Welding frame for a membrane wall

Abstract

 The invention is concerned with a method for protecting a membrane wall of an incinerator by mounting it in a special frame and providing onto it a protecting, clad welded cover. The frame maintains the initially substantially flat membrane wall in a curved shape by plastically deforming it into at least one, preferably at least two mutually perpendicular directions by bending. The frame clamps the membrane wall such that the membrane wall can shift in its plane. Due to the contraction at the clad welding side due to clad welding, the plastically (and thus permanent) flexural deformation that is given to the membrane wall before clad welding, is compensated.

Description

[0001] The proposal is to mount a membrane wall, or part thereof, of an incinerator in a special frame during cladding, wherein the steam pipes of carbon steel (e.g. in the range from ST35-8 tot 13 chrome) are provided with a protecting, nickel containing (e.g. stainless steel (RVS)) covering by means of clad welding (preferably straight clad welding, i.e. weld beads extending in longitudinal direction). The invention is applicable to newly built and overhauled membrane walls. In the following, this protective coating is called RVS.

[0002] The membrane wall is e.g. provided for a waste incinerator. The membrane wall serves as side boundary of the incineration space, the temperature of which can be in the range of e.g. 700-800 degrees Celsius. The membrane wall is cooled by the steam guided by vertically upward extending steam pipes. The membrane wall can however also be provided for different incinerators and possibly be cooled by another fluid flowing through the pipes, like water.

[0003] The membrane wall can be provided as separation wall or as bulkhead (exposed to the fire at two or one side, respectively). The side of the membrane wall facing the fire and the corroding environment is protected by clad welding. The invention offers most advantages with a membrane wall that must be protected at only one side.

[0004] An example of a membrane wall is given in US-A-3.404.663 (particularly fig. 5 and 6) or EP-A-1.493.968 (particularly fig. 1). As a rule, the membrane wall is made of a plurality of in a common plane provided, parallel and straight steel tubes with round cross section, wherein the spacing between two neighbouring tubes is filled with a solid steel strip that is welded to both tubes, and wherein the strip is provided in the area of the smallest distance between the tubes. The tubes have closed peripheral walls and super heated steam passes there through.

[0005] Convenient RVS qualities contain Fe, C, alloying substances and also Ni and Cr. The layer thickness of the clad weld layer is preferably between 1.8 and 2.5 cm.

[0006] With the welding frame the initially substantially flat membrane wall is maintained in a curved shape by plastically deforming it into at least one, preferably at least two mutually perpendicular directions by bending. Preferably the membrane wall is mounted to the frame such that it, or a part of it, such as a peripheral wall, can displace, such as shift, within its plane in at least one, preferably two mutually perpendicular directions. This can e.g. be obtained by mounting the membrane wall to the frame by clamping.

[0007] The plastically deforming bending is preferably carried out such that the membrane wall is curved in two directions, wherein its convex (i.e. bulging) side is clad welded. Due to the contraction at the clad welding side due to clad welding, the plastically (and thus permanent) flexural deformation that is given to the membrane wall before clad welding, compensated. Preferably the membrane wall is flexed plastically in such a rate, that after clad welding and removing from the welding frame, the permanent flexural deformation that is given to the membrane wall, is substantially compensated, such that a substantially flat, at a single side clad welded membrane wall is obtained. In other words, the membrane wall is pre-flexed, taking account of the to be expected contraction due to clad welding.

[0008] The longitudinal contraction can measure 100 mm with a 6 m long membrane wall.

[0009] The welding frame preferably has a plate, approximately corresponding to the length and width of the membrane wall and having a curvature corresponding to the desired curvature in longitudinal and width direction of the membrane wall.

[0010] With a view to efficiency it is preferred that the welding frame is designed to simultaneously mount two membrane walls substantially mirror symmetric and opposite each other in a lying position.

[0011] The drawing illustrates in the single figure a part of a preferred embodiment of a welding frame according to the invention. Illustrated are two elongate, flat form plates (form elements/form surfaces) that mutually registered lay opposite each other and of which the longitudinal ends have a smaller spacing than their centres. Between their centres and their longitudinal parts the form plates follow a smoothly curved shape, substantially according to a circle arc segment. The form plates are kept in the in a single direction curved shape at mutual distance by rod like spacers, which obviously have a smaller length at the longitudinal ends compared to closer to the longitudinal centres of the form plates.

[0012] The form plates are at their lower longitudinal end commonly pivoting mounted in a space frame, to move between substantially horizontal and vertical positions.

[0013] In the horizontal position, a flat membrane wall (not shown in the drawing) can be mounted at the top side of the upper form plate. To provide that the membrane wall is curved in two directions, a rigid central shaft (profile element; spacer) is placed between the form plate and the membrane wall. The central shaft (not shown in the drawing) extends centrally across the form plate in longitudinal direction, has a constant height along its length, is curved in longitudinal direction to follow the curvature of the form plate, and extends at least to the longitudinal ends of the membrane wall.

[0014] The membrane wall has a smaller width compared to the form plate, such that the form plate projects at both sides beyond the membrane wall.

[0015] The membrane wall is now, resting onto the form plate and the central shaft, curved plastically. For that, mutually spaced rigid cross rods (pressing element) are located at the side opposite the form plate, extending perpendicular to the length of the form plate, the ends of which are mounted by elongated bolts (tension elements) to the at both sides beyond the membrane wall extending longitudinal edges of the form plate.

