US3746322A

US3746322A - Gas scrubber

Info

Publication number: US3746322A
Application number: US00214627A
Authority: US
Inventors: A Sawyer
Original assignee: Andco Inc
Current assignee: Andco Inc
Priority date: 1972-01-03
Filing date: 1972-01-03
Publication date: 1973-07-17
Anticipated expiration: 1990-07-17

Abstract

Apparatus for removing particulate material from a gas stream traveling through a duct comprising a pair of members each provided with a corresponding plurality of passages and arranged to cooperatively define a corresponding plurality of venturi passages extending generally parallel to the direction of flow of the gas stream and spaced around the axis of the duct. The members are relatively movable for varying the size of the venturi throats and for completely closing the passages when desired. Opposed sidewalls shaped to cooperatively define each venturi passage are carried by corresponding ones of the movable members whereby the configuration of the venturi passages is maintained throughout the entire range of adjustment. Liquid is supplied to the upstream member and the venturi inlets defined thereby are of a configuration effecting a substantially uniform distribution of the liquid to the passages.

Description

Sawyer 1111 3,746,322 1 1 July 17, 1973 GAS SCRUBBER Inventor: Alan B. Sawyer, North Tonawanda,

[52] US. Cl 261/53, 261/109, 261/112,

261/113, 261/D1G. 54 int. Cl. B011 3/04 Field of Search 261/53, 62, 108-113,

261/DIG. 54

References Cited UNITED STATES PATENTS 3/1916 Ferguson 261/114 VT 5/1916 Ferguson 261/62 6/1934 Ketterer 26l/D1G. 54

2/1953 Olney 261/114 JP 7/1971 Katyal 261/11 B A l 60 A 1 Primary Examiner-Tim R. Miles Assistant Examiner-Steven H. Markowitv. Att0rney-Christel & Bean [57] ABSTRACT Apparatus for removing particulate material from a gas stream traveling through a duct comprising a pair of members each provided with a corresponding plurality of passages and arranged to cooperatively define a corresponding pluralityof venturi passages extending generally parallel to the direction of flow of the gas stream and spaced around the axis of the duct. The members are relatively movable for varying the size of the venturi throats and for completely closing the passages when desired. Opposed sidewalls shaped to cooperatively define each venturi passage are carried by corresponding ones of the movable members whereby the configuration of the venturi passages is maintained throughout the entire range of adjustment. Liquid is supplied to the upstream member and the venturi inlets defined thereby are of a configuration effecting a sub stantially uniform distribution of the liquid to the passages.

9 Claims, 5 Drawing Figures PATENIED SHEET 1 0F 2 ens scnunnsn BACKGROUND OF THE INVENTION This invention relates to the gas scrubber art, and more particularly, to a new and improved wet collector advantageously including various desirable attributes of both the orifice and venturi types.

Wet collectors of the orifice type are well known and offer the advantages of relative simplicity and low cost. However, these capabilities are limited, making them unsuitable for many installations. Wet collectors of the venturi type are capable of higher collection efficiencies, the collection efficiency increasing with higher pressure drops, and some venturi type collectors are designed with adjustable throats to allow a range of pressure drops for a given gas volume. Further adjustment and regulation of the pressure drop to achieve effective agglomeration has been accomplished by the provision of movable dampers in conventional venturi type scrubbers, but only with the expenditure of con siderable energy. Also, such venturi scrubbers are relatively large and expensive.

A wet collector constructed to advantageously include various desirable attributes of both the orifice and venturi types is taught by Selway in US. Pat. application Ser. No. 102,817 filed Dec. 30, 1970 and assigned to the assignee of the present invention. Briefly, the wet collector of that application utilizes first and second relatively movable members having corresponding passages which cooperatively define venturi passages in a manner permitting variation in the size of the venturi throats with a relatively small expenditure of energy. The members are identical in construction and are relatively movable between a full open position and a full closed position. Liquid is supplied at the periphery of a surface of one of the members and rises to the level of one of the venturi passage inlet openings, the inlet openings being arranged so as to create a pressure differential which distributes the liquid uniformly into the openings.

