CA1130220A - Air scrubber operating method - Google Patents
Air scrubber operating methodInfo
- Publication number
- CA1130220A CA1130220A CA338,108A CA338108A CA1130220A CA 1130220 A CA1130220 A CA 1130220A CA 338108 A CA338108 A CA 338108A CA 1130220 A CA1130220 A CA 1130220A
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- Canada
- Prior art keywords
- particles
- liquid
- aerosol particles
- scrubber
- air
- 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.)
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Abstract
TITLE
AIR SCRUBBER OPERATING METHOD
ABSTRACT
An air scrubber is operated to reduce the rate of escape of scrubbing-liquid particles from the scrubber along with the clean-air output. The scrubbing liquid is broken into finely divided particles which are mixed with the air and then concentrated together in a recapture region. The particles are preferably divided more finely than otherwise possible by adding a surface-active agent to the liquid, and electric field effects are created to produce electric image attraction between the concentrated particles. This is done either by producing static electric charges on the particles or by electrically charging an element in the region of the concentrated particles. The concentrated particles are made substantially more likely to reagglomerate and become more readily re-captured by adding a surface-active agent reducing liquid surface tension or an electrolyte increasing the conductivity of the liquid, or both. A preferred electrolyte for water as a scrubbing liquid is calcium chloride or sodium chloride. The electrolyte alone, the surfactant alone, and the combination of elec-trolyte and surfactant each effects substantially more liquid particle agglomeration and much less escape of liquid particles and entrained pollutants in the output from the scrubber.
AIR SCRUBBER OPERATING METHOD
ABSTRACT
An air scrubber is operated to reduce the rate of escape of scrubbing-liquid particles from the scrubber along with the clean-air output. The scrubbing liquid is broken into finely divided particles which are mixed with the air and then concentrated together in a recapture region. The particles are preferably divided more finely than otherwise possible by adding a surface-active agent to the liquid, and electric field effects are created to produce electric image attraction between the concentrated particles. This is done either by producing static electric charges on the particles or by electrically charging an element in the region of the concentrated particles. The concentrated particles are made substantially more likely to reagglomerate and become more readily re-captured by adding a surface-active agent reducing liquid surface tension or an electrolyte increasing the conductivity of the liquid, or both. A preferred electrolyte for water as a scrubbing liquid is calcium chloride or sodium chloride. The electrolyte alone, the surfactant alone, and the combination of elec-trolyte and surfactant each effects substantially more liquid particle agglomeration and much less escape of liquid particles and entrained pollutants in the output from the scrubber.
Description
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TITLE
AIR SCRIlBBER OPERATIN~ METHO~
BACKGROUND OF THF. INVENT1ON
The invention evolved from experience and experiments with an air scrubber that breaks a scrubbing liquid into finely divided particles that are mixed with the air to catch airborne pollutants and are then cen-s trifugally concentrated and subs~antially recaptured before the clean air is output from the scrubber. ~x-periments showed that the fîner the particle size and the greater liquid surface area exposed to the air, the more thoroughly ~he air is cleanecl. However, smaller 10 particle size is accompanied by the disadvantage of liquid ~articles carrying bits of the captured pollu-tants being able to escape wlth the clean-air Olltp-lt because of the difeiculty of recapturing a great multitude of extremely small aerosol particles~ So 15 to make the scrubber as efficient as possibl~, it is important to take advantage of the ability of extremely small liquid particles to clean the air better, and then it is important to recapture sub-stantially all the liquid particles to make the output 20 air as clean as possible, even though recapture of extremely small particles is difficult.
The invention involves the discovery that adding small proportions of the right materials to the scrubbing liquid significantly enhances the recapture 25 of liquid particles for a great improvement in the air c]eaning ability of the scrubber. The invention aims at increasing scruhber efficiency both by breaking the scrubbing liquid into a great multitude of extremely fine particles to mix an enormous liquid surface area 30 in with the polluted air to capture a high percentage ,~
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.
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of a wide variety of pollutants and also greatly facil-itating the recapture of substantially all the liquid particles to insure that liquld and pollutants do not escape with the cleaned air. The invention also aims at economy and versatility in removing many different pollutants and contaminants from air.
SUMMARY OF THE INVENTION
One concept important to the invention is realization that reagglomeration of particles or merger of one particle with another facilitates particle recapture by increasing the average size and mass of t'ne particles. The effect of p~lenomena such as static electric charges, presence of ions, liquid conductivity, and liquid surface tension on the interactions between finely divided aerosol particles is only partially understood so that predicting mechanisms and materials that can facilitate reagglomeration oE liquid particles is presently impractical~ In Eact, knowledge oE how the invention works is still incomplete ancl the reasons why some additives help and others don't are still uncertain.
