US2910275A - Desuper-heater construction for heat exchanger - Google Patents

Description

R. W. MUNRO Oct. 27, 1959 DESUFER-HEATER CONSTRUCTION FOR HEAT EXCHANGER 5 Sheets-Sheet 1 Filed Aug. 7, 1956 IN1/EN TOR. Raben? WI Mam QWA BY I

ATTRNEYS R. w. MUNRO Oct. 27, 1959 3 Sheets-Sheet 2 IN1/EN ToR. Rober?! W Munro ATTORNEYS 3 Sheets-Sheet 3 INVENTOR.

Oct. 27, 1959 R. w. MUNRO OESUPER-HEATER CONSTRUCTION FOR HEAT EXOHANGER Filed Aug. 7, wsa

, boiler.

saturated steam at the available steam pressure.

DESUPER-HEATER CNSTRUCTION FOR HEA EXCHANGER ARobert W.' Munro, Cynwyd, Pa., assgnor to The Griscom-Russell Company, Massillon, Ohio, a corporation of Delaware Application August 7, 1956, Serial No.1602,62`7

3 Claims. (Cl. 257-43) v Thiszinvention relates to a heat exchanger, and more particularly it pertains to a desuperheater therefor.

Heat exchangers are employed to preheat water supplied to steam boilers. Ordinarily a portion of exhaust steam is led to the exchanger through which water is circulated. Heat from the exhaust steam is transmitted Vtothe water, raising the temperature before it enters Vthe In heating the water, the exhaust steam entering the exchanger gives up its heat and condenses when corning in contact with heat exchange tubesthrough which rthe 'water passes.

I The economy and other benefits of using exhaust steam,

-such as `extracted from a turbine, for progressive heating of water on its way to the boiler have long been recog- '.nized. Briey, the chief advantages derived are fuel savings and increased boiler capacity, the latter of which results in better sustained power. The primary problem in water heater construction is to provide the .most complete and eflicient transfer of heat from the steam in the shell of the heater to the water llowing through the heat exchange tubes.

Where highly superheated stearn is available, it is de sirable in the interest ,of over-all plant economy to heat the water to a temperature equal to or above that of This is accomplished by providing a desuperheating chamber, commonly called a desuperheaterf within the shell of the exchanger whereby the water is furtherlieatedto the highest possible temperature before its passage from the exchanger to the boiler.

l Heretofore desuperheaters have been composed of a single elongated enclosure around a portion of the heat exchange tubes-for keeping the highly superheated steam in lintimate contact with the tubes until its superheat has been reduced or eliminated. This permits cross-over of temperatures; that is, heating the boiler feed water a -few degrees above the dry and saturated temperature ofthe extraction steam. After the water in the final tube pass extracts the superheat from the steam, the v'desuperheated steam is distributed throughout the remainder of the shell, commonly called the condensing zone, enclosing. all ofthe heat exchange tubes. Here the water yis heated practically to the saturated steam temperature before reaching the final pass through the desuperheater.

"quired in the condensing zone to obtain equivalent over- 'all eiciency may be more of a disadvantage than the *advantage gained by ladding the desuperheat zone.

United States Patent v 2,910,275 Patented Oct; 27, 195:9

Fice

'I have discovered that this diculty may be overcome by splitting the steam flow and reducing its length of travel in the desuperheater, as by providing two or more desuperheat zones each of substantially shorter length than the prior elongated zone. Such arrangement substantially reduces the pressure drop in the desuperheat zone but lprovides the feed water with several added degrees of heat.

Thus, in accordance with the invention, by providing --heat exchange tubes at an advanced location of flow,

the Zones being in end-to-end abutment with respect to each other. y

It is another object of this invention to provide desuperheat means for increasing the temperature of feed water in a heat exchanger without substantially decreasing the heating steam pressure as it passes through the desuperheat means.

It is another object of this invention to provide desuperheat means for increasing the temperature of feed water in a heat exchanger without substantially lowering the saturation temperature of the steam passing through the desuperheat means.

It is another object of this invention to provide desuperheat means for adding heat extracted from superhea-ted steam to feed water in a heat exchanger without increasing the area of the heat exchange tubes in the condensing zone of the heater.

