CA1114313A - Electrostatic aerosol scrubber - Google Patents
Electrostatic aerosol scrubberInfo
- Publication number
- CA1114313A CA1114313A CA292,035A CA292035A CA1114313A CA 1114313 A CA1114313 A CA 1114313A CA 292035 A CA292035 A CA 292035A CA 1114313 A CA1114313 A CA 1114313A
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- Prior art keywords
- bubble
- chamber
- liquid
- spray
- scrubber
- Prior art date
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Abstract
ELECTROSTATIC AEROSOL SCRUBBER
Abstract of the Disclosure A method and apparatus for removing entrained particulate matter from a gas stream in which the particles are charged with an electrostatic charge of one polarity, droplets of electrostatically charged liquid are sprayed into the gas stream and the resultant mixture injected into a bubble-forming mechanism wherein bubbles are formed by the gas containing the charged particulate matter and liquid droplets. The smaller mass charged particles are attracted toward and collect upon the charged spray droplets or bubbles. Liquid containing the particulate matter then is removed from the gas stream via known techniques.
Abstract of the Disclosure A method and apparatus for removing entrained particulate matter from a gas stream in which the particles are charged with an electrostatic charge of one polarity, droplets of electrostatically charged liquid are sprayed into the gas stream and the resultant mixture injected into a bubble-forming mechanism wherein bubbles are formed by the gas containing the charged particulate matter and liquid droplets. The smaller mass charged particles are attracted toward and collect upon the charged spray droplets or bubbles. Liquid containing the particulate matter then is removed from the gas stream via known techniques.
Description
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rhe cleansing of industrial exha~lst gases using wet electrostatic scrubbers techniques is well-known. Such apparatus uses fine wflter spray droplets or cascading sheets of water in place ol` the conventional solid collector plates of an electrostatic precipitator. The interaction of a finely atomized water spray uniformly charged to one polarity, with an oppositely charged aerosol, creates a cors~bineà spray scurbber and collector apparatus wherein charged particles are physically captured by the water droplets or cascading sheet of water enhanced by the attraction of the charged particles toward the oppositely charged spray droplets or sheet of water. ~ollowing Coulomb's Law, 10 the small particles are attracted toward and captured by the water droplets or sheet.
Such apparatus is shown in United States Patents, ~,3S7,354 and 2,357,355, wherein an electrostatic dust precipitator utilizing liquid spray is disclosed. United States Patent 3,331,192 discloses an electrostatic precipitator apparatus of the liquid spray type in which aerosol particles are charged to one polarity, liquid spray droplets are oppositely charged and the gas stream carrying the aerosol is contacted with the liquid spray droplets ~s a result, the particulate matter migrates to the liquid spray droplets and is collected. In this device the contact between the liquid spray and the aerosol-containing gus stream is carried out in a large open container.
The well-known processes noted above, while permitting removal of 20 relatively larger particles from a gas stream have too small and inefficient a contact between the aerosol particulate matter in the gas stream and the droplets to remove the relatively smaller particles to the extent necessary to meet current air pollution standards. This invention provides additional improvements in the contaminated aerosol charging apparatus, the liquid spray charging apparatus, the method and apparatus for colltacting the charged particulate material and the oppositely charged liquid, and in the arrangement of all these improved components to create a more efficient and commercially feasible wet electrostatic scrubber and collector of aerosol particles.
Objects of the Invention It is an objeet of this invention to provide air pollution control equipment in 30 which aerosol particles may be removed from a gas stream.
It is a furt~Ler object of this invention to provide apparatus for separating aerosol particles from a gas stream wherein improved gas-liquid contact, enhanced by electrostatic forces, is utili~ed to improve collection efficieney.
It iS tl tUI'illel' ol)ject 0~' this inventioll to provide a spray tower-type aerosol treatment fncility conrlected in conjllnction with a bubble-forming gas-liquid scrubbing apparatus, both of which have the perfolmance thereof enhanced by the imposition of electrostatic charges upon the particulate and liquid components of the system.
It is a still ~ulther~ and rmore specific, object of this invent;on to ;mprove the collection eff;ciency obtained in prior art spray tower-l;ype electrostatic precipitators by operating such precipitators in conjunction with a wliqlle gas-liquid containing device, in which intimate contact between the charged aerosol particle-containing gas stream and an electrostatically charged scrubber liquid is obtained, and in which extencled residence time is provided for such contact whereby improved collection efficiency results.
Summary of the Invention The cleansing of industrial exhaust gases containing contaminating aerosol particles, such as ely ash, is undertaken more effectively, feasibly, and efficiently by an improved series of spray towers combined with a novel bubble type gas-liquid contact means using electrostatic charges to enhance the contact in which more effectivescrubbiJIg and collection occurs of contaminate aerosol particles from commercial exhaust gases.
The improvements include:
1) enhanced charging of the aerosol particles utilizing a direct current potential between rough or smooth surface corona discharge electrodes and spaced apart nondischarge electrodes, wherein a flow OI dry air is used to purge the high-voltage leads and insulators for the corona zone and to limit the aerosol particle llow into the insulator area to keep the insulator as clean as possible;
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rhe cleansing of industrial exha~lst gases using wet electrostatic scrubbers techniques is well-known. Such apparatus uses fine wflter spray droplets or cascading sheets of water in place ol` the conventional solid collector plates of an electrostatic precipitator. The interaction of a finely atomized water spray uniformly charged to one polarity, with an oppositely charged aerosol, creates a cors~bineà spray scurbber and collector apparatus wherein charged particles are physically captured by the water droplets or cascading sheet of water enhanced by the attraction of the charged particles toward the oppositely charged spray droplets or sheet of water. ~ollowing Coulomb's Law, 10 the small particles are attracted toward and captured by the water droplets or sheet.
Such apparatus is shown in United States Patents, ~,3S7,354 and 2,357,355, wherein an electrostatic dust precipitator utilizing liquid spray is disclosed. United States Patent 3,331,192 discloses an electrostatic precipitator apparatus of the liquid spray type in which aerosol particles are charged to one polarity, liquid spray droplets are oppositely charged and the gas stream carrying the aerosol is contacted with the liquid spray droplets ~s a result, the particulate matter migrates to the liquid spray droplets and is collected. In this device the contact between the liquid spray and the aerosol-containing gus stream is carried out in a large open container.
The well-known processes noted above, while permitting removal of 20 relatively larger particles from a gas stream have too small and inefficient a contact between the aerosol particulate matter in the gas stream and the droplets to remove the relatively smaller particles to the extent necessary to meet current air pollution standards. This invention provides additional improvements in the contaminated aerosol charging apparatus, the liquid spray charging apparatus, the method and apparatus for colltacting the charged particulate material and the oppositely charged liquid, and in the arrangement of all these improved components to create a more efficient and commercially feasible wet electrostatic scrubber and collector of aerosol particles.
Objects of the Invention It is an objeet of this invention to provide air pollution control equipment in 30 which aerosol particles may be removed from a gas stream.
It is a furt~Ler object of this invention to provide apparatus for separating aerosol particles from a gas stream wherein improved gas-liquid contact, enhanced by electrostatic forces, is utili~ed to improve collection efficieney.
It iS tl tUI'illel' ol)ject 0~' this inventioll to provide a spray tower-type aerosol treatment fncility conrlected in conjllnction with a bubble-forming gas-liquid scrubbing apparatus, both of which have the perfolmance thereof enhanced by the imposition of electrostatic charges upon the particulate and liquid components of the system.
It is a still ~ulther~ and rmore specific, object of this invent;on to ;mprove the collection eff;ciency obtained in prior art spray tower-l;ype electrostatic precipitators by operating such precipitators in conjunction with a wliqlle gas-liquid containing device, in which intimate contact between the charged aerosol particle-containing gas stream and an electrostatically charged scrubber liquid is obtained, and in which extencled residence time is provided for such contact whereby improved collection efficiency results.
Summary of the Invention The cleansing of industrial exhaust gases containing contaminating aerosol particles, such as ely ash, is undertaken more effectively, feasibly, and efficiently by an improved series of spray towers combined with a novel bubble type gas-liquid contact means using electrostatic charges to enhance the contact in which more effectivescrubbiJIg and collection occurs of contaminate aerosol particles from commercial exhaust gases.
The improvements include:
1) enhanced charging of the aerosol particles utilizing a direct current potential between rough or smooth surface corona discharge electrodes and spaced apart nondischarge electrodes, wherein a flow OI dry air is used to purge the high-voltage leads and insulators for the corona zone and to limit the aerosol particle llow into the insulator area to keep the insulator as clean as possible;
2) an electrically isolated system constructed of insulating material, such as fiberglass reinforced polyester to retard leakage and consumption OI electrical energy;
3) more effective interaction flows of charged cleansing liquid droplets and aerosol particles are undertaken in the spray towers, by effective arrangement of the spray no~zle exits, and employment of nonmetallic materials;
4) providing bubble-forming apparatus, such as a perforated plate or preferably a multiple plate, packed tswer, gas-liguid contacting apparatus which contains one or more layers of liquid bub~le-forming medium, said medium having an electrostatic 3~:~
chalge di~feling from that c~large imposecl upon the particulate matter and upon the liquid droplets. rhe gas containing the chalged particulate matter ancl chargecl liquid droplets is caused to flow upwardly tlllough the bubble-forming device, whereby intimate gas-liquid contact is e~fected by the formation of bubbles in a layer of liquid foam.
