GB2110950A - Rotary apparatus for gas-liquid contacting - Google Patents

Abstract

Rotary gas-liquid contacting apparatus includes a permeable element 29 mounted for rotation upon a shaft, gas feed means to the apparatus in the form of a fan, forming part of a rotor 21, mounted upon the shaft to rotate with the rotor, and seals 37 to minimise by passing of the gas-liquid contacting element 29 by the gas. <IMAGE>

Description

SPECIFICATION Rotary apparatus for gas-liquid contacting This invention concerns gas-liquid contacting apparatus of the type in which the contacting takes place within a rotated permeable element. In the term "gas" we include also vapours.

Rotary apparatus for gas-liquid contacting has been described in many patent specifications, typical of which are UK Patent No. 757,149 to Claes Wilhelm Pilo and our European Specification No. 0,002,568.

Such apparatus has a wide number of uses, including distillation, absorption, gas-treatment of liquids as for purging one or more components from liquid mixtures and liquid-treatment of gases as for dissolving one or more components from gas mixtures.

One advantage of such apparatus, especially when operated at rotational speeds which are high enough to impart to a liquid outwardly-directed accelerations which are a multiple of that due to gravity, is that the fluid flow capacity of the rotary apparatus may be much higher than that of conventional static apparatus of similar overall size. Expressing this advantage in another way, rotary apparatus of this type for a specific duty may be much smaller and more compact than static apparatus of equivalent fluid-flow capacity. Thus not only may such rotary apparatus be cheaper to construct and install, it also may be much more attractive to use in situations where only limited space is available, for example on oil rigs and other off-shore installations.However, the ancillary apparatus necessarily associated with the rotary apparatus, for example pumps, reboilers, condensers and the like, if of conventional design may take up a disproportionate amount of the available space. There is theefore an incentive to modify the design of such ancillary apparatus so as to exploit to greater advantage the size benefits of the rotary gas-liquid contacting apparatus.

We have now devised gas-liquid contacting apparatus which can be operated without the need for a separate gas pump.

According to the invention, gas-liquid contacting apparatus comprises a permeable element mounted upon a shaft for rotation within a chamber; liquid feed means positioned to feed liquid to a radially inner part of the permeable element (with respect to its axis of rotation); liquid outlet means from the chamber; gas feed means to the chamber comprising a fan mounted upon the shaft for rotation therewith; a gas outlet positioned to receive gas from a radially inner part of the permeable element; and a seal so disposed as to prevent or minimise the passage of gas direct from the gas feed means to the gas outlet.

The permeable element may take any of a variety of forms, including those which we have described in our above-mentioned European Specification No.

0,002,568 and in our European Specification No.

0,020,055. We especially prefer that the element be formed from a material of at least 80% voidage and/or having an interfacial area of at least 1,500 m2/m3, especially a material comprising strands, fibres or filaments. Among these materials, we more especially prefer to use the knitted metal product sold under the Registered Trade Mark "Knitmesh" or the metallic skeletal foam product sold under the Registered Trade Mark "Retimet".

Advantageously the permeable element is so mounted upon the shaft and so shaped that it is rotationally symmetrical about the shaft and can therefore be rotated at high speeds without putting any out-of-balance loads on the shaft. In a preferred form, the element is in the form of an annulus about the shaft as axis.

Operation of the apparatus requires a generally outward flow of liquid through the permeable element away from the axis of rotation of the permeable element and it is therefore necessary that the liquid be supplied to a radially inner part of the element. If the permeable element is in a form which is hollow at its axis, for example in the form of an annulus, then the liquid feed means may conveniently be positioned within the hollow axial zone, to enable liquid to be fed direct to a radially inner face of the element.

Liquid having passed through the permeable element is discharged from a radially outer part of the element into the surrounding chamber. For example, it may be discharged from an outer cylindrical surface of the element. From the chamber, the liquid is removed via liquid outlet means, for example a liquid discharge pipe. If the liquid outlet means leads from the chamber to a zone of lower pressure than that in the chamber, for example if it discharges to atmosphere, loss of pressure via the liquid outlet may be avoided by incorporating an appropriate gas-restraining device, for example a liquid lute, in the outlet system.

