US3479994A

US3479994A - Enclosure for vapor generator

Info

Publication number: US3479994A
Application number: US702456A
Authority: US
Inventors: Edward W Kreider; John A Lavey
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 1968-02-01
Filing date: 1968-02-01
Publication date: 1969-11-25
Anticipated expiration: 1986-11-25
Also published as: DK125491B; FI48874C; GB1249733A; FI48874B; NL6901574A; ES363159A1; FR2001120A1; BE727753A

Description

Nov. 25, 1969 E. w. KREIDER ET AL ENCLOSURE FOR VAPOR GENERATOR 3 Sheets-Sheet 1 Filed Feb. l, 1968 mvENToRs Edward W. Kreider John A. Lavey Nov. 25, w69 E, W, KREIDER ET AL 3,479,994

ENCLOSURE FOR VAPOR GENERATOR Filed Feb. l, 1968 5 Sheets-Sheet 2 NOV. 25, l959 E, W, KRE|DER ET AL 3,479,994

ENCLOSURE FOR VAPOR GENERATOR Filed Feb. l, 1968 3 Sheets-Sheet 5 United States Patent O 3,479,994 ENCLOSURE FOR VAPOR GENERATOR Edward W. Kreider, Wadsworth, and John A. Lavey, Barberton, Ohio, assignors to The Babcock & Wilcox Company, New York, N.Y., a corporation of New York Filed Feb. 1, 1968, Ser. No. 702,456 Int. Cl. F22b 37/24 U.S. Cl. 122-494 11 Claims ABSTRACT OF THE DISCLOSURE An enclosure adapted to be mounted on a vapor generator having a furnace chamber of substantially rectangular cross-section defined by four walls. The enclosure generally includes a wrapper mounted on the furnace walls for relative movement with respect to the walls. In the area where the wrapper extends around a corner of the furnace chamber, an arcuately shaped expansion joint is provided. Trusses are provided for supporting the wrapper such that the wrapper acts to relieve stresses which develop in the trusses, two trusses being provided on opposite or adjacent walls of the furnace chamber and interconnected to one another via the wrapper. The ends of the trusses are thus physically connected together to relieve stresses in the trusses.

Background and summary of the invention Modern vapor generators have upright furnace chambers defined by a plurality of walls made up of tubes within which fluid vaporizes. The tubes are lengthwise contiguously interconnected to one another to form the tube walls which are supplied with fluid via headers disposed at their lower ends, the vapor being collected at the upper ends of the tube walls. Combustion gases for heating the tube walls are supplied to the lower portion of the furnace chamber by burning fuel in burners supplied with preheated air via a windbox, the air being pressurized for upward ilow through the furnace chamber wherein its heat values are trans erred to the tube walls. Some of the combustion gases are recirculated via gas recirculation and/ or gas tempering vestibules from which the gas is respectively recirculated to the lower and/or upper parts of the furnace chamber for balancing temperatures within vapor heaters and minimizing slag deposits thereon. Upward extension of some of the tubes in the furnace walls may be interrupted 'for interconnection to one another within a mixing header to average the steam-water quality of the uid before it is allowed to continue its upward iiow. The mixing header extends outwardly from the furnace walls and is surrounded by a vestibule forming a dead space for insulating purposes.

The windbox and vestibules are box-like enclosures mounted on and outwardly extending from the furnace wall. Generally, at least one of the enclosures provided partially or completely encircles a discrete length of the furnace wall and laterally extends therefrom, thus for-ming a continuous passageway about a transverse section of the wall. Usually a plurality of such enclosures serving as conduits are provided to conduct gases such as air and/or recirculated gas around the furnace, or to provide a dead space for insulating purposes. The enclosures must be mounted to accommodate the lengthwise thermal expansion of the furnace walls during start-up and shuntdown as well as during operation, and must support thelr own dead weight. In addition, transverse movement of the furnace walls caused by variations in furnace pressure during start-up, shut-down and/or abnormal operation of the unit must be accounted for by allowing for relative motion between the furnace wall and enclosures. Still further, since the temperature of one part of an ICC enclosure may be considerably different from the temperature of another part of the enclosure due to its proximity to the furnace wall and/or to radiation from gas within the enclosure or from the furnace chamber, the enclosures must themselves be constructed and arranged to accommodate differential-thermal expansions of their parts.

