GB2294419A - Handling foraminous sheets in industrial catalysis - Google Patents

Abstract

A foraminous sheet for use in catalysis (36) is placed upon a former (12) that supports the sheet (36) in a compact curved configuration during storage and transportation but which, during installation of the sheet in a catalytic reactor (38), releases the sheet (36) into a flat configuration in situ within the reactor (38). <IMAGE>

Description

HANDLING FORAMINOUS SHEETS IN INDUSTRIAL CATALYSIS This invention relates to the art of catalysis and contemplates methods and apparatus for storing, transporting, installing and removing the large foraminous sheets commonly encountered in the industrial application of catalysis.

Foraminous sheets are widely used in industrial catalysis, for example in the oxidation of ammonia to produce nitric acid or in the production of hydrogen cyanide. The sheets are usually densely woven or knitted from metal wires. By way of example, the sheets may be catalyst sheets or getter sheets made of precious metals such as platinum, palladium and alloys thereof, or may be support sheets made of relatively inexpensive metals such as stainless steel.

The sheets are usually circular to suit the cross-section of most commercial catalytic reactors, although other cross-sectional shapes such as hexagons and squares are also known. When in use in a catalytic reactor, several such sheets are usually disposed one above another in a multi-layered pack that spans the full width of the reactor and is oriented perpendicularly with respect to the flow of reactants through the reactor. The reactants undergo the desired reaction as they flow through the successive catalytic sheets of the pack.

Getter sheets may be provided in or associated with the pack, these being situated downstream of or interleaved with the catalytic sheets to recover catalytic material that, under the high temperatures of reaction, gradually evaporates from the catalytic sheets to become entrained in the stream of reactants. Support sheets situated underneath or interleaved with the catalyst or getter sheets provide the assembly with the requisite mechanical strength.

The pack may be assembled sheet-by-sheet in situ within the reactor, or may be preassembled as a unit that is installed in the reactor in a single operation. To maintain the integrity of the unit, the edge regions of its constituent sheets are usually fixed together by welding.

Units of two or more sheets (usually containing at least four sheets) are becoming increasingly popular as they shorten installation times and hence minimise expensive downtime of a catalytic reactor. Use of such a unit obviates several repeated and painstaking positioning steps that are otherwise needed to ensure that each individual sheet is correctly in register with its neighbours and with the walls of the reactor.

Further, the risk of contamination is lessened because the sheets within the unit are protected by the sheets outside the unit.

For brevity, this specification will hereafter use the word 'sheet' as encompassing both a single foraminous sheet and a unit of two or more foraminous sheets, unless the context requires otherwise.

The foraminous sheets used in catalysis are notable for their substantial size and cost.

Commercial reactors range in diameter from approximately one to five metres; a sheet for use in such a reactor must be at least as wide as the diameter of the reactor and will contain many kilometres of metal wire. Consequently, where the wire is of precious metal, especially platinum/rhodium alloy as is common, the material cost of each sheet may be enormous.

The sheer size of the sheet, and its considerable weight resulting from the use of extremely dense metals, are severe hindrances to storage, transportation and installation.

These problems are exacerbated by the awkwardness of handling the sheet, which is mechanically weak, readily creased or wrinkled, and sensitive to contamination when handled on installation.

Creasing creates local thickening of the sheet, which tends to increase the residence time of reactants as they flow through the sheet to the extent that, in the production of hydrogen cyanide, carbon deposits gradually form on the creased parts of the sheet.

These deposits shroud parts of the catalytic surface, reducing catalytic efficiency, and combine chemically with the material of the sheet, leading to embrittlement and, ullimately, mechanical failure.

Creasing may also bend some of the metal wires constituting the sheet through acute angles: this creates stress concentrations that further increase the risk of mechanical failure in use.

Carbon deposits may also result from contamination caused by contact of the sheet with, for example, organic materials (grease, oil and so on); damaging contamination may result merely from the touch of an ungloved hand during installation of the sheet.

Further, some contaminants such as iron may chemically poison the catalytic surface of the sheet material, potentially rendering the sheet useless.

At present, sheets are usually rolled up for the purposes of storage and transportation, to be unrolled during installation in a reactor. For the most compact roll configuration, the sheet is rolled from one side to the other like a carpet.

