CA1277953C - Stack gas emissions control system - Google Patents
Stack gas emissions control systemInfo
- Publication number
- CA1277953C CA1277953C CA000479957A CA479957A CA1277953C CA 1277953 C CA1277953 C CA 1277953C CA 000479957 A CA000479957 A CA 000479957A CA 479957 A CA479957 A CA 479957A CA 1277953 C CA1277953 C CA 1277953C
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- CA
- Canada
- Prior art keywords
- cathode
- anode
- exhaust gas
- reactor
- glow discharge
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
- B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
- B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
- B03C3/02—Plant or installations having external electricity supply
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/46—Removing components of defined structure
- B01D53/60—Simultaneously removing sulfur oxides and nitrogen oxides
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
- Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Biomedical Technology (AREA)
- Environmental & Geological Engineering (AREA)
- Analytical Chemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Treating Waste Gases (AREA)
Abstract
A B S T R A C T
TREATING STACK GASES WITH GLOW DISCHARGE EMPLOYING
PIN CATHODES AND PLANAR ANODES
A method is described for use in a plenum in the stack or flue ducts of a fossil fueled combustion system to eliminate or substantially reduce SOx and NOx emissions from the stack exhaust. The method uses an electrically operated stable glow discharge maintained in a conversion reactor between separate resistively ballasted pins and opposing plane electrodes disposed in said plenum. The reactor of this invention electronically activates, reacts and chemically modifies the selected pollutants to result in a thermodynamically stable solid product which can be removed and disposed suitably.
TREATING STACK GASES WITH GLOW DISCHARGE EMPLOYING
PIN CATHODES AND PLANAR ANODES
A method is described for use in a plenum in the stack or flue ducts of a fossil fueled combustion system to eliminate or substantially reduce SOx and NOx emissions from the stack exhaust. The method uses an electrically operated stable glow discharge maintained in a conversion reactor between separate resistively ballasted pins and opposing plane electrodes disposed in said plenum. The reactor of this invention electronically activates, reacts and chemically modifies the selected pollutants to result in a thermodynamically stable solid product which can be removed and disposed suitably.
Description
t ` ~ 77953 PIN CATHODES AND PLANAR ANODES
Field of the Invention:
The invention generally relates to a method and apparatus for controlling gaseous pollution. More specifi-cally, the invention provides a method and techniquewherein a combustion system exhaust gas flow containing SX
and N0X emissions is reacted to convert the SX and N0X
into a thermodynamically stable and less objectional exhaust product which can be easily collected and disposed.
Descri~tion of the Prior Art:
~ Several technigues are presently known for the control o airborne pollutants. Examples of these tech-niques include inertial separation, scrubbing, filtration, electrostatic precipitation, electron beam irradiation ; 15 electro-photoioniZatiOn and catalysis. Cyclone separators producing an abrupt change in direction of rapidly flowing gas streams effect separation of entrained solids by differences in the inertial forces acting on such solids as compared to the entraining gas. Cyclones have the advan-tage of simplicity of design, high capacity and easy maintenance. At best, however, such inertial separation devices are efficient only in extracting relatively large particles from the entraining gas and of course they are completely unable to separate contaminant gases present in the main body of gas or air being treated. On the other hand, scrubbing or the reacting of a qas by contacting it ~ , ~
779~
with a fine spray of liquid such as water or chemical slurries has the advantage of relatively low equipment cost. However, there are operational disadvan~ages with scrubbers, including handling of resultant slurry or sludge, the corrosion of equipment and microbiological growth problems. In most insta~ces, such devices are limited in practice to the removal of relatively coarse particles from a gas, and any separation of gaseous pollu-tant S02 is dependent upon the relative solubilities of the pollutant and main gas components in water or other liquid.
Catalytic beds are widely employed to treat various gaseous systems. Such beds are, however, very specific as to reactant and complementary catalyst, they require precise temperature control and they are extremely sensitive to poisons. Both gaseous species and particulates tend to poison the catalyst and cause reduced catalytic activity.
Electrostatic precipitation is widely used in applications and in spite of high initial equipment cost and operating expense, this system may represent the only practical procedure for obtaining acceptably low levels of solid airborne particulates in gas or air streams exhausted to atmosphere. The procedure employed, of course, involves the application of high voltages to electrode arrays such that the gas near the electrodes is ionized and the parti-cles suspended in the gas acquire a charge from contact .with the gas .ions. Such charged particles then migrate from contact with the gas ions. Such charged particles then migrate to an electrode of opposite charge and, as the gas flows over the electrode array, the charged particles attach themselves to the electrodes. Removal of the accumulated solid particles in most cases is accomplished by mechanically vibrating the electrodes to discharge the cakes of collected dust into a collection bin. Although the system is versatile and efficient in removing small solid particles from an atmosphere where the particle size is extremely small, it does have some serious limitations, the most significant of which is the fact that only :
~277953 .
particulate matter can be eliminated. In addition, the physical and electrical characteristics of some particulate materials prevent them from being collected efficiently by an electrostatic precipitator. Electron beam irradiation systems have several major disadvantages including the use of high energy electrons (> 5Q0 KeV), the requirement for a fragile beam window to allow the beam into the gas duct and the need for an expensive electron beam accelerator exter-; nal to the gas duct and the shielding required for protec-tion rom X-rays generated by the accelerator.
Electro-photoionization effects the removal of contaminants through the combined action on the gas stream of a high intensity electrical field and electromagnetic radiation whereby the electrostatic precipitation of solid contami-nants and the electrochemical and photochemical transforma-tion of gaseous contaminants to elemental or non-contaminant form takes place. The field is induced by oppositely charged electrodes causing excitation of the particulate and gaseous contaminants to a state or condi-tion causing dark current flow and/or glow dischargebetween the electrodes. Concurrently with such high voltage excitation, the gas stream is subjected to electro-magnetic radiation in the ultraviolet range in order to produce photoionization which sustains the electrochemical and photochemical transformation. Presently, with the exception of the e-beam driven system, all of the afore-described systems will remove only one of the major gaseous S02/N0x species, with each process requiring serial operation.
