EP0596781A1 - Sheet of tubes for heat exchange, more particularly for superheater, which tubes are sorrounded by a refractory lining - Google Patents

Abstract

The heat-exchanger sheet (N) comprises tubes having parallel branches (1, 2, 3, 4) whose axes are located substantially in one and the same plane (P), intended to be arranged vertically when the sheet (N) is installed in the working position. The sheet (N) includes, on each side, means (M1, M2) for holding the refractory (protective) lining (covering) (R), extending in a plane parallel to the exchanger sheet (N); linkage means (L) are provided between the holding means (M1, M2) located on each side of the sheet, the abovementioned linkage means (L) passing through the exchanger sheet (N) between the parallel adjacent branches (1, 2, 3, 4). <IMAGE>

Description

The invention relates to a ply of tubes for heat exchange of the kind that include tubes having parallel branches whose axes are located substantially in one and the same plane, these axes being generally arranged vertically when the ply is installed in working position, the branches being connected to each other at their ends by transverse parts, in particular curved parts, the tubes being surrounded by a protective coating of refractory material, in particular refractory concrete.

The heat exchange is intended to occur between a first fluid circulating inside the tubes, and a second fluid circulating outside the tubes. Generally, the first fluid is a cold fluid to be heated, and is constituted by a liquid, while the second fluid is a hot fluid constituted in particular by combustion gases.

The invention relates more particularly, because it is in this case that its application is of most interest but not exclusively, such a sheet of tubes for boiler superheater. In this case, the liquid circulating inside the tubes is water, intended to be heated by the combustion gases or fumes circulating outside the sheet.

The protective coating is necessary to protect the tubes against corrosion of the fumes, since the combustion gases can be chlorinated, sulphurized, or other, especially when they come from incinerators. In addition, it is necessary to protect the tubes against abrasion of fuel dust, an abrasion which is all the more sensitive as the temperature is higher and the particles move with a greater relative speed relative to the layers of tubes.

Up to now, a refractory concrete protection has been used, which poses the problem of making this refractory concrete hold on the sheet of tubes. We have therefore provided attachment zones on the tubes by fixing, by welding or electro-forging, on the tubes, orthogonally to the axis of the tubes, steel pins or studs generally called "studs"; these pins are preferably inclined at 45 ° relative to the mean plane of the sheet and are staggered on the tubes, on both sides of the sheet. The sheet of tubes is then covered, on both sides, with a layer of refractory concrete which comes to hang on the pins mentioned above.

Such a solution has a significant drawback: the metal tubes of the sheet and the protective refractory concrete do not have the same coefficient of expansion and the result is that the concrete cracks and the combustion gases pass inside the cracks. and take off the concrete from the tube. Finally, the protective concrete falls in plates. This results in a rapid attack of the web tubes as soon as they are discovered. Destruction of the superheater layer can occur within 6 to 8 months, which means shutting down the boiler for repairs.

The object of the invention is, above all, to provide a sheet of tubes for heat exchange which no longer has or to a lesser degree the drawback mentioned above, while remaining of a relatively simple and economical construction.

According to the invention, a sheet of heat exchange tubes, of the kind defined above, is characterized in that it comprises, on each side, means for holding the protective coating, extending in a plane parallel to the sheet. exchanger, and that connecting means are provided between the holding means located on each side of the ply, the aforesaid connecting means passing through the exchanger ply between adjacent tube branches.

Preferably, these connecting means between the holding means extend perpendicular to the plane of the sheet.

Said holding means comprise transverse blades pressing against the ply, parallel to the mean plane of the ply, these blades having a longitudinal direction extending perpendicular to the direction of the axes of the tubes.

Preferably, the holding means comprise, on each side of the ply, a honeycomb structure fixed to the transverse blades and whose mean plane is parallel to that of the ply, this structure being suitable for receiving the coating of protective material; said honeycomb structure has cells formed by identical regular polygons, in particular hexagons.

Advantageously, the connecting means comprise spacer combs arranged between two adjacent tube branches, and extending in the longitudinal direction of the branches, these combs comprising hooking means extending transversely to their longitudinal edges suitable for cooperating with the means of support.

The spacer combs may have, on their longitudinal edges, projecting tongues intended to cooperate with corresponding openings provided on the transverse blades, these tongues being distributed in such a way that an isolated tongue is followed by a pair of close tongues l one of the other.

