CA1171351A - Passive self-cleaning aerosol scrubber - Google Patents
Passive self-cleaning aerosol scrubberInfo
- Publication number
- CA1171351A CA1171351A CA000376379A CA376379A CA1171351A CA 1171351 A CA1171351 A CA 1171351A CA 000376379 A CA000376379 A CA 000376379A CA 376379 A CA376379 A CA 376379A CA 1171351 A CA1171351 A CA 1171351A
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- CA
- Canada
- Prior art keywords
- liquid
- gas
- container
- porous bed
- enclosure
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D47/00—Separating dispersed particles from gases, air or vapours by liquid as separating agent
- B01D47/02—Separating dispersed particles from gases, air or vapours by liquid as separating agent by passing the gas or air or vapour over or through a liquid bath
- B01D47/021—Separating dispersed particles from gases, air or vapours by liquid as separating agent by passing the gas or air or vapour over or through a liquid bath by bubbling the gas through a liquid bath
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D47/00—Separating dispersed particles from gases, air or vapours by liquid as separating agent
- B01D47/14—Packed scrubbers
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- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Separation Of Particles Using Liquids (AREA)
- Treating Waste Gases (AREA)
- Gas Separation By Absorption (AREA)
Abstract
PASSIVE SELF-CLEANING AEROSOL SCRUBBER
Abstract of the Disclosure A liquid-tight enclosure is partially filled with water. A container supports a porous bed of sand and gravel that is partially submerged in the liquid. The lower end of the porous bed is spaced upward from the bottom of the enclosure. A gas delivery duct feeds gas to a location vertically beneath the porous bed to enable a stream of gas to pass upwardly through the porous bed, drawing water with it to continuously clean the gravel.
Abstract of the Disclosure A liquid-tight enclosure is partially filled with water. A container supports a porous bed of sand and gravel that is partially submerged in the liquid. The lower end of the porous bed is spaced upward from the bottom of the enclosure. A gas delivery duct feeds gas to a location vertically beneath the porous bed to enable a stream of gas to pass upwardly through the porous bed, drawing water with it to continuously clean the gravel.
Description
-- l --PASSIVE SELF-CLEANING AEROSOL SCRUBBER
The present invention relates generally to aerosol scrubbers and more particularly to aerosol scrubbers utilizing a porous bed in combination with a scrubbing liqu;d.
The present disclosure arose from an effort to devise an air cleanin~
system for use in conjunc~ion with containment buildings and facilities for nuclear reactors. The purpose of the specific air cleaning system was to limit release of aerosol-particles and absorbable gases, including radio-active materials, from containment facilities during postulated major accidents. A system was devised which requires no energy while in the passive state, and no active energy other than pressurization of the stream of gas being scrubbed. While in its passive state, the system is instantly aYailable for usage.
The disclosed system merges desirable features of both a pool type scrubber and a sand or gravel filter into a hybrid type of scrubber.
A pool type scrubber consists of a gas inlet duct projecting downwardly into a pool of liquid. Gas flows from the inlet duct into the pool of l;quid, beaks into bubbles, and then flows upwardly through the pool.
Aerosols are removed from the gas in the bubbles by various forces, which 20 generally are very dependent upon bubble diameter. Although devices can be added to the outlet of the gas duct to reduce the bubble size, these systems charackeristically produce relatively large gas bubbles and are subject to .' '~ .
1 17135~
plugging by aerosol deposition. Aerosol removal is correspondingly low.
However, pool type scrubbers haYe the desirable feature of bejng capable of handling a large mass of collected material as it is removed from the stream of gas.
Sand or gravel filters are constructed using layers of graded granular material with the largest gran~lar sizes normally positioned at the bottom of the filter bed and successive layers of smaller granules arranged upwardly from the bottom layer. Gas containing aerosols pass from the bottom to the top of the bed. Aerosol is removed by inertia9 diffusion, interception and gravity forces. Because of the layers of fine sized granules at the upper portions of such a bed, sand or gravel f;lters demonstrate a high aerosol removal efficiency. However, because such a bed contains a limited vo;d volume, the filter can handle only a small amount of collected material per unit volume of filter and then must be replaced, flushed or otherwise cleaned.
The disclosed hybrid scrubber conslsts of a porous bed at least par-tially submerged within a pool of liquid. The porous bed might contain granular material such as sand or gravel. The liquid might be water. A
pressurized stream of air or other gas laden with aerosol is directed to tlle ' bottom of the bed. It distributes itself across the bed and flows upwardly through~the irregular channels formed in the bed interst;ces. Aerosol is removed from the gas by interception, diffusion, inertia forces, particle growth, and settling. The porous bed itself is continuously cleaned by liquid entrained with the gas. The clean gas exits from the top of the porous bed.
~he invention, in its broadest aspect, contemplates a gas scrubbing apparatus for removing particulate matter from a stream of pressurized gas and oomprises a liquid-tight enclosure, a quantity of liquid within the enclosu~e partially filling its interior to a liquid surface elevation, and an open ended container positioned wi~hin the enclosure and having gas ~713~
impervious upright side walls extending upward from a lower end submerged in the liquid. A porous ked surrounded by the gas impervious side walls of the upright container extends vertical~y upward within the container frcm a kottom end openly submerged in the liquid and is spaced above the lower end of the gas impervious upright side walls of the container to a top end. An inlet duct means extends into the enclosure and includes a discharge opening at a submerged location in the liquid positioned keneath the porous bgd for direct,ing a stream of pressurlzed gas and particulate matter to the bottom of the porous bed. me top end of the parous ked is open to liquid flow effected by differential apparent density between liquid within and without the upright container to thereby permit liquid entrained within the stream of gas to be returned by gravity from within the con-tainer to the liquid remaining within the enclosure and to there~y permit the self-cleaning o the porous bed. An outlet duct means is open through the lS enclosure at an elevation above the liquid surface elevation within it for dischæ ging the stream of gas following its passage through the porous bed.