According to the invention there is provided a method of operating an air scrubber that finely divides a scrub-bing liquid into aerosol particles mixed with airborne pollutants, said method reducing the rate of escape from said scrubber of pol:Lutants that combine with said scrubbing liquid, said method comprising: a. adding a suface active agent to said scrubbing liquid so said scrubber divides said liquid into fine aerosol particles containing said surface active agent and having a large surface area for combining with said pollutants in air mixed with said aerosol particles; b. applying sufficient turbulent force in dividing said scrubbing liquid into said aerosol particles to produce substantial static elec-tric charges on said aerosol particles, said particles being fine enough so said charges produce substantial interparticle attractive forces; c. forming a flow of air and said aerosol particles combined ~7ith said pollutants ~3~2~20 - 2a -captured from said air along a surface arranyed to direct said flow in a curved path for centrifugally concentrating said pollutant bearing aerosol particles against said surface; d. driving said flow with suEficient veloclty relative to the radius of curvature of said path so that said centrifugal concentration of said pollutant bearing aerosol particles is adequate to make said interparticle attractive forces from said static electric charges on said aerosol particles effective for substantially increasing contacts between said ccncentrated aerosol particles; e. using the presence of said surface active agent in said pollutant bearing aerosol particles that contact each other to substantially facilitate merger of said contacting aerosol particles with each other and with liquid moving along said surface; f. centrifugally separating said merged liquid from said air in the region of said s~rface to remove substantially all liquicl and pollutant material from said Elow; and 9. outputting cleaned air from said scrubber by directing said flow to a regiorl outside said scrubber aEter centrifug~lly separating said merged liquid within said scrubber.
Preferably, an electrolyte is added to the scrub-bing liquid to enhance the conductivity of the aerosol - particles.
The inventive method includes breaking the scrubbing liquid into finely divided particles, which are mixed with contaminated air to capture pollutants from the air. Before the clean air is output from the scrubber r the particles are concentrated together in a particle recapture region of the scrubber where electric fie:ld effects produce electric image attraction between the particles. The concentrated parti-cles are made substantially more likely to reagglomerate and thereby become more readily captured by adding at least one material to the scrubbing liquid. The reag-glomerated particles are then substantially recapturedto reduce the rate of escape of particles along with the clean-air output Erom the scrubber. The added material '" ' .
, .
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is pre~erably one or both of two different mat~rials, each of which -facilitates the recapture of particles, and the addi~ive materials preferably cooperate with each other to improve by more than 30 times the ability 5 of the scrubber to recapture particles. The ~wo additives are a surface~active agent and a material substantially increasing the conductivity of the scrubbin~
liquid, such as a small proportion of an electrolyte.
The electrolyte must not vaporize within the scrubber 10 or react with air or the scrubbing liquid, and when the electrolyte and surface~active agent are used together, they must be compatible and nonreactive with each other. [Jse of either material produces si~nificant improvements, which are multiplied when both materials 15 are used. Ilse of a surfactant has the additional advantage of allowing the scrubbing liquid to be broken into a greater number o smaller particles to increase the liq-lid surface area and the cleaning ability of the scrubbing liquid so that efficiencies are increased 20 both by cleaning the air more thoroughly and reducing the escape of liquid and pollutants -from the scrubber.
nRAWING
The drawing schematically shows a partially cut~away, elevational ~iew oi~ alscrubber operated by 25 the inventive method.
DETAILED DESCRIPTION
The invention evolved with experience and experiments with a scrubber such as shown in the drawing for breaking a scrubbing liquid into fine particles, 30 centrifugally concentrating the particles, and recap~
turing the particles from the air before it is output ~rom the scrubber. ~lowever, the invention is not limited to the particular scrubber shown or any particular type of scrubber. The scruhber must break up ~he liquid into 35 particles tha~ mix with and clean the air, and since the ~ 322~
particle recapture involves reagglomeration of particles, it is important that the partiles be concentrated in a recapture region so that they can interact and merge with each other. The way the partlcles are concentrated and recaptured, and the way they are formed in the first place, can vary considerably, as is already known to those skilled in the art. Experience with the particular scrubber used in developing the inventive method suggests that the same basic method can be applied to other scrub-bers to produce comparable improvements in efficiency.
To aid in describing the inventive methocl, an example of a scrubber 10 capable of practicing the inventive method is shown in the drawing. Scrubber 10 is also described ln greater detail in my U.S. Patent No.
3,960,524, and entitled AIR SCRUBBER. The inventive method can be applied to a variety of air scrubbers, however, so scrubber 10 and my U.S. Patent are merely to provide an example of: one preferred scrubber that can b~ used in practicing the inventive method, Scrubber 10 has an outer annular chamher 11 inside of outer cylindrical wall 40 and an inner annular chamber 12 outside of cylindrical wall 41, with chambers 11 and 12 separated by a cylindrical common wall 13. A fan 14 having blades 15 breaks a quantity o~ scrubbing liquid into finely divided aerosol particles and forces the airand liquid particle mixture to move in a helical flow upward at high velocity inside inner chamber 12. Most of the liquid and a portion of the air recirculates through a slot 16, back into outer chamber 11, and back through fan 14. Contaminated air enters through input 17, circulates through scrubber 10, and after cleaning, is returned to the ambient temperature through output 18.
~ ~ 3~ Z2~
Some of the scrubbing liquid particles pass beyond slot 16 but pass t}lrough a downstream slot 19 which is preferably adjustable or slowly collect;ng the scrubbing liquid in a drain 20 leacling to a waste scrubbing 5 liquid collector 21. A supply 22 inputs clean scrubbing liquid into scrubber 10 through line 23 at a relatively slow rate so that a substantially constant volume of scrubbing liquid is constantly brcsken into liquid aerosol particles and circula~ed rapidly round and round within 10 scrubber 10 for cleaning the air.
