US 2956787 A
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Oct. 18, 1960 s. H. s. RAUB 2,956,787
HEAT INTERCHANGER Filed May 28, 1957 I INVENTOR SAMUEL H'. s. RAUB ATTORNEY United t s eht HEAT INTERCHANGER Samuel H. S. Raub, Bay Village, Ohio, assiguor to Union Carbide Corporation, a corporation of New York Filed May 28, 1957, Ser. No. 662,082 '1 Claim. 011257-236 This invention relates to heat interchangers and more particularly to apparatus of this character containing nonmetallic tubes of carbon or graphite construction for conducting corrosive fluids therethroug-h.
Heat interchangers of this character comprise bundles of tubes extending between tube sheets, and are provided with baffles spaced along the tubes and assembled as a unit for installation in the heat exchanger shell. Heretofore the full weight of the baffle assembly has been carried by the tubes.
Heat interchangers of carbon or graphite are plagued by their fragility. During delivery and installation, it is common for the heat interchangers to be mishandled, dropped and otherwise shocked. This mishandling has heretofore resulted in numerous failures of heat interchanger members, entailing great expense for repairs. These failures, in the majority of instances, were tube breakage principally localized at or immediate to the tube sheets.
In the event of sudden shock, such as dropping one end of the heat exchanger, the weight of the baffles is added to the weight of the tubes, tending to break off the tubes at the face of the tube sheet. Since each tube has both ends rigidly cemented into the tube sheets, it acts as a beam with fixed ends, and maximum stress occurs at the fixed ends.
Investigations have found that the cause of such failures were the batlles adjacent to the tube sheets. These adjacent bafiles, when heretofore heat interchangers were shocked as by dropping one end, hammered against the tube bundle and sheared the tubes. Since the tube bundle, including baffles, of the carbon or graphite heat interchanger must be removable as a whole unit, attempts were directed to finding means for supporting the baifles independent of the tubes, but as an integral part of the tube bundles for removal purposes. The obvious expedient, as shown by heat exchanger art, of supporting baflles by welding or otherwise securing to the heat interchanger shell was thus unemployable.
The main object of the present invention is to avoid the difliculties referred to above, and to support the weight of the baflles independently of the tubes.
Other objects are to support the weight of the baffles by tie rods independently of the tubes secured to the tube sheets, to prevent the tie rods from corroding and adhering to the tube sheets, and to permit the tie rods to slide relative to the tube sheets in response to difference in thermal expansion from that of the tubes.
According to the present invention the weight of the baflles is supported by tie rods along which the baffles are spaced, and the ends of the tie rods are received in sockets in the tube sheets. When the tie rods are of metal subject to corrosion, a corrosion resistant ferrule is interposed between the end of the tie rod and the tube sheet, to permit relative sliding.
The present heat interchanger construction circumvents tube failures by the novel expedient of supporting baffles adjacent to the tube sheets by tie rods independent of the tubes, the whole tube bundle assembly including tubes,
baflies and tie rods being removable as one unit.
In the drawings:
Fig. 1 is a vertical longitudinal section through a heat Fig. 5 is an end elevation of the structure shown in" Fig. 4.
The heat exchanger shown in the drawings comprises a steel pipe shell 10 welded between an inlet end casting 12 and an outlet end casting 14. Inside the shell 10 is mounted a bundle of carbon or graphite tubes 16, spaced" as shown in Fig. 2, which pass through correspondingly" spaced holes in baflles 18. The bafiles are spaced alongthe tie rods 20 which pass through the batlies.
A fixed tube sheet 22 of carbon or graphite is bolted to the outlet casting 14, and communicated with an inlet 24 for corrosive fluid. A floating tube sheet 26 of carbon or graphite is bolted to the inlet casting 12, and communicates with an outlet 28 for the corrosive fluid.
The ends of the carbon or graphite tubes 16 are cemented into sockets 32 in the tube sheets as shown in Fig. 3. The ends of the tie rods 20 enter sockets 34 in the tube sheets.