There are several prior art patents and publica-tions directed to removal of particulate matter such as 5, ' dust particles from a plenum containing gas or air.
U.S. Patent 3,917,470 to Xmris et al. deals with an electrostatic precipitator which uses an optical elec-trostatic generator. The-arrangement includes a collection electrvde which typically has a liquid surface. U.S.
Patent 3,979,193 teaches an apparatus for controlling the , , , --~ ~z7~953 amount of polluting substances within the exhaust of an internal combustion of polluting substances within the exhaust o an internal combustion engine, wherein the exhaust passes through a corona producing chamber.
U.S. Patent 3,869,302 to Machi et al., teaches subjecting NOx-502 containing gases to irradiation with an ionizing radiation of ultraviolet light. The process necessitates the use of an electron beam unit. In the same tenor, two publications from Radiation Phys. Chem. Vol. 24, No. 1, 1984 pages 117-127, and pages 129-143 (Shui et al.
and Feldman et al. respectively) deal with the use of electron beam units in flue gas treatment for removal of NOx and S02. These prior art arrangements use undesirable high voltage supplies, e.g. 6KV, are very expensive, complicated for operation and maintenance as well as not wholly reliable as they lack simplicity.
It is an object of this invention to provide a simple inexpensive and efficient system for the simultane-ous removal of gaseous NOx and SX constituents from a main stream of gas in a single process reactor by converting the gaseous constituents into nongaseous products e.g. solids.
It is another object of this invention to provide an emissions control system for converting and removing gaseous pollutants in large scale applications such as in fossil fuel combustion facilities and the like.
SUMMARY OF THE INVENTION
The present invention in its broad form comprises a method for converting and removing selected gaseous pollutants of an exhaust gas generated by a combustion apparatus by converting said gaseous pollutants into nongaseous products, said method comprising: using a conversion reactor in communication with said combustion apparatus and disposed in-the path of said exhaust gas so that the exhaust gas generated thereby circulates through said reactor, the reactor including electronic anode means and cathode means spaced from anode means, said cathode and anode being disposed within said ~eactor to effect . .
1~:7'795~3 s substantial contact with the exhaust gas circulated there-through, and providing a predetermined d.c. potential between said cathode means and said anode means, astab-lishing a uniform stable glow discharge in the exhaust gas and converting the selected gaseous pollutants by selective electronic activation and reaction, and effecting a chemi-cal modification of said gaseous poIlutants into a thermo-dynamically stable solid product, which can be removed and disposed.
In a preferred embodiment, a conversion reactor and method are described for use in the stack or flue ducts of a fossil fueled combustion system to eliminate or substantially convert Sx and NOX emissions into removable solids. The method includes maintaining an electrically operated stable glow discharge between separate resistively ballasted pins and opposing plane electrodes or coaxially arranged electrodes. The conversion reactor of this inveittion electronically activates a~d chemically modifies D l~
the selected pollutants to ~ender a thermodynamically stable solid product. This solid product can then be removed by standard available processes for particulate removal.
BRIEF DESCRIPTION OF THE DRAWINGS
A more detailed understanding of the invention may be had rom the following description of a preferred embodiment, given by way of example and to be studied in conjunction with the accompanying drawing wherein:
Figure 1 is a schematical representation of an apparatus for the simultaneous cemoval of NOX and SO2 constituents from stack gas emissions, using tha teachings of ~his invention;
- Figure 2 is a somewhat schematical representation in elevation of the emission control device of this inven-tion placed in the exhaust flow to be controlled;
Eigure 3 is a schematical, plan view of an emission control device of this invention lltilized in a modular embodiment;
- 6 ~ 77 9~
( ` Eigures 4A, 4B, 4C and 4D are somewhat schematic representations of examples of several modules which can be utilized in the emissions control device of Figures 3, all ; according to the teachinqs of this invention; ant S Figure S is a somewhat schematical representation in elevation of an alternative em~odiment of the emission control device of this invention placed in the exhaust`flow ; of a combustion apparatus.
DESCRIPTION OF T~E P~EFERRED EMBOD~MENT
The application and general placement of a stac~
gas emissions control system according to this invention can be initially understood in the schematical representa-tion of a gas flue duct network of Figure 1. The inve~tion is an electrically driven glow discharge system located in such a manner as to efficiently couple the energy of the electrons o the glow discharge systems with the gas stream to be detoxified. The electron energy average i5 5 eV and thereore more closely matches the bond energies of simple chemical species. The flue gas stream flows through the glow discharge volume where electronically activated , species are produced. The half life of these species may ,; be in excess of 5 ms which for stream velocities in excess of 80 feet per second will increase the reaction volume beyond the actual physical dimensions of the glow discharge ''!~ 25 devices.
; ~ The apparatu~ which i8 whematically illustrated in Figure 1 includos a fuel supply 11 which is introduced $nto a combustion device 13 by a pump means 15 through line 17. The combustion device 13 i~ a conventional burner of the type supplied with a fossil fuel fired electrical power generatlon plant or the like. Exhaust from the combustion device 13 i9 conveyed by duct means 21 to a conversion reactor comprising the glow di~charge ~ystem according to this invention and generally indicated by the reference character 19. Typically, a first dust collector system 23 of conventional design is disposed between the glow discharge sy-tem 19 and the combustion device 13. The first dust : 1 ~'' JBi, ,................................... .
:: :
,~ .
7795~
collector system 23 include~ a dust bag 2s, control valves 27 and bypass duct 29. A fan means 31 is disposed along duct mean~ 21 to a~sist in the operation of the dust collector sy~tem 23 and to maintain desired exhaust gas flow through the S glow discharge system 19.