In the operation of the wet collector of the foregoing application, the configuration of the venturi passage defining walls is altered slightly as the members are moved between full open and full closed positions. While this usually will be of little or no concern under some operating conditions, it is believed desirable to provide such a wet collector having the additional capability of maintaining the same configuration in the venturi passage defining walls as the members are moved to vary the passage size.

SUMMARY OF THE INVENTION It is therefore an object of this invention to combine the various desirable features of the orifice and venturi It is a further object of this invention to provide such a wet collector wherein the pressure drop can be varied to provide effective agglomeration for various particle sizes and wherein a particular pressure drop can he maintained despite varying flow conditions, all with a relatively minimal expenditure of energy.

It is a further object of this invention to provide such a wet collector wherein the pressure drop can be varied over a significantly large range and can accommodate a wide range of gas flow conditions.

It is a further object of this invention to provide such.

passages in a manner permitting variation in the size of i the venturi throats with a relatively small expenditure of energy. Each of the venturi passages is defined, in part, by first and second walls carried by said first and second movable members, respectively. Each of the walls has a configuration for cooperatively defining, one with the other, the corresponding venturi passage, and the configuration is exactly maintained when the members are moved to vary the size of the venturi throats. Liquid is supplied at the periphery of a surface of one of the members and rises to the level of the venturi passage inlet openings, the inlet openings being of a shape creating a pressure differential which distributes the liquid uniformly into the openings.

The foregoing and additional advantages and characterizing features of the present invention will become clearly apparent from the ensuing detailed description together with the included drawings wherein:

BRIEF DESCRIPTION OF THE DRAWING FIGURES FIG. 1 is a fragmentary elevational view, partly schematic, showing the apparatus of the present invention as it would appear in use;

FIG. 2 is a horizontal cross sectional view on an enlarged scale taken about on line 2-2 of FIG. 1;

FIG. 3 is a developed vertical sectional view on a further enlarged scale taken about on line 3 3 of FIG. 2 showing the apparatus in a full opened condition;

FIG. 4 is a developed vertical sectional view similar to that of FIG. 3 but showing the apparatus in a full closed position; and

FIG. 5 is a developed vertical sectional view similar to that of FIG. 3 but taken about on line 5 5 of FIG. 2 and on a somewhat reduced scale.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT FIG. 1 illustrates apparatus It) oi the present inven tion arranged to remove particulate material from a gas stream traveling through a duct II. The direction of flow of the gas stream is indicated by the arrow 12. The gas can be the effluent from a blast furnace, in which case the upstream end of duct II is suitably connected to the furnace exhaust, but it will be appreciated that apparatus of the present invention has the capability of scrubbing gas obtained from any of a wide variety of sources.

In the illustrated embodiment apparatus 10 comprises a first member 14 and a second member I6 dcfining a plurality of venturi passages spaced around the axis of duct 11 and disposed generally parallel to the direction of flow of the gas stream as will be described in detail. The apparatus 10 further comprises means for supplying liquid to the inlets of the passages, in particular to member 14, in the form of a supply conduit indicated schematically at 18 connected to a liquid source (not shown), a water control device 20, and a liquid distributing conduit 22 in communication with member 14 and connected through a conduit 24 to control device 20. In a presently preferred form, member 14 includes a generally horizontal planar surface, and liquid is supplied to that surface at or near the periphery thereof by conduit 22 whereupon the liquid level rises to the passage inlets.

