GB2144650A

GB2144650A - Gas scrubber

Info

Publication number: GB2144650A
Application number: GB8417449A
Authority: GB
Inventors: Abdus Saleem
Original assignee: General Electric Environmental Services Inc
Current assignee: General Electric Environmental Services Inc
Priority date: 1983-08-12
Filing date: 1984-07-09
Publication date: 1985-03-13
Also published as: GB2144650B; GB8417449D0; NL8402481A; DE3426015A1; JPS60255129A

Abstract

Apparatus for effecting intimate contact of gases and liquids comprises a housing containing a liquid in its lower portion and having disc-shaped impellers (24) for spraying liquid into the gas-liquid contact space, which impellers rotate on parallel shafts (23) axially disposed in the housing and supported above the liquid so that the lower portions of the impellers are immersed in it. Fresh liquid may be introduced (17) beneath the point where the gas is removed (32), and spent liquid removed (18) from the reservoir beneath the point where the gas is introduced (30), to provide countercurrent flow. In one embodiment the apparatus is used to remove sulphur dioxide and fly ash from the flue gas generated by burning coal by employing pulverized limestone or lime in water as the liquid spray in the gas-liquid contact space. <IMAGE>

Description

SPECIFICATION Gas Stream Scrubber Devices The present invention relates to a scrubber device for removing gaseous and/or particulate matter from a gas stream, and more particularly, to a device for generating a liquid spray of large volume from a body of liquid such that the liquid constituting the spray comes into substantial intimate contact with a gaseous medium passing above the body of liquid. Such devices are useful for extracting solid or soluble constituents from an industrial exhaust gas stream, or for cooling a gaseous medium by evaporation due to contact of the liquid spray with the gaseous medium.

Prior art devices, such as that described in U.S.

Patent No. 1,462,363, form a liquid spray by means of cylinders of large surface area arranged to rotate on a cental shaft and supported above a body of liquid in a manner such that the upper surface of the liquid only slightly touches and is nearly tangent to the lowermost part of the surfaces of the cylinders. When the revolving cylinders touch the surface of the liquid, a thin film of liquid adheres thereto and, as the cylinders rotate, centrifugal force throws the liquid film from the cylinder surfaces as a fine spray distributed above the cylinders. In U.S. Patent No.

1,462,363, the cylinder dips into the liquid very slightly because the power necessary to turn the cylinder is very greatly increased and the spraying effect is largely destroyed if even a small portion of the cylinder is below the level of the surface of the liquid. The inadequacy of certain discs is discussed in U.S. Patent No. 1 462,363 because they cause a considerable flow of liquid in the direction of the movement of the edge of the disc touching the liquid due to the friction of the water on the sides of the discs. Other prior art devices, for example, that described in U.S. Patent No.

1,361,607, employ rotating, inclined discs or impellers to cause a liquid spray to be formed above a body of liquid, but they are similarly limited to dipping only slightly into the body of liquid from which the spray is formed. The peripheral surface (edges) of the discs in U.S.

Patent No. 1,361,607 are generally formed with peculiarly constructed edges.

The foregoing limitations are significant in that only limited amounts of liquid can be picked up by the cylinders or impellers and, additionally. minor increases or decreases of the liquid level or turbulence on the liquid surface can result in improper contact of the rotating member with the body of liquid, thereby causing a diminished and irregular spray to be generated. Consequently, it has become the generally accepted practice in the relevant arts to remove gaseous and/or particulate matter from gas streams by various other means.

In most conventional scrubbers, the intimate gas liquid contact requires the use of pumps for spraying a scrubbing liquid into a vessel through which the gas to be cleaned is passed. Other scrubbing devices use vertically stacked perforated trays on which scrubbing liquid is recycled, and gas forced through the perforations or packed columns is scrubbed by scrubbing liquid passing through the perforations. Other devices use sparging pipes to force the gas to be cleaned through a pool of cleaning liquid. While nozzle devices are relatively efficient, they are subject to clogging by particulate matter contained in the liquid and thus are limited in ability to constantly re-expose the liquid to the gaseous medium.Moreover, such devices cannot be employed in situations where a countercurrent flow of liquid and gas is desirable, for example, when it is necessary to recover efficiently constituents removed from a gas stream. It is also disadvantageous to use most devices which depend upon pumps, spray nozzles, perforated trays, column packings, spargers and the various equipment required to operate these elements because of the significant capital costs and subsequent operating and maintenance costs.

