Furnace Wall Containing Spaced, Parallel Water Tubes And Blocks Mounted Thereon

Abstract

In a block-covered furnace wall the face of an individual block turned tods a tube is formed with a radius, which is slightly smaller than one half of the external diameter of the tube. When first applied to a tube the block will thus not make full contact with the tube, but the blocks are, in pairs, forced towards the tubes by wedge shaped members and screw threaded means. To facilitate the necessary deformation each block is provided with a slim waist portion, against which the wedge member bears.

Description

BACKGROUND OF THE INVENTION

With certain types of furnaces, i.e., such for the combustion of waste liquor from the cellulose pulp manufacture and other refuse, the risk of corrosion at the tube walls is very great. This is especially noticeable with the waste liquor combustion furnaces where molten chemical residues collect at the walls. The walls of the furnace are built up of water tubes, the faces of which, turned towards the furnace, are covered by a protective cladding. The risk of corrosion is higher with higher temperature of the tube material. The highest thermal load appears at the lower portion of the furnace, and here the risk of residues collecting at the internal faces of the tubes is also highest, which will bring about a locally increased temperature in the wall and a risk for cracks appearing in the tubes.

A risk for leakage is at hand with all welded joints. The chemical residue collecting at the bottom of a waste liquor combustion furnace will react very forcibly when mixed with water, and if a leak should appear at a tube a dangerous explosion may occur. It therefore is necessary to protect the furnace walls, especially in the lower part of the furnace, in an efficient manner, so corrosive chemicals in gaseous or liquid state do not reach the tubes.

The walls of a furnace are usually composed of a number of parallel, spaced water tubes, the faces of which turned towards the furnace are covered with blocks of fire resistant material, the blocks being retained at the wall by means of suitable devices accessible from outside the wall. The use of compound tubes, i.e., tubes of ordinary steel, encased in a sheathing of corrosion resistant material have also been proposed. Such tubes are, however, expensive to manufacture and difficult to build into the construction, and it is very difficult to repair a furnace wall based upon such tubes. A further, very common manner of protecting the tubes is by welding a large number of short studs to the tubes and to stamp a fire resistant compound onto said studs. One disadvantage with this method is that the attachment of so many studs may damage the tube, and after some time of use the studs are burnt down and will be so short that they have to be substituted by new studs, which means more welding operations. All these welds are a source to leakage from the tube.

SUMMARY OF THE INVENTION

A blocked cover for a tube wall should be arranged in such a manner that it forms a substantially tight slab, which prevents corrosive gases from reaching the tubes, which follows the thermal movements of the tubes and which, should a crack at some tube occur, to a large extent will prevent the water from gushing directly into the furnace. Such a slab is easy to repair as individual blocks may be substituted. A replacement must not necessarily be performed by specially trained workmen, and it it thus possible to perform such an operation at short notice.

According to the invention the face of the individual block turned towards a tube, along at least part of its peripheral extension, is formed with a radius slightly smaller than 1/2 of the external diameter of the tube, whereby the block, when first applied to the tube, will contact the latter along its longitudinal edges only, and that a wedge shaped retaining member is fitted between every two blocks and adapted to be forced towards the blocks at waist portions thereof, located intermediate the longitudinal edge portions and accessible for tightening in the spaces between the tubes.

SHORT DESCRIPTION OF THE DRAWING

FIG. 1 shows a perspective view of a portion of a block covered tube wall,

FIG. 2 shows a horizontal section through two adjacent tubes,

FIG. 3 shows a corresponding section through a wall using a somewhat different type of blocks, and

FIG. 4 shows a horizontal section through a further modified embodiment.

DESCRIPTION OF SOME PREFERRED EMBODIMENTS

A furnace wall is composed of a number of parallel water tubes 10, which are included in the circulation system of a steam boiler, not shown. The tubes are provided with sidewardly directed fins 11, which are welded together to form a wall membrane. The face thereof turned towards the furnace, or at least a substantial part thereof, is covered by blocks 12 of some fire resistant material. These blocks are forced towards the tubes 10 in pairs by means of wedge shaped members 13, which cooperate with clamps 14, arranged externally at the wall, by means of bolts 15 stud welded to the wedge members 13. The bolts pass through matching openings in the fins, and further through the clamps, and tightened by means of nuts.

Such arrangements are, by themselves, well known in the art and the characterizing features here are the shape of the wedge member and the manner of cooperation between the same and the blocks. It is important that the heat absorbed by the blocks through radiation and direct contact with the combustion gases is rapidly transferred to the tubes and therefore the blocks must have a fine contact with the tube.

When using finned tubes it is necessary to take a certain ovality at the tubes into consideration, such ovality being a result of the welding operation joining the fins. The ovality will, however, be largely uniform along the tube and is easy to calculate when designing the blocks. The tubes shall of course be straightened and given a good surface finish before being built into the wall.

With the embodiment shown in FIG. 2 each block 12 is shaped in such a manner that it will extend around about 1/4 of the external circumpherence of the tube. The face of a block turned towards the tube is shaped with a radius, r, which is slightly smaller than 1/2, R, of the external diameter, of the tube. The block will hereby, when first applied to a tube, contact the latter along its outer longitudinal edges only, i.e., at 16 and 17, respectively. The portion between the edges if formed as a slim waist 18, arranged in a plane forming an angle of about 45.degree. with the plane of the wall. When a pressure is applied to this waist by means of the wedge member 13, the block will be brought into a firm contact with the tube all along its inner face. During the mounting a contact compound is preferably smeared at the interfaces between the tube and the block in order to improve the heat transfer.

