EP0355106B1

EP0355106B1 - A rotatable heat exchanger

Info

Publication number: EP0355106B1
Application number: EP88903452A
Authority: EP
Inventors: Gunnar Svensson; Lars Jonsson
Original assignee: ABB Flaekt AB
Current assignee: ABB Technology FLB AB; Flaekt Woods AB
Priority date: 1987-04-16
Filing date: 1988-04-11
Publication date: 1991-09-25
Anticipated expiration: 2008-04-11
Also published as: KR930012242B1; DK164305B; FI894829A0; SE456694B; FI91674C; DK164305C; FI91674B; NO168914C; SE8701606D0; EP0355106A1; DK511289A; NO885517D0; JPH02501851A; NO168914B; DE3865197D1; AU1622988A; JPH0635919B2; WO1988008112A1; ATE67844T1; DK511289D0

Abstract

The present invention relates to a rotary heat exchanger (10) for recovering heat or cold and/or moisture from gas flows. The heat exchanger comprises a casing (12) which incorporates gas-flow channels (16, 18). The heat exchange rotor (22) forms part of a withdrawable rotor unit (55), which also includes a frame (28) on which the rotor is journalled, a transverse wall (56) having an opening for accommodating the rotor, a rotor drive motor (40), and a cover plate (38) which is intended to cover an opening (36) in the casing (12) through which the rotor unit can be withdrawn. Arranged between the transverse wall (56) and the peripheral surface (62) of the rotor (22) is a radially directed peripheral seal (60), to which is connected within the area of the frame (28) an axial seal (82) and a diametrical seal (48) respectively.

Description

The present invention relates to a rotatary heat exchanger of the king set forth in the preamble of claim 1.
Rotatary heat exchangers of this kind are used to recover heat, cold and/or moisture from a first gas flow and transfer the heat, cold and/or moisture recovered to a second gas flow. The first and second gas flows may be, for instance, ventilation air exiting and entering a building, or some other form of gas flows, such as process gas flows. The active part of the rotary heat exchanger, i.e. the rotor, is provided with axially extending channels permitting the through-passage of said gas flows. The rotor may have mutually different diameters, from about 500 mm to about 5000 mm or thereabove, in order to accommodate mutually different gas flows. The length of the rotor in its axial direction may be kept relatively short, normally about 200 mm, even when demands on efficiency are high.
The rotor is embraced by a housing or rotor casing which has formed therein openings which are directed axially towards the gas flow channels in the rotor. In order to prevent the two gases mixing one with the other in the rotor casing, it is necessary to provide the rotor with efficient seals, both across the diameter between the two connecting channels and around the periphery of the rotor. In this regard, prior art rotary heat exchangers have been provided with axially extending peripheral seals arranged on both sides of the rotor. This positioning of the peripheral seals enables the rotor to be removed laterally without needing to remove the peripheral seals, which saves time when carrying out maintenance work, e.g. cleansing the rotor gas-throughflow channels.
In order to achieve the best possible efficiency of a rotary heat-exchanger, it is essential that no air leaks past the seals. All types of leakages are deleterious in this regard. Air which leaks to the same channel will not have taken part in the heat exchange process and will not have delivered or taken-up heat or moisture in the rotor. Leakage to the other channel results in a decrease in the total gas transport in the system, e.g. a reduction in the exhauast air exiting from the system or a reduction in the fresh air supply to a ventilation system. Leakage of this nature can also result in the presence of harmful or undesirable gas components in the wrong place, for instance such leakage may result in the transfer of gasified solvents to a spray booth or some other paint room.
Because the heat exchanger operates in accordance with the counterflow principle, the gas flows will engender a twisting or torsional moment (tilting) which tends to tilt the rotor relative to the rotor casing and its seals. This twisting moment increases very quickly with increasing rotor diameters. Tilting of the rotor in relation to the rotor casing is liable to engender leakage gaps, particularly in the axially directed peripheral seals. The seals which extend diametrically are not normally affected to the same extent, since they are located close to the symmetry plane of the tilting movement. The efficiency of the heat exchanger seals against leakage is impaired considerably with each millimeter of rotor tilt.
In order to avoid tilting of the rotor and therewith the risk of leakage, especially in the case of rotors of large diameters, it has been necessary to provide highly stable rotor journals, which naturally greatly increase costs.
Despite this, it is difficult to prevent the rotor from tilting over the long term, since only slight wear in the rotor journals will quickly result in some millimeters of tilt of the rotor periphery.
Another method of preventing leakage is to use axially extending peripheral seals which are elastically biased into powerful abutment with the peripheral surface of the rotor. The powerful abutment pressure exerted by these seals, however, engender high frictional resistance forces and increase the energy costs of running the heat exchanger. Furthermore, such highly pre-tensioned seals are subjected to a great deal of wear and the seals are therefore quickly worn down, with subsequent leakage problems.
Leakage may also occur as the result of rotor throw or of rotor distortion, since the rotor is often constructed from a comparatively soft material, such as thin aluminium plate. The size of these distortions or deformations is normally in the order of from about 1-3 mm.
By US-A-4473108, there is previously known a rotary heat exchanger constituting a favourable overall improvement of the state in the art, apart from the sealing problem, which is not dealt with by this construction providing seals of the afore-mentioned kind suffering from the said drawbacks, which are illustrated in the below-mentioned Figs. 1-3 and related parts of the description.
In view of the aforesaid deficiencies of prior art rotary heat exchangers, it is the object of the present invention to provide a heat exchanger which will be well sealed around its periphery irrespective of any rotor tilting or rotor deformation that may occur.
These objectives are realized by a rotary heat exchanger constructed in accordance with the invention and having the characteristic features set forth in the characterizing clause of claim 1.
By fitting the rotor drive means to a part which can be withdrawn together with the rotor, it is possible to fit and remove the rotor with the minimum of stoppage or shut-down time.
The invention will now be described in more detail with reference to an exemplifying embodiment thereof and with reference to the accompanying, partly schematic drawings, in which

