US3776302A

US3776302A - Tube and shell heat exchanger

Info

Publication number: US3776302A
Application number: US00225810A
Authority: US
Inventors: R Waszink; M Purnell
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1972-02-14
Filing date: 1972-02-14
Publication date: 1973-12-04
Anticipated expiration: 1990-12-04
Also published as: FR2172170B1; IT979102B; FR2172170A1

Abstract

A tube and shell heat exchanger in which a tube bundle and an encompassing tubular liner extend downwardly into an enlarged main pressure vessel. The lower end of the tube bundle is freely movable during linear expansion in operation and a tubular flow guide at the lower end of the tube bundle is employed in a manner to maintain a predetermined liquid level in the main pressure vessel. The upper end of the tube bundle is supported in a second pressure vessel superimposed on the main vessel and communicating therewith.

Description

United States Patent 1 1 [111 3,776,302

Waszink et al. 1 11 Dec. 4, 1973 [54] TUBE AND SHELL HEAT EXCHANGER 3,635,287 1 1972 Spregue 165/158 x [75] Inventors: Remco P. Waszink, St. Petersburg; 11/1965 Schllt Michael G. Purnell, Tampa, both of Fla.

1/1970 Byerley Primary Examiner-Manuel A. Antonakas 173] Assignee: Westinghouse Electric Corporation, y- Stratum i Pittsburgh, Pa. 22 Filed: Feb. 14, 1972 [571 ABsTRALT A tube and shell heat exchanger in which a tube bun [21] Appl' dle and an encompassing tubular liner extend downwardly into an enlarged main pressure vessel. The 52 us. c1. 165/82, 165/160 lower n of the tube bundle is freely movable during [51] Int. Cl F28f 19/00 linear expansion in Operation and a tubular flow guide 58 Field Of Search 165/157, 158, 160, at t lower end of the tube bundle is p y in a 165/82; 122/32, 34 manner to maintain a predetermined liquid level in the main'pressure vessel. The upper end of the tube bun- 56] Refer Ci dle is supported in a second pressure vessel superim- UNITED STATES PATENTS posed on the main vessel and communicating thereth. 3,126,949 3/1964 Boni, Jr. et a1. 165/158 e p w 2,978,226 4/1961 White 165/82 10 Claims, 4 Drawing Figures O Eiiifiirt 0 VOLUME 34 '58

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31 ,51 II'IM 111 37 33 MINIMUM LEVEL C t 36 k2 L 52 E3? j 32 29 57 s a 1% PATENIEDUEC 4191a 3.776302 SHEET 3 [IF 3 r ll/[1],,

TUBE AND SHELL HEAT EXCHANGER BACKGROUND OF THE INVENTION Heat exchangers of the tube-and-shell type charac- I teristically employ a bundle of tubes, either of the hairi to move in a direction parallel to the axes of the tubes.

Also, when a tube-and-shell heat exchanger is employed to provide transfer of heat between two liquids, provision must be made for free surface venting of retained gases from the heated or primary liquid after undergoing cooling by transfer of heatto a cooler or secondary liquid.

In such a heat exchanger, the entire heat transfer area must be maintained substantially constant at all times, while provision is made for large thermalexpansion of the primary liquid.

Since the inlet and outlet temperatures of the primary fluid vary widely, the nozzle temperatures vary accordingly, and to minimize thermal stresses in the regions of shell penetration by the nozzles, the shell temperatures should be maintained at substantially the same temperature as the nozzles in the immediate area.

For maximum integrity, the entire heat exchanger structure is preferably welded. However, in theevent that servicing is required, ready access to the internal structure such as the tubes, tube sheets, baffles, etc. is required with minimal cutting of the external sheet structure.

This invention provides a heat exchanger arranged in amanner to advantageously solve all of the above problems in a simple yet highly reliable manner.