It is the primary object of the present invention to provide an improved apparatus and method for removing gaseous and/or particulate matter from a gas stream.

It is another object of the present invention to provide an improved apparatus and method for generating a liquid spray of large volume above a reservoir of liquid such that the liquid constituting the spray comes into substantial intimate contact with gaseous medium passing above the liquid.

It is another object of the present invention to provide an apparatus and method for effecting intimate contact of gases and liquids in the form of a spray wherein the apparatus operates independently of the level of a body of liquid from which the spray is generated.

It is a further object of the present invention to provide an improved apparatus and method for scrubbing gases with a liquid spray wherein the flow of liquid from which the spray is generated, is in a direction opposite the flow of gas to be scrubbed.

Another object of the present invention is to provide an improved apparatus and method for scrubbing gases wherein the apparatus is relatively simple in construction, reliable in operation, and requires a minimum of servicing and repairs.

The present invention achieves the foregoing objects by providing an apparatus comprising a housing containing a body of liquid in the lower portion and a gas-liquid contact space in the upper portion thereof. The lower portion of the housing includes liquid inlet and outlet means, and similarly, the upper portion includes gas inlet and outlet means.In one aspect of the present invention, there is provided an improved apparatus for effecting intimate contact of gases and liquids, comprising in combination: (a) an elongate horizontally disposed housing having a lower portion for containing a liquid and an upper portion defining a gas-liquid contact space; (b) means for introducing a gaseous medium into the gas-liquid contact space of the housing and means enabling the gaseous medium to exit from the housing; (c) a plurality of disc-shaped impellers having a configuration on the lateral faces capable of forming a spray of liquid into the gas-liquid contact space, the impellers being mounted on a plurality of rotatable shafts axially disposed in the housing and supported above the liquid such that a lower portion of the impellers is substantially immersed in the liquid; and (d) means for rotating the shafts.

Generally, the present invention enhances operative scrubbing efficiency by the use of rotating disc-shaped impellers having a configuration on the lateral faces capable of forming a spray of liquid into the gas-liquid contact space, the disc-shaped or impellers being mounted on a plurality of rotatable shafts axially disposed in a housing and supported above a scrubbing liquid such that a lower portion of the disc-shaped impellers is substantially immersed in the scrubbing liquid. In certain embodiments the rotating disc-shaped impellers have blade-like protrusions for flinging liquid collected on each of the lateral faces thereof, such impellers being mounted on a plurality of parallel rotating shafts supported above a body of liquid so that the lower portions of the impellers are substantially immersed in the liquid.Because the impellers are substantially immersed in the liquid, the apparatus operates independently of the level of the body of liquid. Additionally, immediately adjacent shafts, and therefore, the impellers thereon, are preferably adapted for contrarotation. When the shafts are rotated, the lateral protrusions of the impellers appear to pick up substantial films of liquid and fling or propel them upward into the gas-liquid contact space as a relatively fine spray evenly distributed above the impellers.

The body of liquid contained in the reservoir or lower portion of the housing can be divided into a plurality of smaller compartments by means of partition walls disposed intermediate the housing end walls. Additionally, the liquid inlet and outlet means can be arranged such that the liquid inlet is at the opposite end of the housing relative to the gas inlet, and the liquid outlet is similarly at the opposite end of the housing relative to the gas outlet with the result that the flow of liquid will be opposite the flow of gas to enhance the efficiency of the apparatus.

Additional components, such as agitation means for keeping the liquid in the reservoir in motion, and air sparger means for oxidation of constituents in the body of liquid, are also provided.

In another aspect of the present invention, there is provided an improved method for scrubbing a gas stream containing contaminants removable by the liquid comprising: (a) introducing a gaseous medium containing the contaminants into one end of a gas-liquid contact space positioned above a reservoir of the liquid; (b) forming a spray of the liquid in the gasliquid contact space; (c) passing the gaseous medium containing the contaminants through the spray of liquid in the gas-liquid contact space whereby a contamination-depleted gas is formed; (d) removing the contamination-depeleted gas from the other end of the gas-liquid contact space;; (e) introducing uncontaminated liquid into the reservoir at a point substantially below the point of removal of contamination-depleted gas whereby the spray of liquid formed in the gasliquid contact space at the point of removal of contamination-depeleted gas is substantially uncontaminated liquid spray; and (f) removing contaminated liquid from the reservoir at a point substantially below the point of introduction of the gasesous medium containing contaminatnts.