I.iquid aerosol particles are ordinarily diffi~
cult to recapture rapidly9 and a substantial quantity of such particles pass beyond slot 19 and into a particle recapture region adjacent cylindrical wall 24, which is 15 contiguous with and extends beyond wall 13. The high~
velocity helical flow upward in ;nner chamher 12 centrifugally concentrates the particles along the inside of wall 24 where the particles, especially if merged or reagglomerated according to the inventive met}lod, 20 pass through holes 25 because o~ a lower pressure in chamber 2fi outside of wall 24. Chamber 26 can open fully into outer chamber 11 or openings 27 in annular plate 42 can adjustably connect chamber 26 to outer chamber 11 to regulate the pressure in chamber 26 and allow 25 the recaptured particles passing through holes 25 to re~
enter outer chamber 11 and recirculate through scrubber 10.
The inventive method greatly increases the e~ficiency of scrubber 10 by facilitating reagglomeration o~ the liquid particles and recapture o-f the reagglom~rated 30 particles through holes 25 so that the clean air passing out of output 18 carries very few liquid particles with it. The inventive methocl also increases the efficiency o scrubber 10 by reducing the surface tension of the scrubbing liquid so that fan 14 breaks the liquid into 35 finer particles presenting a far greater surface area ~ 3~'~2~
to the contaminated air to capture more oE the alrborne pollutants~ The division of the scrubbing liquid into finer particles not only increases the efEiciency of scrubber 10, but also is not a serious disadvantage 5 because of the improvement effected in particle reagglom-eration and particle recapture. Similar improvements Eor similar reasons, can also be made by applying the inventive method of other air scrubbers.
One phenomenon occurring in the inventive 10 method is electric image attraction between the liquid particles concentrated in the recapture region. This involves movement of electrons around the surfaces of the particles to move away rom negative charges and toward positive charges. As the particles pass near 15 each other, the electric imaging effect attracts them together so that they are much more likely to reagglom-erate or merge.
The electric image attraction between the par--ticles is preferably produced by either or hoth of two 20 possible methods. One is to use suficient force in breaking the liquid into particles to also produce substantial static electric charges on the particles.
The static electric charges then create electric field effects that other particles respond to with electric 25 imaging to attract nearby particles to each other. In effect, when the particles are concentrated together, enough of them have static electric charges to produce substantial electric image attraction helping to reag-glomerate particles that come close to each other.
30 Another way is to electrically charge an element in the particle recapture region, and this is preferably done by electrically insulating wall 24 with insulating rings 32 that are preferably flush with contiguous walls 13 and 24 so that an electric charge can be applied 35 to wall 24 from an electrical source 33. The applied charge can be either negative or positive9 because the , , - , : :
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object is not to attract particles to wall 24, but to produce an electric field that the particles respond to by electric imaging so that the particles are thereby attracted to each other and reagglomerated. Experience 5 has shown that a charge of either sign is effective -for this purpose3 which dif-fers significantly in operation from the known concept of giving all particles one charge and then capturing them on an oppositely charged collector. Reagglomeration or merger of one particle 10 with another increases the average size and mass of the par~icles so they are centrifugally separated from the air and recaptured independently of the charge on wall 24.
The scrubbing liquid used in develop;ng the invention is water, and for most air scrubbing processes, 15 water is preferred. However, other scrubbing liquids may be possible. One of the addit;ves to the scrubhing water according to the inventive method is a surface~
active agent, or surfact~nt, schematically illustrated hy a supply 28 coml-ined with a water supply 2~ to ~orm 20 scr~lbbing lic~uid supply 22. ~ ~ide variety oE sur~actants are available, and the ones that have been tried have had the surprising effect of facilitating reagglomeration of water particles. The reason for this is not certain, but it is generally known that surfactants reduce 25 liquid surface tension, and surface tension apparent~y inhibits particle reagglomeration between extremely small aerosol particles. The effective surface tension at the extremely small radii of curvature for fine aerosol particles apparently allows the particles to bounce off 30 each other without merging 7 and reducing the surface tension by adding a surfactant improves the likelihood of merger or reagglomeration of aerosol particles that contact each other. I do not wish to be bound by this particular explanation for the observed effect, 35 but experiments clearly reveal that liquid particle re~
agglomeration is substantially enhanced by the presence of a surface~active agent when electric ima~e attraction occurs between concentrated aerosol particles.
~ 2~
On the basis of present information, most surface~active agents will produce the desired liquid particle reagglomeration, and there is no reason to believe that any surfactant will fail to do this. So 5 the surfactant is preferahly chosen for its compat~
ibility with the pollutants being recaptured and the materials forming the scrubber itself, and the cost of the surfactant. Both ionic and non-ionic surfactants have proven workable~ and although differences in the 10 reagglomeration effectiveness of different surfactants may occur, ~hose skilled in the art can readily practice the invention with any one of a wide variety of sur~
factants.
The amount of surfactant added to the scrubbing 15 liquid is preferably relatively small and on the order of 2% or less by weight for any particular suractant.
It is relatively easy to try different percen~ages and select an optimum proportion, once it is clear what to look for.