In a further embodlment, the top end of the porous bed open to llquid flow can be effected by differential apparent density between the liquid within and without the porous bed.
20- It is a first object of this invention to combine the particle mass collection capability of a pcol scrubber with the removal efficiency of a wetted po~ous filter. The resul~ is a high efficiency filter systen having high particle mass collection capability.
Another object of this invention was to design a high capacity aerosol scrubber which remains in a passive state over periods of months or years, and is instantly ready for use when needed.
Another object is to provide a scrubber having no energy requdrements when in its passive state. When completely enclosed, the apparatus reqlires no maintenance until after it has been used.
An~ther object is to provide a scrukber having low energy requirements during use. The scrubber ls activa~ed 501ely by the gaseous pressure of the stream being cleaned, and requires n~ external pumps or controls.
3 ~ ~
These and further objects will be evident from the following dis-closure and the ~ccompanyLng drawings, which illustrate one preferred form of the invention.
F~g. l shows a schematic ~ross-sectional view through the scrubber;
Fig. 2 shows a modified scrubber.
The scrubber that is the subject of this disclosure basically consists of a porous bed at least partially submerged in a pool of liquid. An incoming stream of gas is directed to the bottom of the bed. Gas flow is induced upwardly by exhausting gas from the outlet duct at the ~op of the apparatus. Gas laden with aerosol passes down the inlet duct and up through the irregular porous channels in the bed. Liquid is purged through the bed due to the difference in density of liquid outside the bed and the effective density of the gas-liquid m~xture inside the bed. This purging action con-tinuously washes the porous bed clean of collected aerosol.
As shown in the drawing, a practical embodiment of the device comprises a liquid-tight enclosure 10 having a bottom ~all lI and connecting upright ~side walls 12 defining an interior liquid tank. The tank is preferably fully enclosed and completed by a top wall 13, but c~n be upwardly open, as will be described below.
A quantity of liquid 14 is contained within enclosure 10. This liquid might be water or any desired liquid that is physically stable and compatible with the structure and usage of the filter. It partially fills the interior liquid tank presented by enclosure 10 to a li~uid surface elevation desig-nated by reference numeral 15.
An open-ended container 16 is positioned within enelosure 10. It has gas impervious upright side walls 17 that extend from a lower end 18 to an upper end 20. The lower end of container 16 is submerged in the liquid 14.
Its upper end 20 is either ad~acent to, above or below the liquid surface elevation shown at 15.
r ~ /
117~3~1 A porous bed 21 of gravel or other filtering material is surrounded by the gas impervious side walls 17 of container 16. Bed 21 extends vertically upward within container 16 from a bottom location spaced above the.lower end 18 of the gas impervious upright side walls 17 of container 16. This location is defined bY a trans.vers.e porous or perforated plate 22 extending across the side walls 17. In the preferred embodiment as shown, approximately half of the vertical height of the porous bed 21 is located beneath the elevation of the liquid surface at 15 and is therefore submerged in the liquid 14.
An inlet duct 23 is provided for directing a stream of pressurized gas and particulate material or aerosol to a submerged location vertically beneath the porous bed 21. This is illustrated as a vertical tube made of gas impervious material and extending through the center of the porous bed f' 21. The inlet duct 23 terminates at an open bottom end 24 positioned at an elevation between the bottom of porous bed 21 and the lower end 18 of the ~- gas impervious container slde walls 17. ~
The top end of the porous bed 21 is illustrated as being covered by a transverse porous or perforated plate 25. While such a plate is desirable, it is not always necessary to keep bed 21 confined. The top end of ~ed 21 is transversely open to liquid flow to:thereby permit liquid entrained with the stream of gas to be returned by gravity over the sides of container 16 to the liquid 14 within the interior liquid tank provided by enclosure 10.
Various materials might be used with;n porous bed 21. The porous material should be insoluble in the liquid. It might constitute natural or 25 .artificial sand or gravel, fi~rous materials, or other packing materials commonly used in either dry or wet filters.
An outlet duct 26 is open through enclosure 10 at an ele~ation above ~17I35~
the liquid surface at 15. Duct 26 d~scharges the stream of gas fol'lowing its passage through the porous bed 21.
The presence of the gas within the container 16 that surrounds the porous bed 21 reduces the apparent densit~ of the liquid 14 ~ithin the bed confines.
Consequently, as the gaseous stream rises through bed 21, liquid flows from within enclosure 10 into the bottom of the bed, moves upwardly, and subse-quently spills over the top. Collected aerosol within porous bed 21 is thereby continuously washed from it. This passive, self-cleaning function of the porous bed 21 is one of the novel features of this device.
The illustrated apparatus effectively removes aerosols from a gaseous stream. The'efficiency of aerosol removal can be adjusted by modifying the depth of the porous bed 21, the size of the packing materials comprising bed 21 and the velocity of the gaseous stream directed through the inlet 'duct 23 and bed 21. The only limitation as to the amount of collected materials which can be accommodated by the apparatus is the volume of the pool of liquid 14 and the solubility of the re~moved aerosol materlals within the liquid. Another limit is the volume of insoluble particles that can be accommodated within the enclosure 10.
The scrubber is a three phase liquid scrubber. The solid phase, com-prising the porous material within the bed 21, is fixed in place. The gasand liquid phases flow concurrently through bed 21. Because of the com-plexity of such a system, tests were conducted to both develop the concept and measure scrubber performance.
A prototype scrubber was constructed substantially as shown in Fig. l.
The bed was .30 m in diameter, .61 m deep, and was packed With basalt rock seived to between ~.95 cm and ~1.27 cm. The cross-sectional area avail-able for gas flow was .069m2. The bed void fraction was .~5+ .050.
~7~3~1 The granular basalt rock used in these tests is charac~eri2ed as having no smooth sides. It ~as screened by hand ;nto three segments. It was retained between horizontal plates 22 and 25 across the container side walls 17. Plates 22 and 25 as tested ~ere made from solid flat sheets with aper-tures formed through them in a staggered pattern and a central aperture toreceive the inlet duct 23. A second type of support plate usable in this apparatus could be fabricated from suitable screen material.
