US2034428A - Heat interchange apparatus - Google Patents

Description

Mal'Ch 17, 1936- w. l.. DE BAUFRE HEAT INTERCHANGE APPARATUS I Filed Aug. 9, 19343y Patented 17, 1936 UNITED STATES PATEN'lj OFFICE nEAr'mrEncnANGE APPARATUS WilliamLane De I aufre, Lincoln, Nebr.- Application August 9, 1934, serial No. 739,073.

` 3 cnims (ci. 257-225) This invention relates toimprovementsin the art of exchanging heat between uids of-dierent temperatures. It is particularly applicable to heat interchange between one fluid under high pressure and two or more fluids under low pressure, as is the case in the rectiiicaton pheric air and other mixed gases.

One object o! the invention is to eliminate the tendency of the high pressure iiuid to force tube sheets from the tubes aiiixed therein, as has heretofore been the case with straight-tube interchangers used in air separation plants, and yet retain the feature oipermitting relative expansion vof shell and tubes without undue strain on l5 eithershellortubes,l o

Another object of the invention-'is to provide means for conducting two or more low pressure iluids through straight tubes in heat exchangev with a high pressure uid surrounding the tubes.

iinother objectof the invention is to'utilize a metal shell of maximum strength due to cold work to withstand the high pressure iluidfand Y yet secure gas .tight joints where the shell -is joined to the heads o! the interchanger. Another object of the invention is to reinforce the cold worked shell where ,the strength has been reduced by annealing in securing gas tightjoints by soldering, brazingor welding.

The foregoing, together with suchother ad vantages 'as may hereinafter appear or are incl-1 dent to the invention, are realized by the construction illustrated in preferred form-in the No. 1,951,185, issued March 13, 1934. They al'ev particularly applicable to high prwire throttle expansion plantsas shown in Pig. 2.' although 40 certain ieatures'are also useful in moderate pressure plants as showninlllg.- 1 ot the above patent. `In such air separation plantscompressed air is cooled in an interchangerby retuming products Vof rectiiication, consisting oi more orv less pure oxygen and nitrogen. Wheresuch in- Vterchangersare .provided in pairs with piping and -valves arranged as shown in the above-nien-A tioned lpatentand the ow o f fluids is quickly clmugedvi'rom one interchanger to the other, the

5. temperatures of the meta'i tubes will .quickly change while the temperatures of the metal shell will change more slowly-'from the old to the new conditions. There will thus be relative explan-A sion or contraction of tubes to shell which would 5; tene to injure the tubes or the o r the Joits' of atmosbetween tubes or shell and tube sheets into whichthe tubes are aiiixed, unless provision is made to eliminate such strains. Interchangers have been built for moderatecompressed air pressures with an expansion joint in the shell. In this 5 construction; however, the full tendency o i' the internal uid pressure to force the heads apart, is exerted upon the means by which, the tubes l are amxed in the tube sheets. While this consaie for very high pressures.r

In'building such interchangers, there is also a problem involved(in constructing the heads for returning two or more fluids through the tubes so that no leakage' of one uid will'occur tothe 15 structionis safe for moderate pressures. it is un- -10 external air 'or'into a compartment containing another'llid. 'For moderate air pressures, the shells ot such interchangers have been made of copper to avoid corrosion. vFor very high air pressures. however, 2()

more desirable thancopper. The strength of such\ 25 P bronzes, however, depends largely on cold work ing, such as would occur. in drawing a tubefor an interchangershell. A In assembling such interchangers, soldering, brazing orwelding is necessary to secure gas tightojoints oi fused 30 metal. The application o! heat for this purpose e would annei the hardened tube, thereby reducing the strength of the cold worked bronze to that of annealed material. During operation, however, in air separation plants and in similar gas 35 Iliquefactio'n processes, the temperatures vin interchangers are low so that advantage could be taken oi the high working stresses permissible in cold, worked bronze.

