CA1158993A - Particle scrubber and related method - Google Patents
Particle scrubber and related methodInfo
- Publication number
- CA1158993A CA1158993A CA000368869A CA368869A CA1158993A CA 1158993 A CA1158993 A CA 1158993A CA 000368869 A CA000368869 A CA 000368869A CA 368869 A CA368869 A CA 368869A CA 1158993 A CA1158993 A CA 1158993A
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Abstract
ABSTRACT OF THE DISCLOSURE
A scrubber device for removing finely divided contaminants from a gas stream is disclosed. The device comprises first and second conduits each of which has an inlet and an outlet with nozzle means and flow guide means disposed adjacent the end of the each outlet. The nozzles are con-figured such that the flow path of the discharge of the first conduit intersects the flow path of the discharge of the second conduit. The flow guide means are configured so as to regulate the flow path of the gas stream through each conduit such that a collision zone is created thereinbetween. Further, the flow guides act so as to improve the collection efficiency of the scrubber. In this manner, contaminants in each respective stream are caused to be removed by inertial impaction. By the use of the scrubber device of the present invention, even finely divided contaminants in the order of 0.1 microns diameter to 3 microns diameter can be removed.
A scrubber device for removing finely divided contaminants from a gas stream is disclosed. The device comprises first and second conduits each of which has an inlet and an outlet with nozzle means and flow guide means disposed adjacent the end of the each outlet. The nozzles are con-figured such that the flow path of the discharge of the first conduit intersects the flow path of the discharge of the second conduit. The flow guide means are configured so as to regulate the flow path of the gas stream through each conduit such that a collision zone is created thereinbetween. Further, the flow guides act so as to improve the collection efficiency of the scrubber. In this manner, contaminants in each respective stream are caused to be removed by inertial impaction. By the use of the scrubber device of the present invention, even finely divided contaminants in the order of 0.1 microns diameter to 3 microns diameter can be removed.
Description
BACKGROUND OF THE INVENTION
The present invention relates to particle scrubbers, and more specifically, to a scrubber device adapted to remove finely divided contaminants ~rom a gas stream.
Concern over the environment has been recognized as being one of the most important problems facing todays' society.
In the past, many industries operated in such.a manner so as to ~, .
', . ' ~`~ 3 r,~
,, `
, ' 1 ~re1easQ to the atmosphere huqe quantities of contaminants,
The present invention relates to particle scrubbers, and more specifically, to a scrubber device adapted to remove finely divided contaminants ~rom a gas stream.
Concern over the environment has been recognized as being one of the most important problems facing todays' society.
In the past, many industries operated in such.a manner so as to ~, .
', . ' ~`~ 3 r,~
,, `
, ' 1 ~re1easQ to the atmosphere huqe quantities of contaminants,
2 ¦such as, for example, gas conta~inants and other small particulate ~aterials, Many cities suffered the blight of having their ¦atmosphere adversely affected by such contaminants. Not only 5 ¦is this unsightly, but such contaminants are believed to be 6 ¦related to certa.in health problems. Most industries have ¦recognized the responsibility to deal with the problem ¦of pollution and have devised various means to control their 9 ¦effluent so as to remove many of the pollutant therefromO In 10 ¦fact, an entire area of technology has evolved in connection 11 ¦with pollution control apparatus and related methods. While the 12 prior art teaches the various techniques to deal with the various 13 types of air and water pollution, it has been found that the 14 smaller the particle in the fluid stream, the more difficult the 15 removal. Thus, while there are a number of prior art devices, 16 especially in connection wlth removing particulate matter from 17 air, such devices have not proved to be as effective when the 18 particulate matter is extremely small. Even with respect to 9 those few devices which can remove very small particulate matter, 20 such devices suffer the shortcomings of being expensive and/or 21 complex. In addition, such devices usually have high power 22 requirements and tend to wear out quickIy because of the abra-23 sion and erosion caused by the action of the high velocity gas, 24 liquid and particle streams.
2.
"33 1 ~ As indicated hereinabove, a number o~ devices referred 2 ¦to as "scrubbers" are available for removing particulate matter.
2.
"33 1 ~ As indicated hereinabove, a number o~ devices referred 2 ¦to as "scrubbers" are available for removing particulate matter.
3 ¦However, before selecting a specific scrubber, a number of con-
4 ¦siderations should be taken into account. For example, the basic
5 ¦mechanism for particle collection from a gas stream should be 1 6 Iconsidered. These mechanisms include: (1) gravitational sedimen-¦tation (this mechanism is usually of little importance for any ---¦particles small enough to re~uire consideration of a scrubber);
9~ (2) centrifugal deposition (particles are "spun out" of a gas 10 ¦stream by a centrifugal force induced by a change in gas flow 11 ¦direction. These mechanisms have been found to be not very 12 leffective on particles smaller than about 5.0 microns in 13 ¦diameter); and (3) inertial impaction and interception (when a 4 ~
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; 22 2~
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~' 1 gas stream flows around a small object, the 'inertia of the particle 2 causes them to continue to move toward the object where some of 3 them are collected. Inertial impaction customarily describes the effect of small-scale changes in flow direction).
Because inertial impaction is effective on particles of extremely small diameters, i.e., 0.1 micron, it has been one 7 of the lmportant collection mechanisms for particle scrubbers.
8 Since this mechanism hinges on the inertia of the particl~s, both g the size and density of the particles are important consideration in determining the ease with which they may be collected. Thus, 11 another consideration in determining the specific type of scrubber 12 to be used i~ the particle diameter. It is been found that the ~ 13 aerodynamic diameter is a more accurate term defining the propertie ; 14 of a particle than the average diameter, and is defined as follows:
16 dpa = dp(PpC') 1/2 18 Where 19 dpa = particle aerodynamic diameter, ~mA;
20 ¦ dp = particle physical diameter, ~m; and 21 C' = Cunninghams correction factor, dimensioniess. ~
22 Other mechanisms which may be considered include Brownian 23 diffucion, thermophoresis, diffusiophoresis, electrostatic precipi-~ 24 tation and particle growth.
; 25 A brief description of some of the various prior art 2 scrubbers will now be presented.
27 One of the most well known types of prior art scrubbers 28 is a scrubber referred to as a "plate scrubber." A plate scrubber ; 29 consists of a vertical tower with one or more plates mounted 4.
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¦transversely inside. Gas comes in at the bottom o~ the tower 2 ¦and must pass through perforations, valves, slots, or other 3 ¦openings in each plate before leaving through the top. Usually, ¦liquid is introduced through the top plate and flows successively ¦across ea~h plate as it moves downward to the liquid exit at the ¦bottom. The gas passing through the opening in each plate mixes 7 ¦with the liquid flowing over it. Gas-liquid contacting causes 8 ¦the mass transfer or particle removal or which the scrubber was ; ¦designed. With respect to plate scrubbers, the chief mechanism 10 ¦of particle collection is inertial impaction from the gas inping-11 ¦ing on the liquid or on the solid members. Particle collection 12 ¦may be aided by atomization of the liquid flowing past openings 13 in the perforated plates. It is presently believed that collection 14 ~efficiencies increase as the perforation diameter decreases which 15 ¦enable a cut diameter of 1.0 ~mA for 1/8" diameter holes in a 16 ¦sieve plate. Thus, it can be seen, that while the plate scrubber 17 is somewhat effective, it is limited in terms of the size of ~8 particles that it can remove.
19 Yet another type of device is referred to as a "preformed-spray scrubber." A preformed spray scrubber collects 21 particles or gases on liquid droplets that have been atomized 22 by spray nozzles. The properties of the droplets are determined 23 by the configuration of the nozzlesl the liquid being atomized 24 and the pressure to the nozzles~ Sprays leaving the nozzles are directed into a chamber that has been shaped so as to conduct the 26 gas through the atomized droplets. Horizontal and vertical gas 27 flow paths have been used, as well as spray-entry flowiny concur-28 rent, countercurrent or crossflow to the gas. ~f the tower is 29 vertica1, the relative velocities between the droplets and the gas ; 30 is ul~imately the terminal 6ettling velocity of the droplets.
5.
` 11 ~ . , I
~ 3 1 An ejector venturi is another type of preformed spray 2 scrubbing device in which a high-pressure spray is used both to 3 collect particles and to move the gas. High relative velocity 4 between the droplets and the gas aid in particle separation.
Preformed sprays have also been used in venturi scrubbers in which
9~ (2) centrifugal deposition (particles are "spun out" of a gas 10 ¦stream by a centrifugal force induced by a change in gas flow 11 ¦direction. These mechanisms have been found to be not very 12 leffective on particles smaller than about 5.0 microns in 13 ¦diameter); and (3) inertial impaction and interception (when a 4 ~
1~ l lq I
18 l ~19~ ~
; 22 2~
2a ~o 3.
~' 1 gas stream flows around a small object, the 'inertia of the particle 2 causes them to continue to move toward the object where some of 3 them are collected. Inertial impaction customarily describes the effect of small-scale changes in flow direction).