Advantageously, the means for holding the covering as well as the connecting means are arranged opposite the tubes of the sheet, so that these tubes can expand independently of the protective covering, the weight of which as well as that of the holding means and connection is supported by the lower transverse parts, in particular loops, connecting the branches of the tubes.

Intermediate retaining means, in particular constituted by bars fixed to the tubes of the heat exchanger ply, may be provided to cooperate with the lower end of partial combs extending over only a fraction of the length of a tube branch, so that the weight of the protective coating is supported in at least one zone of the tube branch other than its lower end.

Advantageously, the means for holding the protective covering comprise at the ends of the ply, both at the lateral and vertical ends, an articulated structure, making it possible to produce a relatively reduced radius of curvature, in particular a "Flexmetal" structure, connected to the means of lateral support.

The invention consists, apart from the arrangements set out above, of a certain number of other arrangements which will be more explicitly discussed below in connection with an exemplary embodiment described with reference to the attached drawings, but which is by no means limiting.

Figure 1 of these drawings is a schematic view of a sheet of tubes for boiler superheater, before coating these tubes with a protective coating of refractory material.

Figure 2 is a simplified perspective view of a section of the tubes of the sheet during the establishment of the means for holding the protective covering and connecting means between the holding means, the sheet being placed horizontally.

Figure 3 is a partial elevational view with parts cut away from the ply equipped with the holding means and the protective coating.

Figure 4 is a section along line IV-IV, Figure 3.

Figure 5 is a plan view of a transverse blade.

FIG. 6 is a plan view of a spacer comb intended to extend along practically the entire length of the branch of a tube.

FIG. 7, finally, is a plan view of two partial spacer combs, extending over a fraction of the length of a branch of a tube.

Referring to FIG. 1 of the drawings, one can see a sheet N of tubes t1, t2, t3, t4 intended for a boiler, to allow a heat exchange between a liquid, generally water, circulating inside. tubes and a hot fluid, usually gases, flowing outside the tubes.

The sheet N is intended more particularly to constitute a superheater element arranged vertically in a boiler; the hot burned gases arrive from the bottom and escape upwards while the water to be heated circulates inside the tubes, for example in the direction of the arrows shown in FIG. 1.

As an indication, the burnt gases are at around 650/700 ° C at the bottom of the sheet and at around 450/500 ° C at the top of the sheet. The height of a sheet N can be approximately 6 meters while the outside diameter of the tubes is generally between 38 and 54 mm approximately. A superheater can comprise several layers N mounted in parallel in the boiler.

The metal tubes t1 .... t4 can be made of more or less highly alloyed steel, in particular chrome / molybdenum steel.

The tube t1 makes it possible to produce a first ply element. It is curved in a zigzag and has parallel vertical branches having at their ends curved parts, such as b substantially in a semicircle. The tubes t2, t3, t4 make it possible to produce a second, a third and a fourth ply element respectively. These elements are designed so that their loops can engage with one another as illustrated in FIG. 1. It should be noted that the tube t1 of the first element is bent, in the lower part, with a very small radius of curvature so that the forward branch and the return branch of this tube are practically adjacent. The radius of curvature of the ends of the other tubes which envelop the first element gradually increases.

The sheet of tubes N comprises in the upper part an inlet area E located at the top left and an outlet area S located at the top right. It is clear that, as required, one can reverse the inlet and the outlet and adopt a reverse circulation direction to that shown for the liquid in the tubes.

At the inputs and outputs, the tubes are interconnected two by two. Thus, the tubes t1 and t2 have a common input e1 and a common output s1, the tubes t3 and t4 have a common input e3 and a common output s3. These inputs e1, e3 and outputs s1, s3 are themselves connected to a collector corresponding to E and S. It is clear that other possibilities of association of the tubes exist. For example, the four tubes could be connected together at the inlet and at the outlet.

The branches, such as 1, 2, 3, 4, of the tubes have their parallel axes and located in the same plane. These branches can be mechanically connected to each other using small steel elements such as 5, diagrammatically shown, welded to the outer wall of the tubes.

When the sheet N has been produced with the tubes, it is then provided with a protective coating of refractory material, generally a coating of refractory concrete R (see FIGS. 3 and 4).