SUMMARY OF THE INVENTION In accordance with the teachings of this invention there is provided a heat exchanger of the tube and shell type in which the shell comprises an enlarged lower main pressure vessel disposed beneath a smallerupper pressure vessel and in fluid communication by way of an elongated tubular liner that encompasses a heat exchange tube bundle and directs primary heating fluid from an inlet in the upper vessel past the tube bundle to the lower vessel. The tubes are supported at their uppermost ends by a fixed tube sheet and channel head structure and are connected at their lowermost ends to a floating tube sheet and channel head structure.

The lowermost end of the tube liner communicates with an upwardly extending flow guide that encompasses the liner and has an annular series of upper openings acting as outlets for the primary fluid into the lower vessel.

The primary fluid outlet is disposed at the bottom of the lower vessel to facilitate complete drainage of the fluid when required, but in operation, a predetermined level of the fluid is maintained in the vessel by the flow guide and the entire space encompassed by the tube liner is filled with primary fluid to enhance heat transfer to the tubes.

The lower tube sheet is of annular shape with a central opening and has the lower end of an elongated downcomer tube attached thereto in fluid communication with the lower channel head, so that, in operation, secondary fluid is directed through the downcomer to the lower channel head and then upwardly through the tubes to the upper channel head and out of the heat ex changer by way of a secondary fluid outlet nozzle.

A further feature of the invention resides in the provision of tube support plates that are of disc shape and of substantially the same diameter as the internal diameter of the liner, which plates are provided with flow holes adjacent each of the tube support holes to distribute the flow of primary fluid in a uniform manner with respect to the heat exchange tubes.

Although any two fluids may be employed for heat exchange, such as liquid-to-liquid, liquid-to-gas and/0r gas-to-gas, in the embodiment disclosed both fluids are preferably liquid with the primary fluid being the heated liquid and effectively to impart heat to the second liquid.

BRIEF DESCRIPTION OF THE DRAWINGS DETAILED DESCRIPTION OF THE INVENTION Referring to the drawings in detail, and especially FIG. 1, there is shown a heat exchanger 10 of thetype known as the tube and shell type, and having a bundle of heat exchange tubes 12 secured at the upper and lower ends through suitable holes. in an upper and a lower tube sheet 14 and 16. The upper tube sheet 14 cooperates with a generally hemitoroidal channel head 18 to form an annular chamber 19 while the lower tube sheet 16. cooperates with a generally hemispherical channel head 20 to .form a chamber 2 2.

The upper channel headand'tube sheet structure 19, 14is carried by an :upper pressurevessel 24of circular shape peripherally attached atits lower end 25 to an elongated cylindrical liner 26. The liner 26 encompasses the bundle of tubes 12, but has its upper peripheral edge portion 27disposed in spaced relation with the upper sheet 14to define an annular inlet 28, and its lower edge portion 29 disposed in slidable abutment with the circular periphery of the lower tube sheet 16.

A cylindrlcal flow guide 30 is disposed in radially spaced encompassing relation withthe liner 26 and has an upper inturned'peripheral flange 31. The flow guide is connected at its loweredge portion to the lower edge 29 of the liner by an annular bottom wall member 32, thereby to define an annular flow passageway 33. Fluid communication betweenthe inner space 34 and the passageway 33 is provided by a plurality of openings 36 formed adjacent the lower edge 29 of the liner. Also, an annularseries of windows 37 in the upper portion of the flow guide 30 are provided to serve as fluid outlets for the passageway 33.

An enlarged main pressure vessel 38 is disposed be neath the upper pressure vessel 24 and defines an enclosed pressure tight chamber 39. The vessel 38 has a cylindrical side wall 40, an upper end bell 41 and a lower end ball 42 welded to each other in a fluid tight manner, and the upper end bell 41 has a circular opening 44 through which the tubes 12 and the liner structure 26 extend downwardly into the chamber 39. The

liner 26 is connected to the end bell 41 in a leakproof manner, such as by a weld joint 44a. Accordingly, the entire structure heretofore recited is supported by the main vessel 38 in this manner.

The upper pressure vessel 24 is provided with a primary inlet nozzle 46 through which a primary heated fluid is admitted and the lower end bell 42 is provided with a primary outlet nozzle 48 through which the cooled primary fluid is withdrawn.