Because inertial impaction is effective on particles of extremely small diameters, i.e., 0.1 micron, it has been one 7 of the lmportant collection mechanisms for particle scrubbers.
8 Since this mechanism hinges on the inertia of the particl~s, both g the size and density of the particles are important consideration in determining the ease with which they may be collected. Thus, 11 another consideration in determining the specific type of scrubber 12 to be used i~ the particle diameter. It is been found that the ~ 13 aerodynamic diameter is a more accurate term defining the propertie ; 14 of a particle than the average diameter, and is defined as follows:
16 dpa = dp(PpC') 1/2 18 Where 19 dpa = particle aerodynamic diameter, ~mA;
20 ¦ dp = particle physical diameter, ~m; and 21 C' = Cunninghams correction factor, dimensioniess. ~
22 Other mechanisms which may be considered include Brownian 23 diffucion, thermophoresis, diffusiophoresis, electrostatic precipi-~ 24 tation and particle growth.
; 25 A brief description of some of the various prior art 2 scrubbers will now be presented.
27 One of the most well known types of prior art scrubbers 28 is a scrubber referred to as a "plate scrubber." A plate scrubber ; 29 consists of a vertical tower with one or more plates mounted 4.
!l ~ 9~ ~
i , .
¦transversely inside. Gas comes in at the bottom o~ the tower 2 ¦and must pass through perforations, valves, slots, or other 3 ¦openings in each plate before leaving through the top. Usually, ¦liquid is introduced through the top plate and flows successively ¦across ea~h plate as it moves downward to the liquid exit at the ¦bottom. The gas passing through the opening in each plate mixes 7 ¦with the liquid flowing over it. Gas-liquid contacting causes 8 ¦the mass transfer or particle removal or which the scrubber was ; ¦designed. With respect to plate scrubbers, the chief mechanism 10 ¦of particle collection is inertial impaction from the gas inping-11 ¦ing on the liquid or on the solid members. Particle collection 12 ¦may be aided by atomization of the liquid flowing past openings 13 in the perforated plates. It is presently believed that collection 14 ~efficiencies increase as the perforation diameter decreases which 15 ¦enable a cut diameter of 1.0 ~mA for 1/8" diameter holes in a 16 ¦sieve plate. Thus, it can be seen, that while the plate scrubber 17 is somewhat effective, it is limited in terms of the size of ~8 particles that it can remove.
19 Yet another type of device is referred to as a "preformed-spray scrubber." A preformed spray scrubber collects 21 particles or gases on liquid droplets that have been atomized 22 by spray nozzles. The properties of the droplets are determined 23 by the configuration of the nozzlesl the liquid being atomized 24 and the pressure to the nozzles~ Sprays leaving the nozzles are directed into a chamber that has been shaped so as to conduct the 26 gas through the atomized droplets. Horizontal and vertical gas 27 flow paths have been used, as well as spray-entry flowiny concur-28 rent, countercurrent or crossflow to the gas. ~f the tower is 29 vertica1, the relative velocities between the droplets and the gas ; 30 is ul~imately the terminal 6ettling velocity of the droplets.
5.
` 11 ~ . , I
~ 3 1 An ejector venturi is another type of preformed spray 2 scrubbing device in which a high-pressure spray is used both to 3 collect particles and to move the gas. High relative velocity 4 between the droplets and the gas aid in particle separation.
Preformed sprays have also been used in venturi scrubbers in which
6 a fan is used to overcome a high gas-phase pressure drop.
7 Particle collection in these preformed-spray devices
8 results fro~ inertial impaction on the droplets. ~fficiency is
9 believed to be a complex function of droplet size, ~as velocity, liquid-gas ratio and droplet trajectory. There is often an opti-11 mum droplet diameter which varies with fluid flow parameters. ~or 12 droplets falling at their terminal settling velocity, the optimum 13 ~roplet diameter for fine particle collection is believed to be 14 around 100 to 500 ~m; for droplets moving at high velocity within a few feet of the spray nozzle, the optimum is smaller.
~6 Yet another type of scrubber is one referred to as a 17 "gas-atomized" spray scrubber which uses a moviny gas stream to 18 first atomize liquid into droplets, and then accelerates the drop-19 lets. Typical of this type of device is a venturi scrubber. High gas velocities of 100-500 ft~/sec. raise the relative velocity 21 between the gas and the liquid droplets, and promote particle 22 collection. Many gas-atomized spray scrubbers incorporate the 23 converging and diverging sections typical of the venturi scrubber, 24 although increase in ~enefits is not necessarily achieved. Li~uid is usually introduced in various places and in different ways in 26 such devices without much effect on collection efficiencies.
27 Particle collection results from internal impaction due to gas 28 flow around the droplets~ Velocity is high and droplet residence 2 tlme short such that diffusional collection and deposition by 6.
li51~ J ~ I
1 other ~orces, such as thermophore~ic forces~ are not very effec-2 tive. It is presently believed that cut diameters down to 3 approximately 0.2 ~ma can be achieved with various venturi scrub-bers.
Other types of scrubbers include centrifugal scrubbers, 6 baffle an~ secondary-flow type scrubbers, impingement and 7 entrainment scrubbers, and moving bed scrubbers.
8 Yet other examples of prior art devices are disclosed in 9 U. S. Patent No. 3,826,D63 and 3,972,6~6. In the '063 patent, an electrostatic agglomeration device is disclosed which is used for 11 air filtering and conditioning syste~. The device comprises an 12 air duct having a pair of channels disposed either within the ~uct 13 or adjacent thereto and opening into the duct at bo~h ends. A
14 plurality of electrically conductive rods are disposed in the channel and are charged electrically positive in one channel and 16 negative in the other channel. As particulate matter flows into 17 the channels, it is ionized by the charges of the electrical 18 rods and agglomerized tc, form larger particle masses which are 19 more easily filterable from the air flowlng through the system.
As can be easily recognized, a rather complex and expensive device 21 is disclosed which, while perhaps useful in certain limited appli-22 cations, has distinct limitations in industrial settings.
23 In the '6~6 patent, the device disclosed therein 24 relates to an apparatus for removing fly ash from a gas s~ream and comprises three concentric vertical stacks or chimneys wherein 26 the outer stack is higher than the inner stack. As exhaust flue 27 gases are directed through the central stack, upon exiting they 28 expand laterally such that the fly ash l5 captured by the 29 intermediate stack and drops down in the annular space formed 3 thereinbetween. Again, such device suffers from being rather ~ 3~
1 complex and therefore limited in its commercial applicability.
2 Other similar devices and apparatus are disclosed in U. S. Patent 3 Nos. 3,332,214; 3,334,470; 3,435,593; 3,549,336; 3,463,098; and 4 4,082,522.
As indicated hereinabove, scrubber performance can be 6 defined in terms of the cut diameter (dp50). Because particle 7 collection efficiency changes with particle si2e for a given 8 operating condition in a scrubber, one needs the relationship between efficiency and particle size. Nost scrubbers that collect particles by internal impaction perform in accordance 11 with the following relationship:
12 ~ Pt = exp - (A dpa~
15 where Pt = particle penetration, fraction;
16 A - empirical constant, dimensionless;
lq B = empirical constant, dimensionless;
18 Ci = inlet particle concentration, g/cm3; and 19 Co = outlet particle concentration, g/cm3 Packed bed and plate type scrubbers performance are 21 described by a value of B = 2.0, whereas for centrifugal scrubbers 22 of the cyclone type, B = 0~7. Gas atomized scrubbers have a value 23 of B = 2.0 over a large portion of the usual operating rangeO
24 Therefore, by using the value of ~ = 2.0 as representative of most scrubbers operating in the inertial impac~ion regime, and plotting 26 the collection efficiency against the ratio of aerodynamic particle 27 diameter to performance cut diameter, a graphical representation 28 may be ~btained. For many prior art devices, performance, espe-29 cially for fine particles, was very low. Thus, there exists a long 8.
~ g~33 1 felt need for a device which while able to ~emove finely divided 2 particulate material, is also efficient and d~es n~t require a 3 huge power input.
4 The present invention represents an advancement in the art of air pollution control, and contains none of the afore-mentioned shortcomings associated with the prior art devices.
7 The present invention provides a relatively simple and straight-8 foward solution to the problem of removal of small particulate 9 matter which otherwise would escape into the atmosphere.
, 11 BRIEF SUMMARY OF THE II~VENTION
12 The present invention is directed to a apparatus and 13 method for cleaning a stream of gas. It is primarily directed 14 to the removal of small particulate matter from the gas stream by means of wet scrubbing. However, the device of the present 16 invention can also be used dry, ~hat is, without the use of 17 additional water or other cleaning liquids. It can be used to 18 agglomerate liquid drops which may be present in the gas stream, 19 and also for mass transfer, that is, the removal of gaseous species from the gas stream by means of absorption or adsorption.