The operation of the glow discharge system 19 will be described in detail below. However, after the treatment of exhaust gas therein, the treated exhaust gas is conveyed ; through duct means 32 to one or more product particulate collector means 33 and 35. One of the particulate collector means 35 can be incorporated into a feedback loop through duct means 37 and blower means 39 in order to convey the treated exhaust gas back throuqh the glow discharge system 19. The finally treated exhaust gas is conveyed through duct means 41 and blower mesns 43 into an exhaust stack 45 for discharge into the atmo~phere. An SO2 and/or NOX gas analyzer device 47 can be in communication with the exhaust duct means 32 as at 49 in order to monitor the output of treated exhaust gas from the glow diwharge ~y~tem 19.
The reactor 19 includes spaced-apart electrodes 51, 53 which are disposed within the reactor with the circulating gas passing between an electrically grounded plane-like anode 51, and a cathode array of pin-like electrodes 53 which are preferably individually resistively ballasted external to the ; 25 reactor and connected to a high voltage d.c. source 55.
Nowever, several pins, as illustrated can be configured to operate from a single ballast device. The number of pin-like electrodes 53 and their spacing in the array, as well as the applied potential and ballasting are determined to maintain a uniform glow diwharge in the gas passing between the anode and cathode array along the path of travel of the air through the reactor. Preferably, the distance between each pin-like cathode and the plane like anode is substantially the same.
.: .
~;~7'795~
` 8 The typical chemical pollutant is electronically activated as a result of the glow discharge which is established in the flowing gas which includes the pollu-tant. The applied d.c. field across the electrodes serves to establish the glow discharge which produces activation of the permanent air components as well as the pollutant, which is then chemically modified or altered within the glow discharge reactor to render the pollutant harmless, or make it more easily separable by filtration.
The averaqe energy of the electrons in the uniform glow discharge which is established between the electrodes is such that there is efficient electronic activation of the pollutant to promote the desired chemical change. The exhaust gas containing the pollutants is forced to flow through the glow discharge reactor at a flow rate such as to prevent formation of an arc between the electrodes, with the flow rate being generally in the range of from about 0.5-l Mach number. The higher the velocity or flow rate of the exhaust gas, the higher the glow discharge current and power input without arc breakdown.
The higher the power input, the greater the emissions control capability of the reactor. The gas pressure within the glow discharge reactor is at about atmospheric pressure or even slightly above. The resultant E/N for this condi-tion ranges from 50 to 100 Td.
A means 59, e.g., screen or other similar element for increasing the turbulence of the gas flowing into the glow discharge reactor can be included at the reactor inlet, such means as a screen or other increases the gas turbulence, thereby the glow discharge power input can be increased for more efficient electronic activation while avoiding arcing.
The electric field applied across the electrodes ~ ' of the glow discharge reactor is such as to provide effi-;35 cient electronic activation of the pollutant, with a typical field qradient of about 7-20 kV per centimeter, and ~gen-rally greater than l kV per centimeter with the upper ' 9 ~7795;3 limit beiny the electric field gradient at which arcing occurs.
This lim~t is dependent upon ~as stream composition and velocity.
In general, the'gas f low and el'ectrical field para-meters can be ~ar~ed while'~aintaining operation in the glow discharge'reg'ime. This permits highly efficient power input to the glow dlscharge, and electronic activation which results in the'simultaneous reduction or elimination of NOX and Sx in constituents from the exhaust gas.
Consider'ing Figure 2, an arrangement of the electrodes 51 and 53'is lllustrated wherein a stable glow discharge im-pressed between individually ballasted pins and planar opposing electrodes is sustained. The conversion reactor 19 is placed within the'exhaust stack or the flue ducts where the exhaust gas is forced to enter the discharge volume at near atmospheric pressure and increased velocity. Increased velocity has been shown to increase the discharge current level prior to breakdown or arclng. The electrode shape and the physical disposition of eLectrodes relative to each other can be used to obtain increased velocity within the'duct. The elevational view of Figure 2 presents a preferred embodiment of the subject conversion reactor within a circular duct member 61. A first plane electrode 51a ls circumferentially disposed about the inside wall of the duct member 61 and a second plane electrode 51b is centrally disposed ' within the duct member. Pin electrodes 53 are generally circum-ferentially disposed between plane electrodes 51a and 51b and a gas flow path is defined between the pin electrodes 53 and the plane electrodes 51a and 51b as shown by the arrows indicated by the reference character 65. It is to be appreciated that as shown in Figure 3!the electrochemical reactor 19 can be con-figured as a plurality of individual modules 77 disposed in asupporting frame means 72 so that multiple module installations can be employed to properly reduce the emissions for various stack sizes and shapes. Figures 4A, B and C represent exemplary pin electrode madules 71a, 71b and 71c respectively with unique configurations of the pin electrode placement as at ` 73a, 73b and 73c reIative to the plane electrode 75a, 75b and 75c respectiveIy. As indicated above, the disposition , ,:
~' .. ...
1;2779~3 of the pin electrodes is one of the factors which contribute~
to the operational capability of the electrochemical reactor of this invention.
In the embodiment of Figure 4D the reactor electrodes s comprise a cylindrical anode 7Sd aligned along the direction of air flow with a cathode pin 73d extending parallel to the longitudinal axis of the cylindrical anode as at the cylindrical anode inlet end. A plurality of ballasted cathode pins may be spaced apart along the length of the cylindrical anode, with each cathode pin terminating along the anode longitudinal axis. A plurality of nested cylin-drical anodes may be provided with cathode pins associated with each anode along the respective cylindrical anode longitudinal axis.
lS Figure S shows an elevational view of a duct member within which is placed an alternative elect-ode configuration. The plane electrodes 51 are disposed on both sides of the pin electrodes 53, thus providing an exhaust gas flow path 65 in which substantial and prolonged contact within the glow discharge region of the electrodes is established. This alternative embodiment is also suitable for modular-type application as discussed above.
