US2614544A - Superheater baffling - Google Patents

Description

Oct- 21, 1952 w. s. PATTERSON ETAL 2,614,544

SUPERHEATER BAFFLING Original Filed Oct. 20, 1943 Wfl/PD 6'. PH TTE/PSON INVE N TORS Patented Oct. 21, 1952- UNITED STATES PATENT o-F-Fic s'" pa'qu'a, N. 15., assig iors to Combustion Engineering supcrheaterylnc a corporationof Dela :originai; application ioctober -20, 1943, Se r ial No. 1 $506,922; Divided and this application February 2.-8-, L946;-Serial--No. 650,971

. ".1 Y invention relates to improvedisuperli'eater installations for steam generating units. icontemplated. hereine, superheater. installationinclu'des; besides the. heat transfer surface, Jmeaiis for confining the'gases within the super- .heater space, for-directing'the' gases overthe heatingsurrace in the desired manner, and for \eontrouirig the quantity of,,tg'as flowing over the superheater. 'Superheaters embodying in some form 'or. other onejormore ofthe'se features a're commonly used on'"all high pressure, "high "cajpaeity steamgenerating' units," but' this invention "relates to severahnover changes in the arrange- "ment" now known to the art, which-will "greatly "increase performance, economyof manufacture, andlife of equipment. Ifisuperheaters forhighpressure steam gene'rators, 'itis common practice to'heat'the steam to 925 F. or higher. One of the limitations h as been'the metal available for fabrication crane tubes' in which thesteam is heated but,- as progress in alloys'teelsproceeds, the -more serious limita- -tions may be mother aspects of design. i-For example, when heating steam to'the present high temperatures -there a definite quantity of heat --abs'orption required for-each" pound of steam,--approx imately 270 B. t.- u'-. 'Inea convection super- 'heatsr, this heat must comefrom the gases passing-oVertheJSuperheater of-twhichu there is a defitnite-gquantity -ioreach ipoundaof steam-,ofr the :order oi m'a'gnitud'eof 1.2. .tTherefore,eachpound rofrgas must give .up.. 225 13. t. .u..or...over, which is equivalent ;to a 'ttemp'erature .drop ofsapproxi- ;.mately:800 .F.

The, lowest capacity at .whichra .superheater. is eexpectedto heat the steam to'maximum temperature isv called the fcontrolpoint? In-designing for, this point, it isidesirable to utilize the avail- @ableheat in the'ggases in the most efficient manner so as to require the least amount of heating :suriace. in tubes arranged on; the'widest. possible spacing-and yet occupying the least possible space and; requiring the lowest possible; entering gas .temperature. The least: amount of heating surface under-given. temperature conditions results fromusing thehighestproduct of mean-temperature difference times: gas. side heattransferrate. Obviously, thel highest prod'uctwill result when reach ofithe'.individuallfactors is the" highest;. an'd,

it is wll'known" intheartof heat transfer that ."it requires: counter flow to. result in the' highest mean temperature difference and gas; fiowtraris- 'v'ersetof the axisioftubes togive the highest heat transferrate', other thing'sbeing equal, such" as, thepowerless resulting'from the frictionbetween "2Claiins. (01. 122 -480 pose of which isto decrease the ,by passedjquanobjects ofthis invention to combine'botnthese desirable features in'the same arrangement.

When operating a convection 'superheatenat capacities above the control point, the'tendency is for-the steam temperature to be higherbecause of higher gas temperature and one met-hod of preventing this is by decreasing'thequantity or [gas 'which is directed over thesuperheatersurface. It is obvious to *one'sk-illed inthea'rtthat the greatest reduction in; steam temperature by this'control means can be obtained with the-least quantity by-passed if the flow of the by-pa'ssed gasesisso directed as-to. comio'letelymiss kall, or.

gases to first contact considerable.;superheater surface in a flow path transverse. to thesaxis'. of thextubes is defeating the purpose. of the bypass and will seriously limit the amountofteimieraturecontrol. It is one of the objects of thisrinvention to disclose a method of. directing theabypassed. gases in the preferred manner, thecpurtity,'.the required sizeof the by-pass, the required (size and cost of byvpass damper, .-and-;;to improve steamtemperature control. 1

Since the by-passed gas doesnotpassover the superheater surface, it enters the by pa'ss at high temperature. Furthermore, it is not-always possible with arrangements heretofore. used "to cool streams of gases of widely different temperatures,

and by-pass amper, which accomplishe ixin of the'twojg'asstrea ms in a portion offlth where steamis' beingigener'at'edjand'.whe

fthe. gases andithetubesurface. It-is one-"of the the by -passed gases to the'same temperature;:as the main bodyofv gaseswhich has passed over the superheater. This has often resulted in two which, without sufficient opportunity to mix -have then been directed over the next sectionof heating surface of the .boiler unit. 'Very frequently the water I heating .economiz'er follows directly after the by-p'ass damper in the. directionwoi gas flow, anda non-uniform gas .teiriperatureand/or velocity entering thislequipment is very, ufid'es'irable. This invention includes. a -novel-arranga ment of a'supei'heater and its as's'o'c'iat d fi s e unit 2. I r? ortance.