In view of the foregoing it should be appreciated that the environment in whichl the enclosures are disposed greatly affects the manner in which they are constructed. Designers are confronted with the complex task of con structing enclosures that resist and/or compensate for a variety of movements without structural failure. Heretofore the task has baffled those skilled in the art. A number of theories have been advanced to explain precisely why a particular enclosure buckled, ruptured or otherwise failed. When one stress has been compensated for, another appears, and so on. In the past, when a new solution was implemented by modifying an enclosure a still newer theory was likely to follow to explain a subsequent failure in the modified enclosure. When an enclosure fails it is usually necessary to shut down the vapor generator to make satisfactory repairs. Revenue losses attributable to down time can never be recouped, thus the expense of a failure may well exceed the direct cost of repair.

In an effort to solve the problem applicants have devised an inventive enclosure assembly which has proven experimentally successful under actual operating conditions. The inventive enclosure is thus a solution to a troublesome and costly problem of long standing. More particularly, since enclosures usually fail at their corners applicants arrangement is primarily concerned with the construction, arrangement and support for the corners of an enclosure.

The inventive enclosure is adapted to be mounted on a vapor generator having a furnace chamber of substantialy rectangular cross-section defined by four walls which, in turn, define four corners. The enclosure comprises a wrapper constructed and arranged for mounting on the furnace walls such that the furnace walls and wrapper may move relative to one another. The wrapper extends around at least one corner of the furnace charnber and laterally from at least two walls of the furnace. An arcuately shaped expansion joint is formed in the wrapper such that it extends around the corner of the furnace wall. A plurality of trusses are provided to support the wrapper such that the wrapper relieves truss stresses.

Brief description of the drawings FIG. 1 is a vertical elevation of a vapor generating unit embodying the invention;

FIG. 2 is a partial three dimensional view of the furnace chamber of the unit shown in FIGURE 1 showing a typical enclosure configuration;

FIG. 3 is a partial top plate view of a corner area of the enclosure shown in FIG. 2;

FIG. 4 is a partial sectional elevation of FIG. 3 taken substantially along the line 4-4 of FIG. 3;

FIG. 5 is a partial sectional elevation of FIG. 3 taken substantially along the line 5-5 of FIG. 3 and substantially enlarged;

FIG. 6 is a partial sectional elevation of FIG. 3 taken substantially along the line 6-6 of FIG. 3;

FIG. 7 is a partial sectional elevation of FIG. 3 taken substantially along the line 77 of FIG. 3;

FIG. 8 is a partial top plan view of the corner area of the truss-work for supporting the enclosure shown in FIG. 2;

FIG. 9 is similar to FIG. 8 showing another embodiment of the truss-work;

FIG. is a partial top plan view of a section of the enclosure;

FIG. 11 is an embodiment of a link according to the invention;

FIG. 12 is a partial sectional elevation of FIG. 8 taken substantially along the line 12-12 of FIG. 8; and

FIG. 13 is a schematic partial elevation of the enclosure of FIG. 2 taken substantially along the line 13-13 of FIG. 2.

Description of the preferred embodiment In the drawings the invention has been illustrated as embodied in a forced flow once-through steam generation unit 10 intended for central station use. However, the inventive arrangement may be adapted to a natural circulation boiler without departing from the spirit and scope of the invention. The particular unit 10 illustrated in FIG. 1 is designed to produce a maximum continuous steam output of 2,500,000 pounds per hour at a pressure of 2500 p.s.i.g. for a total temperature of 1005 F. at the superheater outlet, based on feedwater being supplied at a temperature of 478 F., with provisions for reheating the steam.

The main portions of the unit illustrated include an upright furnace chamber 12 of substantially rectangular cross section defined by a front wall 18, rear wall 20,

side walls

14 and 16, a roof 22, and a floor 24 and having a gas outlet 26 at its upper end opening to a horizontally extending gas pass 28 of vertical cross section formed by a lloor 30 and extensions of the furnace roof 22 and

Walls

14 and 16. Gas pass 28 communicates at its rear 32 end with the upper end of an upright gas passage 34 of rectangular horizontal cross section formed by a front wall 40, a rear wall 42,

side walls

36 and 38 and an extension of the roof 22 of gas pass 28.

