US3368535A

US3368535A - Vapor generator construction

Info

Publication number: US3368535A
Application number: US514780A
Authority: US
Inventors: Konrad S Svendsen; Willburt W Schroedter
Original assignee: Combustion Engineering Inc
Current assignee: Combustion Engineering Inc
Priority date: 1965-12-20
Filing date: 1965-12-20
Publication date: 1968-02-13
Anticipated expiration: 1985-02-13
Also published as: DE1526907A1; NL6617782A; GB1165359A; BE691380A; SE323972B; FR1505755A; ES334662A1

Description

Feb. 13, 1968 K. s. SVENDSEN ETAL VAPOR GENERATOR CONSTRUCTION v5 sheets-sheet 1 Filed Dec. 20, 1965 INVENTOR.

""IIWIll KONRAD svENDsEN l WILLBURT W. SCHROEDTER BY M FIG.

ATTORNEY Feb. 13, 1968 K. s. SVENDSEN' ETAL 3,368,535

VAPOR GENERATOR CONSTRUCTION 5 Sheets-Sheet 2 Filed DeC. 20, 1965 FIG. 2

. INVENTR. KONRAD. SVENDSEN WILLBURT W. SCHROEDTER Bv W? m ATTORNEY Feb. 13, 1968 s. svENDsr-:N ETAL -3,358,535

VAPOR GENERATOR CONSTRUCTION Filed Dec. 20, 1965 5 Sheets-Sheet 5 INVENTOR.

KONRAD svENosEN wlLLBuRT w. scHRoEDTER Bv 2M ATTORNEY v Feb. 13,v 1968 K. s. SVENDSEN ETAL 3,368,535

VAPOR GENERATOR CONSTRUCTION v Filed Dec'. 2o, 1965 v 5 sheets-sheet 4 FIG. 4'

INVENTOR. KONRAD SVENDSEN wlLLBuRT 'CHROEDTER Bv Mw/W ATTORNEY Feb. 13, 1968 K. s. svENDsEN ETAvl. 3,368,535

VAPOR GENERATOR CONSTRUCTION 5 Sheets-Sheet 5 Filed DeC. 20, 1965 FIG. 5

INVENTOR.

KONRAD SVENDSEN WILLBURT W. SCHROEDTER FIG. 6

ATTORNEY United States Patent Oice 3,368,535 Patented Feb. 13, 1968 3,368,535 VAPOR GENERATOR CONSTRUCTION Konrad S. Svendsen, Bloomfield, and Willburt W.

Schroedter, West Hartford, Conn., assignors to Combustion Engineering, Inc., Windsor, Conn., a

corporation of Delaware Filed Dec. 20, 1965, Ser. No. 514,780 20 Claims. (Cl. 122-510) ABSTRACT OF THE DISCLOSURE A construction for stiffening the walls of furnaces and gas passes of vapor generators so that they can withstand sudden increases of pressure within the furance or gas pass. The construction includes vertically extending steel beams positioned about the furnace or gas pass and hung from the upper end in a manner which permits limited lateral movement of the beams. Buckstays are secured to these beams and extend transversely of them with these buckstays being positioned about the furnace or gas pass at vertically spaced elevations. The ends of the buckstays associated with opposite walls of the furnace or gas pass are connected together by means of a tube which in turn is connected into the circuit of the vapor generator so that this tube will thermally expand commensurate with the furnace or gas pass wall tubes.

This invention relates generally to high capacity vapor generators such as currently employed in power plants of the utility industry and has particular relation to such vapor generators of improved construction.

As a result of the demand for ever larger capacity vapor generators the size of the furnaces and gas passageways has increased to such an extent that the buckstays and the vertically extending steel members which provide the necessary stiffening for the furnace and gas pass walls have become excessively heavy. Heretofore, it has been the practice to support this structure from the furnace and gas pass wall itself and more particularly from the tubes that form the inner lining of these walls. Because of the great weight of this structure with these very large units, this, form of construction was accompanied by several undesirable characteristics such as a requirement that the thickness of the tube wall of the tubes lining the furnace and gas pass walls be increased to carry this additional load and the development of stresses within the tubes as a result of this additional load and this additional thickness. These difficulties have been avoided with the present invention wherein the vertically extending steel members at the outer region of the furnace and gas pass walls are supported independently of the walls and the buckstays are in turn supported from these steel members. Furthermore, the buckstays are tied together with fluid carrying ties which thermally expand and contract with the walls of the vapor generator.

