EP1836378A1

EP1836378A1 - Methods and apparatus for power generation

Info

Publication number: EP1836378A1
Application number: EP05818424A
Authority: EP
Inventors: Kenneth William Patterson Drysdale
Original assignee: Renewable Energy Systems Ltd
Current assignee: Renewable Energy Systems Ltd
Priority date: 2004-12-24
Filing date: 2005-12-23
Publication date: 2007-09-26
Also published as: AU2005318868A1; WO2006066347A1; EP1836378A4; US20100126195A1; NZ556092A; BRPI0516416A; US20080289335A1

Abstract

A refrigeration apparatus (7200) includes a heat pump circuit (7201) and a power generation circuit (7100). The power generation circuit (7100) includes an evaporator (701) including a first and a second heat exchanger (710a, 710b), a turbine (702), a condenser (703) and a pump (704). The first heat exchanger (710a) absorbs heat rejected from the heat pump circuit (7201) into a power generation circuit (7100) while the second heat exchanger (710b) further heats the fluid. The power generation circuit (7100) includes a bypass (707) which allows a portion of working liquid to enter the turbine (702) without passing through the evaporator (701). A heat pump (704) with similar bypass is also disclosed. Also disclosed are dual stage turbine design and a nozzle (10300) for a turbine which includes two fluid paths (1011, 1014) that adapted to receive and mix the liquid and vapour streams of working fluid, so that the liquid working fluid is vaporized by the heat from the vapour working fluid.

Description

METHODS AND APPARATUS FOR POWER GENERATION

Field of the Invention

The present invention relates to methods and apparatus for utilizing heat which would otherwise be rejected to the environment, and in particular, but not exclusively to methods and apparatus for generating power from a Rankine type cycle and/or at least reducing the net power consumed by a heat pump apparatus.

Background to the Invention

It is well known that almost every practical thermodynamic system rejects some heat to the environment. In times of cheap energy production this has not been viewed as a problem. However, in recent times energy availability has dwindled, and the cost of energy has begun to rise. Accordingly, a need has been recognized around the world to ensure that any energy consumed is used as efficiently as possible.

Two well known examples of systems which reject a relatively high proportion of the energy they consume as heat are refrigeration cycles and Rankine cycles.

It would be beneficial to develop systems and methods which utilize some of the heat which these apparatus would traditionally waste by rejecting it to the environment.

Object of the Invention

It is an object of a preferred embodiment of the present invention to provide a method and/or an apparatus for power generation which will overcome or ameliorate problems with such methods and/or apparatus, or to at least provide a useful choice.

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 embodiments of the invention. Summary of the Invention

According to one aspect of the present a turbine nozzle includes a first fluid path which includes a first inlet adapted to receive a first working fluid vapour stream, and a first outlet adapted to communicate a jet of said working fluid to a rotor of a turbine, the nozzle further including a second fluid path which includes a second inlet adapted to receive a second substantially liquid working fluid stream and a second outlet adapted to communicate a jet of said second working fluid to the rotor of said turbine, wherein the nozzle is adapted to mix the jets of working fluid so that at least part of the liquid working fluid is vaporised by heat from the working fluid vapour.

Preferably, said first working fluid stream and said second working fluid stream are from a common working fluid circuit.

Preferably, substantially all of the substantially liquid working fluid vapour is vaporised by heat from the substantially vapour working fluid jet.

Preferably, the first and second fluid paths are substantially circular or annular in cross-section.

Preferably, the second outlet is concentric with the first fluid path.

Preferably, the first fluid path has a converging/diverging section adapted to accelerate the stream of working fluid vapour to a mean velocity above the local speed of sound.

Preferably, a section of the first fluid path immediately downstream of the converging/diverging section has a substantially constant cross-section.

Preferably, the second outlet is in the substantially constant cross-section section of the first fluid path.

According to a further aspect of the present invention a turbine means includes at least one rotor and at least one nozzle as described in any of the eight immediately preceding paragraphs for supplying working fluid to the at least one rotor. Preferably, the second working fluid is substantially completely vapourized before impinging on the rotor.