The scrubbing liquor used in the cocurrent OL' countercurrent spray towers is charged via a direct chargirlg technique and is contained wilhin an isolated racycled-type system to minimize power consumption and to protect operating personnel from high voltage hazards. The electrically isolated system necessarily includes electrically isolated entrance means for recycled scrubber liquor and for fresh-water make-up as well as an 10 isolation transformer i`or the power supply. In addition, liquid level controls are especially designed to perrmit complete electrical isolation of the system from its surroundings.
The method taught herein and the apparatus necessary for practice of the method carl be generally described as follows: A gas stream containing aerosol particulate matter, which would otherwise constitute a source of pollution, is first transported to an electl ostatic precipitator seetion in which the aerosol particulate matter is electrostatically charged. The charged aerosol is then contacted with a spray of cleansing liquor which has been charged to an opposite polarity to the charge carried by the aerosol particles in an open space to capture the bulk of the aerosol particles.
A portion of the droplets of cleansing liquor settle to the bottom of the open 20 space and are collected and recycled for further use. A substantial portion of the droplets in the smaller size range is carried in the gas as a dispersion or fog and flows to an adjacent gas-liquid contacting apparatus. The gas-liquid contacting apparatus is preferably a perforated plate-type bubble-forming apparatus, a packed tower, a bubMe tray or other type of gas-liquid contact apparatus which provides intimate contact between the gas and liquid. A layer of liguid is maintained above each plate so that bubbles or foam will be formed during the travel OI the base upwardly through the perforated plate or other bubMe-forming device. The gas stream containing the charged aerosol particles and the injected, electrostatically chnrged liquid droplets is broken up into tiny parts, each surrounded by the skin of a bubble Ol is positioned within the 31~ interstices between bubbles. The liquid used to form the bubbles has imposed upon it an electrostatic charge of a polarity and magnitude differing from the ~3harges imposed upon the spray droplets and the aerosol particles. As a consequence o~ the electrostatic charges on the liquid, on the aerosol particles and on the spray droplets, the aerosol particles are attracted to the droplets, the b~ble skin, or both. The apparatus utilized causes bubbles to be formed and sufficient liquid is present so that a sufficient layer of foam is formed resulting in an adequate contact time between the gas and the liquid. Excellent collection efficiency results.
In accordance with the present invention there :is pro-vided a method for removing aerosol particles from a flowing gaseous stream comprising the steps of passing said flow:ing gaseous stream into chamber means defining a spray chamber and a bubble scrubber chamber, in said chamber means imposing a first electrostatic charge upon ~he particles contained in said flowing gaseous stream and removing from said chamber means at least a portion of said particles having said first electrostatic charge, in said spray chamber contacting the flowing gaseous stream with a spray of liquid, the droplets forming said spray ;-having a second electrostatic charge diEfering in potential from ~ ;
said ~irst electrostatic charge, whereby a portion of said 2~ aerosol particles are collected upon said droplets, and removing from said spray chamber at least a portion of said liquid drop-lets upon which said aerosol particles have been collected, in said bubble scrubber chamber contacting said flowing gaseous stream with a bubble-forming liquid having a third electrostatic charge therein differing in potential from at least one of said first and second electrostatic charges, wherein said flowing gaseous stream forms bubbles and is intimately intermixed with the ~ubble-forming liquid and whereby at least a portion of said aerosol particles are captured by said bubble-forming liquid 3~ and are removed ~rom said flowing gaseous stream, and removing ~ ~ ' ~ 4 -. , .
3~! 3 from said bubble scrubber chamber at least a portion of said bubble-forming liquid containing said aerosol particles, and exhausting said flowing gaseous stream from said chamber means.
In accordance with the present invention there is also provided an electrostatic wet scrubber and collector assembly comprising chamber means defining a spray chamber and a bubble scrubber chamber, said spray chamber and said bubble scrubber chamber being in gaseous communication with each other, said chamber means having an inlet and an outlet, means positioned and arranged with respect to said chamber means for imposing a first electrostatic charge upon particulate matter contained in ~ .
a ~aseous stream passing through said chamber means from said : ~.
inlet to said outlet, spray means associated and arranged with respect to said spray chamber ~or injecting droplets of liquid into said spray chamber, and means associated with said spray .~ means for imposing a second electrostatic charge on said drop- ~
lets said second elec~rostatic charge dif~ering in potential ;
from said first electrostatic charge, whereby said droplets and :; particulate matter are attracted to each other, means associated and arranged with respect to said spray chamber for removing at :
least a portion of said droplets to which particulate matter has been attracted, bubble scrubber means associated and arranged in said bubble scrubber chamber to receive said gaseous stream ~ passing through said cham~er means and to cause said gaseous : s~ream to flow upwardly through said bubble scrubber chamber, said bubble scrubber means containing at least one bubble-forming means ~or supporting a bubble-forming liquid thereon, said bubble scrubber means being positioned to receive said : ~ gaseous s~ream as it flows upwardly through said bubble scrubber chamher, means positioned and arranged with respect to said ~:
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~:, bubble scrubber means ~or imposing a third electrostatic charge on said bubble-forming liquid, said third el.ectrostatic charge having a potential different from at least one of said first and second electrostatic charges, and means, including a sump and a pump, positioned and arranged with respect to said bubble-forming means for recycling said bubble-forming liquid from the bubble scrubber means to said sump and back to said bubble-~orming means.
Description of the Drawings FIGURE 1 is a generalized flow diagram of an electro-static scrubber and collector system;
FIGURE 2 is a schematic cross section o one spray tower and a charged droplet bubble scrubber;
FIGURE 3 is a plan view of one embodiment of an electro-static bubble scrubber;
FIGURE 4 is a cross-sectional view taken along lines 4-4 of FIGURE 3, showing the interior elements of the electro-static bubble scrubber;
FIGURE 5 is a schematic elevational view of an aerosol charging apparatus with one side removed for clarity;
FIGURE 6 is a partial schematic plan view of the aerosol charging apparatus shown in FIGURE 5 in cross section taken along lines 6-6 of FIGURE 5;
FIGURE 7 is a schematic plan view of a spray forming and charging apparatus used to charge cleansing liquid spray drop-lets in towers 120 and 134 of FIGURE l;
FIGURE 8 is a partial cross section taken along lines 8-8 o~ FIGURE 7;
FIGURE 9. is a schematic diagram indicating polarities 30. of electrostatic charges imposed at various locations of the - 4b -~, .. ..
~, 3~L3 electrostatic scrubber for difEerincJ operat:ing conditions;
FIGURES 10-15 are enlarged schematic c:ross sections of respective individual combinations oE drop].ets, aerosol particles and bubbles showing, respectively, obtainable clispersements of electrostatic charges for the conditions shown in FIGURE 9 for the cleansing liquid droplets, the charged aerosol particles, and the bubble structures; and~
FIGURE 16 is an axial, cross-sectional view of another embodiment of an electrostatic bubble scrubber.
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Description of PreEerred Embodimen-ts l~et Electrostatic Scrubber Using One or ~lore Spray Towers in Series with Bubble-Forming Gas-Liquid Contactor In FIGURE 1, a schematic flow diagram of a wet electrostatic scrubber system including :Eeatures of this inventio-n is illustrated. The system shown includes aerosol entering the system through conduit 110 from a source ~not shown), such as the exhaust gas from a coal-fired, power boil-er, a metallurgical kiln, a pulp mill recovery boiler effluent or the like, containing a substantial loading of aerosol particles. This gaseous disper-sion is passed into an initial liquid contacting chamber 112 which functions to cool the incoming gas if necessary and provide an initial contact of the gases with a spray of the liquid used to wash the gas. This interaction be-tween the washing liquid and the gas may or may not be conducted with the aid of an electrostatic charge on the liquid. The liquid not evaporated in the cooling process is drained and returned to the sump 100 through drain 111.
; Gases leave the cooling chamber 112 through conduit 114 and enter the particle-charging zone 116. A suitable structure for the particle-charg-ing zone 116 is an electrostatic precipitator, well-known in the art. A por~
tion of the particulate material may be removed in the particle-charging zone 116 and the gases containing a substantial portion of the aerosol leave through conduct 118 and are injected into a spray tower 120 which is designed to intermix the aerosol containing gases with droplets of cleansing liquid injected into tower 120 through spray nozzle 122. The droplets thus carry an ;~
electrostatic charge opposite in polarity to that charge imposed upon the aerosol particles in the particle-charging zone 116. As shown in FIGURE 1, the cleansing liquid is supplied through line 119 and enters the tower 120 through the top 121 and is discharged into the spray tower through nozzle 122. A high voltage lead 12~ is positioned either in the liquid conduit or projecting outwardly from the nozzle to impose an electrostatic charge on
chalge di~feling from that c~large imposecl upon the particulate matter and upon the liquid droplets. rhe gas containing the chalged particulate matter ancl chargecl liquid droplets is caused to flow upwardly tlllough the bubble-forming device, whereby intimate gas-liquid contact is e~fected by the formation of bubbles in a layer of liquid foam.