21 The device, in a broad description, operates by reason 22 of collisions of gas jets. The gas may contain either particulate 23 or gaseous material which are both referred to herein as contaminants. Such term would also emcompass a combination of particulate and gaseous contaminantsO
26 The major mechanism of particle collection of the device 27 of the present invention is inertial impaction. As discussed here-28 inabove, inertial impaction refers to the collision of one particle 9.
~ ~ .~ ~
1 ¦with another particle or with a surfaceO W~ile the device is 21 configured such that the gas stream may flow around the collector 31 particle or collection surface, the particle being collected has ~¦ sufficient inertia that it is unable to follow the gas stream ~¦ sufficiently to prevent its collision. The use of inertial impac-61 tion in the present invention represents an important collection 71 mechanism for paticles which are about 0.1 micron in diameter and 81 iarger. It is therefore of major importance in the size range 9 ¦which has been designated by the Environmental Protection Agency
~6 Yet another type of scrubber is one referred to as a 17 "gas-atomized" spray scrubber which uses a moviny gas stream to 18 first atomize liquid into droplets, and then accelerates the drop-19 lets. Typical of this type of device is a venturi scrubber. High gas velocities of 100-500 ft~/sec. raise the relative velocity 21 between the gas and the liquid droplets, and promote particle 22 collection. Many gas-atomized spray scrubbers incorporate the 23 converging and diverging sections typical of the venturi scrubber, 24 although increase in ~enefits is not necessarily achieved. Li~uid is usually introduced in various places and in different ways in 26 such devices without much effect on collection efficiencies.
27 Particle collection results from internal impaction due to gas 28 flow around the droplets~ Velocity is high and droplet residence 2 tlme short such that diffusional collection and deposition by 6.
li51~ J ~ I
1 other ~orces, such as thermophore~ic forces~ are not very effec-2 tive. It is presently believed that cut diameters down to 3 approximately 0.2 ~ma can be achieved with various venturi scrub-bers.
Other types of scrubbers include centrifugal scrubbers, 6 baffle an~ secondary-flow type scrubbers, impingement and 7 entrainment scrubbers, and moving bed scrubbers.
8 Yet other examples of prior art devices are disclosed in 9 U. S. Patent No. 3,826,D63 and 3,972,6~6. In the '063 patent, an electrostatic agglomeration device is disclosed which is used for 11 air filtering and conditioning syste~. The device comprises an 12 air duct having a pair of channels disposed either within the ~uct 13 or adjacent thereto and opening into the duct at bo~h ends. A
14 plurality of electrically conductive rods are disposed in the channel and are charged electrically positive in one channel and 16 negative in the other channel. As particulate matter flows into 17 the channels, it is ionized by the charges of the electrical 18 rods and agglomerized tc, form larger particle masses which are 19 more easily filterable from the air flowlng through the system.
As can be easily recognized, a rather complex and expensive device 21 is disclosed which, while perhaps useful in certain limited appli-22 cations, has distinct limitations in industrial settings.
23 In the '6~6 patent, the device disclosed therein 24 relates to an apparatus for removing fly ash from a gas s~ream and comprises three concentric vertical stacks or chimneys wherein 26 the outer stack is higher than the inner stack. As exhaust flue 27 gases are directed through the central stack, upon exiting they 28 expand laterally such that the fly ash l5 captured by the 29 intermediate stack and drops down in the annular space formed 3 thereinbetween. Again, such device suffers from being rather ~ 3~
1 complex and therefore limited in its commercial applicability.
2 Other similar devices and apparatus are disclosed in U. S. Patent 3 Nos. 3,332,214; 3,334,470; 3,435,593; 3,549,336; 3,463,098; and 4 4,082,522.
As indicated hereinabove, scrubber performance can be 6 defined in terms of the cut diameter (dp50). Because particle 7 collection efficiency changes with particle si2e for a given 8 operating condition in a scrubber, one needs the relationship between efficiency and particle size. Nost scrubbers that collect particles by internal impaction perform in accordance 11 with the following relationship:
12 ~ Pt = exp - (A dpa~
15 where Pt = particle penetration, fraction;
16 A - empirical constant, dimensionless;
lq B = empirical constant, dimensionless;
18 Ci = inlet particle concentration, g/cm3; and 19 Co = outlet particle concentration, g/cm3 Packed bed and plate type scrubbers performance are 21 described by a value of B = 2.0, whereas for centrifugal scrubbers 22 of the cyclone type, B = 0~7. Gas atomized scrubbers have a value 23 of B = 2.0 over a large portion of the usual operating rangeO
24 Therefore, by using the value of ~ = 2.0 as representative of most scrubbers operating in the inertial impac~ion regime, and plotting 26 the collection efficiency against the ratio of aerodynamic particle 27 diameter to performance cut diameter, a graphical representation 28 may be ~btained. For many prior art devices, performance, espe-29 cially for fine particles, was very low. Thus, there exists a long 8.
~ g~33 1 felt need for a device which while able to ~emove finely divided 2 particulate material, is also efficient and d~es n~t require a 3 huge power input.
4 The present invention represents an advancement in the art of air pollution control, and contains none of the afore-mentioned shortcomings associated with the prior art devices.
7 The present invention provides a relatively simple and straight-8 foward solution to the problem of removal of small particulate 9 matter which otherwise would escape into the atmosphere.
, 11 BRIEF SUMMARY OF THE II~VENTION
12 The present invention is directed to a apparatus and 13 method for cleaning a stream of gas. It is primarily directed 14 to the removal of small particulate matter from the gas stream by means of wet scrubbing. However, the device of the present 16 invention can also be used dry, ~hat is, without the use of 17 additional water or other cleaning liquids. It can be used to 18 agglomerate liquid drops which may be present in the gas stream, 19 and also for mass transfer, that is, the removal of gaseous species from the gas stream by means of absorption or adsorption.
21 The device, in a broad description, operates by reason 22 of collisions of gas jets. The gas may contain either particulate 23 or gaseous material which are both referred to herein as contaminants. Such term would also emcompass a combination of particulate and gaseous contaminantsO
26 The major mechanism of particle collection of the device 27 of the present invention is inertial impaction. As discussed here-28 inabove, inertial impaction refers to the collision of one particle 9.
~ ~ .~ ~
1 ¦with another particle or with a surfaceO W~ile the device is 21 configured such that the gas stream may flow around the collector 31 particle or collection surface, the particle being collected has ~¦ sufficient inertia that it is unable to follow the gas stream ~¦ sufficiently to prevent its collision. The use of inertial impac-61 tion in the present invention represents an important collection 71 mechanism for paticles which are about 0.1 micron in diameter and 81 iarger. It is therefore of major importance in the size range 9 ¦which has been designated by the Environmental Protection Agency
10 ¦as the "fine particle" range.
11 ¦ When liquid is present or introduced into the gas
12 ¦stream formed in the device of the present invention, it is
13 ¦usually atomized into drops by the action of the high velocity
14 ¦gas stream. These drops also serve to collect particulate lS ¦matter by interial impaction and the other mechanisms discussed 16 ¦hereinabove.
17 I During the time when the individual gas jets are flowing 18 ¦prior to collision, particles will be collected by the entrained 19 ¦drops. Thus, the particle collection process in the individual 20 Igas jet will be the same as it would be in the throat of a venturi 21 ¦scubber or similar device. When collision occurs between 22 ¦intersecting streams there will be further atomization of the 23 liquid into extremely fine drops and further collection of 24 particles and mass transfer upon these drops. Thus, the 25 ~ollision of the gas streams with sufficient velocity to cause 26 removal of the contaminants by inertial impaction represents 27 another distinct improvement over the prior art.
10.
I
1 The advantage o colliding gas jet streams is based 2 on the following. In the conventional types of gas atomized or 3 preatomized scrubbers, the highest relative velocity between the contaminant particles and collector particles (such as the drops) 5 is the velocity of the gas jet relative to the liquid at its 6 point of introduction. The drops in a well designed venturi 7 scrubber will generally obtain a velocity which is 80 to 90 8 percent of the gas velocity. With the device of the pre~ent 9 invention, on the other hand, the relative velocity between the 0 contaminant particle and the collector particle can aL~proach twice the gas jet velocities when the respective orifices face each 12 other in axial aliynment, and the gas in each stream is traveling 13 at the same velocity when they collide.
14 Because of the high relative velocity between the collector particles and the gas stream containing the contaminants 16 upon collison, the efficiency of intertial impaction will be higher 17 in the device of the present invention than would be possible 18 if the relative velocity were limited by the velocity of a single 9 gas jet. As a further consequence of the increased collision efficiency, the gas phase pressure drop required to obtain a given 21 ~eyree o scrub~ing wlll be less in the device of the present 22 invention than in conventional gas atomized or pre-atomized type 23 scrubbers.
2*
11 .
