US3612006A

US3612006A - Expansion seal

Info

Publication number: US3612006A
Application number: US880268A
Authority: US
Inventors: Michael C Santucci
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 1969-11-26
Filing date: 1969-11-26
Publication date: 1971-10-12
Anticipated expiration: 1988-10-12
Also published as: GB1328286A

Abstract

A gastight covering for the roof of a steam generator gas pass enclosure allowing for the passage of fluid-heating tubes terminating at a fixed point of support in an upper adjacent compartment. The covering is seal-welded to the adjoining wall structure and includes deflectable raised portions having perforated sections to admit the penetrating tubes and having the perforated edges seal-welded to the adjoining tube wall. Each raised portion is formed with side and corner sections arranged to readily deflect when subjected to the downward movement of the perforated section caused by the thermal growth of the portion of tube extending above the roof covering.

Description

United States Patent 3,029,798 4/1962 Folds 122/494 1 FOREIGN PATENTS 1,423,998 11/1965 France 122/235 1,134,175 8/! 962 Germany 122/494 Primary Examiner-Kenneth W. Sprague Attorney-J. Maguire ABSTRACT: A gastight covering for the roof of a steam generator gas pass enclosure allowing for the passage of fluidheating tubes terminating at a fixed point of support in an upper adjacent compartment. The covering is seal-welded to the adjoining wall structure and includes deflectable raised portions having perforated sections to admit the penetrating tubes and having the perforated edges seal-welded to the adjoining tube wall. Each raised portion is formed with side and corner sections arranged to readily deflect when subjected to the downward movement of the perforated section caused by the thermal growth of the portion of tube extending above the roof covering.

PATENTEDMHZIQH 3,612,006

SHEU 1 [IF 3 28 I N VE NTOR.

Michael C. San'rucci Z AT ORNEY PATENTEUUBHZIQYI 3,612,006

SHEET 3 OF 3 FLT EXPANSION SEAL BACKGROUND OF THE INVENTION This invention relates generally to vapor generating and superheating units of the type which are top-supported and have fluid-heating tubes extending from the gas pass enclosure through a partition and terminating in an upper compartment. More particularly the invention relates to an improved construction which eliminates leakage of flue gas and entrained ash from the gas pass enclosure into the upper compartment.

The gas pass enclosure of a conventional vapor generating and superheating unit includes a furnace chamber, convection and outlet gas passes, associated boundary walls and a horizontally extending roof forming the partition which separates the gas pass enclosure from the upper compartment commonly referred to as the penthouse. The gas pass enclosure includes convection heating surfaces such as a superheater, reheater and economizer which may have tube ends extending through the roof and into the penthouse for connection to horizontally extending junction headers.

The supporting structure associated with these units includes hangers which attach to the above-mentioned headers to provide a fixed support. As the unit is brought up to operating temperature the tubes connected to these headers undergo thermal expansion in a downward direction from the point of restraint at the header. There is also the horizontal thermal expansion of the header which tends to cumulatively increase the horizontal spacing of the tubes. Thus it has been necessary to maintain a clearance between the penetrating tubes and the edges of the penetration holes in the roof to permit unrestrained longitudinal movement of these tubes relative to the roof tubes. However, these required thermal expansion clearances have permitted some leakage of the combustion gases from the gas pass enclosure into the penthouse. This leakage problem has been a constant source of maintenance difficulty particularly with units firing ash-bearing fuels, where large deposits of ash would tend to accumulate in the penthouse and the thereby hinder inspection and repair of metal parts.

Prior art efi'orts at dealing with this problem have not been altogether satisfactory. One approach has been to introduce air into the penthouse so as to maintain its inside pressure above that of the gases flowing through the gas pass enclosure. This method carries the risk of leakage if pressurizing air is lost, moreover it has proven uneconomical from the standpoint of increased fan'operating and capital costs and thermally inefficient as a result of continued leakage of relatively cooler air into the combustion gas stream. Another approach has been the use of resilient insulation to form a labyrinth-type packing arrangement around the roof penetrations as disclosed in US. Pat. No. 3,277,871 assigned to the assignee of this invention. This latter approach, while recognized as a definite improvement over the prior constructions, was directed to minimizing rather than eliminating the leakage of combustion gases through the clearance space between the penetrating tubes and the edges of the holes penetrating the roof.

SUMMARY OF THE INVENTION In accordance with the present invention a novel construction is provided which eliminates substantially all of the leakage of combustion gases from the gas pass enclosure to the penthouse. This is achieved by placing a flexible metal coverlike enclosure over the top of the roof tubes and sealwelding its peripheral edge to the adjoining section of surrounding wall structure. The covering includes deflectable raised portions having top surfaces perforated with snugly fitting holes for accommodating the passage of upright tube sections and arranged so the edges of each of these holes may be seal-welded to the adjoining surface of the penetrating upright tube section.

