ROTARY REGENERATIVE HEAT EXCHANGER AND A METHOD FOR OPERATING A ROTARY REGENERATIVE HEAT EXCHANGER

Abstract: In a rotary regenerative heat exchanger of the kind having a rotor mounted in a casing, supports are provided for maintaining a certain clearance between the rotor and movable sector plates (6) connected to the casing and located closed to the rotor ends. Each support co-operates through a front surface on a sliding shoe (25) with an end surface (61) on a flange (12) on the rotor. Each support is provided with gas conduit means ending in the gas outlet means in the front surface and being connected to a gas source of a pressure sufficient to establish a gap between the front surface and the end surface (61) so that a cushion of gas is established between the surfaces as the gas escapes from the gas outlet means through the gap. According to the invention a sector plate (6) is provided with only one single gas cushion support located in the region of the symmetry line (69) of the plate (6), and at the outer corners of the plate (6) axially directed stabilizing projections (68) are provided, which face the end surface (61) of the flange (12). These supports (68) prevent tilting of the plate (6) as only one single gas cushion support is provided.

Description: ROTARYREGENERATIVEHEATEXCHANGERANDAMETHODFOR OPERATINGAROTARYREGENERATIVEHEATEXCHANGER. The present invention in a first aspect relates to a rotary regenerative heat exchanger of the kind specified in the preamble of claim 1 and in a second aspect to a method for operating a rotary regenerative heat exchanger as specified in the preamble of claim 6. 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 closed 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. However, problems will occur if the sliding shoe becomes somewhat slanting due to mounting inaccuracy and/or thermal deformations. There will in such cases be a risk that the sliding shoe will contact the flange by only a small part of its sliding surface with unacceptable high contact pressure as a consequence. Furthermore 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 o carbon or graphite on the flanges. The abrasion of the sliding shoe also secures a correct contact with parallel contact surfaces so that the contact takes place on the complete sliding shoe surface. 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. Arrangement of the sliding shoes hovering on air cushions, however, increases the costs. Each shoe will be more sophisticated and thereby circumstantial to manufacture, and gas piping has to be connected to each individual sliding shoe. Common to all the above discussed arrangements of the supports, the contacting as well as the contact-fee types, is that at least two individual supports are provided for each sector plate. The reason for that is to secure a steady supporting of the sector plate and avoid tilting thereof One single support at the middle of the outer periphery of the plate should theoretically be enough since the plate at its inner end is supported by two pivot connections to the fixed centre plate. Due to flexibility of the movable sector plate and/or thermal deformation there will in practice, however, be a risk for the outer edges of the plate to tilt and hit against the rotor, when there is only one support. However, when using the contact-free type of sliding shoe, which is more expensive than the traditional type, there is a desire to reduce the number of such sliding shoes. The object of the present invention therefore is to attain a regenerative heat exchanger of the kind in question in which the number of sliding shoes is as small as possible. This has according to the present invention been achieved in that a rotary regenerative heat exchanger of the kind specified in the preamble of claim 1 has got the features specified in the characterizing portion of that claim and in another aspect in that a method as specified in the preamble of claim 6 includes the measures specified in the characterizing portion of that claim. The device according to the invention thus deviates from the traditional concept of using two or more supports for the sector plate, when supports of the non-contacting type are used. The problem of avoiding tilting is overcome by the stabilizing projections. Since these projections are arranged to normally be out of contact with the end surface on the flange of the rotor, wear problems will not occur. Should, however, there be a tendency for the plate to tilt, a projection will contact the flange and prevent tilting. The contact force in that case will be relatively small, since the stabilizing projections do not have to take part in keeping the plate raised from the flange, but only to counter-act the tilting force. The projections thus function as a kind of stabilizers that occasionally contact the flange, but mostly leave a small clearance in relation thereto. By using only one contact-free support for each sector plate the number of devices for establishing gas cushions is reduced to the half, which lowers the manufacturing and maintenance costs and reduces the risk for failure. Preferably the air cushion support is located in the middle of the periphery of the sector plate with the stabilizing projections at both ends of the periphery. The stabilizing projections should preferably be somewhat shorter than the distance between the plate and the flange and it can be advantageous to make them resilient. These and other advantageous embodiments of the invention are specified in the dependent claims. The invention will be further explained through the following detailed