Finally, it is an object of this invention to provide an' improved heat exchanger construction with ydesuperheating means which substantially eliminates the difficulties enumerated and which obtains the foregoing desiderata in a simple and e'iecti-ve manner.

These and 'other objects and advantages apparent `to those skilled in the art from the following description and claims may be obtained, the stated results achieved and the described diiculties overcome by the discoveries,

principles, apparatus, parts, combinations, subcombinations and elements which comprise the present invention,

the nature of which is set forth in the following statement, preferred embodiments-illustrative of the best modes in which applicant has contemplated applying the principles-are set forth in the following description, and which are particularly and distinctly pointed out 'and lset forth in the appended claims forming part hereof.

Generally, the nature of the discoveries and improvements of the present invention include in a heat'exchanger, a shell forming a steam condensing compartment, a feedwater inlet, a feedwater outlet, a bundle of parallel heat exchange tubes in the shell forming ka pathof flow for feed water from the inlet to the outlet, means including partitions and plates within the sheil forming at least two separate desuperheat' chambers in end-toend abutment with each other, the 'chambers surrounding 'the heat exchange tubes at a zone near the feedwater outlet, each chamber having a separate steam inlet lccated with respect to the tubes at the most advanced location vof tube fluid iiow in each chamber, va steam inlet in the shell connected to lthe Ysteam iniets vof the chambers, and each chamber also having a steam outlet communicating with the condensing compartment of the shell.

By'way of example, the improved -desuperheater construction is illustrated in the accompanying drawings, in4

sectional View taken on the line 3-3 of Fig. 1;

,if 2191022.75.. c

N heating zone 16 includes two separate chambers 21 and 22 in end-to-end abutment with each other fand separated Fig. 4 is a fragmentary enlarged transverse sectional view taken on the line 4 4 of Fig. l; and

Fig. 5 is a longitudinal, sectional view of another embodiment of the invention.

Similar numerals refer to similar parts throughout Vthe various figures of the drawings.

A heat exchanger is generally indicated at I1 in Fig. 1. Though the heat exchanger 1 is horizontally disposed, it is intended to include yboth horizontal and vertical types of heat exchangers, as well as heat exchangers generally having all capacities and pressure conditions from the small low-pressure units suitable for moderately sized industrial plants to the large extreme pressure multistage designs required for large central power generating stations. The device of the present invention is also applicable to basic types of feedwater heaters having either straight tubes Wit-h floating heads or U -tubes Without oating heads.

The heat exchanger 1 includes a shell 2 and a water `box or head member 3 including a tube sheet 4 and forming a head chamber 5. The head chamber 5 is divided into half portions by partitions 6 and 6a forming inlet and outlet chambers 5a and 5b in the usual manner. A feedwater inlet 7 and a feedwater outlet 8 are provided Iin the head member 3 and communicate with the inlet and outlet chambers 5a and 5b on opposite sides of the partition 6. Thus feed water entering the head chamber 5 through inlet 7 and chamber 5a passes through a plurality of U-shaped heat exchange tubes 9 having opposite end portions seated in the tube sheet 4. Thereafter the feed water passes into outlet chamber 5b and out of the heat exchanger through the feedwater outlet 8.

'I'he shell 2 is provided with a steam inlet 10 and a condensate outlet 11, and the shell 2 forms a compartment or condensing zone 12 in which the heat exchange tubes 9 are disposed. The shell 2 is preferably secured to the head member 3 by means of an annular weld 13. The tubes 9 are provided with tube support means including bale plates 14 which are spaced from each other `at preferably equal intervals along the longitudinal axis of the shell 2. The baffle plates 14 are transversely disposed with respect to the shell and are staggered (Fig. 3) to permit the passage of steam in a sinuous path through the compartment 12.