The stack gas emissions control system of this invention can be appreciated through a consideration of a theoretical description of the discharge physics and discharge chemistry kinetics which take place during pollutant control.
Numerical solutions were made to the Boltzmann e~uation to descri'oe a glow discharga operating in air.
The predictions for channeling of the ~lectrical energy are as follows:
Vibrational excitation of N2 4A%
Electronic excitation of N2 42%
Electronic excitation o 2 13%
~S Ionl~.ation 0.25%
Other losses 0.75 ,;
j.. .
11 1~779~3 This indicates that 55% of the electrical energy is channeled to produce electronically excited N2 and 2 which can produce free radicals cuch as 0 and N.
The minor components Sx and N0x can react within the discharge stream by primary electron interaction or by reactions or collisions with the major components. This latter path may provide higher yields of products involving SX and N0x, especially if chain reactions are controlling.
For this reason, a simplistic approach was taken to arFive at a reaction mechanism. Reactions with free radicals could be considered with only those selected for which experimentally determined reaction rate constants were availablë. No chain reaction steps will be assumed. The kinetic mechanism is:
Field of the Invention:
The invention generally relates to a method and apparatus for controlling gaseous pollution. More specifi-cally, the invention provides a method and techniquewherein a combustion system exhaust gas flow containing SX
and N0X emissions is reacted to convert the SX and N0X
into a thermodynamically stable and less objectional exhaust product which can be easily collected and disposed.
Descri~tion of the Prior Art:
~ Several technigues are presently known for the control o airborne pollutants. Examples of these tech-niques include inertial separation, scrubbing, filtration, electrostatic precipitation, electron beam irradiation ; 15 electro-photoioniZatiOn and catalysis. Cyclone separators producing an abrupt change in direction of rapidly flowing gas streams effect separation of entrained solids by differences in the inertial forces acting on such solids as compared to the entraining gas. Cyclones have the advan-tage of simplicity of design, high capacity and easy maintenance. At best, however, such inertial separation devices are efficient only in extracting relatively large particles from the entraining gas and of course they are completely unable to separate contaminant gases present in the main body of gas or air being treated. On the other hand, scrubbing or the reacting of a qas by contacting it ~ , ~
779~
with a fine spray of liquid such as water or chemical slurries has the advantage of relatively low equipment cost. However, there are operational disadvan~ages with scrubbers, including handling of resultant slurry or sludge, the corrosion of equipment and microbiological growth problems. In most insta~ces, such devices are limited in practice to the removal of relatively coarse particles from a gas, and any separation of gaseous pollu-tant S02 is dependent upon the relative solubilities of the pollutant and main gas components in water or other liquid.
Catalytic beds are widely employed to treat various gaseous systems. Such beds are, however, very specific as to reactant and complementary catalyst, they require precise temperature control and they are extremely sensitive to poisons. Both gaseous species and particulates tend to poison the catalyst and cause reduced catalytic activity.
Electrostatic precipitation is widely used in applications and in spite of high initial equipment cost and operating expense, this system may represent the only practical procedure for obtaining acceptably low levels of solid airborne particulates in gas or air streams exhausted to atmosphere. The procedure employed, of course, involves the application of high voltages to electrode arrays such that the gas near the electrodes is ionized and the parti-cles suspended in the gas acquire a charge from contact .with the gas .ions. Such charged particles then migrate from contact with the gas ions. Such charged particles then migrate to an electrode of opposite charge and, as the gas flows over the electrode array, the charged particles attach themselves to the electrodes. Removal of the accumulated solid particles in most cases is accomplished by mechanically vibrating the electrodes to discharge the cakes of collected dust into a collection bin. Although the system is versatile and efficient in removing small solid particles from an atmosphere where the particle size is extremely small, it does have some serious limitations, the most significant of which is the fact that only :
~277953 .
particulate matter can be eliminated. In addition, the physical and electrical characteristics of some particulate materials prevent them from being collected efficiently by an electrostatic precipitator. Electron beam irradiation systems have several major disadvantages including the use of high energy electrons (> 5Q0 KeV), the requirement for a fragile beam window to allow the beam into the gas duct and the need for an expensive electron beam accelerator exter-; nal to the gas duct and the shielding required for protec-tion rom X-rays generated by the accelerator.
Electro-photoionization effects the removal of contaminants through the combined action on the gas stream of a high intensity electrical field and electromagnetic radiation whereby the electrostatic precipitation of solid contami-nants and the electrochemical and photochemical transforma-tion of gaseous contaminants to elemental or non-contaminant form takes place. The field is induced by oppositely charged electrodes causing excitation of the particulate and gaseous contaminants to a state or condi-tion causing dark current flow and/or glow dischargebetween the electrodes. Concurrently with such high voltage excitation, the gas stream is subjected to electro-magnetic radiation in the ultraviolet range in order to produce photoionization which sustains the electrochemical and photochemical transformation. Presently, with the exception of the e-beam driven system, all of the afore-described systems will remove only one of the major gaseous S02/N0x species, with each process requiring serial operation.
There are several prior art patents and publica-tions directed to removal of particulate matter such as 5, ' dust particles from a plenum containing gas or air.
U.S. Patent 3,917,470 to Xmris et al. deals with an electrostatic precipitator which uses an optical elec-trostatic generator. The-arrangement includes a collection electrvde which typically has a liquid surface. U.S.
Patent 3,979,193 teaches an apparatus for controlling the , , , --~ ~z7~953 amount of polluting substances within the exhaust of an internal combustion of polluting substances within the exhaust o an internal combustion engine, wherein the exhaust passes through a corona producing chamber.