In the interchanger-l described herein and 40 shown on the drawing, an arrangement and construction have been adopted which' enables i'uil advantage tobe taken of the high working stresses permissible in-cold worked'bronze, at the change with a high pressure :duid surrounding the The interchanger consists of a number of small straight tubes I within shell 2 and extending between 4tube sheet 3 at the upper end and tube 4V atthe lower end. Tube sheet 3 at the upper end ispart of a casting or forging 5 which has alarg'er'internal diameter than the external -f diameter `offshell 2. The gap between shell 2 VA and head l is filled by sleeve 6 which extends ,beyond` head Vover shell 2.

nur mechnnicai strength of the Joint between lshell. 2 and sleeve l, shell 2 is threaded externally rand sleeve 3 isthreaded internally so that sleeve "3 can' be screwed onto shell 2 and the sleeve held by fatigue cracks startingnirom\ the roots of vfrom the end of shell 2 to cover all portions of f threads atand beyond the edge of the reinforcing sleeve due to concentration of stresses at the y roots of these threads. But by extending sleeve 6 beyond the threaded portion of shell 2, such concentration of stress is avoided by'the reini'orcingaction of sleeve 8. For similar reasons, sleeve l is threaded externally and screwed into head I which is" threaded internally, and head 5 is extended. beyond the threaded portion of sleeve I.

- The joints between shell z and sieeve t and between sleeve 6 and head 5 are made gas tight by soldering, brazing or welding, thus forming fused metal joints. But the heating of the cold,

drawn metalshell 2 in order to solder, braze or weld the joint between it and sleeve 6 results in annealing the end of shell 2 and thereby considerably reducing the strength from that corresponding to the cold drawn condit on. The length of sleeve 6, however. made' such that the annealed portion of shell 2 is reinforced Vby sleeve 6 which extends a sumcient distance shell 2 which have been'sumcientlm heated by soldering, brazing or welding to appreciably re- .duce the strength of the cold worked metal. Sleev should preferably have a close ilt over shell reinforce shell 2 as soon as shell 2 has expanded Zby creep, or' plastic flow, of the metal where the strength has been reduced by annealing.

Sleeve B is extended asumcient distance beyond head 5 to prevent annealing shell 2 beyond sleeve .6 by conduction of heat thereto when the joint between sleeve 6 and head'5 is made gas tight by soldering, bra'zing or welding.

The construction described above and shown 1 by snow and ice in a gas liquefaction plant. The inside diameter of shell 2 is 'but slightly greater than the outside diameter of the bundle of tubes I. In addition to the advantages previously described, the construction shownlenables this recess to be formed lwith a head 5 of simple but in any event, sleeve will effectively,

shape that may be easily machined and forged rather than cast, and thus have the high strength and non-porosity required for gases under high pressure. Q

Small diameter t s I are soldered or brazed into tube sheet 3. bes I are preferably arranged in concentric circles so as to'form a round tube bundle suitable for enclosing in a cylindrical shell 2. This arrangement oftubes I is also suitable for dividing the tubes into two or .more groups for returning products of rectification in an air or other gas separation plant.

In order that returning oxygen may vow through a central group of tubes and returning nitrogen may flow through the remaining t the upper head is arranged as shown on the drawing. A shell 3 with flange 9 is soldered or brazed into a circular groove Il 'in tube sheet- 3 so that shell O nwillfembrace as many openings in tube sheet 3to tubes I l as'may be desired for the returning oxygen. A second shell II 'is then fastened'to tube sheet 3 by ange I2 and bolts I3,

suitable packing material being placed 'between flange I2 and tube sheet 3 to secure 'a gas tight material being placed between flange S and shell II and between flange I! and shell II to secure Sas tight joints. The height of shell II is made such relativeI to' the distance of ilange 8 froml tube sheet s that when 'sneu is bolted to tubesheet 3 by bolts I3, it will also be forced against flange 9. j

Cap Il has inlet pipe Il for returning oxygen to the portion 'of tubes 1 embraced within shell vShell II has inlet'pipe lllfior returning nitrogen to the portion of' tubes I embraced between shell 8 and shell II.

The lower -endsof tubes I are aiiixed in tube sheet l which is made an integral part of floating head I9 by screwing and soldering it therein'or byany .other suitable construction. Due to thehigh gas pressures involved, the outside diameter of oating head I9 must be considerably greater. than the inside diameter and may even be greater than the outside diameter of shell 2.

Outer head 20 therefore has an inside diameter greaterthan the outside diameter of shell 2. The gap between shell 2. and' outer head 2li is filled by sleeve 2 I. The proportions of sleeve 2| relative to shell 2 and to outer head 2l are made as described for sleever 6 and head l, and-for the, same reasons. This commotion alsoprov videsr an annular space suitable for connection with 'the inlet pipe. 22 for the high pressure air to be separated, although the lower end of the interchanger is warml and inlet pipe 22 is not subject to being clogged with ice. The annularl opening between outer head 2l and floating head I9 provides an exit for water which has con' densed out of the compressed air as it is cooled in In order to -keep the returning oxygen separate from' the returning nitrogen, the portion of tubes I containing oxygen are embraced within 15 A packing isA` held in the annular space shown around tube 23 by means of gland 24 and bolts 25.

