GB1573345A

GB1573345A - Wall structures having gas seals and gas seals therefor

Info

Publication number: GB1573345A
Application number: GB4696177A
Authority: GB
Original assignee: Northern Engineering Industries PLC
Current assignee: Rolls Royce Power Engineering PLC
Priority date: 1978-01-06
Filing date: 1978-01-06
Publication date: 1980-08-20

Description

(54) WALL STRUCTURES HAVING GAS SEALS AND GAS SEALS THEREFOR (71) We, NORTHERN ENGINEERING INDUSTRIES LIMITED, a British Company of NEI House, Regent Centre, Newcastle upon Tyne NE3 3SB, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to seal and wall combinations and to seals therefor.

The invention is particularly, though not exclusively, concerned with a wall having a sling extending therethrough and having a seal between the wall and the sling.

For example, in a power generation boiler the boiler is made up of tube-walls and is suspended from a structure by slings which pass from the structure, through the canopy roof of a containment enclosure. The slings may be connected to the tube roof, headers or other pipes or tubes of the boiler. It has been found that leakage occurs at the tube roof causing hot gases to enter the dead space between the tube roof and the canopy roof and when the gases cool to below the dewpoint of the acid vapours contained in the gases the acid condenses on the slings and causes severe corrosions.

The invention provides a seal and wall combination which reduces or eliminates the likelihood of such corrosion in boiler plant. The invention is also applicable elsewhere where sealing is required.

According to the invention there is provided a combination of a seal and a wall of a boiler containment or other enclosure, the wall having an aperture through which a sling or other element extends, in which a member is secured to the sling or other element in gas-tight relationship therewith and spaced from the wall, the seal being hollow and having end openings of similar size and configuration through which the sling or other element extends and the seal being secured at its ends to the member and to the wall around the aperture in gas-tight relationship therewith, and the seal comprising a first flexible layer of acid-resistant gas-impermeable material and a second flexible layer of acid-resistant refractory material, the first layer being at that side of the second layer which is remote from the inside of the enclosure.

Preferably, the member is outside the enclosure.

Preferably, the first layer lies between the second layer and a third flexible layer of refractory material.

A seal for use in the combination according to the invention comprises a flexible envelope of refractory cloth material containing said first layer and also containing further refractory material which, with the adjacent wall of the envelope forms said second layer the envelope having first and second opposite edges and third and fourth opposite edges such that said end openings of the seal can be formed by bringing together first and second marginal portions of the envelope adjacent the first and second edges respectively, said end openings being bounded by said third and fourth edges.

Preferably, such an envelope is rectangular.

Preferably, the length of each of the third and fourth edges is greater than the lengths of the peripheries of the respective openings to enable the openings to be formed by folding the first marginal portion in two about said second edge so that the first marginal portion embraces the second marginal portion.

Preferably, the first layer is made of polytetrafluoroethylene (P.T.F.E.).

Preferably, at least the second layer is made of silica glass material.

Preferably, the first layer lies within an envelope of silica glass cloth material, a batt of silica glass fibres lying within the envelope between the first layer and one wall of the envelope and forming with said one wall said second layer.

Preferably, the end openings of the seal are circular.

A second member, to which the seal is secured at one of its ends, may bound the aperture or be secured to the wall around the aperture.

The first-mentioned member can be a split circular plate the parts of which, when positioned together, define a central aperture for the sling or other element, the parts of the plate each having a flange around its edge. Gaskets are positioned between the mating surfaces of the parts and between the parts and the sling or other element.

Typically, the wall is the canopy roof of a boiler containment, there being in the wall a plurality of apertures having respective slings extending therethrough on which the boiler is suspended.

A seal and wall combination will now be described to illustrate the invention by way of example with reference to the drawings accompanying the provisional specification, in which: Figure 1 is a vertical section, on the line I - I in Figure 2, through the combination; Figure 2 is a horizontal section on the lines II - II in Figure 1; Figure 3 is an enlarged vertical section of part of the seal and wall shown in Figure 1; Figures 4 and 5 are enlarged horizontal part-sections on the lines IV - IV and V - V, respectively, in Figure 1; and also with reference to the accompanying drawing, in which: Figure 6 is a plan of the seal opened out flat.