Countercurrent to the liquid flow through the permeable element, a gas flow is established in a generally inward direction towards the axis of rotation. The gas flow is established by building up a small pressure difference across the permeable element by feeding gas into the surrounding chamber. The gas feed means comprises a fan mounted upon the shaft for rotation with the shaft. The fan may conveniently be mounted within the chamber or within a gas inlet aperture leading directly into the chamber or it may be located in a separate gas supply chamber communicating in turn with the chamber in which the permeable element is located.

If the gas is air, then the gas inlet aperture may communicate directly with the surrounding atmosphere, from which an air supply is drawn by the fan, for example directly into the chamber containing the permeable element.

The fan may if desired be of the airscrew type, giving a linear axial flow-through of gas into the chamber, or it may be a centrifugal fan, that is it may take the form of generally radially-disposed vanes, receiving an axial inflow of air and discharging it outwardly in a generally radial direction towards the outer area of the chamber from which it enters the permeable element. For example, the fan may consist of uniformly spaced radial vanes (or vanes set at an angle to the radius), sandwiched between co-axial flat discs, one of which is apertured to receive the air input.

Gas having passed through the permeable ele ment is discharged from the element at a radially inner part of the element, for example from a cylindrical radially inner surface of the element.

From here it passes from the chamber via a suitable gas outlet, for example a gas discharge pipe, which may conveniently be co-axial with the permeable element. If the gas is air or another gas which is environmentally acceptable under the ambient con ditions, it may if desired be discharged from the gas outlet direct to the surrounding atmosphere.

For effective use of the capacity of the gas-liquid contacting apparatus according to the present invention, it is necessary that by-passing of the permeable element by the gas be prevented or at least mini mised. For this purpose, a seal is provided to prevent or minimise passage of gas direct from the gas feed means to the gas outlet. The seal is disposed between the rotary permeable element and the chamber and may be of the liquid type, for example the type described in our co-pending UK Patent Application No. 8025242, or of the so-called "dry" type, for example a radial or axial labyrinth seal.

For further ensuring the efficiency of the apparatus in use, the faces of the permeable element which lie across the axis of rotation, that is the "end" faces in the case of a cylindrical element, may advantageous ly be sealed to prevent flow of gas and/or liquid therethrough. For example, the element may be confined between plates, eg flat discs, lying trans verse to the axis.

The shaft upon which the permeable element and the fan are carried may usefully be cantilevered, with the permeable element mounted adjacent the free end of the shaft. In this way, access to the axial zone of the element is made more easy and the gas outlet may then be co-axial with the permeable element.

The shaft may be horizontally or vertically disposed or, if desired, at any angle between these two positions.

The shaft may be driven by any desired drive means. For example, it may be driven by an indirect method such as by belt drive. In one form of the invention, the shaft is the output drive shaft of an electric motor, by which it is directly driven in the normal way.

The permeable element is rotated at such a speed that the liquid flowing through it is subjected to a mean acceleration which is a multiple of that due to gravity ('g'). For example the liquid may be subjected to a mean acceleration of at least 10 g, especially at least 100 g, and mean accelerations of the order of 1,000 g or more may be desired.

Depending upon the radial dimensions of the perme able element, such accelerations may readily be achieved by rotating the shaft upon which the element is mounted at a rotational speed of say 1,000 to 3,000 revolutions per minute.

The apparatus according to the invention lends itself readily to designs of a robust and simple type.