Rolling-up the sheet usefully reduces its width in one direction, bringing the dimensions of the rolled sheet to within the capacity of practical transport vehicles, and making the rolled sheet easier to carry and to store. However, creases are inevitably formed when the sheet is rolled up, particularly when rolling-up a multiple-sheet catalyst or getter unit in which the adjacent sheets are unable to slide freely in relation to one another. Catalyst or getter units may, indeed, be difficult or impossible to roll up without creating a 'set' or plastic deformation in the gauzes, which causes installation problems. This may be because such units are much stiffer than individual sheets; as a practical matter, a unit can only be bent, for example to fold it in half.This drawback is particularly unfortunale given the increasing popularity of multiple-sheet catalyst or getter units in relation to individual sheets.

In a variant of the laminated or multi-layered catalyst or getter units mentioned above, the unit comprises spaced-apart top and bottom sheets of knitted or woven mesh that, between them, hold a loosely-packed spun fibrous mass of catalyst or getter material.

Such a unit is all the more difficult to fold or bend without damage because the core of fibrous material is easily crushed. Moreover, the fibrous mass can shift within the unit during storage and transportation under the influence of gravity. Such shifting may lead to local accumulations or concentrations of catalyst or getter material, and corresponding regions lacking the material, which together can ruin the performance of the unit.

We are aware of at least one proposal that aims to overcome the difficulty of handling a large laminated getter unit. In that proposal, the subject of, inter alia, United States Patent No. 4,351,887, the getter unit is divided into a plurality of segments that may be folded or separated to reduce the overall diameter of the unit. A flaw with the proposal is that gaps inevitably remain between the segments when the segments are arranged in planar contiguous relation within a reactor; the gaps render the segmented arrangement quite unsuitable for use in catalytic packs as opposed to getter packs, because reactants may bypass the catalytic packs and so reduce the yield. Even for a getter, gaps are disadvantageous: they reduce the efficiency of recovery and can lead to a damaging phenomenon known as 'streaming'.Streaming occurs when reactant gases head for gaps in the getter and so are concentrated in the regions closest to those gaps in layers adjacent the getter. The concentration of gases may be such as to damage the adjacent layers through overheating, and reduces the efficiency of catalysis because some regions of the catalyst see too much of the reactants and some regions too little.

Whether a sheet is rolled or folded, there is always a risk that it will be crushed during storage, transportation or installation. This may plastically deform the metal wires from which the sheet is made, causing sharp creases that cannot be removed during installation.

Creasing is particularly acute in rolled arrangements where the portion of the sheet towards the centre of the roll is most acutely deformed. The problem is merely mitigated, but not overcome, by bending the sheet to fold it.

Creasing can sometimes be cured by smoothing the sheet after it has been unrolled or unfolded upon installation in a catalytic reactor. However, smoothing is a laborious, lengthy process that increases downtime of the reactor and adds to the risk of contamination of the sheet material. Further, some creases left by rolling may be so severe as to defy smoothing.

The difficulties of installing a sheet in a catalytic reactor are heightened by the location of the reactor in a chemical processing plant; frequently, those installing the sheet must negotiate a maze of ancillary pipework to reach the reactor. Further, the construction of the reactor itself may provide only very limited access to its interior. The reactor is, essentially, a tube that is in two major parts (e.g. a conical gas feeder and the reactor bed) normally joined end-to-end, with the joint being in the vicinity of the sheets contained in the reactor. The parts of the tube are jacked apart and propped to allow access to the sheets, but the resulting gap may be as little as one metre.These factors increase still further the expensive downtime involved in changing the sheet, particularly when a pack of sheets is assembled in situ, and make creasing, contamination or other damage all the more likely.

The removal of a used sheet from a catalytic reactor is also fraught with difficulties.

Whilst it does not matter if the used sheet is creased or contaminated during removal because the sheet will be melted down in a processing operation before its materials are used again, the material of the sheet becomes very brittle after extended use. The brittleness may be such that the material of the sheet can be crumbled into a powder with little effort; accordingly, substantial quantities of valuable material can be lost simply by crumbling away from the sheet as the sheet is manhandled out of the reactor and transported from the chemical plant for processing. In this way, significant and expensive quantities of precious metals may end up uselessly in the reactor, on the floor of the chemical plant, or on the load platform of a lorry carrying the sheet to a processing facility.

