HEAT EXCHANGER

Abstract: A heat exchange unit for hot gas heat recovery has a heat exchange array (2) situated within a heat exchange duct defined between a cylindrical outer casing (1) and an axially slideable inner sleeve (3). The sleeve (3), together with a plug valve (4) at the upper end of the unit, forms a variable position sleeve valve arrangement which simultaneously controls the flow of hot gas through the heat exchange duct and the bypass duct.

Description: HEAT EXCHANGER Field of the Invention This invention relates generally to heat exchangers having internal bypass arrangements which may be actuated to control the bypass of hot gas around a heat exchanger array and to direct gas flow into a bypass circuit. It particularly relates to heat exchangers associated with gas turbines and gas/diesel engines for extracting heat from their exhaust gases. Background of the Invention Heat exchangers of the type used to recover heat from gas turbine or gas/diesel engine exhaust gas are commonly designed with a bypass circuit situated external to the heat exchanger array and its casing, with the exhaust gas flow to the heat exchanger array circuit and the bypass circuit controlled by one or two flap valves or the like, such valves being known as dampers. Arrangements are known in which a single damper controls the flow through both circuits. Alternatively, two damper arrangements are known, in which one damper controls the flow through the heat exchanger array circuit and the other damper controls the flow through the bypass circuit. Both types tend to be heavy, bulky and complicated and when such dampers have been continuously modulated for continuously variable flow control, reliability problems have been experienced. For example, with two damper arrangements, damage to engines has been caused by excessive back-pressure due to both dampers being closed at the same time, instead of one circuit always being open. Brief Description of the Invention According to the present invention, a heat exchange unit for exhaust gas heat recovery has heat exchange duct means, bypass duct means, heat exchange array means situated within the heat exchange duct means, and a variable position sleeve valve arrangement adapted to cause variable amounts of exhaust gas to flow through the bypass duct means instead of the heat exchange duct means, the heat exchange array means surrounding the variable position sleeve valve arrangement and the latter defining the bypass duct means and an inner wall of the heat exchange duct means, the variable position sleeve valve arrangement including sleeve means moveable axially of both duct means thereby simultaneously to control flow of exhaust gas through the heat exchange duct means and the bypass duct means. Preferably, the sleeve means is adapted to be axially continuously moveable between two extreme positions with respect to inlet means for the heat exchange duct means and outlet means for the bypass duct means, whereby at one extreme position the inlet means for the heat exchange duct means is open and the sleeve means obturates outlet means for the bypass duct means and at the other extreme position the sleeve means obturates the inlet means for the heat exchange duct means and the outlet means for the bypass duct means is open. One benefit of the current invention is that the modulating sleeve valve mechanism is an integral part of the heat exchange unit, rather than a separate piece of equipment, and is much simpler in its design than the prior art damper, making modulation more reliable. A further benefit is the intrinsically safe nature of the sleeve valve arrangement, wherein it is not possible to close off both gas flow paths at the same time, thereby protecting the upstream equipment from overpressure damage. A further benefit is that the current invention is lighter and requires less space than the prior art arrangements, which is of considerable benefit in offshore applications. Furthermore in the known designs it is usual for there to be a separate sound attenuator installed in the gas circuit either upstream or down stream of the heat exchanger unit. In the current invention it is possible to favourably design the unit with sound attenuation linings on one or both sides of the sleeve means to damp sound in the bypass duct and/or the heat exchanger duct. It is possible also to provide the bypass duct with a flow splitter situated in the centre of the sleeve means, the flow splitter also having a sound attenuating lining on its surface confronting the sleeve means. These measures would be intended to eliminate the requirement for a separate attenuation device. Further features and advantages of the invention will be apparent from the following description and the claims. Brief Description of the Drawings Exemplary embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is an elevation partly in section along the centreline of a heat exchanger unit in accordance with the invention, with an inner sliding sleeve valve shown positioned for passing hot gas through a heat exchanger array; Figure 2 is an elevation similar to Figure 1 and showing the same heat exchanger unit, but with the sleeve valve shown positioned so that hot gas bypasses the heat exchanger array and passes through a central passage; Figure 3 is an elevation similar to