The compartment 12 is divided into several communieating portions including a subcooling zone 15 and a desuperheating zone generally indicated at 16. The subcooling zone 15 is enclosed between a flat plate member 17 and an arcuate plate member 18, as shown in Figs. 1 and 3, and extends from the tube sheet 4 to the lower U-bent portions of the tubes 9. The arcuate plate 18 is supported on the shell 2 by riding strips 19 (Figs. l and 3) at the lower end thereof to permit relative expansion of the plate 18 and shell 2. The portions of the tubes 9 within the zone 15 are supported by spaced staggered baliie plates 20. 'Ihe subcooling zone 15 encloses the inlet end portions of ysome of the tubes, while the inlet portions of other tubes 9 extend directly through the condensing compartment 12, as shown in Fig. l. The right end (Fig. 1) of the subcooling zone 15 communicates with the condensing compartment 12 while the condensate outlet 11 communicates with the left end of the subcooling zone 15. Y

The desuperheating zone 16 is formed preferably as a box-like structure enclosing the outlet portions of the tubes 9 nearest the tube sheet 4, i.e., at the advanced zone .of water ow nearest the water outlet 8. The desuperby a transverse partition 23.- The box-like structure forming the chamber 21 includes a pair of spaced, parallel, upper and lower plates 24 and 25 that are mounted between opposite portions of an arcuate plate 26.

Likewise, the box-like structure forming the chamber S22-includes a pair of similar upper yand lower plates 27 and 28 mounted between arcuate side plates 29 and 30. rlfhe plates 27 and 28 are aligned with the plates 24 and `25. Moreover, the arcuate plates 29 and 30 are preferably continuations of corresponding portions of the plate 26. Thus the lchambers 21 yand 22 enclose vthe portions of the U-tubes 9 through which the heated feed water passes immediately before leaving the shell of the heat exchanger. Only the outlet end portions of tubes 9 are enclosed in and pass through the desuperheater chambers 21 and 22, the outlet ends of the tubes 9 as shown in Fig. l extending from the tube sheet 4 and outlet chamber 5b successively through the series arranged desuperheater chambers 21 and 22 and then into the condensing compartment 12.

The chambers 21 and 22 are provided with steam inlets 31 and 32 formed at the ends of plates 24 and 27, respectively. Similarly the chambers 21 and 22 are provided with `arcuate segmental steam outlets 33 and 34, respectively. Both steam inlets 31 and 32 are located at advanced zones of ow of the feed water through the tubes 9, i.e. the inlet 31 is adjacent the tube sheet 4 and the inlet 32 is'adjacent the partition 23. On the other hand, the outlets 33 and 34 are located at the other ends of their respective chambers 21 and 22 remote from the inlets 31 and 32. The outlet 33 is located at the end of plate 24 and extends through slots 33a in arcuate portions of the plate 26 adjacent the partition 23. Similarly the outlet 34 is formed by the ends of plates 27, 28, 29 and 30 and a transverse plate 35 forming an end wall for the chamber 22. The partition 23 and the plate 35 are coextensive with the cross section of the chambers 21 and 22.

In addition, spaced staggered bajiie plates 36 and 37 within the chamber 21 provide a devious or sinuous path for the steam moving through the chamber 21 between the inlet 31 and the outlet 33. As shown in Figs. 2 and 3, the baiiies 36 are aligned'in pairs and extend toward each other from opposite sides of plate 26 to provide steam passageways 38 (Fig. 2) therebetween. The baie 37 is centrally disposed in the chamber 21 with vertical edges spaced from the arcuate plate 26 and having sides overlapping the edge portions of the batles 36 forming the steam passageways 38.

The chamber 22 is in like manner provided with spaced staggered bafle plates 39 and 40.

The chambers 21 and 22 are connected to the steam inlet 10 by separate branches 41 and 42 of a steam conduit or passageway formed between the plate 24 and the arcuate plate 26. The end of the conduit branch 42 is provided with an end wall 45 that is coextensive with the conduit cross section and mounted'between adjacent ends of plates 26 and 27 as shown in Figs. 1 and 4. An annular conduit member 43 is securedto the portion of the plate 26 opposite the steam inlet 10 so that the conduit formed by the conduit branches 41 and 42 communicates with the steam inlet 10. Hence, steam entering the shell 12 from a steam source (not shown) enters through the conduit member 43 and flow is divided substantially half in opposite directions to the chambers 21 and 22 in which the steam is desuperheated before entering the condensing zone. A steam bathe plate 44 is preferably provided under the inlet 10 to prevent erosion of the plate 24 by direct steam impingement.