[0016] Between the cross rods and the membrane wall, a second rigid shaft is located onto the longitudinal edge of the membrane wall at both sides of the shaft. This second shaft has a shape and dimension substantially similar to the central shaft.

[0017] Starting from the longitudinal centre of the form plate the rods are tightly pressed onto the membrane wall by tightening the bolts. By this, the cross rods push with their central part directly onto the membrane wall and press the centre of the membrane wall with the under side onto the central shaft. With their longitudinal ends the cross rods press directly onto the second shafts. The second shafts press directly onto the longitudinal edges of the membrane wall and press the longitudinal edges of the membrane wall with the under side onto the top side of the form plate. Thus the membrane wall is curved plastically in the longitudinal and cross direction.

[0018] Subsequently, the cross rods and the second shafts are removed, save the cross rod at each longitudinal end of the membrane wall. Thus the membrane wall is kept clamped onto the central shaft by two cross rods.

[0019] Now the assembly of two form plates is pivoted over approximately 180 degrees to become again in an approximately horizontal position, wherein the second form plate is on top. Onto that, a second membrane wall can now be mounted, wherein the procedure above can be repeated.

[0020] The assembly is then positioned vertically, after which the clad welding can be carried out. For that e.g. a welding robot is located in the space frame. At the side opposite the form plate, weld beads are put on the membrane wall, wherein said weld beads extend mutually parallel in the longitudinal direction of the membrane wall from the one to the opposite longitudinal end. In sideways direction, the weld beads merge without a gap, such that a tight, clad welded cover is created. Preferably the two membrane walls that are mounted to the assembly are simultaneously clad welded, wherein preferably the weld front continuously are opposite each other, relative to the symmetry plane between both form plates.

[0021] Longitudinal and/or width changes of the membrane wall during clad welding can be allowed since the membrane wall can shift relative to its clamped fixture.

[0022] Alternative embodiments according to the invention are feasible. E.g. wherein the cross rods are thickened at both their longitudinal ends or have projections corresponding to the height of the second shafts. Or the cross rods can have a curved shape according to the desired curved shape of the membrane wall. Thus the second shafts can be eliminated. The form plates can be curved in two directions according to the desired curvature of the membrane wall. Thus the central shaft can be eliminated. The shape plates can be replaced by another frame, e.g. made from sections. The welding frame can have a different shape.

Claims

1. Method for protecting a membrane wall of an incinerator by mounting it in a special frame and providing onto it a protecting, clad welded cover, wherein the frame maintains the initially substantially flat membrane wall in a curved shape by plastically deforming it into at least one, preferably at least two mutually perpendicular directions by bending.

2. Method according to claim 1, wherein the frame holds the membrane wall such that the membrane wall, or part thereof, such as a peripheral edge, can displace, e.g. shift, substantially in its plane in at least one, preferably at least two mutually perpendicular directions, e.g. by mounting the membrane wall to the frame by clamping.

3. Method according to claim 1 or 2 wherein, while at the frame, the clad layer is provided onto the convex side of the membrane wall.

4. Method according to claim 1, 2 or 3, wherein due to the contraction at the clad welding side due to clad welding, the plastically (and thus permanent) flexural deformation that is given to the membrane wall before clad welding, is compensated, wherein preferably the membrane wall is flexed plastically in such a rate, that after clad welding and removing from the welding frame, the permanent flexural deformation that is given to the membrane wall, is substantially compensated, such that a substantially flat, at a single side clad welded membrane wall is obtained.

5. Method according to any of the preceding claims, wherein the membrane wall is located onto a supporting surface of the frame, approximately corresponding to the length and width of the membrane wall and having a curvature substantially corresponding to the desired curvature in longitudinal and width direction of the membrane wall.

6. Method according to any of the preceding claims, wherein two membrane walls are substantially mirror symmetric and opposite each other mounted to the frame.

7. Method according to any of the preceding claims, wherein at one side of the membrane wall a rigid central profile or at both sides of the central longitudinal axis a rigid profile in longitudinal direction is used, with preferably a constant height along its length, and preferably curved in longitudinal direction to follow the curvature of the support.

8. Method according to any of the preceding claims, wherein the membrane wall is brought in shape by locating onto it with mutual spacing of crosswise relative to the length extending rigid, separate pressing elements, the longitudinal ends of which project beyond the membrane wall and are mounted to the frame by pulling elements, wherein e.g. these pressing elements have thicker ends or have a projection or a curved shape to bend the membrane wall at its edges.

9. Method according to any of the preceding claims, wherein starting from the centre in longitudinal direction the membrane wall is fixedly clamped, preferably wherein the pressing elements press directly with their centres onto the membrane wall, such that the membrane wall is plastically curved in longitudinal direction and perpendicular thereto.

10. Frame for carrying out the method according to any of the preceding claims, comprising two mutually registered, opposing shaping surfaces, the longitudinal ends of which have a smaller spacing compared to the centres and following a smoothly curved shape, substantially according to a circle arc segment, and at a longitudinal end commonly pivoting mounted, to move between substantially horizontal and vertical positions.

Drawing