Another effect o~ the surace tellsion reduc~
tion from the presence of a surfactant is that the scrubbing liquid is broken into smaller sized particles.
This has a further advantage in creating a much larger liquid surface area to contact the contaminated air, 25 and it helps the liquid catch finer pollutants and a higher percentage of the pollutants presen~. Existing knowledge ahout surfactants makes it predictable that the same applied forces will break the scrubbing liquid into finer particles when a surfactant is present, but 30 the finer particles and a ~reater number of particles would ordinarily indicate that far more particles would escape with the output air because of the difficulty of capturing fine aerosol particles. Surprisingly, this does not occur, because the presence of the surfactant 35 facilitates liquid par~icle reagglomeration and actually .
~L~3~122~
reduces the escape rate of particles. For example, ~ests have shown a six-fold increase in the total number of smaller liquid particles formed when a surfactant is present, but at the same time9 the 5 escape rate of the liquid particles remains the same or reduces, indicating at leas~ a six-fold improvemenk in particle recapture, and o-f~en more than a six-fold improvement, because of ~he improved ability of the liquid particles to reagglomerate.
The other additive to the scrubbing liquid according to the inven~ive method is a material that substantially increases the conductivity of the liquid, such as an electrolyte material 30 schematically shown as added to scrubbing liquid supply 22. The electrolyte 15 or other conductivity enhancing material, hereinater referred to as "electrolyte", al.so facili~atcs re-agglomeration of li~iui(l aerosol particles and works either alone or in cooperation with a surfactant for significantly reducing the escape rate oE liquid along 20 with the air output from the scrubber. The reason why the electrolyte has this e-ffect is not absolutely certain, and I do not wish to be bound hy the reason offered here.
Increasing the conductivity of the scrubbing 25 liquid apparently enhances the electric image attraction between the aerosol particles, probably by making electrons on the particle sur-faces more mobile.
The electric -field eEect from either static electric charges on particles 7 or from a charged element in 30 the recapture region, or both, produces stronger electric image attraction forces between particles when an electrolyte is present so that more reagglomeration and more particle recaptwre occurs than if the conductivity of the scrubbing liquid were lower.
3~2~
Pxperimental measurements have shown that a 20~fold increase in particle recapture is easily obtained by adding an electrolyte making the scrubbing liquid more conductive. I, at the same time, a surfactant is also 5 present reducin~ the surface tension o-f the scrubbing liquid, the combined particle recapture improvement rom the electro~
lyte and the surfactant has been measured at more than 30 fold~
~pparently, the presence of the electrolyte enhances the electric image attraction -forces betwe!en particles 9 and the ;~
10 presence of the sur-factant helps the particles merge, so that very few particles escape when both materials are present.
At least several electrolytes are known to enhance liquid parkicle reagglomeration, and the pre~erred characteristics for a suitahle electrolyte include stability, 15 substantial inability to evaporate within the scrubber, and inability to react with water, whatever surfactant is used, the pollutarlts being capture(l, and the materials of the scrllhber itself~ These conditiolls Ire not diEicult to mcet, and the other considerations are cost. With water 20 as the scrubbing l;(lllid, two electrolytes that are hi~hly satisfactory and preferred for practicing the invention are sodium chloride and calcium chloride. Potassium permanganate also produces the desired reagglomeration efect, but is less stable and easy to use. All of the possible electrolytic 25 materials have no~ been tested yet, and there may be many more electrolytes or other materials increasing the conductivity of the scrubbing liquid that can be used in practicing the invention. ~lso, different electrolytes may be pre-ferred for scrubbing liquids other than water. ~or sodium chloride 30 and calcium chloride, the preferred proportion by weight o-E
electrolyte is 1% to 10%, and more than 5~ produces increasingly less reagglomeration improvement.
Persons skilled in the art and experienced with different scrubbers, surfactants9 and electrolytes~ can make 35 various scrubbing liquids significantly increasing the efficiency of their scrubbers 7 once the particle reagglomeration effect o-f the inventive method is understood.
TITLE
AIR SCRIlBBER OPERATIN~ METHO~
BACKGROUND OF THF. INVENT1ON
The invention evolved from experience and experiments with an air scrubber that breaks a scrubbing liquid into finely divided particles that are mixed with the air to catch airborne pollutants and are then cen-s trifugally concentrated and subs~antially recaptured before the clean air is output from the scrubber. ~x-periments showed that the fîner the particle size and the greater liquid surface area exposed to the air, the more thoroughly ~he air is cleanecl. However, smaller 10 particle size is accompanied by the disadvantage of liquid ~articles carrying bits of the captured pollu-tants being able to escape wlth the clean-air Olltp-lt because of the difeiculty of recapturing a great multitude of extremely small aerosol particles~ So 15 to make the scrubber as efficient as possibl~, it is important to take advantage of the ability of extremely small liquid particles to clean the air better, and then it is important to recapture sub-stantially all the liquid particles to make the output 20 air as clean as possible, even though recapture of extremely small particles is difficult.
The invention involves the discovery that adding small proportions of the right materials to the scrubbing liquid significantly enhances the recapture 25 of liquid particles for a great improvement in the air c]eaning ability of the scrubber. The invention aims at increasing scruhber efficiency both by breaking the scrubbing liquid into a great multitude of extremely fine particles to mix an enormous liquid surface area 30 in with the polluted air to capture a high percentage ,~
: .
