US2987052A - Wall construction for pressurized furnace - Google Patents

Description

Jun 6, 1961 w. H. ARMACOST WALL CONSTRUCTION FOR PRESSURIZED FURNACE Original Filed 001:. 29, 1952 5 Sheets-Sheet 1 INVENTOR. WILBUR H. ARMACOST E L Egg I igi 58 I INVENTQR WILBUR H. ARMACOST June 6, 1961 w. H. ARMACOST 2,987,052

WALL CONSTRUCTION FOR PRESSURIZED FURNACE Fig. 2.

Fig. 3. BY g ATTOR Y June 6, 1961 w. H. ARMACOST WALL CONSTRUCTION FOR PRESSURIZED FURNACE Original Filed Oct. 29, 1952 3 Sheets-Sheet I5 Fig. 6.

Fig. 5.

lNV ENTOR WILBUR H. ARMACOST BY Qffi-fi d ATTOR United States Patent C 2,987,052 WALL CONSTRUCTION FOR PRESSURIZED FURNACE Wilbur H. Armacost, Scarsdale, N.Y., assignor to Combustion Engineers, Inc., a corporation of Delaware Continuation of application Ser. No. 317,520, Oct. 29, 1952. This application Sept. 29, 1958, Ser. No.

6 Claims. (Cl. 122-6) My invention relates to a method of fabricating furnace walls and has specific reference to a water cooled furnace wall of novel pressure resistant design especially adapted for use in the furnace of a controlled circulation steam generator.

In the steam generation field there are two well known types of draft systems employed by boiler designers today, i.e., the forced draft system and the induced draft system. In the forced draft system the combustion supporting air is pumped into the furnace at super-atmospheric pressure while in the induced draft system the pressure within the furnace is reduced to below atmospheric so that the air is drawn into the furnace. Thus in both of these systems there is a differential between the pressure within the furnace and the pressure exteriorly of the furnace, this differential being sufiicient when acting on the large wall area of the furnace to exert a considerable force on the furnace walls tending to collapse or push the same outwardly. With the tremendously high pressure prevailing within the steam generating tubes of modern steam generators of the utility type it is indeed a challenging problem to fabricate for the furnaces of these generators an economically feasible furnace wall that is lined with said steam generating tubes and is capable of withstanding the aforementioned force.

' It is the general object of my invention to provide a method of fabricating such a furnace wall.

A more specific object is to provide a method of fabricating a pressure resistant furnace wall having the inner surface lined with integrally welded steam generating tubes with the outer structure of the wall supported only indirectly from said tubes. A further object is to provide an improved method of fabricating a pressure resistant furnace wall having the inner surface lined with spaced steam generating tubes with the outer structure of the wall supported from spacer members positioned intermediate and welded to said tubes.

Other and further objects of my invention will become apparent to those skilled in the art as the description hereof proceeds.

With the aforementioned objects in view my invention comprises an arrangement, construction and combination of the elements of the furnace wall organized in such a manner as to attain the results desired as hereafter more particularly set forth in the following detailed description of an illustrative embodiment; said embodiment being shown by the accompanying drawings wherein:

FIG. 1 is a vertical section of a modern controlled circulation steam generator having a forced draft furnace the walls of which are constructed in accordance with my invention;

. FIG. 2 is a sectional view of the furnace wall taken generally along line 2-2 of FIG. 1.

FIG. 3 is a perspective view of a portion of said furnace wall showing the construction details thereof.

FIG. 4 is an enlarged horizontal sectional view of a portion of said furnace wall being taken generally along the same line 2-2 as FIG. 2.

FIG. 5 is a vertical section taken generally along line 55 of FIG. 4.

FIG. 6 is a vertical section taken generally along line 6-6 of FIG. 4.

FIG. 7 is a sectional view similar to FIG. 4 but showing a modified form of construction.

While my furnace wall is herein shown and described as incorporated in a controlled circulation boiler of particular design it is to be understood that this is illustrative only and is not to be taken as restrictive since as the description proceeds it will become apparent that my in-. vention may be equally well employed with boilers of other and different designs.

By the term controlled circulation, as used throughout this application, is meant a steam generator having a positive or forced circulation through the various steam generating tubes and provided with restricting orifices dis posed adjacent the inlets of such tubes and so designed as to control the flow therethrough in a predetermined manner to obtain maximum boiler efficiency.