The drawings show a seal and wall combination 10 in a power boiler installation, in which the boiler (not shown) is contained in an enclosure one wall 12 of which is shown. This is the canopy roof and it has apertures 14 (only one shown) through each of which passes a sling 16.

The slings 16 extend downwardly from the suspension structure (not shown) for the boiler to the boiler roof below the canopy roof. During the operation of the boiler, hot gases leak into the dead space 18 between the boiler roof and the wall 12.

The wall 12 has a lower casing 20, a layer of insulating material 22 of, for example, mineral wool, and an upper cladding 24 which seals off the material 22.

The sling 16 is made up of three spaced-apart plates 26, 28 and 30, having connections by which the sling is attached to the suspension structure and the tube roof, respectively. The slings can vary in the number of plates used and can otherwise vary in shape, for example they may be rod slings. The sizes of the apertures 14 vary according to the types of sling which pass through them.

In order to prevent leakage of hot gases from the dead space 18 into the space 32 above the wall 12, each sling has a seal assembly 34 (only one shown).

The sealing assembly includes a member 38, a seal 40 and insulating material 42, for example mineral wool.

The aperture is bounded by a cylindrical member 36 welded at one end to the lower casing 20 of the wall 12. The member 36 extends above the upper casing 24 by an amount sufficient to enable the seal 40 to be secured thereto.

The member 38 is a two-part circular plate 44. Each plate part 44 has a peripheral flange 46. The plate parts 44 together form a central aperture 48 through which passes the sling 16.

Gaskets 50 are located between the mating surfaces of the flanges 46 and between the flanges 46 and the sling plates 26 and 30. The gasket 50 is also located between the plates 26 and 28 and 28 and 30. The plate parts 44 are held together by nuts 52 and bolts 54, which pass through the mating portions of the flanges 46.

The seal 40 (see Figure 3) consists of an envelope 56, which contains an insulating batt 58, and a layer of gas-impermeable material 60. The envelope 56 is made from silica glass cloth material. Such material is available under the trade mark "Refrasil", Grade C-H available from the Chemical and Insulating Co. Limited, England. The insulating batt 58 is also made from a fibrous form of "Refrasil". To ensure that the "Refrasil" batt 58 remains in position in the envelope 56, the batt 58 is loosely stitched to the gas-side wall of the envelope 56 with a "Refrasil" thread.

The layer 60 is a sheet of polytetrafluoroethylene (P.T.F.E.), which is held in position in the envelope 56 by contact adhesive.

The seal 40 is generally rectangular, when flat, so that it can be easily positioned around the members 36 and 38 like a gaiter, (Figures 4 and 5).

The marginal portions 62 and 64 adjacent the end edges of the seal 40 are brought together and the portion 62 is folded in two about the end edge of the portion 64 so that the portion 64 is embraced by the portion 62.

The seal 40 is held in gas-tight relationship with the member 36 and with the flange 46 of the member 38 by respective clips 68 (Figures 1, 2 and 3). Each clip 68 is in two parts, which have first outwardly-extending flanges 70, which can be drawn together by clamps 72 to tighten the clip onto the member 36 or the flanges 46 of the member 38. The clip parts have second outwardly-extending flanges 73 which can be drawn together by a nut and a bolt at 71.

One clip part is stepped at 69to allow the clip parts to overlap as they are drawn together. The geometry of the clips 68 and the clamps 72 is such that the seal 40 is evenly compressed to give a good seal.

Each clamp 72 has a U-shaped body 74, to which is welded a nut 76 co-axial with an aperture in one limb of the body 74, the clamping member being a bolt 78 engaging the nut 76. The length of the bolt 78 is such that when the clamp 72 is fully tightened, the three thicknesses of the seal 40 held beneath the flanges 70 of the clips 68 are compressed to approximately 50% of their original thickness.

Between the upper and lower clamps 72, the interlocking joint 66 is held by clamps 80 (see Figure 5). The clamps 80 each have an L-shaped bar 82 screw-threaded along one limb and having a flat clamp jaw 84 secured to the other limb. A second flat clamp jaw 86 is disposed opposite to the jaw 84 and is secured to a jaw holder 88. The holder 88 is a plate that has been folded on itself and formed with a tubular section 90 at the fold. The tubular section 90 is a sliding fit on the screw-threaded limb of the bar 82. The clamps 80 are tightened by wing nuts 92 engaging the screw-threaded limbs of the bars 82. The use of wing nuts 92 prevents too much pressure being put onto the joint 66. Any similar clamp would also be suitable for this purpose.