The scrubbing liquor used in the cocurrent OL' countercurrent spray towers is charged via a direct chargirlg technique and is contained wilhin an isolated racycled-type system to minimize power consumption and to protect operating personnel from high voltage hazards. The electrically isolated system necessarily includes electrically isolated entrance means for recycled scrubber liquor and for fresh-water make-up as well as an 10 isolation transformer i`or the power supply. In addition, liquid level controls are especially designed to perrmit complete electrical isolation of the system from its surroundings.
The method taught herein and the apparatus necessary for practice of the method carl be generally described as follows: A gas stream containing aerosol particulate matter, which would otherwise constitute a source of pollution, is first transported to an electl ostatic precipitator seetion in which the aerosol particulate matter is electrostatically charged. The charged aerosol is then contacted with a spray of cleansing liquor which has been charged to an opposite polarity to the charge carried by the aerosol particles in an open space to capture the bulk of the aerosol particles.
A portion of the droplets of cleansing liquor settle to the bottom of the open 20 space and are collected and recycled for further use. A substantial portion of the droplets in the smaller size range is carried in the gas as a dispersion or fog and flows to an adjacent gas-liquid contacting apparatus. The gas-liquid contacting apparatus is preferably a perforated plate-type bubble-forming apparatus, a packed tower, a bubMe tray or other type of gas-liquid contact apparatus which provides intimate contact between the gas and liquid. A layer of liguid is maintained above each plate so that bubbles or foam will be formed during the travel OI the base upwardly through the perforated plate or other bubMe-forming device. The gas stream containing the charged aerosol particles and the injected, electrostatically chnrged liquid droplets is broken up into tiny parts, each surrounded by the skin of a bubble Ol is positioned within the 31~ interstices between bubbles. The liquid used to form the bubbles has imposed upon it an electrostatic charge of a polarity and magnitude differing from the ~3harges imposed upon the spray droplets and the aerosol particles. As a consequence o~ the electrostatic charges on the liquid, on the aerosol particles and on the spray droplets, the aerosol particles are attracted to the droplets, the b~ble skin, or both. The apparatus utilized causes bubbles to be formed and sufficient liquid is present so that a sufficient layer of foam is formed resulting in an adequate contact time between the gas and the liquid. Excellent collection efficiency results.
In accordance with the present invention there :is pro-vided a method for removing aerosol particles from a flowing gaseous stream comprising the steps of passing said flow:ing gaseous stream into chamber means defining a spray chamber and a bubble scrubber chamber, in said chamber means imposing a first electrostatic charge upon ~he particles contained in said flowing gaseous stream and removing from said chamber means at least a portion of said particles having said first electrostatic charge, in said spray chamber contacting the flowing gaseous stream with a spray of liquid, the droplets forming said spray ;-having a second electrostatic charge diEfering in potential from ~ ;
said ~irst electrostatic charge, whereby a portion of said 2~ aerosol particles are collected upon said droplets, and removing from said spray chamber at least a portion of said liquid drop-lets upon which said aerosol particles have been collected, in said bubble scrubber chamber contacting said flowing gaseous stream with a bubble-forming liquid having a third electrostatic charge therein differing in potential from at least one of said first and second electrostatic charges, wherein said flowing gaseous stream forms bubbles and is intimately intermixed with the ~ubble-forming liquid and whereby at least a portion of said aerosol particles are captured by said bubble-forming liquid 3~ and are removed ~rom said flowing gaseous stream, and removing ~ ~ ' ~ 4 -. , .
3~! 3 from said bubble scrubber chamber at least a portion of said bubble-forming liquid containing said aerosol particles, and exhausting said flowing gaseous stream from said chamber means.
In accordance with the present invention there is also provided an electrostatic wet scrubber and collector assembly comprising chamber means defining a spray chamber and a bubble scrubber chamber, said spray chamber and said bubble scrubber chamber being in gaseous communication with each other, said chamber means having an inlet and an outlet, means positioned and arranged with respect to said chamber means for imposing a first electrostatic charge upon particulate matter contained in ~ .
a ~aseous stream passing through said chamber means from said : ~.
inlet to said outlet, spray means associated and arranged with respect to said spray chamber ~or injecting droplets of liquid into said spray chamber, and means associated with said spray .~ means for imposing a second electrostatic charge on said drop- ~
lets said second elec~rostatic charge dif~ering in potential ;
from said first electrostatic charge, whereby said droplets and :; particulate matter are attracted to each other, means associated and arranged with respect to said spray chamber for removing at :
least a portion of said droplets to which particulate matter has been attracted, bubble scrubber means associated and arranged in said bubble scrubber chamber to receive said gaseous stream ~ passing through said cham~er means and to cause said gaseous : s~ream to flow upwardly through said bubble scrubber chamber, said bubble scrubber means containing at least one bubble-forming means ~or supporting a bubble-forming liquid thereon, said bubble scrubber means being positioned to receive said : ~ gaseous s~ream as it flows upwardly through said bubble scrubber chamher, means positioned and arranged with respect to said ~:
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~:, bubble scrubber means ~or imposing a third electrostatic charge on said bubble-forming liquid, said third el.ectrostatic charge having a potential different from at least one of said first and second electrostatic charges, and means, including a sump and a pump, positioned and arranged with respect to said bubble-forming means for recycling said bubble-forming liquid from the bubble scrubber means to said sump and back to said bubble-~orming means.
Description of the Drawings FIGURE 1 is a generalized flow diagram of an electro-static scrubber and collector system;
FIGURE 2 is a schematic cross section o one spray tower and a charged droplet bubble scrubber;
FIGURE 3 is a plan view of one embodiment of an electro-static bubble scrubber;
FIGURE 4 is a cross-sectional view taken along lines 4-4 of FIGURE 3, showing the interior elements of the electro-static bubble scrubber;
FIGURE 5 is a schematic elevational view of an aerosol charging apparatus with one side removed for clarity;
FIGURE 6 is a partial schematic plan view of the aerosol charging apparatus shown in FIGURE 5 in cross section taken along lines 6-6 of FIGURE 5;
FIGURE 7 is a schematic plan view of a spray forming and charging apparatus used to charge cleansing liquid spray drop-lets in towers 120 and 134 of FIGURE l;
FIGURE 8 is a partial cross section taken along lines 8-8 o~ FIGURE 7;
FIGURE 9. is a schematic diagram indicating polarities 30. of electrostatic charges imposed at various locations of the - 4b -~, .. ..
~, 3~L3 electrostatic scrubber for difEerincJ operat:ing conditions;
FIGURES 10-15 are enlarged schematic c:ross sections of respective individual combinations oE drop].ets, aerosol particles and bubbles showing, respectively, obtainable clispersements of electrostatic charges for the conditions shown in FIGURE 9 for the cleansing liquid droplets, the charged aerosol particles, and the bubble structures; and~
FIGURE 16 is an axial, cross-sectional view of another embodiment of an electrostatic bubble scrubber.
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Description of PreEerred Embodimen-ts l~et Electrostatic Scrubber Using One or ~lore Spray Towers in Series with Bubble-Forming Gas-Liquid Contactor In FIGURE 1, a schematic flow diagram of a wet electrostatic scrubber system including :Eeatures of this inventio-n is illustrated. The system shown includes aerosol entering the system through conduit 110 from a source ~not shown), such as the exhaust gas from a coal-fired, power boil-er, a metallurgical kiln, a pulp mill recovery boiler effluent or the like, containing a substantial loading of aerosol particles. This gaseous disper-sion is passed into an initial liquid contacting chamber 112 which functions to cool the incoming gas if necessary and provide an initial contact of the gases with a spray of the liquid used to wash the gas. This interaction be-tween the washing liquid and the gas may or may not be conducted with the aid of an electrostatic charge on the liquid. The liquid not evaporated in the cooling process is drained and returned to the sump 100 through drain 111.
; Gases leave the cooling chamber 112 through conduit 114 and enter the particle-charging zone 116. A suitable structure for the particle-charg-ing zone 116 is an electrostatic precipitator, well-known in the art. A por~
tion of the particulate material may be removed in the particle-charging zone 116 and the gases containing a substantial portion of the aerosol leave through conduct 118 and are injected into a spray tower 120 which is designed to intermix the aerosol containing gases with droplets of cleansing liquid injected into tower 120 through spray nozzle 122. The droplets thus carry an ;~
electrostatic charge opposite in polarity to that charge imposed upon the aerosol particles in the particle-charging zone 116. As shown in FIGURE 1, the cleansing liquid is supplied through line 119 and enters the tower 120 through the top 121 and is discharged into the spray tower through nozzle 122. A high voltage lead 12~ is positioned either in the liquid conduit or projecting outwardly from the nozzle to impose an electrostatic charge on
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;X : ' 3~L3 the liquid droplets. Purge air to the nozzle area is supplied through purge air line 125 to keep the pipe to nozzle dry, so that it will not short out to the wall of tower 120 or to the tower top 121. The aerosol particles are then at-tracted to the charged droplets according to .
