EP2951523B1

EP2951523B1 - Shell and tube heat exchanger, end cover and method of manufacturing same

Info

Publication number: EP2951523B1
Application number: EP14701609.1A
Authority: EP
Inventors: Kevin HOWELL
Original assignee: E J Bowman (birmingham) Ltd
Current assignee: E J Bowman (birmingham) Ltd
Priority date: 2013-01-30
Filing date: 2014-01-23
Publication date: 2018-10-31
Anticipated expiration: 2034-01-23
Also published as: GB2510335A; GB2510335B; WO2014118511A1; ES2707951T3; EP2951523A1; CN105190219A; TWI683084B; GB201301613D0; PL2951523T3; TW201437600A

Description

The present invention relates to a shell and tube heat exchanger according to the preamble of claim 1 and to a method of manufacturing such heat exchangers. Such exchangers are known from US 3,804,161 . The preferred embodiments have particular applicability to shell and tube heat exchangers and heat exchangers used in a marine or otherwise corrosive environment.
Shell and tube heat exchanger are well known per se in the prior art and indeed many types of these heat exchangers are commercially available. A brief description of the operation of a shell and tube heat exchanger is now given with reference to the example shown by Figure 1; Figure 2A, showing a longitudinal cross-section of the heat exchanger of Figure 1; and Figure 2B, showing an exploded drawing of the heat exchanger of Figure 1. The heat exchanger 1 comprises an outer shell in the form of a generally cylindrical shell 5 with end covers fixed over each end of the shell 5. The shell 5 has an inlet 11 at one end and an outlet 12 at the other end. These are commonly referred to as shell side ports or nozzles. In the shell 5 there is disposed a tube stack 13. This comprises a plurality of tubes 14 extending longitudinally from one end of the shell 5 to the other. Tubes 14 are held in place by a tube plate 15 at either end, through which the tubes extend 14 and are fixed. This serves to hold the tubes 14 in place as well as providing a sealing engagement with the inner surface of the shell 5. Thus the tubes 14 provide a series of channels through the shell 5 which are sealingly kept separate from the conduit through the shell provided by the shell side ports, inlet 11 and outlet 12. One or more baffles 16 may be included in the tubestack 13 to guide the shell side fluid flow back and forth across the tubes 14, increasing velocity and heat transfer efficiency. The baffles 16 also serve to support the tubes 14 and prevent vibration.
The end covers 10 comprise generally circular plates having bolt holes spaced around the periphery. End covers 10 are bolted onto flanges at either end of the shell 5 via bolts 19 which screw into threaded holes 20 in the ends of the flanges. An O ring seal 22 is disposed between the end cover 10 and the flanges 21 at the ends of the shell 5 to help seal the end cover to the shell 5. End covers have internally threaded ports 24 providing an inlet and outlet 25,26 in fluid communication with the tubes in the tube stack 13. These ports are generally referred to as tube side ports.
A tube stack 13 can be floating to minimise thermal stresses or have a bellows construction. In operation, the fluid to be cooled is pumped through the shell 5 via shell side ports 11 and 12. A cooling fluid is pumped through the tubes 14 via tube side ports 25,26. The tubes 14 provide the heat transfer surface between one fluid flowing through the tubes 14 and the other fluid flowing across the outside of the tubes 14. Thus, heat can be exchanged between the two fluids.
The end cover may also have a further threaded hole 28 therethrough into which is screwed a drain plug 29. By unscrewing the drain plug 29 from the end cover 10, fluid can be drained from the tube side channel running through the heat exchanger 1.
Many variations of this basic example of a shell and tube heat exchanger 1 are known. For example, more than one tube side passes may be made by the tube side fluid. In this case, one or both end cover 10 may provide a pass divider to keep the fluid on different passes separate.
Shell and tube heat exchangers 1 are often used in a corrosive environment. For example, shell and tube heat exchangers 1 can be used with marine engines to cool various fluids associated with the engine. Figure 3 shows a typical arrangement showing the position of various heat exchangers 1 used in cooling a marine engine 500. Sea water is pumped through the tube side ports 25,26 as indicated by arrows 501. The fluid to be cooled from the exhaust manifold and oil coolers on the engine 500 are pumped in a closed loop through shell side ports 11,12 in the respective heat exchangers 1, as indicated by arrows 502, so as to be cooled by the sea water flowing through the tubes 14 in the heat exchangers 1.
As will be appreciated, using sea water as a cooling fluid means that the tube side conduit through the heat exchanger 1 must be corrosion resistant. End covers 10 are removable to allow the tubestack 13 to be removed and replaced if damaged or corroded. Currently, it is known to make the end covers 10 out of brass to resist corrosion. Figures 4A and 4B show an example of an end cover made of brass as known in the prior art. Naval brass, which comprises 40% zinc and 1% tin, is particularly preferred due to the resistance it exhibits against sea water corrosion. However, using brass as a material is relatively expensive, so a less expensive alternative would be beneficial.
Cast iron end covers are sometimes used with fresh water, i.e. not for use with contaminated water or sea water due to corrosion concerns. In less demanding applications, it is known to use plastics end covers, e.g. glass filled nylon. However, in many applications the pressure exerted on the shell side fluid as it is pumped through the heat exchanger means that a plastic end cover is not suitable as it may deform or break under the pressures exerted on it. Furthermore, inlets made from plastic may not be strong enough to support the coupling to external pipes channelling fluid to the tube side of the heat exchanger.