According to a further aspect of the present invention there is provided a dual stage turbine including a housing including a first chamber provided with a first inlet nozzle for supplying a working fluid to a first turbine rotor rotatably connected to the housing within the first chamber, the first chamber including a first outlet adapted to receive working fluid exiting the first turbine rotor, the first outlet connected to a second inlet nozzle provided in a second chamber, the second nozzle supplying a working fluid to a second turbine rotor which is rotatably connected to the housing, the housing further including a second outlet adapted to receive fluid exiting the second turbine rotor, wherein the first and second turbine rotors are independently rotatable.

Preferably, said first and second turbine rotors may be substantially identical.

Preferably, the working fluid from the first nozzle is radially incident on the first rotor.

Preferably, the working fluid from the second nozzle is radially incident on the second rotor.

Preferably, said working fluid exits each said turbine rotor substantially axially.

Preferably, each said turbine rotor is operably connected to an electrical energy generation means.

Preferably, said first inlet nozzle is the turbine nozzle described above.

According to a further aspect of the present invention a heat pump includes a working fluid circuit including, in order, a compressor, a condenser, a receiver, a throttling means, an evaporator, and a first turbine, wherein the circuit further includes a bypass means operable to transfer a proportion of a working fluid within said working fluid circuit from upstream of said throttling means to said first turbine without passing through the throttling means or said evaporator.

Preferably, said bypass means includes working fluid pumping means. Preferably, said working fluid circuit rejects heat to a second working fluid in a second working fluid circuit via first heat exchanger means.

Preferably, said second working fluid circuit includes a second turbine.

Preferably, said second working fluid circuit includes second heat exchanger means operable to add further heat to said second working fluid.

Preferably, said first turbine is a turbine as described above.

According to a further aspect of the present invention a power generation apparatus includes a working fluid circuit including, in order of fluid flow, an evaporator means, a turbine means, a condenser means and a pumping means, wherein the working fluid circuit is adapted to allow a first portion of a working fluid exiting the condenser means to pass through the evaporator means before entering the turbine means, and a second portion of the working fluid to enter the turbine means without passing through the evaporator means.

Preferably, said first turbine is the turbine means described above.

Preferably, the working fluid circuit may include valve means for controlling the ratio of the first portion of working fluid to second portion of working fluid entering the turbine.

Preferably, the working fluid may be a refrigerant.

According to a further aspect of the present invention a refrigeration apparatus includes a heat pump means including an evaporator for cooling a medium to be cooled and a condenser, wherein the condenser rejects heat to an evaporator means of a power generation apparatus as described above.

Preferably, the condenser means of the power generation apparatus may reject heat to an evaporator of a second heat pump. According to a further aspect of the present invention a method of supplying working fluid to a turbine means having a rotor means includes the steps of: directing a jet of substantially vapour working fluid towards the rotor; directing a jet of substantially liquid working fluid towards the rotor, mixing the jets prior to the substantially liquid working fluid jet impinging on the rotor so that at least part of the substantially liquid working fluid vapour is vaporised by heat from the substantially vapour working fluid jet.

Preferably, the method includes directing the jet of working fluid vapour through a fluid path having a converging section.

Preferably, the method includes directing the jet of working fluid vapour through a fluid path having a converging/diverging section.

According to a further aspect of the present invention a heat pump includes a working fluid circuit including, in order, a compressor, a condenser, a receiver, a throttling valve, and an evaporator, the heat pump further including heat exchanger means for rejecting heat to a second working fluid cycle.

According to a further aspect of the present invention there is provided a method of generating power using a pre-existing refrigeration circuit, the method including inserting a heat exchanger upstream of a condenser in the pre-existing refrigeration circuit whereby heat is transferred from the pre-existing refrigeration circuit to working fluid in a heat pump circuit, the heat pump circuit including an evaporator or boiler downstream of the heat exchanger, a turbine downstream of the evaporator or boiler, a condenser downstream of the turbine and means to circulate the working fluid about said heat pump circuit.