Cool secondary fluid is admitted to the lower channel head by a downcomer tube 50 extending through a central passage 51 in the hemitoroidal channel head 18 and downwardly through the tube bundle with its lowermost end portion 52 in sealing abutment with the annular tube sheet 16 and in registry with a central open ing 53 therein.

The tubes 12 are arranged in concentric circular rows, as shown in FIGS. 3 and 4, to form a tube bundle that is devoid of tubes at its center, and the downcomer tube 50 extends downwardly through the center of the tube bundle in centrally spaced relation with a tubular inner wall member 55. The inner wall 55 extends upwardly into sealing abutment with the upper tube sheet 14 at its upper end portion 56 and downwardly into sealing abutment with the lower tube sheet 16 at its lower end portion 57. In this manner, the downcomer 50 is insulated by the annular air space 58 from the inner tubular wall 55 so that the incoming cool secondary fluid flow therethrough is substantially prevented from premature heating by the hot primary fluid flow past the tubes. This is especially important when the secondary fluid is a liquid, since it could be susceptible to premature boiling.

The tubes 12 are supported intermediate their ends in their predetermined positions by a plurality of tube support plates 60. The plates 60 are of disc shape with their outer periphery 61 in substantial abutment with the inner surface 62 of the tubular liner 26 and with their inner periphery 63 in substantial abutment with the outer surface'65 of the inner wall member 55.

The plates 60 are provided with circular tube openings 66 through which the tubes 12 are slidably received, thereby to maintain the tubes in proper position with minimal vibration during operation. In addition, the plates 60 serve as flow baffles and are provided with a plurality of concentric circular rows of fluid flow openings 68, The flow openings 68 constitute the dominant flow passages for the primary fluid flow past the tubes and are further arranged in radial pairs 68a between adjacent pairs of tube openings 66, so that for each tube 12 there is a corresponding pair of openings 68a. Expressed in another manner, each tube opening 66 is flanked by two pairs of flow openings 68a which it shares with its neighboring tube openings, so that the primary fluid flow past each tube 12 may be considered as comprising four streams uniformly distributed about each tube and effective to provide substantially uniform heat exchange between the heated primary fluid flowing about the tubes and the cool secondary fluid flowing through the tubes.

In the embodiment shown, the primary and secondary fluids are both liquids, with the primary liquid acting as the heating liquid and the secondary liquid acting as liquid to be heated.

' During operation, hot primary liquid from any suitable source (not shown) is admitted into the vessel 24 by the primary nozzle 46 and flows downwardly into the liner space 34 into good heat exchange relation with the tubes 12 and through the flow openings 68 in the plates 60. The primary liquid cools as itloses its heat to the secondary liquid flow in the tubes 12, and at the end of its downward flow it is directed through the openings 36 and up through the passage 33 into the chamber 39 by way of the outlet windows 37. As the liquid exits through the windows 37, it flows in downwardly direction due to gravity, -i.e., it undergoes a reversal of direction. During such reversal any entrapped gases in the liquid become separated from the liquid and are collected in the gas space 38a above the level LM of the primary liquid. The level LM is the minimum level of the primary liquid, while the maximum level LE may be attained during operation because of thermal expansion.

The cool secondary liquid is concomitantly admitted by the downcomer 50 to the lower channel head chamber 22 and then flows upwardly through the tubes 12 in counterflow relation with the primary liquid flow, being heated during transit, and exits via the upper channel chamber 19 through the secondary liquid outlet nozzle 70.

As previously pointed out, as the tubes 12 become heated by the primary liquid, they undergo thermal elongation to about the same degree as the inner wall member 55. However, the floating channel head and tube sheet 20, 16 is free to slide within the liner 26 with minimal stress.

In the event that the heat exchanger unit 10 requires servicing, such as to replace or repair one or more of the tubes 12 for example, the entire primary liquid contents may be dumped from the system through the outlet nozzle 48. In this connection, a plurality of suitable drain holes may be provided at the bottom of the upper vessel,and a plurality of suitable drain holes 77 may be provided at the bottom of the flow guide 30. These drain holes are sufficiently small to have an insignificant effect during normal operation.