In accordance with the present invention there is provided a high capacity vapor generator which has a vertically disposed furnace with there being a horizontal gas pass extending from the upper end of the furnace with this gas pass in turn connecting with a vertically extending gas pass. The walls of the furnace and the gas passes are hung from their upper region and are lined with tubular members that extend vertically and are in side-by-side relation with these tubular members being connected into and forming a part of the circuit of the vapor generator. The furnace has a rectangular transverse section and there are numerous vertically spaced horizontally extending stitfener members secured to and supported from the tubes that form the inner surface of the walls of the furnace and the gas passes.

Extending down along side of these stiffener members are a number of horizontally spaced steel beams. These beams are supported from their upper ends from building steel independently of the Walls of the vapor generator and in such a manner that they can move laterally to accommodate movement of the walls as is necessary due to thermal expansion and contraction caused by temperature changes in the walls incident to variations between full operation and a shutdown condition of the vapor generator. The beams that extend along each Wall of the furnace are connected together by buckstays that extend transversely of the furnace walls. Buckstays are provided at several vertically spaced locations and are connected with and supported by the vertically extending beams. The ends of the buckstays at each of these locations which extend transversely of the opposite walls of the furnace are connected together by means of a fluid carrying member. Fluid from the circuit of the vapor generator is conveyed through this member so that thermal expansion will be similar to that of the furnace walls and thus these interconnected buckstays Will move in accordance with this thermal expansion. These beams and buckstays form a framework or cage which expands laterally with the furnace and within which the furnace expands vertically, with this framework being supported independently of the furnace walls.

Accordingly, it is an object of this invention to provide an improved vapor generator.

Another object of the invention is to provide such an improved vapor generator wherein the walls of the generator are hung from their upper regions with buskstays to prevent wall deflection being supported independent of these walls.

A still further object of the invention is to provide such an improved vapor generator supported from its upper region with there being provided a steel framework about the walls of the generator and supported independently of these walls.

A still further object of the invention is to provide such an improved steam generator having a buckstay system wherein opposed buckstays are interconnected by fluid carrying members such that they move laterally in accordance with thermal expansion of the furnace.

A further object of the invention is to provide a vapor generator with an improved buckstay system.

A still further object is to provide an improved vapor generator with a buckstay system wherein opposed buckstays are interconnected with fluid carrying members which are connected into the uid carrying circuit of the vapor generator.

Other features and advantages will be apparent from the specification and claims and from the accompanying drawings which will illustrate an embodiment of the invention which will be described by way of example and in which:

FIGURE 1 is a vertical sectional view of a high capacity vapor generator employing the present invention;

FIGURE 2 is in the nature of a transverse section of the furnace of the generator of FIG. 1 with some of the parts being removed for clarity of illustration;

FIGURE 3 is a perspective view depicting the fluid carrying circuit which interconnects opposed buckstays at the several elevations;

FIGURE 4 is a perspective view of the buckstay system at one elevation and showing the means for and the way in which the opposed buckstays are interconnected;

FIGURE 5 is a detailed illustration of the means by which the fluid carrying ties are interconnected with the buckstays; and

FIGURE 6 is an additional view of this detail taken generally from line 6-6 of FIG. 5.

There is shown in the accompanying drawings a supercritical, high capacity vapor generator capable of producing vapor at a pressure such as 3,500 p.s.i. and at a ternperature of upwards of 1,100 F. The vapor generator includes an upright furnace 10 into which fuel and air are introduced through the burners 12. The fuel is burned within the furnace and the combustion gases pass up through the furnace, out the lateral outlet at the upper end thereof and then through the horizontal gas pass 14 and vertical gas pass 16. Thereafter the gases traverse an air heater (not shown) and finally are conveyed to a stack.

The illustrative once through-flow vapor generator includes a through-flow circuit through which the vaporizable medium of the generator is forced by a feed pump. This through-flow circuit may include an economizer located in the vertical gas pass 16 and which receives the fluid from the feed pump. After traversing the economizer this fluid may be introduced into the mixing chamber 18 through conduit 19 and then conveyed up through the furnace center wall 20. From this center wall the fluid is conveyed down through the downcomer 22 and then into the headers 24 and up through the tubes 40 that line the inner surface of the furnace walls. These tubes are connected with headers at the upper end of the furnace and from these headers a portion of the fluid may be directed to the mixing header 18 through conduit 26 while the remainder may be conveyed through additional heating surface which may include tubes on the roof aild the gas pass walls as well as tubular heat exchanger means disposed within the upper region of the furnace and withing the gas passes. The vaporizable medium is heated to its final desired temperature and is then conveyed to a suitable point of use such as a turbine.

