WO2003008106A1

WO2003008106A1 - Apparatus for gas/liquid contacting

Info

Publication number: WO2003008106A1
Application number: PCT/GB2002/003297
Authority: WO
Inventors: Andrew Bryan Birchall; Michael James Bridge; Gary Francis Coulton; David Gregory Hall; Frederick George Hardy; Jonathan Holgate; Richard Mills; John William Stairmand
Original assignee: Accentus Plc
Priority date: 2001-07-18
Filing date: 2002-07-15
Publication date: 2003-01-30
Also published as: EP1406731B1; ES2242035T3; ATE296165T1; DE60204319D1; DE60204319T2; EP1406731A1; GB0117544D0

Abstract

A gas/liquid contactor apparatus comprises a vortex chamber (12) having at least one tangential inlet port (13) for gas, an axial gas outlet port (14), and, within the chamber, a liquid spray generator (18,19). An upper chamber (31) has a baffle (32) and a gas outlet conduit (33) shaped so that liquid droplets, from any liquid carried over in the gas stream, which collect and coalesce on the underside of the top surfaces of the upper chamber (31) flow, under the combined effect of gravity and the gas flow on the surfaces, outwardly and downwardly to the side wall of the upper chamber (31).

Description

Apparatus for gas/liquid contacting.

The invention relates to apparatus for gas/liquid contacting, and in particular for providing intimate contact between a spray of liquid droplets and a flowing gas to provide an effective scrubbing action with minimum opportunity for any part of the gas flow through the spray to avoid contact with liquid.

The vortex chamber gas/liquid contactor described in patent GB 2282983 is an apparatus which provides a particularly effective gas/liquid contact in this way. The present invention is a development of the apparatus of GB 2282983.

The apparatus is designed to operate with gas and liquid flows such that the liquid droplet size and velocity in relation to the desired gas flow velocity will provide liquid surface area exposure to the gas which is as high as possible without the liquid droplets becoming entrained in the gas stream before they strike the side walls of the vortex chamber, where they coalesce and are able to run down the side wall for collection in the sump below. This involves compromises since smaller droplets give greater liquid surface area exposure to the gas, but smaller droplets are more readily entrained in the gas stream and there is a limit to the extent to which this can be compensated by increasing the droplet velocity. A disadvantage of the form of apparatus as described in GB 2282983 is the lack of flexibility to increase gas flow rates when desired because of excessive carry-over of liquid into the outlet conduit.

It is an object of the present invention to provide an improved gas/liquid contactor apparatus. Some amelioration of the above mentioned disadvantage is achieved by providing a baffle arrangement for the gas to flow past before it enters the outlet duct. However, we have found that particular precautions are necessary in shaping the gas flow passage downstream of the baffle to avoid undesirable accumulations of liquid collecting on surfaces from which coalesced droplets can be driven by the gas flow and released into the fast flowing gas stream exiting from the outlet duct.

According to the invention there is provided a gas/liquid contactor apparatus comprising a vortex chamber having at least one tangential inlet port for gas, an axial gas outlet port, and, within the chamber, a liquid spray generator which when fed with liquid generates a spray of liquid droplets to fill a substantial proportion of the vortex chamber with liquid droplets, a sump and liquid flow passages for returning liquid cascading down the side walls of the vortex chamber to the sump, the axial gas outlet port leading to a further chamber which, in use of the apparatus, is substantially vertically above the said axial gas outlet, a baffle in the said further chamber, which baffle presents a transversely extending surface spaced above the axial gas outlet and the projected area of which encompasses at least the same area as the axial gas outlet, a gas outlet conduit extending upwardly from the top of the said further chamber, and all surfaces of the said further chamber above the baffle being inclined to the horizontal so that any liquid droplets impinging upon them are able to flow downwards under gravity over the surface towards the periphery of the said further chamber, through the bottom wall of which one or more liquid passages are provided for return of liquid to the sump. Preferably the liquid spray generator is of the type in which opposed jets of liquid impinge upon each other and are disrupted to form a spray of droplets and the liquid is supplied to the liquid spray generator under conditions in which the flow is at least partially turbulent, preferably under conditions for which the Reynolds number is greater than 12,000, so that the droplets in the spray are projected outwardly from, and transverse to the flow direction of, the opposed jets of liquid with a random distribution of the angular relationship between the direction of movement of the droplets and the direction of flow of the said opposed jets of liquid.

