NZ552697A - Heat exchange apparatus and heat energy transfer system - Google Patents

Abstract

An energy transfer system (101) includes a vessel (1) containing a thermally conductive liquid (2). First, second and third conduits (3, 7, 11) having respective first, second and third thermally conductive sections (6, 10, 14) are immersed in the liquid. A working fluid is conveyed from the outlet of the second conduit (7) to an energy conversion means (T) capable of converting internal energy in the working fluid to useful work, then to the inlet of the third conduit (11), thereby transferring heat from the working fluid to the thermally conductive liquid. The working fluid is than returned from the outlet of the third conduit to the inlet of the second conduit. The energy conversion means preferably includes a turbopump.

Description

552697 *10055115770* PATENTS FORM NO. 5 Our ref: RC506655NZPR NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION Complete after Provisional No. 552697 Filed: 17 January 2007 HEAT EXCHANGE APPARATUS AND HEAT ENERGY TRANSFER SYSTEM We, RENEWABLE ENERGY SYSTEMS LIMITED a Guernsey company of Avenue House St Julians Avenue, St Peter Port, GY11WA, Guernsey hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: INTELLECTUAL PROPERTY OFFICE OF N.Z -1 - 11 DEC 2007 RECEIVED 300828800J ,DOC:RC:QAKLD 552697 300827908. RC506655NZPR HEAT EXCHANGE APPARATUS AND HEAT ENERGY TRANSFER SYSTEM TECHNICAL FIELD The present invention relates to apparatus and methods for recovering energy, and has particular application to recovery of energy from waste heat.

BACKGROUND TO THE INVENTION Many practical gas or vapour based power generation systems require heat to be rejected to the atmosphere in order to condense the working fluid prior to pumping. Minimising 10 the heat lost at this stage can increase the overall efficiency of the system. Accordingly, it is desirable to transfer some of the superheat and/or latent heat rejected from the working fluid during the condensation process back to the liquid working fluid after it has been through the pump, in order to preheat the working fluid before it is vapourised by an external heat source.

A further problem with such systems may be the energy required to circulate the 15 working fluid around the system. Some systems of the prior art use electric pumps to circulate the working fluid. However, the motors driving such pumps may in some cases only have an efficiency of around 30%. This may mean that the pumps consume an unacceptably large amount of power, which may in turn mean that the system has an unacceptably low thermal efficiency.

In many closed systems in which a working fluid exists in both a liquid and gaseous state, a fluid reservoir or "receiver" is used immediately upstream of a pump in order to ensure that the pump impeller is exposed only to liquid and not vapour. However, installation constraints may not allow the receiver to be positioned near the pump, which can lead to problems with an inadequate pressure head at the inlet to the pump.

OBJECT OF THE INVENTION It is an object of a preferred embodiment of the invention to provide an energy transfer system and/or a waste heat recovery system which will overcome or ameliorate problems with such systems at present, or at least to provide the public with a useful choice.

Other objects of the present invention may become apparent from the following 30 description, which is given by way of example only. 552697 300827908. RC5066S5NZPR SUMMARY OF THE INVENTION According to a first aspect of the present invention there is provided an energy transfer system including: ■ a vessel containing a thermally conductive liquid; ■ a first conduit having an inlet and an outlet outside the vessel, and a first thermally conductive section between the inlet and the outlet immersed in said conductive liquid; ■ a second conduit having an inlet and an outlet outside the vessel, and a second thermally conductive section between the inlet and the outlet immersed in said conductive liquid, the second conduit located, in use, above the first conduit; ■ a third conduit having an inlet and outlet outside the vessel and a third thermally conductive section immersed in said conductive liquid, the third conduit located, in use, below the first conduit; wherein ■ in use the first conduit contains a first fluid and the second conduit contains a 15 working fluid, the saturation temperature of the thermally conductive fluid is greater than a temperature of the first fluid at the inlet to the first conduit, the construction and arrangement being such that the working fluid is conveyed from the outlet of the second conduit to an energy conversion means capable of converting internal energy in the working fluid to useful work, then to the inlet of the third conduit, thereby transferring heat from the working fluid to the 20 thermally conductive liquid, and then returned from the outlet of the third conduit to the inlet of the second conduit.

Preferably the working fluid circulates around a closed system.

Preferably the working fluid enters the energy conversion means as a vapour.

Preferably the energy conversion means includes a turbine.

Preferably vapour is condensed between the inlet to the third conduit and the inlet to the second conduit.