description of preferre embodiments thereof and with reference tot the accompanying drawing, of which fig. 1 is a partial section through a first preferred embodiment of a heat exchanger according t the invention, fig. 2 is an axial section through the support means along line II-II of fig. 1, fig. 3 is a schematic top view of a sector plate according to the first embodiment of the invention, fig. 4 is a schematic section along line IV-IV of fig. 3 and fig. 5 is a view similar to that of fig. 3 and illustrating a second embodiment of the invention. The heat exchanger illustrated in fig. 1 is of conventional type having a stationary casing 1 an a cylindrical rotor 2 containing the 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 a tight as possible and thereby separate the heat exchanging media flowing to and from the roto 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 provide a device, which device forms support means 10 for maintaining a certain clearance between th ends of the sector plates 6, 8 and an upper and lower annular edge flange 12 attached to the rotor along its upper and lower peripheries, each flange having an outer circumferentially continuous end surface 61 for co-operation with a front surface 62 connected to each of the devices 10. Fig. 2 illustrates a part of the casing and the upper edge flange 12 of the rotor and the upper movable sector plate 6. In a hole in the sector plate 6 the device 10 is fixed by screws. The device includes an outer sleeve 15 with a mounting flange 16, which with an intermediate sealing ring 17 is attached to the sector plate 6 by means of screws 18. At its upper end the outer sleeve 15 has an internal thread 19 and within the outer sleeve 15 there is an inner sleeve 20 having an upper part with an external thread, partly screwed into the thread 19. At its lower end the inner sleeve is provided with a packing 22, which sealingly contacts the inside of the outer sleeve 15. The upper end of the inner sleeve 20 is provided with a nut 23 welded thereto and its lower end is provided with a bottom plate 24 welded thereto. On the underside of the bottom plate 24 a gas cushion device 25 in the form of a circular sliding shoe 25 of graphite or carbon is exchangeable attached by means of a recessed screw 26 screwed into the bottom plate 24. The sliding shoe 25 has a front surface 62 facing and being parallel to the circumferentially continuous end surface 61 of the flange 12. The upper end of the outer sleeve 15 is provided with an external annular flange 27 to which the upper end of a sealing bellow 28 of metal is screwed by means of a mounting ring 29, an annular packing 30 and screws 31. The lower end of the bellow 28 is provided with a mounting ring 32, which by means of screws 33 and an intermediate packing 34 is attached in a circular hole in the casing 1 so that a pre- determined axial force will be applied downwards on the plate 6 due to the spring effect of the bellow 28. In parallel with the device 10 and closed at the side thereof a measuring device 13 is provided for measuring the clearance between the plate 6 and the flange 12. It includes a tube 40, attached with its lower end in a hole 41 in the sector plate 6 and with its upper end in a hole 42 in the flange 27, and thus extends within the bellow 28. Inside the tube there is a measuring rod 43, the upper end of which is fixed in the shown position to a sleeve 44 by means of a not β shown spring and an external flange on the rod, which sleeve 44 is screwed on to the tube 40. In that position a scaled part 45 of the upper end of the rod 43 projects out through the sleeve 44, and the bottom end of the rod 43 is aligned with the underside of the sector plate 6. Eventually, as shown, a measuring clock 50 having a measure probe 51 contacting the top end of the scaled part 45 can be provided. Support of the movable sector plate 6 for maintaining a clearance between the plate 6 and the flange 12 is attained through contact-free co-operation between a guiding surface 61 being the outer end surface of the rotating flange 12 and a stationary guided surface 62, being the front surface of the sliding shoe 25. To attain this contact-free co-operation, means are provided for establishing a cushion of gas between these surfaces 61, 62. These means includes a pressurized gas source 64, connected through a pipe 63 to the interior 65 of the sleeve 20 in which the sliding shoe 25 is mounted. Through the sliding shoe 25 channels 66 communicate the interior 65 of the sleeve 20 with outlets 67 in the end surface 62 of the sliding shoe 25. The pressure of the gas is sufficient to force the gas to continuously flow from the outlets 67 and escape between the end surface 62 and the front surface 61, which thereby are pressed away from each other. In that way a cushion of gas is formed between these surfaces 61, 62, having an axial thickness of a fraction of a mm. Since there will be no contact between the surfaces 61, 62 no wear of the sliding shoe will occur. In fig. 3 the upper movable sector plate 6 connected to the fixed centre plate 5 through pivot connections 71 is seen from above. At its outer periphery the sector plate 6 is provided with the sole sliding shoe 25 of the support means 10. The sliding shoe 25 is located in the region o the symmetry line 69 of the sector plate 6 and faces the end surface 61 of the flange 12 of the rotor 2. Since the sector plate 6 at its radially outer end is supported by only one single sliding shoe 25 the plate is less stable, than when using two or more such shoes, and it therefore is a risk that the outer corners of the sector plate 6 might