GB2106418A

GB2106418A - Material exchange tray and method of producing it

Info

Publication number: GB2106418A
Application number: GB08225490A
Authority: GB
Inventors: Ulrich Buhlmann
Original assignee: KUHNI Ltd
Current assignee: KUHNI Ltd
Priority date: 1981-09-08
Filing date: 1982-09-07
Publication date: 1983-04-13
Also published as: DE3229510C2; FR2512351B1; CH653564A5; DE3229510A1; GB2106418B; FR2512351A1

Abstract

A material exchange tray (22) having rigid valves (21) which are formed by covers (25) spaced above openings (23) in the tray (22) and integrally connected therewith by webs (24). Gas inflow slots (26) of the valves (21) are defined between edges (28, 29) of the covers (25) and the edges (23) around openings in the tray (22) which edges are rounded off unlike conventional rigid valves. This yields an increase in gas loading capacity by approx. 30% and a similar reduction in the pressure losses as compared with conventional rigid valves. To produce the tray (22), the covers (25) may be punched out of the tray and the edges of the covers and openings subsequently rounded off by a surface treatment. Preferably, however, no surface treatment is required: The punch is advanced (downwards) only so far as is necessary to shear the tray and the cover is subsequently displaced out of the plane of the tray (22) in the opposite direction (34) so that no sharp edges or burrs occur on those edges bounding the inflow slots. This avoids the need for additional surface treatment. <IMAGE>

Description

SPECIFICATION Material exchange trays and a method of manufacturing such trays This invention relates to material exchange trays and a method for the manufacture thereof.

Material exchange trays such as disclosed, for example, in Swiss Patent specifications Nos.

291 798 and 318804 are formed with so-called "rigid" valves and are manufactured from a metal plate by separating, for example, rectangular strips at their longitudinal sides from the tray by a punch and corresponding matrix and at the same time displacing the strips out of the plane of the plate, the strips remaining integral with the plate by virtue of webs at the ends of the strips which are stretched according to the distance between the resulting cover and the plate. The edges of the strip which forms the cover extend parallel to the edges of the opening formed in the plate. Inflow slots (slot nozzles) for the gaseous or vapor phase are defined between these edges.

Exchange trays are used mainly for rectification and absorption and enable very intimate mixing of the liquid and gaseous or vapour phase. The latter flows through the openings in the tray and, deflected by the covers, flows through the inflow slots into the liquid phase which is spreading out on the tray.

Material exchange trays should in general fulfil three main requirements, namely high loading capacity as regards the throughput of gas, high efficiency (high rate of material exchange) and low pressure losses for the gas flow. Conventional material exchange trays have a high degree of efficiency and compared with other trays such as bubble trays, valve trays with movable valves, e.g.

twist valve trays, cage valve trays, flap valve trays, etc., they have above all the advantage of the structural simplicity and low cost of manufacture, however, they do have limited gas loading capacity and introduce significant losses. The gas loading capacity and pressure losses are mainly determined by the size and number of the valve openings available for the flow of gas. The valve openings of rigid valves consist of the inflow slots between the edges of the covers and of the openings. The size of the inflow slots is limited since the webs connecting the covers to the trays would be stretched beyond their breaking limit and would therefore break if attempts were made to produce rigid valves with very large slots.The number of inflow slots, i.e., of valves is also limited for two reasons: Firstly, if a row of valves are formed close together, the metal of the tray would warp during manufacture due to the high stresses produced. Although this warping could subsequently be corrected by an elaborate process of straightening the tray, there would still remain a second disadvantage which could not be overcome. If valves are arranged too close together side by side, the streams of gas deflected horizontally by the covers would tend to be directed towards each other and would thereby be deflected vertically. This increases the amount of liquid droplets carried along to the next tray, and would adversely affect the efficiency of the tray.

It is therefore one object of the present invention to improve the gas loading capacity and reduce the pressure losses of material exchange trays while avoiding the disadvantages due to an increase in the size and number of the valve openings (inflow slots).

According to one aspect of this invention, we propose a material exchange tray for the exchange of materials between a liquid and a gaseous or vapour phase in a column, in particular for rectification and absorption, comprising covers spaced above openings in the tray and integrally connected with the tray so as to define inflow slots for the gaseous or vapour phase formed between the edges of the covers and of the openings, wherein the said edges are rounded or otherwise smoothly contoured.

According to a second aspect of this invention, we propose a method of manufacturing material exchange trays according to the said one aspect of the invention wherein the covers are formed by displacing out of the plane of the tray material between spaced cuts therein and wherein the edges of the covers and of the openings defining the inflow slots are rounded off or otherwise smoothly contoured either by virtue of the manner in which the covers are formed or by a subsequent surface tratment.

Other features of the invention are set forth in the following and in the appendent claims.

It has surprisingly been found that by rounding off those edges which bound the inflow slots, the gas loading capacity can be increased by ca. 30% and the pressure loss can be reduced by ca. 30 /0.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, of which: Figure 1 is a fragmentary perspective view of a conventional exchange tray showing a rigid valve; Figure 2 is a part cross-section through the rigid valve shown in Figure 1; Figure 3 is a part cross-section of an exchange tray according to the present inventon, and showing a rigid valve in which the edges have been rounded off by a surface treatment; and Figures 4 and 5 respectively illustrate different stages in the manufacture of another exchange tray according to the present invention.