Specific constructions of apparatus embodying the invention will now be described by way of example and with reference to the drawings filed herewith in which:

Figure 1 is a diagrammatic cross sectional view of an apparatus,

Figure 2 is a highly diagrammatic representation of a modified apparatus,

Figure 3 is a plan view of a component of an apparatus such as shown in Figure 1 or 2 , and

Figure 4 is a similar view of a modified component,

Figure 5 is a highly diagrammatic representation of a two-stage apparatus,

Figures 6a, 6b, 6c, 6d, are respectively a partially exploded perspective view, a transverse cross-section, a side view and a longitudinal sectional view of a modified form of nozzle arrangement, Figures 7a, 7b, 7c, are respectively a diagrammatic side view, a longitudinal part sectional view, and a section on line X-X of Figure 7b of another modified form of nozzle arrangement, and

Figures 8a and 8b are respectively a diagrammatic side view and a view at double scale on the line Y-Y of Figure 8a of a nozzle arrangement of the type used in the example of Figure 1 modified by the addition of a baffle plate.

Referring to Figure 1, the apparatus comprises a vortex chamber gas/liquid contactor 11 of the general type described in patent GB 2282983.

The contactor 11 comprises a cylindrical vortex chamber 12 which has a tangential gas inlet port 13 and an axial gas outlet port 14. A liquid feed pipe 15 divides into two branches 16 and 17 which enter into the vortex chamber 12 and terminate in two axially opposed nozzles 18 and 19, respectively. The opposed nozzles are, in this example, aligned with the central axis of the vortex chamber 12. A plate 20 extends across the lower part of the vortex chamber 12 and the portion of the vortex chamber below the plate 20 forms a sump 21 for liquid 22 which is withdrawn through an outlet 23 and recirculated by a pump 24 to the feed pipe 15.

Gas to be contacted with the liquid is fed to the tangential inlet 13 of the vortex chamber 12.

The pump 24 is such as to drive the liquid through the feed pipe 15 and branches 16, 17 so that the flow of the opposed liquid jets emerging from the nozzles 18, 19 is turbulent, having a Reynolds number in excess 12,000. Under these conditions, the impinging jets of liquid at 25 are formed into a spray of droplets which are projected in all directions outwardly from, and transverse to the flow direction of, the opposed jets of liquid. Because of the turbulence in the impinging liquid jets, there is a random distribution of the angular relationship between the direction of movement of the droplets and the direction of flow of the said opposed jets of liquid. The vortex chamber 12 is, in this way, very effectively filled with droplets of liquid which are collected by their impact on the outer wall of the vortex chamber. The collected droplets flow down the outer wall and via pipes 26 into the sump 21, from which this collected liquid is available for re-circulation.

Gas entering the vortex chamber 12 via the tangential inlet port 13 is caused to swirl through the chamber 12 and ultimately exit axially by outlet port 14. The gas is thus subjected to a particularly effective scrubbing interaction with the spray of droplets of the liquid. The gas, having interacted with the liquid is released via outlet port 14. Ideally, the liquid droplet size and velocity relative to the gas velocity are such that there is effective gas liquid interaction but without any carry-over of liquid droplets in the gas emerging from the outlet port 14. However, this is difficult to achieve in practice, particularly if it is required to have some flexibility in the gas flow velocities accommodated by the apparatus.

For removal of liquid droplets which may be carried in this way in gas emerging from outlet port 14, the apparatus is provided with an upper chamber 31 which receives the gas emerging from the outlet port 14 from the vortex chamber 12. A baffle 32 provides a transversely extending surface spaced above the gas outlet port 14. In this example, the baffle is in the form of a horizontal circular plate centred over the outlet port 14 and of diameter greater than the outlet port 14 so that the projected area of the baffle encompasses a greater area than the axial gas outlet port 14.