tilt. In order to avoid this the sector plate is provided with an axially directed stabilizing projection 68 near each end of its outer periphery. As can be seen in fig. 3 these projections 68 are located so that they face the flange 12. Fig. 4 illustrates the function of these projections 68. As mentioned the sector plate 6 is raised solely by the centrally located sliding shoe 25 and the gas cushion established between the shoe 25 and the flange 12. A clearance having a width S thereby is maintained between the sector plate 6 and the flange 12. Should the sector plate 6 tilt the tilting movement is stopped by contact between either of the supports 68 and the flange 12. The supports 68 are slightly shorter than the distance S between the sector plate 6 and the flange 12 so that the projections 68 normally do not contact the flange 12. The contact force between a projection 68 and the flange 12 will be relatively low since the projection does not contribute to maintain the plate raised, but only to prevent the tilting movement. There is therefore no need to concern about wear of these projections or to use self-lubricating material. These projections therefore can be made very simple. The projections 68 preferably are resiliently mounted or made of resilient material in order to attain a smother resistance against tilting and avoid bouncing. Alternatively the sliding shoe 25 can be located on one side of the symmetry line 69 as illustrated in fig. 5. In that case the risk for tilting will be unidirectional and only one supporting projection 68 located at the other side of the symmetry line 69 adjacent to the radial edge 70 of the sector plate 6 is required.

Claims: Claims. 1. Rotary regenerative heat exchanger having a substantially cylindrical rotor (2) mounte in a casing (1), which rotor (2) at at least one of its ends is provided with a circumferentially continuous external end surface (61), 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 closed 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 maintaining a certain clearance between said sector plates (6, 8) and the related rotor end, said support means (10) including gas cushion means (25), each said gas cushion means (25) having a front surface (62 facing said end surface (61), said front surface (62) having gas outlet means (67), said gas outlet means communicating through gas conduit means (63, 65, 66) with a pressurized gas source (64) of a pressure sufficient to establish a gap between said front surface (62) and said end surface (61 ) against the action of said axial force, thereby creating a gas cushion between said front surface (62) and said end surface (61) as said gas escapes from said gas outlet mean (67) through said gap, characterized in that the support means (10) of at least one of said sector plates (6, 8) consists of one single gas cushion means (25), and said sector plate (6, 8) further is provided with at least one axially extending stabilizing projection (68) facing said end surface (61). 2 Rotary regenerative heat exchanger according to claim 1, wherein said single gas cushion means (25) is located in the region of a radial symmetry line (69) in the plane of said sector plate (6, 8) in the radially outer part thereof and said sector plate (6, 8) has one said stabilizing projection (68) on each side of said symmetry line (69), each one located adjacent t a radial edge (70) of said sector plate (6, 8). 3. Rotary regenerative heat exchanger according to claim 1, wherein said single gas cushion means (25) is located on one side of a radial symmetry line (69) in the plane of said sector plate (6, 8) in the radially outer part thereof and said sector plate (6, 8) has one single stabilizing projection (68) on the other side of said symmetry line (69) adjacent to a radial edge (70) of said sector plate (6, 8). 4. Rotary regenerative heat exchanger according to any of claims 1 to 3, wherein each said stabilizing projection (68) has an axial extension that is slightly shorter than the distance (S) between said sector plate (6, 8) and the related end surface (61). 5. Rotary regenerative heat exchanger according to any of claims 1 to 3, wherein each said stabilizing projection (68) is axially resilient. 6. A method for operating a rotary regenerative heat exchanger to maintain a certain clearance between one end of a substantially cylindrical rotor (2) of the heat exchanger and a movable sector plate (6, 8) located closed to said rotor end in an orientation substantially perpendicular to the axis of said rotor (2), said rotor end having a circumferentially continuous end surface (61), said rotor (2) being mounted in a casing (1) and said sector plate (6, 8) being connected to said casing and being affected by a resultant axial force towards said rotor end, said clearance being maintained by supplying gas to support means (10) on said sector plate (6, 8) said support means (10) including gas cushion means (25) having a front surface (62) with gas outlet means (67) and facing said end surface (61), the pressure o said supplied gas being sufficient to establish a gap between said front surface (62) and said end surface (61) against the action of said axial force, thereby creating a gas cushion between said front surface (62) and said end surface (61) as said gas escapes from said gas outlet means (67) through said gap, characterized by supplying said gas to one single support means (10) and providing at least one axially extending stabilizing projection (68) on said sector plate (6, 8), which projection faces said end surface (61).

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