The steam generator here illustrated Referring specifically to the drawings wherein like reference characters are employed throughout to designate like elements, the steam generator of FIG. 1 com prises a vertically disposed furnace 2 of generally rec'- tangular cross section communicating at its upper end with a horizontal gas pass 4 which in turn communicates with the upper end of vertical gas pass 6 leading to air preheater 14. A plurality of vertically spaced burners 8 communicate with the interior of said furnace and are arranged to supply thereto pulverized coal received from pulverizers 10 via conduits 12. Preheated air is introduced into the furnace under pressure via a suitable forced draft fan (not shown) which forces the air through the preheater 14 and duct 16 from whence it is introduced into the furnace at a plurality of vertically spaced points, such introduction insuring complete burning of the fuel passed into the furnace by said burners.

Furnace 2 is of the water cooled type having the interior surface of its walls as well as the floor and ceiling lined with steam generating tubes 18. Said tubes 18 are connected at their lower or inlet ends with orifice drum 20 and at their upper or outlet ends with conventional headers 22 which in turn communicate with steam and water drum 24 through conduits 23. Downcomers 25 (only one being shown) extend down from steam and water drum 24 and communicate at their lower ends with the inlet of pumps 26 (again only one being shown) which in turn have their outlets connected by suitable conduits 28 to orifice drum 20 thereby completing a fluid circuit through which said pumps are effective to circulate boiler water in a direction indicated by the arrows in FIG. 1. Suitable fiow restrictors in the form of orifices (not shown) of predetermined size are associated with the inlet of each of the tubes 18 for the purpose of effectively controlling the flow through each of said tubes.

Disposed within gas passes '4 and 6, respectively, are a plurality of heat exchange devices; namely, high temperature superheater 32, reheater 34, low temperature superheater 30 and economizer 29, which are arranged The construction of the furnace wall Referring specifically to FIGS. 2 to 6, inclusive, each of the water evaporating tubes 18 which, as previously noted, line the interior of furnace 2, is spaced a predetermined distance from its adjacent tubes with the spaces therebetween being substantially filled by metallic rods 36, preferably circular in cross section, extending throughout the entire length of the tubes. Said rods 36 are welded to the tubes between which they are disposed with weld metal completely surrounding said rods throughout their entire length thereby forming an extremely rigid, gas impervious, pressure resistant metallic interior surface for said furnace wall.

At predetermined vertically spaced intervals, suitable outwardly projecting studs 38, in the form ,ofrectang'ular plates, are welded to various of said rods 36 in the inanner best shown by Figs. 3 and 4. Horizontally disposed channel stiffener and support members 40 are positioned between and welded to such studs 3d and have, at horizontally spaced intervals, suitable gusset plates 42 welded thereto. To the outer extremity of said gusset plates 42 are welded two spaced horseshoe fasteners 44 having their centrally disposed openings in alignment and generally parallel with the axis of tubes 18, said aligned openings loosely receiving flanges 46 of buckstay 48 in order to support the buckstay from the wall while allowing relative movement therebetween due to. unequal expansion.

The surface of integrallyvwelded tubes 18 remote from the inner surface of the furnace wall is lined with suitable thermal insulation in the form of an inner row of insulating blocks 50, an outer row of insulating blocks 52 and a layer of plastic insulation 54. All of the insulation is supported solely by studs 38 and channel members 40 and since the inner surface of the furnace wall is a gas tight, pressure resistant, metallic structure no outer metallic casing is necessary.

Heretofore it has been the practice to provide pressurized furnace walls with an outer metallic casing, genorally in the form of sheet steel, in order to retain various packing material in place and thereby maintain said walls substantially fluid tight. However, since the wall of my invention presents an inner metallic surface which in itself is impervious to fluid the need for the outer casing is eliminated resulting in a significant saving of material and labor.

In controlled circulation boilers it is possible to rigidly weld together the steam generating tubes lining the furnace wall along their entire length as herein disclosed. This is due to the fact that a positive circulation of the boiler water substantially eliminates hot spots within the furnace which are the cause of excessive differential expansion. Integrally welding the steam generating tubes of a natural circulation boiler in this manner is, on the contrary, extremely impracticable since upon initially firing such a boiler there is no circulation of water through the steam generating tubes and consequently portions of said tubes become extremely hot while other portions remain relatively cool. This results in excessive dilferential expansion setting up intolerable strains within such a welded wall. It is thus seen that my novel wall construction is particularly well adapted for use with steam generators having a forced circulation and especially the controlled circulation type since by providing a positive flow of water through each tube the chance for hot spots is substantially eliminated.

In fabricating the welded wall herein disclosed in FIGS. 2 to 6 it is practicable (and is actually being carried out by my assignee) to weld the tubes into large panels at the shop and ship these panels to the field. Thus during erection in the field it ismerely necessary to weld these ass /pea various panels together thereby reducing the number of field welds to a minimum.

