GB2338194A

GB2338194A - Wall wiper for mass transfer towers

Info

Publication number: GB2338194A
Application number: GB9812352A
Authority: GB
Inventors: Paul Simpson
Original assignee: Norton Chemical Process Products Corp
Current assignee: Saint Gobain Norpro Corp
Priority date: 1998-06-08
Filing date: 1998-06-08
Publication date: 1999-12-15
Anticipated expiration: 2018-06-08
Also published as: GB9812352D0; GB2338194B

Abstract

The wiper has a cylindrical body (2) with a spacer ring that inhibits deformation of the wiper when under compressive forces, and conventional flaps (3) which are inclined upwardly and outwardly, wherein the ends of the flaps (3) remote from the body (2) are generally in contact with the wall of a mass transfer vessel, e.g. a packed tower, following insertion of the packing into the tower. Typically, the spacer ring is formed around the body member 2 by incising a plurality of parallel spaced cuts 5 in the axial direction then deforming the portions 4 between cuts 5 radially outwards. Wipers minimise the amount of liquid running down the walls of a tower and avoiding contact with packing.

Description

1 1 2338194 WALL WIPERS FOR USE IN MASS TRANSFER TOWERS This invention

relates to wall wipers used in mass (including heat) transfer towers.

Wall wipers are devices intended to improve mass transfer efficiency in such towers by minimising the amount of liquid running down the walls of such a tower and thereby avoiding contact with structured packing units within the tower designed to maximise mass transfer capabilities. These units are intended to provide a plurality of surfaces over which a downflowing liquid can percolate, in thin film flow so far as possible. In all such towers it is important that liquid contacting the wall is is redirected back to the contact-promoting units housed within the tower, rather than simply running all the way down the walls to the base of the tower.

To handle this situation, it is conventional to employ 1Twall wipers', constructed as a set of deflector plates carried on a support ring. The ring is shaped to fit within the tower with the deflector plates in downwardsloping tight contact with the interior of the tower walls. Where the tower is cylindrical, for example, the IN support structure is conventionally a metal cylinder with a diameter slightly less than the internal diameter of the tower and the plates are formed by making spaced, parallel cuts of equal length into the metal of the cylinder from one end, and then bending the metal between the cuts outward to provide deflector plates, the bending being sufficient to bring the ends of each plate into contact with the tower's inner wall when the cylinder, which is now a "wall wiper", is pressed into the tower.

Once inserted, the ends of the bent deflector plates are in tight register with the interior tower wall and the cylindrical ring part of the wall wiper sits on a support device at the desired level inside the tower.

Typically a tower may comprise several packing levels which may all be structured packing or the tower may also contain two or more different types of other liquid/gas contacting systems such as random packing elements or trays. In some constructions, the structures may rest directly on wall wipers subjecting them to stress, and this is particularly true when, as is often more convenient, the tower is loaded with its axis horizontal, the tower then being erected and installed in a vertical orientation before being put into These stresse can have the effect of deforming the wall wiper such that on what will be one side of the erect tower the deflector plates lie parallel to and directly against the wall and on the other side are at right angles to the wall. In either event, the wall wiper will not then do its intended job.

According to the present invention, there is provided a wall wiper comprising a generally cylindrical body member having a plurality of deflector plates attached thereto at one end of the member and extending outwardly from the 1 4 cylinder at an angle to the axis of the cylindrical body member that is less than 90 and characterised in that the cylindrical body member is provided with an exterior spacer ring. The spacer ring may be a separate ring member around the cylindrical body member, or may be formed by forming part of the cylindrical body member into an annular portion of increased diameter relative to the remainder thereof. Such an annular portion is preferably formed adjacent the end of the cylindrical body member to which the deflector plates are attadhed.

Such wall wiper constructions can be manufactured and used for a wide range of applications.

The body member is described as being "generally cylindrical,, and by this is meant that the shape corresponds to the internal shape of the tower into which it is to be fitted. Generally, such towers are circular in cross-section but variations from this model are used in some cases, and the term cylindrical as used herein embraces body members where the cross-section is other than circular, for example elliptical or square. The advantageous properties of the wiper rings according to the present invention are retained irrespective of variations in its overall shape. The major advantage is that using rings accoring to the present invention, a tower may be loaded while in the horizontal position without the weight of the packing flattening the deflector plates on the side of the tower in contact with the ground.

The spacer ring has a dual function in that it limits the degree to which the body member can be displaced towards the wall of the tower in which it is located and it also - 4 provides a deformation mechanism in response to pressure from packing loaded above it that will not involve significant distortion in the positioning of the deflector plates. The spacer ring when formed from the material of the cylindrical body member can have any convenient section (in a plane passing through the vertical axis of the tower) such as U- shaped or V-shaped or even W-shaped (that is a double spacer ring configuration) or may even take the form of a series of concertina folds.

