US3368536A - Bottom supported steam generator - Google Patents

Description

Feb. 13, 1968 R. P. SULLIVAN BOTTOM SUPPORTED STEAM GENERATOR 2 Sheets-Sheet 1 Filed June 13, 1966 FIG 1 INVENTOR. E. R SULLIVAN Feb. 1 3, 1968 I R. P. SULLIVAN 3,368,536

BOTTOM SUPPORTED STEAM GENERATOR Filed June 13, 1966 2 Sheets-Sheet 2 INVENTOR. 2. P. SULL IVAN BY 6% K United States Patent Ofiice 3,363,536 BQTTOM SUPPORTED TEAM GENERATOR Robert P. Sullivan, Chattanooga, Tenn., assignor to Comhustion Engineering, Inc., Windsor, Conm, a corporation of Delaware Filed June 13, 1966, Ser. No. 556,942 7 Claims. (Cl. 122-510) ABSTRACT OF THE DKSCLOSURE A steam generator is formed of two independent stable support structures. One of these is the general steam generating surface including the tubes lining the walls of the unit. A second and independent structure is formed by having the steam drum supported by the downcomers. Flexible tubing connecting these two structurally independent structures permits each one to expand relative to the other. The concentrated loads due to the heating surface located within the fines are thrown into the second independent support structure thereby decreasing the load which must be carried by the first support structure.

This invention relates to steam generators and in particular to those of the bottom supported type.

Steam generators can most readily be supported from the bottom. This is true certainly in the smaller steam generators. However, as the size of the steam generating units increase, the compressive loadings on the support structure create substantial problems. Accordingly, all the large steam generators are supported from above by being hung from building steel.

In the conventional bottom supported unit the steam drum is supported on the tubes of the boiler. Heating surface within the fines of the boiler is supported from headers, or steel which is, in turn supported on the wall tubes of the boiler. These loadings being imposed on the waterwall structure limit the size of unit which may be built and require distribution of loading or bracing so that concentrated loads may be spread out generally throughout the supporting structure.

It is an object of my invention to provide an apparatus whereby large size bottom supported steam generators may be successfully designed.

It is a further object to avoid concentrated loadings in a steam generator at points where these loadings may not be easily carried.

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

With the aforementioned objects in view, the invention comprises an arrangement, construction and combination of the elements of the inventive organization in such a manner as to attain the results desired as hereinafter more particularly set forth in the following detailed description of illustrative embodiments, these embodiments being shown by the accompanying drawings wherein:

FIG. 1 is a sectional side elevation of a steam generator showing generally the method of support of the various components;

FIG. 2 is a plan view showing the relative locations of the steam drum and waterwall outlet headers and the locations of the flexible tube-s connecting these two elements;

FIG. 3 is a plan sectional view taken through a corner of the rear furnace wall and showing the method by 3,368,536 Patented Feb. 13, 1968 which the two side walls are tied together by the rear wall of the furnace;

FIG. 4 is a sectional view through an intermediate downcomer showing the method of supporting a superheater header therefrom; and

FIG. 5 is a side sectional view of FIG. 4.

Concrete support pedestals 2 support the entire steam generator from a multiplicity of support pads 4. The first stable support structure has as its basis the waterwall inlet headers 6. From these headers furnace waterwall tubes 8 which are fluidly connected thereto, pass upwardly lining the walls of the furnace 10. These tubes include the rear wall tubes 8a which line the rear wall of the furnace. The tubes of the front and rear wall cover the roof 12 and join in waterwall outlet header 14. The waterwall tubes lining the side walls of the furnace terminate in waterwall outlet header 16.

Fuel is fired through burners 18 in the lower portion of the furnace 10. Combustion gases formed by the combustion of the fuel pass upwardly through the furnace and out through gas outlet 20 through the flue 22. These gases pass downwardly through the line over the high temperature superheater surface 24, the low temperature superheater surface 23 and the economizer 25. These gases then pass outwardly through gas exit 26 to an air heater (not shown).

Air from this air heater is supplied to the boiler through hot air duct 28 to windbox 30 from which it is supplied as combustion supporting air.