This invention results from our efforts to overcome the difficulties of storage, transportation, installation and removal of foraminous sheets, from which the art of catalysis has suffered for many years.

In a broad sense, the invention resides in the concept of placing a foraminous sheet upon a former that supports the sheet in a compact curved configuration during storage and transportation but that, during installation of the sheet in a catalytic reactor, releases the sheet into a flat configuration in situ within the reactor.

Accordingly, from one aspect, the invention resides in apparatus including a former adapted to support a foraminous sheet in a curved configuration. The invention encompasses such apparatus when carrying a sheet in curved configuration.

From another aspect, the invention resides in a method of storing and transporting a foraminous sheet for use in catalysis, wherein the sheet is held in a curved configuration upon a former.

The invention also resides in a method of handling a foraminous sheet for use in catalysis, comprising the step of bending the foraminous sheet into a curved configuration about a former.

In a further aspect, the invention encompasses a method of installing a foraminous sheet in a catalytic reactor, comprising releasing the sheet from a former in situ within the reactor.

In an extension of the basic invention yet still within the inventive concept, the invention encompasses a method of removing a foraminous sheet from a catalytic reactor, comprising the steps of bending the sheet into a curved configuration about a former in situ within the reactor and subsequently removing the assembly of sheet and former from the reactor.

It is preferred that the sheet is wrapped substantially completely around the former and it is further preferred, though not vital, that the free ends of the sheet are overlapped.

This provides a compact configuration and simplifies the means that retain the sheet in position on the former.

For ease of folding and, ultimately, installation of the sheet in a catalytic reactor, the former should be placed centrally on the sheet such that substantially equally-sized free ends of the sheet are folded over the former. As part of the folding procedure, the sheet is bent along a line around a curved margin of the former and preferably along first and second lines around first and second curved margins of the former. The first and second lines are, suitably, substantially parallel.

Put another way, the sheet, when in the curved configuration, preferably comprises at least one substantially flat area and at least one curved area. These areas may be as follows: a first substantially flat side area; a first curved area; a substantially flat central area; a second curved area; and a second substantially flat side area.

It is not essential that the flat areas of the sheet are truly flat: benefit may be gained simply from having some areas less acutely curved, or flatter, than others. Accordingly, the sheet, when in the curved configuration, may comprise at least one relatively flat area and at least one relatively curved area.

In an advantageously compact arrangement, the first and second side areas lie substantially parallel to one another when the sheet has been folded around the former.

However, this is not essential: the first and second side areas may lie in general planes angled with respect to one another.

When the sheet is in the curved configuration, it is preferred that a greater area of the sheet is relatively flat than is relatively curved. This minimises the risk of creasing and reduces the area of deformation of the sheet.

Any suitable retaining means can clamp the sheet to the former. Conveniently, the retaining means bears against a free end of the sheet. For optimum simplicity, a single or common retaining means bears against first and second free ends of the sheet.

The method of the invention may comprise the step of interposing a protective layer between the sheet and the former, to avoid any contamination of the sheet by the former.

Similarly, a protective covering may be applied to the assembly of sheet and former, to avoid contamination or other damage from external influences. The installation method would then involve removing the protective covering from the assembly before inserting the assembly into a reactor.

When installing the sheet in a reactor, it is most convenient to place the former centrally across the reactor. Opposed ends of the former may be rested upon respective diametrically-opposed sides of the reactor. Any retaining means which clamp the sheet to the former must then be released so that the sheet can be unfolded from around the former into a flat configuration within the reactor.

In a particularly advantageous method, the sheet is unfolded by recovering energy stored during elastic deformation upon folding. In this way, the sheet can be unfolded without touching it, or at least with minimal contact, thus reducing contamination.

The former of the invention suitably includes at least one curved surface, preferably first and second curved surfaces about which the sheet may be bent. For ease of folding and installation of the sheet, the first and second curved surfaces are preferably defined by respective substantially parallel members.

It is preferred that the former includes at least one substantially flat face, preferably including first and second such faces, as a support for any flat regions of the folded sheet. The first and second faces can be substantially parallel to one another for compactness and for ease of folding and installation of the sheet. There may, however, be three, four or more substantially flat faces, the former thus having a generally triangular, rectangular or other polygonal cross-section.