Gas emerging from the outlet port 14 is thus caused to flow outwardly past the baffle 32 before flowing inwardly and making its final exit via gas outlet conduit 33.

Liquid droplets collecting and coalescing on the under surface of baffle 32 fall as large droplets under the combined effect of gravity and the flowing gas. Mostly these large droplets fly outwardly and downwardly to the side wall of the upper chamber 31, and then flow down the side wall. Some droplets may fall either directly back into the vortex chamber via the outlet port 14 or onto the top surface 34 of the vortex chamber 12. Any liquid collecting on the surface 34 in this way, or by direct deposit of liquid droplets from the flowing gas, is returned to the sump 21 via one or more passages, one of which is shown at 35.

We have found that the shape of the gas outlet conduit 33 is important. Conventionally, this would be a simple pipe connected to a central aperture in a flat top plate of the upper chamber 31, the diameter of the aperture corresponding to that of the outlet port 14 from the vortex chamber 12. However, such a configuration results in liquid droplets, which collect on the underside of such a top plate on the upper chamber 31, coalescing and being driven by the gas flow towards the relatively small diameter central outlet pipe. These coalesced droplets can then be entrained into the fast flowing gas in the outlet pipe To avoid this the gas outlet conduit 33 is shaped to provide that all surfaces above the baffle 32 are inclined to the horizontal so that liquid coalescing on them flows under the influence of gravity towards the side wall of the upper chamber 31. The arrangement is such that this flow of collected liquid over the inclined surfaces of the gas outlet conduit guides liquid droplets to flow down the side wall of the upper chamber 31, or at least to fall as droplets onto the top surface 34 of the vortex chamber 12.

For ease of manufacture, a preferred shape for the gas outlet conduit 33 is as shown, with a conical section extending from a diameter at or close to the diameter of the upper chamber 31 to a smaller diameter where the conical section is joined to cylindrical outflow pipe 37. The latter desirably projects inwardly below the top of the conical section, to provide a lip 38, which further helps to ensure that coalesced droplets of liquid on the surface of the conical section are not entrained into the gas flow in the pipe 37.

The angle of the conical section is chosen so that, under the combined effects of gravity and the maximum gas flow velocity for which the contactor is designed, coalesced droplets of liquid which form on the conical section stay on the surface and flow down towards the side wall of the upper chamber 31. In the present example a conical section having an angle of 17 degrees or more to the horizontal has been found to be satisfactory.

The baffle 32 may, with some advantage, be constructed to have a conical top surface, as indicated by the dotted lines 36. Any liquid droplets collecting on the top surface of the baffle 32 and coalescing into larger droplets are then encouraged by gravity to flow down to the edge of the baffle 32 and then fly, with the other liquid droplets collected on the underside of baffle 32, outwardly and downwardly under the combined influences of gravity and the flowing gas towards the side walls of the upper chamber 31.

Figure 2 illustrates in highly diagrammatic form an apparatus similar to that shown in Figure 1 but with a number of improvements some or all of which may be incorporated in the apparatus with advantage.

Referring to Figure 2, components corresponding to those shown in Figure 1 are referenced with the same reference numerals distinguished by the suffix "a" . The improvements are all for the purpose of reducing the possibilities for liquid droplets to be carried over into the exiting gas stream at 41. Thus, in Figure 2 the underside of the roof of the vortex chamber 12a is provided with one or more (three are shown in the Figure 2) concentric downwardly depending lips 43 which serve to trap small liquid droplets carried by the gas approaching the outlet 14a, the droplets coalescing into larger droplets on the lips 43 and falling back into the vortex chamber 12a. This underside of the roof of the vortex chamber 12a is also provided with a series of radially extending vanes 42 which serve to reduce the vortex swirling of the gas at the top of the vortex chamber 12a as it approaches the outlet port 14a.

