ROTARY REGENERATIVE HEAT EXCHANGER WITH SLIDING SHOES

Abstract: A rotary regenerative heat exchanger has a rotor containing a regenerative mass and rotating in a stationary casing. Movable sector plates (6, 8) are arranged at each end of the rotor at a short distance (S) therefrom in order to sealingly separate media ducts. Each sector plate (6, 8) is supported by a pair of support means (10) including sliding shoes (17), which slide on an end surface (11) on a flange (9) at the outer periphery of each rotor end. Portions of the rotor flange (9) might slant, causing misalignment of the sliding shoes (17). According to the invention this problem is overcome in that each sliding shoe (17) is movably mounted in the sector plate (6) allowing the sliding shoe (17) to tilt around a tilting point (0) so that the sliding shoe (17) adapts to the local deviations of the end surface (11) on the rotor flange (9) from the plane perpendicular to the rotor axis.

Description: ROTARY REGENERATIVE HEAT EXCHANGER WITH SLIDING SHOES. The present invention relates to a rotary regenerative heat exchanger of the kind specified in the preamble of claim 1. SE 176 375 discloses a rotary regenerative heat exchanger with a support in the form of rolling bodies, mounted in the outer ends of sector-shaped plates close to both ends of the rotating part and rolling on a flange along the periphery at the top and bottom end of the rotor. It was therethrough intended that a constant clearance should be possible to be maintained between the ends of the sector-shaped plates and the top and bottom end, respectively. The environment for the rollers, however, was found to be to severe. The bearings of the rollers were worn out rapidly and dirt and particles were by the rolling adhered on the flanges and the surfaces of the roller with break downs as a consequence. It has been suggested to replace the rollers by sliding shoes as disclosed in JP, A, 63-315 891. These sliding shoes are made of ceramics in order to attain a high wear resistance. Some kind of external lubrication of the sliding surfaces is required or considerable friction losses has to be accepted. In WO94/01730 an improvement is disclosed by using sliding shoes of carbon or graphite instead of ceramic sliding shoes. Such a sliding shoe eliminates the drawbacks with a sliding shoe of ceramics. In particular graphite has excellent lubrication properties and like carbon has an ability to maintain the flanges of the rotating body clean when adhering a lubricating layer of carbon or graphite on the flanges. Carbon and graphite also have a good acceptance of the high temperature and the acid environment that are present. By the abrasion of the sliding shoes they will gradually be consumed and have to be replaced. The degree of abrasion, however, will vary widely, so that one or more sliding shoes might be worn down so much that the clearance reaches zero, whereas other sliding shoes will be almost unaffected. Each sliding shoe therefore is adjustable in a direction perpendicular to the contact surface. A similar solution is disclosed in WO95/00809, in which there is provided a measuring rod adjacent to the sliding shoe, which measuring rod is directed parallel to the adjustment direction. The measuring rod from a resting position can be momentary brought in contact with the related flange and indicates when the size of the clearance requires advancement of the sliding shoe a distance so that the initial clearance is restored. Another solution is disclosed in SE 9302301-8 in which the abrasion problems are overcome in that the sliding shoe is sliding on a gas cushion created by the supply of pressure gas between the sliding shoe and a flange on the rotor. Abrasion thereby is avoided in that there will be no contact between the sliding shoe and the flange. Each rotor flange has a circumferentially continuous end surface on which the sliding shoes slide. Due to inaccuracy and/or thermal deformations of the rotor flange this end surface often deviates from a planar shape. The surface in practice has waves in the circumferential direction and is therefore perpendicular to the rotor axis only at the tops and bottoms of these waves, whereas it in other parts is slightly inclined. The front surface of each sliding shoe when travelling along the end surface therefore in some parts will be parallel to and in other parts be inclined in relation to the co-operating part of the end surface. It might also be the case that the rotor flange and therewith also the end surface slants in the radial direction so there will not be parallelity between a front surface of a sliding shoe and the end surface neither in the radial direction. For sliding shoes of the contacting type these deviations from a planar shape of the end surface give rise to a problem