AU5199390A

AU5199390A - A heat exchanger

Info

Publication number: AU5199390A
Application number: AU51993/90A
Authority: AU
Inventors: John Brian Clarke; Nigel Patrick Fitzpatrick
Original assignee: Alcan International Ltd Canada; GEC Marconi Ltd; Marconi Co Ltd
Current assignee: Rio Tinto Alcan International Ltd; BAE Systems Electronics Ltd
Priority date: 1989-03-09
Filing date: 1990-03-09
Publication date: 1990-10-09
Also published as: EP0413804A1; GB9005390D0; JPH03505366A; GB2231395B; GB2231395A; CA2028133A1; BR9005735A; KR920700382A; WO1990010839A1; GB8905432D0

Description

A Heat Exchanger

The present invention relates to a heat exchanger and particularly, though not exclusively, to a heat exchanger for use in a power generator plant.

It has been proposed to utilise the temperature differences which can exist in large bodies of water such as^* between the top and bottom of the sea to generate electricity. Similarly situations where industrial processes generate large quantities of water of a different temperature to the surroundings have also been considered as suitable for thermal power generation. However, the temperature differences involved are not great and so if the power generation system relies on expanding a fluid to drive a turbine for example, the fluid must have a fairly low boiling point, e.g. ammonia and the throughput of water must be high to ensure sufficient energy can be provided to the system. Such conditions could pose problems in system and heat exchanger design.

The technique known as rollbonding has previously been used to produce single plate heat exchangers for uses such as domestic refrigerators. In rollbonding, a heat exchange panel is formed by adhering two sheets of material together at selected places followed by forcing a fluid therebetween to force the non-adhered areas apart to form cavities. Henceforth the term "rollbonding" will refer to such a process. The material used is typically aluminum.

The present invention seeks to utilise rollbonding technology in the situations described above.

In accordance with a first aspect of the present invention there is provided a heat exchanger comprising a path for luid flow having a plurality of roUbonded heat exchange elements connected in parallel provided therein, each element having a further fluid path defined therein.

The elements are preferably spaced apart so as to provide low resistance to the flow of fluid through the heat exchanger. Hence a low pressure is required to force fluid through the heat exchanger which can consequently be open to atmosphere pressure if required. The spacing of the elements is selected according to the required throughput of fluid which in turn is dependent upon the temperature of the fluid.

The heat exchanger typically comprises a bank of roUbonded panels having at their edges respective inlet ports arranged adjacent to each other and respective outlet ports also arranged adjacent to each other; an inlet manifold connected to the inlet ports; and an outlet manifold connected to the outlet ports. The inlet and/or outlet manifold can comprise a casting or moulding secured over the inlet and/or outlet ports.

Preferably the heat exchanger comprises banks of heat exchanging elements, each bank having its own inlet and outlet manifolds, the banks being connected in parallel. The manifolds can also be formed by rollbonding. The banks are preferably connected in parallel by couplings which allow each bank to be disconnected without loss of fluid therefrom.

The heat exchanger is typically arranged such that no fluid path extends from an inlet chamber, over a first weir, through the exchanger and thus over surfaces of the heat exchanging elements, and then over a second weir. Conveniently, means are provided for distributing flow of the fluid relatively evenly between the top and bottom of the container.

When the heat exchanger comprises banks of heat exchanger elements the inlet chamber typically extends along one side of the container alongside each bank of elements and separate first weirs direct the second fluid from the inlet chamber towards respective banks.

The invention also provides a power generation system comprising: means for pumping relatively cold water from a large body of water to a first heat exchanger as previously defined, thereby cooling a working fluid passing through the heat exchanger; means for pumping relatively warm water from a large body of which shallow part of the sea to a ^■■second heat exchanger also as previously defined thereby heating and pressurising the working fluid previously cooled by the first mentioned heat exchanger; means for using the pressurised working fluid to derive useful power, and means for recirculating the working fluid back to the first mentioned heat exchanger.

The large bodies of water can be different parts of one body such as the sea when water is pumped from upper and lower regions thereof. Alternated separate sources can be used.

