin or stop extends from each baffle
into respective slots
50. The baffles are of different lengths, with the longest baffle 45 located
at the inlet end of the
mixing chamber, and are adjusted to provide substantially equal air draw for
each DBDPGC 27. The
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flaps also cause turbulence in the exhaust gases flowing through the mixing
chamber and guide the
air from the DBDPGC's into the exhaust gas stream to provide better mixing.
[0033] Rather than passing atmospheric air into inlet 24 and through DBDPGC's
27, with
the apparatus shown in Figs. l-4, it is easy to split the contaminated gas
stream to be treated to direct
a portion of the contaminated gas to be treated to the inlet 24, rather than
drawing in atmospheric air,
or in addition to atmospheric air. Such gas to be treated is passed directly
through the DBDPGC's
and is then mixed with the remainder of the gas to be treated in the mixing
chamber.
[0034] Also, all contaminated gas to be treated can be directed to inlet 24
with the inlet
21 to flue 20 blocked. Thus, all gas to be treated is passed into inlet 24 and
passes though the "hot"
and "ground" electrodes of a DBDPGC, so substantially all such gases are
exposed directly to the
NTP generated by the DBDPGC's. Flue 20 does not act as a mixing chamber in
this configuration in
the same way it does in the configurations previously described. Alternately,
the DBDPGC's could
be mounted in flue 20 so that all gas entering flue 20 through inlet 21 would
pass directly through the
DBDPGC's. In such case, inlet 24 would be blocked or the apparatus would be
configured to
eliminate inlet 24. As previously indicated, in the configuration of Figs. 1-
4, the gases entering inlet
24 pass around transformers 30 to cool them. The gasses passing through the
DBDPGC's also serve
the important function of cooling the electrodes of the DBDPGC's. Thus, when
the gases to be
treated are passed directly through the DBDPGC's, care must be taken to ensure
that the required
cooling of the components needing cooling takes place. Where the contaminated
exhaust gases to be
treated are hot, adequate flow must be provided for cooling or the
contaminated exhaust gases may
need some cooling prior to treatment. Components such as the transformers 30
can be moved out of
the gas stream and located elsewhere for cooling.
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[0035) In general, the configuration that passes all gas to be treated through
the
DBDPGC's is more efficient in terms of energy required to neutralize the odor
molecules and the
organic compounds in the gas to be treated, as the electron activity in the
NTP field assists in
breaking the molecular bonds of the compounds of concern by direct ionization
and the extremely
short lived, higher energy radicals, those with half lives of 100 micro
seconds or less, are available to
effect the oxidation and reduction of the odor molecules and the organic
compounds. In the bypass
or partial bypass modes, the direct ionization of the gas to be treated does
not occur and the short
lived radicals have decayed and are not assisting with the oxidation and
reduction of the odor
molecules and organic compounds in the mixing chamber. In cases where the gas
to be treated needs
unusually high energy to be oxidized and/or reduced, such as in exhaust gases
that would otherwise
have to be incinerated to treat the gas, all of such gas must pass directly
through the NTP, as it is
only within the NTP where the direct ionization occurs and the ROS with the
highest energy levels
are developed and can oxidize and reduce those compounds that need these
conditions to disrupt the
bonds that need a higher energy level to oxidize and/or reduce them.
[0036) While the actual treatment of the gas to be treated may be more
efficient in terms
of energy required to neutralize the odor molecules and the organic compounds
in the gas when all
gas is passed through the DBDPGC's, large volumes of gas would require large
numbers of
DBDPGC's to provide the capacity necessary to pass all gas to be treated
through the DBDPGC's.
Thus, in such instances, and where all the gas to be treated does not
necessarily need to pass through
the NTP field to be effectively treated, a smaller amount of atmospheric air,
or a smaller portion of
gas to be treated, can be passed through a fewer number of DBDPGC's and such
gas then used to
treat the remaining gas by the mixing described.
1?
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[0037] Each of the DBDPGC's 27 includes a rectangular frame 55, Figs. 5-8,
enclosing
and supporting a plurality of alternating electrodes 56 and 57. Electrodes 56
will be referred to as
"hot" electrodes and electrodes 57 will be referred to as "ground" electrodes.