The illustrative once through-flow supercritical vapor generator is provided with a recirculating system which includes the conduit 26 connected with the mixing chamber 18 and the pump 28 in the conduit 30 that leads from the mixing chamber to the inlet of the center or division wall 20. This recirculation system is effective to recirculate a portion of the vaporizable medium through the center wall and the furnace wall tubes. The arrangement may be such that the recirculating system may become effective at a predetermined load such as 80% load and effect a recirculation of fluid for all loads below that load or it may Ibe such as to cause and effect a recirculation of fluid for all loads including 100% load. For a more complete and detailed explanation of such a recirculation system and the purpose and effect thereof reference is made to U.S. 3,135,252 issued lune 2, 1964.

The furnace of the vapor generator of the invention is rectangular in transverse section with one of the pair of opposed side walls including walls identified as 32 and 34 while the walls ^f the other pair are identified as 36 and 38. The inner surface of these walls are lined with and made up of tubes 40 and these tubes are either tangent or provided with small laterally extending fins and are welded together to provide a welded generally gas-tight surface. Outwardly of and in engagement with the tubes 40 is a layer of thermal insulation 42 which is supported by the tubes in known fashion. Also supported by the tubes 40 are the horizontally extending stiffener members 44 in the form of channels or I beams. These stiffener members are connected with and supported by the tubes 40 in a manner which permits limited lateral movement therebetween to accommodate differential expansion and contraction. Such a support arrangement is well known so that the details thereof are not illustrated.

The vapor generator is hung from its upper end from the building steel here identified as 46 and in the illustrative arrangement the furnace walls are hung from this building steel by the hanger rods 48 which extend downwardly from the building steel and are connected with the headers into which the upper ends of the tubes 40 are connected.

In order to prevent excessive deflection of the walls of the furnace incident to sudden increases in pressure within the furnace as when a puff occurs within the furnace there is provided, in accordance with the present invention, a heavy steel cage about the furnace and which includes a heavy buckstay system. This cage is comprised of vertically extending steel I beams 50 positioned at spaced horizontal intervals about the furnace as shown in FIGURE 2. These vertically extending ybeams are not supported from the furnace walls but are supported independently of the furnace walls with each beam being hung from the building steel 46 through a separate support rod 53. The beams 50 that extend down along side each wall of the furnace are in sliding engagement with the stiffener members 44 on the wall and the support rod 53 is so connected that the vertical beams can move laterally as is necessary to accommodate the expansion and contraction of the furnace incident to the temperature changes occasioned by the furnace being put into and taken out of operation. At the vertically spaced

locations

52, 54 and 56, there is provided a buckstay system which extends about the furnace with this system including buckstay trus` 58 extending transversely of wall 42 and a similar buckstay truss 60 extending transversely of wall 34. A large I beam buckstay 62 extends transversely of wall 36 and a similar buckstay 64 extends ransversely of wall 38. These buckstays extend along the outer side of the vertical beams 50 and are secured to these beams by welding.

In order for this structural cage, that is comprised of the vertical beams 50 and the buckstays, to prevent deflection of the furnace walls the extremities of the opposed buckstays at each elevation or in other words the buckstays that extend transversely of the opposed pair of walls are interconnected. It will be appreciated that the furnace will expand and contract considerably between its cold and hot conditions and the means by which the opposed buckstays at each elevation are interconnected mu`st be such as to move these buckstays generally in accordance with this expansion and contraction of the furnace. This is accomplished with the present invention by having the means by which the Ibuckstays are interconnected or what is termed the buckstay ties be comprised of a fluid conveying circuit through which the vaporizable fluid of the vapor generator is conveyed. This is Ibest seen in FIGURE 3 wherein it is shown that each of the

elevations

52, 54 and 56, there is provided a conduit 66 which extends about the furnace. In the illustrative arrangement (FIG. 1) this conduit extends through suitable openings provided in the beams 50. The vaporizable fluid of the generator is conveyed to the conduit 66 at the elevation 56 through the interconnecting conduit 68. The conduits 66 at the several elevations are in series flow relation and are interconnected by conduits 70. The final conduit 66 at elevation 52 is connected with the header 72 at the terminal end of the downcomer by means of the connecting conduit 74. The

several conduits

68, 70 and 74 are such as to accommodate any necessary thermal expansion that may be encountered in these conduits or any movement between the fluid carrying means that they interconnect. Fluid that has thus traversed the center wall is conveyed downwardly through the conduit 66 in series iiow relation. Through this arrangement these conduits 66 will expand in a manner generally similar to that of the furnace walls as the furnace is brought from a cold condition to its realtively high operating temperature.