fore, theqstratification' is of minor im The arrangement has the added, advantage 'of absorbing heat. fror'nj th'etwo gas streams. while they are being mixed, therebymaking-rfioreefie tive use Of-the installed heating .surface' as cyeasingr the eficiency' 0f u it "without additlqnalfmaierialcost heater pass is decreased and, consequently, with g the damper design now in common use, the capacity of the by-pass is very limited unless an unusually large by-pass and correspondingly large and expensive damper is provided. Therefore, it is one Of the features of the proposed arrangement to locate and pivot the damper in such a way as to add resistance in the superheater pass when the damper is opened and thereby insure that the capacity of the by-pass is not wholly dependent on the proportions of the two" parallel gas passes. This novel feature results in a saving in material, expense, and size of equipment, or, alternately, in increased range of superheat control if by-pass and damper are not decreased in size.

The present invention will be best understood upon consideration of the following detailed description of various .embodiments when read in conjunction with the accompanying drawings in which:

Figures 1 and 2 are partial sectional elevations pof'embodiments of the improved superheater and by-passorganization adapted to a steam generatOI'.

This application is a division of that filed in our name on October 20, 1943, under Serial No.

506,922 and which issued on July 2, 1946 as U. S.

Patent 2,403,237.

In Fig. 1 of that parent case (now Patent 2,403,237) there is disclosed a steam generating unit the major part of'which is located beyond the outlet at the top of the furnace (not here shown) and which includes a bank of tubes 5 (see Fig. 1 hereof) connecting steam and water drum top downwardly along the tubes of said bank. The furnace has its rear wall faced with steam generating tubes l2some of which arebent to I forma screen l3 (see Figs. 1 and 2 hereof) over which the gases from the furnace first pass while others form a second screen [4 spaced outwardly from the first. Preferably all of the Walls of the furnace are faced with steam generating tubes.

Between the spaced screens [3 and I4 is one section [6 (see Fig. 1 hereof) of the superheater. In the downpass intermediate the screen 14 and thebank 5 is located another part of the superheater, this may be constructed as a single group of parallel tubes interconnected for serial flow of steam through successive tubes and extending for substantially the full length of the pass wherein installed or it may be constructed as shown in two superimposed groups of tubes WA "and 19A connected for series flow of steam therethrough,

The gases leaving the furnace pass (as indicated by Fig. 1 hereof) over screen l3, section I Got the -superheater, screen i4, and thence downwardly along the tubes of superheater sections superheater section ISA may pass thereacross and ISA and I8A.' Some of the gases upon entering enter the top of the steam generating bank 5, thence pass downwardly through said bank to the gas outlet near the base thereof. The gas flow through said bank may be regulated by damper 28 which thus controls a by-pass around the superheater.

From superheater inlet header 24A steam flows downwardly and serially through superheater groups IBA and IQA to the section l6 as indicated by the arrows. It will be noted that the lower group I8Areceives the coldest steam which then passes to the upper group ISA to meet the hotter gases before leaving that section of the superheater. In this way partial counterfiow of steam and gases is established. From superheater group ISA the steam then passes to superheater section It and after passing through this section is delivered to ofitake header 25A. In general the gases pass over superheater sections 18A, iSA along or parallel to the superheater tubes. The above described arrangement (as shown by Fig. 1 of our parent Patent 2,403,237) is conventional.

Because the heat transfer rate with gases flowing parallel to the axis of tubes is substantially less than that whenfiowing across the tubes, the corresponding sections 18A, [9A (Fig. 1 hereof) of our improved superheater are arranged for a flow of the gases transverse to the axis of the superheater tubes throughout the gas path as well as'for counterflow of the gases with respect to the steam. Figure 1 hereof shows a partial section. of a steam generator and associated superheater with superheater sections 18A and ISA through. which the steam from inlet header 24A flows serially as shown by the arrows to leave the unit by way of outlet header 25A. The steam leaving the front of section WA is conveyed by tubes 26 to tubes at the rear of section ISA; The tubes 26 extend between the two sections and across from the front to the rear thereby forming a support for a special baffle 27 mounted inter-' mediate and separating the sections. Bafile 21 is spaced forwardly from bank baffle 9 and extends forwardly to meet a bafiie 28 mounted on a row of furnace tubes which are spaced forwardly with respect to, the section 18A to form a gas chamber 3|. At about the middle of section I8A a linear bafile 29 extends from the forward bank bafile 9 toward the front side of section ISA; By this arrangementv the furnace gases enter the upper section ISA, flow transversely of the tubes, and in -counterfiow, with respect to the steam flowing through the tubes thence pass downwardly and transversely over the upper portions of the tubes of section [8A in parallel flow with respect to the steam, thence pass through gas chamber 3! and across the lower ends of the tubes of group I8A again in counter flow with respect to the steam flow.

