US3554276A

US3554276A - Integral tube panel

Info

Publication number: US3554276A
Application number: US819371A
Authority: US
Inventors: Hubert G Stallkamp
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 1969-04-25
Filing date: 1969-04-25
Publication date: 1971-01-12
Anticipated expiration: 1988-01-12
Also published as: GB1289048A; ZA702788B; FI50026C; FR2040223A1; FI50026B

Abstract

A gastight panel wall for a vapor generator having a plurality of substantially parallel, laterally spaced tubes and C-shaped metallic webs which extend between and are weld united to adjacent tubes.

Description

United States Patent 5 6] References Cited UNITED STATES PATENTS [72] Inventor HubertG.Stallkamp Akron, Ohio 122/235 165/ 1 68X l22/6X m mW mumwm m L el 9 mh 0w yyw mmn Ah r. I n n p UU 0 e M M C M h T 3 9 oo 336 r 9 9 9 W 8 111 n ///.m 8 0o 4 m m a x 9 1 00 H E 902 t WM 275 at 267 mb nm 2 PA m D. r V. m m C e m J c u M W 91$ 7 Nm 99 9- 11m 1 5 0 W ZHMYM. m mmn em SAJTNa Q de 6e 3 Wm AHPA .l: 253 2247 [[ll Attorney-Joseph M. Mag

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122/6 ABSTRACT: A gastight panel wall for a vapor generator hav- F28f 3/12 ing a plurality of substantially parallel, laterally spaced tubes 165/ 168, and C-shaped metallic webs which extend between and are 181, 183; l22/6A, 235A weld united to ad acent tubes [51] Int. [50] Field Ll/l/l/l PATENTED JAN 1 2 ran- 1 AJJJJJJJA FIG.1

FIG.2-

INVENTOR. Huberf (5. Srallkamp B ATTORNEY INTEGRAL TUBE PANEL comprising integrated multiple tube heat exchange panels.

It is well known to use fluid cooled tubes as a means of cooling the gastight walls of avapor generator. The gastight, fluid cooled walls used today are of two general types (i) ('1) casing type, and (2) panel type.

Modern designs of walls of the casing type usually comprise a gastight metallic casing which defines the walls 'of the vapor generator, with fluid cooled tubes longitudinally positioned and laterally spacedalong the inner surface of the casing to cool the wall; a refractory material placed exterior of the easing to insulate the enclosure;v and a thin metallic skin placed on the outside face of the refractory insulation to protect itand give the unit a finished appearance. Use of the metal casing has necessitated making provisions to reduce the incidences of casing failure resulting from differential thermal expansion stress, gas-side corrosion, flow induced vibration in the pressure parts, and other related complexities associated with operation of the unit. Any such failure resultsin leakage thus screening the body portion from radiant heat. A gap is provided intermediate the ends of the arms to provide com pensation for thermal stresses. Furthermore, lateral saw cuts may be made in the arms as necessary to further minimize thermal stress concentrations. Heat transmitted by the arms to .the body portion of the membrane will be transmitted to adjacent connected tubes through the weld roots, thus maintaining the body portion of the membrane within temperature stress limits.

For a better understanding of the invention, reference is made to the following description of the preferred embodiment thereof, as illustrated in the accompanying drawings.

FIG. 1 is an elevation of a gastight integrated multiple tube heat exchange panel portion constructed in accordance with this invention.

FIG. 2 is a transverse section through an integrated multiple tube heat exchange panel type wall taken along line 2-2 in FIG. 1.

As may beseen from FIG. 2, the heat exchange panel defines the inner face of the wall section 13 of a vapor generator and servesto render the enclosure gastight. It is preferred that an insulating material 11 be placed to the outside of the of the extremely hot gasesinto the'environs of pressure fired units, or leakage of relatively cold ambient air into units which are suction fired; In either case,.the thermal efficiencyof the. unit will be significantly reduced.