The continuous conduit 66 which extends around the furnace is in effect made up of two

parallel legs

76 and 78 and two additional

parallel legs

80 and 82. The

legs

80 and 82 are effective to interconnect the ends of the

buckstays

58 and 60 while the

legs

76 and 78 are effective to interconnect the

buckstays

62 and 64. These legs are connected with their respective buckstays through a suitable connecting arrangement which permits limited lateral movement between the interconnecting leg and the buckstay as will be necessary because of the conduit 66 being continuous and extending about the furnace. These interconnections are shown in detail in FIGURES and 6 and they include a pair of rods 84 one end of which extends through suitable openings 85 provided at the end of the buckstay and the other end of which extends through an opening in collar 86 secured to the particular leg of the conduit 66. Rocker members 88 are mounted on the ends of these rods in engagement with the end of the buckstays and the collar, respectively, with these rocker members being retained in place via nuts 90. Through this arrangement the opposed lbuckstays are secured together and prevented from moving outwardly with relation to each other while lateral movement between the interconnecting leg of conduit 66 and the buckstay is permitted.

It will be appreciated that with the construction and organization of this invention a rugged cage is provided about the furnace of the vapor generator with the furnace moving up and down within this cage as a result of thermal expansion and contraction and with the cage expanding and contracting laterally in a manner generally similar to that of the furnace. While in the illustrative arrangement the fluid carrying means for inter-connecting the buckstays has been disclosed as receiving its fluid from the outlet of the center Wall it may receive its fluid from other portions of the vapor generator such as the outlet of the furnace walls with the requirement being such that the temperature of the fluid flowing through these interconnected fluid carrying members be reasonably close to the temperature of the iiuid flowing through the furnace walls so that thermal exvpanson and contraction will likewise be generally similar and excessive stresses as a result of large differences in thermal expansion will not be encountered.

The arrangement of the invention is useful and advantageous with various vapor generating arrangements including various types of forced ow generators and once through-flow generators. It has particular advantage in a once through-flow generator such as -illustratively shown wherein there is provided a recirculating system in the manner disclosed and where the bu-clcstay interconnecting system receives its fluid from a location in the throughflow system within that portion of the system within which recirculation takes place. The reason for this is that more uniform temperatures are established throughout t-he furnace walls as a result of this recirculation and in instances where the vapor generator is bottled up for a hot restart after being shut down, re-circulation may be continued so that the fluid carrying hot ties that interconnect the opposed buckstays will remain at a temperature generally similar to that of the furnace wall. The fluid carrying hot buckstay tie arrangement of the invention permits a reduction o'f the size of the downcomer 22, which is a cost reduction factor and since the hot tie arrangement does not form either an upright or an inverse U-tufbe larrangement but is merely a downflow circuit in parallel with the downrcomer Z2 problems that have been encountered with fluid ow through parallel circuits when one is in a U-tube configuration will not be experienced.

The invention is of particular advantage in removing the great weight of the 4buclcstay system from the furnace walls. With the very large sizes of furnaces now being designed wherein wall widths of` up to feet are encountered, the buckstays that are utilized are very large and accordingly rvery heavy. By supporting the buckstays from the vertically extending beams 50 which are in turn supported independently of the .furnace walls, the wall thickness of the tubes on the furnace walls do not have to be increased to support this buckstay weight and accordingly may be maintained as thin as possible for the pressures and temperatures that are encountered. This is of substantial advantage with the high pressure high temperature supercritical units Where stresses developed in thickwall tubes are a problem.

Still another advantageous aspect of the construction employed with the invention is that the cage formed by the buckstays and the vertical beams 50 will be o-f advantage and use as a permanent platform and staging that can be used during the erection period.

Accordingly, with the invention an improved vapor generator is provided and particularly an im'proved construction with relation to the buckstay system of the generator.