Figure 1 is a perspective, exploded view of a prior art heat exchanger;
Figure 2 is a longitudinal sectional view of the heat exchanger shown in Figure 1, and illustrates leakage flow;
Figure 3 is a partly cut-away axial view of the heat exchanger shown in Figure 1, and illustrates leakage flow;
Figure 4 is a perspective view of a heat exchanger constructed in accordance with the present invention, and illustrates a rotor unit in a partially withdrawn position, the side plate or cover plate being omitted for the sake of clarity;
Figure 5 is a longitudinal sectional view of the heat exchanger shown in Figure 4, and illustrates the constructional principle of the peripheral seals;
Figure 6 illustrates part of a rotor fitted with a peripheral seal; and
Figures 7a-j illustrate examples of different variants of peripheral seals according to the invention.

Figures 1-3 illustrate an earlier known heat exchanger 10 housed in a casing 22 which incorporates openings 14 for accommodating first and second gas flow channels 16, 18. These gas flows may comprise, for instance, supply air and exhaust air flows in an air ventilation system. The channels are connected to the casing 12 in a standard manner, e.g. with the aid of the indicated connection flanges or pipe-stubs 20. Arranged within the casing is a heat exchange rotor 22 having a closed hub portion 24 surrounded externally by through-flow openings. The rotor shaft, shown solely by the shaft centre axis 26, is journalled or firmly attached to a frame structure 28. The frame structure 28 of the illustrated heat exchanger is known from Applicant's US-A-4479108, and comprises two bars, strips or beams 30 which incorporate the rotor shaft journals or rotor attachment means and which are rigidly connected together by a cross-piece 32. The frame 28 can be inserted into or withdrawn from the casing 12 on rails 34, which are fitted to the inside of the casing between the connection openings 14 of the two gas-flow channels. The rotor and frame pass through an opening 36 in one side wall of the casing which is covered by a side plate 38 or the like, which may be secured to the frame 28. Also fitted in the casing 12 is a drive motor 40, e.g. a belt-drive motor, which is connected to a junction box 44 by means of an electric cable 42. The channel orifices facing the rotor are sealed by means of axially extending peripheral seals 46 and by means of radial seals 48 arranged on the rails 34 or on the bars or the like 30.
When the heat exchanger is working, a first gas flow passes through the channel 16 and delivers its heat to the rotor material. When the rotor rotates across to the other channel 18, the rotor delivers the heat stored therein to the second gas flow. Since gaps 50 will appear, at least with time, between the rotor 22 and primarily the peripheral seals 46, as mentioned above, leakage gas flows 52 will pass on one side of the rotor through the space 54 surrounding the rotor in the casing interior. This leaking gas will pass the rotor and either return to the same channel from which it leaked (c.f. in particular Figure 2) or will enter the other gas-flow channel, as illustrated in Figure 3. Both of these occurrences have deleterious effects, as mentioned above.
The deleterious circumstances and leakage flows described with reference to Figures 1-3 are not limited to the illustrated heat exchanger construction, but are generic with all heat exchangers using axially extending peripheral seals. For example, the same deleterious circumstances are encountered when the rotor is journalled directly on the heat exchanger casing 12 or on a frame which embraces the rotor completely, in the form of an inner housing on which both diametrical seals and axially extending peripheral seals are fitted.
Figure 4 illustrates a construction according to the invention by means of which leakage at the peripheral seals is eliminated. This construction, generally shown at 55, includes a transverse wall 56 provided with an opening 58 for accommodating the rotor 22 on a withdrawable frame 28, and a peripheral seal 60 arranged between the peripheral surface 62 of the rotor and the transverse wall 56. Examples of different variants of the seal 60 are given below with reference to Figures 6 and 7. The transverse wall 56 abuts the floor 64 and the ceiling 66 of the casing 12 through the intermediary of guide and sealing rails 68. To ensure positive abutment with the rails 68, the transverse wall 56 has at least one angled flange web 70, 72 having at its free end an angularly curved stiffening flange 74. Correspondingly, the outer and inner end edges of the transverse wall 56 are each provided with at least one flange web 70, 72 and a stiffening flange 74 for sealing abutment with the rear wall 76 of the casing 12 and with the inner surface of the side cover-plate. In order to enhance the sealing effect afforded hereby, the rear wall 76 and the side cover-plate and/or said at least one flange may be covered with an appropriate material, such as rubber, preferably foamed rubber.
