WO1998028571A1

WO1998028571A1 - Furnace waterwall v-shaped lug attachment structure

Info

Publication number: WO1998028571A1
Application number: PCT/US1997/022207
Authority: WO
Inventors: Xiaoguang Yu
Original assignee: Combustion Engineering, Inc.
Priority date: 1996-12-23
Filing date: 1997-12-05
Publication date: 1998-07-02
Also published as: AU5592998A

Abstract

A lug (30) for attachment to a waterwall (11) and for supporting a load on the waterwall (11) which is a part of steam generation apparatus (10) and which includes a web shaped metal plate formed in a generally arch shape. The arch shape has first and second legs (32, 34), each of the legs (32, 34) being dimensioned and configured for engagement with a part of the axial extent of respective associated tubular members (20) in an associated waterwall (11). In some forms of the invention each of the legs (32, 34) includes a generally planar portion and each of the legs (32, 34) has an axial extremity that is rectilinear. The axial extremity of each leg (32, 34) that is rectilinear may be disposed within the generally planar portion of the leg (32, 34). The lug (30) may be fabricated from a single piece of metal and the generally planar portions in respective legs (32, 34) are disposed in respective planes that intersect at an angle that is less than 90 degrees or even 30 degrees. In still other embodiments of the invention the generally planar portion is disposed in respective legs (32, 34) of the lug (30) that are mutually parallel.

Description

FURNACE WATERWALL V-SHAPED LUG ATTACHMENT STRUCTURE

TECHNICAL FIELD The invention relates to steam generation boilers having steam cooled arrays of tubes which are referred to as waterwalls or merely furnace walls. It is common for furnace wails to be constructed of panels made of tubes joined by fusion welding. Conventionally, adjacent tubes are fixed to each other by a fin that is welded to each of the two adjacent tubes. This is the manner in which the entire furnace wall is constructed. This construction provides a gas-tight

"box" which contains the burning fuel and hot gases. Generally, panels are built up with four tubes, each 75-feet long, welded together simultaneously. Single tubes and four tube subassemblies are added successively to make up panels about five wide.

The non-uniform metal temperatures in respective tubes, portions of individual tubes of a waterwall, and attachments is a major design concern. Because of the manner in which the tubes are interconnected in the conventional design, a substantial difference in metal temperatures in respective portions of individual waterwall tubes, respective tubes or attachments may cause unacceptable stresses in the wall. More specifically, even within one tube there is substantial difference in the temperature of the furnace side of the tube and the temperature of the cold side of the tube. This results in the furnace side expanding more than the cold side. It is desirable to attach a number of structures to the waterwall. So called scallop bar attachments are widely used for attachments to the waterwall. These scallop bars have a plurality of arc shaped recesses extending along one side of a planar plate or bar. The arc shaped recesses are typically dimensioned and configured for engagement with a plurality of parallel, coplanar tubes. Such plates are used in various furnace areas such as the buckstay, the windbox, and the seal box. While scallop plates attachments are satisfactory for many applications, they are not wholly satisfactory for other applications.

When a scallop plate is welded to the cold side of the waterwall, the stiffness of the scallop bar will confine the thermal expansion on the furnace side. Stresses may result from such attachments because the temperatures in the tube wall of such apparatus are not uniform resulting in non-uniform expansion and contraction of the individual tubes in each of the walls. Other stresses may develop because the temperature of the attachment structure and the wall is not uniform. This generates a high compressive stress field on the outside surface of the tubes and a tensile stress field on the inside of the tubes. The stresses may result in cracks on the inside surface of the tubes and in the welds joining the waterwall tubes and the scallop bars.

in those applications having a corrosive environment on the inside of the waterwall tubes, the portion of the tube within the tensile stress field is very vulnerable to corrosion attack. Tubes that are subjected to high temperatures, high stresses and a cycling load in addition to the corrosion attack may even rupture.

Although the invention has particular application to so called supercritical pressure cycle systems, those skilled in the art will recognize that it has application to other systems. Stress levels are particularly high in supercritical pressure cycle systems because of the higher pressures and temperatures than those of more conventional systems. OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide attachment apparatus which will support a load and which will avoid the stresses associated with prior art attachment structures.

Another object of the invention is to provide attachment apparatus that will be less vulnerable to cracks and rupture of either the tubes, the attachment structure or the weld that joins the tubes and the attachment apparatus.

It is an object of the invention to substantial eliminate any vulnerability of the tubes to which the attachment is mounted to rupture as the result of the combination of high temperatures, high stresses and cycling load in addition to corrosion attack of the interior of the tubes.

Yet another object of the present invention is to provide apparatus that is easy to install.

Still another object of the invention is to provide apparatus that is inexpensive to manufacture.

It has now been found that the objects of the invention may be attained in a lug for attachment to a waterwall and for supporting a load on the waterwall which is a part of steam generation apparatus and which includes a web shaped metal plate formed in a generally arch shape, the arch shape having first and second legs, each of the legs being dimensioned and configured for engagement with a part of the axial extent of respective associated tubular members in an associated waterwall.