Generally the "hot"
electrodes will be at either a positive or a negative voltage with respect to
the "ground" electrodes
which are generally at electrical ground, however, the "ground" electrodes do
not have to be at
electrical ground and all that is necessary is that there is a voltage
difference between the "hot" and
"ground" electrodes during operation of the DBDPGC. With an AC voltage, the
difference in
voltage between the "hot" and "ground" electrodes will vary between positive
and negative voltages.
The "hot" electrodes 56 are hermetically sealed by an insulating material such
as a borosilicate glass
58, on both sides of the conductor plate 56. A silicone sealing material 59,
Figs. 6 and 8, seal all
glass edges. An electrical connection tab 60 extends from the glass which
seals the "hot" electrode
56. The "ground" electrodes include electrical connection tabs 61, Figs. 5 and
7.
[0038] DBDPGC frame 55 is formed of a nonconductive material such as ceramic,
Teflon, or other plastic and has small grooves 64 to receive and support
"ground" electrodes 57 and
larger grooves 65 and 66 which receive and support opposite sides of
hermetically sealed "hot"
electrodes 56 as sealed by glass 58. Grooves 66 receive the side of the
hermetically sealed "hot"
electrodes without the electrical connection tab 60, while grooves 65 with the
top portions 68 thereof
extending through the wall of the frame 55, receive the side of the
hermetically sealed "hot"
electrodes with an extended end 69 extending through the through portions 68.
It should be noted
that the material hermetically sealing the "hot" electrodes extends beyond the
perimeter of the "hot"
electrode 56 so that when installed in frame 55, the "hot" electrode 56 is
held in the frame but spaced
from the frame.
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CA 02502382 2005-03-24
[0039] It has been found that the hermetic sealing of the "hot" electrodes is
essential to
satisfactory operation of the DBDPGC in most situations as the air and/or
gases normally being
treated usually have contaminants in the gas passing through the DBDPGC. This
is true even when
the gas is atmospheric air. Contaminants can be condensing water or other
condensing vapors, some
contaminants can be particles of some kind, or there can be a mixture of both
condensing fluids and
particles. When at least one set of the electrodes are not hermetically
sealed, it has been found that
after a period of time in operation, the contaminants cause electrical short
circuits in the DBDPGC's
from "hot" electrodes, across the insulation and support frames to the
"ground" electrodes.
Hermetically sealing at least the "hot" electrodes prevents short circuits
from occurring as no
medium can contact the actual "hot" electrode conductor. The hermetic sealing
normally
incorporates borosilicate glass 58 to cover the internal stainless steel or
other conductive material of
electrodes 56 on both sides, with high voltage silicone sealant 59 around all
glass edges, filling all
gaps to provide the sealing of the conductive electrode part 56 within the
dielectric. Alternatively,
hermetic sealing could involve completely enclosing the stainless steel
portion of the electrode in a
ceramic similar to borosilicate glass. The key consideration is that, except
for the electrical
connection tab, all other parts of the electrode has the hermetic seal and
dielectric integrity
maintained so no short circuit by any conductive means, fluid and/or particle
or any other medium in
contact with the wetted, hermetically sealed electrode surface can contact or
otherwise connect to the
conductive part within. Note the electrical connection tab is not "wetted" by
the gas stream being
treated
[0040] The "ground" electrodes 57 can also be hermetically sealed. As
indicated, the
"ground" electrodes do not actually have to be at ground potential. Further,
sealing all electrodes,
19
CA 02502382 2005-03-24
both "hot" and "ground" electrodes will be required in cases where the
contaminated gas to be treated
is very aggressive and corrosive so would corrode exposed metal parts.
[0041] The physical matching of the electrodes is such that the NTP field
formed
between electrodes is confined to the area where the electrodes directly
oppose each other through
the dielectric medium and as such, this geometry serves to control the NTP and
keep it away from
the support frame so the frame does not suffer damage from the NTP field. The
area of NTP
generation is only the area enclosed by lines 70 in Fig. 7, i.e., the area
inside the perimeter of the
"hot" electrodes.