The system can also include means for using the relatively cold water to produce fresh water by condensing water vapour from the air.

A construction as described above is readily adapted to the requirements of different situations since any required number of identical banks of panels can be placed in a container of suitable size to provide for any required heat transfer rate and any required flow rate.

An advantage of the rollbonding technique is that it allows relatively complex matrix patterns to be formed on the parallel plates of the individual heat exchanging elements thereby providing heat exchanging elements having complex paths for the fluid selected, to optimise heat transfer characteristics. Further .improvement can be obtained by using different matrix patterns for different elements with a bank, those near the outside being different to those near the centre.

The different banks of panels will normally be connected in parallel though it would be possible in alternative constructions to connect some or all of them in series.

Where the banks of panels are connected in parallel they are preferably connected by special self-sealing couplings designed so as to allow any selected bank to be disconnected without the loss of working fluid from within it. In cases where connections have to be made through the bottom of the tank, a special capping device has been designed to prevent spillage of sea water when changing panel banks. These features are considered to be of great significance since they allow any one bank to be removed for inspection replacement, servicing or cleaning whilst the rest of the heat exchanger is still in operation. These features could indeed be used in situations where panels constructed by techniques other than rollbonding (e.g. by extrusion) are employed.

Potential problems are envisaged with the condensing heat exchangers in which the working fluid e.g. ammonia is lead from the bottom of the heat exchanger after condensing. In a plant of the type described the outlet from the heat exchanger might be separated from the circulation pump by a significant distance and it may be required to route the outlet pipe upwardly over the tank side wall. In such a case, the working fluid would be subjected to reduced pressure and as the fluid may be near its boiling point, problems may occur with re-evaporation and the formation of gas-locks in the pipeline so preventing proper flow and affecting the efficiency of the heat exchanger. According to a second aspect of the invention there is provided a condenser comprising: a heat exchange element formed by rollbonding and defining a path for a working fluid to be condensed, the element being contained in a container for a cooling fluid; and means for using condensed pressurised motive fluid to impel condensed working fluid from a bottom region of the element upwardly so as to allow it to be delivered to a region outside the container for" recycling.

The use of the invention therefore overcomes the problem of a gas lock occurring within the condenser outlet pipe by providing a means for applying a raised pressure to drive the fluid from the outlet pipe rather than utilising a reduced pressure to draw the fluid from the pipe. It is particularly preferred that the means for using the pressurised motive fluid is an educator pump or "jet pump" positioned at the bottom of each heat exchange element. The motive fluid used is the same as the working fluid in the heat exchanger but is supplied directly to the jet pump from a high pressure source such as the circulation pump in the -system.

Although the present invention has been described with a specific reference to a heat exchanger, it is envisaged that the condenser may be used with other equipment e.g. within the process industry.

A further embodiment -.of the second aspect of. the invention provides a condenser comprising a heat exchange element defining a path for a working fluid to be condensed, the element being contained in a container for a cooling fluid; and means to impel condensed working fluid from a bottom region of the element upwardly.so as to allow it to be delivered to a region outside the container for recycling wherein the path for a working fluid and means to impel condensed working fluid are integrally formed within the heat exchanger element.

The invention will now be described by way of example, with reference to the accompanying drawings, in which:-

Figure 1 is a schematic overall view of a system constructed in accordance with the invention and having purpose generating electric power;

Figure 2 is a vertical cross section through the line x-x of Figure 1; Figure 3 is a plan view of the heat exchanger of Figure 2;

Figure 4 is a schematic perspective view shown partly broken away (but not shown to scale) of an inlet manifold shown at 35 on Figure 2;

Figure 5 is a view showing, partly in cross-section and partly in elevation, a releasable coupling also indicated generally at 36 on Figure 2;

Figure 6 is a schematic plan view of a manifold layout;

Figure 7 is a diagrammatic view of a system incorporating the record aspect of the invention; and

Figures 8 and 9 are views of alternative forms of heat exchanger element incorporating the second aspect of the invention.