1 The present invention represents an additional and significant improvement in this type oE collision scrubber.
While not to be bound by any theory, it is believed that the "Elow guides" described in detail herein, permit greater Eocusing of the collision zone thereby leading to improved collection efficiencies over the clevice described in the parent application. In the device of the present invention, a housing is configured so as to form an impaction chamber.
Means for directing a gas stream generating source to said chamber provide the chamber with a gas stream containing the undesirable small particulate material to be removed. ~irst and second gas conduits are disposed in the chamber and are joined to the directing means. Each of the conduits has at least one discharge nozzle adjacent one end thereof. The nozzles are arranged on the first and second conduits so as to be in a spaced apart and opposed configuration. In this manner, the flow path of the discharge of the first conduit intersects the flow path of the discharge of the second conduit.
Preferably, each of the conduits are supplied with a source of liquid such that the liquid is caused to intersect the flow path of each gas stream as it flows through the associated c~nduit. Finally, flow guide means are disposed on the discharcJe end of the first and siecond conduits thereby regulating the flow path of the gas streams through each conduit.
~, 3~
1 In the device of the present invention where liquid is introduced into both gas jets of a colliding pair, the following occur:
1. Each jet gives the same scrubbing efficiency that it would if it were a conventional (non-colliding) gas-atomiæed scrubber;
2. In addition to the conventional efficiency, the jet collision causes more particle collection amd mass transfer;
3. The major power input is used to accelerate the liquid in the individual jet to near the gas velocity. Very lit-tle of this power is regained in a conventional gas-atomized scrubber.
Thus, the jet collision scrubber of the present invention utilizes the momentum of the liquid in a more effective manner than the prior art gas-atomized scrubbers to obtain very fine drops and higher collision efficiencies for fine particles; and 4. The extremely fine drops formed by the jet collision provide more surface area for mass transfer than in conventional scrubbers.
5. The flow guides help contain the collisions between .
the two streams thereby insuring the efficiency of removal of the contaminants.
The novel features which are to belleved to be charac-teristic of this invention, both as to its organization and method of operation, together with further objectives and advantages thereof will be better understood from the following ~` description considered in connection with accompanying drawings in which a presently preferred embodiment of the invention is illustrated by way of example. It is to be expressly under-stood, however, that the drawings are ~or the purpose of illustration and description only and are not intended as a definition of the limits of the invention.
.
1 BRIEF DESCRIPTIO~ OF T~IE DRA:~INGS
.~
2 FIGURFI 1 is a perspective view showing the scrubber device 3 o the present invention;
FIGURE 2 is a cutaway view showing the internal aspects 5 of the scrubber device of the present invention;
6 FIG~RE 3 is yet another view of the scrubber device 7 of the present invention;
8 FIGURE 4 is a graph showinq scrubber performance; and 9 FIGURE 5 is a graph showing penetration efficiency.
i 12 Referring first to FIGURE 1, one can see the scrubber 13 device 10 of the present invention. The device 10 has a first 14 conduit 12 and a second conduit 14 extending outwardly from a ; 15 central feed line 16. The first and second conduits 12 and 14 16 feed into a housing forming impaction chamber 18. As is more fully 17 discussed hereinbelow, the first conduit 12 and the second conduit 18 14 are formed such that the discharge from each of these respective 19 conduits intersects and forms an area of impaction generally ; desiginated by numeral 20.
21 Supplying feed line 16 is a gas/contaminant source.
22 Such source may come from a boiler, smokestack, and the like, 23 and contains finely divided contaminants. Disposed along the lengt 24 of feed line 16 is a sampling device 24. Sampling device 24 is well 25 known in the art and will not be discussed in detail herein.
26 Sampling device 24 is used to determine the amount of contaminants 28 which a carried by the incominq gas/contaminant stream.
32 14.
~ I
\
1 ~n en-trainment separator 26 is disposed in chamber 18 adjacent one side thereof. Such entrainment separators generally have a plurality of openings 26a passing therethrough which permits the ef1uent of the respective conduits 12 and 1 to travel out oE the chamber 18. In this manner, further con-taminants are re~oved from the gas stream by the entrainment separator 26. Of course, it is to be understood that a variety of entrainment separators are within the scope of the presen-t invention. Disposed on the other side of the entrainment separator 26 is an air duct 28 which channels the gas from chamber 29 to a desired point of exit. A second sampler 30 is disposed along air duct 28 in such a manner so as to be able to determine the percentage of con-taminants in the discharge from the device 10. Comparing the amount of contaminants entering the device 10 via device 2~ as well as the amount of contaminants leaving chamber 18 by device 30 enables one to determine the efficiency.
The chamber 18 is also equipped with a drain port 32 adjacent the bottom thereof such that if the device 10 is used by introducing water or another cleaning liquid into the inlet gas streams by means of water conduits 36,~such liquid is per-mitted to drain out of the device 10 via drain port 32.
Referring now tQ EIGURES 2 and 3, one can see in greater detail the various aspects of the chamber 18. -More specifically, one can see that the first and second conduits ~5 ~
~ ~ -115t~3 1 12 and 14, ha~e a substantially straight discharge 40 disposed 2 adjacent the end thereof of means of flange members 35.
3 Also ad~acent each end of conduits 12 and 14 is a generally circular flow guide member 22. Each Elow guide member 22 is arranged and configured such tha-t the discharge from the 6 first and second conduit are caused to collide in a collision 7 zone formed between members 22. In the preferred embodiment, 8 guides 22 are parallel and spaced apart. It is understood, g that they can be angled so as to provide for gradually increasing area for flow. To further increase the collision between the dis-11 charges of each respective conduit, nozzles 40 are arranged and 1~ configured such that discharge from each of the nozzles intersects 13 or impacts upon one another in a generally in line manner.
14 It has also been found that by providing the gas jet stream with small particles of water, or of another cleaning 16 liquid, further aids in contaminant removal. ~ccordingly, along 17 the length of each of the nozzles 40, water tube 36 are disposed.
18 Each water tube 36 has a cap 44 adjacent the outlet end thereof.
19 Outlets 46 formed on cap 44 permit the introduction of water into ~. :
the gas stream as indicated by the arrows shown in FIGURE 3. It 21 should be understood, however, that -the wide variety of water out-22 lets are within the scope of the present invention although the 23 preferred outlet is such that the flow path of water is substan-24 tially perpendicular to the flow path of the gas stream in the region of the highest gas velocity. This is thought to cause a 26 better interaction between the contaminants in the gas stream and 27 the water particles formed as the water exits out of tube 36.
28 The operation of the device 10 of the present invention 29 ¦ will n e described.
I' ~ ~_5~C~
~ eferrinq to ~IGURES 1, 2 and 3, on~ can see that the 2 generally rectangular chamber 18 has first conduit 12 and 3 second conduit 14 extending therein such that the respective dis-4 charge nozzles 40 and flow guide members 22 face one another.
5 A gas stream containing the contaminants is caused to flow through 6 feed line 16. Such gas stream comes from a gas/contaminant source which could come from any industrial operation where fine particulate contaminants are a problem.
9 In the preferred embodiment, feed line 16 forms the means 10 by which the gas from the gas stream generatinq source is directed 11 into each of the conduits 12 and 14.
12 After the gas stream has been divided into two generally 13 equal streams, it is caused to flow through the discharge nozzles 14 40 as illustrated in FIGURES 2 and 3. Discharge nozzles 40 are
17 I During the time when the individual gas jets are flowing 18 ¦prior to collision, particles will be collected by the entrained 19 ¦drops. Thus, the particle collection process in the individual 20 Igas jet will be the same as it would be in the throat of a venturi 21 ¦scubber or similar device. When collision occurs between 22 ¦intersecting streams there will be further atomization of the 23 liquid into extremely fine drops and further collection of 24 particles and mass transfer upon these drops. Thus, the 25 ~ollision of the gas streams with sufficient velocity to cause 26 removal of the contaminants by inertial impaction represents 27 another distinct improvement over the prior art.
10.
I
1 The advantage o colliding gas jet streams is based 2 on the following. In the conventional types of gas atomized or 3 preatomized scrubbers, the highest relative velocity between the contaminant particles and collector particles (such as the drops) 5 is the velocity of the gas jet relative to the liquid at its 6 point of introduction. The drops in a well designed venturi 7 scrubber will generally obtain a velocity which is 80 to 90 8 percent of the gas velocity. With the device of the pre~ent 9 invention, on the other hand, the relative velocity between the 0 contaminant particle and the collector particle can aL~proach twice the gas jet velocities when the respective orifices face each 12 other in axial aliynment, and the gas in each stream is traveling 13 at the same velocity when they collide.
14 Because of the high relative velocity between the collector particles and the gas stream containing the contaminants 16 upon collison, the efficiency of intertial impaction will be higher 17 in the device of the present invention than would be possible 18 if the relative velocity were limited by the velocity of a single 9 gas jet. As a further consequence of the increased collision efficiency, the gas phase pressure drop required to obtain a given 21 ~eyree o scrub~ing wlll be less in the device of the present 22 invention than in conventional gas atomized or pre-atomized type 23 scrubbers.