Integrated multiple tube heat exchange panels are now preferred and widely used, sincetheir'useeliminates the need for the metal casing, and thus obviates manyv of theproblems inherent in the metal casingsconstruction. Moreover the panel type wall is more-durable and practically eliminates the possibility of structural failure of theenclosure. At'thesame time,

use of the panel-type construction substantially reduces manu-- facturing costs, since: the individual panels can be shop fabricated and assembled for shipment to the job' sight.

panel 10 to retard the dissipation of heat from the vapor generator. In order to support and protect the insulating material 11 a thinmetal'skin 12 may be placed to'the outside of the insulating material 11.

The-panelll) comprises a plurality of parallel and laterally spaced tubes 14, and C-shaped membranes 15 which are weld united to adjacent tubes 14 as'at 16 The welds 16 may be made'byany suitable means. lt'is preferred that the welds l6 bemade onboth the gas side arid the outer side of the panel 10, as this will create larger weld roots, resulting in better heat transfer'from the membranes=15 to the tubes 14. Furthermore,

Walls of the panel type as presently constructed usually comprise integrated multiple tube heat exchange panels which define the walls of the vvapor generator and form a gastight enclosure; a refractory material placed exterior of theipanels, to

insulate the enclosure; and a thin metallic skin placed to' the outside of the refractory, to protect the refractory; As hitherto constructed, the panels have comprisedaplurality of laterally spaced, parallel and: relatively elongatedtubes with metallic webs or weblike. membranesfused-orwelded-to adjacent tubes, to present a gastight structure whenassembled- The physical dimensions, e.g., tube.diameter and lateral spacing of the tubes within a panel, are essentially a function of the operating pressure, the heat absorption rateper unit of exposed panel'wall area, and the total heat absorption of the flow circuit in which thespanel'is situated. Theabsorptiom characteristics relate directlyto thetube spacing and thus are at determining criterionin calculating the maximum allowable thermal stress limits theintertube membrane may safelyac commodate. Thus in high heat absorption zones, i.e., zones of high radiant heat,- it isnecessary to space the tubes moreclose' ly than in moderate orlow heat absorption zones, so that thermal stresses in the web portion will notexceed .the dictate of safe operatingpractice.

An integrated multiple tube=heatexchange panel, utilizing the novel weblike, membrane of this invention, substantially increases the. allowabletubespacing permitted in panels hitherto; used, particularly in zones of high radiant heat,

thereby'reducing the material andfabricationcosts of a panel;

Dependingon the heat absorption rate, this increase intube spacing may be sufficient to reduce by as much as 30 percent I the number of tubes required in previously used panelsfor the same service conditions.

The improved panel comprises a plurality of substantially parallel, laterally spaced tubes, and C -shaped membranes which extend between and are weld united to adjacent tubes.

The arms of the C-shaped membrane extend generally parallel to the plane containing thelongitudinal axesof the adjacent connected tubes, and are forwardly spaced from the body portion ofthe membrane, i.e., on the gasside of the membrane,

the welds 16 may be made at a lower strength than the walls of tubes so that in the 'event of an enclosurefailure, tube rupture will be prevented.

The arms 17 of themembrane 15'are on' the gas side of the membrane and thus serve-to shield the body portion '18 from theradi'ant heat emitted within enclosure. The heat absorbed planar body portion 18, as this construction'affords shorter travel for heat transferred by conduction. Furthermore, with thebody portion 18 planar and'the-membran'es 15 positioned in the plane commonto the longitudinal centerlines of succes sively adjacenttubes 14, essentially all lateral expansion'due to temperature will occur within this plane; .Sig'nific'a'ii't' amounts of expansion occurring other than in this plane will often tend to cause the panel l0to warp; with "resultant dup of intolerable stresses within the panel 10. This preferred? construction too, results in narrower membranes l5,- aii'd therefore better cooling is achieved.

