US2477950A - Superheater - Google Patents

Description

Aug. 2, 1949. E, G, BAlLEY 2,477,950

SUPERHETER Filed Aug. 5, 1944 W 1 M| 3:11 v

INVENroR.

` B Y' 171/127 5.' ai/ey- ATTORNEY Patented ugr, 1949 SUPERHEATER Ervin G. Bailey, Easton, Pa., assignor to The Babcock & Wilcox Company, Rockleigh, N. J., a corporation of New Jersey Application August 5, 1944, Serial No. 548,176

` maintained at high pressures and is heated to provide a high degree of superheat, the temperature of the superheater tube metal may often be increased sufiiciently to cause the tubes to become warped or bent out of their normal nositions and thus cause their original spacings to be altered. This tendency is accentuated with tubes of small diameter and when the tubes are especially long in .comparison with their diameters. When such tubesare closely spaced, any change from their normal spacing results in a change in the gas fiow area between adjacent tubes which represents a large percentage of changewith respect to the gas flow area for which the apparatus is designed. Between solne tubes the area becomes greater and between others less which results in uneven distribution of heat to the tubes throughout the bank due to the higher or lower values of gas mass flow at different locations.

In the pendant superheater herein disclosed, the tubes are formed in a series of coils or panels where each coil is formed of a number of straight length portions successively connected by return bends at their opposite ends to provide a continuous tube length or conductor from one end of the coil to the other. The coils are suspended from their upper ends allowing the straight length portions to extend downwardly in Vertical planes in transverse relation to the flow of high temperature heating gases. In some instances spacers have been provided between tube lengths in an attempt to maintain normal spacings, but the practice in this respect has been to use metal constructions which in themselves are subject to 5 Claims. (Cl. 2574-248) diflicult to obtain in suitable quantity and specification.

'It is an object of my invention to provide adequate means for maintaining upright lengths of superheater tubes in predetermined spaced relation under conditions of relatively high temperature diferentials between fluids interiorly 'and exteriorly of the tubes.

Another object is to provide means for preserving the normal spaclng of suspended lengths of superheater tubes utilizlng materials readily and economically procurable.

An additional object is to provide in a pendant superheater tube spacer means comprising parts comparable in their heat resistant properties with the metal of the superheater tubes.

A further object of my invention is to provide spacer means for suspended superheater tubes utilizing a minimum of metal parts requiring alloys of special composition, whereby as a result of the materials used, or the arrangement of the component elements, or both, the tube lengths are maintained in predetermined spaced relation under severe conditions of operation.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawing and descriptive matter in which I have illustrated and described a preferred embodiment of my invention.

Fig. 1 of the drawing is a fragmentary sectional elevation of a vapor generating unit embodying the invention in the superheater thereof;

Fig. 2 is .an enlarged fragmentary view of the superheater shown in Fig. 1;

Fig. 3 is a fragmentary elevational view of the superheater shown in Fig. 2, partly in section along line 3-3; i

distortion and fairly rapid destruction due 'toV mally be exposed. Such alloys are necessarily of v special composition and not only are they expensive but under the prevailing conditions are often Fig. 4 is an enlarged side view of a tube spmer element included in the superheater showrrT in previous figures;

Fig. 5 is a transverse section along line 5-5`of Fig. 4;

Fig. 6 is an enlarged fragmentary view of a tube supporting detail shown in Figs. 1 and 2;

vides a useful embodiment ofmy invention, the

arrangement showing the disposition of certain Sections of heat exchange surface in a vapor generating unit known as a radiant-boiler, the general characteristics of which are more fully disclosed in U. 'S. Patent 2,231,8'l2, granted February 18. 1941, on the application of Ervin G. Bailey et al. With boilerl unts of this type, operating in accordance with modern practices, the vapor is generated at high pressures so that for the degree of superheat required, the temperatures of the superheated vapor are correspondingly high, for example, approximately 900 F. or more. Under such conditions of operation it is necessary to subject the superheater to heating gases of relatively high temperatures so that the metal of the tubes will reach a sufliciently high temperature to superheat the vapor. The components of the tube spacer means being disposed exteriorly of and between the superheater tubes are necessarily subjected to the same high temperature heating gases and must therefore be of a character to withstand such gases requlring suitable selection of their material, construction and arrangement.