As shown, the desuperheater chambers 21 and 22 are separate from each other and are each separate from the condensing compartment V12. Further, the desuperheater chambers 21 and 22 are arranged in series enclosing the outlet end portions ofthe tubes 9 from the tube aside/75 sheet4u`nti1`the tubes9pass'through`plate 3S4where the l surfaces thereof are exposed within' the condensing compartment 12'. In this'manner, the'outlet end portions-ofthe'tubes9=enclosed within the desuperheater chambers 21 and 22aremaintained separated from the condensing compartment.

Similarly, the branches 41 and 42 of the passageway connecting the steam inletrV and desuperheater chamber inlets'l 31 and 32are"separate"from' the condensing compartment 12'r and 'from the ldesuperheater chambers 21 and 22. l

When the superheated'steam enters'the chambers-21 and 22 its 'ow is directedinintimate contactwith'the portions vofth`e"tubes'9 'inthe'v chambers by the staggered baffle plates 36, 37, 39 and 40 which create a zigzag course of travel for the steam and thereby assure maximum heat transfer to the tube portions within the chambers 21 and 22 by a continually moving stream of steam. Thereafter the steam leaves the chambers 21 and 22 through the outlets 33 and 34 respectively, whereupon the desuperheated steam enters the condensing zone 12 of the shell where the steam condenses and the feed water is heated practically to the saturated steam temperature before passing in the tubes 9 to the desuperheat zone. The condensate then passes through the subcooling zone where it is further cooled and heats the cold incoming feed water and the condensate then passes out of the shell through the outlet 11.

'I'he device of the present invention provides an improved means for elevating the feed water temperature to the highest possible level before entering the steam boiler. The desuperheat zone 16, being provided with two separate chambers 21 and 22, splits the flow of superheated steam in half. Each of the chambers 21 and 22 is only half the total length of the two so that the length of flow of the superheated steam in the desuperheat zone is only half of the length of iiow in prior desuperheat constructions of the same capacity. In thus providing separate chambers 21 and 22 of relatively short length, the divided flow and shortened length of flow reduces the pressure drop of the superheated steam in owing through the desuperheat zone to approximately one-eighth that in prior constructions. This minimum resulting pressure drop does not substantially lower the saturation temperature of the steam in the condensing zone, so there is no requirement for additional surface in the condensing zone to provide the same amount of heat transfer.

The foregoing results and advantages may similarly be obtained in a construction having more than two separate desuperheat chambers. Thus, three, four or more short length desuperheat chambers may be used. For example, in Fig. 5 another embodiment of the invention is shown in which a heat exchanger 45 is provided with four desuperheat chambers 46, 47, 48 and 49 separate from each other and from the condensing compartment. In all other respects the heat exchanger 45 is similar to the heat exchanger 1. Likewise, the chambers 46, 47, 48 and 49 are similar in construction and operation of the chambers 21 and 22. Thus the chambers 46, 47, 48 and 49 are separated by transverse partitions 50, 51 and 52, respectively. Moreover, the chambers 46, 47, 48 and 49 are provided with steam inlets 53, 54, 55 and 56, as well as with steam outlets 57, 58,' 59 and 60, respectively. The steam inlets 53, 54, 55 and 56 in turn communicate with a steam conduit or manifold 61 similar to the steam conduit portions 41 and 42 in the heat exchanger 1. Also, each chamber 46, 47, 48 and 49 includes spaced staggered baille plates. For example, the desuperheat chamber 46 includes spaced staggered bathe plates 62, 63 and 64, whereby steam passes through said chamber in a zigzag course to insure maximum contact of the steam with heat exchange tubes 65 extending therethrough. -v

Finally, the construction in Fig. 5 also provides im- '6 provedmeansforredueing'thepressure drop ofthesupe heatedsteam' and 'for increasing the feed water temperature" by dividing'thell'owY and shortening -the length of w of the steam Vthroughv the desuperheat'zone."