The gap 19, intermediate the ends of dreamer-lisp vided to reduce thermal stressconcentrations in thefm brane 15 resulting from thermally induceddifferential expang sion. The gap 19 permits the arms 17 and the'body'port'ion'ls toexpand and contract with somedegree of independen This ismost important'when consideringlateralexpansion. t

is of somewhat lesser importance when'consideringth'e l gitudinal differential expansion of adjacent tubes"'1 4.'Stress resulting from longitudinal expansion-of tubes "14, 'hdwe'v may be minimized by lateral saw cuts 20 at spaced'inte 'al the arms 17. These cuts are made when and with thedime'risions required by the operating conditions as they relate-"to the stress limits.

The size of gap 19 is determined for the mostpartbythe" degree of relative expansion'between the arms 17 and the bodyportion'l8, being proportioned to prevent an'excessive v amount of heat from being radiated to the body portion "18, while at the same time of sufficient width to prevent stress" buildup as the arms 17 expand. Some bumback of the arms, which would enlarge the gap, may occur where the arm temperatures are above the oxidation temperature of the metal; the bumback, however, can be expected to reach an equilibrium point, depending on the temperature use limits of the membrane arm materials, i.e., thickness and length, and of course, the metal temperature attained. In any event an analysis of the heat transfer characteristics and the resulting isotherms permit designing the panel so the arms 17 and body portion 18 may be maintained within satisfactory temperature limits.

While the membrane 15 might be made of multiple parts, e.g., body portion 18 and arms 17 welded into a unitary element, it is preferred that each membrane 15 be a single piece, since this results in fewer welds being required during the fabrication of the heat exchange panel, and therefore lower costs.

The improved panel wall shown in the drawings is the embodiment that would be preferred for use in a zone of high radiant heat where the heat absorption rate is of the order of 100,000 Btu/ft hr. The tubes are made of SAl78A carbon steel and are 2inches OD. and 1.732-in. ID. on 4-in. spacings (tube center to tube center). The membranes are inch thick and also made of carbon steel. The gap intermediate the ends of the arms is about one-eighth inch. Lateral cuts are required in this case and are five-eighth deep, one-eighth wide and spaced 2 inches apart.

In this case, the tubes are operating at 1050 p.s.i.g. and under saturated conditions, which means that the fluid temperature is about 550 F. The calculated maximum arm temperature of the membranes under these conditions appears adjacent to the gap intermediate the arms and is 950 F. This is about 50 F. less than the oxidation temperature of carbon steel in flue gases; therefore no bumback will be expected. The temperature at the hottest part of the body portion is about 570 F., or approximately 20 F. above that of the saturated fluid within the tubes, which is well within the 150 F.

differential here permitted as the maximum temperature stress limit.

Were membranes as hitherto used for a panel in the service here described, employed, design requirements would dictate using similar tubes but on 2% -in. center spacings in order to meet the maximum temperature stress limit differential of F. Since the flat projected area of the panel would be the same regardless of the type of membrane used, use of the improved panel reduces the number of tubes by about 30 percent.

From the foregoing, it will be evident that the invention provides an improved multiple tube heat exchange panel for use in a wall of a vapor generator that is exposed to radiant heat; tube requirements are substantially reduced over that hitherto required in panels constructed for similar service conditions while still maintaining the membranes within the required temperature stress limits.

lclaim:

1. In a gastight wall of a vapor generator subject to heating gases, an integrated multiple tube heat exchange panel comprising a plurality of substantially parallel, laterally spaced tubes, and a plurality of C-shaped metallic webs disposed between and weld united to adjacent tubes and each having a body portion rigidly united to next adjacent tubes along the entire length thereof and a pair of arms extending generally parallel to a plane containing the longitudinal axes of the adjacent connected tubes, the arms of each web being spaced from the body portion on the gas side thereof to screen the body portion from radiant heat and from each other to form a gap intermediate the ends of the arms to provide compensation for thermal stresses.

2. In a gastight wall according to claim 1 wherein each of the C-shaped membranes is formed as a single piece.

3. In a gastight wall according to claim 1 wherein the body portion of each of the C-shaped membranes is substantially planar and the arms extend parallel to the body portion.