For convenience of description, the unit shown will be termed a steam generator although it is to be understood that the use of my invention is not limited to steam generation nor to the heating of steam but may be used with equal advantage in association with the generation or heating of other vapors. Referring to the drawing. the. upper portion of the furnace chamber opens directly into a laterally extending heating gas pass l2 in which is disposed a superheater l4 of the pendant vtype having its tubes arranged in a series of serially connected banks |8, 20, and 22. Successive banks are progressively longer advancing toward the furnace to conform to the gradually increasing height of the gas pass |2. A natural circulation bank of boiler tubes IS having a relatively small amount of heating surface is disposed across the outlet from the furnace chamber |0 where it serves as a tubular screen for tempering the combustion gases before reaching the superheater and for limiting radiation to the superheater tubes from the furnace space |0. The unit is provided with an upper steam and water drum |1 to which the upper ends of the boiler tubes |6 are connected and from which certain saturated steam connections l9 are made to the superheater inlet header 2 l, the steam flowing' through successive banks of the superheater in contraflow relation to the flow of heating gas through the pass |2 and finally entering the superheater outlet header 24 for delivery to the point of use.

Each bank of the superheater |4 is formed of multiple loop coils or panels spaced across the width of the heating gas pass |2, each coil or panel providing long and substantially straight tube lengths disposed in a plane parallel to the direction of gas flow with successive tube lengths in' any given bank |0, 20, or 22 engaging one of the beam members 30 which extend transversely of the setting above the roof 22. The Suspension structure for each coil comprises a pair of lugs connected by integral return bend 'portions or loops at their upper and lower ends. Each coil in the rear or inlet bank IB is connected to a corresponding coil in the intermediate bank 20 by means of a return bend 26, whereas connections from the outlet ends of coils in bank 20 to the inlet ends of coils in the front or Outlet bank 22 are made through the intermediate header 28 to allow for a different number of coils in one bank than in the other.

In the superheater shownI each coil is individually suspended from its upper end, as detailed in Figs. 2 and 8 for the coils in bank 22 for example, each set of coil suspensions for the coils 34 each secured to a return bend 36 at the upper end of the coil. the two lugs 34 being secured by means of a bolt 30 to a centrally disposed hanger 40 having suitable connections with the beam member 30 whereby its position longltudinally of the beam is maintained substantially fixed. A strap 42 around the coil inlet tube 44 is secured to one of the return bends 36 and a similar strap 42 around the coil outlet tube 46 'is secured tothe other of the return bends 36.

The lugs 34 and straps 42 thus serve to tle all tube lengths of the coil together at their rupper ends so as to maintain their relative spacings in the'plane of the coil.

The relative spacings of the coils across the width of the bank are maintained by reason of the relatively fixed longitudinal 'positioning of the hangers 40, and by reason of the return bends 36 being embedded in material formlng the roof 32, the upper ends of all tube lengths extending either into or through the roof. The inner side of the roof 32 is -preferably formed of a layer 48 of hardened plastic refractory molded around the tube lengths, while the outer side comprises one or more layers 50 of suitable heat insulating material. The tube spacer elements such as the lugs 34 and straps 42 together with the hanger elements 40 are thus protected from the high temperature heating gases'flowing through the pass |2, and while the construction serves to maintain a predetermined spacing of the tube lengths at their upper ends, there is no restralnt to their longltudinal movement resulting from ex- -pansion or contraction under various temperature conditions.

In an embodiment of the form illustrated it may be found desirable to employ tubes of 21/2 0. D. throughout the superheater with the straight length portions of the tubes in each coil and bank spaced on 5 centers in the direction of gas flow through the gasipass |2,'thereby leaving a clear space of 2% 'between adjacent tubes. Transversely of the pass, the coils may be spaced on 5" centers in the 'front bank 22 and on 31/2 centers in the succeeding banks 20 and |8, the latter leaving a clear space of 1" between adjacent tubes. At these spacings, there may be as many as thirty-seven tubes in each transverse rowl of the front bank 22, and fifty-three tubes in each transverse row of the intermediate bank 20, and of the rear bank |8. The lengths of the banks |8, 20, and 22, and thus the unsupported lengths of the tubes, may range from approximately fifteen feet for the rear bank |8 to approximately twenty feet for the front bank 22, measured from their suspensions at the roof 32.

As a step toward maintaining such tubes in predetermined spaced relation throughout their lengths it is proposed to provide a certain amount of rigidity to the coils by installing ties between component loops of each coil, as shown for example in Fig. 2, where ties 52 as detailed in Figs. 6 and 7 are provided between successive loops adjacent theirlower extremities, the ties being secured as by welding to each central loop 54 at opposite sides at different levels; the outer loops 56 and 58 being bent toward the loop 54 about as shown to enable ties of the smallest dimensions practicable to be used. For coils having the smaller spacing of 31/2 center to center as in banks 18 and 20, additional ties 60 are provided minimum dimensions to be used.