.
~3~36~2~
of a wide variety of pollutants and also greatly facil-itating the recapture of substantially all the liquid particles to insure that liquld and pollutants do not escape with the cleaned air. The invention also aims at economy and versatility in removing many different pollutants and contaminants from air.
SUMMARY OF THE INVENTION
One concept important to the invention is realization that reagglomeration of particles or merger of one particle with another facilitates particle recapture by increasing the average size and mass of t'ne particles. The effect of p~lenomena such as static electric charges, presence of ions, liquid conductivity, and liquid surface tension on the interactions between finely divided aerosol particles is only partially understood so that predicting mechanisms and materials that can facilitate reagglomeration oE liquid particles is presently impractical~ In Eact, knowledge oE how the invention works is still incomplete ancl the reasons why some additives help and others don't are still uncertain.
According to the invention there is provided a method of operating an air scrubber that finely divides a scrub-bing liquid into aerosol particles mixed with airborne pollutants, said method reducing the rate of escape from said scrubber of pol:Lutants that combine with said scrubbing liquid, said method comprising: a. adding a suface active agent to said scrubbing liquid so said scrubber divides said liquid into fine aerosol particles containing said surface active agent and having a large surface area for combining with said pollutants in air mixed with said aerosol particles; b. applying sufficient turbulent force in dividing said scrubbing liquid into said aerosol particles to produce substantial static elec-tric charges on said aerosol particles, said particles being fine enough so said charges produce substantial interparticle attractive forces; c. forming a flow of air and said aerosol particles combined ~7ith said pollutants ~3~2~20 - 2a -captured from said air along a surface arranyed to direct said flow in a curved path for centrifugally concentrating said pollutant bearing aerosol particles against said surface; d. driving said flow with suEficient veloclty relative to the radius of curvature of said path so that said centrifugal concentration of said pollutant bearing aerosol particles is adequate to make said interparticle attractive forces from said static electric charges on said aerosol particles effective for substantially increasing contacts between said ccncentrated aerosol particles; e. using the presence of said surface active agent in said pollutant bearing aerosol particles that contact each other to substantially facilitate merger of said contacting aerosol particles with each other and with liquid moving along said surface; f. centrifugally separating said merged liquid from said air in the region of said s~rface to remove substantially all liquicl and pollutant material from said Elow; and 9. outputting cleaned air from said scrubber by directing said flow to a regiorl outside said scrubber aEter centrifug~lly separating said merged liquid within said scrubber.
Preferably, an electrolyte is added to the scrub-bing liquid to enhance the conductivity of the aerosol - particles.
The inventive method includes breaking the scrubbing liquid into finely divided particles, which are mixed with contaminated air to capture pollutants from the air. Before the clean air is output from the scrubber r the particles are concentrated together in a particle recapture region of the scrubber where electric fie:ld effects produce electric image attraction between the particles. The concentrated parti-cles are made substantially more likely to reagglomerate and thereby become more readily captured by adding at least one material to the scrubbing liquid. The reag-glomerated particles are then substantially recapturedto reduce the rate of escape of particles along with the clean-air output Erom the scrubber. The added material '" ' .
, .
~3~
is pre~erably one or both of two different mat~rials, each of which -facilitates the recapture of particles, and the addi~ive materials preferably cooperate with each other to improve by more than 30 times the ability 5 of the scrubber to recapture particles. The ~wo additives are a surface~active agent and a material substantially increasing the conductivity of the scrubbin~
liquid, such as a small proportion of an electrolyte.
The electrolyte must not vaporize within the scrubber 10 or react with air or the scrubbing liquid, and when the electrolyte and surface~active agent are used together, they must be compatible and nonreactive with each other. [Jse of either material produces si~nificant improvements, which are multiplied when both materials 15 are used. Ilse of a surfactant has the additional advantage of allowing the scrubbing liquid to be broken into a greater number o smaller particles to increase the liq-lid surface area and the cleaning ability of the scrubbing liquid so that efficiencies are increased 20 both by cleaning the air more thoroughly and reducing the escape of liquid and pollutants -from the scrubber.
nRAWING
The drawing schematically shows a partially cut~away, elevational ~iew oi~ alscrubber operated by 25 the inventive method.
DETAILED DESCRIPTION
The invention evolved with experience and experiments with a scrubber such as shown in the drawing for breaking a scrubbing liquid into fine particles, 30 centrifugally concentrating the particles, and recap~
turing the particles from the air before it is output ~rom the scrubber. ~lowever, the invention is not limited to the particular scrubber shown or any particular type of scrubber. The scruhber must break up ~he liquid into 35 particles tha~ mix with and clean the air, and since the ~ 322~
particle recapture involves reagglomeration of particles, it is important that the partiles be concentrated in a recapture region so that they can interact and merge with each other. The way the partlcles are concentrated and recaptured, and the way they are formed in the first place, can vary considerably, as is already known to those skilled in the art. Experience with the particular scrubber used in developing the inventive method suggests that the same basic method can be applied to other scrub-bers to produce comparable improvements in efficiency.