The apparatus further comprises means operatively connected to at least one of the first and

second members

14 and 16, respectively, for causing relative movement of

members

14, 16 in generally parallel planes whereby the throats of the venturi passages defined thereby can be varied in cross sectional area. The

- means for causing relative movement can comprise an hydraulic cylinder 26 suitably mounted or attached toa fixed reference surface relative to duct 11 and apparatus 10. The rod of cylinder 26 is connected to one end of an actuator arm or lever 28, the other end of which is attached or joined to member 16, member 14 being stationary in the illustrated embodiment. The operation of cylinder 26 is controlled as a function of the pressure drop across the apparatus 10 in duct 11 as determined by a first pressure sensing means 30 positioned in duct 11 upstream of apparatus 10 and by a second pressure sensing means 32 positioned in duct 1 1 downstream of apparatus 10. A pressure sensitive control device indicated schematically at 34 in FIG. 1 is connected through a line 35 to sensor 30 and through a line 36 to sensor 32. Device 34, in turn, controls the flow of operating fluid to and from the rod and piston ends of cylinder 26 through lines 37 and 38. The detailed construction of device 34 and of sensing means 30, 32 per se comprise no part of the present invention, and since they are readily commercially available in varioussuitable forms, all readily understood by those skilled in the art, a detailed description thereof is unnecessary.

Referring now to FIGS. 2-5,member 14 is formed to include a generally planar surface 40 and a peripheral edge portion in the form of a skirt-like rim 41 disposed at about a right angle to the plane of surface 40. When member 14 is in the operative position shown in FIG. 1, surface 40 is disposed generally horizontally and rim 41 projects upwardly in an upstream direction therefrom. In addition, rim 41 is of an outer dimension and shape so as to provide a snug-fitting relationship or engagement with the inner surface of duct ,1 1. Member 14 is provided with a plurality of openings each designated 42 spaced around the center thereof and extending through surface 40, which center coincides with the axis of duct 11. In a similar manner, member 16 is formed to include a generally planar surface portion 45 and a peripheral edge portion in the form of a skirt-like rim (not shown) which is disposed at about a right angle with respect to the plane of surface 45. This rim, like rim 4] of member 14, is ofa dimension and configuration so as to engage the inner wall surface of duct 11. In addition, member 16 can be supported in duct 11 by a bearing band 70 FIG. I) suitably attached to or formed on the inner surface of duct 11 and positioned whereby the lower or depending edge of the rim of member 16 is seated thereon. Member 16, like member 14 and duct 11, is circular and is provided with a corresponding plurality of openings, each designated 49, spaced around the center thereof and extending through surface 45, which center coincides with the axis of duct 11.

When assembled in duct 11,

members

14 and 16 are rotatably connected at the centers thereof by suitable means illustrated in the present instance as a bolt and nut 51.

Members

14 and 16 cooperate to define a plurality of venturi passages spaced around the axis of duct 11, and each passage extends generally in the direction of flow of the gas stream. The total number of venturi passages is equal to the number of either of the

openings

42 or 49 in the

members

14 or 16, respectively. Each venturi passage is defined in part by a first sidewall carried by member 14 and extending from a corresponding opening 42. Sidewall 55 comprises a middle portion 56 disposed generally perpendicular to the planar portion 40 of member 14 and first and

second end portions

57 and 58, respectively, separated by middle portion 56. End portion 57 extends upstream from surface 40 of member 14 and is disposed at a relatively acute angle, for example, about 15 degrees, with respect to the direction of flow of the gas stream. End portion 58 extends downstream from surface 45 of member 16 and is disposed at a relatively acute angle, for example 15 degrees, with respect to the direction of the gas stream. Each venturi passage is further defined by a second side wall 60 carried by member l6 and including a middle portion 61 disposed generally perpendicular to planar portion 45 of member 16 and first and

second end portions

62 and 63, respectively. End portion 62 extends upstream from surface 40 of member 14 and is disposed at a relatively acute angle, such as 15 degrees, with respect to the direction of flow of the gas stream. End portion 63 extends downstream from surface 45 of member 16 and is disposed at a relatively acute angle, such as 15 degrees, with respect to the direction of flow of the gas stream. As a result,

walls

55 and 60 present a region defined by the opposed

sidewall end portions

57 and 62 which converges in the direction of flow of the gas stream toward a throat region defined by sidewall

middle portions

56 and 61. The throat'region communicates with a region diverging from the throat in a downstream direction and defined by the opposed

sidewall end portions

58 and 63.