[0042] The excitation of the electrodes will vary according to the
application. The "hot"
electrodes and "ground" electrodes will have opposing polarity so that a NTP
forms in the directly
opposing areas between the electrodes. The electrodes can be excited by
alternating current of either
sine wave, square wave, or other wave shape as deemed effective, with the
"hot" electrode being
either positive or negative with respect to the "ground" electrode at any
given instant of the
alternating current cycle. The voltage between electrodes should be at least
about 4,000 volts and
usually will be in the range of between about 4,000 volts and about 100,000
volts, which is
determined by the actual cell geometry required for a given application. The
frequency should be
between about 50 Hz up to about 50,000 Hz, and in some cases, higher.
[0043] It has been found convenient to group the DBDPGC's in groups of three
where
each DBDPGC is powered by one phase of a three phase power supply. For the
embodiment shown,
Figs. 5 and 6, there are sixteen "hot" electrodes, with seventeen "ground"
electrodes for each of three
DBDPGC's, each DBDPGC powered by one phase of a three phase system. In this
arraxigement, the
"ground" electrodes will actually be electrically connected to ground. When
energized, these
CA 02502382 2005-03-24
electrodes form the NTP field in the directly opposed areas between the
electrodes, i.e., the area
enclosed by lines 70 in Fig. 7. It has been found satisfactory to use a 2000
hertz sine wave, with a
root mean square voltage of 18,000 volts. Alternatively, the ends 71, Fig.S,
of the DBDPGC frame
55 may be made of a conductive material similar to ground electrodes 57 and be
electrically
grounded so as to actually form the two end ground electrodes. In such
situation, separate end
ground electrodes 57 are not necessary and there will be one less ground
electrode 57 than hot
electrode 56 since the ends 71 replace the end ground electrodes 57.
[0044] A satisfactory power supply includes a transformer 30 for each DBDPGC
powered by a frequency invertor that is capable of driving a transformer load.
Depending upon the
transformer used, an additional inductive reactance in series with the primary
may be necessary so
that the combined inductive reactance of the transformer and extra inductor
nearly matches the "live"
capacitance of the DBDPGC's, thus the system runs at "near" electrical
resonance to get maximum
power into the NTP. The term "live" capacitance is needed, as the capacitance
of the "hot" and
"ground" electrodes, when assembled in their frame and measured when the
system is not powered,
differs from that measured when the system is in operation. This is because
the NTP changes the
capacitance of the DBD when in operation so that must be matched by the
inductance and frequency
when in operation to achieve the desired NTP level.
[0045] The three transformers, one for each phase, have the primary windings
connected
in delta arrangement, with the three inductors, if necessary, in series with
each transformer primary
(through a PLC controlled contactor), while the transformer secondary windings
are connected in
grounded wye arrangement. In the event of any failure in one of the "hot"
electrodes, the failed
phase will go out of resonance operation, its power will drop and the current
drop to the faulted
21
CA 02502382 2005-03-24
phase will be detected. A programmable logic controller (PLC) monitors the
difference and will
disconnect the faulted phase. The remaining two phases will continue to
operate at the power level
set. In the event another "hot" electrode loses it's dielectric integrity and
shorts out, that phase also
will be disconnected by the PLC, so that the system can operate with two
failed phases, on a single
phase and single DBDPGC. The PLC monitors all currents to the primary of the
transformers,
selects the maximum current and modulates the signal to the inventor so that
it remains at the
setpoint entered. Changes in the gas being treated, such as temperature,
humidity, plus the effects of
component heating (transformers & inductors) can cause variations in the NTP
developed and the
power consumed, and this is held steady by the PID control algorithm
calculated by the PLC.
[0046] The voltage to the primary of the transformers is varied by the width
of the pulses
delivered to the transformer, through the PLC PID algorithm that controls the
power inventor and this
in turn adjusts the voltage output of the transformers, hence to the "hot" and
"ground" electrodes,
which adjusts the level of the NTP produced. Typically, a closed PID control
loop that monitors the
actual power output of the inventor is measured and controlled to a power
level setpoint that can be
cascaded from another control loop from an ozone sensor, or the setpoint can
be manually entered.