2*
11 .
1 The present invention represents an additional and significant improvement in this type oE collision scrubber.
While not to be bound by any theory, it is believed that the "Elow guides" described in detail herein, permit greater Eocusing of the collision zone thereby leading to improved collection efficiencies over the clevice described in the parent application. In the device of the present invention, a housing is configured so as to form an impaction chamber.
Means for directing a gas stream generating source to said chamber provide the chamber with a gas stream containing the undesirable small particulate material to be removed. ~irst and second gas conduits are disposed in the chamber and are joined to the directing means. Each of the conduits has at least one discharge nozzle adjacent one end thereof. The nozzles are arranged on the first and second conduits so as to be in a spaced apart and opposed configuration. In this manner, the flow path of the discharge of the first conduit intersects the flow path of the discharge of the second conduit.
Preferably, each of the conduits are supplied with a source of liquid such that the liquid is caused to intersect the flow path of each gas stream as it flows through the associated c~nduit. Finally, flow guide means are disposed on the discharcJe end of the first and siecond conduits thereby regulating the flow path of the gas streams through each conduit.
~, 3~
1 In the device of the present invention where liquid is introduced into both gas jets of a colliding pair, the following occur:
1. Each jet gives the same scrubbing efficiency that it would if it were a conventional (non-colliding) gas-atomiæed scrubber;
2. In addition to the conventional efficiency, the jet collision causes more particle collection amd mass transfer;
3. The major power input is used to accelerate the liquid in the individual jet to near the gas velocity. Very lit-tle of this power is regained in a conventional gas-atomized scrubber.
Thus, the jet collision scrubber of the present invention utilizes the momentum of the liquid in a more effective manner than the prior art gas-atomized scrubbers to obtain very fine drops and higher collision efficiencies for fine particles; and 4. The extremely fine drops formed by the jet collision provide more surface area for mass transfer than in conventional scrubbers.
5. The flow guides help contain the collisions between .
the two streams thereby insuring the efficiency of removal of the contaminants.
The novel features which are to belleved to be charac-teristic of this invention, both as to its organization and method of operation, together with further objectives and advantages thereof will be better understood from the following ~` description considered in connection with accompanying drawings in which a presently preferred embodiment of the invention is illustrated by way of example. It is to be expressly under-stood, however, that the drawings are ~or the purpose of illustration and description only and are not intended as a definition of the limits of the invention.
.
1 BRIEF DESCRIPTIO~ OF T~IE DRA:~INGS
.~
2 FIGURFI 1 is a perspective view showing the scrubber device 3 o the present invention;
FIGURE 2 is a cutaway view showing the internal aspects 5 of the scrubber device of the present invention;
6 FIG~RE 3 is yet another view of the scrubber device 7 of the present invention;
8 FIGURE 4 is a graph showinq scrubber performance; and 9 FIGURE 5 is a graph showing penetration efficiency.
i 12 Referring first to FIGURE 1, one can see the scrubber 13 device 10 of the present invention. The device 10 has a first 14 conduit 12 and a second conduit 14 extending outwardly from a ; 15 central feed line 16. The first and second conduits 12 and 14 16 feed into a housing forming impaction chamber 18. As is more fully 17 discussed hereinbelow, the first conduit 12 and the second conduit 18 14 are formed such that the discharge from each of these respective 19 conduits intersects and forms an area of impaction generally ; desiginated by numeral 20.
21 Supplying feed line 16 is a gas/contaminant source.
22 Such source may come from a boiler, smokestack, and the like, 23 and contains finely divided contaminants. Disposed along the lengt 24 of feed line 16 is a sampling device 24. Sampling device 24 is well 25 known in the art and will not be discussed in detail herein.
26 Sampling device 24 is used to determine the amount of contaminants 28 which a carried by the incominq gas/contaminant stream.
32 14.
~ I
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1 ~n en-trainment separator 26 is disposed in chamber 18 adjacent one side thereof. Such entrainment separators generally have a plurality of openings 26a passing therethrough which permits the ef1uent of the respective conduits 12 and 1 to travel out oE the chamber 18. In this manner, further con-taminants are re~oved from the gas stream by the entrainment separator 26. Of course, it is to be understood that a variety of entrainment separators are within the scope of the presen-t invention. Disposed on the other side of the entrainment separator 26 is an air duct 28 which channels the gas from chamber 29 to a desired point of exit. A second sampler 30 is disposed along air duct 28 in such a manner so as to be able to determine the percentage of con-taminants in the discharge from the device 10. Comparing the amount of contaminants entering the device 10 via device 2~ as well as the amount of contaminants leaving chamber 18 by device 30 enables one to determine the efficiency.
The chamber 18 is also equipped with a drain port 32 adjacent the bottom thereof such that if the device 10 is used by introducing water or another cleaning liquid into the inlet gas streams by means of water conduits 36,~such liquid is per-mitted to drain out of the device 10 via drain port 32.
Referring now tQ EIGURES 2 and 3, one can see in greater detail the various aspects of the chamber 18. -More specifically, one can see that the first and second conduits ~5 ~
~ ~ -115t~3 1 12 and 14, ha~e a substantially straight discharge 40 disposed 2 adjacent the end thereof of means of flange members 35.
3 Also ad~acent each end of conduits 12 and 14 is a generally circular flow guide member 22. Each Elow guide member 22 is arranged and configured such tha-t the discharge from the 6 first and second conduit are caused to collide in a collision 7 zone formed between members 22. In the preferred embodiment, 8 guides 22 are parallel and spaced apart. It is understood, g that they can be angled so as to provide for gradually increasing area for flow. To further increase the collision between the dis-11 charges of each respective conduit, nozzles 40 are arranged and 1~ configured such that discharge from each of the nozzles intersects 13 or impacts upon one another in a generally in line manner.
14 It has also been found that by providing the gas jet stream with small particles of water, or of another cleaning 16 liquid, further aids in contaminant removal. ~ccordingly, along 17 the length of each of the nozzles 40, water tube 36 are disposed.
18 Each water tube 36 has a cap 44 adjacent the outlet end thereof.
19 Outlets 46 formed on cap 44 permit the introduction of water into ~. :
the gas stream as indicated by the arrows shown in FIGURE 3. It 21 should be understood, however, that -the wide variety of water out-22 lets are within the scope of the present invention although the 23 preferred outlet is such that the flow path of water is substan-24 tially perpendicular to the flow path of the gas stream in the region of the highest gas velocity. This is thought to cause a 26 better interaction between the contaminants in the gas stream and 27 the water particles formed as the water exits out of tube 36.
28 The operation of the device 10 of the present invention 29 ¦ will n e described.
I' ~ ~_5~C~
~ eferrinq to ~IGURES 1, 2 and 3, on~ can see that the 2 generally rectangular chamber 18 has first conduit 12 and 3 second conduit 14 extending therein such that the respective dis-4 charge nozzles 40 and flow guide members 22 face one another.
5 A gas stream containing the contaminants is caused to flow through 6 feed line 16. Such gas stream comes from a gas/contaminant source which could come from any industrial operation where fine particulate contaminants are a problem.
9 In the preferred embodiment, feed line 16 forms the means 10 by which the gas from the gas stream generatinq source is directed 11 into each of the conduits 12 and 14.
12 After the gas stream has been divided into two generally 13 equal streams, it is caused to flow through the discharge nozzles 14 40 as illustrated in FIGURES 2 and 3. Discharge nozzles 40 are
15 located at each end of conduits 12 and 14. Water, or another
16 scrubbing liquid or suspension, may be introduced through spray
17 outlet nozzles 46. As the gas flows through the discharge nozzles
18 40 at relatively high velocities (i.e., 100 to 500 feet per
19 second) the liquid is atomized, the drops are accelerated by
20 the gas, and particle collection and mass transfer occur. Depend-ing on the time of contact between the gas and liquid, the drops 22 can reach a high percentaqe of the gas velocity (approximately 24 ~ ~80 to 9 ercent).
~7 17.
1 The high velocity gas and the entrained drops are then caused to collide in the chamber 18 in the area impact 20 which is ~ormecl between the ~low guide members 22. When these streams intersect each other, the fine particles are caused to be removed by inertial impaction. The now c:Leaned gas is directed out o~ chamber 18 through the entrainment separator 26 and into the final chamber 29. Any li~uid droplets which collect in the chamber 18 flow out of the device 10 through the drain 32. The now cleaned gas is directed out of the device 10 through outlet duct 28. Here a second sampler 30 is located which also measures the amount of contaminants contained in the outflow so as to be able to calculate the percent of contaminant removal.
As discussed hereinr and as illustrated in FIGURES 1-3 the discharges from each of the nozzles ~0 are caused to impinge upon one another at an angle of approximately 180 (i.e. in a spaced apart and axial aligned configuration~. It is to be understood, however, that other angles of impact are within the scope of the present invention. As will be ~0 appreciated, a variety of other configurations ~or the nozzles 40 are within the scope of the present invention.