After drainage, the entire tube bundle and channel head structure may be removed for ease of servicing by making a peripheral cut around the circumferential wall 72 of the upper vessel either above or below the primary inlet nozzle 46.

Also, since the heat exchanger unit 10 is intended to operate in an upright position, a plurality of mounting brackets 71 are attached to the casing 40 in peripherally spaced relation.

Weclaim as our invention:

1. A heat exchanger comprising a first vertically disposed cylindrical pressure vessel defining a chamber and having an upper opening, a vertically elongated cylindrical liner extending downwardly through said upper opening into said pressure vessel, a second pressure vessel disposed above said first pressure vessel and having a lower opening, said liner having its upper portion extending through said lower opening, a first channel head and tube sheet structure connected to the upper portion of said second pressure vessel, a second channel head and tube sheet structure disposed adjacent the lower end of said liner, a plurality of heat exchange tubes connected to said upper and lower tube sheets in fluid communication with said upper and lower channel heads, a tubular flow guide disposed in encompassing relation with said liner, a first inlet nozzle disposed in said second pressure vessel for admitting a primary fluid into said second pressure vessel and into good heat exchange relation with said tubes, means for directing said primary heated fluid into said flow guide, said flow guide being closed at its bottom end and having at least one outlet in its upper portion communicating with said chamber, a first outlet nozzle disposed in said first pressure vessel for removing said primary fluid from said chamber, a second inlet nozzle disposed in fluid communication with said lower channel head for admitting a secondary fluid into said lower channel head, and a second outlet nozzle disposed in fluid communication with said upper channel head, for removing said secondary fluid from said upper channel head.

2. The structure recited in claim 1 wherein said second channel head and tube sheet structure is in axially slidably disposed relation with the lower portion of said liner to permit free thermal elongation and contraction of the heat exchange tubes in operation.

3. The structure recited in claim 1, in which said second inlet nozzle comprises a downcomer tube extending downwardly through said upper channel head and tube sheet structure into fluid communication with said lower channel head and tube structure.

4. The structure recited in claim 3 in which said upper channel head and tube sheet has a central opening and said lower tube sheet has an opening, and fur ther including an inner tubular wall member extending therebetween and in sealing relation therewith, said downcomer tube being encompassed by said inner wall. 5. The structure recited in claim 4 in which said inner wall is disposed in annularly spaced relation with said downcomer tube.

6. The structure recited in claim 1 and further including a plurality of baffle plates through which said heat exchange tubes extend, said baffle plates being of circular shape and closely fitted to the inner wall of said liner.

7. The structure recited in claim. 6 in which said baffle plates are provided with a first group of tube openings through which the heat-exchange tubes extend in closely fitting relation, and a second group of flow openings to permit flow of the primary fluid in downward direction past said tubes.

8. The structure recited in claim 7 in which at least two flow openings are provided adjacent each of the tube openings.

9. The structure recited in claim in which said flow guide has an inturned annular flange at its upper end disposed in abutment with said liner and said outlet is disposed below said flange.

10. The structure recited in claim 9 in which said last mentioned outlet includes an annular series of outlet windows for said primary fluid.

Claims

4. The structure recited in claim 3 in which said upper channel head and tube sheet has a central opening and said lower tube sheet has an opening, and further including an inner tubular wall member extending therebetween and in sealing relation therewith, said downcomer tube being encompassed by said inner wall.

5. The structure recited in claim 4 in which said inner wall is disposed in annularly spaced relation with said downcomer tube.

7. The structure recited in claim 6 in which said baffle plates are provided with a first group of tube openings through which the heat exchange tubes extend in closely fitting relation, and a second group of flow openings to permit flow of the primary fluid in downward direction past said tubes.

9. The structure recited in claim 1 in which said flow guide has an inturned annular flange at its upper end disposed in abutment with said liner and said outlet is disposed below said flange.