According to a further aspect of the present invention there is provided a method for generating alternating current electric power from an energy recovery system using a source of waste heat, the system including a turbine unit and a generator having a plurality of windings, the generator being operably associated with the turbine, comprising the steps of generating a first alternating current from at least a first of a the plurality of windings, and a second alternating current from at least another from the plurality of windings, increasing the voltage of each alternating current using a transformer, rectifying the output of the transformers to produce a first direct current output and a second direct current output, cumulatively adding the first direct current output to the second direct current output to produce a cumulative direct current output, and inverting the cumulative direct current output to produce alternating current electric power.

Preferably the first and second alternating currents are each produced from a plurality of phase synchronised windings.

Preferably the step of rectifying the output of the transformers includes using a bridge rectifier and filtering the output of the bridge rectifier.

Apparatus for generating alternating current electric power in an energy recovery system from waste heat, the apparatus including a turbine unit and a generator operably associated with the turbine, the generator having a plurality of windings arranged to produce a first alternating current and a second alternating current, a first transformer to increase the voltage of the first alternating current and in the second transformer to increase the voltage of the second alternating current, a first and second rectifying means to rectify the output of each transformer, and the rectified outputs being cumulatively added together to produce a cumulative direct current output, and an inverter means to invert the cumulative direct current output to alternating current electric power.

A method for generating alternating current electric power in an energy recovery system from waste heat, the system including two turbine rotors, each turbine rotor adapted to operate at a different speed, a generator operably associated with each turbine rotor, comprising the steps of: generating a first alternating current using each generator, increasing the alternating current output of each generator using a transformer, rectifying the output of each transformer to produce a direct current output, cumulatively adding the direct current outputs together, and inverting the cumulative direct current output to produce alternating current power.

Apparatus for generating alternating current electric power in a energy recovery system from waste heat, the apparatus including two turbine rotors adapted operate independently, each turbine rotor operably associated with a generator, each generator producing an alternating current which is provided to a transformer, each transformer being operable to increase the voltage of each of the alternating currents, rectifying means to rectify the output of each transformer to produce a first direct current output and a second direct current output, the first and second direct current outputs being cumulatively combined, and an inverter means to invert the cumulative direct current output to provide alternating current electric power.

Brief Description of the Figures

Figure 1 : Is a schematic diagram of a heat pump.

Figure 2: Is a schematic diagram of an alternative embodiment of a heat pump.

Figure 3: Is a schematic diagram of a further alternative embodiment of a heat pump.

Figure 4: Is a schematic diagram of a second working fluid circuit with two turbines in parallel.

Figure 5: Is a schematic diagram of a second working fluid circuit with two turbines in series.

Figure 6: Is a simplified schematic diagram of a power generation apparatus according to a preferred embodiment of the invention.

Figure 7: Is a schematic diagram of a refrigeration apparatus of the present invention, incorporating the power generation apparatus of Figure 6.

Figure 8: Is a schematic diagram of an alternative embodiment of the power generation apparatus of Figure 6. Figure 9: Is a schematic diagram of an alternative power generation apparatus according to one embodiment of the present invention.

Figure 10: Is a diagrammatic cross-section of a turbine nozzle according to the present invention.

Figure 11 Is a diagrammatic cross section of a dual stage turbine of the present invention.

Fig 12 Is a simplified circuit diagram of four generator windings connector in a phase synchronised manner.

Fig 13 Is a simplified circuit diagram of five groups of windings connected as shown in figure 12 together with transformer, rectifier and inverter apparatus arranged to provide a required alternating current output.

Best Modes for Performing the Inventions

The term "fluid" is used here in to denote a liquid, gas, or a mixture of liquid and gas.

The term "working fluid" is used herein to denote any fluid suitable for use with the associated working fluid circuit, whether in a liquid or gaseous state.

The term "heat pump" is used to describe apparatus which are capable of transferring heat from a first medium to a relatively warmer a second medium, for example a phase change heat pump. The term includes embodiments in which heat is, in practice, transferred from a higher temperature medium to a lower temperature medium.