In some forms of the invention each of the legs includes a generally planar portion and each of the legs has an axial extremity that is rectilinear. The axial extremity of each leg that is rectilinear may be disposed within the generally planar portion of that leg. The lug may be fabricated from a single piece of metal and the generally planar portions in respective legs are disposed in respective planes that intersect at an angle that is less than 90 degrees or even 30 degrees. In other forms of the invention the generally planar portions in respective legs are disposed in respective planes that intersect at an angle that is less than 30 degrees. In still other embodiments of the invention the generally planar portion is disposed in respective legs of the lug are mutually parallel.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be better understood by reference to the accompanying drawing in which:

Figure 1 is a side elevational view of a furnace to which attachments in accordance with the present invention may be attached

Figure 2 is a sectional view taken along a horizontal plane passing through one form of an associated waterwall and a V-lug attachment in accordance with one form of the present invention.

Figure 3 is an elevational view in partial section of the V-shaped attachment lug in accordance with one form of the present invention.

Figure 4 is a perspective view of a fragment of the waterwall and V-shaped attachment lug shown in Figures 1 and 2.

Figures 5 and 6 plan views of alternate embodiments of the present invention.

Figure 7 is a perspective view of a prior art scallop plate attachment to a waterwall.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to Figure 1 there is shown a conventional furnace 10, having a central cavity 12 surrounded by a front wall, a rear wall and two opposed side walls. The side walls (not shown) are disposed in spaced relationship and join the front wall and the rear wall. Each of these walls is a waterwall 11 comprising a plurality of tubular members that have respective axes that are substantially parallel and substantially coplanar. The furnace 10 is vertically disposed and has an outlet for combustion gases at its upper end extending from the rear wall thereof. Extending from this outlet is a lateral gas pass 13 which connects with the upper end of a vertically extending gas pass 15 that extends downwardly in parallel relation with the cavity 12. Combustion gases sequentially pass through the cavity 12, the lateral gas pass 13, the vertically extending gas pass 15 and a stack (not shown). The illustrated furnace 10 includes burners 17. It will be understood the present invention may be incorporated in a wide variety of furnace structures and that the illustrated furnace 10 is only one such furnace.

The apparatus in accordance with one form of the present invention is shown in Figures 2-4. The V-shaped lug 10 is shown mounted on an associated waterwall 11. Referring particularly to Figures 2 and 4, it clear that the waterwall 11 comprises a plurality of tubular members 20 that have respective axes that are substantially parallel and substantially coplanar. A planar fin 24 is disposed between adjacent tubular members 20 with the sides of the fin welded to each tubular member it abuts.

In a typical supercritical system the waterwall 11 is manufactured of ASME SA- 213, T22 alloy steel. The individual tubular members have an outside diameter of 1 1/8", a wall thickness of 0.22", a spacing between centerlines of 1 5/8" . The fin has a thickness of 0.25". It will be understood that these dimensions merely describe one preferred embodiment and that the dimensions will vary in other applications.

A preferred embodiment of the invention is the V-shaped lug attachment 30. This lug attachment 30 is a unitary piece of ASME SA-213, T22 alloy steel having a uniform thickness of 3/16". The precise linear dimensions, angular bend material composition and heat treatment will vary with the particular application. In illustrated preferred embodiment the V-shaped lug 30 is manufactured by bending a cold single piece of sheet stock having a thickness of 3/16 of an inch and a width of 2.5 inches. The illustrated lug has a height of 2.0 inches. The V-shaped lug in the illustrated preferred embodiment has first and second planar walls 32, 34 with a bend 36 therebetween. The radius of curvature of the bend is about 3/8 of an inch. The walls 32, 34 have an included angle of approximately 20 degrees. Other applications will have other dimensions.

The preferred form of the lug 11 has planar walls 32, 34 that are disposed in oblique relationship to each other with the free ends of the walls 32, 34 disposed further apart than the ends abutting the bend 36. Ordinarily the free ends of the lug 11 will be joined to adjacent tubualar members 20 and the angle between the walls will be less than 180 degrees and the free ends of the walls will be further apart than the ends of the walls that abut the bend 36.

Referring now to Figures 5 and 6 it will be understood, however, that the walls 32, 34 may be parallel as shown in Figure 5 or have the free ends of the walls 32, 34 spaced even further apart so that the walls 32, 34 are disposed at an included angle of more than 90 degrees and in some cases almost 180 degrees. Still other embodiments of the invention will have a shape approaching a squared off U-shape. In such forms the "bend" includes a planar part. The terms a single metal piece of sheet stock having "first and second planar walls" connected by an axial portion that has a bend therein is used herein to encompass all such embodiments whether they converge at an angle less than 180 degrees or are parallel.

Particularly, in the case of the embodiment of Figure 6 the free ends of the walls 32, 34 may abut tubular members in the waterwall 11 that are not adjacent. For example, the waterwall 11 may have first and second tubular members that are adjacent and a third tubular member that is adjacent to the second tubular member. The embodiment of Figure 6 is particularly suited for engagement with the first and third tubular members.

The thickness and length and width of the plate from which the lug 30 is formed will vary with the specific application. For example, the weight of the article to be supported by the lug 30 will have a bearing on these dimensions.