It is to be noted that the lower end 18 of the container side walls 17 is provided w;th openings 27. They are spaced above the bottom wall 11 of enclosure 10 to prevent re-entrainment of insoluble solids within the liquid and gas stream moving into porous bed 21. The openings 27 permit flow of liquid 14 beneath the porous bed 21. The area between the openings 27 and the bottom of bed 21 constitutes a surrounding skirt within which incoming gas briefly accumulates before it moves upwardly through the porous bed 21.
As ~s evident from Fig. l, the horizontal cross-sectional area of container 16 is substantially less than the inlterior horizontal cross-sectional area withi~ the enclosure 10. The cross-sectional area of con-tainer 16 is a function of the volume of gas which must be passed upwardly through bed 21. The cross-sectional area and depth of liquid 14 within enclosure 10 is a function of the storage capability requ;red for handling aerosol removed from the stream of gas.
The upright side walls 12 of enclosure 10 are spaced transversely out-ward from the side walls 17 of the container 16. This permits flow of liquid into the container 16 from all sides through the openings 27 and permits the liquid exiting from container 16 to spill about its entire periphery.
The specific example of the scrubber utilized cylindrical side walls about the container 16, arranged vertically and centered about a vertical 1~13~
inner axis along the center of the illustrated inlet duct 23. The duct 23 was constructed as a straigh,t vertical tube coaxially centered within the bed 21 along the vertical container axis.
A series of tests were conducted using various sodium-compound aerosols to measure aerosol removal efficiency, using water as the wash liquid within enclosure 10. Table I lists the test parameters showing gas velocity based on a bed cross section area of 0.06~ m2. The flow rate of the gaseous stream was varied during each test and aerosol samples were periodically taken from both the inlet duct 23 and the outlet duct 26. A conventional dry filter was placed downstream of the scrubber in the outlet duct 26 and was leached and analyzed for sodium following each test.
The results of the tests are summarized in Table II. The overall efficiency was calculated using the total mass of sodium collected in the ; scrubber solution and on the fibrous filter. ,The average efficiency was calculated by the arithmetic average of individual'efficiencies determined from instantaneous gas concentration measurements. This data indicates that changing'the granular sizes within bed 21 had no effect on collection.
Reducing the bed height by a factor of 2 increased aerosol penetration by a factor of 7.
` .
g TABL~ I
Test Conditions Test Superficial gas Test Aerosol Source Aerosol Type Puration (~R) Velocity (m/Min) 1. Spray Fire Na2C039.7 2. - 30.
The present invention relates generally to aerosol scrubbers and more particularly to aerosol scrubbers utilizing a porous bed in combination with a scrubbing liqu;d.
The present disclosure arose from an effort to devise an air cleanin~
system for use in conjunc~ion with containment buildings and facilities for nuclear reactors. The purpose of the specific air cleaning system was to limit release of aerosol-particles and absorbable gases, including radio-active materials, from containment facilities during postulated major accidents. A system was devised which requires no energy while in the passive state, and no active energy other than pressurization of the stream of gas being scrubbed. While in its passive state, the system is instantly aYailable for usage.
The disclosed system merges desirable features of both a pool type scrubber and a sand or gravel filter into a hybrid type of scrubber.
A pool type scrubber consists of a gas inlet duct projecting downwardly into a pool of liquid. Gas flows from the inlet duct into the pool of l;quid, beaks into bubbles, and then flows upwardly through the pool.
Aerosols are removed from the gas in the bubbles by various forces, which 20 generally are very dependent upon bubble diameter. Although devices can be added to the outlet of the gas duct to reduce the bubble size, these systems charackeristically produce relatively large gas bubbles and are subject to .' '~ .
1 17135~
plugging by aerosol deposition. Aerosol removal is correspondingly low.
However, pool type scrubbers haYe the desirable feature of bejng capable of handling a large mass of collected material as it is removed from the stream of gas.
Sand or gravel filters are constructed using layers of graded granular material with the largest gran~lar sizes normally positioned at the bottom of the filter bed and successive layers of smaller granules arranged upwardly from the bottom layer. Gas containing aerosols pass from the bottom to the top of the bed. Aerosol is removed by inertia9 diffusion, interception and gravity forces. Because of the layers of fine sized granules at the upper portions of such a bed, sand or gravel f;lters demonstrate a high aerosol removal efficiency. However, because such a bed contains a limited vo;d volume, the filter can handle only a small amount of collected material per unit volume of filter and then must be replaced, flushed or otherwise cleaned.
The disclosed hybrid scrubber conslsts of a porous bed at least par-tially submerged within a pool of liquid. The porous bed might contain granular material such as sand or gravel. The liquid might be water. A
pressurized stream of air or other gas laden with aerosol is directed to tlle ' bottom of the bed. It distributes itself across the bed and flows upwardly through~the irregular channels formed in the bed interst;ces. Aerosol is removed from the gas by interception, diffusion, inertia forces, particle growth, and settling. The porous bed itself is continuously cleaned by liquid entrained with the gas. The clean gas exits from the top of the porous bed.
~he invention, in its broadest aspect, contemplates a gas scrubbing apparatus for removing particulate matter from a stream of pressurized gas and oomprises a liquid-tight enclosure, a quantity of liquid within the enclosu~e partially filling its interior to a liquid surface elevation, and an open ended container positioned wi~hin the enclosure and having gas ~713~
impervious upright side walls extending upward from a lower end submerged in the liquid. A porous ked surrounded by the gas impervious side walls of the upright container extends vertical~y upward within the container frcm a kottom end openly submerged in the liquid and is spaced above the lower end of the gas impervious upright side walls of the container to a top end. An inlet duct means extends into the enclosure and includes a discharge opening at a submerged location in the liquid positioned keneath the porous bgd for direct,ing a stream of pressurlzed gas and particulate matter to the bottom of the porous bed. me top end of the parous ked is open to liquid flow effected by differential apparent density between liquid within and without the upright container to thereby permit liquid entrained within the stream of gas to be returned by gravity from within the con-tainer to the liquid remaining within the enclosure and to there~y permit the self-cleaning o the porous bed. An outlet duct means is open through the lS enclosure at an elevation above the liquid surface elevation within it for dischæ ging the stream of gas following its passage through the porous bed.