The rigid attachment resulting from the sealwelding of the penetrating upright tubes to the roof covering provides a restraint against sidewise motion of the upright tubes caused by the diflerential in thermal expansion between the connect- 1 ing headers and the roof tubes. The raised portions are of substantially rectangular horizontal cross section and have depending side sections, including at least one inclined segment disposed at a predetermined angle to the longitudinal axis of the upright tubes and corner sections including inclined and horizontally disposed segments. These segments are formed of light gauge metal and are arranged so as to readily deflect when subjected to the downward movement of the perforated section caused by the thermally induced growth of the portion of upright tube extending above the roof covering.

The steam generating and superheating unit depicted in the drawings is typical of large central station units and includes a second stage reheat superheater whose outlet tubes extend approximately 9 feet above the roof casing. The outlet tubes are made of heat-resistant alloy to enable them to withstand operating temperatures upwards of 1,000F. The point of rigid attachment between the output tube and the roof covering will experience a downward displacement of approximately onehalf inch due to thermal growth of the tube metal as it is heated from ambient to operating temperature of 1,000F.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional side elevation of a once-through vapor &

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates a top-supported forced flow once-through steam generating and superheating unit for central station use. The main parts of the unit include an upright furnace chamber 10 of substantially rectangular horizontal cross section defined by front wall 11, rear wall 12, opposed side walls 13 and a portion of roof l4 and having a gas outlet 15, at its upper end, openingto a horizontally extending gas passage 16 of substantially rectangular vertical cross section formed by a floor 17 and extensions of the roof l4 and side walls 13. Gas passage 16 communicates at its rear end with the upper end of an upright gas passage 18 of substantially rectangular horizontal cross section formed by a front wall 20, a rear wall 21 and side walls 22 and the remaining portion of roof 14. The lower ends of the furnace front and rear walls communicate with cyclone-type furnaces 24 and slope inwardly and downwardly to form a floor 23 including suitable slag discharge ports (not shown). The cyclone furnaces 24 serve to burn fuel and discharge high-temperature gaseous products of combustion into the furnace chamber 10, while emitting molten ash residue through slag discharge ports (not shown).

The upright boundary walls of furnace chamber 10and gas passages 16 and 18 are formed with spaced parallel tubes having substantially all of their intertube spacing closed by metallic webs. Thesetubes are arranged in panels coplanar with their respective walls and are generally supplied with fluid from lower headers for discharge through upper headers. The furnace front wall 11 extends between lower and

upper header sections

26 and 27, the furnace sidewalls 13 extend between lower and

upper header sections

28 and 29 and the furnace rear wall 12 extends from the lower header 30 with the upper end of a portion of its tubes forming floor 17 of the gas passage 16 and discharging into the rear wall intermediate header 31 and the remaining portion of tubes forming the furnace screen wall 32 and discharging into upper header 33. The sections of sidewalls 13 within gas passage 16 extend between lower and

upper header sections

34 and 35. The front wall 20 of gas passage 18 extends between lower header 36 and the rear wall intermediate header 31, the sidewalls 22 of gas passage 18 extend between lower header 37 and upper header sections 38 and the rear wall 21 of gas passage extends between lower header 39 and upper header 40. A convection pass screen wall is formed between rear wall intermediate header 31 and rear wall upper header 31A. The roof 14 is formed of horizontally extending spaced parallel tubes 41 having their intertube spacing closed by either metallic webs or flat metal fins and includes a metal covering or casing 42 extending over the top surface of the roof tubes 41. The metal covering 42 is generally constructed of heat-resistant metal alloy and comprises a plurality of flat plate members of various predetermined thicknesses having their abutting ends seal-welded together. The peripheral edges of the covering 42 are sealwelded to adjoining surfaces of

sidewalls

13 and 22 and front and rear walls 11 and 21, respectively, to form gastight covering over the top surface of roof tubes 41.

The gas passage 16 contains a secondary superheater 43 and a second stage reheat superheater 44 arranged in series with respect to gas flow. The gas passage 18 contains a primary superheater 45, a first reheat superheater 46 and an economizer 47 also arranged in series with respect to gas flow. The economizer fluid discharges through the outlet tube legs 51 into headers 52 and is conveyed through suitable piping (not shown) to the boundary walls for flow therethrough and including flow through the roof tubes 41 and associated inlet and

outlet headers

53 and 54, respectively. The fluid leaving the boundary walls is further heated during its passage through the primary superheater 45 and discharges through the outlet tube legs 55 into headers 56 for flow through suitable piping including attemperators (not shown) though headers 57 and through the secondary superheater 43 including the inlet, intermediate and

outlet tube legs

58, 59 and 60, respectively for discharge through headers 61. The reheat cycle includes serially passing the fluid to be reheated through the first stage reheat superheater 46 and the second stage reheat superheater 44 for discharge through the outlet tube legs 62 and headers 63.