Each of the venturi passages is completed by opposed end walls which engage corresponding ends of the

sidewalls

55 and 60. In particular, end walls 65 are carried by member 14, extend from openings 42, and contact the radially innermost ends of

sidewalls

55 and 60 relative to the center of member 14. End walls 66 are carried by member 16, extend from openings 49, and are generally coplanar with end walls 65. End walls 66 as a result contact the radially innermost ends of the

sidewall end portions

58 and 63. There also are provided end walls 67 carried by member 14, extending from openings 42, and contacting the radially outermost ends of

sidewall portions

57 and 62. In a similar manner corresponding and generally coplanar end walls 67' are carried by member 16, extend from openings 49, and contact the radially outermost ends of

sidewall end portions

58 and 63.

End walls

65, 66, 67 and 67' are disposed in planes generally perpendicular to

planar portions

40 and 45 of

members

14 and 16. The end walls preferably also are of a height or length (in the direction of gas flow) greater than that of

sidewalls

55 and 60 whereby water flows only over the edges of

sidewalls

55 and 60 into the passage inlet openings. It will be appreciated that side walls 60 have sliding contact with end walls 66 and 67'. Any spacing therebetween is quite sufficient to provide clearance for relative movement.

As a result,

members

14 and 16 cooperate to define a plurality of venturi passages spaced around the axis of duct ill and each extending generally in the direction of flow of the gas stream. When member 14 is located in duct 11 in the operative position of FIG. ll, each passage has an inlet opening defined by the edges of

end walls

65 and 67 and by the edges of

end portions

57 and 62 of

sidewalls

55 and 60, respectively, which inlet opening is in communication with the dirty gas stream. Each of the passages, furthermore, is made to initially converge in the direction of flow of the gas stream or, in other words, in a direction from the inlet opening toward the plane of surface 40. Member 16 preferably is identical to member 14, and when placed in the position of FIG. 1 is inverted relative to member 14 whereby the corresponding passage defining walls in member '16 diverge in a direction away from member 14.

The number of venturi passages cooperatively defined by

members

14 and 16 will vary depending upon the size of duct 11. The end walls of

members

14 and 16 all are disposed generally parallel to the direction of gas flow thereby cooperatively defining relatively straight venturi passage end walls. Sidewalls 55 and 60 of

members

14 and 16, respectively, include

end portions

57 and 62 which converge in the direction of gas flow and end

portions

58 and 63 which diverge in the direction of gas flow. As a result, there is provided a plurality of venturi passages each having a restricted throat defined by the

middle portions

56 and 61 of

sidewalls

55 and 60, respectively. In the present illustration member 16 is disposed so that planar portion 45 is generally horizontal, the rim or flange thereof contacts the inner surface of ductll, and the depending edge of the rimrests on a bearing band 70 or other suitable supporting arrangement whereby member 16 is supported for rotation about the axis of duct 11. Member 14 is then placed on member 16 and supported thereby in a manner defining the venturi passages as described hereinabove. Rim 41 of member 14 should contact or engage the inner wall surface of duct It in a manner providing a fluidtight seal, and in some instances it may be necessary or desirable to enhance the seal such as by a peripheral weld between flange 41 and duct 11. The foregoing arrangement for positioning

members

14 and 16 in duct 11 is illustrative, and other arrangements can bra-employed without departing from the spirit and scope of this invention.

Conduit 22 can be in the form of a manifold encircling duct II, with multiple delivery conduits equally spaced thercaround, and it has been found that adequate distribution can be obtained with the number of delivery conduits equaling one-half the number of venturi passages, as clearly illustrated in FIG. 2.