Preferably the energy transfer system includes pumping means for pumping the condensed working fluid.

Preferably the pumping means includes a turbopump including a turbine chamber and a 30 working fluid reservoir, the turbine chamber provided with an inlet for supplying working fluid to a turbine rotor provided within the turbine chamber, and an outlet for removing working fluid 552697 300827908. RC506655NZPR from the turbine chamber, the turbopump further including a working fluid reservoir including an inlet, an outlet and a pumping means including an impeller provided within the working fluid reservoir adapted to pump working fluid out of the working fluid reservoir through the outlet, wherein the turbine rotor and pumping means impeller are connected to a common shaft so 5 that rotation of the shaft by the turbine rotor rotates the pump impeller.

Preferably the turbine chamber is above the working fluid reservoir when in use.

Preferably the pumping means and energy transfer means include a turbopump provided with an electrical generator including a generator stator and a generator rotor connected to the shaft such that rotation of the shaft rotates the generator rotor, thereby 10 generating electrical potential in the stator.

Preferably at least one of said first and second thermally conductive sections includes an assembly having an inlet manifold, an outlet manifold, and a plurality of thermally conductive tubes extending between said inlet manifold and said outlet manifold.

Preferably at least a portion of the thermally conductive section of said third conduit is 15 located, in use, at or adjacent a base of said vessel.

Preferably at least a portion of the thermally conductive section of said second conduit is located, in use, at or adjacent a top of said vessel.

Preferably wherein the thermally conductive liquid is a thermal oil.

Preferably the vessel is thermally insulated.

Preferably the energy transfer system includes a fourth conduit having an inlet at or adjacent a top of the vessel and an outlet at or adjacent a base of the vessel, and a pumping means for pumping the thermally conductive liquid from the inlet to the outlet of the fourth conduit.

Preferably the energy transfer system includes means for cooling the thermally 25 conductive liquid flowing though the fourth conduit.

Preferably the means for cooling the thermally conductive liquid includes a heat pump.

According to a second aspect of the present invention a waste heat recovery system includes an energy transfer system as described in the first aspect, wherein the first fluid is heated by a waste heat source. 552697 300827908. RC506655NZPR According to a further aspect of the present invention an energy transfer system is substantially as herein described with reference to the accompanying drawings.

Further aspects of the invention, which should be considered in all its novel aspects, will become apparent from the following description given by way of example of possible 5 embodiments of the invention.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a schematic diagram of one possible embodiment of the heat exchange apparatus and a heat recovery system of the present invention.

Figure 2 is a diagrammatic perspective view of a preferred embodiment of a thermally 10 conductive section of a conduit, with a section of one of the tubes removed.

Figure 3 is a diagrammatic cross section side view of a preferred turbopump.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Referring first to Figure 1, a heat exchange apparatus according to one embodiment of the present invention is generally referenced 100. The heat exchange apparatus is part of an 15 energy transfer system such as a waste heat recovery system 101.

The heat exchange apparatus 100 includes a vessel, also referred to herein as a tank 1, within which is provided a thermally conductive liquid 2, for example water or thermal oil.

A first conduit 3 has an inlet 4 and an outlet 5 outside the tank 1, and a first thermally conductive section 6 inside the tank 1 and immersed in the liquid 2.

A second conduit 7 also has an inlet 8 and outlet 9 outside the tank 1, and a second thermally conductive section 10 inside the tank 1 and immersed in the liquid 2.

The second thermally conductive section 10 is located, in use, above the first thermally conductive section 6.

A third conduit 11 having an inlet 12 and outlet 13 outside the tank 1 and a thermally 25 conductive section 14 immersed in the liquid 2, is provided. In use the first conduit 3 carries a fluid which has been heated by a heat source, preferably waste heat. Examples of suitable waste heat sources will be well known to those skilled in the art, and include heat from boiler flues and the like. Thus thermal energy from the source of waste heat is absorbed by the thermally conductive liquid 2. This increase in temperature causes a convection current in the 30 liquid 2 which carries the heated liquid to the second conduit 7 above. 552697 300827908. RC5066S5NZPR If required, the convection current may be complemented by a fourth conduit 15 which has an inlet 16 at or adjacent the top of the tank and an outlet 17 at or adjacent the base of the tank. The thermally conductive liquid 2 is pumped though the fourth conduit 15 by a suitable pump 18. If required, heat may be rejected from the fluid flowing through the fourth conduit by 5 an optional heat exchange/rejection means 19, which may be a liquid/air heat exchanger, a heat pump or any other suitable means of cooling the liquid.