The transverse wall 58 also carries a housing 78 for the rotor drive motor 44. The drive from the motor 44 to the rotor is effected over a drive belt 80 or some equivalent drive means, which connects with the peripheral surface 62 of the rotor. The housing 78 has a sealed lead-through (not visible) through which the cable 42 passes to the junction box 44. In accordance with a first variant, the side cover-plate is securely fitted to the frame 28, in which case the incoming power supply cable to the drive motor is drawn through the cover plate 38 and connected to an electric socket by means of a cable shoe or plug. This enables the rotor to be withdrawn readily from the heat exchanger casing for repair or cleaning purposes, simply by disconnecting the power supply cable and then withdrawing the rotor unit 55 comprising the rotor 22, the frame 28, the transverse wall 56, and the drive means 40 together with the junction box 44. This results in much shorter dismantling and shut-down times, particularly when a serviced standby unit is available for immediate installation. The procedure entailed is thus much quicker than the procedures used in present day techniques, in which the cover plate, drive motor and junction box must each be removed individually, before the rotor can be withdrawn from the heat exchanger casing.
In the case of the embodiment illustrated in Figure 4, two radial seals 48 are arranged on the longitudinal bars or beams 30 of the frame 28, at least on one side. At the rotor periphery the radial seals 48 merge integrally with axially extending peripheral seals 82 which extend to the transverse wall 56. The axial seals 82 present openings for through-passage of the drive belt 80 on the drive-belt side of the transverse wall. This enables the drive belt and peripheral seal arrangement to be configured so as to obtain the minimum of gap, e.g. by driving the motor with an inverted V-belt. Alternatively, the drive belt may be fitted in a groove in the drive rotor so as to lie flush with the peripheral rotor surface 62. It is possible to reduce the area of the leakage gap at the drive-belt through-pass to at most one or two square millimeters. Instead of placing the diametral seals on the bars or beams 30, these seals may be placed on the guide rails. In this case the axial seals 82 are preferably sunk to the plane of the frame 28.
Figure 5 is a cross-sectional view of a heat exchanger constructed in accordance with the invention. The heat exchanger casing of this embodiment has no internal space in which overflow can take place from one channel to the other. Any small leakage flow 84 which might manifest at the peripheral seal 80 passes directly from the one channel side to the other. Even relatively pronounced tilting or deformation of the rotor 22 will only result in insignificant changes in radius at the seal, these changes lying within the normal elastic abutment resilience of the seal. The magnitude of this change in radius can be calculated geometrically. When the rotor is tilted through the angle α, the maximum change in radius resulting therefrom will be (1-cos α)r. A corresponding maximum change at an axially directed peripheral seal is sin α · r. When α = 1° there is obtained 0.0002 · r and 0.0175 · r respectively, while corresponding values for α = 5° are 0.0024 · r and 0.0878 · r respectively. It will be seen from this that the changes in radially arranged peripheral seals caused by tilting of the rotor are negligible in comparison with axially directed peripheral seals.
Leakage as a result of irregularities in rotor attitude is also smaller in the radial direction of the rotor than in its axial direction. Due to the short length and large diameter of the rotor, deformations will occur much more readily in the axial direction than in the radial direction.
Figure 6 illustrates in detail the arrangement of a seal 60 between the transverse walls 56 and the peripheral surface 62 of the rotor. The seal illustrated in Figure 6 corresponds to the variant shown in Figure 9a, and comprises a brush seal 60a secured to the cross wall 56 with the aid of an attachment means 86.
Figure 7 comprises a number of schematic, cross-sectional views of the transverse wall 56, its connecting part to the guide and sealing rail 68, and the peripheral seal against the peripheral surface 62 of the rotor 22. In this regard, the variants illustrated in Figures 9a-9e have on one side a projecting flange 70 provided with a rearwardly curved stiffening flange 74. The variants illustrated in Figures 7f-7j correspond to the above, with the exception that these variants are also provided with a substantially L-shaped edge reinforcement 88 having a long connecting flange 90, a flange web 72 and a stiffening flange 74. The long connecting flange is secured to the transverse wall 56 in some suitable known manner, e.g. by screwing, pop-riveting or spot-welding. The edge reinforcement 88 and the guide and sealing rail 68 are arranged so as to prevent leakage of gas from taking place. The use of an edge reinforcement 88 results in symmetric guidance of the transverse wall 56 in the guide and sealing rails 68.
