US2844360A - Heat exchanger - Google Patents

Description

A. BURl HEAT EXCHANGER July 22, 1958 2 Sheets-Sheet 1 Original Filed Jan. 26, 1955 IN VEN TOR.

u N a 0 EMA m.

July 22, 1958 A. BURI 2,844,360

HEAT EXCHANGER 0riginal Fiied Jan. 26, 1955 2 Sheets-Sheet 2 v I J g 4 )l B F lg. 2

INVENTOR.

A LF'EED BU?! ATTORNEK United States Patent 1 2,844,360 HEAT EXCHANGER Alfred Buri, Winterthur, Switzerland, assignor to Sulzer Freres Societe Anonyme, Winterthur, Switzerland, a corporation of Switzerland Application September 7, 1956, Serial No. 609,049 Claims priority, application Switzerland January 27, 1954 4 Claims. 01. 257-221 The present invention relates to a heat exchanger for steam power plants in which the pressure of at least one heat exchanging fluid is greater than the critical pressure of the fluid, the heat exchanger consisting of a plurality of like elements, each element including an outer conduit and at least one inner conduit disposed within the outer conduit, the outer conduits of a plurality of the units being connected in parallel and the inner conduits of a plurality of the units being also connected in parallel with respect to the flow of the heat exchanging fluid. Such heat exchangers are used as feed water preheaters, steam heated resuperheaters, blow-down coolers, and the like.

Difiiculties are experienced with heat exchangers which are operated at high pressures, particularly super-critical pressures. Problems are involved with respect to the stresses to which the materials are subjected and with respect to sealing the tube system including the inner conduits against the tube system formed by the outer conduits, and also with respect to the sealing off of the heat exchangers to the outside. To provide the necessary strength, the wall thickness of the tubes and of the individual parts of the heat exchanger is increased with increasing operating pressure. Because of the large amounts of fluids which pass through the heat exchangers in modern power plants, the heat exchangers must be subdivided into a plurality of like elements, each element having a primary side and a secondary side, the primary sides being arranged in parallel, and the secondary sides being also arranged in parallel with respect to the flow of the fluid. If the heat exchanger is not subdivided into a plurality of elements, the flow area of a single unit and the pressure exerted on the tube walls would be too great. Subdividing the heat exchanger into a plurality of elements calls for an increased number of sealing and connecting points. In order to provide satisfactory sealing, the flanges interconnecting individual parts of the heat exchanger become greater and more bulky at increased pressures. These flanges do not only require much space but are costly, since the heat exchanger frequently must be operated at temperatures which call for the use of austenitic steel which is considerably more expensive than ferritic steel. 7 The tubes arranged inside the casing are usually rolled into tube plates. The rolling-in of high pressure tubes of great wall thickness is very diflicult.

All these disadvantages can be avoided by constructing the heat exchanger according to the present invention which proposes to weld all connections which are exposed to supercritical pressure, for sealing as Well as for sustaining stresses. Though it is conventional to seal flanges as well as tubes rolled into tube sheets by means of welding and though it has also been endeavored to interconnect individual parts of the heat exchanger by welding, it has never been attempted to provide a See 2 of the welding improves with increasing wall thickness of the connected parts and with increasing pressure exerted by the heat exchanging fluids. There are no faulty weldings of the kind which is unavoidable when welding thin-walled tubes.

The inaccessibility of the interior of the heat exchanger is of particular disadvantage when testing the heat exchanger for leakages. This disadvantage is particularly marked, if it has been found that there is a leakage, and the individual parts of the heat exchanger must be severed in order to find the location of the leakage. In apparatus operated at high pressures, it is not desirable, for example, to screw a plug into an exterior casing and to remove the plug for locating a leakage. The inaccessibility causes no difficulties, if each of the like elements of which the heat exchanger is composed is provided with at least one tube which communicates with the interior of the element and which has a closed end extending outside of the element. The tube is preferably arranged at a portion of the element where liquid accumulates' within the casing or at a place where liquid accumulates within a space surrounded by the casing. If the primary or the secondary part of the heat exchanger is pressure tested, for example, by means of water, leakage liquid will accumulate in the tube. If the closed end of the tube is cut off or a hole is drilled thereinto, it can be ascertained in which of the parallelly arranged elements a leakage has occurred. The tubes are sealed off by welding after the pressure test.