Typical positions of the clamps 72-and 80 are shown diagrammatically in Figure 1.

The seal 40 is further protected at the clamped portions by reinforcements 94, which overlie the upper and lower edges of the seal 40 (Figure 3) and by a reinforcement 96, which is attached to the outside of the marginal portion 62 of the seal 40 (Figure 5). The reinforcements 94 and 96 are of "Refrasil" (Registered Trade Mark) cloth impregnated with P.T.F.E.

Mineral wool 42 is located around the seal 40, in the upper member 38 and around the sling 16 for a short distance above the member 38. The wool 42 is wired on where necessary.

The seal assembly 34 is made up as described below.

If the assembly is being fitted to a new boiler, then the lower member 36 will already be present as part of the wall 12.

If the assembly is being fitted to an existing installation then the marginal part of the wall surrounding the aperture 14 has to be cut away and a member similar to the member 36 welded into position; or alternatively, a member similar to the member 38 is secured around the existing upstanding part of the box structure defining the aperture 14.

The clamps 98 are then fitted to the sling 16 at the position shown in Figure 1. In the particular embodiment shown, the width of the sling 16 is such that the clamps 98 can be the same as the clamps 72. The clamps 98 are lightly tightened onto the sling 16. The gaskets 50 are then threaded between the plates 26,28 and 30 of the sling 16 and positioned on the plate parts 44 of the member 38. The clamps 98 are then tightened and the plate parts 44 are positioned around the sling 16, located on the clamps 98 and are secured together by the nut 52 and bolts 54.

The seal 40 is the positioned around the sling 16 so that the P.T.F.E. layer 60 is as shown in Figure 3. In the region of the member 36, the edges 62 and 64 of the seal 40 are folded to form the lower part of the joint 66. A clip 68 is then fitted and tightened using a G-clamp 72 which is fully tightened to correctly compress the seal 40. The nut and bolt 71 is then tightened to ensure that the seal 40 is correctly compressed against the member 36 to provide adequate sealing. The joint 66 is then progressively formed upwards and clamps 80 are fitted at regular intervals. A clip 68 and G-clamp 72 are then fitted at the top of the seal 40 to secure it to the member 38 in a similar manner to it being secured to the member 36.

Mineral wool 42 is then wired onto the seal 40 and the sling 16 and also located in the member 38.

Instead of flat slings 16, other types of sling could be used, for example rod slings.

In other applications, instead of a sling, an element such as a pipe may pass through the wall and be sealed in relation to it by the invention. The wall may alternatively form a side or a base of a boiler containment or other enclosure.

A number of dimensions have been indicated on the drawings described above and for the particular boiler sling described they are typically: millimeters A 3 B 100 C 1.5 millimeters D 250 E 38 F 150 G 3 H 300 I 400 J 12.5 K 0.8 L 0.127 M 406 N 75 P 3 The seal 40 is shown opened out flat in Figure 6. The seal is rectangular and is typically 1500 mm long and 406 mm wide (dimension "M" above). The reinforcements 94 and 96 are indicated, the latter being typically 150 mm wide.

The seal has first and second opposite edges 200, 202, respectively, and third and fourth opposite edges 204, 206. The marginal portions adjacent the edges 200, 202 are those referred to above and indicated at 62 and 64, respectively, in Figure 5.

The batt 58 is stitched to the envelope 56 at 210.

In an oil-fired boiler, the dewpoint of the acidvapours is typically in the region 145 - 155"C while the temperature in the dead space 18 (Figure 1) is typically 360 - 365"C well above the dewpoint of the vapours.

The P.T.F.E. layer 60 maintains its properties up to about 250"C. The total thickness of the "Refrasil" (Registered Trade Mark) batt 58 and of the mineral wool surrounding the seal 40 is selected to ensure that the layer 60 is kept below that temperature but above the dewpoint of the acid vapours.

Similarly the mineral wool 42 in the member 38 maintains the plate 44 above the dewpoint of the vapours.