In a further embodlment, the top end of the porous bed open to llquid flow can be effected by differential apparent density between the liquid within and without the porous bed.
20- It is a first object of this invention to combine the particle mass collection capability of a pcol scrubber with the removal efficiency of a wetted po~ous filter. The resul~ is a high efficiency filter systen having high particle mass collection capability.
Another object of this invention was to design a high capacity aerosol scrubber which remains in a passive state over periods of months or years, and is instantly ready for use when needed.
Another object is to provide a scrubber having no energy requdrements when in its passive state. When completely enclosed, the apparatus reqlires no maintenance until after it has been used.
An~ther object is to provide a scrukber having low energy requirements during use. The scrubber ls activa~ed 501ely by the gaseous pressure of the stream being cleaned, and requires n~ external pumps or controls.
3 ~ ~
These and further objects will be evident from the following dis-closure and the ~ccompanyLng drawings, which illustrate one preferred form of the invention.
F~g. l shows a schematic ~ross-sectional view through the scrubber;
Fig. 2 shows a modified scrubber.
The scrubber that is the subject of this disclosure basically consists of a porous bed at least partially submerged in a pool of liquid. An incoming stream of gas is directed to the bottom of the bed. Gas flow is induced upwardly by exhausting gas from the outlet duct at the ~op of the apparatus. Gas laden with aerosol passes down the inlet duct and up through the irregular porous channels in the bed. Liquid is purged through the bed due to the difference in density of liquid outside the bed and the effective density of the gas-liquid m~xture inside the bed. This purging action con-tinuously washes the porous bed clean of collected aerosol.
As shown in the drawing, a practical embodiment of the device comprises a liquid-tight enclosure 10 having a bottom ~all lI and connecting upright ~side walls 12 defining an interior liquid tank. The tank is preferably fully enclosed and completed by a top wall 13, but c~n be upwardly open, as will be described below.
A quantity of liquid 14 is contained within enclosure 10. This liquid might be water or any desired liquid that is physically stable and compatible with the structure and usage of the filter. It partially fills the interior liquid tank presented by enclosure 10 to a li~uid surface elevation desig-nated by reference numeral 15.
An open-ended container 16 is positioned within enelosure 10. It has gas impervious upright side walls 17 that extend from a lower end 18 to an upper end 20. The lower end of container 16 is submerged in the liquid 14.
Its upper end 20 is either ad~acent to, above or below the liquid surface elevation shown at 15.
r ~ /
117~3~1 A porous bed 21 of gravel or other filtering material is surrounded by the gas impervious side walls 17 of container 16. Bed 21 extends vertically upward within container 16 from a bottom location spaced above the.lower end 18 of the gas impervious upright side walls 17 of container 16. This location is defined bY a trans.vers.e porous or perforated plate 22 extending across the side walls 17. In the preferred embodiment as shown, approximately half of the vertical height of the porous bed 21 is located beneath the elevation of the liquid surface at 15 and is therefore submerged in the liquid 14.
An inlet duct 23 is provided for directing a stream of pressurized gas and particulate material or aerosol to a submerged location vertically beneath the porous bed 21. This is illustrated as a vertical tube made of gas impervious material and extending through the center of the porous bed f' 21. The inlet duct 23 terminates at an open bottom end 24 positioned at an elevation between the bottom of porous bed 21 and the lower end 18 of the ~- gas impervious container slde walls 17. ~
The top end of the porous bed 21 is illustrated as being covered by a transverse porous or perforated plate 25. While such a plate is desirable, it is not always necessary to keep bed 21 confined. The top end of ~ed 21 is transversely open to liquid flow to:thereby permit liquid entrained with the stream of gas to be returned by gravity over the sides of container 16 to the liquid 14 within the interior liquid tank provided by enclosure 10.
Various materials might be used with;n porous bed 21. The porous material should be insoluble in the liquid. It might constitute natural or 25 .artificial sand or gravel, fi~rous materials, or other packing materials commonly used in either dry or wet filters.
An outlet duct 26 is open through enclosure 10 at an ele~ation above ~17I35~
the liquid surface at 15. Duct 26 d~scharges the stream of gas fol'lowing its passage through the porous bed 21.
The presence of the gas within the container 16 that surrounds the porous bed 21 reduces the apparent densit~ of the liquid 14 ~ithin the bed confines.
Consequently, as the gaseous stream rises through bed 21, liquid flows from within enclosure 10 into the bottom of the bed, moves upwardly, and subse-quently spills over the top. Collected aerosol within porous bed 21 is thereby continuously washed from it. This passive, self-cleaning function of the porous bed 21 is one of the novel features of this device.
The illustrated apparatus effectively removes aerosols from a gaseous stream. The'efficiency of aerosol removal can be adjusted by modifying the depth of the porous bed 21, the size of the packing materials comprising bed 21 and the velocity of the gaseous stream directed through the inlet 'duct 23 and bed 21. The only limitation as to the amount of collected materials which can be accommodated by the apparatus is the volume of the pool of liquid 14 and the solubility of the re~moved aerosol materlals within the liquid. Another limit is the volume of insoluble particles that can be accommodated within the enclosure 10.
The scrubber is a three phase liquid scrubber. The solid phase, com-prising the porous material within the bed 21, is fixed in place. The gasand liquid phases flow concurrently through bed 21. Because of the com-plexity of such a system, tests were conducted to both develop the concept and measure scrubber performance.
A prototype scrubber was constructed substantially as shown in Fig. l.