The Afuel firing section comprises independently operable horizontally extending cyclone type furnaces 44 of relatively small volume and boundary wall area disposed on

opposite walls

18 and 20 at the lower portion of furnace chamber 12 and enclosed by a common windbox 46 supplied with high temperature air from a duct 48 leading from an air heater not shown. Each cyclone furnace 44 is arranged to burn solid fuel at high rates of heat release and separately discharge high temperature gaseous products of combustion and separated ash residue as a molten slag into the lower portion of chamber 12. Floor 24 is formed with suitable openings, not shown, for the discharge of molten slag to a slag tank 50.

Gas pass 28 is occupied by a secondary superheater 52 and a reheater 54 arranged in series with respect to gas llow; while gas pass 34 is occupied, in the direction of gas llow by a primary superheater 56 and an economizer 58.

In the normal operation of the steam generator, combustion air at about 595 F. at a pressure of upwards of 60" w.g. and a relatively coarse crushed fuel is supplied to the cyclone furnaces and the fuel is burned in the furnaces at a sufficiently high rate of heat release to maintain a normal mean temperature therein above the fuel-ash fusion temperature. Ash separates as a molten slag which flows into the lower portion of chamber 12 and is discharged to the slag tank 50, while gases with a relatively small amount of slag particles in suspension discharge into the lower portion of the chamber. The heating gases then flow upwardly through chamber 12 to gas pass 28 and then pass successively over and through the tubes of secondary superheater 52, reheater `54, primary superheater 56 and economizer 58, and'then pass through the air heater 60 before flowing to the stack (not shown). A portion 64 of the relatively cool gases heating gas pass 34 at about 7 00 F. are recycled by a gas fan 66 via duct 64 for introduction into the upper and lower portions of chamber 12 by way of enclosures or

vestibules

68 and 70 via

openings

74 and 72 respectively formed in the boundary walls of chamber 12.

High pressure lluid supplied by a feed pump, not shown,

passes through economizer 58; then flows in parallel through lluid heating circuits of the cyclone furnaces 44 which are constructed and arranged in a manner similar to` that described in U.S. Patent No. 3,081,748, issued Mar. 19, 1963 to P. H. Koch; and then passes to the fluid heating circuits of furnace 12.

Each of the boundary walls of furnace 12 and gas passes 28 and 34 is lined with fluid heating tubes constructed and arranged in a manner similar to that described in U.S. Patent No. 3,237,612, issued Mar. l, 1966 to P. H. Koch et al. Fluid mixing headers 76 are enclosed by a vestibule 78 disposed at a position vertically spaced apart from the

gas vestibules

68 and 70 along the furnace height. After passing through the fluid heating circuitry of furnace 12 and gas passes 28 and 34 the fluid is directed successively through primary superheater 56 and secondary superheater 52 and then to a high pressure turbine, not shown. Partially expanded steam from the turbine flows through reheater 54, then to a reheater turbine, not shown, where linal expansion takes place.

The steam generator is top-supported by structural steel members including upright column members 80 and cross beams, not shown, from which hangers support all walls in a manner similar to that shown in U.S. Patent 3,081,748, issued Mar. 19, 1963 to P. H. Koch.

It should be recognized that with the vapor generating unit 10 being pendently supported the linear thermal eX- pansion of the unit between its cold (non-operating) condition and its hot (operating) condition Will be cumulative and in a downward direction, the vertical movement of the lowermost portion of the unit being greater than the movement of any portion of the unit above its lowermost portion. As an example of the amount of linear thermal expansion involved in a large modern generating unit, it is common for the lowermost portion of a unit to move downwardly by as much as 8 to 10 inches as the temperature of the unit is increased from its non-operating condition to its normal equilibrium condition of operation.

For the purposes of affording lateral support to and to maintain the alignment of the walls of the vapor generating unit, and to reinforce the walls against the effects of the normal positive pressure within the unit as well as possible inordinate pressure surges, a buckstay system 92 comprising. an encircling grid of structural members is provided at intervals about the exterior of the unit 10. It should be recognized that the buckstay grids 82 will not be subject to the same lateral thermal expansion as the walls of the vapor generator because of their different relative positions with respect to the gases of combustion. Provision is thus made to accommodate the resulting movement between the buckstays and walls, for example, as shown in Patent No. 3,301,225, issued Ian. 31, 1967 to H. A. Boe et al.

Provision must also be made to support and maintain the alignment of the

vestibules

68, 70, 78 and windbox 46 with respect to the

tube walls

14, 16, 18 and 20 as they laterally expand and contract and accommodate differences in thermal expansion between these structures and the tube walls. `Providing such a vestibule and/or wind-box structure is the primary object of the present invention.