The benefit of having more than two faces is that the angle between two adjacent faces, and thus the angle of curvature necessary to bend a sheet around two adjacent faces, is lessened. However, compactness may suffer if more than two faces are used.

Of course, it is not essential that the faces of the former are truly or even substantially flat: the faces can simply be areas that are less acutely curved than the areas that connect those faces. Further, the faces of the former need not be distinctly defined by the crosssection of the former: the cross-section may be smoothly curved in, for example, a generally elliptical or convex shape. Such a shape defines relatively shallowly-curved faces connected by more acutely-curved portions.

The former is suitably generally cuboidal having first and second parallel curved margins connected by first and second parallel substantially flat faces. More generally, the former may be defined as an elongate member of polygonal cross-section having at least two relatively curved portions disposed between at least two relatively flat portions.

To minimise distortion and creasing of the sheet, it is preferred that a greater area of the surface of the former is relatively flat than is relatively curved.

The former can have any suitable structure, for example a panel or a frame. Should the structure leave any gaps in the surface of the former, these gaps may be bridged by mesh or fabric.

A shaped protective covering can be provided to fit around the assembly of former and sheet.

The former may include retaining means for holding the sheet on the former, the retaining means preferably being capable of clamping the sheet against the former. The retaining means can be a member that is movable with respect to the former, which member extends centrally along the longitudinal axis of the former. For unrestricted access to the sheet, the retaining member is preferably removable from the former.

To ease transportation and installation, the former can have at least one handle which may be movable with respect to the former, although the facility for movement is not essential. For example, the handle can be retractable into the former, or angularly adjustable. To ease installation in reactors having recessed beds, the handle may be cranked and/or may be located in an upper region of the former.

So that this invention can be more readily understood, reference will now be made to the accompanying drawings that illustrate embodiments and aspects of the invention described by way of example only. in the drawings: Figure 1 is a schematic plan view showing a preferred embodiment of apparatus according to this invention; Figure 2 is a schematic end view corresponding to Figure 1 but to an enlarged scale; Figures 3(a), 3(b) and 3(c) are schematic perspective views of the apparatus of Figures 1 and 2 in use, the successive Figures showing how a foraminous sheet is folded around part of the apparatus for storage and transportation; Figure 4 is a schematic perspective view of the apparatus of Figures 1 and 2 bearing a foraminous sheet folded according to Figures 3(a), (b) and (c) and retained in position ready for storage and transportation;; Figure 5 is a schematic end view corresponding to Figure 4 but to an enlarged scale; Figures 6(a), 6(b) and 6(c) are schematic perspective views of the apparatus of Figures 1 and 2 in use during installation of the foraminous sheet in a catalytic reactor, the successive Figures showing how the sheet is progressively unfolded from the apparatus during that operation; Figure 7 is a partial schematic detail view showing the arrangement of a handle used in the apparatus of Figures 1 and 2; Figure 8 is a partial schematic detail view showing an alternate handle arrangement; Figure 9 is a schematic end view showing a variant of the apparatus of this invention; and Figure 10 is a schematic side view showing the variant illustrated in Figure 9 in use in a reactor having a recessed bed.

Referring first to Figures 1 and 2, apparatus 10 for supporting a foraminous sheet comprises a body constituting a former 12 of generally rectangular planform having parallel long sides 14 connected by parallel short sides 16 that are orthogonal to the long sides 14.

As shown in Figure 2, the former 12 comprises a central hollow box section 18 of generally rectangular cross-section defining a flat upper face 20 and a flat lower face 22 lying parallel to the upper face 20. The long sides 14 of the former 12 are defined by curved side members 24 of semi-circular cross-section attached to respective sides of the box section 18 and whose circular diameter matches the thickness of the box section 18.

This ensures that the outer surface of the former 12, as defined by the side members 24 and the faces 20 and 22, is smooth and substantially uninterrupted by edges or other sharp transitions.

The circular diameter of the curved side members 24 and hence the thickness of the former 12 is preferably in the region of 100 mm although this dimension may be anything from 10 mm upwards, preferably 25 mm upwards.

A retaining member 26 extends along the central longitudinal axis of the upper face 20 and is removably attached to the former 12 by bolts 28 that extend through respective holes in the former 12 and the retaining member 26 and are capped by wing nuts 30.