All of the welds, i.e., the longitudinal welds joining the tubes together, are stress relieved whereby, in accordance with the ASME code, they have little effect upon the strength quality of the tube. With the equipment available at the fabrication shops it is a simple and relatively inexpensive matter to stress relieve these welds and since the few welds made in the field extend longitudinally throughout the length of the panels they may also be economically stress relieved.

Any weld applied directly to the surface of a stream generating tube and not stress relieved has the effect of greatly decreasing the strength quality of the tube and setting up excessive stresses in the tube wall at the loca-- tion of the weld. Thus when support studs for insulation and other wall structure are welded directly to thetubes and not stress relieved, as is common practice in conventional furnace walls, it leaves the tubes in a weakened condition at the location of said weld. To stress relieve the many and scattered support studs required is prohibitively expensive and thus in said conventional furnace walls the tubes are left with these locations of weakness which areever present potential sources of failure.

With my novel wall structure herein disclosed in FIGS. 2 to 6 this undesirable feature is completely eliminated by welding the support lugs to rods 36 disposed between the tubes. This weld has no elfect upon the tubes and since as pointed out above, all of the welds applied directly to the tubes in my novel wall can economically be stress relieved, the tube' is left entirely free of excessive stresses and locations where it is relatively weak.

The modification of FIG. 7 is similar to the embodiment of FIGS. 2 to 6 except that in lieu of spacer rods 36 tubes 118 are formed throughout their length with the diametrically opposed laterally extending extrusions 120 with the edges of adjacent extrusions being immedi' ately adjacent one another or in engagement so that the tube proper of adjacent tubes are in spaced relation with this space being filled with metal. These edges are welded together throughout their length thus forming, as in the case of the previously described embodiment, an extremely rigid, gas impervious, pressure resistant metallic interior surface for the furnace wall.

Welded to said extrusions 120 intermediate certain of said tubes and at predetermined vertically spaced intervals are outwardly projecting studs 38. Said studs 38 support the outer structure of the wall in the same manner as the. previously described embodiment and the details thereof will not be repeated here.

In fabricating the wall of this embodiment of my invention the tubes may also be welded into large panels and stress relieved in the shop thereby reducing the welding and stress relieving required in the field. Although the welding together of these tubes does not weaken them to the extent of the tubes in the previously described embodiment, due to the fact that the weld is more remote from the tube wall, it is still advisable to stress relieve this weld because of the resulting warping if not stress relieved and because this large weld does somewhat weaken the tubes. The relatively small welds required to secure studs 38 to the extrusions at a point intermediate adjacent tubes have no effect on the strength quality of the tubes, however, whereby an extremely practical. and highly desirable pressure resistant wall is produced which requires no separate casing.

Summary From the foregoing. it will be seen that I have provided an improved method of fabricating a water cooled pressure resistant wall particularly adapted for furnaces of controlled circulation boilers with the wall having an inner surface of rigidly welded heat exchange tubes presenting an imperforate metallic inner face and provided with support studs welded intermediate said tubes and arranged to support the outer wall structure. a

"aesaoaa While I have' illustrated and described a preferred embodiment of my novel furnace wall it is to be understood that such is merely illustrative and not restrictive and that variations and modifications may be made therein without departing from the spirit and scope of the invention. I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes and alterations as fall within the purview of my invention.

This application is a continuation of my application Serial No. 317,520, filed October 29, 1952, now abandoned.

What I claim is:

l. The method of constructing a furnace wall which has its inner surface lined with heat exchange tubes constructed and arranged to form a rigid, imperforate metal lic inner face for the wall with the outer portions of the wall being supported from this rigid inner face, comprising the steps of shop assembling panels of parallel tubes by maintaining the tubes in parallel relation with the wall portion of adjacent tubes which is defined as being of uniform thickness perimetrically of the tube and contiguous to and in bounding relation with the passage through the tube being spaced with this wall portion comprising the entire thickness of the tube wall throughout at least a portion of the tube perimeter, providing metal in said space substantially filling the same, welding adjacent tubes together throughout their length, shop stress relieving these panels after this welding, assembling these panels in the field to form an imperforate metallic inner wall face by maintaining the edge tubes of adjacent panels in parallel spaced relation and interconnecting the same throughout their length by welding, stress relieving these welds, supporting stiffener members from this inner face on the outer side thereof by positioning support lugs principally in engagement with the metal intermediate the tubes and welding said support lugs substantially solely to this metal in a manner so as to have no appreciable eifect upon the strength quality of the tubes with this welded joint being the sole connecjtfion of these lugs with this imperforate metallic inner ace.