In describing the invention it should be understood that the inventive arrangement is adaptable to the Windbox 46 and/or

vestibule structures

68, 70, 78 since these structures differ from one another in details which form no part of the invention. Accordingly, there is shown in FIG. 2 a three-sided box-like enclosure 90 such as a windbox 46, or

vestibule

68, 70 or 78 or the like, which is constructed and arranged to be mounted on and laterally extend from the

walls

14, 16, 18 and 20 of the furnace 12 a typical distance of from 5 to 8 feet. The enclosure generally includes an outer Skin or wrapper assembly `92 of metal plate construction supported by trusses and is mounted on the furnace Walls such that relative movement between the wrapper 92 and furnace Wal-ls is accommodated. The wrapper 92 comprises an annular top plate 94 seal welded to and laterally extending from the furnace walls in a substantially horizontal plane encircling the furnace, an annular bottom plate 96 vertically spaced apart from the top plate `94 and seal welded to and laterally extending from the furnace wall in a like horizontal plane, and an annular side plate 95 seal welded to and vertically extending between the top and bottom plate such that it is spaced apart from the furnace wall in planes substantially parallel to each of the furnace walls. The top and

bottom plates

94, 96 are of substantially the same contour and construction, varying from one another in minor details which are equivalents of the inventive arrangement and/or in details which form no part of the invention. Thus in describing the construction and arrangement of top plate 94, the bottom plate 96 is also described.

The top plate 94 has a continuous inner edge 98 disposed adjacent the furnace walls and a continuous outer edge 99 disposed remote from the furnace wall. Since the vertical furnace walls form a four walled structure and since a more simplified description of the top plate will be provided by speaking of the plate as having various portions, it is convenient to describe the top plate as a four cornered member comprising four rounded f corner portions 100 suitably interconnected to one another by four elongated furnace wall portions 102 intermediate the corner portions as generally shown in FIG. 3. Although the top plate is preferably constructed of a plurality of these portions seal welded to one another, it may be otherwise constructed to form a sealed assembly without departing from the spirit and scope of the invention.

As shown in FIGS. 3-6 it is a feature of the invention to connect the inner edge 98 of the furnace wall portions 102 of the top plate 94 to the furnace walls (for example walls 14 and 18) superadjacent the same by first bending these plate portions near their inner edges as shown in FIG. 4 to form an angle in each portion throughout its longitudinal length which is preferably greater than 90, and then seal welding the inner edge 98 to a tie bar 105 mounted on the outer face of the furnace wall 14. By bending the inner edge upwardly each furnace wall portion 102 of the top plate 94 is provided with an elongated tab 104 by which the top plate may be pendently supported n the furnace Wall. The term tie bar 102 is a generic term describing an elongated member seal welded to the furnace wall and extending across the width of the furnace wall in a substantially horizontal plane and at substantially right angles to the Vertical longitudinal axis of the furnace wall tubes to act as a support and structural tie. Thus the elongated furnace Wall portions 102 of the top plate 94 are secured to the furnace walls by flexible tabs 104, flexible in a manner which provides for lateral motion of the furnace walls and/or the furnace wall portions of the top plate. The corner portions 100 of the top plate are also bent in substantially the same manner as the furnace wall portions 102 to provide tabs 106 for connection to the corners 19 of the furnace wall.

As shown in FIGS. 3, and 6 the ends of the furnace wall portions of the top plate near furnace corners, and particularly the tab 104 thereof, are spaced apart from the furnace wall to allow for greater thermal expansion of the corners 19 -of the furnace walls than is allowed for intermediate the corners. A like remark may be made regarding the entire tab 106 of the corner portion 100. The

tabs

104, 106 as shown are too short to be connected to the furnace wall in the vicinity of the furnace corner 19 and provide proper clearance. To compensate for the size of the tabs and allow for expansion of the corner of the furnace, a tab extension 108 is provided which is an elongated breather plate bent around the corner. The breather plate has a lower edge 110 seal welded to the

tabs

104, 106 of the corner and furnace wall portions of the top plate, an upper edge 112 seal welded to the furnace wall at a vertical elevation above tab 106,

and side edges 114 directly seal welded to tube wall or boxed in by a filler plate 116 seal welded to the side edges and tube walls to bridge the gaps intermediate the breather 108 and