Coulomb's Law, some are captured by the droplets and removed through the drain 126. lVhile many particles are removed by this first spray tower 120, tiny particles of aerosol tend to carry over in the gas stream, leaving the spray tower through conduit 128. This aerosol gas-containing gas stream is then passed through a second aerosol charging zone - 5a -130 where a negative potential is imposed upon the aerosol particles and then passed into a second sprfly tower 134 through conduit 132. Spray tower 134 is a similar structure to spray tower 120 flnd functions in a substnntially identical marlrler. Liquid containing certain additional quantities of the aerosol particles is drained out througll drain 136 and the washed gases leave the tower 134 ~hrough conduit 138. Again these gases contain a certain quantity of the aerosol particles which have not as yet been rernoved from the gas streaïn in the first and second spray towers, as well as a fog or dispersion of small liquid droplets.
'l'he aerosol containing gases are then passed into bubble scrubber 1~ directly through conduit 137 or the gas stream may again be charged in particle-charging zone 140 and then passed into bubble scrubber 14k. A liquid containing a high electrostatic charge opposite to that charge carried by the aerosol particles is passed counter-currently (downwardly) to the flow of the gases in the bubble scrubber 14~. A bubble generator 143, in the forrm of a perforated plate or other gas-liquid contacting device is utilized to promote intimate gas-liquid contact. The gases passing through the bubble plate structure cause the liquid resting on top of the bubble plates to foam and the gases are encapsulated within bubbles or arera~J~a~c~ bubbles formed in the process. The liquid may drain slowly down through the perforated plate 143 or may be taken off of the plate and recycled through the particle removal system (i.e., settling tank~. The resulting close proximity of the charged particles to the electrostatically charged surface film forming the bubble, coupled with the long residence time obtained by a bubble plate device enh~nces the capture characterisbcs of the system whereby the difficult-to-remove aerosol particles are captured with a substantially improved et'ficiency. Gases then pass out through a rmist eliminator 150 through exhaust fan 152 and then discharged to the atmosphere.
The liquid is supplied to the towers and the bubble scrubber by pump 1û2 through the conduit system shown. Pump 102 removes liquid from sump 100 which has level controls 105 installed therein to control the level of liquid. Fresh water makeup 104 is injected through isolation injector 195 to prevent flow of electrical current into the supply lines for fresh water makeup. Similarly, the recyeled liquid enters sump 100 through isolation injector 106 to prevent flow of current through the recycle lines.
Sump 100~ pump 102 and conduit 103 are maintained at an elevated voltage, usually positive, and must be insulated and isolated from the rest of the system. This is best ac~omplished by the use of nonconductive materials of construction for those parts which contact the liquid.
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In ~IGUKI~ ~, one spray tOWel' 13~ arld bubble scrubber 145 are schematically shown. rhe aerosol containing gase~, such as those emitted from a coal-fiIed power boile~, enter at ~as inlet 34 and pass through an aerosoI particle charger 36 operated by a high voltage power supply 38 irnposing a negative, high voltage direct current upon the electrostatic charger. rhe particulate matter in the gases receives a strong electrostatic charge t`rom electrodes 7~ and the charged gases flre then directed into the spray tower 13'1.
Locatecl above the gas entrance i9 a liquid spray electrostatic charging means 42 used to impose R high voltage upon liquid droplets formed therein. The power 10 supply 39 provides a high voltage current to the charging means 42. A cleansing liquid enters through pipe 44 and continues on to the spray nozzles 46. Insulated high voltage leads 48 extend into the liquid near the spray nozzle 46. Leads 48 are Imcovered at their ends in the pipes 44 near the spray nozzles 46. Through the interior of the eharging means 4~, clean dry purge air is directed from pipe 80 as a purge to protect the nozzles 46 and the exposed pipe 44 from deposits of substances which may cause arcing, electrical short circuiting, or other malfunction of the droplet charging system.
Spray tower 134 is preferably constructed of a materi~l having insulating properties, such as fiberglass reinforced polyester, epoxy resins, ceramics or other suitable material which provides both the insulating properties necessary and the 20 resistance to corrosion to the particular system being employed. By having the tower structure itself constructed of an insulating material, the electrostatically charged droplets and particles tend less to migrate to the walls, and, as a consequence, remain in the area in which the maximum contact between the charged aerosol containing gases and liquid droplets is achieved.
The spray tower 134 is shown equipped with an auxiliary spray means 42a to inject additional electrostatically charged droplets of cleansing liquid through nozzles 46a.
Some of the larger droplets injected at spray means 42 and 42a may settle out ancl be collected at the bottom of tower 134. Liquid is returned to the sump 100 by drain line 136.
The remainder of the liquid is carried over into charged droplet bubble scrubber 145 in the 30 form of a fog or tiny droplets of liquid, each having an electrostatic charge thereon. The gases carrying any remaining charged aerosol particles and the liquid dro~lets noted above pass from tower 134 into scrubber 145 through duct 135. A pair of perforated bubble plates 143 and 1~3' are positioned horixontally withirl bubble scrubber 145. Both plates are siæed so thRt gases may l`Iow upwardly through the perforations 141 and 1~14' therein while liquid flows slowly downwardly through the perforations. A substantial liquid level h and h' is maintained on top of each performated plate during operations by injection of a flow of liquid through supply pipe lS0. Gases flowing upwardly throllgh the perforations form small bubbles in the liquid and as a result are in intimate contact therewith. The liquid is charged to a high voltage by power supply 147 and as a result, the charged particles and droplets are collected in the film forming the bubbles. The gases, cleansed of the particles, pass out through~ eliminator 148 to the atmosphere.
FIGURES 3 and 4 show one preferred embodiment of the charged droplet ~ ~ bubble scrubber device. FIGURE 3 is a plan view showing the upper perforated plate ~,f having high-voltage supply cable 152 connected thereto. The high-voltage supply cable is attached to one of the four plate spacers 153. The liquor-feed supply conduit 154 carries a plurality of spray nozzles 155. Electrostatic isolating baffles 157 and 187 serve to prevent the high voltage imposed upon the scrubber from being grounded out through the walls of the device.
In the scrubber zone, best seen in FIGURE 4, a packed column area 160 is comprised of a pair of parallel spaced-apart perforated metal bubble plates 148 and 150.
These bubble plates are spaced apart by plate spacers 153 and may contain packing 158, if 20 desired, to increase the gas-liquid contact area. An overflow drain downcomer 162 permits liquid flow from the packed portion of the scrubber seciton to the drain. During operation, a head of water is maintained in the overflow drain, so that air does not pass upwardly through the drain. The assembled plates are nestled within the bubble plate support 164, which is preferably constructed of a nonconducting material, such as fiberglass reinforced polyester, other plastic substance, or a ceramic. Bubble plate support 164 serves to position the bubble plate assembly 160 in a spaced-apart relationship with the shell 166. High-voltage cable 152 serves to maintain the bubMe plate assembly and the liquid contained therein at a suitably high potential, thus imposing an electrostatic charge upon the liquid contained therein. In the embodirnent shown, the Iiquor supply is 30 electrically isolated from the high-voltage bubble plate assembly and is grounded.
In operation, liquid is fed to the bubble plate assembly thrau~h liquor feed supply conduit 154 onto upper perforated plate 150. ~imultaneously, gases conta;ning 3~33 particulate matter are caused to flow upwarclly through lower perforated plate 148 and upper perforated plate 150. The counter-current flow of liquid and gas cause the formation of bubbles at plates 1~}8 and 150 with the resultant formation of a foam of substantial depth of each plate. The packing 158 serves to further provide additional surface for contact o~' the gas and liquid. The gas containing an electrostatically charged aerosol is thus intimately contacted with the liquid having an opposite charge. Following Coulomb's Law, the particulate matter ;s attracted to and captured by the liquid. Since tiny bubbles are formed and intimate contaet results, a very substantially improved collection efficiency is thus obtained. The liquid which is fed to the upper surface of 10~ upper perforated plat~ 150 passes downwardly through the perforations into the packed h ~ h ~
~intermediate zone~58 and co~tinues to~ravel downwardly to plate 148. The influence of upwardly flowing air slows the downward progress of the liquid and, at steady state conditions, a mass balance is achieved with slowed downward flow of liquid and upward flow of aerosol-containing gases. When the level of liquid in the zone between plates 148 and 150 reaches the upper level of overflow drain downcomer 162, the liquid is free to flow downwardly through the drain. 'I'his prevents flooding of the packed section of the bubble scrubber 160.
Isolating baffle 157 prevents flow of liquids to the shell 166. Drainholes 169 and 169' in the upper isolated baffle serve to drain any liquid which may flow through the shell area. Liners 172 and 172'Amade of polytetrafluoroethylene or other material which is reslstant to wetting may be used to aid in electrically isolating the system and to aid in maintaining the system as clean as possible.
1~1 The lower isolating baffle ~ similarly serves to isolate the system electrically and drainholes 171 and 171' permit excess moisture to drain back into the interior of the scrubber section. The isolating baffles are constructed of an insulated substance, such as fiberglass reinforced polyester, other suitable plastics or ceramic materials.
In describing the multiple spray tower wet electrostatic scrubber illustrated ~.~ in FIGUR~ reference was rnade to the corona discharge aerosol partiele-charger 36. In 30 the schematic view of ~IGURES 5 and 6, an arrangement of the corona wire frame 74 of discharge electrodes 76 is shown in its relative position to the collection plates 78 serving as the nondischarge electrodes. The corona discharge ele.ctrodes 76 are preferably formed _9_ in a helix as shown to increase the available surface for corona and thereby to enhance the effectiveness of the particle chflrging eunctions of the apparatus.