As shown in Figs'ii and 7. each tie 52 or .60 is in the nature of a link for-med of separate U-shaped members tt 'and tt whose free ends are secured to the respective tube lengths as by welds 88.' the relative proportions of the'members 6| and being such as to permit a limited amount of movement between connected tube lengths.

' As a further step toward xaintaining the superheater tubes in predetermiried spaced relation. the coils in each of the banks i 8, 20.` and 22 are tied together in groups at their bottom ends and the groups restrained against relative movement transversely of the gas pass if. For this purpose blocks or tile w of the form shown in Figs. 'i and 5 are installed within at least: one selected series of loops at the bottom end of each bank, for example within each series of central loops 5d as shown in Fig. 2. Each block 'iii is preferably formed with a plurality of recesses 12 and the blocks are installed in a continuous series throughout the width of the bank. Recesses 'M representing apsproximately half-Sections of the recesses 12 are formed at the ends of individual blocks so that when the blocks are assembled within the'loops the half-Sections on adjoining blocks combine to provide the equivalent of a full-section recess 12 with the result that all coils of the series are restrained against lateral movement to substantially the same extent. The length of each complete series of blocks for any one of the banks is slightly less than the width of the gas pass if to provide a small clearance space at each end to allow for expansion of the blocks and thus obviate any binding at the side walls of the pass.

The inner ends of the'block recesses 'E2 and 'Hi are curved to a radius slightly greater than the radius of the tubes which they engage, the curvature of each full recess 12 extending throughout an arc of approximately 180 and that of 'each half-section recess 'M throughout .an arc of approximately 90. Those portions of the' block adjoining the curved inner end of each recess are shaped as at 'it to provide a contour conforrningV to the tube surfaces within the loops. The

recesses terminate at their outer ends in side wall i against the tube surfaces over a considerable area due to the'formation of the blocks at and adloining the recesses 12 and 1d. Although the blocks may not have accurate fitted contact with the tubes, nevertheless the character and extent of engagement are such that heat is transferred metallic in composition, and one having suiilcient strength to resist damage during handling and at the high temperatures normally 'encountered in service. If metaliic blocks are to be used, these would necessarily have to be made of thev special alloys previously mentioned and would requlre accurate fitting to the tubes to provide adequate heat transfer; howevenif in the construction of i the superheater the use of metals is to be held to a' minimum, various high heat resistant refractories may suitably. be emplo'yed; for example, a ,hard burned flre brick having a kaolin base; or carborundum, for'exampie, including refractories of similar characteristics having carborimdum as a base.

Installation or removal of the blocks 'Id can be readily accomplished without disrupting the assembly and installation of the superheater coils.

In order to install a block it may be inserted edgew'ise into a longitudinal lane 84 between adjacent coils and'then rotated about a Vertical axis into the--desired transverse 'lane tt where it is turned to extend horizontally and then lowered into position within the loop 56. In order to remove a block, the foregoing Operations are reversed. If the thickness ,of the block should be somewhat greater than the width of the longitudinal lane 8d. the adjacent tube lengths may be temporarily sprung apart to permit passage of the block.

'est loop .54, as in the present arrangement,

places them at the iowermost part of the bank and farthest from the overhead coil suspensions w where the tubesiare also maintained in predetermined spaced relation. Allv intermediate portions of the tube lengths arefthus subject to the restraint provided at their opposite ends, so that with each coil acting as a unit as a result of component tube lengths being tied together, the tendency of the tube lengths to become displaced from their normal positions is reduced to a minimum. By employing tube spacer means such as blocks 'iii embraced and supported entirely within a lower loop 5d, for example, there is an advantage that in this position the blocks are disposed rearwardly of at least one row of tubes so that a considerable lportiori of their area ls vshielded from direct impingement by the high temperature heating gases whereby their overall Operating temperatures are maintained at a minimum, considering also that there is a continuous transfer of heat from the blocks due to their extended area of engagement with the tube'walls.

I claim:

l. In a superheater, the combinationof tubes having substantially straight tube length portions arranged upright in substantially parallel upright planes spaced across the fiow of heating ,gases, said tubes including return bend portions each connecting the lower ends of a pair of said straight length portions in a different one of said planes to provide a depending loop in each from the blocks to the tubes at a rate enabling the material 'of the blocks to be maintained at safe operating temperatures.