Figures 7a-e and 7f-j illustrate corresponding variants of peripheral seals on a transverse wall 56 without or with an edge reinforcement 88. The variants 9a and 9f include a peripheral seal 60 having a brush-type sealing element 60a and an attachment means 86. The variants illustrated in Figures 7b and 7g include a seal which has the form of an elastic lip, e.g. a rubber lip 60b, and which has an upwardly folded side edge in abutment with the peripheral surface 62. This seal may exhibit a double fold, in which case the free end is folded in respective directions. In the case of a single seal, the upwardly folded side will face the gas flow, so that the gas pressure will urge the rubber lip against the peripheral surface of the rotor and therewith amplify the sealing effect. In the case of a single seal, a seal 60b shall be directed in different directions in the two channels 16, 18. Figures 7c and 7h illustrate a felt seal or a multifold lip seal 60c having an attachment means 86. Figures 9d and 9i illustrate a radially extending labyrinth seal 60d, which also includes a part which is secured to the peripheral surface 62 of the rotor. As mentioned in the aforegoing, tilting of the rotor results in a marked deviation in the axial direction, but only an insignificant deviation in the radial direction. Consequently, the labyrinth seal 60d must be sufficiently flexible to take-up such axial deviations.
Figures 7e and 7j illustrate a seal 60e provided with a brush-sealing element corresponding to the seal 60a in Figure 7a and 7f, but with a differently configured attachment element 86′. The attachment element 86′ includes a flange or cuff 96 which projects axially outwards from the transverse wall 56 and which is preferably made of a resilient material, such as rubber. The flange 96 is attached to a holder part 98, which carries the actual seal. Sealing elements 60b, 60c and 60d may also be used. The seal 60e affords a given degree of elastic adjustment to wear in the flange or the cuff 96, and because it can be fitted and dismantled readily in the axial direction greatly facilitates maintenance.
The heat exchanger frame 28 may have a configuration different to that of the illustrated embodiment. For example, the frame may also include braces which extend perpendicularly to the bars or beams 30, which are connected to the transverse wall 56 and guided by the guide and sealing rail 68. According to another variant, the frame may comprise a casing or housing which totally embraces the rotor. This housing has a stationary transverse wall 56 fitted to the inside thereof and is displaceable into and out of the outer heat exchanger casing 12.
The illustrated embodiment comprises a rotor which has a horizontal shaft and which can be displaced linearly in a horizontal direction. It will be understood, however, that the rotor may be provided with vertically extending gas channels and a vertical shaft and arranged for with-drawal and insertion in a horizontal direction. Although other orientations of the rotor shaft and the direction in which the rotor is withdrawn are also conceivable in principle, but result in practical problems and should therefore be avoided.
In addition to electrical connections, the junction box 44 may also accommodate other types of electrical component, such as a rotor speed control device, automatically activated or externally activated emergency stop means or electric switches, and parts of different instruments for monitoring the function of the heat exchanger.
Such electrical components are within themselves known to the art and the novelty represented by such components resides in the positioning of said components on a heat exchanger part which can be withdrawn from the heat exchanger casing together with the rotor.
According to a second embodiment of the invention, the side cover-plate 38 is separate from the frame 28 and is fitted to the casing 12 on, e.g., hinges (not shown). This enables the casing opening to be exposed for inspection, e.g., while the heat exchanger is working, without needing to remove the entire rotor unit. In the case of this embodiment the electric cable is not drawn through the cover plate and may advantageously be connected to an electric socket fitted to the inside of the casing, or alternatively connected to an electric socket on the rotor unit, preferably to the junction box.
The junction box may, alternatively, be placed on a stationary part of the casing 12, e.g. on an external surface thereof. In this case, the electric cable 42 is drawn through the cover plate 38 and connected to the junction box by means of a plug or cable shoe.
Additional electric cables for powering, e.g., measuring instruments and monitoring and operating devices, may be connected in a corresponding manner, with the aid of plugs or the like which enable the cables to be quickly disconnected.
Instead of a drive belt which passes around the rotor, the rotor may be driven, e.g., by a friction drive against the peripheral surface 62 of the rotor, in a known manner. This eliminates the necessity of the belt groove and therewith obviates subsequent leakage risks at the peripheral seal 82.
As will be understood from the aforegoing, the rotor 22, the frame 28, the transverse wall 56, the radially directed peripheral seal 60, the side cover-plate 38 (when fitted), the drive motor 40 and, when fitted, the junction box 44 together form a rotor unit 55 which can be withdrawn from and inserted into the heat exchanger casing 12 in the form of a single package. When inserted into the casing 12, the rotor unit is sealed against the casing walls in the flow direction and between the channels by means of the guide and sealing rails 68 and the diametral seals arranged in connection with the bars or beams 30 and/or corresponding guide rails 34.