Referring firstly to Figure 1, cold water from near the sea bottom is pumped by pumps 1 through an inlet 2 to a heat exchanger 3 (the "condenser") . A working fluid, which in this case is ammonia (though it could alternatively be one of a range of HCFC/HFC or other fluids having the right characteristics for the application) is cooled and condensed in the heat exchanger.

It is then pumped by a pump 4 into a second heat exchanger 5 (the "evaporator") where it evaporates, obtaining its latent heat from warm water which is supplied by pumps 7 from an inlet 8 close to the sea surface. Water from inlet 8 is intermittently treated by a chlorinating plant 5A so as to prevent accumulation of fouling organisms on the plates of the heat exchanger 5. The resulting ammonia gas under pressure is used to drive ^;a turbine 9 which is connected to an electricity generator, not shown. The ammonia gas then passes back into the heat exchanger 3 where it is once again condensed by the cold water from the sea bed.

After passing through the heat exchanger 3 the sea water, which may still be cold with respect to the air temperature can be passed, through a condenser 10 which is used to condense moisture from the air to provide a source of fresh water. The sea water is then returned to the sea at some suitable distance from the surface water inlet (8) region.

A sluice 12 can be used to bypass the heat exchanger 3 at any time when the flow through the heat exchanger 3 has to be altered or when complete shut down of the power generation system is required, although such shut-down is very unlikely when using the techniques of this invention.

The heat exchanger 3 is supported on steel beams 13 and 14 and on square section supports such as indicated by reference numeral 15. The square section supports a large tank formed by side walls 16A, base panels 16B and end walls 16D. The top of the tank is open at the inlet and outlet ends, and the centre part (containing the panel banks) are covered by unsealed lightweight decking which keeps the surface of the flowing water to the level of the tops of the panels and supports the weight of maintenance personnel, allowing clear access for inspection etc. of panel banks. It is intended that the decking could be held in position either by its own weight, or by simple quick-release fastenings. A feature of the construction of this tank is that it is made from standard panels which are bolted together with the inter-position of waterproof seals. A tank of any desired size can thus be erected depending on the requirements for a particular situation.

Cold water from the pumps 1 passes from a pipe 17 not an inlet manifold 18 shown on Figure 3. This manifold has eight branches each of which leads to a corresponding hole in the wall 16A of the tank, each hole being the entry point into one of the tank compartments. The compartment (of which eight are shown in Figure 3) have two main functions:- Firstly they divide up the heat exchanger into convenient modules which may each be isolated from the rest (and drained if necessary) in the event of working fluid leakage or other emergency. It is particularly important to have this facility in the case of toxic/hazardous working fluids (such as ammonia) which might dissolve in the water and contaminate the mariculture, aside from normal safety consideration; secondly depending on the level of maintenance required, they offer a choice of either uncoupling and changing single panel banks or closing and draining a whole compartment (e.g. where major tank cleaning operations are being carried out) . They also impart stiffness to the long walls of the tank, so that less supporting steelwork is needed at the side walls.

After passing through each hole, the water enters a settling chamber 19 and a riser 20 leading to a weir 21. When there is excessive water flow (such as in a temporary situation where one of the other sections has to be closed for maintenance etc.) any excess water passes over an overflow weir 22 to be expelled at an overflow outlet 23. Normally however all the water passes over the weir 21 and into a vertical distributor 24A (with barrier plate 16C mounted above) which is supported on the partition walls and floor of the tank. The effect of the distribution device 24A is to ensure that the water flow is distributed evenly between the top and bottom of the tank between the heat exchanger elements 25. The latter are arranged in banks of eight as shown best in Figure 3. After passing the heat exchanger elements 25 the water enters a second vertical distributor 24.B which acts in reverse to collect the' water flow and pass it towards a second weir 26 where it overflows into a water outlet manifold 27. This leads to an outlet pipe 28 and thence to the settling tanks 11 as shown on Figure 1.

The heat exchanger 5 shown in Figure 1 is constructed on similar principles to the heat exchanger 3 though a different number of banks of heat exchanger panels of different rollbond pattern configuration, are required.