tube walls

14 and 18. In the preferred embodiment the side edges 116 of the corner breather 108 are disposed substantially flush with the furnace walls by bending the corner breather plate toward the furnace wall along two diagonal bend lines 118, one of which is shown in FIG. 6. Each bend line 118 commences at t-he upper edge 112 of the breather plate and at a point superadjacent the furnace corner, and extends to the lower edge 110 of the breather plate and to a point adjacent one of the side edges 114. Each of the bend lines subtends an angle of approximately 45 from the upper edge of the breather plate. After bending, the side edges 114 of the corner breather are seal welded directly to the tube walls, a filler bar 116 being used at the side edges intermediate each side edge and the tube wall if necessary to effect a seal 4weld therebetween. A filler bar 120 may also be provided at the upper edge of the breather plate intermediate the upper edge 112 and the tube walls if necessary to effect a seal weld therebetween.

It is a feature of the invention to provide each of the corner portions of the top plate with an arcuately shaped expansion joint 122 formed intermediate its inner and outer edges. The joint 122 is formed by providing an opening 124 which is preferably an arcuate slot in the corner portion of the top plate, and bridging the slot 124 with an expandable and contractable cover plate 126 seal welded to the corner portion. The cover plate 126 is preferably an elongated arcuate member having an accordian pleat-like transverse cross-section as shown in FIG. 5. The pleat-like cover plate 126 may also have an inverted V-shaped cross-section or have one or more folds therein without departing from the spirit and scope of the invention. The end edges 128 of the cover plate at the ends of the arc are covered with a conveniently shaped plate 130, the cover plate 126 and corner portion of the top plate 94 being seal welded thereto to complete the expansion joint 122. It should be appreciated that arcuately shaped expansion joints relieve thermal expansion stresses in the furnace wall portions of the top plate as well as in the corner portions of the top plate since stresses which build up in the furnace wall portions are transmitted to the corner portions where they are then relieved. A like remark may be made for top plate stresses due to furnace pressures and puffs.

As shown in FIG. 7 it is a feature of the invention to connect the outer edge of the top plate to the top edge 0f the wrapper side wall 98 by first bending the top of the side wall adjacent its top end edge at right angles, and then seal welding the elongated tab 132 thus formed to the lower surface of the top plate 94. This construction strengthens the outer edge 99 of the top plate and aids in the prevention of wrapper buckling. The bottom plate 96 is similarly connected to the bottom of the wrapper side plate.

In view of the foregoing discussion it should be appreciated that the wrapper may be formed to extend around a single corner or more formed by the furnace walls, the corner or corners of the wrapper, as the case may be, being provided with an expansion joint, as hereinbefore described. For this type of enclosure the wrapper plate may be extended to the furnace walls at the free ends of the foreshortened furnace wall portions of the top and bottom plates and edgewise mounted on the furnace walls as the top and bottom plates are mounted thereon, filler plates and/or bars being provided as necessary.

As indicated in FIG. 2 the wrapper is supported in place by upper 134 and lower 136 truss assemblies mounted within the wrapper which are carried on the tube walls, serving to dampen buckling and distortion stresses caused by pressure ring the unit and/or relieving stresses due to any abnormal operating condition such as a furnace puff. The

truss assemblies

134, 136 as shown in FIG. 8 and 9 are connected to the furnace walls at vertically spaced intervals and laterally extend from the walls in transverse planes, each truss assembly being made up of four truss structures endwise interconnected to one another as hereinafter described to encircle the furnace wall in a given horizontal plane. For the purpose of this application a truss structure is an arrangement of members such as pipes, channels, beams, bars or rods, or the like, arranged in a geometric form or combination of forms for supporting a load over a wide area, and is characterized in that it cannot be deformed by the application of an exterior force without deformation of one or more of its members.

In the embodiments shown in FIGS. 8 and 9, (a truss or truss structure 140 is an arrangement of elongated members including an inner chord 142 adapted to be mounted adjacent one of the furnace walls, an outer chord 144 of greater length than the inner chord 142 and spaced apart from the inner chord 142 so that it is disposed remote from the furnace wall and substantially parallel to the inner chord, and a plurality of crossmembers 146 endwise extending off-normal between the

chords

142, 144 at intervals along the longitudinal lengths of the chords. The cross-members 146 are thus arranged in a geometric pattern of adjacent triangles, the base lines of the adjacent triangles being described by first one chord and then the other chord. The end cross-members 150 each extend directly between opposing ends of the chords. Gusset plates 148 may be provided to facilitate welding the ends of the cross-members to the chords. It is seen that the end cross-members are also disposed at an Gif-normal angle with respect to the longitudinal length of each of the chords because the outer chord 144 is of longer longitudinal length than the inner chord 142, the u inner chord 142 being foreshortened such that it does not extend into the planes defined by the furnace walls next adjacent the wall with which the inner chord is associated.