The present invention overcomes the problems, disadvantages and limitations of the prior art discussed above by providing an apparatus and method which does not involve the use of nozzles or rotating cylinders. The present invention is effective for generating a liquid spray from a body of liquid, such that minor variations in liquid level do not adversely affect efficient operation of the apparatus.

In the accompanying drawings, by way of example only:- Figure 1 is a perspective broken away view of apparatus embodying the present invention; Figure 2 is a cross-sectional view taken along line 2-2 of Figure 1, and showing a configuration of impellers mounted on two rotatable shafts, the impellers being partially immersed in the liquid; Figure 3 is a longitudinal sectional view taken along line 3-3 of Figure 2, and showing the use of partitions to form compartments for containing liquid, oppositely disposed liquid inlet and outlet means, and oppositely disposed gas inlet and outlet means for effecting a countercurrent flow of gas and liquid through the apparatus; and Figure 4 is a cross-sectional view similar to that shown in Figure 2, and showing a configuration of impellers mounted on four rotatable shafts, the impellers being partially immersed in the liquid.

Figure 1 of the drawings illustrates the apparatus of the present invention for effecting intimate contact of gases and liquids. The device comprises an elongated housing or chamber 10.

In the preferred embodiments, housing or chamber 10 is substantially cylindrical. However, the housing or chamber may also be in the form of various other shapes, configurations and geometrical designs which permit the scrubbing of gases by the intimate contact of gases and liquids. In Figure 1, housing 10 is horizontally disposed on a plurality of support members 11, such support members having a semicircular section removed to receive and fit the lower surface of the cylindrical housing. The scrubbing devices of the present invention are substantially horizontal to provide effective scrubbing of gases with the liquid spray and to provide a substantially level body of liquid in which the impellers are immersed.

Although the apparatus of the present invention may be constructed of any suitable material, such as, metal, plastic or the like, when the apparatus of the invention is used for "scrubbing" industrial exhaust gas streams, it is important that housing 10 be constructed of an acid- and alkali-resistant material due to the corrosive nature of the substances with which it comes into contact, for example, alkaline scrubbing solution and acidic constituents of the gas stream.

It is useful for understanding the invention to divide, conceptually, horizontally disposed housing 10 into a lower portion 12 and an upper portion 13, as indicated in the drawings, by visualizing a horizontal plane passing through the longitudinal axis of the housing. During normal operation of the apparatus, housing lower portion 12 contains a body of liquid 14 which is maintained at a level such that the upper surface 15 thereof is located immediately below the conceptualized plane. Within the limits described hereinbelow, the extent to which liquid surface 15 is below the conceptualized plane, is not important for proper generation of liquid spray 16 (not shown in Figure 1) during operation of the apparatus.It is preferable, however that means be provided for maintaining the body of liquid 14 at a predetermined level relative to the axes of the impellers, for example, by supplying liquid at a liquid inlet and by controlling the flow of liquid at a liquid outlet, inlet 17 and outlet 18 being disposed in the walls of housing lower portion 12, thus eliminating the possibility of improper operation due to insufficient or overly abundant liquid. Liquid inlet and liquid outlet means are described in detail in Figure 3.

As used herein, there are no limits upon the portion of the housing occupied by the lower portion (reservoir) containing liquid and the upper portion defining the gas-liquid contact space, as long as there is sufficient contact space for the effective scrubbing of the gas with the liquid in the gasliquid contact space. In most embodiments, and in those illustrated in the drawings, the lower portion for containing liquid (the reservoir) is in the approximately lower one-half of the housing, and the upper portion defining the gas-liquid contact space is in the approximately upper onehalf of the housing.However, the upper and lower portions of other scrubbing devices can be divided as desired, for example, 60% upper portion and 40% lower portion, 40% upper portion and 60% lower portion, 70% upper portion and 30% lower portion, and the like.