The bed was .30 m in diameter, .61 m deep, and was packed With basalt rock seived to between ~.95 cm and ~1.27 cm. The cross-sectional area avail-able for gas flow was .069m2. The bed void fraction was .~5+ .050.
~7~3~1 The granular basalt rock used in these tests is charac~eri2ed as having no smooth sides. It ~as screened by hand ;nto three segments. It was retained between horizontal plates 22 and 25 across the container side walls 17. Plates 22 and 25 as tested ~ere made from solid flat sheets with aper-tures formed through them in a staggered pattern and a central aperture toreceive the inlet duct 23. A second type of support plate usable in this apparatus could be fabricated from suitable screen material.
It is to be noted that the lower end 18 of the container side walls 17 is provided w;th openings 27. They are spaced above the bottom wall 11 of enclosure 10 to prevent re-entrainment of insoluble solids within the liquid and gas stream moving into porous bed 21. The openings 27 permit flow of liquid 14 beneath the porous bed 21. The area between the openings 27 and the bottom of bed 21 constitutes a surrounding skirt within which incoming gas briefly accumulates before it moves upwardly through the porous bed 21.
As ~s evident from Fig. l, the horizontal cross-sectional area of container 16 is substantially less than the inlterior horizontal cross-sectional area withi~ the enclosure 10. The cross-sectional area of con-tainer 16 is a function of the volume of gas which must be passed upwardly through bed 21. The cross-sectional area and depth of liquid 14 within enclosure 10 is a function of the storage capability requ;red for handling aerosol removed from the stream of gas.
The upright side walls 12 of enclosure 10 are spaced transversely out-ward from the side walls 17 of the container 16. This permits flow of liquid into the container 16 from all sides through the openings 27 and permits the liquid exiting from container 16 to spill about its entire periphery.
The specific example of the scrubber utilized cylindrical side walls about the container 16, arranged vertically and centered about a vertical 1~13~
inner axis along the center of the illustrated inlet duct 23. The duct 23 was constructed as a straigh,t vertical tube coaxially centered within the bed 21 along the vertical container axis.
A series of tests were conducted using various sodium-compound aerosols to measure aerosol removal efficiency, using water as the wash liquid within enclosure 10. Table I lists the test parameters showing gas velocity based on a bed cross section area of 0.06~ m2. The flow rate of the gaseous stream was varied during each test and aerosol samples were periodically taken from both the inlet duct 23 and the outlet duct 26. A conventional dry filter was placed downstream of the scrubber in the outlet duct 26 and was leached and analyzed for sodium following each test.
The results of the tests are summarized in Table II. The overall efficiency was calculated using the total mass of sodium collected in the ; scrubber solution and on the fibrous filter. ,The average efficiency was calculated by the arithmetic average of individual'efficiencies determined from instantaneous gas concentration measurements. This data indicates that changing'the granular sizes within bed 21 had no effect on collection.
Reducing the bed height by a factor of 2 increased aerosol penetration by a factor of 7.
` .
g TABL~ I
Test Conditions Test Superficial gas Test Aerosol Source Aerosol Type Puration (~R) Velocity (m/Min) 1. Spray Fire Na2C039.7 2. - 30.
2. Pool Fire Na2024.3 1.2 - 22.
3- Pool Fire Na2022.7 2. - 27.
4- Pool Fire Na2024.0 .8 - 20.
5. Spray Fire NaOH24. 17. - 27.
TABLE II
Test Results Overall AverageNa Mass Col- Parameteral Test Efficiency Efficiencylected (grams) Tested 1. 99.8 99.18 748 Type of aerosol 2. 99.8 99.97 590 Type of aerosol 3. 98.6 98.78 401 Reduced Bed height (.305 m) 4. 99.8 99.97 566 Reduced size of packing (.64-.95 cm) 5. 99.996 99.998 ;4,517 Fiber ele~ent added In the final test listed in Tables I and II, a po1ypropylehe f;ber element was added to the scrubber to eliminate mist entrainment and to enhance capture of small particles. The fiber unit measured .61 m OD by .46 m ID by .61 m long. It was placed directly over the porous bed 21.
Gas leaving the bed 21 flowed upward into the central region of the fiber unit and then horizontally through the f;brous materials. Water droplets entrained ;n the gas that left the porous bed 21 continuously wash-d the .
.
~1713~1 -lo-collec;ted aerosol from the fiber unit. The particular test reported in Tables I and II was performed using a NaO~I aerosol. The pressure drop across the fiber unit remained constant throughout the test, indicating that the fibers within it were sufficientl~ washed by the entrained water. This demonstrated the i-ncreased removal efficiency available by combining the hybrid scrubber with an available fi~rous filter. A schematic illustration of this modified scrubber is shown in Fig. 2. The fiber unit is indicated at 2~. All other elements of the apparatus are as previously disclosed, and are indicated by the reference numerals previously explained.
Hydraulic tests were performed without aerosols for various bed con-figurations to measure pressure drop, water circulation rate, and water level effects. Pressure drop through the porous bed 2l was found to be independent of gas flow rate at rates between gas superficial velocities of .002 to ~.507 m/s. The pressure drop through the apparatus was found to be primarily due to the static liquid head at the submerged open botton end 24 of inlet duct 23. The internal water circulation rate was found to be a function of the gas flow rate, bed depth, granular size and inlet duct submergence. In checking water flow rate versus gas flow rate for various bed parameters using a granular rock bed, water was found to be pumped at a decreasing rate as the water level dropped until the level was down to about one half the bed depth. Ihe test parameter having the greatest effect on water flow rate was the depth of submergence of the inlet duct 23.
The present apparatus is capable of handling a gaseous stream at pressures of lO-50 psi, which are typically containment pressures for vessels utilized in nuclear reactor installations. Gaseous streams vented -From such containment vessels may be throttled as necessary in order to meet flow rate limitations of a particular scrubber apparatus. No other pumping of the ~13~
gaseous stream is required, thereby eliminating any energy requirements for activation of the scrubber.