In the space between the top 34a of the vortex chamber 12a and the baffle 32a a series of radially extending thin vertical plates 44 is provided. These plates 44 serve further to reduce swirling of the gas in this region and also serve as baffles trapping liquid droplets that may have carried over in the gas as it exits through outlet port 14a. The baffle 32a is provided at its outer periphery with a downwardly projecting circumferential lip 45, which serves to prevent liquid droplets driven along the underside of the baffle 32a from running around the outside edge onto the top of the baffle 32a, from where the liquid could become re- entrained into the gas .

A further feature shown in Figure 2 is the provision of a lute or "U" bend 46 in the gas outlet pipe. Liquid disentrained from the gas by its passage round this "U" bend is returned to the sump 21a via pipe 47.

Liquid droplets returning to the top 34a of the vortex chamber 12a are driven by the gas flow towards the periphery from where the liquid is returned via one or more passages to the sump 21a. Figure 2 shows an improvement in which a circumferential trough 48 is provided around the periphery at the top 34a of the vortex chamber 12a to collect this liquid and direct it towards the passages to the sump 21a. In the example shown in Figure 2, these passages are provided by one or more pipes, one of which is shown at 49 in the Figure, and which is positioned outside the vortex chamber 12a so as to avoid the introduction of an obstruction in the vortex chamber 12a.

Figure 3 shows dramatically a view of the top 34 of the vortex chamber 12 with its outlet port 14 as configured in the example of Figure 1 (and also Figure 2) . Figure 4 shows a modification in which the single large outlet port 14 is replaced by a multiplicity of smaller holes 51. This arrangement serves as a vortex breaker to reduce the vorticity of the gas and thus reduce its energy and momentum as it enters the space between the top 34 of the vortex chamber 12 and the baffle 32. Further provision for disentraining of liquid from the out-flowing gas may comprise:

(i) increasing the diameter of the pipe 37 so as to reduce the velocity of the exiting gas thereby encouraging disentrainment of liquid droplets.

(ii) extending the pipe 37 down into contact with the top of baffle 32 and providing access into the pipe 37 for the flowing gas by a plurality of apertures in this extension of the pipe 37. The apertured pipe wall thus functions effectively as a further baffle trapping entrained liquid droplets.

(iii) a heat transfer coil may be provided in the gas flow path downstream of the outlet port 14. Cooled, such a coil will encourage condensation and reduce the amount of liquid vapour in the gas stream. Heated, it could vaporise liquid droplets. Heat to such a coil could be provided by a heat exchange arrangement with the incoming gas .

(iv) the vortex chamber may be reshaped so that both its roof and base are in the form of a shallow, upwardly pointing cone to encourage flow of liquid away from the axial gas outlet port 14, whilst maintaining the cross- sectional area of the chamber.

(v) a coarse mesh pad may be incorporated in the gas flow path downstream of the outlet port 14.

To provide more than 1 stage of treatment in a vortex chamber gas/liquid contactor, multiple stages may readily be applied, for example, by choosing any suitable multiple stage version as described in patent GB 2282983. Figure 5 illustrates highly diagrammatically a two- stage arrangement with a modification for alleviating the problem of supporting, in the upper stage, a sump containing sufficient liquid to seal the passageways draining into the sump against possible blow through of gas at the pressure at which it is introduced into the vortex chamber. Components in the upper stage of the apparatus as shown in Figure 5 corresponding to those in Figure 1 are referenced with the same reference numerals, distinguished by suffix "b" . The sump 21b of the upper stage is connected by pipe 51 to overflow down into the sump of the lower stage from where liquid is drawn to the pump 24b for supply to the nozzle pairs. However, the sump 21b of the upper stage differs from that of the lower stage in that its base is formed with a "top hat" section 52. This configuration serves to reduce the volume and weight of liquid in the sump 21 whilst maintaining an adequate liquid head to prevent blow through of gas from the vortex chamber 12b.

A possible alternative to the arrangement shown in Figure 5 is for the drain down passages from an upper vortex chamber to lead directly into the sump of the lower vortex chamber.