A' completely welded heat exchanger which is operated at supercritical pressure cannot have any movable connection-between individual parts, as they are used, for example, in the form of membranes, for compensating different heat expansions. It is of advantage to shape the outer conduit as well as the conduits arranged within the outer conduit like hair pins, the cross section of the outer conduit being greater at the bend than at the legs of the hair pin If the outer and inner conduits of the heat exchanger are interconnected at the open ends of the legs of the hair pin, these conduits can expand into the bend. If the heat expansion is uniform, the relative position of the inner and outer conduits is maintained. If the heat expansion is not uniform, the increased cross section of the outer conduit at its bend provides sulficient space for relative displacement of the outer and inner conduits. v

The novel features which are considered characteristic of the inventiona're set forth with particularity in the appended claims. The invention itself however and additional objects and advantages thereof will best be understood from the following description of an embodiment thereof when read in conjunction with the accom completely welded construction of a heat exchanger operating at supercritical pressures. The advantages of such a construction, to wit: good sealing at highest pressures, strength of connections, quick assembly, savings in space, material and cost, by far exceed the only disadvantage, i. e. the inaccessibility of the interior of the heat exchanger. It should be considered that the quality pa'nying drawing, in which Fig. 1 -is-a part sectional side view of a heat exchanger according to the invention;

t Fig. 2 is' a top view of a heat exchanger according to the invention; 7

Fig. 3 illustrates a section of the heat exchanger shown in Fig. l, the section being taken along the line AA. The same numerals designate the same parts in all figures.

Fig. 2 illustrates a heat exchanger according to the 3 or plate element 8. The ends of the inner conduits or tubes 7 extend through the tube plates 8 and are welded thereinto. Each tube plate element 8 has a tubular extension 8 which forms an integral part with the element and which is welded at 8" to an end of the outer tube or shell 6. The tubes 7 terminate in spaces formed by covers 9. One of the covers 9 is connected by means of a conduit 10 with a collector 3. The cover at the other end of the heat exchanger element is connected by means of a conduit 10" with a collector 3". As seen in Fig. 1 the covers 9 have cylindrical rim portions extending coaxially of the tube plates 8 and of the shell 6, the cylindrical rim portions abutting against and being welded to the outer faces of the plates 8.

A tubular inlet header 2' connects one end portion of the outer tubes or shells 6 of a plurality of elements. The shell 6 whose diameter is smaller than that of the header 2' extends transversely through the latter and is welded thereto. A first heat exchanging fluid supplied to the header 2' enters through apertures 11' into the interior of the outer tube 6. The first fluid will be substantially equally distributed into all elements connected to the header 2'. The first heat exchanging fluid leaves the shells 6 through apertures 11" and enters an outlet header 2" through which it is removed from the heat exchanger. A second heat exchanging fluid is preferably supplied through the header 3 and is distributed through the conduits 10" into the inner conduits 7 of individual heat exchanger elements through which it flows in counterflow relation to the first heat exchanging fluid which flows through the outer conduit or shell. The second heat exchanging fluid leaves the heat exchanger element through the conduit 10' and enters the collector 3'. It is of minor importance which of the heat exchanger elements has the higher temperature, although a better heat exchange is possible if the fluid of higher temperature flows inside the tubes 7. It is of great importance which of the heat exchanging fluids has the higher pressure particularly supercritical pressure. This fluid is preferably conducted inside the tubes 7, because otherwise the wall thickness of the casing 6 would have to be too great.

The cross section of the tubular shell 6 is enlarged at the bend 12, so that there is suflicient space for a relative movement of the outer conduit and of the inner conduits 7 in case of different heat expansion of these conduits. The enlargement of the cross section of the outer conduit at the bend facilitates assembly of the heat exchanger. Several welding seams can be saved if the individual conduit portions or sections 13 and 14 are cut from seamless tubes. After the conduit portion 13 has been welded to the straight leg portion of the outer conduit, the tubes 7 are inserted, the tube sections 14 having previously been pushed past the lower portion (Fig. 1) of the conduit 6. Thereupon, the sections 14 are individually put in place and welded to the previously connected section. Finally, the portion 15 which consists of two longitudinal halves is inserted, and one half is welded to the adjacent parts 14 and 6'. Thereupon, the other half is welded to the first half and to the adjacent parts 14 and 6'.