Figure 2, showing an alternative embodiment of the invention; Figure 4A is a side elevation of the sleeve valve showing how it may be guided to slide up and down within the heat exchanger unit; Figure 4B is an enlarged view on section line B-B in Figure 4A; Figures 4C and 4D show in side elevation and sectional plan view respectively an enlarged detail of the guide mechanism, Figure 4D being a view on section D-D in Figure 4C; and Figures 5 and 6 are sketches in part-sectional side elevation of alternative embodiments of the invention. Detailed Description of Embodiments of the Invention The heat exchange units shown in the Figures are exhaust gas heat recovery units suitable for use, e.g., in the offshore oil and gas industries. The units are generally cylindrical in shape and are drawn with their major axes oriented vertically. As indicated in Figure 1 , such a unit is intended to receive hot gas 10 through gas inlet duct 34 from a gas turbine engine or other type of engine (not shown), cool the gas by heat exchange with a fluid circulating in a heat exchanger array 2, and pass the cooled gas 18 onwards for venting from the gas exit duct 7 to a stack, or for further use. The heat exchange fluid 36 is passed in and out of the heat exchanger array 2 through concentric pipes 38, and can be used as process fluid or for generating steam, or the like. Referring to Figures 1 and 2 together, the heat exchange unit comprises a generally cylindrical outer casing or shell 1, containing an annular heat exchanger array 2, an internal sleeve valve 3, and a valve plug 4. The sleeve valve 3 is slideable axially within the heat exchanger array 2 between two extreme positions. In Figure 1 , the sleeve valve 3 is shown at its upper extreme position, so that the valve sleeve's central passage 19, termed a bypass duct, is effectively obturated, with substantially all the exhaust gas passing through the heat exchanger array 2. In this position, the required gas seal to prevent flow through the bypass duct 19 is provided when an upper "knife edge" 14 of sleeve valve 3 buts against a valve seat 13 provided on the valve plug 4. In Figure 2 the sleeve valve 3 is shown at its lower extreme position, such that substantially all the hot gas 10 passes through the bypass duct 19, so bypassing the heat exchanger array 2. In this position, a frusto-conical valve seat 12 on the bottom of sleeve valve 3 forms a gas seal with a complementary frusto-conical valve seat 11 attached to the shell 1 below the heat exchanger array 2, so causing the hot gas 10 to pass through the bypass duct 19 and out past the valve plug 4 through the annular opening 16 between the plug 4 and the outer components. The plug 4 is supported at its axial position within the bypass duct 19, concentric with the shell 1, by means of a centre post 40 which extends along the shell's longitudinal axis. Centre post 40 is itself supported from the shell 1 by means of struts 9 and 15 which are provided respectively at the top and bottom of the centre post 40. There should be at least three struts at each of the top and bottom positions, these struts being equiangularly spaced around the assembly. As shown particularly in the right-hand (non-sectioned) part of Figure 1, the sleeve valve 3 is attached at its lower end to rods 20 for moving the sleeve valve axially up and down within the heat exchanger unit. The rods pass through gas seals 17 , and are actuated by one or more actuation devices 9 attached to the gas inlet duct 22 by support plates 30. The actuation devices 9 may be hydraulic, pneumatic, electrical, or manually operated. For example, the rods 20 and hence the sleeve valve 3 may be raised and lowered by means of ball screw devices on lead screws driven by electric motors. Again, there should be at least three rods 20, each driven by an actuation device, equiangularly spaced around the assembly. Advantageously, air 32 may be introduced into the lower heat exchanger space 21 through gas seals 17, or alternatively into a space created by a multiple seated seal (not shown), for the purpose of performing a sealing function by achieving complete isolation of the heat exchanger circuit from the hot gas 10. Additionally, or alternatively, such air may be utilised to remove unwanted heat from the working fluid within the heat exchanger array 2 when the hot gas 10 passes only through the bypass duct 19. For noise absorption within the heat exchanger duct, sound attenuation linings 5 and 6 are provided respectively on the inside of the shell 1 and on the outside of sleeve valve 3. The sound attenuation lining also has a temperature insulating function to reduce heat loss through the walls of the heat exchanger duct. Figure 3 shows a preferred embodiment of the invention. As in Figure 2, the unit is shown with the bypass duct in the extreme open position, but here the valve plug 4 is provided with a downward extension 8 which passes axially through the bypass duct 19 concentric with the shell 1 and centre post 40. The extension 8 acts as a flow splitter and has a cylindrical upper portion and a lower conical end portion. To provide improved sound attenuation in the bypass duct 19, the outer surface of the cylindrical portion of the flow splitter 8, confronting the sleeve valve 3, has a sound attenuating lining 35 over at least part of