What is needed is an end cover that gives sufficient strength and rigidity for demanding applications, whilst retaining corrosion resistance to, for example, sea water, whilst being less expensive than using conventional materials such as naval brass. In particular, naval brass connections are preferable for the sea water inlet and drain plugs. The material used needs to be sufficiently rigid over the area of the bolt hole. The end cover should not deflect around the O ring sealing face up to pressures of 30 bar or more.
According to a first aspect of the present invention, there is provide a shell and tube heat exchanger according to claim 1.
The use of plastics keeps the cost of the end cover down as well as being corrosion resistant for applications where corrosive fluids are passed through the heat exchanger, e.g. sea water. The metal plate member provides structural rigidity to the plastics body and means that the end cover can cope with higher pressures than the plastics alone could cope with. The metal need not be corrosion resistance, since it can be fully enclosed by plastics, or at least mostly enclosed by plastics such that at least the parts of the metal plate that would come into contact with corrosive fluids are shielded. This creates an end cover at lower cost, which can cope with higher pressures and is corrosion resistant compared with prior art end covers for shell and tube heat exchangers.
Preferably the metal plate is between 0.5mm and 3mm thick.
Preferably the metal plate extends over the majority of the radial extent of the end cover.
Preferably the metal plate is formed from pressed steel, optionally having a zinc coating.
Preferably the metal plate member is generally dome shape having a flange at its periphery corresponding in position to the bearing face between the end cover and the shell.
In an embodiment, the end cover has a sealing face for bearing against the shell having two or more bolt holes for bolting the end cover to the shell, wherein the bearing face is bowed between the bolt holes so that it is resiliently biased against the shell when the end cover is bolted to the shell. The resiliency of the end cover means that the bowed portion is "sprung" against the shell, creating a better seal in the regions that are further away from the bolt holes and which therefore are not less directly clamped by the bolted connections. The degree of bowing preferably increases smoothly to a maximum height approximately centrally between the bolt holes. Preferably, the bowed portions are arranged so that a generally similar sealing pressure is maintained around the periphery of the end cover. This means that the end cover is advantageously capable of handling greater pressures for a given clamping force.
In an embodiment, the end cover comprises at least one metal insert adapted for receiving a fastener and being encased by the plastics body. This provides the means for more secure and reliable connections to be made to the end cover for whatever reason compared with connecting directly to the plastics material.
In an embodiment at least one metal insert is a port member providing an inlet to the tube side of the heat exchanger.
In an embodiment the port member is internally threaded for connection.
In an embodiment at least one insert provides has a threaded connection for receiving a drain plug.
Preferably at least one metal insert comprises a metal sleeve providing a through hole in bearing portion of the end cover, wherein a threaded fastener clamps the end cover to the shell of the heat exchanger through the metal sleeve. This helps achieve a greater clamping force without risking damage to the plastics material around outer periphery of the end cover and the bearing face.
In an embodiment, at least one metal sleeve mechanically interlocks with the metal plate member. This helps stabilise the metal sleeve during manufacture and also helps direct the forces from the bolted connection from the bolts to the metal plate, thereby relieving stresses on the plastic material.
In an embodiment, at least one metal sleeve has a circumferential groove around at least a portion of its exterior surface, and wherein the metal plate has at least one cut away portion at its periphery arranged to mechanically interlock with the circumferential groove. This is a preferred way of interlocking the sleeves with the plate.
In an embodiment, the plastics is overmoulded to the metal plate member and/or at least one metal insert.
In an embodiment, the insert is made from brass.
According to a second aspect of the present invention, there is provided a method of manufacturing a shell and tube heat exchanger as described above, the method comprising: positioning the metal plate member in an injection moulding tool and moulding plastics over the metal plate member.
Preferably, the heat exchanger comprises at least one metal insert adapted for receiving a fastener and being partially encased by the plastics body, the method comprising positioning the at least one metal insert on a dowel to precisely position the insert in the injection mounding tool before moulding plastics over the insert and metal plate member.
In an embodiment the metal inserts comprise plural metal sleeves providing through holes in the bearing portion of the end cover for clamping the end cover to the shell of the heat exchanger by threaded fasteners through the metal sleeves, the method comprising mechanically interlocking the metal sleeves with the metal plate member before moulding the plastics.
According to a third aspect of the present invention, there is provided an end cover for a shell and tube heat exchanger, the end cover comprising:

a plastics body;
a metal plate member encased by the plastics body to provide structural rigidity to the plastics body.

In embodiments, the end cover comprises the additional features of any embodiment described above.
Embodiments may have particular advantages when employed in methods of heat exchanging when the tube side passed through the heat exchanger is corrosive, such as sea water when used as a cooling fluid in a heat exchanger arranged to cool a marine engine or the like.
It will be appreciated that any features expressed herein as being provided "in one example" or as being "preferable" may be provided in combination with any one or more other such features together with any one or more of the aspects of the present invention.
Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 shows a prior art shell and tube heat exchanger;
Figure 2A shows a longitudinal cross section of a heat exchanger of Figure 1;
Figure 2B shows an exploded drawing of the heat exchanger of Figure 1;
Figure 3 shows heat exchangers being used to cool a marine engine;
Figures 4A and 4B show respectively a cross sectional view and plan view of a prior art end cover for a heat exchanger;
Figures 5A and 5B show respectively front and rear end views of an example of an end cover according to an embodiment of the present invention;
Figures 6A and 6B show respectively a longitudinal cross sectional view and end plan view of the port inserts of the end cover of Figures 5A and 5B;
Figures 7A and 7B show respectively longitudinal cross section and end plan view of the insert for the drain plug in the end cover of Figures 5A and 5B;
Figures 8A and 8B show respectively a longitudinal cross sectional view and end plan view of an insert for a drain plug of Figures 5A and 5B;
Figure 9A shows a plan view of the end cover of Figures 5A and 5B;
Figure 9B shows the end cover from the rear;
Figures 9C and 9D show cross sectional views of the end cover.
Figure 10 shows a perspective view of a steel pressing for the end cover of Figures 5A and 5B.