When the tie rods 20 are of steel or other metal subject to corrosion, which might otherwise rust fast to the socket and fail to slip with thermal expansion or contraction, the ends of the tie rods are capped with a ferrule 36 of brass or other corrosion resistant metal, and the ferrule inserted into the socket 34. These ferrules are not necessary when a sufllciently corrosion resistant rod material is used, such as No. 302 stainless steel would be in many applications.
As shown in Figs. 4 and 5, the baffles 18 are fixed to the tie rods 20, as by welding shown at 40. The tubes 16 pass through the bafiles 18 substantially freely, the clearance 38 shown being exaggerated, and in practice a few of the tubes may even fit fairly tightly in the bafiles due to imperfect extrusion causing some of the tubes to bend.
It is essential that the weight and stress distribution of the respective members of the heat interchanger be carefully observed. An important feature of the heat interchanger centers around the removable tube bundle assembly which permits the weight of the tubes 16 and baflles 18 to be supported independent of each other. Neither the Weights of the tubes 16 are supported by the baffles 18, nor that of the baffles 18 supported by the tubes 16. The tubes 16 pass through the baffles 18 and are fixedly secured within the tube sheets 22 and 26 at their ends, and it is these ends which carry essentially the whole weight of the tubes. The baffles 18 traverse the tube bundle and perform normal heat exchange purposes only, that being the intermittent distribution of exchange fluid between the tubes 16. The tubes 16 pass through and are substantially loosely received by the baflles 18. The tie rods 20 are slidably fitted in corrosion resistant sockets within the tube sheets 22 and 26. Tie rods 20 support the bafiles 18 so that the weight of the baffles is not distributed over the tubes 16. Baffles 18 are fixedly secured to the tie rods 20 as by Welding for the purpose of assuring that baifle inertia upon shock is not transmitted to the tubes 16.
In essence then, the novel removable tube bundle assembly of the heat interchanger provides separate and stress independent structural systems. One such system consists of the tubes 16 which carry their own weight and inertia upon shock independent of the weight and inertia Patented Oct. 18', 1960 of the bafiies 18. The other system comprises the tie rods The advantages ofthe heat interchanger in summary.
are that such apparatus provides a removable tube bundle assembly comprising tubes, baffies andtie rods support, such assembly also providing means integral therewith for supporting bafiies independent of the interchanger tubes for preventing breakage of such tubes upon shock.
This application is a continuation-in-part of application Serial No. 578,009, filed April 13, 1956, now abandoned.
What is claimed is:
A heat exchanger comprising a metallic shell; an impervious graphite tube sheet fixed to one end of said shell; an impervious graphite floating tube sheet at the opposite end of said shell; a bundle of substantially parallel impervious graphite tubes extending between said tube sheets and communicating with corresponding apertures through said tube sheets; a multiplicity of metallic tie rods extending between said tube sheets and slidably mounted in blind holes therein; and at least one baflle spaced intermediate said tube sheets supported solely by said tie rods 4. and spaced from said tubes and from said shell, said tubes each passing through an orifice in said bafiie of a diameter larger than the diameter of each of said tubes.
References Cited in the file of this patent UNITED STATES PATENTS 596,874 Hand Ian. 4, 1898 827,479 Towne July 31, 1906 1,159,775 Kerr Nov. 9, 1915 2,181,486 Jenkins Nov. 28, 1939 2,447,259 Lucke Aug. 17, 1948 2,460,660 Tinker Feb. 1, 1949 2,461,636 Gaylor Feb. 15, 1949 2,498,145 Tinker Feb. 21, 1950 2,581,121 McCurdy et al Ian. 1, 1952 2,715,516 Reinold et a1. Aug. 16, 1955 FOREIGN PATENTS 514,948 Great Britain Nov. 22, 1939 OTHER REFERENCES National Carbon Company, Inc., Pamphlet-Catalog, July 1947, section M-8000-D; form No. CP-8M-7-47, pages 4 and 5.