The wedge shaped member 13 preferably has the same height as the blocks and will cooperate with two blocks. The top angle of the wedge member is somewhat bigger than the angle formed between the side faces of two adjacent blocks 12, whereby the wedge member with its outer edges initially will apply the pressure at the waist portions of two blocks.

The wedge shaped member will, in the same manner as the blocks, be subjected to radiation from the furnace, but the heat transfer therefrom will not be as good as the transfer from the blocks. It therefore is advantageous to provide the member with a number of horizontally arranged grooves 22. These bring about an effect of stacked fins, which reduces the surface subjected to direct radiation, while simultaneously the internal, heat transferring surface remains unchanged.

With the embodiment shown in FIG. 3 each block 19 is designed to cover about 1/2 of the circumference of the tube and is furthermore shaped in such a manner that each half thereof substantially corresponds to a block according to FIG. 2, i.e. the block will initially be aligned with the tube along its edge portions 16, as well as along an intermediate portion 20. Each block will thus be equipped with two waists 18, and the wedge members 13 will also here force the waist towards the tube. In order to facilitate the deformation of the blocks, each block is provided with an external, transverse slot 21. Alternatively the block may be shaped in such a manner that it initially will align with the tubes along its edge portions 16 only. On such occasion the complete face between these edge portions is shaped with a radius smaller than half the external diameter of the tube.

In FIG. 1 only some of the wedge members, for the sake of simplicity, are shown as provided with "stacked fins." All members are of course shaped in this manner, and it is evident that the exposed faces of the blocks may be formed in the same manner.

In order that the attachment of the blocks shall remain uninfluenced by changing temperatures, when starting up or cutting down the combustion, the clamps ought to be resilient, or alternatively spring members may be introduced between the latter and the nuts.

When applying the invention to an existing furnace, where the tubes originally have been protected by some conventional means, or perhaps even been unprotected, it may be difficult to arrange the clamping means at the outside of the wall, which usually is encased in heat insulating material. To remove this insulation in order to mount the clamp could be a tedious work.

An embodiment suited for work along one side of the wall only is shown in FIG. 4, in which the components basically are similar to those of FIG. 2.

The tubes are denoted by 10. They are interconnected by means of fins 30 and the external face of the wall is covered by an insulation 31 of arbitrary type. The faces of the tubes turned towards the furnace are covered by blocks 12, which each shows a slim waist 18. These waists make it possible to force two adjacent blocks towards the pertaining tubes by means of a wedge shaped member 13.

The tightening of the members is here brought about by bolts 32, which are stud welded to the fins 30 and have sufficient length to present a threaded end outside the wedge member when passed into a matching through bore therein. A nut 33 is threaded onto the extended end of the bolt and the complete mounting work can be done from inside the furnace.

Claims

What I claim is:

1. In a furnace wall containing spaced parallel water tubes, fire resistant blocks at the faces of the tubes turned towards the furnace and means for retaining the blocks at the wall, the improvement that the face of an individual block turned towards one of the tubes along at least part of its peripheral extension is formed with a radius slightly smaller than one half of the external diameter of the tube, whereby the block, when first applied to one of the tubes, will contact the latter along two spaced longitudinal edges only, the block between said edges being formed with reduced thickness to provide a slim waist portion, and that the means for retaining the blocks to the wall includes a wedge shaped member designed to be fitted between every two blocks mounted in the same horizontal plane, and further means for forcing the wedge member towards the wall.

2. The furnace wall according to claim 1, in which each block is designed to enclose about 1/2 of the circumference of a tube, the waist portion of the block being located at an angle of about 45.degree. to the plane of the wall.

3. The furnace wall according to claim 1, in which each block is designed to enclose about 1/2 of the circumference of a tube, and having a waist portion located to each side of a plane perpendicular to the wall and including the center line of the tube.

4. The furnace wall according to claim 3, in which each block, at its face turned towards the furnace, is provided with a longitudinally running groove located in the said perpendicular plane.

5. The furnace wall according to claim 1, in which each block is formed with an external surface arranged at an angle to the plane of the wall, the wedge members having a top angle slightly in excess of the angle formed by said surfaces of two adjacent, unbiased blocks, the wedge member having such an extension that it, in untightened position, will abut the waists of the pertaining blocks.

6. The furnace wall according to claim 1, in which the faces of the wedge members turned towards the furnace are each provided with a number of parallel, horizontally arranged slots.

7. The furnace wall according to claim 1, in which the tubes are interconnected by fins to form a membrane wall, the feature that each wedge member is provided with at least one stud welded bolt, the fins being provided with matching openings for the passage of said at least one bolt and clamping means outside the membrane wall for tightening the wedge shaped members.

8. The furnace wall according to claim 1, in which the tubes are interconnected by fins to form a membrane wall, the feature that bolts are stud welded to the face of the fins presented towards the furnace, the wedge members being provided with matching openings and the bolts having sufficient length to present a threaded end outside the wedge member.