The upper portion of the housing is provided with conventional means for introducing the gaseous medium to be scrubbed into the gasliquid contact space and means enabling the scrubbed gaseous medium to exit from the gasliquid contact as illustrated in Figure 3 and discussed in more detail below.

As shown in Figure 1, two rotatable shafts 23 having a plurality of disc-shaped impellers 24 having protrusions 25 extending outwardly of the lateral faces of disc-shaped impellers 24 are positioned longitudinally in elongated housing 10.

The disc-shaped impellers are immersed in liquid 14 in lower portion 12 of the housing so that the rotation of the impellers flings a spray of the liquid into the upper portion of the housing, that is, into the gas-liquid contact space, in the region above the impellers. Shafts 23 are axially mounted by conventional means in the housing a predetermined distance above the body of liquid such that the lower halves of the impellers are substantially immersed in the body of liquid.

The impeller means 22 comprise a plurality of rotary shafts 23 carrying a plurality of disc-shaped impellers 24 having bladelike protrusions 25 extending outwardly of the lateral faces thereof.

The impellers 24 are serially affixed to each of the rotary shafts 23. The rotary shafts 23 are supported above the body of liquid 14 such that the shafts are parallel with the longitudinal axis of the housing 10 and such that the lower halves of the impellers 24 are substantially immersed in the liquid. Rotary motion is imparted to the shafts 23 by a source of power located externally of the housing 10, such as a motor as shown in Figure 3, or the like, thereby causing the bladelike protrusions 25 to throw liquid as spray upwardly into the gas-liquid contact space 13 in the housing 10. Spray 16 is illustrated in Figures 2, 3 and 4.

As used herein, the disc-shaped impellers are "substantially immersed" in the liquid such that a substantial portion of the protrusions 25 extends into the liquid during rotation of shafts 23.

Naturally, a portion of the disc-shaped impeller must extend into the gas-liquid contact space to propel or fling the liquid into the upper portion of the housing, and for example, when 50% of the disc-shaped impeller is immersed in the liquid, 50% of the disc-shaped impeller extends into the gas-liquid contact space.

As shown in Figure 2, by substantially immersing the lower one-half of the impellers 24 into the body of liquid 14 allows bladelike protrusions 25 to fling liquid upwardly into the gas-liquid contact space 13 where the liquid surface 15 is below rotary shaft 23 and above the lowermost circumferential edge of the impellers 24.

The configuration on the lateral faces of the disc-shaped impeller can be any geometrical protrusion or design which will form a spray of liquid when the impeller is substantially immersed and rotated in the liquid. Bladelike protrusions 25 on the lateral faces of the discs or disc-shaped impellers 24 are preferred configurations in the scrubbing devices of the present invention. The protrusion can be mounted on one side of the disc or both sides of the disc.

Although any number of disc-shaped impellers 24 can be mounted on each rotary shaft 23, it is preferred that the impellers be aligned parallel to one another to provide a more uniform spray 16 in the gas-liquid contact space 13. It is further preferred that each rotary shaft 23 be caused to counter rotate relative to adjacent shafts and that at least four such shafts be provided. Such arrangement is desirable in that it will cause the greatest overlap of spray generated by the individual impellers 24.

Increasing or decreasing the number of impellers 24 on each shaft 23 causes a proportional increase or decrease in the volume of spray 16 generated. Thus, the optimum gas-liquid contact can readily be obtained by altering the number of impellers 24 on rotary shafts 23.

Moreover, the characteristics of the spary 1 6 can be varied for different uses of the invention. For example, the size of the liquid droplets comprising the spray 16 and the angle of spraying can be changed by providing impellers 24 of different sizes, changing the design of the lateral protrusions 25 on the impellers, or by increasing or decreasing the rotational velocity of the shafts 23.

The liquid level may be maintained at any desired level, as desired, by conventional means, for example, by pump means and weir means.

Figure 3 illustrates one preferred embodiment of the present invention for supplying and removing liquids from the reservoir by liquid inlet means 17 and liquid outlet means 18. The body of liquid 14 may be maintained at a predetermined level relative to the axes of the impellers by supplying liquid at liquid inlet 17 and by controlling the flow of liquid from the reservoir or body of liquid 14 by liquid outlet 18. Thus, there may be provided means for maintaining the liquid at a predetermined level relative to the axes of the shafts, that is, so that the level of liquid is maintained at a uniform distance from shafts 23.