An upper chamber or penthouse 64 extends upwardly from the roof 14 and laterally beyond the boundary walls of the unit to form an insulated chamber for housing the headers, and tubes and piping contained therein. The penthouse roof 65 is upwardly spaced a considerable distance from the roof 14 and is rigidly connected to the penthouse front, rear and

side walls

66, 67 and 68, respectively. These walls extend downwardly from the roof, then project laterally inward and rigidly tie onto the

boundary walls

11, 21 and 13 of the unit a short distance below roof 14.

The vapor generator is top-supported by structural steel members including upright columns 69 and cross beams 70. The support for the unit is provided by a plurality of hangers 71 extending downwardly from the beams 70, some of which rigidly attach onto roof 14 while the remainder are selectively attached to headers situated in the penthouse. The tubes connecting to the headers through their respective tube legs, have their fixed points with respect to thermal expansion at the header connection and thus will expand downwardly as the metal is heated to its operating temperature. The furnace and convection pass screen wall tube legs and the

tube legs

51, 55, 58, 59, 60 and 62 penetrate the covering 42 at their respective raised portions 72. These tube legs are rigidly connected to the covering 42 at the point of penetration by seal-welding the edges of the penetration holes to the adjoining circumferential surfaces of the tubes passing therethrough. The raised portions 72 provide the flexibility of construction which enables the covering 42 to absorb the downward expansion caused by the thermal growth of the sections of tube leg located between the covering and the penthouse headers.

In FIGS. 2, 3 and 4 there are shown detail views with particular emphasis on a typical raised portion of the covering 42. The raised portion which is shown is associated with the inlet tube legs 58 of the secondary superheater 43. Roof tubes 41 extend along a horizontal plane with their intertube spacing being closed by web plates 73 with the exception of the area where the inlet tube legs 58 pass through the roof. Here the roof tubes now designated as 41A are off-set to provide the necessary clearance for the passage of tube legs 58. Refractory-retaining plates 74 extend along the longitudinal axis of the roof tubes 41 and are arranged to cover the penetration area while providing unrestricted passage for the inlet tube legs 58. A layer of castable refractory 75 is poured on top of the roof tubes 41 thereby insulating the covering 42 from the high-temperature combustion gases. The bottom end of hanger 71 is attached to a roof tie 76 forming part of the roof-supporting structure. Each of the raised portions 72 comprise a perforated top section 72A, upright side sections including vertical and

inclined segments

72B and 72C and corner sections 720. A rectangular expansion fold 77 is formed on the top section 72A and extends over the width of the raised portion 72. Cooperating angular expansion folds 78 are also formed on top section 72A and extend along both sides of the tube legs 58 in a direction parallel to the longitudinal axis of roof tubes 41 and normal to the rectangular fold 77. These expansion folds are arranged to absorb the surface thermal growth of the metal covering 42 as it is being heated to operating temperature. A rigid tie bar 79 is welded to the roof tubes 41 and extends across the width of the roof parallel to and in abutting relationship with the outside rows of inlet tube legs 58 to restrain fore-and-aft movement of these tubes. Block insulation 81 is inserted between the vertical segments 72B and the adjacent rows of inlet tube legs 58 to provide a uniform metal temperature gradient for covering 42 between a high-temperature area such as where the covering attaches to the tubes 58 and a lower temperature area as where the covering attaches to the tie bar 79.

FIG. 5 shows an enlarged perspective detail of the corner section 721) of a typical raised portion of covering 42. The comer section 72D is usually die-formed and comprises upper and lower upright segments extending parallel and horizontally spaced from one another and are joined by a laterally extending segment 72C1. The upper segment 72B] is formed with a top surface extending parallel to perforated section 72A and with end surfaces which are coplanar with the adjacent side segments 728, these end surfaces are interconnected by a curved surface. The lower segments 72B2 extend parallel to the corresponding side segments 72B and have their adjacent ends normal to one another. The laterally extending segment 72C1 includes a horizontally extending surface interposed between the curved surface of segment 72181 and portions of segments 7282. The horizontal surface of segment 72C1 is bounded on each side by sloping triangular surfaces which connect it to the adjacent side segments 72C. The comer section 72D has its bottom end seal-welded to the base portion of covering 42, its side ends to the corresponding edges of

segments

72B and 72C and its top end to the perforated segment 72A. The construction of corner section 72D is such as to enable the segment 72C! to deflect when subjected to the stress components created at the juncture of adjoining sides by the downward motion of the perforated section 72A.