Accordin'gly, by splitting 'the flow of steamthrough 'a plurality of desuperheating chambers' it is possible to `add extradegrees Vof'heat tothe feed water before it entersthe boilerwithout' substantially lowering the saturation" temperature of the' steam in' the condensing zone. Lower pressure' inthe condensing zone would result in a reducedsaturation' temperature and'inV subsequent less efficient heat exchange in the condensing zone unless increased heat exchange surfaces are provided inlthe forinmofmore or Alonger'h`eat`ex'chan`ge tubes. This in turn would involve increased size and weight of the equipment. 'Ilhus the use of the improved desuperheater construction of the invention, in place of the prior construction, provides greater eiciency of heat extraction than was heretofore gained by the use of a single elongated desuperheating zone.

The pressure drop diiculty inherent in the single elongated desuperheating zone construction is overcome by the use of more than one chamber each having a part of the length of the single elongated zone, because the pressure drop in the shorter zones is only approximately one-eighth (for two chambers) of the pressure drop in a single elongated zone.

In the foregoing description certain terms have been used for brevity, clearness and understanding, but no unnecessary limitations are to be implied therefrom beyond the requirements of the prior art, because such words are used for descriptive purposes herein and are intended to be broadly construed.

Moreover, the embodiment of the improved construction illustrated and described herein is by way of example `and the scope of the present invention is not limited .to the exact details `of construction shown.

Having now described the features, construction and principles of the invention, the characteristics of the new desuperheater construction, and the advantageous, new and useful results provided; the new and useful discoveries, principles, parts, elements, combinations, subcombinations, structures and arrangements and mechanical equivalents thereof obvious to those skilled in th art are set forth in the appended claims.

I claim:

l. Desuperheater `construction for a heat exchanger mcluding a Itubular shell, a tube sheet at one end of the shell forming with the shell a steam condensing compartment, a plurality of tubes extending from the tube sheet within the shell, the tubes having inlet and outlet ends, Ifeedwater inlet means communicating with the tube inlet ends, feedwater outlet means communicating with the tube outlet ends; spaced upper and lower plates extending from the tube sheet into the shell having longitudinal edges, side plates connected with the longitudinal edges of the upper and lower plates; a lirst transverse plate connected to the upper, lower and side plates :at the ends of the latter remote from the tube sheet; a second ytransverse plate connected to the upper, lower and side plates intermediate the tube sheet and said first transverse plate; the upper, lower, side and rst transverse plates forming with said second transverse plate a first box-like desuperheater chamber separate from said condensing lcompartment, .the upper, lower, side and second transverse plates forming with the tube sheet la secondV box-like desuperheater chamber separate from said first desuperheater chamber andfrom said condensing compartment; said desuperheater chambers being arranged in series with respect to the tubes; the outlet end portions of .the tubes extending from the tube sheet Ithrough said second desuperheater chamber, then through said second transverse plate, then through said first desuperheater chamber, then through said rst transverse plate and then into the condensing compartment; a first inlet opening formed in the upper plate adjacent the second transverse plate communicating with the rst desuperheater chamber, a second'inlet opening formed in said upper plate adjacent the tube sheet communicating with Ithe'se'cond desuperheater chamber, a rst outlet opening formed in the 10W- er plate adjacent the first transverse plate communicating between the rst desuperheater chamber and the condensing compartment, a second outlet opening formed in the lower plate adjacent the second transverse plate communicating between the second desuperheater chamber and the condensing compartment; a steam inlet for the shell, a condensate outlet for the shell; and walls forming a passageway separate from said condensing compartment and from each of said rst and second desuperheater chambers connecting said steaminlet with'both-ofssaid rst and second desuperheater ,chamber inlet openings. 2. The construction deinedin claimV 1 in which Athe side plates are arcuatelyvshaped and in which the spaced upper and lower plates are parallel. i

3. The construction defined in vclaim 1 in which the side plates are spaced from the shell. k References Cited in the le of this patent UNITED STATES PATENTS 2,812,164 Thompson Nov. S, 1957

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