On each side of the sheet N (see FIG. 4) provision is made for holding means M1, M2 of the protective covering, these holding means extending in a plane parallel to the mean plane P of the exchanger sheet. In addition, connection means L are provided between the holding means M1, M2 located on each side of the ply, the aforesaid connecting means L passing through the exchanger ply N between adjacent parallel branches of tube 1, 2, 3, 4 ....

The holding means M1, M2, comprise, on each side of the ply, transverse blades 5, clearly visible in FIG. 5. These transverse blades are tangent to the tubes and are located in a plane parallel to the mean plane P of the ply , the longitudinal direction of the blades 5 being orthogonal to the axes of the branches of the tubes. Several parallel transverse blades 5 are arranged on each side of the sheet; the distance between the axes of two neighboring blades 5 is equal D as illustrated in FIG. 3.

Each blade 5 has a series of equidistant openings 6 and, interposed between the openings 6, pairs of openings 7, 8. The openings have, for example, a rectangular shape. The openings 6 are centered on the longitudinal center line 9 of the blade 5. The long side of the opening 6 is orthogonal to this line 9.

The openings 7 and 8 of the same pair are symmetrical with respect to the line 9 and have a large side orthogonal to the line 9. The dimensions of the openings 7 and 8 are slightly smaller than those of the openings 6. The mean transverse line d 'a pair of openings 7, 8 is equidistant from the openings 6 located on either side.

As will be explained in more detail below, the connecting means L make it possible to assemble two transverse blades 5 located on either side of the ply N, at the same height.

The holding means further comprise, on each side of the ply N, a honeycomb structure A fixed to the transverse blades 5 and whose mean plane is parallel to that of the ply N. The honeycomb structure comprises cells or housings 10 formed by prisms with regular polygonal outline, the generaters of these prisms being orthogonal to the mean plane of the ply N. The housings 10 are open on their two faces parallel to said ply N. Advantageously, the housings 10 have a regular hexagonal outline and the structure A is constituted by a layer of a material known under the commercial name of "Hexmetal". If we denote by p the pitch of the alveolar structure (see Figure 3), p being equal to the distance between the centers of two adjacent polygons, we choose the distance D, defined above, equal to 1.5p.

The honeycomb structure A is welded in zones such as 11 on the transverse blades 5.

The connecting means L between the holding means M1, M2, extend perpendicular to the mean plane P of the sheet, and include spacer combs 12 (see FIG. 6) constituted by rectangular dishes placed between two branches such as 1, 2 adjacent tubes. The large dimension of a comb 12 is parallel to the axis of the branches 1, 2 and the plane of this comb is orthogonal to the plane P.

Each comb 12 has, on its longitudinal edges, indentations or transverse tongues 13 regularly distributed and pairs of tongues 14, 15 close to each other, located at equal distance from two tongues 13. The spacing of the tongues 14 and 15 corresponds to that of the openings 7, 8 in FIG. 5 so that these tongues can penetrate these openings. It should be noted that in the sheet produced, as illustrated in FIGS. 2 to 4, the plane of a spacer comb 12 is orthogonal to the plane of a transverse blade 5 and, moreover, the longitudinal direction of a comb 12 is orthogonal to the longitudinal direction of a transverse blade 5. Thus, the different tongues of the same spacer comb 12 cooperate with openings 6 and 7, 8 of different blades 5. The connection between the combs 12 and the transverse blades 5 is obtained by folding the tabs 13, 14, 15 through the openings 6 and 7.8 so that the sheet N of tubes is trapped between the transverse blades 5. place between two tabs 14, 15 a transverse partitioning of the honeycomb structure A as illustrated in FIG. 3; the tongues 13 located on either side of this pair of tongues 14, 15 will be located in the middle of the adjacent housings, in the direction of the axis of the tubes, due to the relationship D = 1.5 p. It is thus easy to correctly position the honeycomb structure.

The implementation of holding means M1, M2 and connecting means L is as follows.

After having prepared the sheet N illustrated in FIG. 1, it is placed horizontally on suitable supports (not shown). Between two branches of adjacent tubes such as 1, 2 of the tablecloth, a spacer comb 12. It should be noted that these branches 1, 2 must be spaced apart by a sufficient space, for example 3 mm to allow the insertion of the comb 12 perpendicular to the mean plane P.