Generally, the liquid inlet disposed in the lower portion of the housing also provides means for introducing fresh liquid into the housing, and the liquid outlet disposed in the lower portion of the housing, also provides means for removing spent liquid from the housing. In preferred embodiments, liquid inlet 17 is substantially opposite liquid outlet 18.

Figure 3 also illustrates means for introducing the gaseous medium to be scrubbed into the gasliquid contact area and means enabling the gaseous medium exit from housing 10. The gaseous medium enters housing 10 at duct 30 and exits housing 10 at duct 32. The flow of gas in housing 10 is illustrated by arrows 34. Gas entering duct 30 flowing in the direction of arrows 34 is scrubbed by liquid 16 in the form of a mist or spray, in upper portion 13 of housing 10.

The scrubbed gas then exits housing 10 at duct 32 and may be directed to a vent means, a stack and the like (not shown).

In many instances it is desirable to create a countercurrent flow of gaseous medium and liquid 14 during operation of the apparatus, for example, when removing soluble constituents from an industrial exhaust gas stream. Such a countercurrent flow allows maximum loading of the body of liquid 14 with constituents removed from the gaseous medium and is is therefore specially useful when recovery of such constituents is important. To achieve the countercurrent flow in preferred embodiments of the present invention, a liquid inlet is disposed in the lower portion of the housing beneath the means enabling gaseous medium to exit the housing, and a liquid outlet is disposed opposite the inlet in the housing beneath the means for introducing gaseous medium into the housing such that gaseous medium and liquid flow oppositely through the housing.Alternatively stated, the liquid inlet is positioned in the lower portion of the housing adjacent the means for enabling the gasesous medium to exit from the housing, and the liquid outlet is positioned in the lower portion of the housing adjacent the means for introducing the gaseous medium into the gasliquid contact space.

In the embodiment in Figure 3, a countercurrent flow of gaseous medium and liquid is obtained by arranging liquid inlet 17 below gas outlet duct 32 and liquid outlet 18 below gas inlet duct 30 such that the gaseous medium and the liquid are introduced into and withdrawn from the housing 10 at opposite ends thereof. In accordance with the present invention, a more effective counterfiow may be obtained by additionally providing at least one partition wall 26 in the liquid reservoir lower portion 12 of housing 10 to form a plurality of liquid-containing compartments 27. Thus, in certain preferred embodiments of the present invention, there is at least one partition wall disposed in the lower portion for containing liquid to form a plurality of liquid-containing compartments and means for passing the liquid between compartments.

Partition wall 26 is effective to allow flow of liquid between adjoining compartments 27, preferably by liquid flow over the upper surface of partition wall 26 as a weir, but other means, such as walls having perforations, or the like may also be used. Thus, there may be at least one partition wall in the lower portion of the housing to form a plurality of liquid-containing compartments, the surface of the partition wall nearest the surface of the liquid being submerged in the liquid sufficient to allow liquid flow between the compartments.

End wall 19 forms the outer end wall of lower portion or reservoir 12 and upper portion 13.

When partition walls are placed in the reservoir or lower portion 12, gaseous medium passing through the gas-liquid contact space 13 becomes purified as it approaches gas outlet means 21, and the compartments 27 nearer the liquid outlet means 18 contain progressively greater amounts of constituents removed from the gaseous medium. To prevent particulate matter from settling to the bottom of compartments 27, conventional agitation means 28 may be provided therein for keeping the liquid 14 in motion and particulate matter in suspension. As shown in Figures 2-4, stirring means 28 by driven motors 36 provide the appropriate agitation. Particulate matter exiting through the liquid outlet 18 can be extracted from the liquid by conventional methods, for example by filtration or settling.

In certain instances, it is desirable to oxidize or react dissolved substances (contaminants) in the liquid in reservoir or lower portion 12. These dissolved substances are often contaminants or constituents resulting from the intimate gas/liquid contact. The oxidation or reaction can be accomplished by injecting air or other medium into the liquid which causes the oxidation or reaction of the contaminant or contaminants. The medium injected into the liquid can be another liquid, but in preferred embodiments, it is a gas.