Compactness may be achieved as a result of the incorporation of gas-liquid contacting apparatus and fan into a single unit. Since the permeable element and fan are mounted on a common shaft, a single power supply serves these separate features and there is no need for independent control of the gas flow rate on the one hand and the rate of rotation of the element on the other. The apparatus is particularly suited for large-volume continuous operations, such as gas treatment of liquids, for example purging, aeration or oxidation of liquids, and liquid treatment of gases, for example continuous dissolving of gases in liquids. Thus depending upon the specific function which the apparatus is performing, the gas may be air (performing a physical or chemical function), a gas involved in chemical reaction with the liquid, e.g. oxygen or hydrogen, or an inert gas such as nitrogen.

Whatever the function, physical or chemical, which the gas-liquid contacting apparatus is being used to perform, it is convenient to run the shaft at a steady rotational speed and thus provide a steady gas flow rate. If it is desired to vary the ratio of gas and liquid being brought into contact, this is readily achieved by varying the liquid flow rate into the apparatus. Thus for example, if air or oxygen is being used to contact a liquid with which it can form inflammable or explosive mixtures, the operation may be maintained within safe limits of gas/liquid ratio by varying the liquid flow rate in this way.

The invention will now be further described by reference to the accompanying drawings, in which Fig. 1 illustrates, in vertical section, a form of gas-liquid contacting apparatus according to the present invention; and Fig. 2 illustrates, also in vertical section, an alternative form of gas-liquid contacting apparatus according to the present invention.

Referring firstly to Fig. 1, a vertical shaft 1, cantilevered for rotation in bearings 2, carries a centrifugal fan 3 which by means of the shaft 1 is rotated within an air chamber 4. The fan 3 consists of radial vanes 5, symmetrically disposed about the shaft 1 and retained between a flat disc 6 and a dished annular plate 7, apertured at 8 to allow passage of air into the fan and thence to the air chamber 4.

Upon the upper surface of the disc 6 for rotation therewith is secured a permeable element 9, which is illustrated diagrammatically and consists of an annulus or "Retimet" metallic skeletal foam. The annulus may be a single block but is more conveniently assembled from smaller blocks or strips. The upper face of the element 9 is sealed by an annular plate 10, which serves also to retain the element 9 secure against the disc 6.

The air chamber 4 is provided with an air inlet aperture 11 and an air outlet pipe 12, both being disposed co-axially with respect to the shaft 1. Liquid is introduced to the apparatus via liquid feed pipes 13, 13, the lower ends of which are perforated to enable liquid to be directed on to the inner cylindrical face of the permeable element 9. Liquid having passed through the element 9 in a generally outward direction under the influence of the centrifugal effect arising from rotation of the element 9, is thrown off from the outer face of the element 9 into the chamber 4, whence it is removed via a liquid discharge pipe 14.

In operation of the apparatus, air is sucked by the centrifugal fan 3 direct from atmosphere via the air inlet aperture 11 into the chamber 4, thus producing a small positive pressure within the chamber. Loss of pressure by leakage of air back around the fan 3 is minimised by means of a radial labyrinth seal 15.

By-passing of the element 9 by the air is minimised by a second radial labyrinth seal 16. Thus the air passes under pressure through the permeable element 9, within which the contacting of air and liquid takes place. From the inner face of the element 9, air is removed via air outlet pipe 12.

The design of apparatus illustrated in Fig. 2 is even more compact than that of Fig. 1. Referring to Fig. 2, a rotor designated generally by the numeral 21 is mounted upon a shaft 22 for rotation within a chamber 23. The rotor 21 consists of a centrifugal fan having radial vanes 24, symmetrically disposed about the shaft 22 and retained between a flat upper plate 25 and a dished annular plate 26, apertured at 27 to allow passage of air into the fan. Supported upon the plate 25 and retained in place by an annular retaining plate 28 is a permeable element 29, which is illustrated diagrammatically and consists of an annulus of "Retimet" metallic skeletal foam.

The chamber 23 is defined by twomembers 30 and 31, which together form a squat cylindrical housing around the rotor 21 and are supported upon a cylindrical base member 32, which is provided with circular apertures 33,33 about its cylindrical surface to permit ingress of air.