To aid in describing the inventive methocl, an example of a scrubber 10 capable of practicing the inventive method is shown in the drawing. Scrubber 10 is also described ln greater detail in my U.S. Patent No.
3,960,524, and entitled AIR SCRUBBER. The inventive method can be applied to a variety of air scrubbers, however, so scrubber 10 and my U.S. Patent are merely to provide an example of: one preferred scrubber that can b~ used in practicing the inventive method, Scrubber 10 has an outer annular chamher 11 inside of outer cylindrical wall 40 and an inner annular chamber 12 outside of cylindrical wall 41, with chambers 11 and 12 separated by a cylindrical common wall 13. A fan 14 having blades 15 breaks a quantity o~ scrubbing liquid into finely divided aerosol particles and forces the airand liquid particle mixture to move in a helical flow upward at high velocity inside inner chamber 12. Most of the liquid and a portion of the air recirculates through a slot 16, back into outer chamber 11, and back through fan 14. Contaminated air enters through input 17, circulates through scrubber 10, and after cleaning, is returned to the ambient temperature through output 18.
~ ~ 3~ Z2~
Some of the scrubbing liquid particles pass beyond slot 16 but pass t}lrough a downstream slot 19 which is preferably adjustable or slowly collect;ng the scrubbing liquid in a drain 20 leacling to a waste scrubbing 5 liquid collector 21. A supply 22 inputs clean scrubbing liquid into scrubber 10 through line 23 at a relatively slow rate so that a substantially constant volume of scrubbing liquid is constantly brcsken into liquid aerosol particles and circula~ed rapidly round and round within 10 scrubber 10 for cleaning the air.
I.iquid aerosol particles are ordinarily diffi~
cult to recapture rapidly9 and a substantial quantity of such particles pass beyond slot 19 and into a particle recapture region adjacent cylindrical wall 24, which is 15 contiguous with and extends beyond wall 13. The high~
velocity helical flow upward in ;nner chamher 12 centrifugally concentrates the particles along the inside of wall 24 where the particles, especially if merged or reagglomerated according to the inventive met}lod, 20 pass through holes 25 because o~ a lower pressure in chamber 2fi outside of wall 24. Chamber 26 can open fully into outer chamber 11 or openings 27 in annular plate 42 can adjustably connect chamber 26 to outer chamber 11 to regulate the pressure in chamber 26 and allow 25 the recaptured particles passing through holes 25 to re~
enter outer chamber 11 and recirculate through scrubber 10.
The inventive method greatly increases the e~ficiency of scrubber 10 by facilitating reagglomeration o~ the liquid particles and recapture o-f the reagglom~rated 30 particles through holes 25 so that the clean air passing out of output 18 carries very few liquid particles with it. The inventive methocl also increases the efficiency o scrubber 10 by reducing the surface tension of the scrubbing liquid so that fan 14 breaks the liquid into 35 finer particles presenting a far greater surface area ~ 3~'~2~
to the contaminated air to capture more oE the alrborne pollutants~ The division of the scrubbing liquid into finer particles not only increases the efEiciency of scrubber 10, but also is not a serious disadvantage 5 because of the improvement effected in particle reagglom-eration and particle recapture. Similar improvements Eor similar reasons, can also be made by applying the inventive method of other air scrubbers.
One phenomenon occurring in the inventive 10 method is electric image attraction between the liquid particles concentrated in the recapture region. This involves movement of electrons around the surfaces of the particles to move away rom negative charges and toward positive charges. As the particles pass near 15 each other, the electric imaging effect attracts them together so that they are much more likely to reagglom-erate or merge.
The electric image attraction between the par--ticles is preferably produced by either or hoth of two 20 possible methods. One is to use suficient force in breaking the liquid into particles to also produce substantial static electric charges on the particles.
The static electric charges then create electric field effects that other particles respond to with electric 25 imaging to attract nearby particles to each other. In effect, when the particles are concentrated together, enough of them have static electric charges to produce substantial electric image attraction helping to reag-glomerate particles that come close to each other.
30 Another way is to electrically charge an element in the particle recapture region, and this is preferably done by electrically insulating wall 24 with insulating rings 32 that are preferably flush with contiguous walls 13 and 24 so that an electric charge can be applied 35 to wall 24 from an electrical source 33. The applied charge can be either negative or positive9 because the , , - , : :
. , .
~3~2~
object is not to attract particles to wall 24, but to produce an electric field that the particles respond to by electric imaging so that the particles are thereby attracted to each other and reagglomerated. Experience 5 has shown that a charge of either sign is effective -for this purpose3 which dif-fers significantly in operation from the known concept of giving all particles one charge and then capturing them on an oppositely charged collector. Reagglomeration or merger of one particle 10 with another increases the average size and mass of the par~icles so they are centrifugally separated from the air and recaptured independently of the charge on wall 24.