Other system states, such as contactor status, for incoming power to the
inventor, contactor to each of
the transformer/invertor phases is also monitored and displayed by the PLC
system. An important
interlock monitored by the PLC is the DBDPGC differential pressure, which
represents the gasflow
through the DBDPGC's. Normally, this number (three) of DBDPGC's needs a
minimum of 3000
ACFM of gas for electrode cooling at 70 degrees F, but a flow of 5000 ACFM is
preferred. In this
embodiment, this results in a differential pressure of 0.8 inches of water at
3000 ACFM and up to 1.5
inches of water at 5000 ACFM. The gas must be filtered to the extent of
removing coarse particles
22
CA 02502382 2005-03-24
and debris that might not pass between the gas flow space separating the "hot"
and "ground"
electrodes. Should the filter clog and the system draft not pass enough gas
through the DBDPGC's,
as indicated by a drop in differential pressure, the PLC will sense this and
disable the power to the
unit and present and alarm indication. This is needed, otherwise the DBDPGC's
will overheat and
the dielectric hermetic seal of the "hot" electrodes will break, destroying
the dielectric integrity
resulting in malfunction.
[0047] This embodiment as described will be rated for 25 kilowatts, measured
as the
power input to the invertor. Such system has been successfully used to treat
odor from a pet food
production facility, treating 20,000 ACFM of air that was used to dry and cool
the feed.
[0048] Other embodiments are possible, with different DBDPGC dimensions,
different
airflows, different power densities and different power ratings. Single-phase
units, for small
airflows, are possible, typically using power from 500 watts up to
approximately 3000 watts.
Systems needing more power are typically powered with three-phase power,
though some power
supplies, accepting three phase in and single phase out, with different power
electronics, such as
SCR control and different IGBT arrangements and much higher frequencies, are
possible.
[0049) In choosing a power and gas flow design to implement in a given
application that
needs odorNOC abatement, the following considerations are important:
x Due to the wide ranging nature of differing industrial odors and the inexact
science of
determining the specific composition, potency, and the energy needed to
oxidize and/or reduce a
given mix of odorous complex organic molecules and/or VOCs, the systems are
sized for
unknown odor applications by operating a pilot sized system at the odor site.
23
CA 02502382 2005-03-24
x The pilot sized system has all the same flow paths as the full-scale system
and is operated with a
scaled down, known odorous and or VOC laden airflow from the process to be
treated in concert
with adjustable power and frequency levels with various air flow
configurations to determine the
optimum operation configuration, residence time and joules per liter density
required to treat the
gas.
x The determination of the appropriate mix and flow of odorous and/or non-
odorous air to the pilot
inputs depends on the nature and potency of the odors. In cases where the odor
is highly
concentrated and cannot be treated by any other means, except, possibly
incineration, or if the
odorous air flow can all pass through the DBDPGC cell, then it is best to
configure all odorous
air to pass through the DBDPGC.
x In applications where the odor is diluted and of a potency that does not
need to be passed directly
through the DBDPGC to be neutralized and the air stream is large, then the
system may best pass
only ambient air through the DBDPGC and inject the Activated Oxygen and
Hydroxyl Species
(AOHS) formed by the DBDPGC into the odorous air stream to provide the
treatment. This
configuration can also have odorous air pass through the DBDPGC in place of
ambient, non-
odorous air and achieve the same effect.
x In applications where some extremely high concentration or difficult to
oxidize and/or reduce
odors and/or V OCs need to be treated, that are only treatable otherwise
through incineration, then
such must pass entirely through the DBDPGC, as only the most active AOHS that
operate
entirely within the NTP field will neutralize such difficult odors or VOCs. In
such applications,
the lesser reactive AOHS species may still exist in the air exiting the
DBDPGC, so it is useful to
process some less concentrated, or odors that do not require the most
energetic ROS to be treated
24
CA 02502382 2005-03-24
at that point, and they are admitted to the Odor Removal System through the
DBDPGC bypass
input. In this configuration the pilot and full scale Odor Removal System will
treat both odor
sources at the same time.
Once an energy level has been established for given air flow rates to each
system input for a given
odor source or combination of sources, the full scale system can then be
sized.
[0050] The system illustrated in Figs. 1-4 is in a bypass system
configuration, using a
total of 5000 actual cubic feet of atmospheric air per minute (ACFM) through
the DBDPGC's, to be
activated by the NTP to create the reactive oxygen species that are mixed with
the gas to be treated.