A second independent stable support structure is also supported from pads 4. Steam drum 32 has two straight downcomers 34 extending from each end thereof. As these downcomers extend downwardly, the distance between the two downcomers increases. These downcomers along with the steam drum form a triangular support arrangement which supports the steam drum in the stable structure independent of the furnace support. The steam drum of the second stable support arrangement is connected with the waterwall outlet headers 14 and 16 of the first stable support arrangement through 5 in OD. flexible tubes 35 to permit differential expansion of the two support arrangements. These tubes are of sufficient length to avoid the transmittal of any significant vertical forces from the headers to the drum, and to avoid excessive stresses due to relative horizontal movement of the drum and headers.

One wall of the due 22 is formed by the tubes 8a so that the wall is common with the furnace. As can be seen in FIG. 3 the tubes of this wall are joined by webs 36 which are securely welded to the tubes on either side. This wall is, therefore, gas-tight except at the gas outlet 20 where the tubes are offset to permit gas flow through the wall. Two other opposite sides of the flue are formed by steam generating tubes 38. These tubes are in parallel flow relation with the tubes lining the furnace walls and, therefore, are supplied from the lower waterwall headers 6 and discharge into the upper waterwall header 16. The fourth wall of the flue is formed of steam heating tubes 40 which convey steam downwardly from the steam drum 32 to the steam support tube inlet header 42.

A plurality of U-bolts 44 pass over the steam drum 32 at a plurality of locations. These U-bolts, in turn, support a steel framework 46. Low temperature steam from the steam support tube inlet header 42 passes upwardly through steam support tubes 48 through the support framework 46. The steam flow through these tubes con tinues downwardly through steam support tubes 50 to the low temperature superheater inlet header 52.

The steam support tubes 48 and 50 are fastened to the steam superheating surfaces 23 and 24 so as to support the weight of these surfaces. The steam support tubes, in turn, are supported from the framework 46, this framework, in turn, being supported through U-bolts 44 from steam drum 32. Therefore, the weight of the steam superheating surface is thrown into the second stable support structure through the steam drum 32.

Steam from the low temperature superheater inlet header 52 passes through the low temperature superheater 2.3, the intermediate superheater headers 54 and the high temperature superheater 24 to the superheater outlet header 55. From this header the steam is conveyed to a steam turbine or other point of use.

Feedwater being returned to the steam generator enters economizer inlet header 53 to the economizer heating surface 25. This heated water is collected in economizer outlet header 5% and conveyed to the steam drum 32. This water then circulates through the downcomers and steam generating tubes in a conventional manner with steam being conveyed outwardly from the top of the drum through the steam tubes 46.

Intermediate downcomers 62 convey a portion of the recirculating fluid to the waterwall inlet header 6. These intermediate downcomers pass vertically parallel to the flue at a location outside the flue. The superheater headers such as 56 are supported from the downcomers as illustrated in FIGS. 4 and 5. Support bracket 64 is arranged so that the header may be rigidly supported vertically but some lateral sliding movement is permitted.

Both of the stable support structures contain generally saturated water with the water in the second support structure comprised of the steam drum and downcomers being slightly cooler due to the introduction of water in the steam drum 32. Since the downcomers are not absorbing heat, they will generally operate, during steady state operation, at approximately the temperature of the water. Since the furnace wall tubes are receiving heat, the metal temperature of the tubes is higher than that of the water and this is generally considered to be in the order of 50. Since the furnace wall tubes tend to be hotter, they will expand more than the downcomer system, and some vertical differential expansion must be taken between the steam drum 32 and the waterwall outlet headers 14 and 16 to allow for this. Furthermore, the steam drum and downcomers are generally massive structures as compared to the thin waterwall tubes. During startup as the water temperature is increasing, the temperature of the downcomers and steam drum will tend to lag considerably behind the temperature of the waterwall tubes. During this time there is considerable differential expansion between the two support structures not only in the vertical direction but also in the direction longitudinal to the steam drum.