The retaining member 26 is of rectangular cross-section and may be solid, as shown, or hollow.

Handles 32 are provided in two pairs, one pair at each end of the former 12 in the manner of a stretcher. The handles 32 are simple tubes or bars received in longitudinal channels 34 fixed within the box section 18 as shown. It is preferred that the handles 32 are slidably retractable, as will be explained below with reference to Figure 7.

The embodiment illustrated is fabricated from sheets and/or extrusions of aluminium, selected for lightness and strength. Lightness is important to reduce transport cosls, particularly by air, and to ease manhandling during transportation and installation.

Strength is imporlant to resist deformation, knocks and general wear and tear in use.

Figures 3(a), 3(b) and 3(c) show, in succession, how a foraminous sheet 36 is folded around the former 12 for storage and transportation.

In Figure 3(a), the former 12 (with the retaining member 26 removed) is placed centrally on the sheet 36 with the respective ends of the former 12 overlapping the sheet 36, preferably by a substantially equal amount. A sheet of inert packing material such as brown paper (not shown) may be interposed between the former 12 and the sheet 36 if it is desired to separate the former 12 from the sheet 36 in order to minimise contamination. The free sides 36A and 36B of the sheet 36 are then lifted as shown in Figure 3(b) and folded over onto the upper face 20 of the former 12 in an overlapping formation as shown in Figure 3(c).

It will be apparent that the sheet 36 bears against the curved side members 24 as it is folded over the former 12; the gentle radius of the side members 24 avoids creasing during the folding operation. Once folded as shown, all parts of the sheet 36 are supported by the former 12 that therefore resists crushing or bending forces during transportation and so prevents the creation of any new creases after folding.

When the folding operation has been completed, the retaining member 26 is reatlached to the former 12 using the bolts 28 and nuts 30 as shown in Figures 4 and 5, with the retaining member lying upon the overlapped sides 36A and 36B of the sheet 36. The nuts 30 are done up as loosely as possible to minimise any creasing caused by the retaining member 26, yet sufficiently tightly that the retaining member 26 securely clamps the sheet 36 to the former 12.

Once the retaining member 26 has been re-attached to the former 12, the assembly of apparatus 10 and sheet 36 is ready for storage or transportation. For optimum protection, however, it is desirable that the assembly is wrapped or otherwise covered in protective materials (not shown) before it is stored or transported. These materials can be pliable sheets of, for example, thick brown paper held in place with string or adhesive tape, and may include rigid shaped sections such as elongate plastics shields of semi-circular section for the vulnerable side members 24. It is, of course, entirely possible to provide a specially-shaped rigid cover of, for example, glass-fibre reinforced plastics material.

Such a cover could shroud the entire assembly and may be made in interlocking sections to allow access to the assembly when required.

The assembly of apparatus 10 and sheet 36 may be stored or transported in any desired orientation. In a particularly convenient orientation, the assembly is placed on its side, supported by one of the side members 24. This allows a plurality of similar assemblies to be placed side-by side in a storage chamber such that any one of those assemblies can be withdrawn in endwise manner whenever required for use, without disturbing the other assemblies in the chamber.

The procedure for installing a sheet in a catalytic reactor is essentially the reverse of the folding procedure illustrated in Figures 3(a), 3(b) and 3(c) and will now be described with reference to Figures 6(a), 6(b) and 6(c).

Briefly, the assembly of apparatus 10 and sheet 36 is carried to the vicinity of the reactor 38 and, just before installation, any external protective materials are removed.

After this, the assembly is lowered onto the reactor 38, with the retaining member 26 uppermost and with respective ends of the lower face 22 of former 12 resting upon respective diametrically-opposed walls of the reactor 38. The edges of the sheet 36 must be suitably aligned with respect to the walls of the reactor 38. The retaining member 26 is then removed from the former 12 of apparatus 10; Figure 6(a) shows the assembly at that stage.

Referring now to Figure 6(b), the overlapping sides 36A and 36B of the sheet 36 are unfolded until finally, as shown in Figure 6(c), the sheet 36 is fully unfolded and lies flat across the reactor. The former 12, and any remaining packing materials, are then removed to make way for the installation of a further sheet 36 or for the reassembly of the reactor 38.