Thus, in certain embodiments of the present invention, a gaseous medium is introduced into the liquid in the reservoir to cause oxidation of at least some of the contaminants or constituents in the contaminated liquid. Conventional means may be provided for introducing a gaseous medium into the liquid to cause oxidation of the constituents dissolved in the liquid as a result of intimate gas-liquid contact.

For example, in Figure 3, when it is desired to oxidize matter in liquid 14, air sparger means 29 may be installed in a compartment or compartments 27 formed by housing end wall 19 and partition wall 26 and/or by adjacent partition walls 26. If the apparatus is used to remove sulfur oxides from a flue gas generated by a coal burning power plant, an air sparger can be used to convert calcium sulfur salts into gypsum for use in cement and wallboard manufacture. In this instance, the contamination depleted or scrubbed gas is a gas depleted of sulfur oxides.

Because the gaseous medium passes through gas-liquid contact space 13 with substantial velocity, spray 16 tends to be blown into gaseous medium outlet duct 32. Accordingly, in certain embodiments, it is desirable to provide means for removing liquid contained in the contaminationdepleted or scrubbed gas. Demister means 40 proximal or interior of outlet duct 32 may be used to retain the spray 16 within the gas-liquid contact space 13. Moreover, such demister means 40 serves to minimize exhaust stack corrosion due to acid condensation.

In one preferred embodiment of the present invention, there is provided an improved apparatus for effecting intimate contact of gases and liquids, comprising in combination: (a) an elongated horizontally disposed housing having a lower portion for containing a liquid and an upper portion defining a gas-liquid contact space; (b) means for introducing a gaseous medium into the gas-liquid contact space of the housing and means enabling the gaseous medium to exit from the housing; (c) a plurality of disc-shaped impellers having protrusions extending outwardly of the lateral faces thereof, the impellers being mounted on at least four rotatable shafts axially disposed in the housing and supported above the liquid such that the lower halves of the impellers are substantially immersed in the liquid; (d) means for rotating immediately adjacent shafts in opposite directions; (e) a liquid inlet disposed in the lower portion of the housing and a liquid outlet disposed in the lower portion of the housing; and (f) at least one partition wall in a position intermediate the ends of the lower portion of the housing to form a plurality of liquidcontaining compartments. Optionally, agitation means may be disposed in the lower portion of the housing for maintaining the liquid in constant motion; means may be provided for introducing a gaseous medium into the liquid to cause precipitation of constituents dissolved in the liquid as a result of intimate gas-liquid contact; and/or means may be disposed in the means enabling gaseous medium to exit the housing to prevent loss of liquid spray from the housing.

In one specific method of the present invention where sulfur dioxide is removed from a gaseous stream by the use of calcium-containing compounds in water, for example, pulverised limestone or lime, (a) the gaseous stream or medium containing the sulfur dioxide is introduced into one end of a gas-liquid contact space positioned above a reservoir of the calciumcontaining water; (b) a spray of the calciumcontaining water is formed in the gas-liquid contact space; (c) the gaseous medium containing the sulfur dioxide gas is passed through the spray of calcium-containing water in the gas-liquid contact space whereby a gas depleted of sulfur dioxide is formed; (d) the gaseous medium depleted of sulfur dioxide is removed from the other end of the gas-liquid contact space positioned above a reservoir of the calcium-containing liquid; (e) fresh calciumcontaining water is introduced into the reservoir at a point substantially below the point of removal of sulfur dioxide-depleted gas whereby the spray of calcium-containing water formed in the gasliquid contact space at the point of removal of sulfur dioxide-depleted gas is substantially concontaminated calcium-containing water spray; (f) air is introduced into the calcium-containing water in the reservoir to convert calcium-sulfur salts contained therein into gypsum-containing water; (g) the gypsum-containing water is removed from the reservoir at a point substantially below the point of introduction of the gaseous medium containing sulfur dioxide; and (h) the gypsum is recovered. The calciumcontaining water may be agitated in the reservoir to maintain the precipitated gypsum in suspension.

