MULTI-DISC HEAT EXCHANGER

Abstract: A hollow disc for use in a heat exchanger comprises a pair of plates (1) connected at their outer periphery (2) and spaced apart adjacent their centres (3). Each plate (1) is corrugated annularly with at least one corrugation (5). The two plates are held together intermediately by means of a single ring of stay bolts (6) affixed to and between the plates.

Description: MULTI-DISC HEAT EXCHANGER The present invention relates to a heat exchanger, to discs for use therein, and to a method of making such discs. It is known to produce multi-disc heat exchangers in which a plurality of discs are fixed to a ' longitudinally extending rotor. Each disc is hollow and communicates with a passage in the rotor for a heat exchange medium, such as steam, to pass to and from each disc. The discs are generally formed from a pair of annular stainless steel discs welded together at their outer edge and fixed to the rotor at their inner edge to be spaced one from another whereby the cross section of each disc is essentially a double cone. The plates are held together by at least two rings of stay bolts, perhaps even four, each ring generally having 36 bolts welded between the plates. Such discs may often fail because of failure in the stay bolts. The pressure within the hollow disc then compounds the problem. it is an object of the present invention to provide a disc for a heat exchanger which overcomes such disadvantages. According to a first aspect of the present invention there is provided a hollow disc for use in a heat exchanger comprising a pair of plates connected at their outer periphery and spaced apart adjacent their centres, each plate being corrugated annularly with at least one corrugation. Preferably there are two annular corrugations. The two plates are preferably held together by means of a single ring of stay bolts affixed to and between the plates. The corrugations may project externally of the disc. Alternatively they may project internally into the disc. In this latter case, the, one or both corrugations may have the internal surfaces of respective plates joined e.g. by welding at these points. According to a second aspect of the invention there is provided a method of manufacturing a heat exchange disc comprising the steps of providing a pair of generally frustoconical rollers, one roller of said pair having at least one portion of increased diameter and the other of said pair having a corresponding portion of decreased diameter; providing a generally dish shaped annular disc of material; arranging said rollers so that their contact faces extend along a line generally at the same angle to horizontal as that between the base and the edge of the dished plate; and rotating at least one of said pair of rollers, whereby the disc is deformed to have at least one corrugation. According to a third aspect of the invention, there is provided a stay bolt for a hollow heat exchange disc comprising a stem having shoulder means adapted to contact respective interior surfaces of the disc around stay bolt holes in the plates forming the disc, to form a backing during subsequent welding. The two shoulder means of each stay bolt are preferably angled, one with respect to the other, at an angle which corresponds substantially to the angle between the plates of the disc . According to a fourth aspect of the invention there is provided a heat exchanger comprising a plurality of hollow discs of substantially double conical cross-section into which a pressurised heat exchange medium may be fed and which may> be rotated in contact with a material to be treated, each of said discs comprising a pair of substantially annular plates each having at least one corrugation extending substantially concentrically about the plate, and a plurality of stay bolts arranged along a concentric circle at a median radius to connect the plates together. Preferably, any or all of the above aspects may be used in combination. An embodiment of the invention will now be more particularly described by way of example and with reference to the accompanying drawings, in which: FIGURE 1 is an elevation of a disc embodying the invention; FIGURE 2 is a part cross sectional view of the disc of Figure 1; FIGURE 3 is a side elevation of a stay bolt embodying the invention; and FIGURE 4 is a . side elevation of a roller for use in the method of the invention. Referring now to the drawings, Figures 1 and 2 show a heat exchange disc. It is constructed from two annular discs 1 of stainless steel, approximately 8mm thick. These are joined together around their periphery by a fillet weld 2. At their interior periphery, i.e. around the central aperture 3, each plate is welded to a stainless steel tube 4, acting as a rotor axis, spaced one from another. In a heat exchanger, a plurality of such hollow discs are connected to the rotor axis along its length. Steam, possibly at a pressure of 6-7 bar is fed into one end of the rotor axis and thence through connecting holes into each disc. The assembly is rotated within a container for the material to be treated. The steam condenses within the discs and the water is directed back into the rotor axis. Problems have been encountered with the plates of some discs bulging apart because of the high pressure within them. Hitherto, it has been usual to locate seventy-two stay bolts, arranged in two concentric circles, between the plates. However, these bolts are liable to give, not as may be expected, by failure of the weld joining them to the plate, but by fracture within the head of the bolt. The present invention seeks to overcome this problem in two ways. Firstly, the profile of each plate is corrugated annularly to improve its stiffness. Secondly, the design of stay bolt has been improved. This enables discs to be used which have only thirty-two stay bolts. Each plate 1 is formed with two annular corrugations 5. In the embodiment shown, these extend externally of the general plane of the plate, but it is possible to make them internal. These increase the stiffness of the plates to such an extent that only one circle of thirty-two stay bolts 6 are required. They are located between the two corrugations and their design is shown more clearly in Figure 3. Each bolt 6 comprises a stem 7 and two shouldered heads 8. The heads 8 are angled one with respect to the other to correspond with the angle of the plates 1 of the disc 2. It is thus important that they are oriented correctly. Each head 8 comprises a shoulder 9 intended to contact an interior face of the plate 1. An angled head 10 is intended to fit within a hole in the plate. The weld material, when applied from the outside of the disc will fill the triangular cross section space and the shoulder 9 acts as a backing, helping to prevent coking. The joint thus formed is far less prone to failure than existing stay bolt welds. In order to produce the corrugated profile of each plate, an annular dished plate is rolled between a pair of shaped rollers. One of them, 11, is shown in Figure 4. The other corresponds in a reverse manner. Each roller has a generally frustoconical shape with sides angled to correspond to the angle the plate will assume when connected into a disc. The roller shown has two annular protruberances 12, which act to form the corrugations 5 when the plate is rolled between the roller 11 and the complementary roller (i.e. having corresponding annular grooves). As may be seen, the use of more highly engineered stay bolts makes each one more expensive but allows a dramatic decrease in their number. This also saves on welding time and costs. The corrugations of the plates increases their stiffness so that the lesser number of finely welded stay bolts can hold the plates together, and give them increased resistance to bursting. The design of the stay bolts is such that they are less prone to cracking, which can lead to failure, than the bolts used hitherto.