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tube'26 which is soldered or brazed into a groove 21 in tube sheet 4. Tube 26 lis of a diameter suitable for the fiowof oxygen involved and is enlarged at the upper end to fit into groove 21. Tube 26 projects through tube 23 to a flange 28 for connecting with outside oxygen piping. The annular space between tubes 23 and 26 serves for returning nitrogen which may be recovered if desired through pipe 29. Or, this annular space can be left open to the atmosphere for discarding the nitrogen by simply providing braces for internal pipe 26 to support the same. A solidly brazed or welded construction is shown in the drawing for, pipes 23, 26, etc. A flanged and bolted construction could be used as described and shown at the upper end of the interchanger for the returning oxygen and nitrogen tubes, but this will usually be unnecessary at the warm end of the interchanger.

In the operation o the lnterchanger shown in the drawing, very high pressure compressed air enters pipe 22 at about room temperature and ows up in the space within shell 2 surrounding tubes I. The compressed air may be-caused to flow back and forth across the tubes by bailles 3 I. The compressed air finally leaves through pipe I cooled to a very low temperature.

Returning oxygen and nitrogen at very low temperatures enter pipes I1 and I8 and flow down through tubes I in heat interchangewith the compressed air flowing up and across these tubes. The returning oxygen and nitrogen arethereby warmed nearly to room' temperature before leaving through pipes 28 and 29, respectively.

During the cooling of the compressed air, water vapor' will be frozen out of the compressed air and will accumulate as snow and ice around tubes I.v When this occurs to an extent which appreciably increases the pressure drop or decreases the heat transfer, the oxygen and nitrogen may be returned through another interchanger. The warm air entering pipe 22 will then melt the'snow and ice and will warm tubes I and shell 2. The resulting water may be drained out through drain pipell.

Any relative expansion of tubes I and shell 2 will cause floating head I9 to move relative to outer head 20. Such movement can take place without setting up undue strains by reason of the stuftlng box with suitable packing material In operation, this interchanger is not subjected to high temperatures which would anneal any of the metals used therein. Cold worked metal can therefore be used with high working stresses which are safe for metal in `such condition. During construction, however, certain parts become annealed by reason of high temperatures experienced in soldering, brazing or welding tosecure the fused metal joints necessary in gas processing, particularly under high pressure. -The construction claimed in this patent application enables such annealed parts to be reinforced, thus permitting full advantage to be taken of the high working stresses' permissible in non-annealed parts.- 'Ihis is of particular advantage with high gas pressures.

While these improvements have been made particularly for use with high gas pressures they are also of advantage with moderate pressures.

What I claim his:

1. An interchanger for heat exchange between two fluids flowing through tubes and a third fluid surrounding said tubes, including a tube sheet into which said tubes are aillxed, a shell.

fastened to said tube sheet so as to embrace a portion of said tubes, a flange attached td said shell, a cap, a flange attached to said cap, a pipe connection to said cap, a second shell clamped vbetween said ilangesand fastened to said tube sheet so as to embrace said tubes, a pipe connection to said second shell, whereby two fluids flowing through the two pipe connections respectively flow through the portion of said tubes embraced by the first shell and the remaining tubes embraced between the two shells and are brought into heat exchange with a third fluid surrounding said tubes.

2. An interchanger for heat exchange between two fluids flowing through tubes and a third fluid surrounding said tubes, including a tube sheet into which said tubes are alxed, a floating head afilxed to said tube sheet, an outer head surrounding said iloating head, a tube `connected to said floating head and projecting through said outer head, an .inner tube projecting through said tube 'and fastened to said tube sheet so as to embrace a portion o'f said tubes, and a stuillng box in said outer head and surrounding said tube and filled with packing material, whereby two fluids ilowing through said inner tube and the annular space between the two tubes respectively ow through the' portion of said tubes embraced by said inner tube and the remaining tubes and whereby said floating head may move relative to said outer head without leakage of a third fluid surrounding said tubes and said floating head.

3. An interchanger for heat exchange between fluids flowing throughtubes and another iluid surrounding said tubes, including a multiple-compartment head having' an inner compartment partially bounded by a flanged shell, a cap with a flange attached thereto, and an outer compartment partially bounded by a shell clamped between said flang'es, whereby leakage of fluid from the inner compartment into the outer compartment or intol the atmosphere is prevented.

WILLIAM LANE DE BAUFRE. y

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