The upper and

lower truss assemblies

134, 136 each include four trusses 140 endwise interconnected to one another in a horizontal plane and encircling the furnace walls. The outer chords 144 of the upper and lower trusses 140 as mounted on any particular furnace wall, are rigidly interconnected to one another by a plurality of vertically oriented elongated members 152 such as pipes, posts, beams, bars or rods, or the like, spaced apart from one another at regular intervals along the longitudinal lengths of the outer chords 144 of opposing trusses and endwise welded in place to these chords. As

shown in FIGS. 8-10, the posts 152 are mounted on the outer side of the outer chord 144 to act as supports for the wrapper side plate or plates 98, the wrapper side being seal welded to the posts 152. The inner chord 142 of each truss is mounted for endwise motion (by means well known in the art) with respect to the center of its length where it is rigidly connected (by means Well known in the art) to the furnace wall next adjacent the inner chord. For example, in the preferred embodiment an elongated tie bar 154 is lain against the side of each of tube walls in a plane parallel to the longitudinal length of an inner chord, and is welded in place to the tube wall. As shown in U.|S. Patent No. 3,301,225, issued Ian. 31, 1967 to H. A. Boe et al., an inner chord 142 (corresponding to the buckstay of that patent) may be mounted for movement with respect to the tie bar 154 via an outwardly extending tie plate 156 Welded to the tie bar and having welded thereto tie clips 158 which loosely engage the inner chord to restrain the inner chord from movement in a direction perpendicular to the associated tube wall, while permitting endwise movement of the inner chord. However, in the preferred embodiment, clearances (numbered 64A and i64B in said patent) are undesirable, such clearances forming no part of the present invention. Rigidly connecting (not shown) the center of the longitudinal length of the inner chord of each truss to its associated tube wall at the point on the tube wall next adjacent the center of the inner chord by means well known in the art allows for different thermal expansion of the tube wall towards the corners 19 of the furnace, and uniform expansion of the ends of the inner chords towards these corners.

Referring particularly to FIG. 8 wherein a typical corner of a windbox or vestibule is shown, it is seen that the trusses are endwise interconnected to one another via movable links extending between the adjacent ends of the inner chords of the trusses and the outer chords of the next adjacent trusses. It is a feature of the invention to so interconnect the trusses. However, as shown in FIG. 9 which will hereinafter be more fully described, in one embodiment only the tie bars are rigidly interconnected to one another. In the prior art it has been common to either interconnect the trusses to one another via a exible interconnection connected to the ends of associated tie bars or flexibly interconnect the ends of the tie bar associated with one truss to the end members of the next adjacent trusses.

It should be appreciated that since the tie bars 154 are disposed superadjacent their respective tube walls, the temperature of their environment is greater than that of the inner chords 142. The inner chords 142 of the preferred embodiment are laterally spaced apart from their respective tube walls a distance of approximately 6". In practice it has been found that because of the temperature differentials the ends of a given tie bar 154 extend a greater incremental distance than the ends of the inner chord of the truss associated with that tie bar. Further, and for the same reason the ends of the outer chord 144 of a given truss 140 extend a lesser incremental distance than the ends of the inner chord 142 of the same truss. Thus the stresses imposed on trusses 140 connected according to the preferred embodiment are less per increment of change in furnace temperature because the truss members extend less than the tie bars and are connected by movable links. Further, in applications where the furnace is pressurized and/or during abnormal operation of a non-pressurized furnace the stresses appear to be more easily absorbed or otherwise accommodated by the trusses when they are interconnected by movable links arranged according to the present invention. Each of the movable links acts as a tension link which moves sufiiciently to avoid failure thereof in compression when the trusses to which they are connected expand and contract due to changes in temperature. A movable link basically comprises a rigid bar, pipe, channel, beam or rod, or the like, which has one end pivoted to the inner chord of one truss and the other end pivoted to the outer chord of the next adjacent truss.