Inview of the relatively high temperature zones in which the blocks 10 are installed, it is essential that the blocks be fabricated of a high heat resistant refractory material. either 4metallic or nonplane in transverse alignment with corresponding depending loops in successive parallel planes, means for suspending said tubes from their upper ends only, and means for holding said aligned loops in predetermined horizontally spaced relation comprising a spacer member gravitationally seated and supported solely on and within said return bend portions providing said transversely aligned loops, said spacer member having its lower portion formed with recesses each embracing a return bend portion 7 in a different one of said planes throughout an upper surface portion thereof, said spacer member providing projections separating adjacent recesses and extending downwardly between successive return bend portions to a point below the tube centers thereof.

2. In a superheater, the combination of coils of tubes having substantially straight tube length portions arranged upright in substantially parallel upright planes spaced across the flow of heating gases, said tubes including integral return bend portions connecting successive straight length portions at their upper and lower ends to provide a succession of coil loops in each of said planes, i'tcluding a depending corresponding depending loops in successive adjacent planes, means for suspending said coils4 from their upper ends only, and means for holding said coils in predetermined horizontally spaced relation eomprising spacer means gravitationally seated and supported solely on and within said return bend portions forming the lower ends of said transversely aligned loops, said spacer means providing recesses each embracing a depencling loop in one of said planes and having a curved inner portion engaging the return bend portion of a loop substantially throughout the upper half of its tubular periphery, each of said recesses having side wall portions extending downwardly between adjacent loops to approximately the bottom end portions thereof.

3. In a superheater, the combination of tubes having substantially straight tube length' portions arranged upright in substantially parallel upright planes spaced across the flow of heating gases, said tubes including integral return bend portions each connecting the lower ends of a pair of said straight length portions in a different one of said planes to provide a depending loop in each-plane in alignment throughout with corresponding depending loops in successive adjacent planes, means for suspending said loops from their upper ends only, and means for holding said aligned loops in predetermined horizontally spaced relation comprising a spacer member gravitationally seated and supported solely on and within said return bend portions forming the lower closed ends of said transversely aligned loops, said spacer member having its lower portion formed with recesses each embracing a return bend portion in a different one of said planes throughout an upper surface portion thereof, said spacer member providing projections separating adjacent recesses and extending downwardly between adjacent loops to at least the lowermost extremities thereof, said spacer member havingan upper portion disposed between straight length tube portions forming the upright legs of said aligned loops and providing a thickness substantially equal to the horizontal distance between said legs so as to prevent rotational dlslodgement of said member from its normal seated position and thereby maintain said proiections in operative position between adjacent retum bend portions.

4. In a superheater, the combination of tubes forming depending loops in substantially parallel upright planes spaced acrossthe flow of heating gases. said tubes having substantially straight tube' length portions forming the upright legs of said loops and having integral return bend portions of substantially semicircular formation forming the lower closed ends of said loops, said loops being arranged so as to provide a loop in one of said planes in transverse alignment throughout with corresponding loops in successive adjacent planes, means for suspending said loops from their upper ends only, and means for holding said aligned loop in predetermined horizontally spaced relation comprising a spacer member gravitationally seated and supported solely on and within the return bend portions of said transversely aligned loops. said spacer member having its lower portion formed with recesses each embracng a return bend portion in a different one of said planes, with projections separating adjacent recesses and extending downwardly between adjacent loops to at least the lowermost extremities thereof, said spacer member extending upwardly within said aligned loops above the center of curvature of said return bend portions and having its upper portion formed with planar side walls lying parallel to and adjacent straight length tube portions forming the upright legs of said loops, said upper member portion substantially filling the space between said legs throughout the upward extent of said walls so as to prevent rotational dislodgement of saidv member from its normal upright operative position.

5. In a superheater, the combination as specified in claim 4 wherein the legs of 'the aligned loops are disposed in substantially parallel planes and the upper portion of the spacer member is formed with parallel side walls providing a thickness substantially equal to the horizontal distance between said legs.

ERVIN G. BAJLEY.

REFER'ENCES CITED The-following referemces are of record in the file of this patent:

UNITED STA'I'ES PATENTS Number Name Date 551,680 Meier Dec. 17, 1895 1,875,l42 Price Aug. 30, 1932 1,941,258 Gordon Dec. 26, 1933 2,134,713 Gilg Nov. 1, 1938 2,183,496. Peters Dec. 12, 1939 2,245,209 Maya,...l June 10, 1941 2,252,071 Gay Aug. 12, 1941 2,328,039 TOomey et al. Aug. 31, 1943

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