U.S. Patent 3,869,302 to Machi et al., teaches subjecting NOx-502 containing gases to irradiation with an ionizing radiation of ultraviolet light. The process necessitates the use of an electron beam unit. In the same tenor, two publications from Radiation Phys. Chem. Vol. 24, No. 1, 1984 pages 117-127, and pages 129-143 (Shui et al.
and Feldman et al. respectively) deal with the use of electron beam units in flue gas treatment for removal of NOx and S02. These prior art arrangements use undesirable high voltage supplies, e.g. 6KV, are very expensive, complicated for operation and maintenance as well as not wholly reliable as they lack simplicity.
It is an object of this invention to provide a simple inexpensive and efficient system for the simultane-ous removal of gaseous NOx and SX constituents from a main stream of gas in a single process reactor by converting the gaseous constituents into nongaseous products e.g. solids.
It is another object of this invention to provide an emissions control system for converting and removing gaseous pollutants in large scale applications such as in fossil fuel combustion facilities and the like.
SUMMARY OF THE INVENTION
The present invention in its broad form comprises a method for converting and removing selected gaseous pollutants of an exhaust gas generated by a combustion apparatus by converting said gaseous pollutants into nongaseous products, said method comprising: using a conversion reactor in communication with said combustion apparatus and disposed in-the path of said exhaust gas so that the exhaust gas generated thereby circulates through said reactor, the reactor including electronic anode means and cathode means spaced from anode means, said cathode and anode being disposed within said ~eactor to effect . .
1~:7'795~3 s substantial contact with the exhaust gas circulated there-through, and providing a predetermined d.c. potential between said cathode means and said anode means, astab-lishing a uniform stable glow discharge in the exhaust gas and converting the selected gaseous pollutants by selective electronic activation and reaction, and effecting a chemi-cal modification of said gaseous poIlutants into a thermo-dynamically stable solid product, which can be removed and disposed.
In a preferred embodiment, a conversion reactor and method are described for use in the stack or flue ducts of a fossil fueled combustion system to eliminate or substantially convert Sx and NOX emissions into removable solids. The method includes maintaining an electrically operated stable glow discharge between separate resistively ballasted pins and opposing plane electrodes or coaxially arranged electrodes. The conversion reactor of this inveittion electronically activates a~d chemically modifies D l~
the selected pollutants to ~ender a thermodynamically stable solid product. This solid product can then be removed by standard available processes for particulate removal.
BRIEF DESCRIPTION OF THE DRAWINGS
A more detailed understanding of the invention may be had rom the following description of a preferred embodiment, given by way of example and to be studied in conjunction with the accompanying drawing wherein:
Figure 1 is a schematical representation of an apparatus for the simultaneous cemoval of NOX and SO2 constituents from stack gas emissions, using tha teachings of ~his invention;
- Figure 2 is a somewhat schematical representation in elevation of the emission control device of this inven-tion placed in the exhaust flow to be controlled;
Eigure 3 is a schematical, plan view of an emission control device of this invention lltilized in a modular embodiment;
- 6 ~ 77 9~
( ` Eigures 4A, 4B, 4C and 4D are somewhat schematic representations of examples of several modules which can be utilized in the emissions control device of Figures 3, all ; according to the teachinqs of this invention; ant S Figure S is a somewhat schematical representation in elevation of an alternative em~odiment of the emission control device of this invention placed in the exhaust`flow ; of a combustion apparatus.
DESCRIPTION OF T~E P~EFERRED EMBOD~MENT
The application and general placement of a stac~
gas emissions control system according to this invention can be initially understood in the schematical representa-tion of a gas flue duct network of Figure 1. The inve~tion is an electrically driven glow discharge system located in such a manner as to efficiently couple the energy of the electrons o the glow discharge systems with the gas stream to be detoxified. The electron energy average i5 5 eV and thereore more closely matches the bond energies of simple chemical species. The flue gas stream flows through the glow discharge volume where electronically activated , species are produced. The half life of these species may ,; be in excess of 5 ms which for stream velocities in excess of 80 feet per second will increase the reaction volume beyond the actual physical dimensions of the glow discharge ''!~ 25 devices.
; ~ The apparatu~ which i8 whematically illustrated in Figure 1 includos a fuel supply 11 which is introduced $nto a combustion device 13 by a pump means 15 through line 17. The combustion device 13 i~ a conventional burner of the type supplied with a fossil fuel fired electrical power generatlon plant or the like. Exhaust from the combustion device 13 i9 conveyed by duct means 21 to a conversion reactor comprising the glow di~charge ~ystem according to this invention and generally indicated by the reference character 19. Typically, a first dust collector system 23 of conventional design is disposed between the glow discharge sy-tem 19 and the combustion device 13. The first dust : 1 ~'' JBi, ,................................... .
:: :
,~ .
7795~
collector system 23 include~ a dust bag 2s, control valves 27 and bypass duct 29. A fan means 31 is disposed along duct mean~ 21 to a~sist in the operation of the dust collector sy~tem 23 and to maintain desired exhaust gas flow through the S glow discharge system 19.
The operation of the glow discharge system 19 will be described in detail below. However, after the treatment of exhaust gas therein, the treated exhaust gas is conveyed ; through duct means 32 to one or more product particulate collector means 33 and 35. One of the particulate collector means 35 can be incorporated into a feedback loop through duct means 37 and blower means 39 in order to convey the treated exhaust gas back throuqh the glow discharge system 19. The finally treated exhaust gas is conveyed through duct means 41 and blower mesns 43 into an exhaust stack 45 for discharge into the atmo~phere. An SO2 and/or NOX gas analyzer device 47 can be in communication with the exhaust duct means 32 as at 49 in order to monitor the output of treated exhaust gas from the glow diwharge ~y~tem 19.
The reactor 19 includes spaced-apart electrodes 51, 53 which are disposed within the reactor with the circulating gas passing between an electrically grounded plane-like anode 51, and a cathode array of pin-like electrodes 53 which are preferably individually resistively ballasted external to the ; 25 reactor and connected to a high voltage d.c. source 55.