When testing the present invention during installation of a unit of several sheets, it was found that the release of elastic deformation of the unit caused the unit to unfold of its own accord without external assistance, thus minimising the risk of contamination still further.

The former 12 can be returned to the catalytic reactor 38 when it is desired to remove the sheet 36. Removal is essentially a reversal of the installation procedure described above with reference to Figures 6(a), 6(b) and 6(c). Accordingly, the removal procedure need not be described in detail save to say that it is advisable to wrap the sheet 36 in a suitable covering at the earliest opportunity after it has been folded around the former 12. This is intended to protect the sheet against crumbling or abrasion, and to catch any material that may neverlheless crumble from the sheet.

It has already been mentioned that the handles 32 are, advantageously, slidably retractable; Figure 7 illustrates an arrangement that achieves this. It will be seen in that drawing that the handle 32 is received by a longitudinal channel 34 and can slide along its longitudinal axis within the channel 34. The channel 34 has a straight longitudinal slot 40 that receives a transverse pin 42 attached to the handle 32 and restrains the movement of the handle 32 between an extended position (as shown) and a retracted position (not shown).

Figure 8 illustrates a variant of the handle arrangement of Figure 7 and like numerals refer to like parts. In the variant of Figure 8, the handle 32 is cranked and is pivotable through 90" about the longitudinal axis of the handle portion within the channel 34.

In a fully-extended installation position as shown in Figure 8, the handle 32 is cranked upwardly and the pin 42 is received by a transverse circumferential leg 44 provided at one end of the slot 40 in the channel 34; this handle position is intended to ease installation in catalytic reactors that have beds recessed below the peripheral reactor wall. In a partially-extended carrying position (not shown), the handle 32 is cranked outwardly for stability and the pin 42 is received by a detent 46 in the slot 40. The detent 46 uses the weight of the apparatus 10 to lock the handle 32 in the carrying position.

Further to suit catalytic reactors having recessed beds, the ends and corners of the former 12, when viewed in plan, may be rounded to fit within the curve of the peripheral reactor wall.

Referring finally to Figures 9 and 10 of the drawings, these illustrate a variant in which the former 12 is of generally triangular cross-section. The triangular cross-section illustrated is generally equilateral, although other triangular shapes such as the isosceles type are possible and, indeed, it is not essential that the triangle has any line of symmetry.

It will be noted that, in the embodiment of Figures 9 and 10, the free sides 36A and 36B of the sheet 36 are bent through only 1200 as opposed to the 1800 deflection required in the embodiment illustrated in Figures 1 to 8. This reduces the risk of creasing of the sheet 36, at the cost of an increase in the height of the apparatus.

A removable retaining member 26 attached to the upper apex of the former 12 by a bolt 28 and wing nut 30 clamps the free ends of the sheet 36 to the former 12. The retaining member 26 is an elongate plate curved to match the curvature of the upper apex of the former 12, and has edge regions angled at 60 to one another.

The increase in the height of the apparatus that follows from the use of a triangular or similarly deep former is not necessarily a disadvantage, as Figure 10 makes clear. In that drawing, the apparatus comprises handles 32 that extend longitudinally from the ends of the former 12 and are located at or near to the uppermost apex 12A of the former. The handles 32 may be individual and preferably retractable, or may simply be the opposed ends of a long pole that extends through the hollow interior of the former 12 and protrudes from both ends thereof.

Figure 10 shows how the elevated location of the handles 32 on the former 12 facilitates installation of a sheet 36 in a reactor 38 having a recessed bed and thus employing a dished catalyst 'basket' 48. This arrangement prevents the handles 32 fouling the relatively raised peripheral wall of the reactor 38.

Many variations are possible within the ambit of the present invention. For example, the former may be constructed from materials other than aluminium, such as wood or fibrereinforced composites, and a combination of materials can be used. The former may have a structure other than a box section, such as a ladder-like framework of beams. To provide an uninterrupted bearing surface for a foraminous sheet, any gaps in the structure of the former can be bridged by a mesh or fabric of natural, synthetic or metallic fibres or wires.

In the preferred embodiment illustrated in Figures 1 to 8, the long sides of the former are approximately three times the length of the short sides (say three metres by one metre) although this is not essential; any suitable ratio between the long sides and the short sides is possible. For example, the long sides could be between two and four times the length of the short sides.

