Note: Descriptions are shown in the official language in which they were submitted.
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
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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.
26
28
29
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2.
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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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18 l
~19~ ~
; 22
2~
28
2a
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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
17
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
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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.
32
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~ 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
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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
32
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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
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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
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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.
28
29
31
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.
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29
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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.
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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
11 DETAILED DESCRIPTION OF THE INVENTION
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.
31
32 14.
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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
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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.
32 16
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~ 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).
26
~7
28
29
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
- 18 -
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33
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.
TABLE 1
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 "
2-6
~ 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:
16
17 TABLE 3
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 , _
24
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:
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~ 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.
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'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.
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