The apparatus of the present invention operates in the following manner. Liquid, usually water, is delivered by conduits 22 to member 14 at the periphery thereof and onto horizontal planar surface 40. The liquid fills the trough or reservoir defined by rimor flange 4i and the various end walls 65, 6'7 and sidewalls 55 and 60 defining the venturi passage portions in member 14. The level of the liquid rises until it reaches the height of sidewalls 55, whereupon the liquid enters the inlet portions of the passages and flows generally in a direction indicated by the dashed lines 7?. in FIG. 3. Sidewalls S5, 60 are of a height slightly less than that of the

end walls

65,67 and function as weirs over which the liquid flows. The liquid is atomized in the venturi passages by the moving gas stream, in a manner familiar to those skilled in the art, and the liquid droplets agglomerate with the solid particles in the gas stream. The relatively clean gas together with the agglomerated liquid drops and particles leave the venturi passages generally in a direction indicated by the arrows 74 in FIG. 3 for subsequent separation of the liquid and agglomerated particles. In particular, separation of the agglomerated liquid drops and particles from the gas stream can be accomplished by gravity, by effecting an abrupt change in the direction of flow, or by other methods and apparatus well known to those familiar with the art.

Substantially uniform distribution of liquid or water along the entire length of

end portions

57 and 62 of

sidewalls

55 and 60, respectively, is accomplished by creation of a pressure differential in a radial direction across each of the venturi passage inlet openings. The pressure at or near the center of member M is made lower than the pressure at the periphery of member 14 by having each venturi passage inlet opening of a generally pie-shaped configuration as shown in FIG. 2. In other words, each of the passage inlet openings has spaced apart side edges extending generally radially outwardly relative to the center of member 14 which edges define therebetween an acute included angle. Therefore, the venturi passages are of progressively decreasing cross-sectional area, proceeding radially. inwardly from the outer end walls 67, whereby the velocity of the gas passing through the passages increases progressively, again proceeding radially inwardly from end walls 67. This results in a pressure gradient or progressively decreasing, radially inward form across member 14, producing a pressure differential causing liquid to flow radially inwardly across surface 40 of member 14. In addition, it has been found that this configuration of the inlet openings adds more impetus to the fluid flow through the venturi throats.

To achieve the desired degree of agglomeration for optimum operation of apparatus 1.0 it is necessary that the atomized liquid droplets be of a size substantially equal to that of the particles to be removed from the gas stream. The size of the liquid drops is, in turn, a function of the pressure drop across apparatus 10, Le. between the upstream side of member 14 and the downstream side of member l6. Accordingly, for a given size of particle present in the gas stream, it may be necessary to vary the pressure drop to form liquid drops of the required size. In addition, if a characteristic of the flow should happen to change, such as the volume, an adjustment most probably will be necessary to maintain the desired pressure drop.

According to the present invention, the throat of each venturi passage can be varied in size by a simple relative movement of members 1-4, 16, and this is accomplished with a relatively minimal energy expenditure arising from the action of essentially only shearing forces on members l4, 16. In addition, this variation is provided by the apparatus of the present invention in a manner maintaining the same configuration of the venturi passages throughout the full range of adjustment. Referring now to FIGS. 3 and 4, member 14 is moved by rotation in a plane normal to the direction of gas flow to vary the throat size of the venturi passages cooperatively defined by

members

14 and 16. For example, member 16 can be rotated relative to member 14 between a fully opened position where

sidewall portions

56, 61 are spaced apart as shown in FIG. 3 and a fully closed position where

portions

56, 61 are in contact as shown in FIG. 4. During such movement, the portion of each venturi passage configuration defined by sidewalls 55 and 60 is maintained the same throughout this range of adjustment by virtue of the fact that sidewall 55 is carried by member 14 and sidewall 60, is carried by member 60 and these sidewalls do not change shape. When member 16 is rotated, each sidewall 60 is moved in its entirety toward and away from its associated sidewall 55, such movement being in the region provided by openings 42 in member 14 and openings 49 in member 16.