The former can be of any length, provided that its length exceeds the width of the sheet that it is intended to carry. The width, thickness and cross-sectional shape of the former determine how far the sheet extends around the former when folded; it is not essential that the ends of the sheet overlap or even that the sheet extends all the way around the former. A degree of overlap is preferred because it makes for the most compact arrangement without causing creasing, and simplifies the retaining means which, as the free ends of the folded sheet occupy the same location, needs to retain the sheet at only one area of contact.However, it is also possible for the sheet to extend only part of the way around the former, as shown in Figure 9; preferably, as also shown in Figure 9, the edges of the folded sheet are close enough that a single retaining means will suffice by clamping both edges but, if the edges are too far apart, more than one retaining means may be used.

The curved side members need not be semi-circular or even part-circular in crosssection; any cross-sectional shape may be employed provided that it does not impose any sharp changes of angle upon the foraminous sheet that it supports. Accordingly, it is preferred that any edges are avoided or, if present, are rounded or radiused.

Similarly, the retaining member need not be of rectangular cross-section; any crosssection that resists creasing of the sheet held underneath the retaining member (but preferably defining a large and substantially flat under-surface) may be employed.

Whilst it is preferred that the retaining member is entirely removable from the former so as not to hinder the mounting of a foraminous sheet on the former or release from it, it is also possible for the retaining member to be permanently attached to yet movable away from the former to mount and release the sheet.

Castors or wheels can be attached to the former to facilitate movement of the apparatus during storage, transportation and installation.

The rigid handles described above may be replaced by or supplemented with flexible handles such as straps of canvas or other robust material attached to suitable locations at or near to the ends of the former. These straps facilitate lowering of the former into a recessed reactor bed.

The present invention may be embodied in many other specific forms without departing from its essential attributes; accordingly, reference should be made to the appended claims and other general statements herein rather than to the foregoing specific description as indicating the scope of the invention.

Claims (63)

1. A method of handling a foraminous sheet for use in catalysis, comprising the step of bending the foraminous sheet into a curved configuration about a former.

2. The method of claim 1, wherein the sheet is wrapped substantially completely around the former.

3. The method of claim 2, wherein free ends of the sheet are overlapped.

4. The method of any preceding claim, wherein the former is placed centrally on the sheet and free ends of the sheet are folded over the former.

5. The method of any preceding claim, wherein the sheet is bent along a line around a curved margin of the former.

6. The method of claim 5, wherein the sheet is bent along first and second lines around first and second curved margins of the former.

7. The method of claim 6, wherein the first and second lines are substantially parallel.

8. The method of any preceding claim, wherein the sheet, when in the curved configuration, comprises at least one relatively flat area and at least one relatively curved area.

9. The method of claim 8, wherein the sheet comprises the following areas: a first substantially flat side area; a first curved area; a substantially flat central area; a second curved area; and a second substantially flat side area.

10. The method of claim 9, wherein the first and second side areas lie substantially parallel to one another on the former.

11. The method of claim 9, wherein the first and second side areas lie in planes angled with respect to one another.

12. The method of any of claims 8 to 11, wherein, when in the curved configuration, a greater area of the sheet is relatively flat than is relatively curved.

13. The method of any preceding claim, wherein a retaining means clamps the sheet to the former.

14. The method of claim 13, wherein the retaining means bears against a free end of the sheet.

15. The method of claim 14, wherein a common retaining means bears against first and second free ends of the sheet.

16. The method of any preceding claim, comprising the step of interposing a protective layer between the sheet and the former.

17. The method of any preceding claim, comprising the step of applying a protective covering to the assembly of sheet and former.

18. A method of installing a foraminous sheet in a catalytic reactor, comprising placing an assembly of the sheet and a former into the reactor, the sheet being carried in a curved configuration by the former; releasing the sheet from the curved configuration in situ within the reactor; and removing the former from the reactor.

19. The method of claim 18, comprising removing any protective covering from the assembly before inserting the assembly into the reactor.

20. The method of claim 18 or claim 19, comprising placing the former centrally across the reactor.

21. The method of claim 20, comprising resting the opposed ends of the former on respective diametrically-opposed sides of the reactor.

22. The method of any of claims 18 to 21, comprising releasing retaining means that clamp the sheet to the former.

23. The method of any of claims 18 to 22, comprising unfolding the sheet from around the former into a flat configuration.