In this particular embodiment, as the sling 16 is a large heat sink, the mineral wool 42 is also wrapped -around the sling 16 so that the temperature of the sling in the region 100 is kept above the dew point of the vapours.

It is considered that the open form of the seal assembly 34 allows gases to circulate within it, thus avoiding stagnation of the gases in the assembly and excessive lowering of the temperature of the gases and the assembly.

The substantially cylindrical design of the seal assembly is preferred since this allows the seal 40 to be relatively easily sealed against the members 36 and 38 and avoids possible areas of stagnation. With other configurations, the sealing of the seal 40 to the members 36 and 38 would then be more difficult and stagnant areas could be formed. The seal would probably have to be of a special tailored shape and would be more prone to tearing or fatigue damage.

Two experimental seal assemblies 34 were made substantially as described above, except that they did not have the reinforcements 94 and 96 and one did not have the "Refrasil" (Registered Trade Mark) batt 58 stitched into position in the envelope 56. The assemblies were then installed in a power station for an experimental period of six months, after which they were removed and examined.

Examination of the assemblies showed: (a) that they were dry indicating that substantially no acid deposition had occurred, i.e.

the temperature of the seal 40 has been maintained; (b) the gas-side of the seal 40 was only very lightly stained; (c) the P.T.F.E. layer 60 was completely intact even in the region of the folded joint 66; (d) the batt 58, which was not stitched into position in the envelope 56, had slipped down slightly but still basically covered the layer 60; (e) where the batts 58 had been compressed by the clips 68 and clamps 72 and 80, they still had mechanical integrity including resilience which indicates that the assembly could have been reinstalled and properly resealed; and (f) the overall appearance of the assemblies was very good indicating a service life much longer than the experimental six month period and that the assemblies would be re-usable after removal to allow inspection of the sling.

In a modification, the member 38 may be positioned within the containment enclosure instead of outside as shown. It is believed that the insulating material 42 would not be necessary since the seal is in the hot space 18 and its external temperature will consequently remain sufficiently high. However, some corresponding insulating material could, of course, be used if it was found necessary.

This form of construction is not preferred for use in boiler plant since inspection of the seals and slings would be made considerably more difficult. The seal would extend downwardly (in the case of roof slings) and the clips corresponding to the clips 68 would not be accessible from the space 32. Instead they would be accessible only from the dead space 18.

In a further modification, the seal may be made as a tube at the outset, in which case the sling or other element would have to be passed through the seal during construction of the boiler plant. In general, in boiler plant the seal will be a gaiter type which can be assembled about the sling. Such seals will be used generally both for new installations and for retrofitting to existing plant.

WHAT WE CLAIM IS: 1. A combination of a seal and a wall of a boiler containment or other enclosure, the wall having an aperture through which a sling or other element extends, in which a member is secured to the sling or other element in gas-tight relationship therewith and spaced from the wall, the seal being hollow and having end openings of similar size and configuration through which the sling or other element extends and the seal being secured at its ends to the member and to the wall around the aperture in gas-tight relationship therewith, and the seal comprising a first flexible layer of acid-resistant gas-impermeable material and a second flexible layer of acid-resistant refractory material, the first layer being at that side of the second layer which is remote from the inside of the enclosure.

2. A combination according to claim 1, in which the member is outside the enclosure.

3. A combination according to claim 1, in which the member is inside the enclosure.

4. A combination according to any preceding claim, in which the first layer lies between the second layer and a third flexible layer of refractory material.

5. A combination according to any preceding claim, in which the first layer is of P.T.F.E.

6. A combination according to any preceding claim, in which the seal is installed like a gaiter about the member and has edge marginal portions brought together in gas-tight relationship.

7. A combination according to claim 6, in which one marginal portion is folded in two about the edge of the other marginal portion to embrace that other marginal portion.

8. A combination according to claim 6 or claim 7, in which the marginal portions are pressed together by clamps.

9. A combination according to any preceding claim, in which the seal is held against the member by a clip encircling the seal and under stress to maintain the gas-tight relationship.

10. A combination according to any preceding claim, in which the seal is held by a clip against a further member bounding the aperture or secured to the wall around the aperture, the clip encircling the seal and being under stress to maintain the gas-tight relationship.