its length. Additionally, the lower part of the sleeve valve 3 is provided with a sound attenuating lining 42 on its internal surface. However, the top one fifth, approximately, of the sleeve valve 3 is not covered by lining 42, so as to avoid disturbing or restricting the flow of gas through the annular exit 16 of the bypass duct. As shown in Figures 4 A to 4D, lateral support of the sleeve, additional to that provided by rods 20, is required to prevent undue vibration of the sleeve valve and can be achieved in a number of different ways. In this embodiment the sleeve 3 is provided with three guide rails 24 secured to its external surface. These guide rails 24 extend lengthwise of the sleeve and are spaced 120 degrees apart around it. Similarly, the shell 1 of the unit is provided with three guide rails 22 which confront the rails 2. Dimensions are chosen so that there is a small clearance 44 between the confronting surfaces of the rails. Pairs of guide plates 23 are attached near the top and bottom of rails 22 and extend therefrom to embrace the rails 24 with a small clearance so as to prevent the rails 24 on the sleeve 3 from moving out of registration with the rails 22 on the shell 1. As shown in Figures 4A, 4C and 4D, the bottom portion of each rail 24 on the sleeve 3 comprises a roller mechanism 25, in which a roller wheel 46 is free to run along the surface of rail 22 by rotating on an axle 47. Axle 47 is held at each end by bearing plates 49, which are attached to the upper end of a roller block 48. Block 48 is in turn attached at its upper and lower ends to the rail 24 through vibration absorbing joints 45. As will be seen from Figure 4A, a similar roller mechanism is provided at the upper end of each rail 22 on the shell 1. Roller mechanism 25 ' differs from roller mechanism 25 only in that its roller block 48 1 is attached to rail 22 and its roller runs along the surface of rail 24. Figures 5 and 6 sketch alternative embodiments of the invention to illustrate alternative methods of guiding the sleeve valve 3. In Figures 5 and 6, similar items are given the same reference numbers as in Figures 1 to 4 and will not be further described, since they differ only in detailed dimensions and shape. In Figure 5, the sleeve 3, shown in its lowest position, is guided by four rods 53 connected at top and bottom to the outer casing 1. The valve plug 4 is also supported and by the rods 53 in order to align centrally with the sleeve 3. The sleeve 3 is permitted to slide along the rods by tubular bearings 54 attached to the sleeve 3. An additional feature of this embodiment is that the valve plug 4 is permitted to slide a small distance axially up the rods 53 to provide a means of limiting the load applied to the sleeve 3 and plug 4 by the actuator devices 9. This is to prevent damaging the equipment in the event of excessive axial upward movement of the sleeve 3 for any reason. In Figure 6, the unit is shown with the sleeve 3 in its uppermost position, i. e. with the bypass duct closed. In this embodiment, the plug seal 4 has a cylindrical extension 58 which extends axially down through the bypass duct 19 to a position below the valve seat 11. The top end of the plug 4 is laterally supported by plug support rods 55 which are attached to the outer casing 1. The valve sleeve 3 is guided and laterally supported from the plug 4 by two guide bearings 56. Although Figures 1 to 6 above show the sleeve valve 3 in its two extreme positions, it should of course be understood that the position of the sleeve is variable according to the input from the actuators 9, so that intermediate positions could be adopted, thereby allowing some of the hot gas 10 to pass through the bypass duct 19 and some through the heat exchanger array 2. Furthermore, although in the above-described arrangements the sleeve 3 defines both the bypass duct 19 and the inner wall of the heat exchange duct, it would also be possible to have an inner structural wall, additional to the moveable sleeve 3, to perform the function of dividing the bypass duct from the heat exchanger array. There are other ways of arranging the internals of the heat exchanger apart from those shown in Figures 1 to 6 above which could be developed within the scope of this invention. The casing 1, heat exchanger duct and internal bypass duct 19 are preferably cylindrical, however, shapes having a non-circular cross section are also functional. The heat exchanger may also be configured to operate with the exhaust gas flowing in the opposite direction to that shown in the figures with only relatively minor modifications to the internals. The heat exchanger is most suited to operation in a vertical arrangement as shown in all figures, however, it may also be operated in any other position, including horizontal and upside down, again with relatively minor modifications to the internals. The heat exchanger internals may also be altered to allow the plug to be situated at the other end of the heat exchanger, which may be beneficial in certain applications. The position of the actuators and attachment of the actuator rods may be changed from the lower end of the heat exchanger to the upper end. The sleeve may be actuated and guided by alternative means to those described above and as shown in the Figures, again within the scope of this invention.