Nowever, several pins, as illustrated can be configured to operate from a single ballast device. The number of pin-like electrodes 53 and their spacing in the array, as well as the applied potential and ballasting are determined to maintain a uniform glow diwharge in the gas passing between the anode and cathode array along the path of travel of the air through the reactor. Preferably, the distance between each pin-like cathode and the plane like anode is substantially the same.
.: .
~;~7'795~
` 8 The typical chemical pollutant is electronically activated as a result of the glow discharge which is established in the flowing gas which includes the pollu-tant. The applied d.c. field across the electrodes serves to establish the glow discharge which produces activation of the permanent air components as well as the pollutant, which is then chemically modified or altered within the glow discharge reactor to render the pollutant harmless, or make it more easily separable by filtration.
The averaqe energy of the electrons in the uniform glow discharge which is established between the electrodes is such that there is efficient electronic activation of the pollutant to promote the desired chemical change. The exhaust gas containing the pollutants is forced to flow through the glow discharge reactor at a flow rate such as to prevent formation of an arc between the electrodes, with the flow rate being generally in the range of from about 0.5-l Mach number. The higher the velocity or flow rate of the exhaust gas, the higher the glow discharge current and power input without arc breakdown.
The higher the power input, the greater the emissions control capability of the reactor. The gas pressure within the glow discharge reactor is at about atmospheric pressure or even slightly above. The resultant E/N for this condi-tion ranges from 50 to 100 Td.
A means 59, e.g., screen or other similar element for increasing the turbulence of the gas flowing into the glow discharge reactor can be included at the reactor inlet, such means as a screen or other increases the gas turbulence, thereby the glow discharge power input can be increased for more efficient electronic activation while avoiding arcing.
The electric field applied across the electrodes ~ ' of the glow discharge reactor is such as to provide effi-;35 cient electronic activation of the pollutant, with a typical field qradient of about 7-20 kV per centimeter, and ~gen-rally greater than l kV per centimeter with the upper ' 9 ~7795;3 limit beiny the electric field gradient at which arcing occurs.
This lim~t is dependent upon ~as stream composition and velocity.
In general, the'gas f low and el'ectrical field para-meters can be ~ar~ed while'~aintaining operation in the glow discharge'reg'ime. This permits highly efficient power input to the glow dlscharge, and electronic activation which results in the'simultaneous reduction or elimination of NOX and Sx in constituents from the exhaust gas.
Consider'ing Figure 2, an arrangement of the electrodes 51 and 53'is lllustrated wherein a stable glow discharge im-pressed between individually ballasted pins and planar opposing electrodes is sustained. The conversion reactor 19 is placed within the'exhaust stack or the flue ducts where the exhaust gas is forced to enter the discharge volume at near atmospheric pressure and increased velocity. Increased velocity has been shown to increase the discharge current level prior to breakdown or arclng. The electrode shape and the physical disposition of eLectrodes relative to each other can be used to obtain increased velocity within the'duct. The elevational view of Figure 2 presents a preferred embodiment of the subject conversion reactor within a circular duct member 61. A first plane electrode 51a ls circumferentially disposed about the inside wall of the duct member 61 and a second plane electrode 51b is centrally disposed ' within the duct member. Pin electrodes 53 are generally circum-ferentially disposed between plane electrodes 51a and 51b and a gas flow path is defined between the pin electrodes 53 and the plane electrodes 51a and 51b as shown by the arrows indicated by the reference character 65. It is to be appreciated that as shown in Figure 3!the electrochemical reactor 19 can be con-figured as a plurality of individual modules 77 disposed in asupporting frame means 72 so that multiple module installations can be employed to properly reduce the emissions for various stack sizes and shapes. Figures 4A, B and C represent exemplary pin electrode madules 71a, 71b and 71c respectively with unique configurations of the pin electrode placement as at ` 73a, 73b and 73c reIative to the plane electrode 75a, 75b and 75c respectiveIy. As indicated above, the disposition , ,:
~' .. ...
1;2779~3 of the pin electrodes is one of the factors which contribute~
to the operational capability of the electrochemical reactor of this invention.
In the embodiment of Figure 4D the reactor electrodes s comprise a cylindrical anode 7Sd aligned along the direction of air flow with a cathode pin 73d extending parallel to the longitudinal axis of the cylindrical anode as at the cylindrical anode inlet end. A plurality of ballasted cathode pins may be spaced apart along the length of the cylindrical anode, with each cathode pin terminating along the anode longitudinal axis. A plurality of nested cylin-drical anodes may be provided with cathode pins associated with each anode along the respective cylindrical anode longitudinal axis.
lS Figure S shows an elevational view of a duct member within which is placed an alternative elect-ode configuration. The plane electrodes 51 are disposed on both sides of the pin electrodes 53, thus providing an exhaust gas flow path 65 in which substantial and prolonged contact within the glow discharge region of the electrodes is established. This alternative embodiment is also suitable for modular-type application as discussed above.
The stack gas emissions control system of this invention can be appreciated through a consideration of a theoretical description of the discharge physics and discharge chemistry kinetics which take place during pollutant control.
Numerical solutions were made to the Boltzmann e~uation to descri'oe a glow discharga operating in air.
The predictions for channeling of the ~lectrical energy are as follows:
Vibrational excitation of N2 4A%
Electronic excitation of N2 42%
Electronic excitation o 2 13%
~S Ionl~.ation 0.25%
Other losses 0.75 ,;
j.. .
11 1~779~3 This indicates that 55% of the electrical energy is channeled to produce electronically excited N2 and 2 which can produce free radicals cuch as 0 and N.
The minor components Sx and N0x can react within the discharge stream by primary electron interaction or by reactions or collisions with the major components. This latter path may provide higher yields of products involving SX and N0x, especially if chain reactions are controlling.