'i ^l Also in describing the wet electrostatic scrubber illustrated in FIGURE~
reference was made to a droplet-charger 42. In FIGIJRES 7 and 8, one embodiment of a cleansing liquid droplet-churger ~2 is illustrated. FIGURE 7 indicates the positions of the no7zles ~6 in the spray tower 32 with their respective insulators 50, liquid supply pipes 44, purge air ducts 80, and high voltage leads 4~. In ~IGURE ~, talcen on line 8--8 of ~I~URE
7, part of the components of the direct wire or direct voltage droplet charger 42 are illustrated in a partial cross section. The cleaning liquid is directed do~vnwardly into pipes 10 '14, then charged at uncovered end 81 of high voltage leads 48, and thereafter emitted through the spray noz~les 46 as electrostatically positively charged droplets 82 ready to start their scrubbing function. It is to be noted that nonconductive piping 44 for the liquid is preferred to reduce the loss of electrical energy.
One embodiment of this Wet Electrostatic Scrubber, schematically illustrated in FIGURES 2 and 3, involves the effective use of both electrostaticaIly charged liquid droplets and electrostatically charged liquid bubbles ta collect oppositely charged aerosol particles, for example from contaminated aerosol gases enroute to and/or up an exhaust stack. rhe charged liquid droplets may be of either equal or opposite polarity from the bubbles of cleansing liquids.
The corona wires are connected to a high-voltage power supply and ionize the gases and incoming aerosol particles. The nondischarge electrodes are connected to ground. The cleansing liquid droplets are generated by discharging liquids under pressure from spray nozzles, or by discharging liquids, not under pressure, but in the presence of flowing air under pressure, as occurs when a pneumatic nozzle is used.
The liquid electrostatic charge is imparted by a corona generator which is connected to a high voltage power supply. The spray tower chamber walls are constructed of either conductive or nonconductive materials, or a comMnation of them. The liquid supply lines are made of nonconductive materials, and they are connected to the chamber walls of using fittings that provide for the entry and discharge of dry clean air which 30 purges the volume around the nonconductive material, serving to keep the noncondll3ctive suppl~ line materials and some other materials dry and, therefore, substantially free of insoluble deposits.
10~
$
I`he chnrged aerosol particles and the oppositely charged cleansing liquid droplets tlow through perforated plate~, which is made frorn a conductive material.
: ' ~
This perforated plate 1~ contains a plurality of apertures 144 through which the gases, aerosol particles, and liquid droplets entralned in the gases flow. The gas, particle and droplet mixture then bubbles through a layer of liquid and f~am maintained at u level h on top of perforated plate 1~8. ï`he liquid flows countercurrently to the gases downwardly through apertures 144. The liquid may contain a foaming agent or surfactant to assist in the generation and stabilization of the bubbles, thereby increasing the contact time between the liquid and the aerosol containing gases.
In the embodiment shown in FIGURE 2, the foam is raised to a positive polarity in the range of 30 KV by the power supply~8. rhe flow rates of the liquid and gases through the gas-liquid contactor 145 are regulated so that the two phase gas-liquid foam on top of the perforated plate 143 and 143' is maintained at a depth OI from about 2 to about 24 inches. The gases flow upwardly through the apertures 144 and 144' and the liquid flows downwardly through the same apertures, providing excellent gas-liquid contact.
The charged aerosol particles are collected upon the surfaces eharged to the opposite polarity, which are the surfaces on either or both of the liquid droplets or the bubbles. Aerosol particle collection will occur upon both the inside and outside surfaces 20 of the respective bubbles. The liquid and foam maintained at a given level upon the perforated plate is electrostatically charged by a high voltage power supply to a polarity either the same or opposite from the liquid droplet, and to a polarity either the same or opposite from the aerosol particles.
In FIGURE 9 a schematic representation of the gas flow and electrostatic charge modes useful in this invention is shown. Aerosol containing gases enter the apparatus through conduit 34 and flow into charging section 130. An electrostatic charge is imposed thereon. Liquid enters tower 134 with an electrostatic charge and enters bubble scrubber 145 maintained at an elevated potential. I.iquid is removed from the gas stream in precipitator 148. The workable polarities and electrostatic charging voltages 30 are set forth in Table 1.
3:~
Tablc l A B C D
Condition Corona Spray Bubble Mist Figure Section Tower Scrubber F.liminator I-30 to -~00 kv-~1 to S0 kv~1 to 50 kv-~30 to lO0 kv 10 II-30 to -400 kv-1 to 50 kv~1 to 50 kv~30 to 100 kv 11 III-30 to -~00 kv+1 to 50 kv-1 to S0 kv-30 to 100 kv 12 IV+30 to ~400 kv~1 to 50 kv-1 to 50 kv-30 to lO0 kv13 V~30 to 400 kv-l to 50 kv-l to 50 kv+30 to 100 kv 14 VI+30 to 400 kv-1 to 50 kv+1 to 50 kv+30 to 100 kv 15 For each mode of operation set forth in Table 1, reference is made to FIGURES 10-15 which show schematically the conditions in bubble scrubber 145.
In FIGUXE lO, the bubble b is charged positively and is shown sur-rounded by liquid. The droplets are charged positively while the particles are charged negatively. Thus the negatively charged particles are attracted - to the inside and outside surfaces of the positively charged bubble and are further attracted to the positively charged droplet thus the particles are collected upon both the droplets and the surfaces of the bubble.
In FIGURE 11, the bubble b is charged positively and is shown sur-rounded by liquid. The particle p is charged negatively, and the droplet d is charged negatively. The negatively charged particles are repelled by the negatively charged droplet, which is located inside the bubble, and are at-tracted to and collected UpOII the positively charged inside surface of the bubble.
In FIGURE 12, the bubble is charged negatively, and is shown sur-rounded by liquid. The droplet is charged positively, and particles are charged negatively The negatively charged particles are repelled by the negativ~ly charged bubble surface and are attracted to the positively charged droplets.
3.~3 In FIGURr 13, the bubble is charged negatively, the dro~plets are charged positively and the particles are charged posi.tively. The particles are repelled by -the droplets and attracted by the inside and outside sur-face of the bubble.
In FIGURE 14, the bubble is negatively charged~ the droplets are negatively charged and the particles are positively charged. Both the drop-lets and the bubble inside and outside surfaces attract the particles.
In FIGURE 15, the bubble is positively charged and shown in liq-uid. The droplets are negatively charged and the particles are positively charged. Particles are repelled by the bubble surface and attracted to droplets.
The following operating parameters have been found workable by the inventor for the overall system shown in FIGURES 1 and 2;
1. Power supply to corona section 116 or 130 - 30 to ~0 kilo-volts.
- 12a -2. Power supply to water or liquor bubble section 145 -- l to 50 kilovolts.
3. Power supply to water Ol liquor spray section 134 -- l to 50 kilovolts.
4. Water flow to water c>r liquor spray section 134 -- O.l to 50 gallons per l,000 actual cubic feet of gas.
5. Water flow in bubble sections 14S -- 0.1 to 50 gallons per l,000 actual cubic feet (water can be recycled.)
;X : ' 3~L3 the liquid droplets. Purge air to the nozzle area is supplied through purge air line 125 to keep the pipe to nozzle dry, so that it will not short out to the wall of tower 120 or to the tower top 121. The aerosol particles are then at-tracted to the charged droplets according to .
Coulomb's Law, some are captured by the droplets and removed through the drain 126. lVhile many particles are removed by this first spray tower 120, tiny particles of aerosol tend to carry over in the gas stream, leaving the spray tower through conduit 128. This aerosol gas-containing gas stream is then passed through a second aerosol charging zone - 5a -130 where a negative potential is imposed upon the aerosol particles and then passed into a second sprfly tower 134 through conduit 132. Spray tower 134 is a similar structure to spray tower 120 flnd functions in a substnntially identical marlrler. Liquid containing certain additional quantities of the aerosol particles is drained out througll drain 136 and the washed gases leave the tower 134 ~hrough conduit 138. Again these gases contain a certain quantity of the aerosol particles which have not as yet been rernoved from the gas streaïn in the first and second spray towers, as well as a fog or dispersion of small liquid droplets.
'l'he aerosol containing gases are then passed into bubble scrubber 1~ directly through conduit 137 or the gas stream may again be charged in particle-charging zone 140 and then passed into bubble scrubber 14k. A liquid containing a high electrostatic charge opposite to that charge carried by the aerosol particles is passed counter-currently (downwardly) to the flow of the gases in the bubble scrubber 14~. A bubble generator 143, in the forrm of a perforated plate or other gas-liquid contacting device is utilized to promote intimate gas-liquid contact. The gases passing through the bubble plate structure cause the liquid resting on top of the bubble plates to foam and the gases are encapsulated within bubbles or arera~J~a~c~ bubbles formed in the process. The liquid may drain slowly down through the perforated plate 143 or may be taken off of the plate and recycled through the particle removal system (i.e., settling tank~. The resulting close proximity of the charged particles to the electrostatically charged surface film forming the bubble, coupled with the long residence time obtained by a bubble plate device enh~nces the capture characterisbcs of the system whereby the difficult-to-remove aerosol particles are captured with a substantially improved et'ficiency. Gases then pass out through a rmist eliminator 150 through exhaust fan 152 and then discharged to the atmosphere.