Claims: CLAIMS: 1. A heat exchange unit for hot gas heat recovery has heat exchange duct means, bypass duct means, heat exchange array means situated within the heat exchange duct means, and a variable position sleeve valve arrangement adapted to cause variable amounts of hot gas to flow through the bypass duct means instead of though the heat exchange duct means, the heat exchange array means surrounding the variable position sleeve valve arrangement, the variable position damper valve arrangement including sleeve means moveable axially of both duct means thereby simultaneously to control flow of hot gas through the heat exchange duct means and the bypass duct means. 2. A heat exchange unit according to claim 1, in which the sleeve means defines the bypass duct means and an inner wall of the heat exchange duct means. 3. A heat exchange unit according to claim 1 or claim 2, in which the sleeve means is adapted to be axially moveable between two extreme positions with respect to inlet means for the heat exchange duct means and outlet means for the bypass duct means, whereby at one extreme position the inlet means for the heat exchange duct means is open and the sleeve means obturates outlet means for the bypass duct means and at the other extreme position the sleeve means obturates the inlet means for the heat exchange duct means and the outlet means for the bypass duct means is open. 4. A heat exchange unit with an intrinsically safe internal bypass valve comprising: an outer casing; a peripherally and longitudinally extending heat exchanger array; a sleeve valve moveable axially relative to the heat exchanger array; a valve plug: an outer casing valve seat; and actuation means for the sleeve valve; whereby the internal sleeve valve forms the intrinsically safe valve, sleeve means being movable axially of the heat exchanger by the actuation device to create a gas seal on the valve plug one extreme of axial travel in order to cause the gas to flow through the heat exchanger array and at the other extreme of travel to create a gas seal on the outer casing valve seat in order to cause the gas to flow through a bypass duct comprising a central passageway of the valve sleeve, thereby bypassing the heat exchanger array. 5. A heat exchange unit according to claim 4, including means for introducing sealing air to an annular space between the outer casing valve seat and the heat exchanger array. 6. A heat exchange unit according to any preceding claim, the heat exchange unit being arranged in series with an engine to receive exhaust gas therefrom. 7. A heat exchange unit according to any preceding claim, wherein the bypass duct includes sound attenuation linings to reduce the sound levels emitting from the unit. 8. A heat exchange unit according to any preceding claim, wherein the bypass duct is provided with a flow splitter to help guide the hot gas through the unit. . 9. A heat exchanger according to claim 8 as dependent from claim 4, wherein the flow splitter comprises an extension of the valve plug.

Inventors: JAMIESON RICHARD, WICKHAM MARK, JAMIESON, RICHARD, WICKHAM, MARK
Applicants: ALSTOM UK LTD, JAMIESON RICHARD, WICKHAM MARK, ALSTOM UK LTD., JAMIESON, RICHARD, WICKHAM, MARK
Application year: 1999
Main classification: F28D7
IPC codes: F28D7, F28F27