Figures 5A and 5B show example of an end cover 100 according to an embodiment of the present invention. Figure 5A shows a perspective view from the front, and Figure 5B shows a perspective view from the rear. The end cover 100 can for example be used with the shell and tube heat exchanger 1 in Figures 1 to 3. As the person skilled in the art will appreciate, many types of shell and tube heat exchanger are known, and the end cover 100 of the present invention can be modified to work with different designs of heat exchanger using well known principles.
The end cover 100 is a generally dome shaped member for attaching to and covering an end of the shell 5 of the heat exchanger and having a tube side port 101 which can be used as an inlet or outlet as desired and depending on which end of the shell 5 it is attached. Referring to Figure 5B which shows the end cover 100 from the rear (i.e. from the shell side), the end cover 100 has a central dome portion 106 surrounded by a sealing face 107 around the periphery of the dome portion 105 which bears against and creates a seal with the end of the shell of the heat exchanger 10. The end cover 100 has three bolt holes 102 through the sealing face 107 for bolting the end cover 100 to the shell 5 of the heat exchanger 1. The end cover 100 also has an optional hole for a drain plug 103.
Still referring to Figure 5B, the rear of the end cover 100 has an internal lip 108 for receiving the tube stack of the heat exchanger 1. The rear of the end cover 100 also has a central rib 109 adjacent the port 101 which extends from the surface of the central dome portion 106 towards the shell 5 and which helps channel the fluids going through the heat exchanger 1.
The end cover 100 comprises a thin metal member 110 moulded into a plastics or plastics composite body 105. Preferably glass filled nylon is used for the plastics moulding to form the plastics body 105. 50% GFN or any other suitable moulded plastic and plastic composite material can be used. The thin metal member 110 is shown by Figure 10. The thin metal member 100 has a dome shaped central portion and a planar peripheral flange, corresponding to the dome shape 106 and sealing face 107 of overall end cover 100. The thin metal member 110 is preferably a mild steel pressing, which is optionally zinc plated to give improved chemical resistance. Inserts 115,120,125 are moulded into the plastic to reinforce the various holes 101,102,103 in the end cover 100.
The tube side port 101 has an internally threaded insert 115 is moulded into the plastic body of the end cover 100. Insert 115 is shown by Figures 6A and 6B. As can be seen, the insert 115 comprises a generally tubular body 116 with internal threading 117 to provide the female connection to the inlet port 101. The tubular body 116 has a flanged end 118 and axial ribs 119 to help secure the insert 115 in position in the moulded plastic body. The insert 115 is preferably made from brass or some other strong, corrosion resistant material.
Similarly, the drain plug 103 has an insert 120 comprising a generally tubular body 121 having a threaded internal surface 122. The body 121 also has a flange 123 at one end and optionally ribs or other external features to help prevent the insert 120 from moving in the moulded plastic. The inserts are shown by Figures 8A and 8B. The insert 120 is preferably made from brass or some other strong, corrosion resistant material.
Reinforcing inserts 125 are also provided for the bolt holes 102. The inserts 125 are shown in plan view and cross section by Figures 7A and 7B. The insert 125 comprises a generally tubular body 126 extending through the bolt hole 102. The insert 125 also has one or more circumferential grooves in the body 126 which can help keep the insert 125 in position in the moulded plastic body. The inserts 125 are preferably made from metal.
Referring back to Figure 10, the dome shaped metal insert 110 is preferably between 0.5mm and 3mm thick, 1.5mm thick in this example, with a 5mm radius bottom flange 111 corresponding to the sealing face of the end cover 100 to provide extra support. The flange 111 preferably has cut-out portions 112 for supporting the bolt hole inserts 125. The cut-outs 112 form generally semi-circular insets in the thin metal member 110 which fit into the grooves 127 in the inserts 125. This allows forces from the bolted connection to be transmitted via the bolt hole inserts 125 to the dome shaped steel member 110, thus distributing stresses across the entirety of the end cover 100.
The dome shaped member 110 also has additional cut-outs 113 corresponding to the location of the tube side port inserts 115 and the drain plug inserts 120, so that these inserts can project through the member 110.
Figures 9A and 9B show plan views of the end cover from the front and rear respectively, and Figures 9C and 9D show cross sections taken along lines A-A and B-B. These show the positioning of the various inserts within the plastics body.
Referring to Figure 9B, the sealing face 107 is preferably generally planar but bows outward slightly in the areas 107a between the bolt holes 102 in the direction towards the shell 5. In this way, when the cover 100 is clamped to the shell 5 of the heat exchanger 1 by the bolts, the bowed portions 107a are resiliently biased against the shell of the heat exchanger 1. This helps create a good seal all around the periphery of the end cover 100 and particularly in the areas of the sealing face 107 that are further away from the clamping force of the bolts.
In order to manufacture the end cover 100, the dome shaped metal member 110 and the five inserts 115,120,125 for the bolt holes, drain plug insert and tube side port can be assembled inside an injection moulding tool and then the six parts completely encased in a plastics moulding, preferably a 50% glass filled nylon, to give the end cover 100. Precision dowels in the injection moulding tool are used to hold the bolt hole inserts to improve the accuracy of the bolt hole circle. Further dowels can be used for the tube side port inlet insert 115 and the drain plug insert 120. As described above, the dome shaped member 110 preferably engages with the circumferential grooves 127 on the bolt hole inserts 125, and is thus held in position within the injection moulding tool.
Thus an end cover 100 is provided that is relatively simple and inexpensive to manufacture, while retaining the advantages of using a completely naval brass end cover. In particular, brass connections and preferably naval brass connections are provided for the port insert 115 and drain plug insert 120. This is beneficial in preventing corrosion when sea water is pumped through the tubes of the heat exchanger 1 via these ports and to provide a strong corrosion resistant threaded connection to the male connection to the heat exchanger 1. At the same time, the use of relatively expensive brass is minimised. The plastic used for the main body of the end cover is reinforced by the steel pressing 110. The steel pressing 110 provides rigidity to the end cover 100 by which the plastic alone cannot provide. The end cover 100 can thus be used in high pressure applications (e.g. in preferred embodiments up to 20 bar operating pressure and tested to 30 bar) without deflecting around the O ring sealing face of the shell. The arrangement of bolt hole inserts 125, preferably interlocking with the steel pressing 110, provides rigidity around the bolt hole clamping and distributes stress throughout the end cover 100. Accordingly, a low cost and simple to manufacture end cover 100 is provided by the preferred embodiment of the present invention that can be used with high pressure, high corrosive applications such as heat exchangers for marine engines and the like.
Embodiments of the present invention have been described with particular reference to the example illustrated. However, it will be appreciated that variations and modifications may be made to the examples described within the scope of the present invention.