In use a working fluid flows through the second conduit 7. The working fluid is in a liquid state at inlet 8, being at a temperature of approximately 8°C in a preferred embodiment and comprising R124 for example. In a preferred embodiment the temperature of the liquid 2 10 entering the base of the tank is preferably maintained at approximately 8°C in order to cool the working fluid exiting the third conduit 11 to a similar temperature.

The working fluid absorbs energy from liquid 2 upon entering thermally conductive section 10, and flashes to vapour. In a preferred embodiment the temperature of the liquid 2 at the top of the tank is approximately 90°C, and the working fluid exits outlet 8 at approximately 15 that temperature.

The working fluid, in a vapour state, is provided to an energy conversion means capable of converting internal energy in the working fluid to useful work. In a preferred embodiment this effectively allows heat such as waste heat from the fluid in first conduit 3 to be recovered for performing useful work. In a preferred embodiment the energy conversion means comprises a 20 turbine, or multiple turbines in parallel.

In a preferred embodiment the working fluid vapour exits the turbine at a temperature of approximately 60°C and a pressure of around 4 bar. The turbine allows energy to be extracted from the fluid in the first conduit 3 via the working fluid in the form of mechanical energy and may be directly converted to electrical energy using known techniques, The turbine is 25 preferably a turbopump, referenced T, that is, a device having in combination a turbine and pump. A suitable turbopump is described further below. The turbopump is preferably provided with an electrical generator or alternator for converting the internal energy of the working fluid into electrical energy.

The working fluid is then supplied to inlet 12 of third conduit 11, and energy is absorbed 30 by thermally conductive liquid 2 from the thermally conductive section 14. In a preferred embodiment the temperature of the working liquid at outlet 13 is approximately 8°C.

Depending on the properties of the working fluid and the system generally, a means of rejecting heat, such as a liquid/air heat exchanger or a heat pump H may be required to ensure 552697 300827908. RC506655NZPR that the temperature of the working fluid is sufficiently low (e.g. approximately 86C (for R124) for the working fluid to be returned to a liquid state for supply to a reservoir or receiver. The receiver may be a separate component (not shown), or more preferably may be integrated into a pump or turbopump T as is described further below. The liquid working fluid is then pumped 5 to the inlet 8 of the second conduit 7 by suitable pumping means. The pumping means is preferably also part of turbopump T. One or more further pumps (not shown), for example standard electric pumps, may additionally or alternatively be provided, for example if a lift pump is required upstream of the turbopump, or if an auxiliary pump is required for startup. The working fluid is provided to the inlet 8 at the appropriate pressure e.g. 15 bar.

The thermally conductive liquid 2 is selected to have a saturation temperature greater than the maximum temperature of the working fluid at the inlet to the third conduit 11, and greater than the maximum temperature of the fluid in the first conduit 3, and so does not boil when heated by the first conduit 3.

In a preferred embodiment the third thermally conductive section 14 is at or adjacent the 15 base of the tank 1 and the second thermally conductive section 10 is at or adjacent the top of the tank 1. In a preferred embodiment the first thermally conductive section 6 is provided between the first and second thermally conductive sections.

The tank 1 is preferably shaped as a body of rotation about a vertical axis and preferably has a bottom portion 20 which is of a larger diameter than the top portion 21. In 20 some embodiments the sides of the tank may taper upwards, while in other embodiments the change in diameter may be a step.

The tank 1 is preferably made from a relatively thermally insulating material and/or is substantially surrounded by thermal insulation so as to minimise any heat loss through the walls.

In a preferred embodiment the shape and dimensions of the first, second and third thermally conductive sections are selected such that a required amount of heat is transferred to or from the working fluid and the thermally conductive liquid 2 when the working fluid is flowing at a required pressure and flow rate. However, in some embodiments it may be necessary to add or remove extra heat to the fluid 2 in order to ensure that sufficient heat is transferred to 30 the working fluid.

In another embodiment (not shown) the waste heat recovery system may use a number of heat exchange apparatus 100 and turbines T in series. In this embodiment the refrigerant vapour exiting a first turbine T at around 60°C and 4 bar is supplied to the third conduit 9 of a 552697 300827908. RC506655NZPR second heat exchange apparatus. The second heat exchange apparatus may not require a first conduit 3, but may instead rely on the third conduit to supply heat to liquid 2 (although a first conduit may still be provided to add further heat if required), and a second turbine (or "stage") is supplied from the second conduit 7 of the second heat exchange apparatus. The 5 working fluid exiting the output of the second turbine may be returned to the third conduit of the first heat exchanger 100. It will be seen that many stages may be cascaded in this manner.