Claims

1. A rotary heat exchanger for recovering heat or cold and/or moisture from one of two gas flows, which are provided to be guided in parallel relation to each other through a channel each (16, 18) connecting to openings (14) in a casing (12) containing a rotor (22) having axial throughgoing openings for gas flow, which rotor is journalled on a frame (28) which may be withdrawn through a side opening (36) in said easing, seals (48; 60; 82) being provided to counteract non-desirable leakage around the rotor, characterized in that the withdrawable frame has mounted thereon a transverse wall (56) having a circular opening (58) for the rotor (22) and being provided to abut in sealing relation walls (64, 66) of said casing which are parallel to the direction of movement of the frame (28) via guide and sealing rails (68), the respective sides of the transverse wall (56) being bent at right angle to form guide and sealing flanges (70, 72) which are in parallel relation to and abut the web of said rails (68), that both the other sides of the tranverse wall are provided to abut the closed rear side (76) and a plate (38) covering said side opening (36) of the casing, and that within the circular opening (58) there is provided a peripheral seal (60) which preferably is supported by the transverse wall, and to which connects within the area of the frame (28) an axial seal (82) and a radial seal (48), respectively.

2. A heat exchanger according to claim 1, characterized in that the drive motor (40) is mounted on the transverse wall (56), preferably in a housing (78) constructed on said transverse wall.

3. A heat exchanger according to claim 1, characterized in that the plate covering the casing opening (36) is firmly secured to the frame (28) and/or the transverse wall (56); in that the plate is constructed so as to sealingly abut the outer edge of the transverse wall (56); and in that the plate can be withdrawn integrally with the frame (28) and the transverse wall (56).

4. A heat exchanger according to one or more of claims 1-3, characterized in that the electric power cable (42) connected to the drive-motor (40) may be detachably connected to a stationary electric contact (not shown), and/ or in that the junction box (44) of the drive motor (40) is arranged in a manner to be withdrawable together with the rotor (22) and the frame (28), preferably mounted on the transverse wall (56).

5. A heat exchanger according to one or more of the preceding claims, characterized in that the transverse wall (56) presents at least one stiffening flange (74) projecting from the free end of flange web (70, 72), which abuts said rails in sealing co-action therewith.

6. A heat exchanger according to claim 1, characterized in that the peripheral seals have through-passing openings for accommodating the rotor drive belt (80).

7. A heat exchanger according to one or more of claims 1-6, characterized in that the radially directed peripheral seal (60) between the transverse wall (56) and the peripheral surface of the rotor comprises a brush seal (60a), a single or double-fold elastic lip, preferably a rubber lip (60b) having upwardly or outwardly folded side edges in abutment with the peripheral surface (62), or a multifold lip seal (60c), and in that said sealing element (16a, 16b, 16c) is attached directly to the transverse wall (56) or through the intermediary of a separate attachment element (86).

8. A heat exchanger according to any of claims 1-6, characterized in that the radially directed peripheral seal (60) comprises a labyrinth seal, in that part of the labyrinth seal is arranged on the transverse wall (56) while a further part of the labyrinth seal is arranged on the peripheral surface (62) of the rotor, and in that the labyrinth seal presents sealing surfaces having a radial extension (60d) or sealing surfaces (60e) which extend parallel with the peripheral surface (62) of the rotor (22).