Claims

A shell and tube heat exchanger comprising:
a shell (5) containing a tube stack (13), a shell inlet (11) and a shell outlet (!2) by which fluid to be cooled can be made to flow across the tubes (14) in the tube stack (13); and

at least one dome-shaped end cover (100) attached to an end of the shell (5), the end cover comprising:
a plastics or plastic composite body; at least one port (115) in the end cover in fluid communication with the tubes (14) of the tube stack by which a cooling fluid can be made to flow in the tubes, the shell and tube heat exchanger being characterised by

a metal plate member (110) completely encased by the plastics body to provide structural rigidity to the plastics body.
A heat exchanger according to claim 1, wherein the metal plate (110) extends over the majority of the radial extent of the end cover.
A heat exchanger according to claim 1 or claim 2, wherein the metal plate (110) is formed from pressed steel, optionally having a zinc coating.
A heat exchanger according to any of claims 1 to 3, wherein the metal plate member is generally dome shape having a flange (111) at its periphery corresponding in position to the sealing face between the end cover and the shell.
A heat exchanger according to any of claims 1 to 4, wherein the end cover (100) has a sealing face for bearing against the shell having two or more bolt holes for bolting the end cover to the shell, wherein the bearing face is bowed between the bolt holes so that it is resiliently biased against the shell when the end cover is bolted to the shell.
A heat exchanger according to any preceding claim, comprising at least one metal insert (120) adapted for receiving a fastener and being encased by the plastics body.
A heat exchanger according to claim 6, wherein at least one metal insert is a port member providing an inlet to the tube side of the heat exchanger.
A heat exchanger according to any of claims 6 to 7, wherein at least one metal insert comprises a metal sleeve (125) providing a through hole in bearing portion of the end cover, wherein a threaded fastener clamps the end cover to the shell of the heat exchanger through the metal sleeve.
A heat exchanger according to claim 8, wherein at least one metal sleeve mechanically interlocks with the metal plate member.
A heat exchanger according to claim 9, wherein at least one metal sleeve has a circumferential groove (127) around at least a portion of its exterior surface, and wherein the metal plate has at least one cut away portion (112) at its periphery arranged to mechanically interlock with the circumferential groove.
A heat exchanger according to any preceding claim, wherein the plastics is overmoulded to the metal plate member and/or at least one metal insert.
A heat exchanger according to any preceding claim, wherein the insert is made from brass.
A method of manufacturing a shell and tube heat exchanger according to any preceding claim, the method comprising: positioning the metal plate member in an injection moulding tool and moulding plastics over the metal plate member.
A method according to claim 13, wherein the heat exchanger comprises at least one metal insert adapted for receiving a fastener and being partially encased by the plastics body, the method comprising positioning the at least one metal insert on a dowel to precisely position the insert in the injection mounding tool before moulding plastics over the insert and metal plate member.
A method according to claim 14, wherein the metal inserts comprise plural metal sleeves providing through holes in the bearing portion of the end cover for clamping the end cover to the shell of the heat exchanger by threaded fasteners through the metal sleeves, the method comprising mechanically interlocking the metal sleeves with the metal plate member before moulding the plastics.