In one embodiment the top portion 21 of the heat exchange apparatus 100 has a diameter of around 500mm and a height of around 500mm, while the bottom portion 20 has a diameter of around 1000-1500mm and a height of around 500mm. The first, second and third 10 conduits may be made from 32mm ID copper pipe.

In some embodiments the thermally conductive sections may be coils of thermally conductive material such as copper pipe. However, in a more preferred embodiment shown in Figure 2, one or more of the conduits includes an assembly, generally referenced 200, which includes an inlet manifold 22, an outlet manifold 23 and a plurality of thermally conductive 15 conduit sections 24 extending between the inlet and outlet manifolds. The thermally conductive sections 24 are preferably copper tube having substantially the same internal diameter as the inlet 25 to the inlet manifold. The manifolds 22, 23 are preferably substantially circular in cross section, with the copper tubes 24 arranged parallel to the central axis of the circular section. The copper tubes 24 may be arranged in any suitable pattern, provided there is sufficient space 20 between each adjacent tube for the thermally conductive liquid to move therebetween. Multiple inlets and outlets may be connected to each manifold e.g. for supplying multiple turbines in parallel.

In a preferred embodiment a web or mesh of thermally conductive material 26 may be provided within, and in contact with, an inner surface of the tubes 24. This web may increase 25 the surface area of thermally conductive material in contact with the working fluid, and thereby increase the heat transfer between the working fluid and the thermally conductive liquid.

This design provides a large surface area for heat to be conducted between the copper tubes and the thermally conductive liquid, while minimising the pressure loss experienced by the working fluid as it flows through the conductive section in use.

Those skilled in the art will appreciate that the present invention allows heat unused by the turbine to be returned to the heat exchanger apparatus for recovery.

Referring next to Figure 3, a turbopump for use with the waste heat recovery system 101 described above is generally referenced 300. 552697 300827908. RC506655NZPR The turbopump 300 includes a central shaft 27 on which are provided a pump impeller 28 and turbine rotor 29. By mounting the pump impeller 28 on the same shaft as the turbine rotor 29, power transmission losses, such as would be incurred in converting the rotational power of the turbine rotor to electrical power to drive an electric pump, are minimised.

The turbopump 300 includes an integral fluid reservoir or receiver 30, and the impeller 28 is positioned towards the bottom of the receiver. By positioning the pump impeller 28 at or adjacent to the bottom of the receiver 30 the impeller 28 is surrounded by liquid working fluid under relatively high pressure. Integrating the receiver 28 with the pump housing 31 also reduces the overall size of the system and reduces manufacturing costs.

The receiver has an inlet 32 for receiving the working fluid, and an outlet 33 through which the fluid is pumped by the impeller 28.

The turbine rotor 29 may be of any suitable design such as is known to those skilled in the art, and is preferably a radial flow design. The turbine rotor 29 is provided within a chamber 34 having an inlet nozzle 35 for supplying pressurized working fluid to the rotor 29 and an outlet 15 36 through which the working fluid can exit after it has passed through the chamber 34.

In the embodiment shown the turbopump 300 is provided with an electrical generator or alternator, generally referenced 400, including a rotor 37 and a stator 38, but in other embodiments the generator 400 may be omitted, for example if a mechanical power output is required rather than an electrical output, or if no power is to be extracted from the turbopump.

The generator rotor 37, stator 38 and bearings 39 are preferably sprayed with a mixture of lubricating oil and liquid working fluid from one or more suitably placed capillary tubes 40, as described in international application No. PCT/AU2005/001956. The oil collects in a sump 41 and flows through an orifice 42 to the receiver 30. The electrical configuration of the generator 400 is preferably also as described in international application No.PCT/AU2005/001956, 25 although other suitable generator/alternator configurations may also be used.

While the generator 400 is shown above the turbine rotor 29 in Figure 3, in some embodiments it may be more convenient to locate the turbine rotor 29 above the generator section 400, as shown schematically in Figure 1.

Those skilled in the art will appreciate that the present invention provides an energy 30 transfer system which allows transfer of thermal energy to mechanical and/or electrical work, with a minimum of energy wasted as heat rejected to the environment. 552697 300827808. RC506B55NZPR Where in the foregoing description, reference has been made to specific components or integers of the invention having known equivalents, then such equivalents are herein incorporated as if individually set forth.