The tests conducted on the experimental model indicate that a passive self~cleaning aerosol scrubber can be designed based on a superficial gas velocity of .507 m/s and a bed depth of .608 m. The aerosol removal efficiency can be predicted to exceed 99% for the aerosols that might be expected in a nuclear installation. Aerosol removal efficiency would exceed 99.9% for all feasible particle distributions if a passive fibrous filter is included as indicated in Fig. 2.
In this apparatus, an airlift is used to circulate wash liquid through the packing within porous bed21.. The packing is kept clean during use of the scrubber without requiring utilization of external liquid pumps, which would in turn require a source of energy. This ;s extremely important under i those conditions where electric power is not available.
Removal efficiency of the scrubber can be designed to have the value requ;red for any particular application. A high removal efficiency for small part;cles can be realized. This is a distinct advantage over submerged tubes, where largebubbles lead to low removal efficiencies for finer particles.
Because the porous bed 21 is continually wetted, trapped~dust will be either dissolved or washed from the bed material. Therefore, large masses of airborne particles can be trapped without plugging the porous bed 21.
As compared to a simple submerged tube, this apparatus has a much lower pressure drop in a device designed to yield the same removal efficiency.
This results from the breaking of the gas stream into small parcels as it enters the porous bed 21.
All of the flow paths through the porous bed 21, which are small in size, arc washed by the liquid and therefore will not plug. The inlet duct, ~1713~
which is not washed, can be as large~as desired to assure that plugging will be prevented. This is a great improvelnent over other bubble breakup devices, such as the use of small diameter submerged tubes.
The present device can be built of simple, readily available components which are eas-ily fabricated. It should be capable of being constructed at relatively low cost.
The apparatus has high reliability and can perform as designed after years of non-operating stand-by status. Only the liquid level would need to be maintained periodically. No intricate parts or controls are needed for the functioning of the scrubber and no auxiliary power is required. The device therefore has few failure modes, and very high rei;ability.
TABLE II
Test Results Overall AverageNa Mass Col- Parameteral Test Efficiency Efficiencylected (grams) Tested 1. 99.8 99.18 748 Type of aerosol 2. 99.8 99.97 590 Type of aerosol 3. 98.6 98.78 401 Reduced Bed height (.305 m) 4. 99.8 99.97 566 Reduced size of packing (.64-.95 cm) 5. 99.996 99.998 ;4,517 Fiber ele~ent added In the final test listed in Tables I and II, a po1ypropylehe f;ber element was added to the scrubber to eliminate mist entrainment and to enhance capture of small particles. The fiber unit measured .61 m OD by .46 m ID by .61 m long. It was placed directly over the porous bed 21.
Gas leaving the bed 21 flowed upward into the central region of the fiber unit and then horizontally through the f;brous materials. Water droplets entrained ;n the gas that left the porous bed 21 continuously wash-d the .
.
~1713~1 -lo-collec;ted aerosol from the fiber unit. The particular test reported in Tables I and II was performed using a NaO~I aerosol. The pressure drop across the fiber unit remained constant throughout the test, indicating that the fibers within it were sufficientl~ washed by the entrained water. This demonstrated the i-ncreased removal efficiency available by combining the hybrid scrubber with an available fi~rous filter. A schematic illustration of this modified scrubber is shown in Fig. 2. The fiber unit is indicated at 2~. All other elements of the apparatus are as previously disclosed, and are indicated by the reference numerals previously explained.
Hydraulic tests were performed without aerosols for various bed con-figurations to measure pressure drop, water circulation rate, and water level effects. Pressure drop through the porous bed 2l was found to be independent of gas flow rate at rates between gas superficial velocities of .002 to ~.507 m/s. The pressure drop through the apparatus was found to be primarily due to the static liquid head at the submerged open botton end 24 of inlet duct 23. The internal water circulation rate was found to be a function of the gas flow rate, bed depth, granular size and inlet duct submergence. In checking water flow rate versus gas flow rate for various bed parameters using a granular rock bed, water was found to be pumped at a decreasing rate as the water level dropped until the level was down to about one half the bed depth. Ihe test parameter having the greatest effect on water flow rate was the depth of submergence of the inlet duct 23.
The present apparatus is capable of handling a gaseous stream at pressures of lO-50 psi, which are typically containment pressures for vessels utilized in nuclear reactor installations. Gaseous streams vented -From such containment vessels may be throttled as necessary in order to meet flow rate limitations of a particular scrubber apparatus. No other pumping of the ~13~
gaseous stream is required, thereby eliminating any energy requirements for activation of the scrubber.
The tests conducted on the experimental model indicate that a passive self~cleaning aerosol scrubber can be designed based on a superficial gas velocity of .507 m/s and a bed depth of .608 m. The aerosol removal efficiency can be predicted to exceed 99% for the aerosols that might be expected in a nuclear installation. Aerosol removal efficiency would exceed 99.9% for all feasible particle distributions if a passive fibrous filter is included as indicated in Fig. 2.
In this apparatus, an airlift is used to circulate wash liquid through the packing within porous bed21.. The packing is kept clean during use of the scrubber without requiring utilization of external liquid pumps, which would in turn require a source of energy. This ;s extremely important under i those conditions where electric power is not available.
Removal efficiency of the scrubber can be designed to have the value requ;red for any particular application. A high removal efficiency for small part;cles can be realized. This is a distinct advantage over submerged tubes, where largebubbles lead to low removal efficiencies for finer particles.
Because the porous bed 21 is continually wetted, trapped~dust will be either dissolved or washed from the bed material. Therefore, large masses of airborne particles can be trapped without plugging the porous bed 21.
As compared to a simple submerged tube, this apparatus has a much lower pressure drop in a device designed to yield the same removal efficiency.
This results from the breaking of the gas stream into small parcels as it enters the porous bed 21.