E~AMPLES .
- A device as illustrated in FIGURE 1 was constructed with two 3 inch diameter pipes used as the discharge nozzles 40. Two water nozzles were used to introduce water into the respective contaminant-containing gas inlet streams. Mounted adjacent each end of the nozzles 40 are outwardly extending flanges 22 so as to form a 2 inch gap thereinbetween. In the tests, the water was introduced into each stream of gas. The 3 n nozzles were located such tha-t the water spray would strike ,~"
1 the nozzle just inside of the entrance where water was sprayed out at a rate of 2.5 to 10 gallons per thousand cubic feet oE air (gal/MCF).
With respect to the experimental data obtained from the device, reference is made to Tables 1 and 2 set forth hereinbelow. By plotting the cut diameter versus the scrubber pressure drop, one can determine the cut diameter and like information. From such a plot, for a pressure drop of appro~imately 8 inches WC and higher, this type of scrubber 1~ would be ~fficient for removing sub-micron diameter particles.
SCRUBBER TESTS WITH SPRAY ~ATER INJECTION
Run ~ ~P, in. W.C. L/G, gal/MCF dp50'~mA
__ 1 8 7 N.A.
2 " " N.A.
3 " " 0.6 4 " " 0.6 " ~.5 <0.5 - 6 " 10 0.85 7 5 7 1.1 8 " " 1.1 9 " 10 approx. 0.4 ' 10 '" " 1.0 .
11 - 8 " N.A.
12 12.5 7 1.0 13 " " approx. 0.4 14 " 2.5 " 0.45 " 2.5 " 0.~5 T~BLE 2 SCRUBBER TESTS WITH JET WATER INJECTION
Run # ~P, in W.C. L/G, gal/MCF 0.55 2-2 " " 0.55 2-3 " 15.5 0.37 2-4 " " <0.3 2-5 9 7.5 "
~ 19 --1 Referring now to FIGURE 4, the device 10 of the present invention is compared to a prior art device. The present invention is shown in curve ~ and the prior device is shown in curve B. One can see that Eor a 2 inch gap between the flow guide member 22, the scrubber device 10 of the present invention gives substantially better performance in terms of lower particle penetration at the same gas velocity and liquid/gas ratio.
Referring now to FIGURE 5, one can see that the device of the present invention gives the same penetration as a venturi scrubber when operated with less pressure drop (16.2" W.C.3 and liquid/gas ratio, QL/QG, (10 gal/MCF) than the venturi. The venturi had a pressure drop of 19" W.C~ and a liquid/gas ratio of 15 gal/MCF. Thus, for a given pressure drop, better particle collection efficiency can be achieved by the device 10 and less water is required. While not to be bound by any theory, it is believed that such improved results are due, at least in substantial part, by the improved characteristics of the. .
collision zone formed between the flow guide members 22.
In further explanation of the.present invention, one can view the device 10 as belng divided into three basic parts~ the throat section (the distance traveled by the .~ gas jet between the point of liguid introduction~and the point of collision) (2) the "collision zone"; and (3) the "fog zone" (the region between the collision zone and the entrainment . separator).
. - 20 -T1 THE THROAT SECTIO~
_ 2 Particle collection efficiency was found to depend 3 upon the collection efficiency of the individual water droplets 4 and the number of water droplets which the gas stream encountered.
5 Both the efficiency of a drop and the number of drops are at 6 maximum when the water is first introduced and decreases as 7 the drops are accelerated and the relative velocity between 8 the drops and gasses decreases.
9 The collection efficiency of the throat section for a 10 given particle size is believed to depend upon the effective length 11 of the throat section~ Once the drop has reached nearly the qas 12 velocity, there is little benefit in continuing the contact 13 between liquid and gas. The relationship between drop velocity 14 and throat length is illustrated by the data in the following 15 tabulation:
18 _ ~hroat Length, 1~ LT, ~t 0.5 0.75 1.0 1.52.0 _ _ -Velocity ratio 2~ FL 0.76 0.81 0.B5 0.~0.92 22 , _ 26 }
27 ., 1 The ratio of the drop velocity at the end of the throat to the gas velocity in the throat, FL, has been predicted as a :Eunc-tion o~ the throat length, I.T, for 100.0 diamete.r water drops in the gas stream. As can be seen Erom rrable 3, with a throat lencJth o~ one foot, the drops w:ill reach approximately 80~ of the gas velocity and therefore the relative velocity be-tween the drops and the gas will be about 15~ of the gas velocity. If the gas velocity were two hundred feet per second, the relative velocity would decrease to thirty feet per second.
1~ For a given liquid/gas ratio, the drop holdup is propor-tional to the ratio of gas velocity to drop velocity, thus, to the reciprocal of FI. Thus, it can be seen that as the drops are accelerated both the collision efficiency of a drop and the ; drop holdup decrease. Since the scrubber collection efficiency is dependent upon the product of drop holdup and collection efficiency for a single drop, the effectiveness of the scrubber is greatest over the initial part of the throat. ~Based on the above, the length of the throat is chosen to be one to three feet, and preferably, one to two feet. Other throat lengths are within the scope o~ this invention.
COLLISION ZONE
.
When a pa.ir of gas jets and their entrained li~uid drops collide, several phenomena have been found to take place.
Some of the drops will collide with drops moving in the other direction and will shatter into smaller drops. These smaller drops will have a particle collection efficiency during the period when their relative velocity to the gas stream is high.
Because the drops are small, they will be more rapidly accelerated than larger drops. O-ther drops will penetrate into the opposing jet and will transfer their momentum to the gas In the process of being slowed down and moved in a radially out-- 22 ~
ward direction, the drops will collect particles from the gas.
The use o~ the flow guide members 22 which are preferably discs but may also have other configurations provide a means for pressure recovery from the high velocity gas and li.quid stream. B~ the use o:E such members, for a given pressure d:rop better partic:Le collection effici.enc~ is achieved with less water than that of prior art scrubbers. In the preferred embodiment, the outside diameter of the flow guide is three times that of the thorat. If the spacing between the two flow guide members 22 is uniform, the outlet (radial) flow area is three times that of the inlet radial flow area (i.e., the cylindrical area for flow formed.between the two nozzles 40).
Thus, the velocity head at the outlet (i.e., through the cylin-d~ical area for flow adjacent the periphery of the flow guides . 22) would be 1/9 times that of the inlet radial flow area where the gas enters the flow guide, if the velocity distribution were : re~ular. The spacing can be varied such that the relationship between the flow area and the radial position is as desired.
Thus, the pressure region in the radial flow region which acts 2~ essentially as a diffuser, would be optimized.
FOG ZONE
The particle-collection efficiency in the fog zone is believed to be related to diffusion and to a lesser e~tent upon inertial impaction..The major contribution of the fog zone in the performance of diffusional transfer operation such as the collection of submicron particles and gas absorption.
While a wide variety of theoretical considerations as well as specific configurations have been disclosed and described herein, the conditions which readily.give satisfactory operation of the scrubber device 10 of the present invention are as follows:
~ 3 ;~, ;
1. Uniform distribution of water across the gas stream in the throat section. This causes more complete atomization of the li~uid and higher collection effieiency in the throat section;
2. The throat length should be sufficient that atomization atomization can occur~ Note that the throat length is not restricted to that enclosed by the nozzles. The gas stream emerging from the nozzle can continue to accelerate the liquid for some distance before it diffuses;
tO 3. The jets are aligned such that the jets will collide in axial alignment, i.e. 180 apart in the preferred embodiment;
4. The flow guide members 22 have a maximum area for radial flow which is approximately 3 times that of the inlet radial flow area; and 5. Uniform liquid distribution between the pairs of jets. It is desired because it will equalize gas flow and collection efficiency in both throat sections.
In terms of the preferred embodiment, the liquid dis-tribution into the entrance of the nozzles should be in the form of a coarse spray or several jets of liquid directed so as to cause uniform distribution of liquid over the nozzle cross-section. The amount of liquid used can vary from 2.5 to about 25 gallons per thousand cubic feet of gas passed through each conduit 12 and 14 respectively. A substantially straight nozzle of approximately one foot in length has found to produce extremely good results as it provides each jet that much distance for liquid acceleration. This also helps insure that in the event of unequal liquid distribution between the throat sections, the collision zone will be located close enough to the midpoint between the nozzles such that each throat section will have had the opportunity for substantially complete drop acceleration.
'33 The gas jets are preferably directly opposed one another, and the distance between the nozzle ends is regulated by the volume-tric gas flow and the velocities desired in the collision and fog zones. In the preferred embodiment, the distance between the nozzle ends .is approximately 1/2 to 5 nozzle diameters and the velocity of each of the gas streams is approximately 100 feet per second to approximately 500 feet per second.