Fig. 3 is a bottom view on an enlarged scale of the tube plate element 8. The tubes 7 are connected with the plate by means of welds 16. A tube 17 is provided for simplifying testing of the heat exchanger with respect to leakages. The bore 18 of the tube 17 is closed at the free end of the tube and communicates through a bore 19 in the plate 8 with the interior of the cavity formed by the cover 9. For pressure testing the heat exchanger, a pressure liquid is pumped into the outer conduit through one of the collectors 2' or 2". Leakage liquid would pass into the tube 7 or into the space formed by the cover 9. By cutting off the closed end of the tube 17 or drilling a hole thereinto, it can be ascertained which of the elements of the heat exchanger is leaking. Only this particular element requires closer inspection and repair. The bore 19 can be so arranged that the interior of the tube 17 communicates with the interior of the outer conduit 6. In that case, a pressure liquid would be supplied through one of the collectors 3' or 3", it being possible to use a considerably higher testing pressure than when pumping liquid into the outer conduit. If the heat exchanger is in a position other than that shown in Fig. 2, the tube 17 must be connected to a portion where pressure liquid will accumulate. If, for example, the heat exchanger is so suspended that the bends are on top, the tubes 17 would preferably be connected to the bends in the conduits 10' and 10".

While a specific embodiment of the invention has been shown and described, it will be apparent to those skilled in the art that various changes, modifications, substitutions, additions and omissions may be made therein withp out departing from the spirit and scope of the invention as set forth in the appended claims.

This, application is a continuation of applicants prior application No. 484,109 filed January 26, 1955, now abandoned.

What is claimed is:

l. A heat exchanger for indirectly transferring heat between fluids of different temperatures, comprising a continuous tubular shell having a hair-pin configuration and including a curved portion and two straight end portions, an inlet header connected with one of said end portions for supplying one of the heat exchanging fluids into said shell, an outlet header connected with the other of said end portions for removing the heat exchanging fluid from said shell, two tube plates individually having an annular rim extending coaxially of and being connected with the outer end of one of said end portions for closing the ends of said shell, each of said tube plates having a plurality of bores extending parallel to the longitudinal axis of said shell, a plurality of tubes placed in parallel relation inside and longitudinally of said tubular shell, the ends of said tubes being individually received in said bores, each of said tube plates having an outer face, and two covers individually having a cylindrical rim portion extending coaxially of said shell andabutting against and being connected with one of said faces, said tube plates being the only connection between said covers and said end portions, an inlet pipe connected with one of said covers for supplying the second fluid to said tubes, and an outlet pipe' connected with the other of said covers for removing the second fluid from said tubes.

2. A heat exchanger as defined in claim 1, said annular rim of said tube plates being in the form of a tubular extension forming an integral part of said plates and being welded to an end of said shell.

3. A heat exchanger as defined in claim 1 in which the diameter of said tubular shell increases adjacent to said curved portion and the diameter of said curved portion is greater than the diameter of the end portions of said shell and in which the curved portion of the shell is made up of a plurality of endwisely connected tubular sections. 4. A heat exchanger as defined in claim 1 in which said inlet header and said outlet header are tubular and have a diameter which is greater than the diameter of said end portions, the latter being individually placed at a right angle with regard to the respective header and individually extending transversely through said headers, the portions of'said end portions which are within said headers having a plurality of perforations affording flow of the first fluid from said inlet header into said shell and flow of the first fluid from said shell into said outlet header.

References Cited in the file of this patent UNITED STATES PATENTS 1,924,272 Cofiin Aug. 29, 1933 2,404,335 Whittle' July 16, 1946 2,520,755 Brown Aug. 29, 1950 2,612,350 Stadler Sept. 30, 1952

Images