In the embodiment shown in FIG. 11 a given link 160 is an assembly comprising three elongated bars including a movable center link 162 and two link extension members 164, each of the extension members 164 being welded to one of the ends of the center link to extend its longitudinal length as necessary for bridging the distance between the inner chord 142 of one truss and the outer chord 144 of the next adjacent truss. The end of each extension member 164 which is remote from the center link 162 is bored to receive a bolt 166. The outer and inner chords of each truss are respectively provided with gusset plates 148 welded in place at the ends of the chords and bored to receive the bolt 166. The same gusset plates 148 used to connect the end cross-members to the chords may be used for this purpose. The movable interconnection between the

chords

142, 144 are then completed by aligning the borings in registry, then passing the bolt 166 through the aligned openings and fixing it in place by means well known in the art such that it acts as a pivot. i

In the preferred embodiment shown in FIG. 8 the links are variations of the basic link and the above described link embodiment, the links connected to the ends of adjacent trusses differing from one another in some details. A first link A comprises a movable center link 162A and one link extension member 164A, the extension member 164A having one end welded to the inner chord 142 of a first truss and the other end pivotally connected to one end of the center link 162A, while the end of the center link remote from the extension member 164A is pivoted to a gusset plate 148 which is Welded in place to the outer chord 144 of the next adjacent second truss. A second link 160B comprises a movable center link 162B and a three section extension member 164B, the extension member 164B and movable member 162B being endwise interconnected to one another and to the first and second trusses as hereinbefore described except that the inner chord of the second truss and outer chord of the first truss are used. The extension member 164B of the second link 162B is made in three sections to provide an opening in this extension member through which the extension member 164A of the first link 160A may be passed for endwise interconnection as hereinbefore described. In FIGS. 8 and l2 it is seen that the three sectioned member 164B includes a first stub having one end welded to the inner chord 142 of the second truss and a free end 171, a second stub 172 having one end pivoted to its associated center link 162B and a free end 173 spaced apart from the free end 171 of the first stub 170, and a pair of stubs 174 facewise spaced apart from one another and sandwiching the free ends 171, 173 of the first and

second stubs

170, 172 and endwise Welded thereto thus forming a passageway 175 between thefree ends of the stubs through which the extension member 164A of the first link 160A may pass.

In the course of experimental development of the invention it was found that when the wrapper 92 arrangement was mounted on the furnace walls as hereinbefore indicated and supporting trusses 140 were provided and mounted to encircle the furnace wall as hereinbefore indicated, and there were no

movable links

160, 160A, 160B provided interconnecting the trusses to one another as hereinbefore described, and the tie bars 154 associated with the inner chords of each truss assembly were endwise rigidly interconnected around the furnace corners with a rigid plate as shown in FIG. 9 the enclosures did not fail but retained their gas impermeability. Accordingly, it is an alternate feature of the invention to provide such a tie bar interconnection in combination with the wrapper and trusses. It is understood, of course, that in this embodiment the Wrapper itself acts as a stress member transmitting the induced stresses through the associated corners and furnace wall portions. That is, the ends of the truss assemblies associated with each of t-he furnace walls are physically connected together via the corner portions and furnace wall portions of the top and bottom plates of the wrapper rather than through the tie bars. In the preferred embodiment where movable links are used the trusses are structurally tied together via the movable links and the top and bottom plates of the wrapper rather than through the tie bars. In either embodiment the wrappers to some extent compensates for changes in size of the supporting trusses and distributes stresses due to furnace pressure and truss thermal expansion amongst the trusses. In this regard it should be noted that in any of the embodiments of the invention the top and bottom plates of the wrapper are either welded to the trusses and posts directly or affixed thereto via tie clips by means well known in the art. Still further, the furnace wall portions of the top and bottom plates and side plate or plates of the wrapper may be provided with V-breathers well known in the art to aid in relieving stresses longitudinally of the transverse lengths of the wrapper.

As shown in FIGURE 13 a plurality of diagonally oriented cross struts each having one end connected to a furnace wall and the other end connected either to a post and/or outer chord of a truss are provided to aid in vertically supporting the trusses. It should be apreciated that such struts may be mounted within or outside of the enclosure, and extend upwardly or downwardly from a post and/or outer chord to the furnace wall without departing from the spirit and scope of the invention.