For this reason, a simplistic approach was taken to arFive at a reaction mechanism. Reactions with free radicals could be considered with only those selected for which experimentally determined reaction rate constants were availablë. No chain reaction steps will be assumed. The kinetic mechanism is:
2* ~ 20 (1) ~ 22 ' 3 ~ 2 (2) ~ 3 ~ 22 (3) 20 + 2 ~ 22 (4) N2* ' 2N (5) N ~ 2 ~ ~ N0 (6) 2N0 ~ 2 ' 2N02 (7) o ~ 2S02 ~ 53 ~ S2 (8) S02* ~ S02 ~ S03 ~ S0 (9) S0 I S03 ~ 2S02 (10) S0 ~ 03 ~ S02 ~ 2 (11) 2N02 ~ 3 ' N205 ~ 2 (12) N205 ~ 2S03 ~ (N2)2527 (13) 2S02 l 3N02 ~ (No)25207 (14) What ha~ been described is a system which can be installed in the stack or flue gas ducts of a fossil fuel combustion system to eliminate or substantially reduce Sx ~ and N0x pollutants in the exhaust gas. The system includes '~ an electrically operated stable glow discharge maintained between separate resistively ballasted pins and an opposing plane.
~'~ ' `.
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'~7 7 9 S 3 Page 11-1 51,040 IDENTIFICATION OF REFERENCE NUMERALS USED IN THE DRAWINGS
LEGEND REF. NO. FIGURE
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'~7 7 9 S 3 Page 11-1 51,040 IDENTIFICATION OF REFERENCE NUMERALS USED IN THE DRAWINGS
LEGEND REF. NO. FIGURE
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Claims (13)
1. A method for converting and removing selected gaseous pollutants of an exhaust gas generated by a combustion apparatus by converting said gaseous pollutants into nongaseous products, said method comprising:
using a conversion reactor in communication with said combustion apparatus and disposed in the path of said exhaust gas so that the exhaust gas generated by combustion circulates through said reactor, the reactor including electronic anode and cathode spaced from anode, said cathode and anode being disposed within said reactor to effect substantial contact with the exhaust gas circulated therethrough, and providing a predetermined d.c. potential between said cathode and said anode, establishing a uniform stable glow discharge in the exhaust gas and converting the selected gaseous pollutants by selective electronic activation and reaction, and effecting a chemical modification of said gaseous pollutants into a thermodynamically stable solid product which can be removed and disposed.
using a conversion reactor in communication with said combustion apparatus and disposed in the path of said exhaust gas so that the exhaust gas generated by combustion circulates through said reactor, the reactor including electronic anode and cathode spaced from anode, said cathode and anode being disposed within said reactor to effect substantial contact with the exhaust gas circulated therethrough, and providing a predetermined d.c. potential between said cathode and said anode, establishing a uniform stable glow discharge in the exhaust gas and converting the selected gaseous pollutants by selective electronic activation and reaction, and effecting a chemical modification of said gaseous pollutants into a thermodynamically stable solid product which can be removed and disposed.
2. The method according to claim 1 including the step of using filter means in communication with the reactor for filtering the stable solid product from the exhaust gas.
3. The method according to claim 1 including the step of disposing said electronic cathode in the form of an array of spaced-apart tine shaped cathode members which are spaced from a generally planar anode member, which cathode members are resistively ballasted and including the step of connecting said cathode members to a high voltage d.c. source.
4. The method according to claim 3 including the step of controlling the exhaust gas pressure, the linear velocity, the flow rate of said gaseous pollutants, and controlling the d.c.
potential between the cathode and anode to maintain a uniform stable glow discharge in said path defined between the cathode and anode.
potential between the cathode and anode to maintain a uniform stable glow discharge in said path defined between the cathode and anode.
5. The method according to claim 4 wherein the pollutants are SOx and NOx emissions generated by the combustion apparatus.
6. The method according to claim 3 wherein said array of spaced-apart tine shaped cathode members and the planar member comprise a modular unit for disposition within the reactor.
7. The method according to claim 6 wherein the reactor includes a predetermined number of modular units.
8. The method according to claim 1 wherein said anode is in the form of a cylindrical anode, the longitudinal axis of which is aligned along the direction of gas circulation and said cathode comprises at least one cathode pin arranged along the longitudinal axis of the cylindrical anode.
9. The method according to claim 8 wherein the cathode is in the form of a plurality of ballasted cathode pins spaced apart along the length of the cylindrical anode, with each said cathode pin terminating along the anode longitudinal axis.
10. The method according to claim 8 wherein a plurality of cylindrical anodes in a nested relationship is provided, each of said cylindrical anodes including at least one cathode pin along the respective longitudinal axis thereof.
11. A system for controlling SOx and NOx emissions of an exhaust gas flow generated by a combustion apparatus comprising in conjunction with the combustion apparatus:
an electrochemical reactor in communication with said combustion apparatus wherein the exhaust gas generated thereby circulates through said electrochemical reactor which includes an inlet and an outlet with the inlet coupled to a fan means whereby the exhaust gas from the combustion apparatus is circulated through said electrochemical reactor at a flow rate of from about 0.5 to 1 Mach number, which reactor includes a predetermined number of hexagonal modular units each comprising electronic cathode means spaced from anode means, each of which is disposed within said reactor to as to effect substantial contact with the exhaust gas circulated therethrough, said electronic cathode means comprising an array of spaced-apart pin-type cathode members spaced from a plane anode member, and means for providing a d.c. potential between said cathode means which are resistively balanced, and said anode means for establishing a uniform stable glow discharge current so as to provide efficient electronic activation of SOx and NOx whereby a field gradient of between about 7-20 kV per centimeter is established so that arcing does not occur and whereby the higher the velocity of the exhaust gas through said electrochemical reactor, the higher the glow discharge current possible without arc breakdown in the exhaust gas wherein SOx and NOx are electronically activated or reacted to effect the chemical modification thereof, thus providing a thermodynamically stable solid product, and filter means in communication with said electrochemical reactor outlet means for filtering the stable solid product from the electrochemically treated exhaust gas.
