ROTARY REGENERATIVE HEAT EXCHANGER AND A METHOD FOR OPERATING SUCH 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 (S) between the rotor and movable sector plates (6) connected to the casing and located close to the rotor ends. Each support co-operates through a front surface (12) on gas cushion means (17) with an end surface (11) on a flange (9) on the rotor. Each support is provided with gas conduit means ending in the gas outlet means (16) in the front surface (12) and being connected to a gas source (22) of a pressure sufficient to establish a gap between the front surface (12) and the end surface (11) 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 with a front surface (12) of elongated shape, having its longer extension directed circumferentially along said end surface (11).

Description: ROTARYREGENERATIVEHEATEXCHANGERANDA METHODFOROPERATINGSUCHHEATEXCHANGER. 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 such heat exchanger as specified in the preamble of claim 8. 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 ha an ability to maintain the flanges of the rotating body clean when adhering a lubricating layer 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 i 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 8 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 in that the support is elongated so that the outer part of the sector plate is stabilized in the circumferential direction. 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. Due to the elongated shape, the air cushion will have a larger circumferential extension, and the area of the air cushion can be increased. Thereby a sufficient raising force from the air cushion can be attained at a lower pressure of the supplied gas in comparison with a conventional pair of circular air cushions. Since the requirement on the pressure level of the gas source thus will be lower, the running costs for the gas supply is reduced. The angular extension of the front surface preferably is more than half the angular extension the sector plate in order to attain a sufficiently stabilized support by the air cushion and it should preferably be symmetrically located. Preferably the gas outlet has a corresponding elongated shape, whereby a uniform distributio of the gas is promoted. These and other advantageous embodiments are specified in the dependent claims. The invention will be further explained through the following detailed description of a preferred embodiment thereof and with reference to the accompanying drawings, of which fig. 1 is a partial axial section through a first preferred embodiment of the invention, fig. 2 is a view taken along line II-II of fig. 1, fig. 3 is a view similar to that of fig. 2, illustrating a second embodiment of the invention- fig. 4 is a view similar to that of fig. 2, illustrating a third embodiment of the invention- fig. 5 is a schematic section along line V-V of fig. 2, and fig. 6 is a view similar to that of fig. 5, illustrating a fourth 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 provided a device, which device forms support means 10 for maintaining a certain clearances between the 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. In fig. 2 the sector plate 6 is seen from the outside and co-operates with the end surface 11 of the rotor end flange 9. Through a sleeve 15 pressure gas is supplied to a sliding shoe forming gas cushion means with a front surface facing the end surface 11 of the flange 9. The front surface 12 of the sliding shoe is arc-shaped and limited by two concentric circular arcs 14 and 15. The sliding shoe is symmetrically arranged in relation to a symmetry line 19 of the sector plate 6 and extends along the flange 9 about two thirds of the angular extension of the sector plate. The gas supplied through the sleeve 15 is distributed through channels in the sliding shoe to an arc-shaped groove 16 in the front surface 12 of the sliding shoe, and creates an air cushion between the front surface 12 of the sliding shoe and the end surface 11 of the flange 9. Although only one gas cushion supports the sector plate 6 the support will be stable and without risk for tilting due to the elongated shape of the gas cushion. Fig. 3 illustrates the support 10 through a section therethrough. The arc-shaped sliding shoe 17 is rigidly attached to the sector plate 6 and projects a short distance from the internal surface 28 of the sector plate 6. In the front surface 12 of the sliding shoe 17 the groove 16 forming the gas outlet means extends along almost the entire length of the front surface. Through a plurality of channels 27 the groove 16 communicates with the opposite side of the sliding shoe. This side is covered by a closure member 18 of the same shape as the sliding shoe 17. The closure member has a gas inlet opening 25 and a distribution groove 26 through which the inlet opening 25 and the channels 27 communicate. A circular sleeve 15 is attached to the closure member 18 around the gas inlet opening 25, which sleeve extends out through a circular hole in the casing 1, and the opposite end of the sleeve 15 is through a gas conduit 23 connected to a pressure gas source 22. Between a flange 20 attached to the sleeve 15 and the casing 1 a sealing bellow 21 is provided, so that a predetermined axial force will be applied downwards on the plate 6 du to the spring effect of the bellow 21. In operation pressure gas flows through conduit 23, the interior 24 of the sleeve 15, the inlet opening 25, the distribution groove 26 and the channels 27 to the groove 16. The pressure o the gas keeps the front surface 12 of the sliding shoe 17 raised from the end surface 11 of th flange 9 against the action of the force from the bellow 21, so that the gas is allowed to esca through these surfaces, thereby creating the elongated air cushion. Fig. 6 illustrates an alternative embodiment of the support 10, in which the front surface 12" co-operating with the end surface 11 of the flange 9 is formed by a part of the inner surface 2 of the sector plate 6. The clearance S between the sector plate 6 and the end flange thereby will be more narrow. In order to avoid contact between the plate 6 and the flange the groove 12' extends circumferentially almost to the ends of the sector plate so that the air cushion wil receive a corresponding extension. Figs. 3 and 4 illustrate alternative shapes of the front surface 12', 12", respectively. In fig. 3 the front surface 12' is rectangular, limited by two straight lines 13', 14', and in fig. 4 the fro surface is crescent-shaped, limited by two non-concentric circular arcs 13", 14".