Although this invention has been described by way of example and with reference to 5 possible embodiments thereof, it is to be understood that modifications or improvements may be made thereto without departing from the spirit or scope of the appended claims. 552697 300827908. RC50S656NZPR

Claims (19)

1. An energy transfer system including: ■ a vessel containing a thermally conductive liquid; ■ a first conduit having an inlet and an outlet outside the vessel, and a first thermally 5 conductive section between the inlet and the outlet immersed in said conductive liquid; ■ a second conduit having an inlet and an outlet outside the vessel, and a second thermally conductive section between the inlet and the outlet immersed in said conductive liquid, the second conduit located, in use, above the first conduit; ■ a third conduit having an inlet and outlet outside the vessel and a third thermally 10 conductive section immersed in said thermally conductive liquid, the third conduit located, in use, below the first conduit; wherein ■ in use the first conduit contains a first fluid and the second conduit contains a working fluid, the saturation temperature of the thermally conductive fluid is greater than a temperature of the first fluid at the inlet to the first conduit, the construction and 15 arrangement being such that the working fluid is conveyed from the outlet of the second conduit to an energy conversion means capable of converting internal energy in the working fluid to useful work, then to the inlet of the third conduit, thereby transferring heat from the working fluid to the thermally conductive liquid, and then returned from the outlet of the third conduit to the inlet of the second conduit. 20

2. The energy transfer system of claim 1 wherein the working fluid circulates around a closed system.

3. The energy transfer system of claim 2 wherein the working fluid enters the energy conversion means as a vapour.

4. The energy transfer system of claim 3 wherein the energy conversion means includes a 25 turbine.

5. The energy transfer system of claim 3 or 4 wherein the vapour is condensed between the inlet to the third conduit and the inlet to the second conduit.

6. The energy transfer system of claim 5 including pumping means for pumping the condensed working fluid, 30 7. The energy transfer system of claim 6, wherein the pumping means includes a turbopump including a turbine chamber and a working fluid reservoir, the turbine 552697

300827908. RC506655NZPR -12- chamber provided with an inlet for supplying working fluid to a turbine rotor provided within the turbine chamber, and an outlet for removing working fluid from the turbine chamber, the turbopump further including a working fluid reservoir including an inlet, an outlet and a pumping means including an impeller provided within the working fluid 5 reservoir adapted to pump working fluid out of the working fluid reservoir through the outlet, wherein the turbine rotor and pumping means impeller are connected to a common shaft so that rotation of the shaft by the turbine rotor rotates the pump impeller.

8. The energy transfer system of claim 7 wherein the turbine chamber is above the working fluid reservoir when in use. 10

9. The energy transfer system of any one of claims 1-6 wherein the pumping means and energy transfer means include a turbopump provided with an electrical generator including a generator stator and a generator rotor connected to the shaft such that rotation of the shaft rotates the generator rotor, thereby generating electrical potential in the stator. 15

10. The energy transfer system of any one of the preceding claims wherein at least one of said first and second thermally conductive sections includes an assembly having an inlet manifold, an outlet manifold, and a plurality of thermally conductive tubes extending between said inlet manifold and said outlet manifold.

11. The energy transfer system of any one of the preceding claims wherein at least a 20 portion of the thermally conductive section of said third conduit is located, in use, at or adjacent a base of said vessel.

12. The energy transfer system of any one of the preceding claims wherein at least a portion of the thermally conductive section of said second conduit is located, in use, at or adjacent a top of said vessel. 25

13. The energy transfer system of any one of the preceding claims wherein the thermally conductive liquid is a thermal oil.

14. The energy transfer system of any one of the preceding claims wherein the vessel is thermally insulated.

15. The energy transfer system of any one of the preceding claims wherein the energy 30 transfer system includes a fourth conduit having an inlet at or adjacent a top of the vessel and an outlet at or adjacent a base of the vessel, and a second pumping means 552697

300827908. RC50B655NZPR - 13- for pumping the thermally conductive liquid from the inlet to the outlet of the fourth conduit.

16. The energy transfer system of claim 15 including means for cooling the thermally conductive liquid flowing though the fourth conduit.

17. The energy transfer system of claim 16 wherein the means for cooling the thermally conductive liquid includes a heat pump.

18. A waste heat recovery system including the energy transfer system of any one of the preceding claims, wherein the first fluid is heated by a waste heat source.

19. An energy transfer system substantially as herein described with reference to the accompanying figures.