Air sucked into the apparatus via apertures 33 by means of the fan, passes through the aperture 27 past the vanes 24 and into the chamber 23. Under the pressure in the chamber 23 created by the action of the fan, which pressure is higher than that at the centre of the permeable element 29, which may be open to the atmosphere, air from the chamber 23 penetrates the interstices of the element 29 and flows inwardly through the element towards its centre. On emerging at the inner face of the element, the air is discharged from the apparatus via an axially disposed gas outlet pipe 34.

By-passing of the element 29 by the air in the chamber 23 is minimised by a labyrinth seal 37 and back-flow of air to the inlet apertures 33 is minimised buy a labyrinth seal 38.

Liquid to be treated in the apparatus is introduced via inlet pipes 35,35, which are perforated at their lower ends to allow jets of liquid to impinge upon the inner face of the element 29. Under the influence of the centrifugal effect arising from rotation of the rotor 21, liquid passes through the element 29 in a generally outward direction and, as it flows, is in repeated contact with gas flowing inwardly through the element. After emerging from the outer face of the element into the chamber 23, liquid is discharged from the apparatus via a liquid outlet pipe 36. The pipe is shown in the drawings as parallel to the axis of the apparatus but may advantageously be inclined to that position in a direction tangential with respect to the rotor so as to improve liquid flow from the apparatus. A liquid lute (not shown) is included in the liquid line from the pipe 36 to avoid loss of air pressure by that route.

The two forms of apparatus of Figs. 1 and 2 respectively are both illustrated and descirbed as mounted with their axes vertical but it is equally suitable that they be mounted with their axes horizontal or inclined. However the orientation and/ or the location of the liquid outlet pipe 14 or36 may usefully be changed so as to take account of the orientation of the axis of the apparatus and the resulting gravitational influence on liquid to be discharged from the apparatus.

Claims (10)

1. Gas-liquid contacting apparatus comprising a permeable element mounted upon a shaft for rotation within a chamber; liquid feed means positioned to feed liquid to a radially inner part of the permeable element (with respect to its axis or rotation); liquid outlet means from the chamber; gas feed means to the chamber comprising a fan mounted upon the shaft for rotation therewith; a gas outlet positioned to receive gas from a radially inner part of the permeable element; and a seal so disposed as to prevent or minimise the passage of gas direct from the gas feed means to the gas outlet.

2. Gas-liquid contacting apparatus as claimed in claim 1, in which the permeable element is formed from a material of at least 80 per cent voidage and/or having an interfacial area of at least 1,500 m2/m3.

3. Gas-liquid contacting apparatus as claimed in Claim 2, in which the permeable element is formed from a material comprising strands, fibres orfilaments.

4. Gas-liquid contacting apparatus as claimed in claim 3, in which said material is a knitted metal or a metallic skeletal foam.

5. Gas-liquid contacting apparatus as claimed in any of the preceding claims, in which the permeable element is an annulus about the shaft as axis.

6. Gas-liquid contacting apparatus as claimed in claim 5, in which the liquid feed means is positioned within the hollow axial zone of the annulus.

7. Gas-liquid contacting apparatus as claimed in any of the preceding claims, in which the fan is located within the chamber.

8. Gas-liquid contacting apparatus as claimed in any of claims 1 to 6, in which the fan is located in a gas supply chamber, separate from and communicating with the chamber in which the permeable element is located.

9. Gas-liquid contacting apparatus as claimed in any of the preceding claims, in which the fan is a centrifugal fan.

10. Gas-liquid contacting apparatus comprising an annular permeable element, formed from a material of at least 80 per cent voidage and mounted symmetrically upon a shaft for rotation, about the axis of the annulus, within a chamber; liquid feed means positioned within the hollow axial zone of the annulus to feed liquid to the radially inner face of the annulus; liquid outlet means from the chamber; gas feed means to the chamber comprising a centrifugal fan mounted upon the shaft for rotation therewith; a gas outlet positioned adjacent the axial zone of the annulus; and a seal so disposed as to prevent or minimise the passage of gas direct from the gas feed means to the gas outlet.