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 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 (S) between said sector plates (6, 8) and the related rotor end, said support means (10) including gas cushion means (17), each said gas cushion means (17) having a front surface (12) facing said end surface (11), said front surface (12) having gas outlet means (16), said gas outlet means communicating through gas conduit means (23, 24, 25, 26, 27) with a pressurized gas source (22) of a pressure sufficient to establish a gap between said front surface (12) and said end surface (11) against the action of said axial force, thereby creating a gas cushion between said front surface (12) and said end surface (11) as said gas escapes from said gas outlet means (16) 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 (17) and that the front surface (12) of said gas cushion means has an elongated shape, having its longer extension directed circumferentially along said end surface (11). 2. Rotary regenerative heat exchanger according to claim 1, wherein said front surface (12) is radially limited by two concentric circular arcs (13, 14) and having substantially a sausage-shape. 3. Rotary regenerative heat exchanger according to claim 1, wherein said front surface (12') is radially limited by two parallel straight lines (13', 14'), and having a substantially rectangular shape. 4. Rotary regenerative heat exchanger according to claim 1, wherein said front surface (12") is radially limited by two non-concentric circular arcs (13", 14") and having substantially a crescent-shape. 5. Rotary regenerative heat exchanger according to any of claims 1 to 4, wherein the angular extension of said front surface (12) is more than half the angular extension of said sector plate (6, 8), and said front surface (12) is symmetrically located relative to a radial symmetry ( 19) line in the plane of said sector plate (6, 8). 6. Rotary regenerative heat exchanger according to any of claims 1 to 5, wherein said ga outlet means (16) is a groove extending in the longitudinal direction of said front surface (12) 7. Rotary regenerative heat exchanger according to claim 1 or 2, wherein said front surface (12'") is a part of the internal surface (28) of said sector plate (6, 8). 8. A method for operating a rotary regenerative heat exchanger to maintain a certain clearance (S) between one end of a substantially cylindrical rotor (2) of the heat exchanger an 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 continuou end surface (11), said rotor (2) being mounted in a casing (1) and said sector plate (6, 8) bein connected to said casing and being affected by a resultant axial force towards said rotor end, said clearance (S) being maintained by supplying gas to support means (10) on said sector plate (6, 8) said support means (10) including gas cushion means (17) having a front surface (12) with gas outlet means (16) and facing said end surface (11), the pressure of said supplied gas being sufficient to establish a gap between said front surface (12) and said end surface (11 against the action of said axial force, thereby creating a gas cushion between said front surfac (12) and said end surface (11) as said gas escapes from said gas outlet means (16) through sai gap, characterized by supplying said gas to one single support means (10) and arranging said single support means (10) to form an elongated gas cushion, extending along said end surface (11).

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