The conventional exchange tray 2 illustrated in Figure 1 is for the exchange of material between a liquid and a gaseous or vapour phase in a column used for rectification or absorption, and has rigid valves 1 (one shown) each having a cover 5 spaced above an opening 3 in the metal tray 2, the cover 5 being integrally connected with the tray 2 by webs 4. Two inflow slots 6 for the gaseous or vapour phase are defined between the edges of the cover 5 and of the opening 3.

Conventional valves are manufactured by means of a punch (not shown) advancing in the direction of arrow 7 and a corresponding matrix (not shown) situated on the opposite side, so as to shear the tray along parallel lines and displace the metal between the lines out of the place of the tray, thus forming the cover 6 spaced above the resulting openings 3 and integrally connected with the tray 2 by webs 4. Due to the method of manufacture employed, the edges 8 and 9 of the inflow slots 6 so formed are extremely sharp and, furthermore, burrs (shown enlarged) are created along these edges. We have found that these sharp edges and burrs reduce the gas loading capacity and increase the pressure losses of conventional material exchange trays 2.

In the valves 11 and 21 shown in Figures 3 and 5, the parts corresponding to parts 2 to 9 are indicated by the reference numerals 12 to 19 and 22 to 29. The exchange trays 12, 22 are made of stainless steel plate, which has optimum properties as regards corrosion resistance for most cases in practice, but which unavoidably forms relatively large burrs when it is punched out. Rigid valves 1 produced by conventional techniques would have burrs projecting from the edges 8. 9 into the inflow slots 6 and would thereby considerably reduce the gas loading capacity and create high pressure losses.

In the valves 11 and 12 of trays according to the invention, the edges 18, 19 and 28, 29 bounding the inflow slots 16 and 26 are not sharp but are rounded off and thus free from burrs. This yields a higher gas loading capacity and lower pressure losses than is possible with conventional rigid valves.

The first stage in the production of the valve 11 illustrated in Figure 3 is a punching operation as for the conventional valve 1. In a second stage, however, the edges 1 8, 1 9 bounding the inflow slots 6 are rounded off by a surface treatment which may be mechanical, for example, sand blasting, grinding or blunting, chemical for example, pickling or electrochemical for example, electrolytic polishing. Mechanical treatment by sand blasting is, however, difficult in that the sand blasting nozzle must always be directed precisely to the edges of each valve which are to be rounded off. Equally difficult is the process of mechanically grinding or knocking off the individual edges.Chemical and electrochemical surface treatments are simpler but they expose the entire surface of the exchange tray 1 2 to the treatment, whereby the wetting properties of the tray are altered, and this may have a deleterious effect on the exchange of materials, depending on the liquid phase employed. In order to avoid this, the chemical treatment may be restricted to the edges 1 8, 1 9 facing each other at the boundaries of the inflow slots 1 6, for example by applying the acid solution used for pickling only to these edges, but this is also difficult, in much the same way as the mechanical treatment.

The method of manufacture described below the reference to Figures 4 and 5 avoids the difficulties inherent in the surface treatments. It is simple, requires no after treatment of the tray and causes no change in the surface characteristics of the tray. As shown in Figure 4, the two longitudinal sides of the cover 25 of the rigid valve 21 are sheared from the tray 22 by a punching operation in which the punch 32, which carries two parallel cutting blades 30, 31 spaced apart, advanced in the direction of the arrow 33 only as far as is necessary to shear the material cover 25.

The corresponding punch matrix required for the process has again been omitted from the drawing for the sake of clarity. In a second stage, sheared strip is displaced out of the plane of the tray 22 in a direction opposite to the direction of movement 33 of the punch 32 by means of a pressure ram (not shown) of suitable shape. Since the cover 25 is displaced in the opposite direction to the movement of the punch 32, the sharp edges 35, 36 on which the burrs are formed are not edges which bound the inflow slots 26 of the valve 21 which slots 26 are therefore bounded by the round edges 28, 29.

In the examples illustrated, the covers are formed by strips extending parallel to the trays, but the covers could also have a different form, for example they could be circular, and they could extend obliquely to the tray.

Claims

1. A material exchange tray for the exchange of materials between a liquid and a gaseous or vapour phase in a column, in particular for rectification and absorption, comprising covers spaced above openings in the tray and integrally connected with the tray so as to define inflow slots for the gaseous or vapour phase formed between the edges of the covers and of the openings wherein the said edges are rounded or otherwise smoothly contoured.

2. A method of manufacturing a material exchange tray according to claim 1, wherein the covers are formed by displacing out of the plane of the tray material between spaced cuts therein and wherein the edges of the covers and of the openings defining the inflow slots are rounded off or otherwise smoothly contoured either by virtue of the manner in which the covers are formed or by a subsequent surface treatment.

3. A method according to claim 2 wherein the said cuts are formed by shearing the material of the tray along spaced lines.

4. A method according to claim 2 or claim 3, wherein shearing is effected by means of a punch having spaced cutting edges and which is advanced only so far as is necessary to shear the material of the tray and wherein the said material is displaced out of the plane of the tray to form the cover in a direction opposite to that of the advancement of the punch, whereby the edges of the cover and the opening defining the inflow slots do not carry burrs formed during shearing but are rounded off or otherwise smoothly contoured.

5. A method according to claim 2 or claim 3, wherein the said edges are rounded off by chemical and/or electrochemical surface treatment.

6. A method according to claim 2 or claim 3, wherein the said edges are rounded off by a mechanical treatment.

7. A method of manufacturing a material exchange tray substantially as hereinbefore described with reference to Figures 3 to 5 of the accompanying drawings.

8. A material exchange tray constructed and arranged substantially as hereinbefore described with reference to and as illustrated in Figures 3 to 5 of the accompanying drawings.