Above superheater section I9Ais a baffle 32 which baffle extends from baffie '9 over section 19A at a level above the tubes of section I6. In this way any gas that is by-passed through the boiler bank 5 is forced to pass above the top of the superheater and out of contact therewith. In the conventional arrangement of our parent Patent 2,403,237 (Fig.1 thereof) the by-passed gases flow over the superheater sections l6, l9 and thence into the by-pass so considerable superheat is generated, which tends to minimize the control of superheat through by-passing the gases because-the rate of heat. transfer at this point in thesuperheater is still relatively high; or an excessive amount of gasesmust be bypassed to obtain the desired control. According to the improved arrangement shown in Figure 1 hereof, these objections are completely overcome. It is an advantage to by-pass the gases coming from the top of the furnace rather than from a point lower down in the furnace since the gases that reach the top of the furnace have given up more of their heat to the furnace tubes and are relatively cooler thereby resulting in less heat to be absorbed in the by-pass and less severe service on the baflies, dampers etc.

A further advantage of our arrangement of Figure 1 hereof is that the by-pass damper 20 is located at a lower point of the tube bank and bafiie Ill extends downwardly across the bent parts of the tubes, as shown at IDA, in the lower part of the bank so as to direct the gases downwardly into the stream from the superheater pass. The gases leaving the by-pass may be hotter than those leaving the superheater and by this arrangement intermingle with the latter below the tubes of the banks and pass over the bottom ends of the tube bank to be thoroughly mixed so as to enter the economizer (see device 8 of our parent Patent-2,403,237) at a uniform temperature. This distinguishes from the arrangement shown in our parent Patent 2,403,237 (Fig. 1 thereof) where because the gases flow through a, shorter by-pass with less heat absorbing surface they leave and are then directed upwardly into one part of the economizer which is therefore in danger of becoming overheated.

In the modification shown in Figure 2 hereof, some of the furnace tubes l2 which form the support of the baffle 28 between the furnace and the superheater, pass between the superheater sections 183 and [93. The path of steam flow through the tubes as shown by the arrows is somewhat different from that in Figure 1 with the result that the gases flow across the tubes of section IBB in counterflow with respect to the steam as in Figure 1 thence across the upper portion of the section I8B in counterflow instead of parallel as in Figure 1 and thence across the lower portion of section I83 in parallel flow rather than counterflow as in Figure 1. Obviously additional superheater sections may be added in additional passes wherein the steam flow will be generally counter to the gas flow.

While several modifications of the invention have been illustrated and described in detail it is to be understood that the invention is not limited to the precise forms or arrangements shown but comprehends other alternatives and mechanical equivalents of the apparatus herein illustrated and falling within the scope of the appended claims.

What we claim is:

'1. A steam generator comprising a watercooled furnace with a gas outlet near its upper end; a steam superheater located adjacent to and in communication with the gas outlet and .below the plane of the furnace roof including a multiplicity of parallel tubular fluid heating elements each comprised of substantially vertically disposed tubes interconnected by return bends to form a continuous. path for steam flow; means at the lower end of said superheater constituting a path for discharge of said furnace gases after heat-imparting contact with said superheater tubes; means forming a by-pass around said superheater to by-pass part of the furnace gases and leading into the said superheater tubes gas discharge path, said by-pass means comprising a rear 'wall that is separated from said superheater by said by-pass; a control damper at the outlet end of said by-pass and hingedly mounted at a point intermediate the said by-pass outlet and the lower end of said superheater and at a point remote from said rear wall; heat absorbing surface arranged in the bypass and comprising a substantially vertically disposed bank of steam generating tubes having a lower portion extending below the elevation of the by-pass damper into the aforesaid discharge path of gases from said superheater and said bypass; and baflle means extending from the lower end of said rear wall across the by-pass heating surface tubes above said discharge path and above said lower steam generating tubes portion to require flow of the by-pass gases past said damper so that when the damper is opened the gases from the superheater pass and those from the by-pass are mixed and subsequently passed over the surface of the said lower steam generating tubes portion.

2. A steam generator comprising a vertically elongated furnace with a lateral gas outlet at its upper end for discharging hot combustion gases, said lateral outlet including means forming an upper gas flow path and a lower gas flow path parallel therewith, said lower gas flow path having a downwardly extending first gas flow p ss subjoined thereto; a multiplicity of tubular superheater elements located within said lower parallelflow path and extending thereacross toestablish cross fiow of said combustion 'gases thereover; means forming a by-pass around said superheater for said furnace gases, said by-pass including said upper gas flow path and a downwardly extending second gas flow pass subjoined thereto; steam generating tubes in said second pass; and a control damper at the outlet of said by-pass and associated with both said first and second gas flow passes to proportionately distribute furnace gases flowing over the steam generating tubes through said by-pass and over said superheater elements.

WARD S. PATTERSON.

ELNO M. POWELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,363,714 Broido Dec. 28, 1920 2,254,373 Langvand Sept. 2, 1941 2,271,643 Jacobus Feb. 1942 2,403,237 Powell et a1. July 2, 1946 FOREIGN PATENTS Number Country Date 51,659 Austria Jan. 10, 1912

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