In a typical nozzle arrangement (an example of which, with a modification, is shown in Figure 8, described more fully below) the required accuracy and rigidity of relative location of the nozzles 18 and 19 is secured by tie bars (referenced 61 in Figure 8) . A disadvantage of the presence of such tie bars is that they present obstructions to the spray of liquid droplets from the impinging liquid jets issuing from the nozzles 18, 19. Not only do these obstructions create "shadow" regions in the vortex chamber which the spray of liquid droplets does not reach, but also the droplets impinging on the tie bars tend to break up into smaller droplets more easily entrained into the gas flow.

To avoid or reduce these problems modified nozzle assembly designs may be adopted. For example, a nozzle assembly designed as described in WO 01/08809 may be adopted. Figures 6 and 7 illustrate further alternatives. Referring to Figure 6 relative axial location and separation of the nozzles 18, 19 is provided by a cruciform insert 53 which is received as an interference fit in grooves within the nozzles.

In the arrangement shown in Figure 7, the nozzles 18, 19 are formed with integral end plates and are joined together by a neck region 54. The end plates and are provided with apertures 56, 57, 58, 59 which, in this example, form effectively two pairs of opposed nozzle outlets. The presence of the neck region 54 prevents each nozzle pair from providing 360 degrees spray, but together the two pairs of opposed nozzles provide spray extending around a full 360 degrees. It will be appreciated that more than two pairs of opposed nozzles may be provided in a nozzle head of this design.

Figure 8 shows a nozzle arrangement in which the relative axial location and separation of the nozzles is provided by tie bars 61. A further problem we have identified with this form of nozzle structure is that many of the liquid droplets broken up and/or deflected by the tie bars 61 fly directly up towards the outlet port

14 and become entrained with the exiting gas. Figure 8 shows a solution to this problem by providing on the upper nozzle a circular baffle plate 62 positioned and dimensioned to intercept any liquid droplets flying directly towards the outlet port 14. We believe that this problem does not occur to any serious extent with the above described nozzle assembly designs which avoid the use of tie bars. However, it will be appreciated that a similar shape, size and positioning of baffle plate may be provided with any of these nozzle assembly designs if they are found to generate stray liquid droplet spray in the direction of the outlet port 14.

An alternative approach for avoiding or reducing the problem of spray from a nozzle assembly flying directly up towards the outlet port 14 is to position the nozzle assembly off-centre so that it is not directly under the axial gas outlet port 14. To avoid non-uniformity in the spray distribution within the vortex chamber it may be desirable to position more than one nozzle assembly off- centre, but symmetrically disposed within the vortex chamber .

In some circumstances using a symmetrical arrangement with oppositely directed impinging liquid jets of equal velocity, it is difficult to provide for the spray to extend fully up to the top of the vortex chamber. A solution to this problem is to adopt a "biased" nozzle operation using, for example, a larger nozzle outlet aperture for the lower nozzle than for the upper nozzle. This will tend to bias the droplet spray distribution upwardly. It may be appropriate (but not necessarily essential) also to position such a biased nozzle below the centreline of the vortex chamber. Since nozzle assemblies designed to bias the spray upwardly are more likely to send spray directly towards the outlet port 14, it may be advisable also with such nozzles to adopt an off-centre arrangement such as described above.

The invention is not restricted to the details of the foregoing example. For instance, the gas outlet conduit need not necessarily be right conical as shown, but may have a curved shape in cross section, for example trumpet shaped. However, it is important that any such curvature is limited to avoid presenting a surface to the gas flow which would permit the gas to drive coalesced droplets along that surface towards the gas outlet conduit. The baffle 32 should have a diameter which at least matches the diameter of the outlet port 14, but is preferably as shown with a diameter significantly greater than that of the outlet port 14.