11. A combination according to any preceding claim, in which the seal consists of an envelope containing the first layer and also containing further refractory cloth material which, with the adjacent wall of the envelope, forms said second layer.

12. A combination according to claim 4 or any preceding claim dependent thereon, in which the total thickness of said second and third layers is two inches.

13. A combination according to any preceding claim, in which said refractory material is "Refrasil" (Registered Trade Mark) material.

14. A combination according to any preceding claim, in which the seal is like a gaiter and which when opened out flat is rectangular.

15. A combination according to any preceding claim, in which the seal has reinforcement where it engages the member and the wall, the reinforcement being of refractory cloth material impregnated with P.T.F.E.

16. A combination according to claim 8 or to any preceding claim dependent thereon, in which the seal has reinforcement where it is engaged by the clamps, the reinforcement consisting of refractory cloth material impregnated with P.T.F.E.

17. A seal for use in the combination claimed in any preceding claim comprising a flexible envelope of refractory cloth material containing said first layer and also containing further

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. (e) where the batts 58 had been compressed by the clips 68 and clamps 72 and 80, they still had mechanical integrity including resilience which indicates that the assembly could have been reinstalled and properly resealed; and (f) the overall appearance of the assemblies was very good indicating a service life much longer than the experimental six month period and that the assemblies would be re-usable after removal to allow inspection of the sling. In a modification, the member 38 may be positioned within the containment enclosure instead of outside as shown. It is believed that the insulating material 42 would not be necessary since the seal is in the hot space 18 and its external temperature will consequently remain sufficiently high. However, some corresponding insulating material could, of course, be used if it was found necessary. This form of construction is not preferred for use in boiler plant since inspection of the seals and slings would be made considerably more difficult. The seal would extend downwardly (in the case of roof slings) and the clips corresponding to the clips 68 would not be accessible from the space 32. Instead they would be accessible only from the dead space 18. In a further modification, the seal may be made as a tube at the outset, in which case the sling or other element would have to be passed through the seal during construction of the boiler plant. In general, in boiler plant the seal will be a gaiter type which can be assembled about the sling. Such seals will be used generally both for new installations and for retrofitting to existing plant. WHAT WE CLAIM IS:

1. A combination of a seal and a wall of a boiler containment or other enclosure, the wall having an aperture through which a sling or other element extends, in which a member is secured to the sling or other element in gas-tight relationship therewith and spaced from the wall, the seal being hollow and having end openings of similar size and configuration through which the sling or other element extends and the seal being secured at its ends to the member and to the wall around the aperture in gas-tight relationship therewith, and the seal comprising a first flexible layer of acid-resistant gas-impermeable material and a second flexible layer of acid-resistant refractory material, the first layer being at that side of the second layer which is remote from the inside of the enclosure.

refractory material which, with the adjacent wall of the envelope, forms said second layer the envelope having first and second opposite edges and third and fourth opposite edges such that said end opening of the seal can be formed by bringing together first and second marginal portions of the envelope adjacent the first and second edges respectively, said end openings being bounded by said third and fourth edges.

18. A seal according to claim 17, in which the envelope is generally rectangular.

19. A seal according to claim 17 or 18, in which the length of each of the third and fourth edges is greater than the lengths of the peripheries of the respective openings to enable the openings to be formed by folding the first marginal portion in two about said second edge so that the first marginal portion embraces the second marginal portion.

20. A seal according to claim 17, 18 or 19, in which the first layer is of P.T.F.E.

21. A seal according to any one of claims 17 to 20, in which the refractory material is "Refrasil" (Registered Trade Mark) material.

22. A seal according to any one of claims 17 to 21, in which a reinforcement of refractory cloth material impregnated with P.T.F.E. overlies the third and fourth edges of the seal.

23. A seal according to any one of claims 17 to 22, in which areinforcement of refractory cloth material impregnated with P.T.F.E. overlies the first marginal portion of the seal.

24. A combination according to claim 1, substantially as herein described with reference to the drawings accompanying the provisional specification and with reference to the accompanying drawing.

25. A seal according to claim 17, substantially as herein described with reference to the drawings accompanying the provisional specification and with reference to the accompanying drawing.