in that the sliding shoe does not contact the end surface with its entire front surface but only on a part thereof, resulting in an unacceptable high contact pressure. The sliding shoe therethrough will be worn out more rapidly than if these surfaces were parallel and there is also a risk for damage of the sliding shoe. And for a sliding shoe of the gas cushion type, the non-parallelity of the surfaces has the consequence that the gas escapes from the gap unsymmetrically. The gas cushion thereby looses its bearing ability so that there will be contact between the end surface and a part of the front surface. The object of the present invention therefore is to attain a rotary regenerative heat exchanger in which the above discussed problem is overcome. According to the invention this has been achieved in that a rotary regenerative heat exchanger of the kind specified in the preamble of claim 1 includes the features specified in the characterizing portion of the claim. By mounting the sliding shoe so that its front surface is free to tilt, this surface will be able to follow the end surface of the rotor flange and thereby automatically adapt to local deviations in the orientation of the end surface from its theoretical plane perpendicular to the axis of the rotor. The tilting is arranged to occur around a tilting point so that the front surface can tilt both in the circumferential direction and the radial direction as well as combined. The front surface of the sliding shoe thereby automatically will be maintained in parallel to the front surface on the rotor flange and secure a proper sliding shoe function It is preferred to axially locate the tilting point as close to the front surface as possible in order to avoid moment on the sliding shoe from the friction force generated between the front surface and the end surface. For contacting sliding shoes this friction force is relatively high, whereas the friction force for gas cushion sliding shoes is much smaller. Claims 2 to 4 specify preferred embodiments of the invention by defining advantageous locations of the tilting point at which the effect of the friction force is minimized. The mounting means for the sliding shoe preferably includes co-operating spherical mounting surfaces. Thereby a simple and reliable construction for an optimal localisation of the tilting point can be achieved. Such an advantageous embodiment is specified in claim 5. The invention will be further explained through the following detailed description of preferred embodiments thereof and with reference to the accompanying drawings of which, fig. 1 is a partial axial section through a rotary heat exchanger according to the invention, fig. 2 is a view of a detail of fig. 1, fig. 3 is a schematic circumferential section through a sliding shoe according to prior art, fig. 4 is a schematic axial section through a sliding shoe according to prior art, fig. 5 is a section corresponding to that of fig. 3 but showing the principle of a sliding shoe according to the present invention, fig. 6 is a circumferential section through a sliding shoe according to a first embodiment of the invention, and fig. 7 is a section similar to that of fig. 6 showing a second embodiment of the invention. The heat exchanger illustrated in fig. 1 is of conventional type having a stationary casing 1 and a cylindrical rotor 2 containing a regenerative mass 3. The rotor has a hub 4 and an upper fixed sector shaped centre plate 5 with a movable sector plate 6 pivotally connected thereto and corresponding lower fixed centre plate 7 and movable sector plate 8. The two sets of plates 5, 6 and 7, 8 have the function to seal against the upper and lower ends of the rotor 2 as tight as possible and thereby separate the heat exchanging media flowing to and from the rotor through axial openings connected to media ducts (not shown). For that purpose the radially outer ends of each of the movable sector plates 6, 8 are provided with a device, which device forms support means 10 for maintaining a certain clearance (S) between the ends of the sector plates 6, 8 and an upper and lower annular edge flange 9 attached to the rotor along its upper and lower peripheries, each flange having an outer circumferentially continuous end surface 11 for co-operation with a front surface on the sliding shoe 17 of each support means 10. Each of the movable sector plates 6, 8 is affected by a predetermined force towards the rotor 2, which force is established by the weight of the sector plate and/or additional means, e.g. counter- weights (not shown), and the support means 10 take up these forces. Fig. 2 schematically illustrates the sector plate 6 co-operating with the upper rotor flange 9 in a view as seen from outside the periphery of the flange. The plate 6 has two supports 10, each with