What is claimed is:

1. In combination with a vapor generator having a furnace chamber of substantially rectangular cross-section defined by four walls which define four corners, an improved enclosure with provision to be mounted on some of the furnace walls such that the enclosure and furnace walls may move relative to one another, the enclosure comprising a three-sided wrapper means extending around at least one corner of the furnace chamber and laterally from at least two of the furnace walls, one side of the wrapper means extending between the other sides thereof and being spaced apart from said at least two furnace walls and substantially parallel thereto, means providing for relative motion between the furnace walls and enclosure including an arcuately shaped expansion joint formed in at least one of said other sides of the wrapper means and extending around said at least one corner, and truss means connected to the wrapper means for supporting the wrapper means.

2. The enclosure according to claim 1 wherein the truss means comprises, at least two trusses spaced apart from one another and mounted on different furnace walls, and the trusses connected to the wrapper means such that the trusses are physically connected together via the wrapper means to relieve truss stresses.

3. The enclosure according to claim 1 wherein the wrapper means is formed to extend around more than one of the corners of the furnace chamber and laterally from more than two of the furnace walls, and more than one arcuately shaped expansion joint is formed in the wrapper means.

4. The enclosure according to claim 3 wherein the truss means comprises, four trusses spaced apart from one another in a substantially common plane with one truss mounted on each of the walls of the furnace charnber, and the trusses connected to the wrapper means such that at least one end of each truss is connected to an end of the next adjacent truss via the wrapper means to relieve stresses in the trusses.

5. The enclosure according to claim 3 wherein the truss means comprises a first truss assembly of four trusses spaced apart from one another in a substantially horizontal common plane with one truss mounted on each of the walls of the furnace chamber and a second truss assembly of like construction and arrangement mounted on the furnace walls in a plane vertically spaced apart from the plane of the rst truss assembly each of the trusses havlng an inner chord and an outer chord, and a plurality of movable links, each link having one end pivoted to the inner chord of one truss and the other end pivoted to the outer chord of the next adjacent truss mounted in the same plane on the next adjacent furnace wall.

6. The enclosure according to claim 5 wherein each link comprises three elongated bars including a center member and two link extension members, each extension member being welded to one of the ends of the center member to extend its longitudinal length, the link being pivoted to the outer and inner chords by pivoting one extension member to the inner chord of one truss and the other exteniron member to the outer chord of said next adjacent russ.

u 7. The enclosure according to claim 5 wherein each link comprises a movable center member and an extenslon member, the extension member having one end welded to the inner chord, the link being pivoted to the lnner and outer chords by pivoting one end of the center member to the extension member and the other end to the outer chord.

8. The enclosure according to claim 5 wherein each link comprises a movable center member and an extension member, the extension member having one end welded to the outer chord, the link being pivoted to the inner and outer chords by pivoting one end of the center member to the extension member and the other end to the inner chord.

9. The enclosure according to claim 5 wherein each link comprises a center member and an extension member, each of the extension members having one end welded to one of said chords of one truss and the other end pivoted to one of the ends of the center member, the other end of the center member being pivoted to the other of said chords of said next adjacent truss, and some of said extension members constructed and arranged to provide a passageway through which other of said extension members may be passed.

10. The inclosure according to claim 2 wherein each ot the trusses has an inner chord, a tie bar is connected to each of the inner chords such that the inner chord and its associated tie bar are movable relative to one another, and at least one end of each of the tie bars is rigidly connected to an end of another tie bar.

11. The enclosure according to claim 1 wherein the other sides of the wrapper means comprises a top plate mounted on at least two of the furnace walls and a bottom plate mounted on said at least two furnace walls and facewise spaced apart from the top plate, and said one side comprises a side plate sealed to and extending Ebetween the top and bottom plates, and the means providing for relative motion between the furnace walls and enclosure further comprises the top and bottom plates being respectively adaptmi to be mounted on at least said two furnace walls by means of tab portions thereof, each tab portion being angular with respect to its associated plate, and the tabs mounted on the furnace wall to act as exible sections of their associated plates such that the wrapper and furnace walls may move with respect to one another.

References Cited UNITED STATES PATENTS 3,007,455 11/1961 Lieb et al. 122-6 3,203,376 8/ 1965 Engelhardt 122-6 XR 3,277,870 10/1966 Reale 122-6 3,368,535 2/1968 Svendsen et al 122-510 KENNETH W. SPRAGUE, Primary Examiner U.S. C1. X.R.