These manifolds, one per compartment, may be made in several ways, including roUbonded aluminium. Each manifold 30 inlet is connected to a main manifold (not shown) which is simply a large pipe suitably situated, running along the length of the heat exchanger, and having (for this particular eight compartment design) eight branch outlets. Each manifold 30 has sixteen outlets, each connected to a panel manifold 34, as shown in Figure 5. Each manifold 34 is shown as an aluminium casting formed with interior channels arranged to connect with the open inlet part of the heat exchanger panels and secured in position with adhesive.

Each heat exchanger panel 25 is formed by two sheets aluminium (titanium could alternatively be used) connected together using a rollbonding technique so as to create a complex matrix pattern of channels within. The different panels of a bank could be provided with different matrix patterns, those at the outside of a bank, for instance being different from layers near the centre so as to optimise heat transfer characteristics. In another embodiment of the invention (not shown) the channels of adjacent panels could be deliberately arranged so as to be not immediately facing each other. In this way the raised portions presented by one panel could be made to face the depressed portions between the channels of the adjacent panel or panels, thereby allowing adjacent panels to be more closely spaced than would otherwise be possible. --

The working fluid cools and condenses in its passage through the panels and issues via manifold 35, quick release coupling 36 as shown in Figure 5, flexible pipe 37, roUbonded manifold 38 and then passes through outlet line 39 to the pump 4. The self sealing, releasable couplings are especially designed so that they can be disconnected for removal of a bank of panels without the loss of working fluid. To this end the coupling has a sealing mechanism in each of two separable halves of it. The act of separating the two halves causes the sealing mechanisms to operate on both halves and they do so in such a way as substantially to avoid any leakage. A suitable self-sealing coupling of this type is made by Heat Transfer Engineers (HTE) Ltd.

It is believed that the principles of the invention as embodied in the illustrated design are likely to achieve efficient heat transfer without incurring a pressure loss of more than five or six centimeters head of water.

The system shown in Figure 7 utilises the second aspect of the invention and comprises a circulation pump A which delivers condensed fluid via a pipe to an evaporation B in a tank C containing relatively warm water. The evaporated fluid is used to drive a turbine D and is subsequently fed to a condenser E in a tank H of relatively cold water. A jet pump F is provided at the outlet from the condenser E to drive condensed fluid back to the pump a. A separate feed line G is taken directly from the outlet of the pump A to drive the jet pump E. Figure 8 shows the ^"condenser E comprising a heat exchange element 10 having a pathway 11 for working fluid 12 defined therein by rollbonding. A fluid delivery line 30 connects to the element 10 at an upper region thereof at an inlet 31 and the condensed working fluid leaves the element 10 at an outlet 15 provided at a lower region thereof.

The feed line G provides pressurised, condensed motive fluid directly to a jet pump 13 which is provided adjacent the outlet 15, the jet pump 13 and the outlet 15 feeding into an outlet pipe 18. The jet pump 13 comprises a nozzle 16 for motive fluid and a cavity 17 defined in the outlet pipe 18 adjacen the nozzle 16 and outlet 15.

Referring now to Figure 9, the condenser shown therein has essentially the same components as described in relation to Figure 8 above and identified by the same reference numerals with the suffix 'A'. However, in this case the heat exchange element 10A, jet pump 13A and outlet pipe 18A are formed integrally by rollbonding. In this case the feed line 14A is at least partially formed in the heat exchanger 10A by rollbonding, a separate inlet 32A being provided for connection to the line G. In operation, both of the embodiments shown in Figures 8 and 9 function in the same manner. In each case the condenser forms part of a plant as described in relation to Figure 7, i.e. condenser 3 in tank 3A or condenser E in tank H. The working fluid is supplied from the circulation pump 4, A to the delivery line 30, 30A. The flow of working fluid 12, 12A is directed into the pathway 11, 11A in the heat exchange element 10, 10A and is condensed in the pathway 11, 11A and delivered to the outlet 15, 15A and into the outlet pipe 18, 18A. The motive fluid, which is at higher pressure than the condensing working fluid, is delivered directly to the jet pump 13, 13A from the circulation pump 4, A where it is emitted from the nozzle