a sliding shoe 17 sliding on the end surface 1 1 of the rotor flange 9 as the flange rotates in the direction of the arrow. Figs. 3 and 4 represent prior art and are for the purpose to schematically illustrate the problem to be solved by the invention. Fig. 3 shows how the wave-shape of the rotor flange 9' in the circumferential direction in some positions, causes non-parallelity between the front surface 12' of the sliding shoe 17' and the end surface 1 1' of the rotor flange 9', resulting in reduced contact area or, in the case of a gas cushion sliding shoe, in failure of the bearing ability of the gas cushion In fig. 4, being an axial section through the sliding shoe, the corresponding effect when the rotor flange 9' slants radially is illustrated. Fig. 5 is a schematic section corresponding to that of fig. 3 and illustrates the operating principle of a sliding shoe according to the invention. The support means 10 is movably mounted in the sector plate 6 in a way allowing the sliding shoe 17 with its front surface 12 to be free to tilt so that the front surface 12 automatically adapts to the momentary direction of the end surface 1 1 on the rotor flange 9. These surfaces thereby will be maintained in parallel and assure a proper sliding, either by contact or on a gas cushion. It is to be understood that the deviations of the end surface 1 1 from the plane perpendicular to the rotor axis are strongly exaggerated in the figures in order to more clearly illustrate the problem and its solution. A first embodiment of the invention is illustrated in fig. 6 which is a section through the sliding shoe. The sliding shoe 17 in this embodiment is of the contacting type, sliding with its front surface 12 on the end surface 1 1 of the rotor flange 9, which rotates in the direction of the arrow. The sliding shoe is made of carbon or graphite and is attached to a metal rear plate 18 connected to a threaded bolt 19. The bolt 19 extends through a meshing threaded hole in a cup-shaped mounting element 20, having an upper spherical mounting surface 22. The sliding shoe 17 extends through an opening 25 in the sector plate 6, and a sleeve 24 is attached on the sector plate around the opening 25. At its upper end the sleeve 24 is provided with an inwardly directed sleeve flange 21 of spherical shape, and the bolt 18 projects out through the central opening 26 found by this flange 21. The sleeve flange 21 has an internal spherical bearing surface 23 of substantially the same radius (R) as the mounting surface 22 of the mounting element 20. The bearing surface 23 of the sleeve flange 21 is supported by the mounting surface 22 of the mounting element 20. The opening 26 formed by the sleeve flange 21 is somewhat wider than the bolt 19 and the mounting unit 20 does not reach the sleeve 24. Thereby the mounting unit 20 is free to slide on the sleeve flange 21 so that the mounting unit 20 and the sleeve flange 21 constitute movable mounting means for the slide shoe. In order to reduce the friction between the mounting surface 22 and the bearing surface 23 either or both of them preferably are coated with graphite, polythetraflourethylen or the like. The radius of the mounting and bearing surfaces 22, 23 has its centre 0 centrally on the front surface 12 of the sliding shoe 17. In the figure the slide shoe is in a position where the end surface 11 of the rotor flange 9 is perpendicular to the rotor axis, the axis of the sliding shoe 17 being perpendicular to the end surface and the sector plate 6 and the rotor flange being parallel. When the rotor flange 9 travels as indicated by the arrow and an inclining portion of the rotor flange 9 reaches the sliding shoe 17, the end surface 11 tends to tilt the sliding shoe 17, and" since the sliding shoe is movably mounted as described above, the sliding shoe ks free to tilt around the centre 0 of the spherical mounting surface 22 and follow the end surface 11. The sliding shoe thus will become angulary offset from the position in the figure, whereas the position of the sector plate 6 remains unchanged. The sliding of sliding shoe 17 on the flange 9 causes abrasion of the front surface 1 1. It is therefore necessary to axially adjust the sliding shoe at regular intervals to compensate for this wear in order to maintain the clearance S. This is accomplished by screwing the bolt 19 downwards a distance t, so that the sector plate 6 will be raised correspondingly. Such adjustments can be made until the sliding shoe is consumed and has to be exchanged. Due to the adjustments for wear compensation the centre of the spherical mounting surface 22 cannot be maintained constantly at the front surface 1 1, but be within a short distance therefrom; from t/2 above the surface immediately after adjustment to t/2 beyond the surface just before the next