The liquid is supplied to the towers and the bubble scrubber by pump 1û2 through the conduit system shown. Pump 102 removes liquid from sump 100 which has level controls 105 installed therein to control the level of liquid. Fresh water makeup 104 is injected through isolation injector 195 to prevent flow of electrical current into the supply lines for fresh water makeup. Similarly, the recyeled liquid enters sump 100 through isolation injector 106 to prevent flow of current through the recycle lines.
Sump 100~ pump 102 and conduit 103 are maintained at an elevated voltage, usually positive, and must be insulated and isolated from the rest of the system. This is best ac~omplished by the use of nonconductive materials of construction for those parts which contact the liquid.
p~
In ~IGUKI~ ~, one spray tOWel' 13~ arld bubble scrubber 145 are schematically shown. rhe aerosol containing gase~, such as those emitted from a coal-fiIed power boile~, enter at ~as inlet 34 and pass through an aerosoI particle charger 36 operated by a high voltage power supply 38 irnposing a negative, high voltage direct current upon the electrostatic charger. rhe particulate matter in the gases receives a strong electrostatic charge t`rom electrodes 7~ and the charged gases flre then directed into the spray tower 13'1.
Locatecl above the gas entrance i9 a liquid spray electrostatic charging means 42 used to impose R high voltage upon liquid droplets formed therein. The power 10 supply 39 provides a high voltage current to the charging means 42. A cleansing liquid enters through pipe 44 and continues on to the spray nozzles 46. Insulated high voltage leads 48 extend into the liquid near the spray nozzle 46. Leads 48 are Imcovered at their ends in the pipes 44 near the spray nozzles 46. Through the interior of the eharging means 4~, clean dry purge air is directed from pipe 80 as a purge to protect the nozzles 46 and the exposed pipe 44 from deposits of substances which may cause arcing, electrical short circuiting, or other malfunction of the droplet charging system.
Spray tower 134 is preferably constructed of a materi~l having insulating properties, such as fiberglass reinforced polyester, epoxy resins, ceramics or other suitable material which provides both the insulating properties necessary and the 20 resistance to corrosion to the particular system being employed. By having the tower structure itself constructed of an insulating material, the electrostatically charged droplets and particles tend less to migrate to the walls, and, as a consequence, remain in the area in which the maximum contact between the charged aerosol containing gases and liquid droplets is achieved.
The spray tower 134 is shown equipped with an auxiliary spray means 42a to inject additional electrostatically charged droplets of cleansing liquid through nozzles 46a.
Some of the larger droplets injected at spray means 42 and 42a may settle out ancl be collected at the bottom of tower 134. Liquid is returned to the sump 100 by drain line 136.
The remainder of the liquid is carried over into charged droplet bubble scrubber 145 in the 30 form of a fog or tiny droplets of liquid, each having an electrostatic charge thereon. The gases carrying any remaining charged aerosol particles and the liquid dro~lets noted above pass from tower 134 into scrubber 145 through duct 135. A pair of perforated bubble plates 143 and 1~3' are positioned horixontally withirl bubble scrubber 145. Both plates are siæed so thRt gases may l`Iow upwardly through the perforations 141 and 1~14' therein while liquid flows slowly downwardly through the perforations. A substantial liquid level h and h' is maintained on top of each performated plate during operations by injection of a flow of liquid through supply pipe lS0. Gases flowing upwardly throllgh the perforations form small bubbles in the liquid and as a result are in intimate contact therewith. The liquid is charged to a high voltage by power supply 147 and as a result, the charged particles and droplets are collected in the film forming the bubbles. The gases, cleansed of the particles, pass out through~ eliminator 148 to the atmosphere.
FIGURES 3 and 4 show one preferred embodiment of the charged droplet ~ ~ bubble scrubber device. FIGURE 3 is a plan view showing the upper perforated plate ~,f having high-voltage supply cable 152 connected thereto. The high-voltage supply cable is attached to one of the four plate spacers 153. The liquor-feed supply conduit 154 carries a plurality of spray nozzles 155. Electrostatic isolating baffles 157 and 187 serve to prevent the high voltage imposed upon the scrubber from being grounded out through the walls of the device.
In the scrubber zone, best seen in FIGURE 4, a packed column area 160 is comprised of a pair of parallel spaced-apart perforated metal bubble plates 148 and 150.
These bubble plates are spaced apart by plate spacers 153 and may contain packing 158, if 20 desired, to increase the gas-liquid contact area. An overflow drain downcomer 162 permits liquid flow from the packed portion of the scrubber seciton to the drain. During operation, a head of water is maintained in the overflow drain, so that air does not pass upwardly through the drain. The assembled plates are nestled within the bubble plate support 164, which is preferably constructed of a nonconducting material, such as fiberglass reinforced polyester, other plastic substance, or a ceramic. Bubble plate support 164 serves to position the bubble plate assembly 160 in a spaced-apart relationship with the shell 166. High-voltage cable 152 serves to maintain the bubMe plate assembly and the liquid contained therein at a suitably high potential, thus imposing an electrostatic charge upon the liquid contained therein. In the embodirnent shown, the Iiquor supply is 30 electrically isolated from the high-voltage bubble plate assembly and is grounded.
In operation, liquid is fed to the bubble plate assembly thrau~h liquor feed supply conduit 154 onto upper perforated plate 150. ~imultaneously, gases conta;ning 3~33 particulate matter are caused to flow upwarclly through lower perforated plate 148 and upper perforated plate 150. The counter-current flow of liquid and gas cause the formation of bubbles at plates 1~}8 and 150 with the resultant formation of a foam of substantial depth of each plate. The packing 158 serves to further provide additional surface for contact o~' the gas and liquid. The gas containing an electrostatically charged aerosol is thus intimately contacted with the liquid having an opposite charge. Following Coulomb's Law, the particulate matter ;s attracted to and captured by the liquid. Since tiny bubbles are formed and intimate contaet results, a very substantially improved collection efficiency is thus obtained. The liquid which is fed to the upper surface of 10~ upper perforated plat~ 150 passes downwardly through the perforations into the packed h ~ h ~
~intermediate zone~58 and co~tinues to~ravel downwardly to plate 148. The influence of upwardly flowing air slows the downward progress of the liquid and, at steady state conditions, a mass balance is achieved with slowed downward flow of liquid and upward flow of aerosol-containing gases. When the level of liquid in the zone between plates 148 and 150 reaches the upper level of overflow drain downcomer 162, the liquid is free to flow downwardly through the drain. 'I'his prevents flooding of the packed section of the bubble scrubber 160.
Isolating baffle 157 prevents flow of liquids to the shell 166. Drainholes 169 and 169' in the upper isolated baffle serve to drain any liquid which may flow through the shell area. Liners 172 and 172'Amade of polytetrafluoroethylene or other material which is reslstant to wetting may be used to aid in electrically isolating the system and to aid in maintaining the system as clean as possible.
1~1 The lower isolating baffle ~ similarly serves to isolate the system electrically and drainholes 171 and 171' permit excess moisture to drain back into the interior of the scrubber section. The isolating baffles are constructed of an insulated substance, such as fiberglass reinforced polyester, other suitable plastics or ceramic materials.
In describing the multiple spray tower wet electrostatic scrubber illustrated ~.~ in FIGUR~ reference was rnade to the corona discharge aerosol partiele-charger 36. In 30 the schematic view of ~IGURES 5 and 6, an arrangement of the corona wire frame 74 of discharge electrodes 76 is shown in its relative position to the collection plates 78 serving as the nondischarge electrodes. The corona discharge ele.ctrodes 76 are preferably formed _9_ in a helix as shown to increase the available surface for corona and thereby to enhance the effectiveness of the particle chflrging eunctions of the apparatus.
'i ^l Also in describing the wet electrostatic scrubber illustrated in FIGURE~
reference was made to a droplet-charger 42. In FIGIJRES 7 and 8, one embodiment of a cleansing liquid droplet-churger ~2 is illustrated. FIGURE 7 indicates the positions of the no7zles ~6 in the spray tower 32 with their respective insulators 50, liquid supply pipes 44, purge air ducts 80, and high voltage leads 4~. In ~IGURE ~, talcen on line 8--8 of ~I~URE
7, part of the components of the direct wire or direct voltage droplet charger 42 are illustrated in a partial cross section. The cleaning liquid is directed do~vnwardly into pipes 10 '14, then charged at uncovered end 81 of high voltage leads 48, and thereafter emitted through the spray noz~les 46 as electrostatically positively charged droplets 82 ready to start their scrubbing function. It is to be noted that nonconductive piping 44 for the liquid is preferred to reduce the loss of electrical energy.
One embodiment of this Wet Electrostatic Scrubber, schematically illustrated in FIGURES 2 and 3, involves the effective use of both electrostaticaIly charged liquid droplets and electrostatically charged liquid bubbles ta collect oppositely charged aerosol particles, for example from contaminated aerosol gases enroute to and/or up an exhaust stack. rhe charged liquid droplets may be of either equal or opposite polarity from the bubbles of cleansing liquids.
The corona wires are connected to a high-voltage power supply and ionize the gases and incoming aerosol particles. The nondischarge electrodes are connected to ground. The cleansing liquid droplets are generated by discharging liquids under pressure from spray nozzles, or by discharging liquids, not under pressure, but in the presence of flowing air under pressure, as occurs when a pneumatic nozzle is used.