2. The method of constructing a furnace wall made up of a plurality of layers and which has a layer of parallel tubes formed into a fluid impervious pressure resistant structure from which other portions of the wall are supported comprising shop assembling panels of said tubes by maintaining the tubes in parallel relation, with the wall portion of adjacent tubes which is defined as being of uniform thickness perimetrically of the tube and contiguous to and in bounding relation with the passage through the tube being spaced with this wall portion comprising the entire thickness of the tube wall throughout at least a portion of the tube perimeter, providing metal in said space substantially filling the same throughout the length of the tubes, welding the adjacent tubes of the panels together throughout their length and shop stress relieving these welds, assembling these panels in the field to form an imperforate metallic layer of a furnace wall with the tubes of the panels being free of any substantial stresses, positioning support lugs principally in engagement with the metal intermediate the tubes and welding said support lugs substantially solely to this metal in a manner so as to have no appreciable efiect upon the strength quality of the tubes and so these lugs extend laterally of the imperforate metallic layer formed by the tubes and with this welded joint being the sole connection of these lugs with this imperforate metallic layer, with these lugs being adapted to support other structure.

3. The method of fabricating a furnace wall made up of a plurality of layers and which has its inner surface lined with heat exchange tubes constructed and arranged to form a rigid, imperforate metallic inner face for the wall with the outer portions of the wall being supported from this rigid inner face, comprising the steps of main? taining the tubes in parallel relation with the wall poi-tion of adjacent tubes which is defined as being of uniform thickness perimetrically of the tube and contiguous to and in bounding relation with the passage through the tube being spaced with this wall portion comprising the entire thickness of the tube wall throughout at least a portion of the tube perimeter, providing metal in said space substantially filling the same, welding adjacent tubes together throughout their length, stress relieving these welds, positioning support lugs principally in engagement with the metal intermediate the tubes and, welding said support lugs substantially solely to this metal in a manner so as to have no appreciable efiect upon the strength quality of the tubes and with this welded joint being the sole connection of these lugs with this imperforate metallic inner face, these lugs being adapted to support other structure.

4. The method of constructinga furnace wall made up of a plurality of layers and which has its inner surface lined with heat exchange tubes constructed and arranged to form a rigid, imperforate metallic inner face for the wall with the outer portions of the wall being supported from this rigid inner face, comprising the steps of shop assembling panels of parallel spaced tubes by interposing metallic spacer rods between adjacent tubes throughout their length, shop welding these tubes together throughout their length and across said rods shop stress relieving these panels after this welding, assembling these panels in the field to form an i rnperforate metallic inner wall face with the tubes of the panels being free of any substantial stresses, positioning support lugs principally in engagement with the metal intermediate the tubes and welding said support lugs substantially solely to this metal in a manner so as to have no appreciable effect upon the strength quality of the tubes, and with this welded joint being the sole connection of these lugs with this imperforate metallic inner face, these lugs being adapted to support other structure.

5. The method of constructing a furnace wall made up of a plurality of layers and which has its inner surface lined with metallic heat exchange tubes which are provided with generally diametrically opposed, longitudinally extending fins with these tubes being constructed and arranged to form a rigid, imperforate metallic inner face for the wall with the outer portions of the wall being supported fro-m this rigid inner face, comprising the steps of shop assembling panels of parallel tubes by positioning the same with the edges of their fins juxtaposed and weld ing these edges together throughout the length of the tube, shop stress relieving these panels after this welding, assembling these panels in the field to form an imperforate metallic inner wall face with the tubes of the panels being free of any substantial stresses, positioning support lugs principally in engagement with the metal intermediate the tube proper of adjacent tubes and welding said support lugs substantially solely to this metal in a manner so as to have no appreciable effect upon the strength quality of the tubes and with this welded joint being the sole connection of these lugs with this imperforate metallic inner face, these lugs being adapted to support other structure.

6. The method of fabricating a furnace wall which is made up of a plurality of layers one of which is heat exchange tubes rigidly secured together into a metallic layer comprising the steps of maintaining the tubes in parallel relation with the wall portion of adjacent tubes which is defined as being of uniform thickness permetrically of the tube and contiguous to and in bounding relation with the passage through the tube being spaced with this wall portion comprising the entire thickness of the tube wall tthroughout at least a portion of the tube perimeter, providing metal in said space substantially filling the same, welding adjacent tubes together throughout their length, stress relieving these welds, positioning References Cited in the ;fi1eof this patent UNITED STATES PATENTS Murray et a1 Now. 30, 1926 Jacobus May 22,1234 Inskeep et a1 Sept. 22,, 1942 Witzke May 15, 1951 Har dgrove Apr. 5,, 1955

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