It is to be understood that the invention is not limited to the specific embodiment herein illustrated and described but may be used in other ways without departure from its spirit and that various changes can be made which would come Within t'he scope of the invention which is limited only by the appended claims.

We claim:

1. In a Vapor generator an elongated furnace having its inner surface lined with heat exchange tubes, s'aid furnace having pairs of opposed side walls, pairs of opposed buckstays extending transversely of said opposed walls and means interconnecting the lcorresponding ends of the two buckstays in the opposed pair, said means including tube means disposed outwardly of said heat exchange tubes lining the furnace and extending generally the -Width of the lwall intermed-iate said corresponding ends, means directing the -vaporizable medium of the vapor generator through said tube means after it has been art least partially heated and means connecting the tube means at a location adjacent the furnace corner with said corresponding ends.

2. The organization of claiml including means supporting said buckstays independently of the furnace wall.

3. The organization of cl-aim 2 wherein the support for the buckstays comprises vertical beams disposed about the furnace and supported from albov-e in a manner that permits limited lateral movement to accommodate furnace expansion, said beams being in engagement with a wall of the furnace.

4. The organization of claim 1 wherein said t-ube means comprises a tubular member extending around said furnace at the location of the opposed .pair of buckstays.

5. A vapor generator having a circuit through which a vaporizable fluid is conveyed and is converted to superheated vapor, said circuit including a plurality of tubular members in parallel side-Iby-side relation forming the inner surface of an enclos-ure through which enclosure hot cornbustion gases pass, said enclosure having two pairs of opposed side walls, buckstays disposed about said side walls at spaced locations, means interconnecting the corresponding ends of buckstays adjacent the two walls of each pair at each location, said means includ-ing a tube extending transversely of the wall intermediate said end-s and connected with said ends adjacent the juncture of the side walls so that the buckstays are restrained from moving laterally outward of said enclosure, and means interconnecting the tube with said circuit so that heated fluid flows therethrough.

6. The vapor generator of claim 5 wherein said means is interconnected with said circuit upstream of said tubular members and such that vaporizalble fluid ows through said mean-s immediately prior to passage through said tubular members.

7. In a vapor generator having an upright fluid cooled furnace of rectangular transverse configuration, horizontally extending buckstays at spaced vertical elevations disposed about the furnace adjacent the walls thereof, the corresponding ends of the parallel buckstays at each elevation being interconnected by fluid carrying means, and means directing the vaporizable fluid of the vapor generator through said fluid carrying means.

8. The organization of claim 7 wherein the means interconnecting the ends of the buckstays comprises a conduit extending about the furnace at said elevations and means interconnecting said conduit with the buckstays in a manner permitting limited horizontal movement therebetween.

9. A once through ow vapor generator having an upright furnace of rectangular transverse section, a through flow circuit through which the vaporizable medium of the generator is forced and including vertically extending tubes in side-by-side relation lining the inner surface of furnace walls, buckstays disposed about the furnace at spaced vertical elevations, means supporting the buckstays independently of the furnace walls and in a manner permitting limited lateral movement outwardly of the furnace, horizontally extending conduit means interconnecting the corresponding ends of the buckstays extending across opposed walls of the furnace at each of said elevations to inhibit the same from moving outwardly of the furnace, means conveying heated uid from the through ow circuit at a location where its temperature is at least approximately as high as the temperature of the through flow fluid entering the said furnace wall tubes to and through said conduit means and back to the through ow circuit.

10. The vapor generator of claim 9 wherein said horizontally extending conduit means comprises a conduit extending about the furnace at each of said elevations, with the several conduits being connected in series ow relation.

11. The vapor generator of claim 10 wherein said conduit is connected with the ends of the buckstay in a manner permitting limited lateral movement therebetween.

12. The vapor generator of claim 9 including vertically extending steel beams disposed along the outer region of each furnace wall in sliding engagement therewith, said beams being supported from above independently of the furnace wall and in a manner permitting limited lateral movement to accommodate movement of the furnace walls resulting from thermal expansion and contraction, said buckstays being secured to and supported by said beams.

13. The vapor generator of claim 9 wherein the furnace has a vertically extending tubular center wall forming part of the through flow circuit and connected thereinto upstream of the furnace wall tubes and for upow of fiuid therethrough, and said means conveying uid from the through flow circuit directing fiuid, after passage through said center wall, down through the conduit means at said elevations in series and then up through the furnace wall tubes.