The spacer ring should not impede the function of the deflector plates and thus it is preferred that the greatest diameter of the spacer ring should not exceed the greatest separation between the deflector plates on opposed sides of the wall wiper.

A convenient way to make the spacer ring when this is integral with the material of the cylindrical body member is to provide a series of parallel spaced cuts in the direction of the axis of the cylinder and in the location of the spacer ring. These cuts divide the spacer ring into a plurality of parallel segments aligned in the direction of the axis of the cylinder and permit the formation of the ring from the material of the cylinder without stretching of the metal from which the cylindrical body member is constructed. They also render the spacer ring more easy to deform in response to imposed loads from above.

Alternatively the spacer ring can be provided by a belt attachment around the exterior surface of the body member and giving it, in effect, a locally increased exterior diameter. The belt attachment can be a channel member of the same material as the cylindrical body member or it could be made from a tot ally dissimilar material provided this would not be severely deteriorated by the environment in which it is expected to operate. Certain kinds of resistant rubber can often prove suitable materials from which to construct such a belt member and would provide a certain resiliency as an added attractive feature.

The deflector plates are preferably integral with the body member but they can also be attached to it by welding, e.g plasma welding, or by some other mechanical fixing expedient such as a series of bolts or so- called "hog-ring" clamps, formed by deforming a short piece of wire into a generally circular shape passing through the material of the cylindrical body member and the material of the deflector plates. The plates and body member may have a series of preformed holes to receive such clamps. In some ways, this latter approach is preferred since it permits shaped deflector plates to be used, the width of the plate increasing away from its attachment to the cylindrical body member, thus a-voiding the gaps that would otherwise result from providing the deflector plates as integral extensions of the body member that have simply been deformed outwards.

The material from which the wall wiper is constructed depends to some extent on the environment in which it is to be used. Generally, a metal is preferred such as stainless steel. This has the advantage of being resistant to moderately high temperatures and more corrosive environments while being sufficiently springy to absorb deformations without breakage. In some environments, however, certain plastics may supply a balance of acceptable properties.

In a preferred tower structure, the wall wipers are used at vertically spaced intervals surrounding structured packing beds. The wall wipers may be made to fit towers of a wide range of diameter, e.g. from a few centimetres to several metres.

The invention is illustrated by way of example with reference to the accompanying drawings, in which Figure 1 is a perspective diagrammatic illustration of a cylindrical wall wiper before insertion in a tower, Figure 2 is a section of the wall wiper of Figure 1, on an enlarged scale, and Figures 3a to 3d are axial sections through one side of a wall wiper illustrating four alternative integral spacer ring constructions.

Referring to the drawings, a wall wiper 1 comprises a body member 2 which terminates in wipers 3 formed by incising a plurality of parallel cuts 6 in the body member in the axial direction and the bending of the flaps thus formed outwards to form the wipers 3. A spacer ring is formed around the body member by incising a plurality of parallel spaced cuts 5 in the axial direction and deforming the portions 4 between the cuts 5 radially outwards.

Figure 3 (a) shows an axial section of one side of the wall wiper of Figure 1. Figures 3 (b), (c) and (d) show like sections of alternative embodiments of the - 7 invention.

Claims

1. A wall wiper comprising a generally cylindrical body member having a plurality of deflector plates attached thereto at one end of the member and extending outwardly from the cylinder at an angle to the axis of the cylindrical body member that is less than 90, characterised in that the body of the cylindrical body member is provided with an exterior spacer ring.

2. A wall wiper according to Claim 1 in which the spacer ring is formed integrally with the cylindrical body member and comprises a plurality of parallel segments aligned in the direction of the axis of the cylindrical body member and deformed outwardly relative to the cylindrical portion thereof.

3. A wall wiper according to Claim 1 in which the spacer ring has the form of at least two concertina pleats.

4. A wall wiper substantially as hereinbefore described with reference to the accompanying drawings.

4. A wall wiper according to any one of Claims 1 to 3 in which the greatest diameter of the spacer ring is less than the greatest outward separation between deflector plates on opposite sides of the wall wiper.

5. A wall wiper substantially as hereinbefore described with reference to the accompanying drawings.

9 AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS 1. A wall wiper comprising a generally cylindrical body member having a plurality of deflector plates attached thereto at one end of the member and extending outwardly from the cylinder at an angle to the axis of the cylindrical body member that is less than 90, characterised in that the cylindrical body member is provided with an exterior spacer ring adjacent the end of the member to which the deflector plates are attached; the exterior spacer ring being formed integrally with the cylindrical body member and comprising a plurality of parallel segments aligned in the direction of the axis of the cylindrical body member and deformed outwardly relative to the cylindrical portion thereof.

2. A wall wiper according to Claim 1 in which the spacer ring has the form of at least two concertina pleats.

3. A wall wiper according to Claim 1 or 2 in which the greatest diameter of the spacer ring is less than the greatest outward separation between deflector plates on opposite sides of the wall wiper.