Figure 4 illustrates an embodiment of the present invention wherein four rotatable shafts are used in housing 10 to support a plurality of disc-shaped impellers on each shaft. Each rotatable shaft is preferably rotated independently of the other shafts for example by a motor 48 as illustrated in Figure 3, so that immediately adjacent shafts can be contra-rotated. As shown by the arrows in Figure 4, the shaft nearest one wall is rotated counterclockwise; the next adjacent shaft is rotated clockwise; the next adjacent shaft is rotated counterclockwise; and the shaft nearest the other wall is rotated clockwise. Naturally, each shaft may also be rotated opposite that shown in Figure 4 to achieve the preferred embodiment of the present invention which provides means for contra rotating immediately adjacent shafts.

While other modifications of the invention and variations thereof which may be employed within the scope of the invention have not been described, the invention is intended to include such modifications as may be embraced within the following claims.

Claims

1. Improved apparatus for effecting intimate contact of gases and liquids, comprising in combination: (a) an elongated horizontally disposed housing having a lower portion for containing a liquid and an upper portion defining a gas-liquid contact space; (b) means for introducing a gaseous medium into the gas-liquid contact space of the housing and means enabling the gaseous medium to exit from the housing; (c) a plurality of disc-shaped impellers capable of forming a spray of liquid into the gas-liquid contact space, the impellers being mounted on a plurality of rotatable shafts axially disposed in the housing and supported above the liquid such that a lower portion of the impellers is substantially immersed in the liquid; and (d) means for rotating the shafts.

2. The apparatus of Claim 1, further comprising a liquid inlet disposed in the lower portion of the housing, the liquid inlet providing means for introducing fresh liquid into the housing, and a liquid outlet disposed in the lower portion of the housing, the liquid outlet providing means for removing spent liquid from the housing.

3. The apparatus of Claim 2 wherein the liquid inlet is substantially opposite the liquid outlet.

4. The apparatus of Claim 2 wherein the liquid inlet is positioned in the lower portion of the housing adjacent the means for enabling the gaseous medium to exit from the housing and the liquid outlet is positioned in the lower portion of the housing adjacent the means for introducing the gaseous medium into the gas-liquid contact space.

5. The apparatus of Claim 1 further comprising at least one partition wall disposed in the lower portion for containing liquid to form a plurality of liquid-containing compartments and means for passing the liquid between compartments.

6. The apparatus of Claim 1 further comprising means for maintaining the liquid at a predetermined level relative to the axes of the shafts.

7. The apparatus of Claim 6 wherein the means for maintaining the liquid at a predetermined level comprises a liquid inlet disposed in the lower portion of the housing beneath the means enabling gaseous medium to exit the housing, and a liquid outlet disposed opposite the inlet in the housing beneath the means for introducing gaseous medium into the housing such that gaseous medium and liquid flow oppositely through the housing.

8. The apparatus of Claim 7 further comprising at least one partition wall in the lower portion of the housing to form a plurality of liquid-containing compartments, the surface of the partition wall nearest the surface of the liquid being submerged in the liquid sufficient to allow liquid flow between the compartments.

9. The apparatus of Claim 1 comprising at least four rotatable shafts having a plurality of discshaped impellers on each shaft.

10. The apparatus of Claim 1, wherein the means for rotating the shafts includes means for contra-rotating immediately adjacent shafts.

11. The apparatus of Claim 1 wherein the plurality of rotatable shafts comprises at least four shafts and said apparatus further comprises means for rotating adjacent shafts in opposite directions.

12. The apparatus of Claim 1 further comprising agitation means disposed in the lower portion of the housing for maintaining the liquid in constant motion.

13. The apparatus of Claim 1 further comprising means for introducing a gaseous medium into the liquid to cause oxidation of constituents dissolved in the liquid as a result of intimate gas-liquid contact.

14. The apparatus of Claim 1 , further comprising de-mister means to prevent loss of liquid spary from the housing, the de-mister means being disposed in the means enabling gaseous medium to exit the housing.

15. The apparatus of Claim 1 wherein the discshaped impeller having a configuration capable of forming a spray of liquid into the gas-liquid contact space has protrusions extending outwardly of the lateral faces thereof.