adjustment. This distance, however, is very small so that the moment around the tilting point 0 due to the friction between the front surface 12 and the end surface 1 1 in practice will be negligible. A second embodiment of the invention in which gas cushion sliding shoes are used is illustrated in fig. 7. This figure shows the sliding shoe 17a co-operating with an inclined part of the rotor flange 9a. The sliding shoe has an axial channel 30 extending therethrough, which channel through a hose 31 is connected to a source of gas of a pressure sufficient to establish a gas cushion between the sliding shoe 17a and the rotor flange 9a. The function of the movable mounting means of this embodiment is similar to that of the above described first embodiment, and the radius (R) of the special mounting surface 22a has its centre in the gap between the front surface 12a and the end surface 1 1a. As can be seen the slide shoe 17a is tilted in relation to the sector plate 6a guided by the mounting surface 23a of the sleeve flange 21a. Although a gas cushion sliding shoe theoretically operates without contact and therefore should require neither axial adjustment nor a material such as graphite, it is preferred to use such material since contact under certain conditions might occur. It is also possible to provide the sliding shoe 17a with axial adjustment means corresponding to that of the first embodiment (fig. 6) in order to compensate for the wear due to such unintended contact. In the described embodiments the sliding shoe has ability to tilt both circumferentially and radially. It should, however, be understood that the sliding shoe can be arranged to allow to tilt only in either of these directions, e.g. only circumferentially. In that case the mounting and bearing surfaces have cylindrical shape instead of spherical. The special mounting and bearing surfaces can be provided with gas supply means for establishing a gas cushion between these surfaces in order to reduce the friction therebetween.

Claims: Claims: 1. Rotary regenerative heat exchanger having a substantially cylindrical rotor (2) mounted in a casing (1), which rotor (2) at at least one of its ends is provided with a circumferentially continuous external end surface (11), and which casing (1) is provided with plates (5, 6, 7, 8) at at least one of said rotor ends in an orientation substantially perpendicular to the axis of said rotor (2) and close to the related rotor end, said plates (5, 6, 7, 8) including movable sector plates (6, 8), each said sector plate (6, 8) being affected by a resultant axial force towards the related rotor end and being provided with support means (10) for substantially maintaining a certain clearance (S) between said sector plates (6, 8) and the related rotor end, each said support means (10) including a sliding shoe (17; 17a) having a front surface (12; 12a) facing said end surface (1 1) and mounting means (20, 21) for said slide shoe (17; 17a), characterized in that said mounting means (20, 21) of at least one of said support means (10) is a movable mounting means allowing said front surface (12; 12a) to tilt around a tilting point (0) positioned close to the said end surface (1 1). 2. Rotary regenerative heat exchanger according to claim 1, having said front surface (12) sliding with contact on said end surface (11) and including adjustment means (19) for axial adjustment of the position of said front surface (12) to compensate for abrasion of said front surface ( 12) at intervals corresponding to a certain thickness (t) of the abrasion and wherein said tilting point (0) is located within a certain axial distance from said front surface, which distance is smaller than said thickness (t). 3. Rotary regenerative heat exchanger according to claim 2, wherein said certain axial distance does not exceed half said thickness (t). 4. Rotary regenerative heat exchanger according to claim 1 with gas supply means (30, 31) for supplying gas to said front surface (12a) of a pressure sufficient to establish a gap between said front surface (12a) and said end surface (1 1) so that said front surface (12a) slides without contact on said end surface (1 1) on a gas cushion, and wherein said tilting point (0) is located within said gap. 5. Rotary regenerative heat exchanger according to any of claims 1 to 4, wherein said movable mounting means (21, 22) includes a mounting surface (22) rigidly connected to said sliding shoe (17; 17a) and co-operating with a bearing surface (23) on said support means (10), said mounting surface (22) being a spherical surface, the centre of which defines said tilting point (0).

Inventors: KARLSSON KURT, WESTERLUND DAG, KARLSSON, KURT, WESTERLUND, DAG
Applicants: LJUNGSTROEM TECHNOLOGY AB
Application year: 1996
Main classification: F28D19
IPC codes: F28D19