It should be understood that in the examples described herein various shapes such as cylindrical shapes are described, other configurations can be used using the same principles. It will thus be apparent to one skill in the art that other changes and modifications can be made without departing from the spere or scope of the present invention as defined and claimed herein.
For example, while the various conduits and chambers are general-ly made up of metal, other materials such as plastics reinforced materials, concrete and like are also within the scope of the present invention. The chamber 18 is shown as having a box-like rectangular construction. However, a cylindrical chamber is also within the scope of this invention. Further, various confi-~ gurations other than circular can be used for the gas dischargenozzIes 40. For example, the nozzles 40 can have rounded or convergent inlets which tend to reduce pressure drop, or they can have a generally rectangular cross-section. Likewise, flow guides 22 can also have a generally rec-tangular configuration. Finally means for moving the water nozzles 46 along the length of the discharge nozzles 40 are also within the scope of this invention.
This invention, therefore, is not to be limited t~ the specific embodiments described and disclosed herein.
.
~'3i'
~7 17.
1 The high velocity gas and the entrained drops are then caused to collide in the chamber 18 in the area impact 20 which is ~ormecl between the ~low guide members 22. When these streams intersect each other, the fine particles are caused to be removed by inertial impaction. The now c:Leaned gas is directed out o~ chamber 18 through the entrainment separator 26 and into the final chamber 29. Any li~uid droplets which collect in the chamber 18 flow out of the device 10 through the drain 32. The now cleaned gas is directed out of the device 10 through outlet duct 28. Here a second sampler 30 is located which also measures the amount of contaminants contained in the outflow so as to be able to calculate the percent of contaminant removal.
As discussed hereinr and as illustrated in FIGURES 1-3 the discharges from each of the nozzles ~0 are caused to impinge upon one another at an angle of approximately 180 (i.e. in a spaced apart and axial aligned configuration~. It is to be understood, however, that other angles of impact are within the scope of the present invention. As will be ~0 appreciated, a variety of other configurations ~or the nozzles 40 are within the scope of the present invention.
E~AMPLES .
- A device as illustrated in FIGURE 1 was constructed with two 3 inch diameter pipes used as the discharge nozzles 40. Two water nozzles were used to introduce water into the respective contaminant-containing gas inlet streams. Mounted adjacent each end of the nozzles 40 are outwardly extending flanges 22 so as to form a 2 inch gap thereinbetween. In the tests, the water was introduced into each stream of gas. The 3 n nozzles were located such tha-t the water spray would strike ,~"
1 the nozzle just inside of the entrance where water was sprayed out at a rate of 2.5 to 10 gallons per thousand cubic feet oE air (gal/MCF).
With respect to the experimental data obtained from the device, reference is made to Tables 1 and 2 set forth hereinbelow. By plotting the cut diameter versus the scrubber pressure drop, one can determine the cut diameter and like information. From such a plot, for a pressure drop of appro~imately 8 inches WC and higher, this type of scrubber 1~ would be ~fficient for removing sub-micron diameter particles.
SCRUBBER TESTS WITH SPRAY ~ATER INJECTION
Run ~ ~P, in. W.C. L/G, gal/MCF dp50'~mA
__ 1 8 7 N.A.
2 " " N.A.
3 " " 0.6 4 " " 0.6 " ~.5 <0.5 - 6 " 10 0.85 7 5 7 1.1 8 " " 1.1 9 " 10 approx. 0.4 ' 10 '" " 1.0 .
11 - 8 " N.A.
12 12.5 7 1.0 13 " " approx. 0.4 14 " 2.5 " 0.45 " 2.5 " 0.~5 T~BLE 2 SCRUBBER TESTS WITH JET WATER INJECTION
Run # ~P, in W.C. L/G, gal/MCF 0.55 2-2 " " 0.55 2-3 " 15.5 0.37 2-4 " " <0.3 2-5 9 7.5 "
~ 19 --1 Referring now to FIGURE 4, the device 10 of the present invention is compared to a prior art device. The present invention is shown in curve ~ and the prior device is shown in curve B. One can see that Eor a 2 inch gap between the flow guide member 22, the scrubber device 10 of the present invention gives substantially better performance in terms of lower particle penetration at the same gas velocity and liquid/gas ratio.
Referring now to FIGURE 5, one can see that the device of the present invention gives the same penetration as a venturi scrubber when operated with less pressure drop (16.2" W.C.3 and liquid/gas ratio, QL/QG, (10 gal/MCF) than the venturi. The venturi had a pressure drop of 19" W.C~ and a liquid/gas ratio of 15 gal/MCF. Thus, for a given pressure drop, better particle collection efficiency can be achieved by the device 10 and less water is required. While not to be bound by any theory, it is believed that such improved results are due, at least in substantial part, by the improved characteristics of the. .
collision zone formed between the flow guide members 22.
In further explanation of the.present invention, one can view the device 10 as belng divided into three basic parts~ the throat section (the distance traveled by the .~ gas jet between the point of liguid introduction~and the point of collision) (2) the "collision zone"; and (3) the "fog zone" (the region between the collision zone and the entrainment . separator).
. - 20 -T1 THE THROAT SECTIO~
_ 2 Particle collection efficiency was found to depend 3 upon the collection efficiency of the individual water droplets 4 and the number of water droplets which the gas stream encountered.
5 Both the efficiency of a drop and the number of drops are at 6 maximum when the water is first introduced and decreases as 7 the drops are accelerated and the relative velocity between 8 the drops and gasses decreases.
9 The collection efficiency of the throat section for a 10 given particle size is believed to depend upon the effective length 11 of the throat section~ Once the drop has reached nearly the qas 12 velocity, there is little benefit in continuing the contact 13 between liquid and gas. The relationship between drop velocity 14 and throat length is illustrated by the data in the following 15 tabulation:
18 _ ~hroat Length, 1~ LT, ~t 0.5 0.75 1.0 1.52.0 _ _ -Velocity ratio 2~ FL 0.76 0.81 0.B5 0.~0.92 22 , _ 26 }
27 ., 1 The ratio of the drop velocity at the end of the throat to the gas velocity in the throat, FL, has been predicted as a :Eunc-tion o~ the throat length, I.T, for 100.0 diamete.r water drops in the gas stream. As can be seen Erom rrable 3, with a throat lencJth o~ one foot, the drops w:ill reach approximately 80~ of the gas velocity and therefore the relative velocity be-tween the drops and the gas will be about 15~ of the gas velocity. If the gas velocity were two hundred feet per second, the relative velocity would decrease to thirty feet per second.
1~ For a given liquid/gas ratio, the drop holdup is propor-tional to the ratio of gas velocity to drop velocity, thus, to the reciprocal of FI. Thus, it can be seen that as the drops are accelerated both the collision efficiency of a drop and the ; drop holdup decrease. Since the scrubber collection efficiency is dependent upon the product of drop holdup and collection efficiency for a single drop, the effectiveness of the scrubber is greatest over the initial part of the throat. ~Based on the above, the length of the throat is chosen to be one to three feet, and preferably, one to two feet. Other throat lengths are within the scope o~ this invention.
COLLISION ZONE
.
When a pa.ir of gas jets and their entrained li~uid drops collide, several phenomena have been found to take place.
Some of the drops will collide with drops moving in the other direction and will shatter into smaller drops. These smaller drops will have a particle collection efficiency during the period when their relative velocity to the gas stream is high.
Because the drops are small, they will be more rapidly accelerated than larger drops. O-ther drops will penetrate into the opposing jet and will transfer their momentum to the gas In the process of being slowed down and moved in a radially out-- 22 ~
ward direction, the drops will collect particles from the gas.
The use o~ the flow guide members 22 which are preferably discs but may also have other configurations provide a means for pressure recovery from the high velocity gas and li.quid stream. B~ the use o:E such members, for a given pressure d:rop better partic:Le collection effici.enc~ is achieved with less water than that of prior art scrubbers. In the preferred embodiment, the outside diameter of the flow guide is three times that of the thorat. If the spacing between the two flow guide members 22 is uniform, the outlet (radial) flow area is three times that of the inlet radial flow area (i.e., the cylindrical area for flow formed.between the two nozzles 40).
Thus, the velocity head at the outlet (i.e., through the cylin-d~ical area for flow adjacent the periphery of the flow guides . 22) would be 1/9 times that of the inlet radial flow area where the gas enters the flow guide, if the velocity distribution were : re~ular. The spacing can be varied such that the relationship between the flow area and the radial position is as desired.
Thus, the pressure region in the radial flow region which acts 2~ essentially as a diffuser, would be optimized.
FOG ZONE
The particle-collection efficiency in the fog zone is believed to be related to diffusion and to a lesser e~tent upon inertial impaction..The major contribution of the fog zone in the performance of diffusional transfer operation such as the collection of submicron particles and gas absorption.