The liquid electrostatic charge is imparted by a corona generator which is connected to a high voltage power supply. The spray tower chamber walls are constructed of either conductive or nonconductive materials, or a comMnation of them. The liquid supply lines are made of nonconductive materials, and they are connected to the chamber walls of using fittings that provide for the entry and discharge of dry clean air which 30 purges the volume around the nonconductive material, serving to keep the noncondll3ctive suppl~ line materials and some other materials dry and, therefore, substantially free of insoluble deposits.
10~
$
I`he chnrged aerosol particles and the oppositely charged cleansing liquid droplets tlow through perforated plate~, which is made frorn a conductive material.
: ' ~
This perforated plate 1~ contains a plurality of apertures 144 through which the gases, aerosol particles, and liquid droplets entralned in the gases flow. The gas, particle and droplet mixture then bubbles through a layer of liquid and f~am maintained at u level h on top of perforated plate 1~8. ï`he liquid flows countercurrently to the gases downwardly through apertures 144. The liquid may contain a foaming agent or surfactant to assist in the generation and stabilization of the bubbles, thereby increasing the contact time between the liquid and the aerosol containing gases.
In the embodiment shown in FIGURE 2, the foam is raised to a positive polarity in the range of 30 KV by the power supply~8. rhe flow rates of the liquid and gases through the gas-liquid contactor 145 are regulated so that the two phase gas-liquid foam on top of the perforated plate 143 and 143' is maintained at a depth OI from about 2 to about 24 inches. The gases flow upwardly through the apertures 144 and 144' and the liquid flows downwardly through the same apertures, providing excellent gas-liquid contact.
The charged aerosol particles are collected upon the surfaces eharged to the opposite polarity, which are the surfaces on either or both of the liquid droplets or the bubbles. Aerosol particle collection will occur upon both the inside and outside surfaces 20 of the respective bubbles. The liquid and foam maintained at a given level upon the perforated plate is electrostatically charged by a high voltage power supply to a polarity either the same or opposite from the liquid droplet, and to a polarity either the same or opposite from the aerosol particles.
In FIGURE 9 a schematic representation of the gas flow and electrostatic charge modes useful in this invention is shown. Aerosol containing gases enter the apparatus through conduit 34 and flow into charging section 130. An electrostatic charge is imposed thereon. Liquid enters tower 134 with an electrostatic charge and enters bubble scrubber 145 maintained at an elevated potential. I.iquid is removed from the gas stream in precipitator 148. The workable polarities and electrostatic charging voltages 30 are set forth in Table 1.
3:~
Tablc l A B C D
Condition Corona Spray Bubble Mist Figure Section Tower Scrubber F.liminator I-30 to -~00 kv-~1 to S0 kv~1 to 50 kv-~30 to lO0 kv 10 II-30 to -400 kv-1 to 50 kv~1 to 50 kv~30 to 100 kv 11 III-30 to -~00 kv+1 to 50 kv-1 to S0 kv-30 to 100 kv 12 IV+30 to ~400 kv~1 to 50 kv-1 to 50 kv-30 to lO0 kv13 V~30 to 400 kv-l to 50 kv-l to 50 kv+30 to 100 kv 14 VI+30 to 400 kv-1 to 50 kv+1 to 50 kv+30 to 100 kv 15 For each mode of operation set forth in Table 1, reference is made to FIGURES 10-15 which show schematically the conditions in bubble scrubber 145.
In FIGUXE lO, the bubble b is charged positively and is shown sur-rounded by liquid. The droplets are charged positively while the particles are charged negatively. Thus the negatively charged particles are attracted - to the inside and outside surfaces of the positively charged bubble and are further attracted to the positively charged droplet thus the particles are collected upon both the droplets and the surfaces of the bubble.
In FIGURE 11, the bubble b is charged positively and is shown sur-rounded by liquid. The particle p is charged negatively, and the droplet d is charged negatively. The negatively charged particles are repelled by the negatively charged droplet, which is located inside the bubble, and are at-tracted to and collected UpOII the positively charged inside surface of the bubble.
In FIGURE 12, the bubble is charged negatively, and is shown sur-rounded by liquid. The droplet is charged positively, and particles are charged negatively The negatively charged particles are repelled by the negativ~ly charged bubble surface and are attracted to the positively charged droplets.
3.~3 In FIGURr 13, the bubble is charged negatively, the dro~plets are charged positively and the particles are charged posi.tively. The particles are repelled by -the droplets and attracted by the inside and outside sur-face of the bubble.
In FIGURE 14, the bubble is negatively charged~ the droplets are negatively charged and the particles are positively charged. Both the drop-lets and the bubble inside and outside surfaces attract the particles.
In FIGURE 15, the bubble is positively charged and shown in liq-uid. The droplets are negatively charged and the particles are positively charged. Particles are repelled by the bubble surface and attracted to droplets.
The following operating parameters have been found workable by the inventor for the overall system shown in FIGURES 1 and 2;
1. Power supply to corona section 116 or 130 - 30 to ~0 kilo-volts.
- 12a -2. Power supply to water or liquor bubble section 145 -- l to 50 kilovolts.
3. Power supply to water Ol liquor spray section 134 -- l to 50 kilovolts.
4. Water flow to water c>r liquor spray section 134 -- O.l to 50 gallons per l,000 actual cubic feet of gas.
5. Water flow in bubble sections 14S -- 0.1 to 50 gallons per l,000 actual cubic feet (water can be recycled.)
6. Gas flow rate in spray towers -- 1 to 30 feet per second.
7. Gas flow rate in bubble sections--1 to 20 feet per second.
8. G~s flow rate in corona sections 130 -- 1 to 50 feet per second.
In FIGllRE 16, there is seen a second embodiment of the charged bubble scrubber which is operatively positioned downstream of both a particle-charging section and the charged droplet spray tower 134 (not shown). The charged bubble scrubber 245 is sirmilar to the device shown in FIGURES 1 and 2. In this embodiment, the aerosol-containing gases, after having been charged in an -~* aerosol particle-charger (not shown), enter the bubble scrubber in the direction shown by arrow 2Ul, the particulate matter in the gases having a strong electrostatic charge imposed thereon by the aerosol particle-charger. The gases are preferably passed through a liquid spray tower prior to entering bubble scrubber 245, so that a fog of tiny droplets, having received an electrostatic charge in the spray tower, are carried over with the aerosol-containing gases into bubble scrubber 245. An upper bubble plate 243' and a lower bubble plate 243 are shown positioned axially within a cylindrical shell 230. The plates are supported on an am~ul~r rib 231 and are spaced apart from eaeh other by spacers 253. Downcomers 262 and 262' permit liquid to flow from the upper surface of the plate downwardly to the subjacent plate or out of the system. Liquid is rmaintained at a level h and h' on plates 243 and 243', respectively. A high-voltage cable 252 is shown connected directly to one of the plate spacers 253 and has imposed thereupon a high voltage in the range of 1 to 50 kilovolts DC.
Several of the bubble plates may be stacked serially one upon the other to provide the necessary amount of gas-liquid contact.
The washing liquor is supplied from a grounded sump source through liquor supply pipe 254 and enters the charged bubble scrubber through nozzles 255. The no~zles are positioned sufficiently above the uppermost plate so that electrical isolation between the liquor supply 254 and the plate is maintained. The flow of liquor to the plates will be at such a rate such RS to rnaintain a predetermined level about the plate. Drainage from the upper plate 24;3' feeds the lower plate 243 so that a suf~icient head is maintained on lower plate 243. The level o~ liquid on each plate assumes a maximum governed by the location of the overflow drain downcomer 2B2. Charging of the liquor on the bubble plates is accomplished by imposing a high voltage on cable 252. Since the plates are constlucted ' ~ ` of conductive material, such as stainless steel, the voltage imposed upon upper plate t~ i s is conducted to the lower plate 2~ so that all of the ]iquid on each of the plates is maintained at a high voltage. As the air stream is forced up through the bubble plates, the charged liguor will attract and remove the entrapped, oppositely charged particles, as 10 well as absorbing soluble gases and capturing the charged water droplets entrained in the gases.
The shell 230 of the charged bubble scrubber is constructed of a nonconductive substance, such as a fiberglass reinforced polyester, other suitable plastic materials or ceramics. The baffles 270 and 257 each serve to isolate the charged bubble scrubber from adjacent zones of the apparatus. This is necessary so that a high voltage may be maintained in the bubble scrubber zone which is opposite in polarity to the high -s voltage imposed upon the particles at other locations in the apparatus. Preferably the J
charged bubble scrubber walls will be lined with a Teflon liner 272 to aid in maintaining the electrical isolation.