While the invention has been described with reference to the preferred embodiment, it is evident that various changes may be made therein without departing from the spirit of the invention. It is therefore intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A vapor generator and superheating apparatus, the combination of:

wall structure defining a shell having upper and lower com partments,

an internal horizontal substantially gastight partition between the upper and lower compartments,

said lower compartment including a furnace chamber,

a plurality of headers disposed in the upper compartment,

a plurality of rows of upright tubes, each extending through the partition into the upper compartment and connected to at least one of the headers,

said partition comprising,

a plurality of horizontally extending, fluid conducting tubes arranged closely spaced in at least one row at the bottom of the partition, and

a metal covering having its periphery seal-welded to the adjoining wall structure, said covering being formed with at least one deflectable raised portion, said raised portion being of generally rectangular cross section and including a perforated section extending along a plane substantially parallel to and spaced above the plane of said horizontal tubes, a plurality of side sections interconnecting the perforated section to the portion of the covering adjacent to the horizontal tubes, said upright tubes passing through the perforated section and being seal-welded thereto, and each of said side sections including at least one segment formed of a substantially smooth surface and lying in a plane inclined with respect to said perforated section for providing the flexibility to accommodate vertical movement of the upright tubes relative to said horizontal tubes.

2. in an apparatus according to claim 1, the combination as set forth wherein adjacent side sections are connected at their ends by partially curved comer sections, each of the corner sections including at least one segment formed of a substantially smooth surface and lying in a plane generally parallel and displaced from the plane of said perforated section for providing the flexibility in said raised portion.

3. In an apparatus according to claim 1, the combination as set forth wherein the covering includes a plurality of metal members having their abutting ends seal-welded to one another, with at least one of the members being formed with a plurality of circular openings, each of the openings accommodating the passage of one of said upright tubes and having its circumferential edge seal-welded to the adjoining surface of the upright tube passing therethrough.

4. In an apparatus according to claim 1, the combination as set forth wherein said perforated section is formed with a plurality of protruding folds set at spaced intervals and extending along a part thereof in a direction parallel to the longitudinal extent of the horizontal tubes, said folds being of generally triangular cross section 5. In an apparatus according to claim 1, the combination as set forth wherein said perforated section is formed with at least one protruding fold extending along a part thereof in a direction normal to the longitudinal extent of the horizontal horizontal tubes, said fold being of generally rectangular cross sections.

Claims

1. A vapor generator and superheating apparatus, the combination of: wall structure defining a shell having upper and lower compartments, an internal horizontal substantially gastight partition between the upper and lower compartments, said lower compartment including a furnace chamber, a plurality of headers disposed in the upper compartment, a plurality of rows of upright tubes, each extending through the partition into the upper compartment and connected to at least one of the headers, said partition comprising, a plurality of horizontally extending, fluid conducting tubes arranged closely spaced in at least one row at the bottom of the partition, and a metal covering having its periphery seal-welded to the adjoining wall structure, said covering being formed with at least one deflectable raised portion, said raised portion being of generally rectangular cross section and including a perforated section extending along a plane substantially parallel to and spaced above the plane of said horizontal tubes, a plurality of side sections interconnecting the perforated section to the portion of the covering adjacent to the horizontal tubes, said upright tubes passing through the perforated section and being seal-welded thereto, and each of said side sections including at least one segment formed of a substantially smooth surface and lying in a plane inclined with respect to said perforated section for providing the flexibility to accommodate vertical movement of the upright tubes relative to said horizontal tubes.

2. In an apparatus according to claim 1, the combination as set forth wherein adjacent side sections are connected at their ends by partially curved corner sections, each of the corner sections including at least one segment formed of a substantially smooth surface and lying in a plane generally parallel and displaced from the plane of said perforated section for providing the flexibility in said raised portion.

4. In an apparatus according to claim 1, the combination as set forth wherein said perforated section is formed with a plurality of protruding folds set at spaced intervals and extending alOng a part thereof in a direction parallel to the longitudinal extent of the horizontal tubes, said folds being of generally triangular cross section

5. In an apparatus according to claim 1, the combination as set forth wherein said perforated section is formed with at least one protruding fold extending along a part thereof in a direction normal to the longitudinal extent of the horizontal horizontal tubes, said fold being of generally rectangular cross sections.