While a wide variety of theoretical considerations as well as specific configurations have been disclosed and described herein, the conditions which readily.give satisfactory operation of the scrubber device 10 of the present invention are as follows:
~ 3 ;~, ;
1. Uniform distribution of water across the gas stream in the throat section. This causes more complete atomization of the li~uid and higher collection effieiency in the throat section;
2. The throat length should be sufficient that atomization atomization can occur~ Note that the throat length is not restricted to that enclosed by the nozzles. The gas stream emerging from the nozzle can continue to accelerate the liquid for some distance before it diffuses;
tO 3. The jets are aligned such that the jets will collide in axial alignment, i.e. 180 apart in the preferred embodiment;
4. The flow guide members 22 have a maximum area for radial flow which is approximately 3 times that of the inlet radial flow area; and 5. Uniform liquid distribution between the pairs of jets. It is desired because it will equalize gas flow and collection efficiency in both throat sections.
In terms of the preferred embodiment, the liquid dis-tribution into the entrance of the nozzles should be in the form of a coarse spray or several jets of liquid directed so as to cause uniform distribution of liquid over the nozzle cross-section. The amount of liquid used can vary from 2.5 to about 25 gallons per thousand cubic feet of gas passed through each conduit 12 and 14 respectively. A substantially straight nozzle of approximately one foot in length has found to produce extremely good results as it provides each jet that much distance for liquid acceleration. This also helps insure that in the event of unequal liquid distribution between the throat sections, the collision zone will be located close enough to the midpoint between the nozzles such that each throat section will have had the opportunity for substantially complete drop acceleration.
'33 The gas jets are preferably directly opposed one another, and the distance between the nozzle ends is regulated by the volume-tric gas flow and the velocities desired in the collision and fog zones. In the preferred embodiment, the distance between the nozzle ends .is approximately 1/2 to 5 nozzle diameters and the velocity of each of the gas streams is approximately 100 feet per second to approximately 500 feet per second.
It should be understood that in the examples described herein various shapes such as cylindrical shapes are described, other configurations can be used using the same principles. It will thus be apparent to one skill in the art that other changes and modifications can be made without departing from the spere or scope of the present invention as defined and claimed herein.
For example, while the various conduits and chambers are general-ly made up of metal, other materials such as plastics reinforced materials, concrete and like are also within the scope of the present invention. The chamber 18 is shown as having a box-like rectangular construction. However, a cylindrical chamber is also within the scope of this invention. Further, various confi-~ gurations other than circular can be used for the gas dischargenozzIes 40. For example, the nozzles 40 can have rounded or convergent inlets which tend to reduce pressure drop, or they can have a generally rectangular cross-section. Likewise, flow guides 22 can also have a generally rec-tangular configuration. Finally means for moving the water nozzles 46 along the length of the discharge nozzles 40 are also within the scope of this invention.
This invention, therefore, is not to be limited t~ the specific embodiments described and disclosed herein.
.
~'3i'
Claims (11)
1. A scrubber for removing finely divided contaminants from a gas stream by inertial impaction comprising a housing forming an impaction chamber, a gas stream generating source, first and second conduits disposed in said chamber, each said conduit having an inlet and an outlet, means for directing said stream containing said finely divided contaminants from said gas stream generating source to each said conduit, substantially straight nozzle means disposed adjacent each said outlet and configured such that the flow path of the gas stream through said first conduit intersects the flow path of the gas stream through said second conduit, and outwardly extending flow guide flange members disposed on said first and second conduits adjacent each said nozzle means for re-gulating the flow path of the gas stream as it is discharged from each conduit such that improved collection efficiency of the contaminants is achieved.
2. A scrubber device according to claim 1 wherein said nozzle means on said first conduit is in substantial axial alignment with said nozzle means on said second conduit.
3. A scrubber device according to claim 1 wherein means for supplying a liquid is disposed in each said conduit adjacent the associated nozzle means.
4. A scrubber device for removing small particulate material from a gas stream by inertial impaction comprising:
a housing forming an impaction chamber;
means for directing a gas stream generating source to said chamber;
4. A scrubber device for removing small particulate material from a gas stream by inertial impaction comprising:
a housing forming an impaction chamber;
means for directing a gas stream generating source to said chamber;
Claim 4 continued...
first and second conduits disposed in said chamber and joined to said directing means, each said conduit having at least one discharge nozzle adjacent one end thereof, said discharge nozzle on said first conduit arranged in a spaced apart and opposed configuration with respect to said discharge nozzle on said second conduit such that the flow path of the discharge from said first conduit intersects the flow path of the discharge from said second conduit;
means for supplying a liquid disposed in said device adjacent each said discharge nozzle, said means for supplying a liquid configured such that liquid is caused to intersect the flow path of said gas stream;and flow guide means disposed on said first and second conduits adjacent each said nozzle means for regulating the flow path of the gas stream as it is discharged from each conduit such that improved collection efficiency of the contaminants is achieved.
first and second conduits disposed in said chamber and joined to said directing means, each said conduit having at least one discharge nozzle adjacent one end thereof, said discharge nozzle on said first conduit arranged in a spaced apart and opposed configuration with respect to said discharge nozzle on said second conduit such that the flow path of the discharge from said first conduit intersects the flow path of the discharge from said second conduit;
means for supplying a liquid disposed in said device adjacent each said discharge nozzle, said means for supplying a liquid configured such that liquid is caused to intersect the flow path of said gas stream;and flow guide means disposed on said first and second conduits adjacent each said nozzle means for regulating the flow path of the gas stream as it is discharged from each conduit such that improved collection efficiency of the contaminants is achieved.
5. A scrubber device according to claim 4 wherein the diameter of said flow guide means is approximately three times the inside diameter of said discharge nozzle.
6. A scrubber device according to claim 4 wherein said means for supplying a liquid comprises first and second tubes axially disposed within said first and second conduits respectively, each said tube having a series of orthogonal openings configured to form a liquid spray.
7. A scrubber device according to claim 4 wherein each said flow guide means comprises an outwardly extending flange member.
8. A scrubber device according to claim 7 wherein each said flange member has a generally circular configuration.
9. A scrubber device according to claim 7 wherein each said flange member has a generally rectangular configuration.
10. A method for removing various finely divided contaminants form a gas stream by inertial impaction and interception comprising the steps of:
(a) passing a first stream of gas containing said contaminants through a first conduit having a first discharge nozzle and an outwardly extending flow guide means adjacent one end thereof;
(b) providing said first stream of gas with finely divided liquid droplets such that said droplets are entrained by said first gas stream and are caused to accelerate and to impinge upon said contaminants in said first gas stream so as to encourage the removal of said contaminants by inertial impaction;
(c) passing a second stream of gas containing said contaminants through a second conduit having a second discharge nozzle and an outwardly extending flow guide means disposed adjacent one end thereof;
(d) providing said second stream of gas with finely divided liquid droplets such that said droplets are entrained by said second gas stream and are caused to accelerate and to impinge upon said contaminants in said second gas stream so as to encourage removal of said contaminants by inertial impaction;
and (e) controlling the direction and flow rates of said first gas stream through said first discharge nozzle and said second gas stream through said second discharge nozzle such that
10. A method for removing various finely divided contaminants form a gas stream by inertial impaction and interception comprising the steps of:
(a) passing a first stream of gas containing said contaminants through a first conduit having a first discharge nozzle and an outwardly extending flow guide means adjacent one end thereof;
(b) providing said first stream of gas with finely divided liquid droplets such that said droplets are entrained by said first gas stream and are caused to accelerate and to impinge upon said contaminants in said first gas stream so as to encourage the removal of said contaminants by inertial impaction;
(c) passing a second stream of gas containing said contaminants through a second conduit having a second discharge nozzle and an outwardly extending flow guide means disposed adjacent one end thereof;
(d) providing said second stream of gas with finely divided liquid droplets such that said droplets are entrained by said second gas stream and are caused to accelerate and to impinge upon said contaminants in said second gas stream so as to encourage removal of said contaminants by inertial impaction;
and (e) controlling the direction and flow rates of said first gas stream through said first discharge nozzle and said second gas stream through said second discharge nozzle such that
Claim 10 continued...
said streams are caused to intersect and to form a collision zone between said flow guide means whereby the contaminants in each respective stream are further removed by inertial impaction.
said streams are caused to intersect and to form a collision zone between said flow guide means whereby the contaminants in each respective stream are further removed by inertial impaction.
11. The method according to claim 10 wherein the discharge velocity of each gas stream is between 100 to 500 feet per second.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000368869A CA1158993A (en) | 1981-01-20 | 1981-01-20 | Particle scrubber and related method |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000368869A CA1158993A (en) | 1981-01-20 | 1981-01-20 | Particle scrubber and related method |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1158993A true CA1158993A (en) | 1983-12-20 |
Family
ID=4118962
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000368869A Expired CA1158993A (en) | 1981-01-20 | 1981-01-20 | Particle scrubber and related method |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1158993A (en) |
-
1981
- 1981-01-20 CA CA000368869A patent/CA1158993A/en not_active Expired
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