During this positioning, the combs 12 rest on jigs (not shown) arranged below the horizontal sheet N. On the side of the upper face of the ply N, the transverse blades 5 are put in place, as shown in FIG. 2. The tongues 13, and 14, 15 of the various combs are engaged in the openings 6, 7 and 8 of the blades 5 respective. The tongues are folded back to ensure the connection between the combs 12 and the blades 5; for certain tube areas, it may be more practical to ensure the connection by welding. Then the honeycomb structure A is put in place on the blades 5 by introducing, between the tongues 14, 15 suitably folded and sufficiently spaced apart by construction, a partitioning of the structure A. Under these conditions, the honeycomb structure A rests perfectly on flat on all transverse blades 5.

Welding is then carried out in the zones such as 11 (see FIG. 3) of the walls of the honeycomb structure A on the blades 5.

The sheet N is then turned over so that its horizontal lower face, which is not yet equipped with the blades 5 and the honeycomb structure A, becomes the upper face, and this face is fitted as explained above.

After this positioning of the holding means M1, M2 and of the connecting means L, the honeycomb structure A of refractory concrete R is covered on both sides of the sheet N as shown diagrammatically in FIGS. 3 and 4.

The refractory concrete is retained not only in the housings 10 of the honeycomb structure A but also by the transverse blades 5 below which it passes.

There is thus a very good connection of the concrete R with the holding means M1, M2 and therefore with the sheet of tubes N as a whole, but there is practically no attachment of the concrete to the tubes in the longitudinal direction. , that is to say in a direction parallel to the axis of the branches of the tubes. When the tablecloth N is in placed vertically, the tubes are hooked by their upper part and will therefore be able to expand longitudinally practically independently of the concrete. This will result in less cracking of the concrete R which, in any case, is retained in the housings 10 of the honeycomb structure A.

At a lateral edge such as 16 (FIGS. 3 and 4) of the ply N, the honeycomb structure A would not allow bending along a radius of curvature sufficiently small to surround the branch 1 of the tube at a short distance. In this zone of the lateral edge 16, the honeycomb structure A is replaced by an articulated structure F made up of elements 17 of sheet metal folded according to a profile in trapezoidal notches, as visible in FIG. 3. The successive elements 17 are slightly nested one in the others and connected by articulation rods 18 which extend parallel to the axes of the branches 1, 2 of the ply. Such an articulated structure F is commercially available and known under the name of "Flexmetal".

At the top and bottom of the sheet N, a similar articulated structure F is put in place in the same way to surround the upper and lower edges.

The connection between the articulated structure F conformed to the lateral edge 16, and the cellular structures M1, M2 located on each side of the sheet N can be produced by welding. For example, the honeycomb structure A is bordered on each side of the sheet by an end plate 19, welded to the honeycomb structure A. The edges of the articulated structure F are then welded to this dish 19. openings 20 to allow the passage of refractory concrete R. As a variant, provision may be made for the transverse blades 5 to rotate around the end tubes forming the edge of the ply N and to be connected by welding from one face to the other of the tablecloth N; in this case, the structure F can be welded not only on the structures A on the two faces of the sheet N but also on the blades 5 in their curved zones.

When the spacer combs 12 extend along the entire length of the parallel branches of the tubes of the vertical web N, without being abutted in the vertical direction against a retaining member fixed to the tubes of the web, these tubes can expand so totally independent of refractory concrete R, since sliding is possible between the outer surface of the tubes and the concrete. The risk of cracking of the concrete, due to differences in expansion, is considerably reduced.

This solution can however have a slight drawback because all of the holding means M1, M2 and the refractory lining R carry by gravity, via the lower ends of the combs 12, in the concavity of loops such as b (see figure 1) tubes. Significant constraints may appear in these areas.

To avoid such constraints, partial spacer combs 112 (FIG. 7) can be produced, that is to say of which the length is only a fraction of the height h (FIG. 1) of the space between two adjacent branches.

To retain a partial comb 112 relative to a tube branch such as 1 (see FIG. 7), bars such as 21, of reduced length, are arranged on the outer cylindrical surface of the branch 1, fixed by welding to the outer surface of the branch 1. According to the representation of FIG. 7, the branch 1 is represented horizontal, but it should be understood that, when the sheet is installed in the boiler, the branch 1 is vertical and, with it, the bar 21, the axis is parallel to that of branch 1. Under these conditions, if the partial comb 112 located to the left of the bar 21 in FIG. 7, becomes the upper partial comb when the branch 1 is placed in the vertical position, the lower edge 22 of this partial comb 112 will come to bear against the adjacent end of the bar 21.