The scrubbing liquid used in develop;ng the invention is water, and for most air scrubbing processes, 15 water is preferred. However, other scrubbing liquids may be possible. One of the addit;ves to the scrubhing water according to the inventive method is a surface~
active agent, or surfact~nt, schematically illustrated hy a supply 28 coml-ined with a water supply 2~ to ~orm 20 scr~lbbing lic~uid supply 22. ~ ~ide variety oE sur~actants are available, and the ones that have been tried have had the surprising effect of facilitating reagglomeration of water particles. The reason for this is not certain, but it is generally known that surfactants reduce 25 liquid surface tension, and surface tension apparent~y inhibits particle reagglomeration between extremely small aerosol particles. The effective surface tension at the extremely small radii of curvature for fine aerosol particles apparently allows the particles to bounce off 30 each other without merging 7 and reducing the surface tension by adding a surfactant improves the likelihood of merger or reagglomeration of aerosol particles that contact each other. I do not wish to be bound by this particular explanation for the observed effect, 35 but experiments clearly reveal that liquid particle re~
agglomeration is substantially enhanced by the presence of a surface~active agent when electric ima~e attraction occurs between concentrated aerosol particles.
~ 2~
On the basis of present information, most surface~active agents will produce the desired liquid particle reagglomeration, and there is no reason to believe that any surfactant will fail to do this. So 5 the surfactant is preferahly chosen for its compat~
ibility with the pollutants being recaptured and the materials forming the scrubber itself, and the cost of the surfactant. Both ionic and non-ionic surfactants have proven workable~ and although differences in the 10 reagglomeration effectiveness of different surfactants may occur, ~hose skilled in the art can readily practice the invention with any one of a wide variety of sur~
factants.
The amount of surfactant added to the scrubbing 15 liquid is preferably relatively small and on the order of 2% or less by weight for any particular suractant.
It is relatively easy to try different percen~ages and select an optimum proportion, once it is clear what to look for.
Another effect o~ the surace tellsion reduc~
tion from the presence of a surfactant is that the scrubbing liquid is broken into smaller sized particles.
This has a further advantage in creating a much larger liquid surface area to contact the contaminated air, 25 and it helps the liquid catch finer pollutants and a higher percentage of the pollutants presen~. Existing knowledge ahout surfactants makes it predictable that the same applied forces will break the scrubbing liquid into finer particles when a surfactant is present, but 30 the finer particles and a ~reater number of particles would ordinarily indicate that far more particles would escape with the output air because of the difficulty of capturing fine aerosol particles. Surprisingly, this does not occur, because the presence of the surfactant 35 facilitates liquid par~icle reagglomeration and actually .
~L~3~122~
reduces the escape rate of particles. For example, ~ests have shown a six-fold increase in the total number of smaller liquid particles formed when a surfactant is present, but at the same time9 the 5 escape rate of the liquid particles remains the same or reduces, indicating at leas~ a six-fold improvemenk in particle recapture, and o-f~en more than a six-fold improvement, because of ~he improved ability of the liquid particles to reagglomerate.
The other additive to the scrubbing liquid according to the inven~ive method is a material that substantially increases the conductivity of the liquid, such as an electrolyte material 30 schematically shown as added to scrubbing liquid supply 22. The electrolyte 15 or other conductivity enhancing material, hereinater referred to as "electrolyte", al.so facili~atcs re-agglomeration of li~iui(l aerosol particles and works either alone or in cooperation with a surfactant for significantly reducing the escape rate oE liquid along 20 with the air output from the scrubber. The reason why the electrolyte has this e-ffect is not absolutely certain, and I do not wish to be bound hy the reason offered here.
Increasing the conductivity of the scrubbing 25 liquid apparently enhances the electric image attraction between the aerosol particles, probably by making electrons on the particle sur-faces more mobile.
The electric -field eEect from either static electric charges on particles 7 or from a charged element in 30 the recapture region, or both, produces stronger electric image attraction forces between particles when an electrolyte is present so that more reagglomeration and more particle recaptwre occurs than if the conductivity of the scrubbing liquid were lower.
3~2~
Pxperimental measurements have shown that a 20~fold increase in particle recapture is easily obtained by adding an electrolyte making the scrubbing liquid more conductive. I, at the same time, a surfactant is also 5 present reducin~ the surface tension o-f the scrubbing liquid, the combined particle recapture improvement rom the electro~
lyte and the surfactant has been measured at more than 30 fold~
~pparently, the presence of the electrolyte enhances the electric image attraction -forces betwe!en particles 9 and the ;~
10 presence of the sur-factant helps the particles merge, so that very few particles escape when both materials are present.
At least several electrolytes are known to enhance liquid parkicle reagglomeration, and the pre~erred characteristics for a suitahle electrolyte include stability, 15 substantial inability to evaporate within the scrubber, and inability to react with water, whatever surfactant is used, the pollutarlts being capture(l, and the materials of the scrllhber itself~ These conditiolls Ire not diEicult to mcet, and the other considerations are cost. With water 20 as the scrubbing l;(lllid, two electrolytes that are hi~hly satisfactory and preferred for practicing the invention are sodium chloride and calcium chloride. Potassium permanganate also produces the desired reagglomeration efect, but is less stable and easy to use. All of the possible electrolytic 25 materials have no~ been tested yet, and there may be many more electrolytes or other materials increasing the conductivity of the scrubbing liquid that can be used in practicing the invention. ~lso, different electrolytes may be pre-ferred for scrubbing liquids other than water. ~or sodium chloride 30 and calcium chloride, the preferred proportion by weight o-E
electrolyte is 1% to 10%, and more than 5~ produces increasingly less reagglomeration improvement.