,~ ~r~R~
In FIGllRE 16, there is seen a second embodiment of the charged bubble scrubber which is operatively positioned downstream of both a particle-charging section and the charged droplet spray tower 134 (not shown). The charged bubble scrubber 245 is sirmilar to the device shown in FIGURES 1 and 2. In this embodiment, the aerosol-containing gases, after having been charged in an -~* aerosol particle-charger (not shown), enter the bubble scrubber in the direction shown by arrow 2Ul, the particulate matter in the gases having a strong electrostatic charge imposed thereon by the aerosol particle-charger. The gases are preferably passed through a liquid spray tower prior to entering bubble scrubber 245, so that a fog of tiny droplets, having received an electrostatic charge in the spray tower, are carried over with the aerosol-containing gases into bubble scrubber 245. An upper bubble plate 243' and a lower bubble plate 243 are shown positioned axially within a cylindrical shell 230. The plates are supported on an am~ul~r rib 231 and are spaced apart from eaeh other by spacers 253. Downcomers 262 and 262' permit liquid to flow from the upper surface of the plate downwardly to the subjacent plate or out of the system. Liquid is rmaintained at a level h and h' on plates 243 and 243', respectively. A high-voltage cable 252 is shown connected directly to one of the plate spacers 253 and has imposed thereupon a high voltage in the range of 1 to 50 kilovolts DC.
Several of the bubble plates may be stacked serially one upon the other to provide the necessary amount of gas-liquid contact.
The washing liquor is supplied from a grounded sump source through liquor supply pipe 254 and enters the charged bubble scrubber through nozzles 255. The no~zles are positioned sufficiently above the uppermost plate so that electrical isolation between the liquor supply 254 and the plate is maintained. The flow of liquor to the plates will be at such a rate such RS to rnaintain a predetermined level about the plate. Drainage from the upper plate 24;3' feeds the lower plate 243 so that a suf~icient head is maintained on lower plate 243. The level o~ liquid on each plate assumes a maximum governed by the location of the overflow drain downcomer 2B2. Charging of the liquor on the bubble plates is accomplished by imposing a high voltage on cable 252. Since the plates are constlucted ' ~ ` of conductive material, such as stainless steel, the voltage imposed upon upper plate t~ i s is conducted to the lower plate 2~ so that all of the ]iquid on each of the plates is maintained at a high voltage. As the air stream is forced up through the bubble plates, the charged liguor will attract and remove the entrapped, oppositely charged particles, as 10 well as absorbing soluble gases and capturing the charged water droplets entrained in the gases.
The shell 230 of the charged bubble scrubber is constructed of a nonconductive substance, such as a fiberglass reinforced polyester, other suitable plastic materials or ceramics. The baffles 270 and 257 each serve to isolate the charged bubble scrubber from adjacent zones of the apparatus. This is necessary so that a high voltage may be maintained in the bubble scrubber zone which is opposite in polarity to the high -s voltage imposed upon the particles at other locations in the apparatus. Preferably the J
charged bubble scrubber walls will be lined with a Teflon liner 272 to aid in maintaining the electrical isolation.
,~ ~r~R~
Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for removing aerosol particles from a flowing gaseous stream comprising the steps of:
passing said flowing gaseous stream into chamber means defining a spray chamber and a bubble scrubber chamber, in said chamber means imposing a first electrostatic charge upon the particles contained in said flowing gaseous stream and removing from said chamber means at least a portion of said particles having said first electrostatic charge, in said spray chamber contacting the flowing gaseous stream with a spray of liquid, the droplets forming said spray having a second electrostatic charge differing in potential from said first electrostatic charge, whereby a portion of said aerosol particles are collected upon said droplets, and removing from said spray chamber at least a portion of said liquid droplets upon which said aerosol particles have been collected, in said bubble scrubber chamber contacting said flowing gaseous stream with a bubble-forming liquid having a third electrostatic charge therein differing in potential from at least one of said first and second electrostatic charges, wherein said flowing gaseous stream forms bubbles and is intimately intermixed with the bubble-forming liquid and whereby at least portion of said aerosol particles are captured by said bubble-forming liquid and are removed from said flowing gaseous stream, and removing from said bubble scrubber chamber at least a portion of said bubble-forming liquid containing said aerosol particles, and exhausting said flowing gaseous stream from said chamber means.
passing said flowing gaseous stream into chamber means defining a spray chamber and a bubble scrubber chamber, in said chamber means imposing a first electrostatic charge upon the particles contained in said flowing gaseous stream and removing from said chamber means at least a portion of said particles having said first electrostatic charge, in said spray chamber contacting the flowing gaseous stream with a spray of liquid, the droplets forming said spray having a second electrostatic charge differing in potential from said first electrostatic charge, whereby a portion of said aerosol particles are collected upon said droplets, and removing from said spray chamber at least a portion of said liquid droplets upon which said aerosol particles have been collected, in said bubble scrubber chamber contacting said flowing gaseous stream with a bubble-forming liquid having a third electrostatic charge therein differing in potential from at least one of said first and second electrostatic charges, wherein said flowing gaseous stream forms bubbles and is intimately intermixed with the bubble-forming liquid and whereby at least portion of said aerosol particles are captured by said bubble-forming liquid and are removed from said flowing gaseous stream, and removing from said bubble scrubber chamber at least a portion of said bubble-forming liquid containing said aerosol particles, and exhausting said flowing gaseous stream from said chamber means.
2. The method of claim 1 wherein said third electrostatic charge has a different polarity from at least one of said first and second electrostatic charges.
3. The method of claim 1 wherein said gaseous stream is contacted with said spray of liquid after said first electro-static charge is imposed upon the aerosol particles in said gaseous stream.
4. The method of claim 1 wherein said gaseous stream is contacted with said bubble-forming liquid after being contacted with said spray of liquid.
5. An electrostatic wet scrubber and collector assembly comprising:
chamber means defining a spray chamber and a bubble scrubber chamber, said spray chamber and said bubble scrubber chamber being in gaseous communication with each other, said chamber means having an inlet and an outlet;
means positioned and arranged with respect to said cham-her means for imposing a first electrostatic charge upon partic-ulate matter contained in a gaseous stream passing through said chamber means from said inlet to said outlet;
spray means associated and arranged with respect to said spray chamber for injecting droplets of liquid into said spray chamber, and means associated with said spray means for imposing a second electrostatic charge on said droplets said second electrostatic charge differing in potential from said first electrostatic charge, whereby said droplets and particulate matter are attracted to each other, means associated and arranged with respect to said spray chamber for removing at least a portion of said droplets to which particulate matter has been attracted, bubble scrubber means associated and arranged in said bubble scrubber chamber to receive said gaseous stream passing through said chamber means and to cause said gaseous stream to flow upwardly through said bubble scrubber chamber, said bubble scrubber means containing at least one bubble-forming means for supporting a bubble-forming liquid thereon, said bubble scrubber means being positioned to receive said gaseous stream as it flows upwardly through said bubble scrubber chamber, means positioned and arranged with respect to said bubble scrubber means for imposing a third electrostatic charge on said bubble-forming liquid, said third electrostatic charge having a potential different from at least one of said first and second electrostatic charges, and means, including a sump and a pump, positioned and arranged with respect to said bubble-forming means for recycling said bubble-forming liquid from the bubble scrubber means to said sump and back to said bubble-forming means.
chamber means defining a spray chamber and a bubble scrubber chamber, said spray chamber and said bubble scrubber chamber being in gaseous communication with each other, said chamber means having an inlet and an outlet;
means positioned and arranged with respect to said cham-her means for imposing a first electrostatic charge upon partic-ulate matter contained in a gaseous stream passing through said chamber means from said inlet to said outlet;
spray means associated and arranged with respect to said spray chamber for injecting droplets of liquid into said spray chamber, and means associated with said spray means for imposing a second electrostatic charge on said droplets said second electrostatic charge differing in potential from said first electrostatic charge, whereby said droplets and particulate matter are attracted to each other, means associated and arranged with respect to said spray chamber for removing at least a portion of said droplets to which particulate matter has been attracted, bubble scrubber means associated and arranged in said bubble scrubber chamber to receive said gaseous stream passing through said chamber means and to cause said gaseous stream to flow upwardly through said bubble scrubber chamber, said bubble scrubber means containing at least one bubble-forming means for supporting a bubble-forming liquid thereon, said bubble scrubber means being positioned to receive said gaseous stream as it flows upwardly through said bubble scrubber chamber, means positioned and arranged with respect to said bubble scrubber means for imposing a third electrostatic charge on said bubble-forming liquid, said third electrostatic charge having a potential different from at least one of said first and second electrostatic charges, and means, including a sump and a pump, positioned and arranged with respect to said bubble-forming means for recycling said bubble-forming liquid from the bubble scrubber means to said sump and back to said bubble-forming means.
6. The assembly of claim 5 wherein said means for imposing said third electrostatic charge imposes a charge which has a different polarity from at least one of said first and second electrostatic charges.
7. The assembly of claim 5 wherein said spray chamber and said bubble scrubber are serially arranged so that a gaseous stream passing through said chamber means will first pass through said spray chamber.
8. The assembly of claim 5 wherein said means for imposing said first electrostatic charge is arranged and positioned with respect to said spray chamber so that said first electrostatic charge is imposed upon said aerosol particles before said gaseous stream enters said spray chamber.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US75298876A | 1976-12-21 | 1976-12-21 | |
| US752,988 | 1976-12-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1114313A true CA1114313A (en) | 1981-12-15 |
Family
ID=25028710
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA292,035A Expired CA1114313A (en) | 1976-12-21 | 1977-11-29 | Electrostatic aerosol scrubber |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1114313A (en) |
-
1977
- 1977-11-29 CA CA292,035A patent/CA1114313A/en not_active Expired
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