The treated gas volume can be from 5000 ACFM up to 50,000 ACFM, depending on
the
concentration of the odor or VOC needing treatment. This same configuration
could also pass gas in
a mix, in that some of the gas to be treated flows through the NTP field. In
this configuration, the
gas passing through the NTP field is not only treated to remove the pollutant
of concern, but also is
activated so that it can treat other air.
[0051] A further feature of the invention is that the efficiency of the odor
removal can,
with some odors and/or VOCs, be directly monitored and automatically
controlled using an ozone
monitor. Ozone is one of the longest-lived ROS species that are formed to
treat the odorous gas and
there is usually a small amount of residual ozone in the treated gas stream
when enough ROS has
been created to neutralize the odor and/or VOC levels in the case of odors
and/or VOCs that are
treatable with the longer lived ROS species. As the power applied to the
DBDPGC's controls the
amount of ROS produced (within the limits of the DBDPGC's power handling
rating), the power can
be modulated automatically to maintain a small residual ozone level, to match
EPA or local authority
guidelines. Since adjusting the power to the DBDPGC's controls the NTP level,
hence the amount
CA 02502382 2005-03-24
of ROS created, then the level of ROS required to treat any combination of gas
flow and contaminant
level is modulated so enough ROS is produced to fully oxidize and/or reduce
the odors and/or VOCs
contained in the gas stream and leave a small residual ozone in the discharge.
In the case where the
small residual ozone drops, it means that there is an increase in the odor
and/or VOCs to be treated
so the automatic control loop can increase power to the DBDPGC's to increase
the NTP field which
in turn generates more ROS species to meet the treatment demand. In the case
where the residual
ozone increases, then the odor and/or VOC load has decreased so the automatic
control can reduce
the power to maintain the small residual ozone setpoint to stay within
authority limits for ozone
emissions. In cases where the gas to be treated must all pass through the NTP
field for effective
treatment, due to the high energy requirement of the ROS species, then it
might not be possible to
close the control loop using ozone as the process variable, as the gas being
treated would not
consume the lower energy ROS species of which ozone is a member. In such cases
a manual
operation level might have to be set.
[0052] Also incorporated into the control of this invention is a Programmable
Logic
Controller (PLC) that interlocks all safety devices and controls the on/off
functions of the system
according to factory needs. In other words, it will automatically shut down
when the factory halts
production and/or isolate a fault and give an alarm message if such occurs in
the system.
[0053] The system of the invention can be added on to existing factories or
integrated as
part of a new plant design. The changes in equipment are minimal to integrate
this technology into a
factory and the only operating consumable commodity is electricity. Further,
the technology is
scalable to any size from small domestic sized units for kitchen odors of a
few hundred ACFM, all
the way to the largest factories that release tens of thousands of ACFM and
more of odorous and/or
26
CA 02502382 2005-03-24
VOC pollutant laden air into the environment. When large volumes of air,
and/or extremely high
odor load in combination with large air volumes must be treated, multiple
units can be combined in
parallel to treat the air.
[0054] While the invention has been described as apparatus for treatment of
odor and
volatile organic compound contaminants in gas emissions, the invention can be
used in a variety of
other applications to oxidize and/or reduce a compound or compounds of concern
to a desired form.
One such application would be to reduce the hydrocarbon content in air
emission applications to an
acceptable level prior to release into the atmosphere. Gas fumes such as
combustibles and even H2S
from oil wells or other processes can be oxidized and reduced using this
technology that otherwise
would require burning or flaring to prior to being discharged into the
atmosphere. In many cases,
additional fuel, such as propane, is needed to keep a flare in combustion when
the concentration of
combustibles in the gas to be emitted falls below the ignition point. With
this technology, an
ignition concentration is not required to fully oxidize and reduce the gas,
the NTP is able to fully
oxidize and reduce the gas to be treated regardless of the hydrocarbon level.
Other hydrocarbon
compounds, such as those containing chlorine and fluorine are also treatable
by this invention.
[0055] Whereas the invention is here illustrated and described with reference
to
embodiments thereof presently contemplated as the best mode of carrying out
the invention in actual
practice, it is to be understood that various changes may be made in adapting
the invention to
different embodiments and to the availability of improved materials (power
supplies or ceramics for
example) without departing from the broader inventive concepts disclosed
herein and comprehended
by the claims that follow.
27