24. The method of claim 23, comprising unfolding the sheet by recovering energy stored in elastic deformation upon folding.

25. The method of claim 24, wherein the sheet is unfolded without the necessity of touching the sheet.

26. The method of any of claims 18 to 25, comprising the step of removing any protective layer interposed between the sheet and the former.

27. A method of installing a foraminous sheet in a catalytic reactor, comprising releasing the sheet from a former in situ within the reactor.

28. A method of removing a foraminous sheet from a catalytic reactor, comprising the steps of bending the sheet into a curved configuration about a former in situ within the reactor and subsequently removing the assembly of sheet and former from the reactor.

29. The method of claim 28, comprising the step of wrapping the assembly of sheet and former in a covering.

30. A method of storing or transporting a foraminous sheet for use in catalysis, wherein the sheet is held in a curved configuration upon a former.

31. Apparatus for use in the method of any preceding claim, the apparatus including a former adapted to support a foraminous sheet in a curved configuration.

32. Apparatus according to claim 31, wherein the former includes at least one curved surface.

33. Apparatus according to claim 32, wherein the former includes first and second curved surfaces.

34. Apparatus according to claim 33, wherein the first and second curved surfaces are defined by respective substantially parallel members.

35. Apparatus according to any of claims 31 to 34, wherein the former includes at least one substantially flat face.

36. Apparatus according to claim 35, wherein the former includes first and second faces.

37. Apparatus according to claim 36, wherein the first and second faces are substantially parallel.

38. Apparatus according to any of claims 31 to 37, wherein the former includes at least one relatively flat surface portion and at least one relatively curved surface portion.

39. Apparatus according to any of claims 31 to 38, wherein a greater area of the surface of the former is substantially flat than is curved.

40. Apparatus according to any of claims 31 to 39, wherein the former is generally cuboidal having first and second parallel curved margins connected by first and second parallel substantially flat faces.

41. Apparatus according to any of claims 31 to 39, wherein the cross-section of the former is generally convex or elliptical.

42. Apparatus according to any of claims 31 to 41, wherein the former includes retaining means for holding the sheet on the former.

43. Apparatus according to claim 42, wherein the retaining means is capable of clamping the sheet against the former.

44. Apparatus according to claim 43, wherein the retaining means includes a retaining member that is movable with respect to the former.

45. Apparatus according to claim 44, wherein the retaining member extends centrally along the longitudinal axis of the former.

46. Apparatus according to claim 44 or claim 45, wherein the retaining member is removable from the former.

47. Apparatus according to any of claims 31 to 46, wherein the former has at least one handle.

48. Apparatus according to claim 47, wherein the handle is movable with respect to the former.

49. Apparatus according to claim 48, wherein the handle is retractable into the former.

50. Apparatus according to claim 48 or claim 49, wherein the handle is angularly adjustable.

51. Apparatus according to claim 50, wherein the handle is cranked.

52. Apparatus according to any of claims 47 to 51, wherein the handle is located in an upper region of the former.

53. Apparatus according to any of claims 31 to 52, wherein the former is a panel.

54. Apparatus according to any of claims 31 to 53, wherein the former is a frame.

55. Apparatus according to claim any of claims 31 to 54, wherein any gaps in the surface of the former are bridged by mesh or fabric.

56. Apparatus according to any of claims 31 to 55, wherein the former comprises extruded members.

57. Apparatus according to any of claims 31 to 56 and including a protective covering shaped to fit around the assembly of former and sheet.

58. Apparatus according to any of claims 31 to 57, when carrying a foraminous sheet in curved configuration.

59. A method of storing or transporting a foraminous sheet for use in catalysis, substantially as hereinbefore described with reference to or as illustrated in any of the accompanying drawings.

60. A method of installing a foraminous sheet in a catalytic reactor, substantially as hereinbefore described with reference to or as illustrated in any of the accompanying drawings.

61. A method of handling a foraminous sheet for use in catalysis, substantially as hereinbefore described with reference to or as illustrated in any of the accompanying drawings.

62. A method of removing a foraminous sheet from a catalytic reactor, substantially as hereinbefore described with reference to or as illustrated in any of the accompanying drawings.

63. Apparatus substantially as hereinbefore described with reference to or as illustrated in any of the accompanying drawings.