an electrochemical reactor in communication with said combustion apparatus wherein the exhaust gas generated thereby circulates through said electrochemical reactor which includes an inlet and an outlet with the inlet coupled to a fan means whereby the exhaust gas from the combustion apparatus is circulated through said electrochemical reactor at a flow rate of from about 0.5 to 1 Mach number, which reactor includes a predetermined number of hexagonal modular units each comprising electronic cathode means spaced from anode means, each of which is disposed within said reactor to as to effect substantial contact with the exhaust gas circulated therethrough, said electronic cathode means comprising an array of spaced-apart pin-type cathode members spaced from a plane anode member, and means for providing a d.c. potential between said cathode means which are resistively balanced, and said anode means for establishing a uniform stable glow discharge current so as to provide efficient electronic activation of SOx and NOx whereby a field gradient of between about 7-20 kV per centimeter is established so that arcing does not occur and whereby the higher the velocity of the exhaust gas through said electrochemical reactor, the higher the glow discharge current possible without arc breakdown in the exhaust gas wherein SOx and NOx are electronically activated or reacted to effect the chemical modification thereof, thus providing a thermodynamically stable solid product, and filter means in communication with said electrochemical reactor outlet means for filtering the stable solid product from the electrochemically treated exhaust gas.
12. The system for controlling selected pollutants according to claim 11 wherein the pin-type cathode members which are resistively ballasted are connected to the high voltage d.c. source.
13. The system for controlling selected pollutants according to claim 12 wherein exhaust gas pressure and linear velocity, in addition to the flow rate, and the d.c. potential maintained between the cathode means and anode means are controllable to maintain a uniform stable glow discharge in the volume defined between the cathode means and anode means.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US60534884A | 1984-04-30 | 1984-04-30 | |
| US605,348 | 1984-04-30 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1277953C true CA1277953C (en) | 1990-12-18 |
Family
ID=24423286
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000479957A Expired - Lifetime CA1277953C (en) | 1984-04-30 | 1985-04-24 | Stack gas emissions control system |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS6118424A (en) |
| KR (1) | KR920010275B1 (en) |
| CA (1) | CA1277953C (en) |
| DE (1) | DE3515143A1 (en) |
| GB (1) | GB2158055B (en) |
| IL (1) | IL74856A (en) |
| SE (1) | SE8501858L (en) |
Families Citing this family (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3624803A1 (en) * | 1986-07-23 | 1988-01-28 | Hoelter Heinz | Apparatus and method for improving the efficiency of bactericidal and fungicidal chemisorption filters and corresponding room air filters and motor vehicle cabin air filters with the aid of electrical charges or discharges |
| US4735633A (en) | 1987-06-23 | 1988-04-05 | Chiu Kin Chung R | Method and system for vapor extraction from gases |
| JPH0827017B2 (en) * | 1987-06-29 | 1996-03-21 | 松下電器産業株式会社 | Water heater |
| FI83481C (en) | 1989-08-25 | 1993-10-25 | Airtunnel Ltd Oy | REFERENCE FOUNDATION FOR LENGTH, ROEKGASER ELLER MOTSVARANDE |
| JPH0822367B2 (en) * | 1992-11-27 | 1996-03-06 | 富士通株式会社 | Gas purification equipment |
| DE19534950C2 (en) * | 1995-09-20 | 1998-07-02 | Siemens Ag | Device for the plasma chemical decomposition and / or destruction of pollutants |
| US6119455A (en) * | 1996-08-30 | 2000-09-19 | Siemens Aktiengesellschaft | Process and device for purifying exhaust gases containing nitrogen oxides |
| DE19635232A1 (en) * | 1996-08-30 | 1998-03-05 | Siemens Ag | Method and device for the plasma chemical decomposition and / or destruction of pollutants |
| DE19738038A1 (en) * | 1997-08-30 | 1999-03-04 | Nukem Gmbh | Removing halogenated hydrocarbon(s) from exhaust gases |
| US6576202B1 (en) | 2000-04-21 | 2003-06-10 | Kin-Chung Ray Chiu | Highly efficient compact capacitance coupled plasma reactor/generator and method |
| FR2864142B1 (en) * | 2003-12-19 | 2007-08-24 | Renault Sas | ELECTROSTATIC FILTRATION SYSTEM FOR EXHAUST GASES OF AN INTERNAL COMBUSTION ENGINE |
| CN110184095A (en) * | 2019-05-28 | 2019-08-30 | 中国航天空气动力技术研究院 | A kind of solid waste pyrolytic gasification purified synthesis gas processing method and processing device |
-
1985
- 1985-04-09 IL IL74856A patent/IL74856A/en unknown
- 1985-04-16 SE SE8501858A patent/SE8501858L/en not_active Application Discontinuation
- 1985-04-22 GB GB08510189A patent/GB2158055B/en not_active Expired
- 1985-04-24 CA CA000479957A patent/CA1277953C/en not_active Expired - Lifetime
- 1985-04-25 JP JP60090779A patent/JPS6118424A/en active Pending
- 1985-04-26 DE DE19853515143 patent/DE3515143A1/en not_active Withdrawn
- 1985-04-29 KR KR1019850002881A patent/KR920010275B1/en active IP Right Grant
Also Published As
| Publication number | Publication date |
|---|---|
| GB8510189D0 (en) | 1985-05-30 |
| IL74856A (en) | 1988-07-31 |
| GB2158055B (en) | 1988-02-10 |
| KR920010275B1 (en) | 1992-11-21 |
| SE8501858L (en) | 1985-10-31 |
| KR850007570A (en) | 1985-12-07 |
| DE3515143A1 (en) | 1985-10-31 |
| GB2158055A (en) | 1985-11-06 |
| JPS6118424A (en) | 1986-01-27 |
| IL74856A0 (en) | 1985-07-31 |
| SE8501858D0 (en) | 1985-04-16 |
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