Of course, one can provide several bars 21 or equivalent elements, along the same branch 1, each bar taking charge of the associated upper partial comb. Instead of the bar 21, it is possible to provide a welded plate perpendicular to the mean plane of the sheet or any other welded retaining part.

By operating in this way, the weight of the holding means M1, M2, the connecting means L and of the refractory concrete covering R is distributed at several points along the length of the branches 1, 2 ... of the tubes of the sheet.

The concrete coating is then no longer completely independent of the ply of tubes, due to these vertical stops 21, so that zones of preferential cracking can occur, in particular due to the differences in thermal expansion. To reduce these risks, sufficient clearance is provided between the bars 21 and the neighboring edge 23 of the lower partial combs, located below the bars when the ply N is arranged vertically.

In any case, the honeycomb structure A has a certain elasticity and can withstand differential deformation while continuing to mesh the coating of refractory concrete R.

A sheet of tubes, for heat exchange, provided with a protective coating produced in accordance with the invention has a considerably increased service life which largely counterbalances the slight increase in cost of protecting the sheet.

Claims (10)

Tube of tubes for heat exchange, in particular for superheater, comprising tubes having parallel branches whose axes are located substantially in one and the same plane, the branches being connected to each other, at their ends, by transverse parts, in particular curved parts, the tubes being surrounded by a protective coating of refractory material, characterized in that it comprises, on each side, means for holding (M1, M2) the protective coating, extending in a plane parallel to the heat exchanger ply (N), and that connection means (L) are provided between the holding means (M1, M2) located on each side of the ply, the aforesaid connection means (L ) passing through the exchanger ply (N) between adjacent tube branches (1, 2, 3, 4 ...). Tube layer according to claim 1, characterized in that the connecting means (L) between the holding means (M1, M2) extend perpendicular to the plane of the sheet. Tube layer according to one of the preceding claims, characterized in that the holding means (M1, M2) comprise transverse blades (5) pressing against the sheet (N), parallel to the mean plane (P) of the sheet, these blades (5) having a longitudinal direction extending perpendicular to the direction of the axes of the tubes. Tube layer according to claim 3, characterized in that the holding means (M1, M2) comprise, on each side of the ply (N), a honeycomb structure (A) fixed to the transverse blades (5) and the mean plane is parallel to that of the sheet, this structure (A) being suitable for receiving the coating of protective material (R). Tube layer according to claim 4, characterized in that the honeycomb structure (A) comprises cells (10) formed by identical regular polygons, in particular hexagons. Tube layer according to one of the preceding claims, characterized in that the connecting means (L) comprise spacer combs (12, 112) disposed between two adjacent branches (1, 2, 3, 4), and s' extending in the longitudinal direction of the branches, these combs (12, 112) comprising hooking means (13, 14, 15) extending transversely to their longitudinal edges suitable for cooperating with the holding means (M1, M2). Tube layer according to all of claims 3 and 6, characterized in that the spacer combs (12, 112) have, on their longitudinal edges, projecting tongues (13; 14, 15) intended to cooperate with openings corresponding (6; 7, 8) provided on the transverse blades (5), these tabs (13; 14, 15) being distributed in such a way that an insulated tab (13) is followed by a pair of tabs (14, 15) close to each other. Tube layer according to one of the preceding claims, characterized in that the holding means (M1, M2) of the covering as well as the connecting means (L) are arranged opposite the tubes of the sheet, of so that these tubes can expand independently of the protective covering (R), the weight of which as well as that of the retaining structure is supported by the lower transverse connecting parts of the tubes, in particular the loops ( b ). Tube layer according to one of Claims 1 to 7, characterized in that intermediate retaining means, in particular constituted by bars (21) fixed to the tubes of the heat exchanger layer (N), are provided to cooperate with a lower end of combs (112) extending over only a fraction of the length of a branch of tube, so that the weight of the protective coating (R) is taken care of in at least one zone of the tube branch other than its lower end. Tube layer according to any one of the preceding claims, characterized in that the holding means (M1, M2) of the protective coating (R) comprise at the ends of the sheet (N), both at the lateral and vertical ends, an articulated structure (F), making it possible to produce a relatively reduced radius of curvature, in particular a "Flexmetal" structure, connected to the lateral holding means (M1, M2).

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