Claims: C L A I S 1. A hollow disc for use in a heat exchanger, comprises a pair of plates connected at their outer periphery and spaced apart adjacent their centres, each plate being corrugated annularly with at least one corrugation. 2. A disc as claimed in Claim 1, wherein there are two annular corrugations. 3. A disc as claimed in either Claim 1 or Claim 2, where the two plates are held together by means of a single ring of stay bolts affixed to and between the plates. 4. A disc as claimed in any one of the preceding claims, wherein the corrugations project externally of the disc. 5. A disc as claimed in any one of Claims 1 to 3, wherein the corrugations project internally into the disc. 6. A disc as claimed in Claim 5, wherein the, one or both corrugations have the internal surfaces of respective plates joined e.g. by welding at these points. 7. A method of manufacturing a heat exchange disc comprises the steps of providing a pair of generally frustoconical rollers, one roller of said pair having at least one portion of increased diameter and the other of said pair having a corresponding portion of decreased diameter; providing a generally dish shaped annular disc of material; arranging said rollers so that their contact faces extend along a line generally at the same angle to horizontal as that between the base and the edge of the dished plate; and rotating at least one of said pair of rollers, whereby the disc is deformed to have at least one corrugation. 8. A stay bolt for a hollow heat exchange disc comprises a stem having shoulder means adapted to contact respective interior surfaces of the disc around stay bolt holes in the plates forming the disc, to form a backing during subsequent welding. 9. A stay bolt as claimed in Claim 8, wherein the two shoulder means of each stay bolt are angled, one with respect to the other, at an angle which corresponds substantially to the angle between the plates of the disc. 10. A heat exchanger comprising a plurality of hollow discs of substantially double conical cross-section ■ into which a pressurised heat exchange medium may be fed and which may be rotated in contact with a material to be treated, each of said discs comprising a pair of substantially annular plates each having at least one corrugation extending substantially concentrically about the plate, and a plurality of stay bolts arranged along a concentric circle at a median radius to connect the plates together.

Inventors: WYKES DAVID JOHN, WYKES, DAVID, JOHN
Applicants: WYKES ENGINEERING CO RUSHDEN L, WYKES ENGINEERING CO. (RUSHDEN) LTD.
Application year: 1993
Main classification: F28D11
IPC codes: F28D11