End walls 66 and 67' do move relative to their associated

end walls

65 and 66, but without interrupting or otherwise altering the end wall configuration in the space between the side walls, whereby only the width of the venturi passage end walls changes.

In the embodiment illustrated in FIG. 1, movement of member 16 is effected by an hydraulic cylinder 26, and movement of the cylinder rod is transmitted through arm 28 to rotate the member 16. Movement of member 16 to vary the size of the venturi throats is performed as a function of a pressure difference, under control of device 34 connected to'cylinder 26 and to the pressure sensing means 30 and 32. Accordingly, member 16 is moved automatically to vary the cross sectional size of the venturi passage throats as a function of the pressure drop existing between the region upstream of member 14 and the region downstream-of member 16. Of course, the relative positioning of members l4 and 16 to selectively vary the throat size can be accomplished manually.

When a liquid or water seal is desired, this is accomplished by the apparatus of the present invention in a convenient, easy and economical manner. Member 16 simply is moved or rotated to the position of full closure indicated in FIG. 4. The supply of liquid to member 14 is continued, in a sufficient amount to effect a seal across the blocked throats of the passages notwithstanding spaces which may exist between

members

14, 16 because of manufacturing tolerances. it should be noted that member 14 is in liquid-tight engagement with'the duct wall, as by a welded seam or other means Apparatus of the present invention is suitable for use with ducts of various diameters and requires only slight modification. For use in a relatively small duct, it has been found desirable to provide four venturi passages cooperatively defined by

members

14 and 16. For relatively larger ducts the number of venturi passages is increased to as many as eight. it has been found that increasing the overall diameter of members l4, 16 requires a larger number of passages each of a relatively smaller included angle.

The apparatus 10 of the present invention is of a relatively simple construction, easily assembled and operated, and economical to manufacture particularly when

members

14 and 16 are of identical construction. The apparatus has a high collection efficiency, approaching and sometimes exceeding that of a conventional venturi scrubber, while requiring a minimal expenditure of energy for varying the throat size of the venturi passages and requiring only a relatively small space. In addition, the configuration or shape of the venturi passages is maintained throughout the full range of variation in the throat size, without interruption in either side or end walls. Effective liquid distribution is obtained by a radial pressure differential across the upstream side of the scrubber. In addition, the apparatus permits a water seal to be provided in a convenient and easy manner for isolating the system in which it is included.

It is therefore apparent that the present invention accomplishes its intended objects. While a single specific embodiment has been described in detail, this has been done by way of illustration without thought of limitation.

I claim:

1 Apparatus for removing particulate material from a gas stream traveling through a duct, said apparatus comprising:

a. a first member positioned in said duct and pro vided with a plurality of openings;

b. a second member positioned in said duct adjacent said first member on the downstream side thereof, said second member being provided with a corresponding plurality of openings; I

c. a plurality of walls carried by said first and second members for defining a plurality of venturi passages when the openings of said first and second members are brought into alignment;

d. said walls including first and second sidewalls for each of said venturi passages and carried by said first and second members, respectively, said sidewalls being shaped to cooperatively define therebetween the corresponding venturi passage;

e. means for causing relative movement of said first and second members thereby to vary the size of said venturi passages; and

f. means for delivering liquid to the inlets of said passages.

2. Apparatus according to claim 1 wherein each of said first and second members comprises a generally planar portion from which said passage defining walls extend and a peripheral edge portion adjacent the wall of said duct.

3. Apparatus according to claim 2 wherein each of said sidewalls includes first and second end portions separated by a middle portion disposed generally perpendicular to the planar portions of the corresponding first and second members, said first end portions extending in a direction upstream from said first member and disposed at a relatively acute angle with respect to the direction of the gas stream so as to be converging toward said middle portions, and said second end portions extending in a direction downstream from said second member and disposed at a relatively acute angle with respect to the direction of the gas stream so as to be diverging from said middle portions.