Persons skilled in the art and experienced with different scrubbers, surfactants9 and electrolytes~ can make 35 various scrubbing liquids significantly increasing the efficiency of their scrubbers 7 once the particle reagglomeration effect o-f the inventive method is understood.
Claims (6)
1. A method of operating an air scrubber that finely divides a scrubbing liquid into aerosol particles mixed with airborne pollutants, said method reducing the rate of escape from said scrubber of pollutants that combine with said scrubbing liquid, said method comprising:
a. adding a suface active agent to said scrubbing liquid so said scrubber divides said liquid into fine aerosol particles containing said surface active agent and having a large surface area for combining with said pollutants in air mixed with said aerosol particles;
b. applying sufficient turbulent force in dividing said scrubbing liquid into said aerosol particles to produce substantial static electric charges on said aerosol par-ticles, said particles being fine enough so said charges produce substantial interparticle attractive forces;
c. forming a flow of air and said aerosol particles com-bined with said pollutants captured from said air along a surface arranged to direct said flow in a curved path for centrifugally concentrating said pollutant bearing aerosol particles against said surface;
d. driving said flow with sufficient velocity relative to the radius of curvature of said path so that said centrifugal concentration of said pollutant bearing aerosol particles is adequate to make said interparticle attractive forces from said static electric charges on said aerosol particles effective for substantially increasing contacts between said concentrated aerosol particles;
e. using the presence of said surface active agent in said pollutant bearing aerosol particles that contact each other to substantially facilitate merger of said contacting aerosol particles with each other and with liquid moving along said surface;
f. centrifugally separating said merged liquid from said air in the region of said surface to remove substantially all liquid and pollutant material from said flow; and g. outputting cleaned air from said scrubber by directing said flow to a region outside said scrubber after centri-fugally separating said merged liquid within said scrubber.
a. adding a suface active agent to said scrubbing liquid so said scrubber divides said liquid into fine aerosol particles containing said surface active agent and having a large surface area for combining with said pollutants in air mixed with said aerosol particles;
b. applying sufficient turbulent force in dividing said scrubbing liquid into said aerosol particles to produce substantial static electric charges on said aerosol par-ticles, said particles being fine enough so said charges produce substantial interparticle attractive forces;
c. forming a flow of air and said aerosol particles com-bined with said pollutants captured from said air along a surface arranged to direct said flow in a curved path for centrifugally concentrating said pollutant bearing aerosol particles against said surface;
d. driving said flow with sufficient velocity relative to the radius of curvature of said path so that said centrifugal concentration of said pollutant bearing aerosol particles is adequate to make said interparticle attractive forces from said static electric charges on said aerosol particles effective for substantially increasing contacts between said concentrated aerosol particles;
e. using the presence of said surface active agent in said pollutant bearing aerosol particles that contact each other to substantially facilitate merger of said contacting aerosol particles with each other and with liquid moving along said surface;
f. centrifugally separating said merged liquid from said air in the region of said surface to remove substantially all liquid and pollutant material from said flow; and g. outputting cleaned air from said scrubber by directing said flow to a region outside said scrubber after centri-fugally separating said merged liquid within said scrubber.
2. The method of claim 1 including adding an electrolyte to said scrubbing liquid to enhance the conductivity of said aerosol particles so that said static electric charges further increase said contacts between said concentrated aerosol particles.
3. The method of claim 2 wherein said electrolyte is selected from the group consisting of calcium chloride and sodium chloride.
4. The method of claim 1 including electrically charging an element in the region of said surface to increase said contacts between said concentrated aerosol particles in response to said static electric charges.
5. The method of claim 4 including adding an electro-lyte to said scrubbing liquid to enhance the conductivity of said aerosol particles so that said static electric charges further increase said contacts between said concentrated aerosol particles.
6. The method of claim 5 wherein said electrolyte is selected from the group consisting of calcium chloride and sodium chloride.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA338,108A CA1130220A (en) | 1979-10-22 | 1979-10-22 | Air scrubber operating method |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA338,108A CA1130220A (en) | 1979-10-22 | 1979-10-22 | Air scrubber operating method |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1130220A true CA1130220A (en) | 1982-08-24 |
Family
ID=4115397
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA338,108A Expired CA1130220A (en) | 1979-10-22 | 1979-10-22 | Air scrubber operating method |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1130220A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0546342A2 (en) * | 1991-11-14 | 1993-06-16 | Matsushita Electric Industrial Co., Ltd. | A self-metabolic functional material |
-
1979
- 1979-10-22 CA CA338,108A patent/CA1130220A/en not_active Expired
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0546342A2 (en) * | 1991-11-14 | 1993-06-16 | Matsushita Electric Industrial Co., Ltd. | A self-metabolic functional material |
| US5424041A (en) * | 1991-11-14 | 1995-06-13 | Matsushita Electric Industrial Co., Ltd. | Self-metabolic functional material |
| EP0546342B1 (en) * | 1991-11-14 | 1996-08-14 | Matsushita Electric Industrial Co., Ltd. | A self-metabolic functional material |
| US5552111A (en) * | 1991-11-14 | 1996-09-03 | Matsushita Electric Industrial | Self-metabolic functional material |
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