16. Improved apparatus for effecting intimate contact of gases and liquids, comprising in combination: (a) an elongate horizontally disposed housing having a lower portion for containing a liquid and an upper portion defining a gas-liquid contact space; (b) means for introducing a gaseous medium into the gas-liquid contact space of the housing and means enabling the gaseous medium to exit from the housing; (c) a plurality of disc-shaped impellers having protrusions extending outwardly of the lateral faces thereof, the impellers being mounted on at least four rotatable shafts axially disposed in the housing and supported above the liquid such that the lower halves of the impellers are substantially immersed in the liquid:: (d) means for rotating immediately adjacent shafts in opposite directions; (e) a liquid inlet disposed in the lower portion of the housing and a liquid outlet disposed in the lower portion of the housing; and (f) at least one partition wall in a position intermediate the ends of the lower portion of the housing to form a plurality of liquid-containing compartments.

17. The apparatus of Claim 16 further comprising agitation means disposed in the lower portion of the housing for maintaining the liquid in constant motion.

18. The apparatus of Claim 16 further comprising means for introducing a gaseous medium into the liquid to cause oxidation of constituents dissolved in the liquid as a result of intimate gas-liquid contact.

19. The apparatus of Claim 16 further comprising means disposed in the means enabling gaseous medium to exit the housing to prevent loss of liquid spray from the housing.

20. A method for scrubbing a gas stream containing contaminants removable by a liquid comprising: (a) introducing a gaseous medium containing the contaminants into one end of a gas-liquid contact space positioned above a reservoir of the liquid; (b) forming a spray of the liquid in the gas liquid contact space; (c) passing the gaseous medium containing the contaminants through the spary of liquid in the gas-liquid contact space whereby a contamination-depleted gas is formed; (d) removing the contamination-depleted gas from the other end of the gas-liquid contact space; (e) introducing uncontaminated liquid into the reservoir at a point substantially below the point of removal of contamination-depleted gas whereby the spray of liquid formed in the gasliquid contact space at the point of removal of contamination-depeleted gas is substantially uncontaminated liquid spray; and (f) removing contaminated liquid from the reservoir at a point substantially below the point of introduction of the gaseous medium containing contaminants.

21. The method of Claim 20 further comprising maintaining the liquid at a predetermined level in the reservoir.

22. The method of Claim 20 further comprising agitating the liquid in the reservoir.

23. The method of Claim 20 further comprising introducing a gaseous medium into the liquid in the reservoir to cause oxidation of at least some of the contaminants in the contaminated liquid.

24. The method of Claim 20 further comprising removing liquid contained in the contaminationdepleted gas.

25. A method for removing sulfur dioxide from a gaseous stream by the use of a calciumcontaining compound in water, comprising: (a) introducing the gaseous medium containing the sulfur dioxide into one end of a gas-liquid contact space positioned above a reservoir of the calcium-containing water; (b) forming a spray of the calcium-containing water in the gas-liquid contact space; (c) passing the gaseous medium containing the sulfur dioxide gas through the spray of calciumcontaining water in the gas-liquid contact space whereby a gas depleted of sulfur dioxide is formed; (d) removing the gaseous medium depleted of sulfur dioxide from the other end of the gas-liquid contact space positioned above a reservoir of the calcium-containing liquid;; (e) introducing fresh calcium-containing water into the reservoir at a point substantially below the point of removal of sulfur dioxide-depleted gas whereby the spray of calcium-containing water formed in the gas-liquid contact space at the point of removal of sulfure dioxide-depleted gas is substantially uncontaminated calciumcontaining water spray; (f) introducing air into the calcium-containing water in the reservoir to convert calcium-sulfure salts contained therein into gypsum-containing water; (g) removing the gypsum-containing water from the reservoir at a point substantially below the point of introduction of the gaseous medium containing sulfur dioxide; and (h) recovering the gypsum.

26. The method of Claim 25 further comprising agitating the calcium-containing water in the reservoir to maintain the precipitated gypsum in suspension.

27. The method of Claim 25 wherein the calcium-containing compound is lime.

28. The method of Claim 25 wherein the calcium-containing compound is pulverised limestone or lime.

29. Apparatus for effecting intimate contact of gases and liquids, the apparatus being substantially as herein described with reference to the accompanying drawings.

30. A method of scrubbing a contaminated gas stream, the method being substantially as herein described with reference to the accompanying drawings.