All of the flow paths through the porous bed 21, which are small in size, arc washed by the liquid and therefore will not plug. The inlet duct, ~1713~
which is not washed, can be as large~as desired to assure that plugging will be prevented. This is a great improvelnent over other bubble breakup devices, such as the use of small diameter submerged tubes.
The present device can be built of simple, readily available components which are eas-ily fabricated. It should be capable of being constructed at relatively low cost.
The apparatus has high reliability and can perform as designed after years of non-operating stand-by status. Only the liquid level would need to be maintained periodically. No intricate parts or controls are needed for the functioning of the scrubber and no auxiliary power is required. The device therefore has few failure modes, and very high rei;ability.
Claims (10)
1. A gas scrubbing apparatus for removing particulate matter from a stream of pressurized gas comprising:
a liquid-tight enclosure;
a quantity of liquid within the enclosure partially filling its interior to a liquid surface elevation;
an open ended container positioned within the enclosure and having gas impervious upright side walls extending upward from a lower end submersed in the liquid.
a porous bed surrounded by the gas impervious side walls of the upright container and extending vertically upward within the container from a bottom end openly submerged in the liquid and spaced above the lower end of the gas impervious upright side walls of the container to a top end;
inlet duct means extending into the enclosure and including a discharge opening at a submerged location in the liquid positioned beneath the porous bed for directing a stream of pressurized gas and particulate matter to the bottom of the porous bed;
the top end of the porous bed being open to liquid flow effected by differential apparent density between liquid within and without the upright container to thereby permit liquid entrained within the stream of gas to be returned by gravity from within the container to the liquid remaining within the enclosure and to thereby permit the self-cleaning of the porous bed; and outlet duct means open through the enclosure at an elevation above the liquid surface elevation within it for discharging the stream of gas following its passage through the porous bed.
a liquid-tight enclosure;
a quantity of liquid within the enclosure partially filling its interior to a liquid surface elevation;
an open ended container positioned within the enclosure and having gas impervious upright side walls extending upward from a lower end submersed in the liquid.
a porous bed surrounded by the gas impervious side walls of the upright container and extending vertically upward within the container from a bottom end openly submerged in the liquid and spaced above the lower end of the gas impervious upright side walls of the container to a top end;
inlet duct means extending into the enclosure and including a discharge opening at a submerged location in the liquid positioned beneath the porous bed for directing a stream of pressurized gas and particulate matter to the bottom of the porous bed;
the top end of the porous bed being open to liquid flow effected by differential apparent density between liquid within and without the upright container to thereby permit liquid entrained within the stream of gas to be returned by gravity from within the container to the liquid remaining within the enclosure and to thereby permit the self-cleaning of the porous bed; and outlet duct means open through the enclosure at an elevation above the liquid surface elevation within it for discharging the stream of gas following its passage through the porous bed.
2. A gas scrubbing apparatus as set out in claim 1 wherein the hori-zontal cross-sectional area of the container is less than the interior hori-zontal-cross-sectional area within the enclosure.
3. A gas scrubbing apparatus as set out in claim 1 wherein the enclo-sure interior is bounded by upright solid walls spaced transversely outward from the side walls of the container.
4. A gas scrubbing apparatus as set out in claim 1 wherein the gas delivery conduit means comprises a vertical tube extending through the porous bed and terminating at an open bottom end at an elevation between that of the bottom of the porous bed and that of the lower end of the container side walls.
5. A gas scrubbing apparatus as set out in claim 1 wherein the porous bed comprises a packed bed of granular material that is insoluble in the liquid.
6. A gas scrubbing apparatus for removing particulate matter from a stream of pressurized gas comprising:
a liquid-tight enclosure having a bottom wall and connecting upright side walls defining an interior liquid tank;
a quantity of liquid within the enclosure filling the interior liquid tank to a liquid surface elevation;
an upright open ended container positioned within the enclosure and having gas impervious upright side walls extending from a lower end submerged in the liquid to an upper end, the side walls of the container being spaced inwardly from the upright side walls of the enclosure;
a porous bed surrounded by the gas impervious side walls of the upright container and extending vertically upward within the container from a location spaced above the lower end of the gas impervious upright side walls of the container, at least half of the vertical height of the porous bed being submerged in the liquid;
inlet duct means for directing a stream of pressurized gas and parti-culate matter to a submerged location vertically beneath the porous bed, said inlet duct means comprising an upright tube of gas impervious material extending through the porous bed and terminating at an open bottom end positioned at an elevation between that of the bottom of the porous bed and that of the lower end of the gas impervious container side walls;
the top end of the porous bed being open to liquid flow effected by differential apparent density between liquid within and without the upright container to thereby permit a portion of the liquid entrained within the stream of gas to be returned by gravity from within the container to the liquid remaining within the interior liquid tank and to thereby permit the self-cleaning of the porous bed; and outlet duct means open through the enclosure at an elevation above the liquid surface elevation within it for discharging the stream of gas following its passage through the porous bed.
a liquid-tight enclosure having a bottom wall and connecting upright side walls defining an interior liquid tank;
a quantity of liquid within the enclosure filling the interior liquid tank to a liquid surface elevation;
an upright open ended container positioned within the enclosure and having gas impervious upright side walls extending from a lower end submerged in the liquid to an upper end, the side walls of the container being spaced inwardly from the upright side walls of the enclosure;
a porous bed surrounded by the gas impervious side walls of the upright container and extending vertically upward within the container from a location spaced above the lower end of the gas impervious upright side walls of the container, at least half of the vertical height of the porous bed being submerged in the liquid;
inlet duct means for directing a stream of pressurized gas and parti-culate matter to a submerged location vertically beneath the porous bed, said inlet duct means comprising an upright tube of gas impervious material extending through the porous bed and terminating at an open bottom end positioned at an elevation between that of the bottom of the porous bed and that of the lower end of the gas impervious container side walls;
the top end of the porous bed being open to liquid flow effected by differential apparent density between liquid within and without the upright container to thereby permit a portion of the liquid entrained within the stream of gas to be returned by gravity from within the container to the liquid remaining within the interior liquid tank and to thereby permit the self-cleaning of the porous bed; and outlet duct means open through the enclosure at an elevation above the liquid surface elevation within it for discharging the stream of gas following its passage through the porous bed.