14. The once-through flow vapor generator of claim 9 wherein a recirculating system is imposed on a portion of the once through ow circuit including the portion comprised of the furnace wall tubes, and wherein the means for conveying heated fluid from the through ow circuit to said conduit means and returning it to the through flow circuit is connected into the portion of the through iiow circuit upon which the recirculating system is superimposed.

15. A vapor generator comprising an upright furnace of rectangular transverse configuration and having its inner surface lined with vertically extending heat exchange tubes, stifener members extending across the walls of the furnace and supported from said tubes, vertically extending steel beams extending down along said walls in sliding engagement with said stitfener members, means supporting said beams from their upper region independent of the furnace walls and said support means permitting lateral movement of said beams to accommodate movement of the furnace walls due to temperature changes, said beams carrying horizontally extending buckstays at spaced elevations and means interconnecting the corresponding ends of the buckstays extending transversely of opposed furnace walls at each elevation.

16. In a vapor generator an elongated furnace having its inner surface lined with heat exchange tubes, said furnace having pairs of opposed side walls, pairs of opposed buckstays extending transversely of said opposed walls and means interconnecting the two buckstays in the opposed pair, said means including a tubular member disposed outwardly of said heat exchange tubes lining the furnace and extending around said furnace at the location of the opposed pair of buckstays, means connecting said tubular member with each of the buckstays at the outer ends of the buckstays and in a manner permitting limited lateral movement between said member and said buckstay, and means directing the vaporizable medium of the vapor generator through said tube means after it has been at least partially heated.

17. A vapor generator having a circuit through which a vaporizable fluid is conveyed and is converted to superheated vapor, said circuit including a plurality of tubular members in parallel side-by-side relation forming the inner surface of an enclosure through which enclosure hot combustion gases pass, said enclosure having two pairs of opposed side walls, buckstays disposed about said side walls at spaced locations, means interconnecting the ends of buckstays adjacent the two walls of each pair at each location, said means including a tubular member interconnected with said circuit so that heated fluid flows therethrough, said tubular member extending about the enclosure and interconnected with the buckstays at the corners thereof and in a manner permitting limited relative movement between said member and the buckstay.

18. A vapor generator having a circut through which a vaporizable fluid is conveyed and is converted to superheated vapor, said circuit including a plurality of tubular members in parallel side-by-side relation forming the inner surface of a vertically disposed enclosure through which enclosure hot combustion gases pass, said enclosure having two pairs of opposed side walls, buckstays disposed about said side walls at spaced locations, means interconnecting the ends of buckstays adjacent the two walls of each pair at each location, said means including a tubular member interconnected with said circuit so that heated fiuid flows therethrough, vertically extending structural steel members positioned about said enclosure and hung from above in a manner providing limited lateral movement outwardly of said enclosure, and with said buckstays being secured to and supported by said steel members.

19. A vapor generator comprising an upright furnace of rectangular transverse configuration and having its inner surface lined with vertically extending heat exchange tubes, stiffener members extending across the walls of the furnace and supported from said tubes, vertically extending steel beams extending down along said walls in sliding engagement with said stiffener members, said beams being supported from above independent of the furnace walls and in a manner permitting lateral movement thereof to accommodate movement of the furnace walls due to temperature changes, said beams carrying horizontally extending buckstays at spaced elevations, horizontally extending conduit means interconnecting the corresponding ends of the buckstays extending transversely of opposed furnace walls at each elevation, and means conveying fiuid through said conduit means whereby it thermally expands and contracts simulta-neously with and in an amount generally commensurate with the furnace wall.

20. In a vapor generator, an upright elongated furnace having heat exchange tubes lining its walls, said furnace being of a rectangular transverse conguration, tube runs extending across one pair of opposed furnace walls outwardly thereof and at vertically spaced locations throughout the furnace height, buckstay means extending across the other pair of opposed furnace Walls at similar locations, said tube runs forming an interconnection between the corresponding ends of the buckstays and preventing them from moving laterally outward of their overlying furnace wall, and means directing iluid of the vapor generator through said runs.

References Cited UNITED STATES PATENTS 2,773,487 12/1956 Walter etal. 122-6 FOREIGN PATENTS 874,063 8/ 1961 Great Britain. 1,009,034 11/1965 Great Britain.

KENNETH W. SPRAGUE, Primary Examinez'.