16, 16A into the cavity 17, 17A. The pressure in the cavity

17, 17A is lower than in the pathway 11, 11A so condensed working fluid 12, 12A will always flow from the outlet 15, 15A. The motive fluid from the jet pump 13, 13A provides pressure to the fluid in the outlet pipe 18, 18A and serves to drive the fluid from the condenser to the circulation pump. In this manner, the formation of gas bubbles is reduced and even if bubbles do form, the action of the pump means that fluid is driven from the condenser E to the circulation pump A. The jet pump described has the advantage that it is easily formed during the production of the condenser and requires no moving parts and is essentially maintenance free. However, other types of pumps could still be used to provide pressurised motive fluid at the outlet from the heat exchange element.

Claims

1. A heat exchanger comprising a path for fluid, the path passing through roUbonded (as herein defined) heat exchanging elements connected in parallel.

2. A heat exchanger according to claim 1 comprising: a bank of roUbonded panels having at their edges respective^' inlet ports arranged adjacent to each other and respective outlet ports also arranged adjacent to each other; an inlet manifold connected to the outlet ports.

3. A heat exchanger according to claim 2 in which the inlet and/or outlet manifold comprises a casting or moulding secured over the inlet and/or outlet ports.

4. A heat exchanger according to claim 2 in which the elements are located in a container defining a second path for a second fluid, the interior of the container being exposed to atmospheric pressure.

5. A heat exchanger according to claim 2 comprising banks of heat exchanging elements, each bank having its own inlet and outlet manifolds, the banks being connected in parallel.

6. A heat exchanger according to claim 5 in which the banks are connected in parallel by couplings which allow each bank to be disconnected without loss of fluid therefrom.

7. A heat exchanger according to claim 4 in which the second path for the second fluid extends from an inlet chamber, over a first weir, through the container and thus over surfaces of the heat exchanging elements, and then over a second weir.

8. A heat exchanger according to claim 7 comprising means for distributing flow of the second fluid relatively evenly between the top and bottom of the container.

9. A heat exchanger according to claim 7 when dependent on claims 4 and 5 in which the inlet chamber extends along one side of the container alongside each bank of elements and in which separate first weirs direct the second fluid from the inlet chamber towards respective banks.

10. A heat exchanger according to claim 5 in which the banks are connected in parallel by roUbonded manifolds.

11. A heat exchanger according to claim 1 in which the elements are of aluminium or titanium.

12. a power generation system comprising: means for pumping relatively cold water from a relatively deep part of the sea to a first heat exchanger constructed in accordance with any preceding claim, thereby cooling a working fluid passing through the heat exchanger, means for pumping relatively warm water from a relatively shallow part of the sea to a second heat exchanger also constructed in accordance with any preceding claim thereby heating and pressurising the working fluid previously cooled by the first mentioned heat exchanger, means for using the pressurised working fluid to derive useful power, and means for recirculating the working fluid back to the first mentioned heat exchanger.

13. A power generation system according to claim 12 comprising means for using the relatively cold water to produce fresh water by condensing water vapour from the air.

14. A heat exchanger according to claim 2 in which adjacent elements are arranged face to face and have different profiles so the channels defined by one element face spaces between channels of an adjacent element.

15. A condenser comprising a heat exchange element formed by rollbonding defining a path for a working fluid to be condensed, the element being contained in a container for a cooling fluid; and means for using condensed, pressurised motive fluid to impel condensed working fluid from a bottom region of the element upwardly so as to allow it to be delivered to a region outside the container for recycling.

16. A condenser comprising a heat exchange element as claimed in claim 15, wherein the path for a motive fluid and means to impel condensed working fluid are integrally formed within the heat exchange element.

17. A condenser according to claim 15 wherein the means to impel the condensed working fluid is a jet pump.

18. A condenser as claimed in claim 15 wherein the motive fluid used by the jet pump is the same as the working fluid delivered to the heat exchange element.