The apparatus may be modified to operate in accordance with the method described in our co-pending patent application No. GB01 14116.7

Claims

1. A gas/liquid contactor apparatus comprising a vortex chamber (12; 12a; 12b) having at least one tangential inlet port (13; 13a; 13b) for gas, an axial gas outlet port (14; 14a; 14b) , and, within the chamber (12;12a; 12b) , a liquid spray generator (18, 19; 18a, 19a; 18b, 19b) which when fed with liquid generates a spray of liquid droplets to fill a substantial proportion of the vortex chamber (12;12a;12b) with liquid droplets, a sump (21 ; 21a;21b) and liquid flow passages (26; 26a; 26b) for returning liquid cascading down the side walls of the vortex chamber (12 ; 12a,-12b) to the sump (21;21a,-21b) , the axial gas outlet port (14; 14a; 14b) leading to a further chamber (31; 31a; 31b) which, in use of the apparatus, is substantially vertically above the said axial gas outlet (14 ; 14a; 14b) , characterised by the features in combination comprising a baffle (32 ; 32a; 32b) in the said further chamber (31; 31a;31b) , which baffle (32;32a;32b) presents a transversely extending surface spaced above the axial gas outlet (14; 14a; 14b) and the projected area of which encompasses at least the same area as the axial gas outlet (14;14a,-14b) , a gas outlet conduit (37; 37a; 37b) extending upwardly from the top of the said further chamber (31;31a; 31b) , and all surfaces of the said further chamber (31; 31a; 31b) above the baffle (31; 32a; 32b) being inclined to the horizontal so that any liquid droplets impinging upon them are able to flow downwards under gravity over the surface towards the periphery of the said further chamber (31;31a; 31b) , through the bottom wall of which one or more liquid passages (35; 49; 35b) are provided for return of liquid to the sump (21;21a,-2lb) .

2. A gas/liquid contactor apparatus as claimed in claim 1, wherein the liquid spray generator (18, 19; 18a, 19a; - 16 -

18b, 19b) is of the type in which opposed jets of liquid impinge upon each other and are disrupted to form a spray of droplets and the liquid is supplied to the liquid spray generator under conditions in which the flow is at least partially turbulent, so that the droplets in the spray are projected outwardly from, and transverse to the flow direction of, the opposed jets of liquid with a random distribution of the angular relationship between the direction of movement of the droplets and the direction of flow of the said opposed jets of liquid.

3. A gas/liquid contactor apparatus as claimed in claim 2, wherein the liquid is supplied to the liquid spray generator under conditions for which the Reynolds number is greater than 12,000.

4. A gas/liquid contactor apparatus as claimed in any of claims 1 to 3 , wherein the gas outlet conduit has at least one region of conical form extending from a diameter matching or close to matching that of the said further chamber (31; 31a; 31b) to a smaller diameter where gas passes into a cylindrical outflow pipe (37;37a,-37b) .

5. A gas/liquid contactor apparatus as claimed in any of the preceding claims, further characterised in that the underside of the roof of the vortex chamber (12; 12a; 12b) is provided with one or more concentric downwardly depending lips (43) which serve to trap small liquid droplets carried by the gas approaching the outlet port (14;14a;14b) , the droplets coalescing into larger droplets on the lip or lips (43) and falling back into the vortex chamber (12 ; 12a; 12b) .

6. A gas/liquid contactor apparatus as claimed in any of the preceding claims, further characterised in that the underside of the roof of the vortex chamber (12; 12a; 12b) is provided with a series of radially extending vanes (42) which serve to reduce the vortex swirling of the gas at the top of the vortex chamber (12; 12a; 12b) as it approaches the outlet port (14; 14a; 14b) .

7. A gas/liquid contactor apparatus as claimed in any of the preceding claims, further characterised in that a series of radially extending thin vertical plates (44) is provided in the space between the top (34a) of the vortex chamber (12a) and the baffle (32a) .

8. A gas/liquid contactor apparatus as claimed in any of the preceding claims, further characterised in that the baffle (32a) is provided at its outer periphery with a downwardly projecting circumferential lip (45) .

9. A gas/liquid contactor apparatus as claimed in any of the preceding claims, further characterised in that a circumferential trough (48) is provided around the periphery at the top (34) a of the vortex chamber (12a) .

10. A gas/liquid contactor apparatus as claimed in any of the preceding claims, further characterised in that between the liquid spray generator (18, 19; 18a, 19a; 18b, 19b) and the outlet port (14 ; 14a,- 14b) the is provided a baffle plate (62) positioned and dimensioned to intercept any liquid droplets flying directly towards the outlet port (14 ; 14a; 14b) .