Analysis of the structure that includes a lug 30 mounted on a waterwall 11 has established that the lug 30 has little affect on the stresses within the waterwall 11. A particular feature of the present invention is that the lug 30 accomplishes the purpose of attaching to the waterwall 11 and the purpose of supporting a load without substantially constraining the movement of the individual tubular members 20 in the waterwall 11. This is in marked contrast to the conventional scallop bar plates 40, shown in Figure 7, that are typically welded to a plurality of adjacent tubular members 30 and the intermediate fins 24. Such plates, particularly at supercritical system operating temperatures, cause stress because (1) they do not expand and contract concurrently with the waterwall to which the are very securely attached and (2) the geometry of the scallop plate 40 does not allow the degree of movement that is possible with a bend 36. The geometry of the lug in accordance with the present invention allows movement in the waterwall at the same time that the lug is supporting a load. Thus, the invention does not produce the stress levels inherent in some prior art structures.

Although the preferred embodiment and the other embodiments of the invention illustrated herein are fabricated by providing a single piece of sheet metal or plate and then bending that sheet or plate to produce the illustrated lug it will be understood that the invention may properly be called web shaped. The term "web" will be understood from the usage in other fields. In civil engineering the web is the vertical strip between the upper and lower flanges of a rail or girder.

In the paper making field the term web refers to the continuous length of paper formed when paper pulp moves through a paper making machine. The same term is used in the newspaper publishing field to describe a printing press. In the zoology field the term is used to describe the membrane between the digits of animals such as frogs. In the textile field it is used to describe the fabric as it is being woven on a loom. Similarly, the term is used in the plastics field to describe sheet plastic material.

It will be seen that each of the illustrated embodiments of the invention is characterized by a web shaped member having a first axial part that attaches to a first tubular member in a waterwall and a second axial part that attaches to a second tubular member in a waterwall. An axial part of the web shaped member that is intermediate the first and second axial parts is arch shaped. That arch shape allows relative movement of the tubular members in the waterwall 11 to which the lug is attached without imposing large stresses in the waterwall or lug. Although fabricating the lug of the present invention from a single plate or single sheet of metal is ordinarily the most economical method of fabrication, those skilled in the art will recognize that overall arch shape may be achieved with other structures.

It will be seen that the arch shape allows relative motion of the tubular members because the arch shaped lug provides the desired rigidity for support of a load while simultaneously allowing sufficient flexibility to allow relative movement between the tubular members in the waterwall.

The preferred embodiment is manufactured from a plate that is elongated and the axial extremities of the plate are attached to respective tubular members. Those skilled in the art will recognize that other embodiments might carry very large loads and could even be manufactured from a very wide plate that was not elongated.

The invention has been described with reference to its illustrated preferred embodiment. Persons skilled in the art of such devices may upon disclosure to the teachings herein, conceive other variations. Such variations are deemed to be encompassed by the disclosure, the invention being delimited only by the following claims.

Claims

Having thus described my invention, I claim:

1. A lug for attachment to an associated waterwall and for supporting a load on the waterwall which comprises:

a web shaped metal plate formed in a generally arch shape, said arch shape having first and second legs, each of said legs being dimensioned and configured for engagement with a part of the axial extent of respective associated tubular members in an associated waterwall.

2. The lug as described in claim 1 wherein:

each of said legs includes a generally planar portion.

3. The lug as described in claim 2 wherein:

each of said legs has an axial extremity that is rectilinear.

4. The lug as described in claim 3 wherein:

each axial extremity of each leg that is rectilinear is disposed within said generally planar portion of that leg.

5. The lug as described in claim 4 wherein:

said lug is fabricated from a single piece of metal.

6. The lug as described in claim 5 wherein:

said generally planar portions in respective legs are disposed in respective planes that intersect at an angle that is less than 90 degrees.

7. The lug as described in claim 6 wherein:

said generally planar portions in respective legs are disposed in respective planes that intersect at an angle that is less than 30 degrees.

8. The lug as described in claim 5 wherein said generally planar portion in respective legs of said lug are mutually parallel.

an arch shaped portion

9. Steam generation apparatus which includes:

a furnace having a central cavity surrounded by a front wall, a rear wall and two opposed side walls, each of said walls being a waterwall comprising a plurality of tubular members that have respective axes that are substantially parallel and substantially coplanar; and

a lug for attachment to one of said waterwalls and for supporting a load on the waterwall, said lug including a web shaped metal plate formed in a generally arch shape, said arch shape having first and second legs, each of said legs being dimensioned and configured for engagement with a part of the axial extent of respective associated tubular members in said waterwall.

10. The apparatus as described in claim 9 wherein:

each of said legs includes a generally planar portion.

11. The apparatus as described in claim 10 wherein:

each of said legs has an axial extremity that is rectilinear.

12. The apparatus as described in claim 11 wherein:

13. The apparatus as described in claim 12 wherein:

said lug is fabricated from a single piece of metal.

14. The apparatus as described in claim 13 wherein:

15. The apparatus as described in claim 14 wherein:

16. The apparatus as described in claim 13 wherein said generally planar portion in respective legs of said lug are mutually parallel.