4. Apparatus according to claim 3 wherein one of each opposed pair of said sidewalls defining each of said venturi passages is moved in its entirety relative to the other thereof between an open position wherein said middle portions are spaced apart to a closed position wherein said middle portions are in contact in response to relative movement of said first and second members.

5. Apparatus according to claim I wherein said members are identical in construction, and are relatively movable between a full open and a full closed position.

6. Apparatus according to claim 2 wherein said first and second members are disposed generally horizontally in said duct and wherein said liquid delivering means comprises conduit means positioned to deliver liquid to said planar portion of said first member near said peripheral edge portion thereof whereby liquid rises to a level corresponding to the height of said sidewalls and then flows into said passages defined by said walls.

7. Apparatus according to claim 6 wherein said walls defining each of said venturi passages are positioned relative to each other so as to define passage inlet openings having a configuration which gives rise to a pressure differential between the center of said planar portion and said peripheral edge portion of said first memher for distributing liquid substantially uniformly to said passages.

8. Apparatus according to claim'7 wherein each of said passage inlet openings has spaced apart edges extending generally radially outwardly relative to the center of said planar portion which edges define an acute included angle.

9. Apparatus according to claim 1 further including: a. first pressure sensing means positioned in said duct upstream from said first member relative to the direction of flow of said gas stream; b. second pressure sensing means positioned in said duct downstream from said second member rela tive to the direction of flow of said gas stream; and control means connected to said first and second sensing means and responsive to the pressure difference measured therebetween, said control meansbeing connected in controlling relation to said means causing relative movement between said first and second members whereby the throats of said venturi passages are varied in response to changes in the pressure drop across said apparatus.

Claims

2. Apparatus according to claim 1 wherein each of said first and second members comprises a generally planar portion from which said passage defining walls extend and a peripheral edge portion adjacent the wall of said duct.
3. Apparatus according to claim 2 wherein each of said sidewalls includes first and second end portions separated by a middle portion disposed generally perpendicular to the planar portions of the corresponding first and second members, said fIrst end portions extending in a direction upstream from said first member and disposed at a relatively acute angle with respect to the direction of the gas stream so as to be converging toward said middle portions, and said second end portions extending in a direction downstream from said second member and disposed at a relatively acute angle with respect to the direction of the gas stream so as to be diverging from said middle portions.
4. Apparatus according to claim 3 wherein one of each opposed pair of said sidewalls defining each of said venturi passages is moved in its entirety relative to the other thereof between an open position wherein said middle portions are spaced apart to a closed position wherein said middle portions are in contact in response to relative movement of said first and second members.
5. Apparatus according to claim 1 wherein said members are identical in construction, and are relatively movable between a full open and a full closed position.
6. Apparatus according to claim 2 wherein said first and second members are disposed generally horizontally in said duct and wherein said liquid delivering means comprises conduit means positioned to deliver liquid to said planar portion of said first member near said peripheral edge portion thereof whereby liquid rises to a level corresponding to the height of said sidewalls and then flows into said passages defined by said walls.
7. Apparatus according to claim 6 wherein said walls defining each of said venturi passages are positioned relative to each other so as to define passage inlet openings having a configuration which gives rise to a pressure differential between the center of said planar portion and said peripheral edge portion of said first member for distributing liquid substantially uniformly to said passages.
8. Apparatus according to claim 7 wherein each of said passage inlet openings has spaced apart edges extending generally radially outwardly relative to the center of said planar portion which edges define an acute included angle.
9. Apparatus according to claim 1 further including: a. first pressure sensing means positioned in said duct upstream from said first member relative to the direction of flow of said gas stream; b. second pressure sensing means positioned in said duct downstream from said second member relative to the direction of flow of said gas stream; and c. control means connected to said first and second sensing means and responsive to the pressure difference measured therebetween, said control means being connected in controlling relation to said means causing relative movement between said first and second members whereby the throats of said venturi passages are varied in response to changes in the pressure drop across said apparatus.