The support of steam drum 3?; independent of the furnace structure avoids the problem of carrying the load of the steam drum on headers 16. The introduction of the heavy concentrated load in these headers would first tend to put substantial load on the wall tubes in the general area of the support point and, secondly, would require that the headers 16 be designed to carry a substantial load. Not only would a heavy load have to be required, but since the steam drum 32 heats up at a different rate than the furnace structure, provision would have to be made for sliding at the support point where the drum 32 rests on header 16. The independent support of the steam drum by the use of two independent stable support structures precludes the introduction of heavy normal and frictional loading on the steam generator wall structure.

In the present invention the steam drum is located above and passes across the rear flue 22. The superheater elements are supported from this steam drum at a large number of locations. If it were not for the steam drum 4 at this location, a separate independent rigid structure would have to be passed across the top of the unit to support all these superheater elements. Furthermore, the concentrated load of all these elements would be thrown into the side walls on either side of the flue. If a conventionally supported steam drum were located in this area, not only would the load of the heavy drum itself be imposed on the walls, but also the load of all the superheater elements.

All the walls of the furnace are of the welded wall type with web 36 being welded intermediate adjacent tubes. The side walls 38 of the flue are also of this welded wall construction. This construction increases the rigidity of the first stable support structure.

While I have illustrated and described a preferred embodiment of my invention 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 as fall within the purview of my invention.

What I claim is:

1. A bottom supported steam generator comprising a steam drum; rigid downcomers fluidly connected to, and extending downwardly from said steam drum and supporting said steam drum; said downcomers arranged to form a first stable support structure with said drum; a furnace for the burning of fuel therein resulting in the formation of combustion gases; vertical tubes lining the walls of said furnace; upper headers at the top of and fluidly connected to said vertical tubes, each header joining a multiplicity of tubes, and said header being supported on said vertical tubes; said vertical tubes and upper header forming a second stable support structure, said second stable support structure being structurally independent of said first stable support structure; means for fluidly connecting the lower end of said downcomers to the lower ends of said vertical tubes; and all fluid connections for conveying fluid from said upper headers to said steam drum comprising flexible tubes fluidly connecting said upper headers to said steam drum.

2. An apparatus as in claim 1 where in forming said first stable structure said steam drum has two tubular downcomers extending from each end thereof; said downcomers being generally straight and the distance between the two downcomers being greater at the lower end than at the upper end so as to form a triangular support arrangement.

3. An apparatus as in claim 1 wherein said flexible tubes connecting said upper headers to said steam drum are located in the area generally above the furnace while said steam drum is supported eccentrically of said area.

4. An apparatus as in claim 1 wherein said furnace has burners at one end thereof and a gas outlet at the other end thereof; a flue for the conduction of the gases leaving said furnace vertically parallel to said furnace; heating surface located in said flue; means for conducting steam from said steam drum to said heating surface; said steam drum being located directly over said flue; means for supporting said heating surface from said steam drum at a plurality of locations across said flue.

5. An apparatus as in claim 1 wherein said second stable support arrangement includes webs intermediate the furnace wall tubes with said webs being welded to the adjacent tubes whereby a solid welded furnace wall structure is formed.

6. An apparatus as in claim 5 wherein said furnace has burners at one end thereof and a gas outlet at the other end thereof; a flue for the conduction of gases leaving said furnace vertically parallel to said furnace; one wall of said flue being formed of the tubes lining one wall of said furnace; steam generating tubes lining two other opposite walls of said flue; steam heating tubes forming a fourth wall of said flue.

5 6 7. An apparatus as in claim 4 having also downcorn- References Cited ers intermediate the downconiers as the remote ends of UNITED S AT S PATENTS the drum said downcorners passing downwardly parallel 439 684 11/1880 Pratt 122 235 to the gas flow in said flue at a location outside f Said 1 997215 4/1935 g; 122 510 flue; a header fluidly connected to said heating surface 5 2:979:041 4/1961 Youmr 122 51O for supplying steam to said heating surface; and me n 2,938,063 19 1 v g 121-336 for supporting said headers from said intermediate downcomers. KENNETH W. SPRAGUE, Primary Examiner.

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