7. A gas scrubbing apparatus as set out in claim 6 wherein the gas impervious side walls of the container are vertical and centered about a vertical container axis.
8. A gas scrubbing apparatus as set out in claim 6 wherein the gas impervious side walls of the container are vertical and centered about a vertical container axis;
the upright tube of said gas delivery conduit means being coaxially centered within the porous bed along said vertical container axis.
the upright tube of said gas delivery conduit means being coaxially centered within the porous bed along said vertical container axis.
9. A gas scrubbing apparatus as set out in claim 6 further comprising:
fibrous filter means upwardly adjacent to the top end of the porous bed for receiving the gas and entrained liquid as it leaves the porous bed and prior to discharge of the gas at said outlet duct means.
fibrous filter means upwardly adjacent to the top end of the porous bed for receiving the gas and entrained liquid as it leaves the porous bed and prior to discharge of the gas at said outlet duct means.
10. A gas scrubbing apparatus for removing particulate matter from a stream of pressurized gas comprising:
a liquid-tight enclosure;
a quantitiy of liquid within the enclosure partially filling its interior to a liquid surface elevation;
an open ended container positioned within the enclosure and having gas impervious upright side walls extending upward from a lower end submerged in the liquid;
a porous bed adjacent the gas impervious side walls of the upright con-tainer and extending vertically upward adjacent the container from a bottom end openly submerged in the liquid and spaced above the lower end of the gas impervious upright side walls of the container to a top end;
inlet duct means extending into the enclosure and including discharge opening at a submerged location in the liquid positioned beneath the porous bed for directing a stream of pressurized gas and particulate matter to the bottom of the porous bed;
the top end of the porous bed being open to liquid flow effected by differential apparent density between liquid within and without the porous bed to thereby permit liquid entrained within the stream of gas to be returned by gravity to the liquid remaining within the enclosure and to there permit the self-cleaning of the porous bed; and outlet duct means open through the enclosure at an elevation above the liquid surface elevation within it for discharging the stream of gas following its passage through the porous bed.
a liquid-tight enclosure;
a quantitiy of liquid within the enclosure partially filling its interior to a liquid surface elevation;
an open ended container positioned within the enclosure and having gas impervious upright side walls extending upward from a lower end submerged in the liquid;
a porous bed adjacent the gas impervious side walls of the upright con-tainer and extending vertically upward adjacent the container from a bottom end openly submerged in the liquid and spaced above the lower end of the gas impervious upright side walls of the container to a top end;
inlet duct means extending into the enclosure and including discharge opening at a submerged location in the liquid positioned beneath the porous bed for directing a stream of pressurized gas and particulate matter to the bottom of the porous bed;
the top end of the porous bed being open to liquid flow effected by differential apparent density between liquid within and without the porous bed to thereby permit liquid entrained within the stream of gas to be returned by gravity to the liquid remaining within the enclosure and to there permit the self-cleaning of the porous bed; and outlet duct means open through the enclosure at an elevation above the liquid surface elevation within it for discharging the stream of gas following its passage through the porous bed.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US14595480A | 1980-05-02 | 1980-05-02 | |
| US145,954 | 1980-05-02 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1171351A true CA1171351A (en) | 1984-07-24 |
Family
ID=22515296
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000376379A Expired CA1171351A (en) | 1980-05-02 | 1981-04-28 | Passive self-cleaning aerosol scrubber |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS573098A (en) |
| CA (1) | CA1171351A (en) |
| DE (1) | DE3117357A1 (en) |
| GB (1) | GB2074893B (en) |
| SE (1) | SE448682B (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2003025544A1 (en) * | 2001-09-14 | 2003-03-27 | Teknologisk Institut | Aggregate for segregation of substances from gasses |
| US9502144B2 (en) * | 2012-07-06 | 2016-11-22 | Westinghouse Electric Company Llc | Filter for a nuclear reactor containment ventilation system |
| CN106139775A (en) * | 2016-07-18 | 2016-11-23 | 长江水利委员会长江科学院 | A kind of in a liquid by dispersed for the gas device and method for microbubble |
| CN111744334A (en) * | 2020-07-31 | 2020-10-09 | 武汉第二船舶设计研究所(中国船舶重工集团公司第七一九研究所) | Radioactive waste gas discharge system suitable for ocean nuclear power platform |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US328033A (en) * | 1885-10-13 | hitchcock | ||
| GB187999A (en) * | 1921-08-12 | 1922-11-09 | James William Parker | Improvements in gas scrubbers |
| US1838511A (en) * | 1927-05-11 | 1931-12-29 | Walter C Wilson | Device for cleaning air |
| US4083703A (en) * | 1973-07-30 | 1978-04-11 | Becker-Udwin, Inc. | Processing of gas streams |
| JPS5169270A (en) * | 1974-12-11 | 1976-06-15 | Masao Matsushita | SHUJINKI |
-
1981
- 1981-04-27 GB GB8112963A patent/GB2074893B/en not_active Expired
- 1981-04-28 CA CA000376379A patent/CA1171351A/en not_active Expired
- 1981-04-29 SE SE8102723A patent/SE448682B/en not_active IP Right Cessation
- 1981-05-02 DE DE19813117357 patent/DE3117357A1/en not_active Ceased
- 1981-05-02 JP JP6756581A patent/JPS573098A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| GB2074893B (en) | 1984-01-11 |
| SE448682B (en) | 1987-03-16 |
| SE8102723L (en) | 1981-11-03 |
| DE3117357A1 (en) | 1982-05-27 |
| GB2074893A (en) | 1981-11-11 |
| JPH0218128B2 (en) | 1990-04-24 |
| JPS573098A (en) | 1982-01-08 |
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