The term "turbine" is used to describe a turbomachine which converts energy from a working fluid vapour to useful power. Where the context requires it, the term "turbine" includes devices which incorporate means to generate electrical power.

The terms "upstream" and "downstream" are used to indicate a direction relative to the normal flow of working fluid. Referring first to Figure 1 , a heat pump according to one possible embodiment of " the present invention is generally referenced 1100.

The heat pump 1100 includes a first closed working fluid circuit 1101 which includes, in order according to the flow of working fluid, a compressor 101 , a condenser 102, a receiver 103, a throttling or Tx valve 404 and an evaporator 105. A first turbine 106 is provided between the compressor 101 and condenser 102. A second turbine 106a may optionally be included between the evaporator 105 and the compressor 101.

The working fluid circuit 1101 further includes a bypass 107 which allows liquid working fluid to pass from upstream of the Tx valve 104 to the turbine 106 without passing through the compressor 101. A pump 108 may be provided in the bypass 107 to pump the liquid working fluid to the turbine 106.

A control means 109 may monitor one or more operating parameters of the heat pump 1100, for example heat transfer from the evaporator 105 and/or required power from the turbine 106, and may adjust the speed of the compressor 101 and the flow rate through the bypass 107, for example by varying the speed of the pump 108, so as to minimise the net power consumed by the heat pump 1100, while keeping one or more of said operating parameters within predetermined limits.

The working fluid which flows through the bypass 107 exchanges heat with and is warmed by the working fluid exiting the compressor 101 , and flashes to vapour prior to entering the turbine 106. Turbine 106 may be a turbine such as that described below with reference to Figure 10 or 11.

In some embodiments the heat transferred out of the circuit 1101 by the condenser 102 and/or into the circuit 1101 by the evaporator 105 may also be controlled by the control means 109, for example by varying the flow of the cooling/heating medium. Both the heating and cooling mediums may be ambient air.

Those skilled in the art will appreciate pumping the working fluid in its liquid state is substantially more efficient than moving the fluid at the same flow rate with a compressor. Therefore, by allowing a portion of the working fluid to bypass the compressor, the flow rate around the cycle may be substantially maintained while reducing the energy consumed by the system. Referring next to Figure 2 a heat pump apparatus according to another embodiment of the present invention is generally referenced 2200.

The heat pump 2200 includes a first closed working fluid circuit 2101 which is substantially identical to the working fluid circuit 1100 described above, and a second working fluid circuit 2102 which includes, in order, a pump 210, an evaporator/boiler 211 , a turbine 212, a condenser 213 and a receiver 214. A non return valve (not shown) is preferably provided immediately upstream of the evaporator/boiler.

Heat is exchanged from the first working fluid circuit 2101 to the second working fluid circuit 2102 via a heat exchanger 215 which is located upstream of the evaporator/boiler 211 in the second working fluid circuit 2101. The heat exchanger is preferably positioned between the turbine 206 and Tx valve 204 of the first working fluid cycle 2101.

The evaporator/boiler 211 receives preheated working fluid from the heat exchanger 215 and heats it further until it is a vapour at a suitable temperature and pressure for introduction into the turbine 212. The heat input for the evaporator/boiler 211 may be obtained from any suitable source, for example waste steam, external combustion of fossil fuels and/or solar heating. In some embodiments it may be possible to substantially vapourise the working fluid using heat from ambient air.

In a preferred embodiment the evaporator/boiler is a heat exchanger.

Heat balance in the second refrigerant circuit 2102 is maintained by the condenser

213. As with the condenser 102 and evaporator 105 of the first circuit 1101 , the heat rejected by the condenser 213 may be controlled by controlling the flow of cooling medium over the condenser 213. This is preferably controlled by a control means 209.

Use of a second circuit 2102 may further decrease the net energy required by the heat pump 2200 due to the additional power generated by the turbine 212.

Referring next to Figure 3, in an alternative embodiment a heat pump apparatus 3300 may be based on a substantially standard refrigeration circuit 3103 including a compressor 301 , a condenser 302, a receiver 303, a throttling or Tx valve 304, and an evaporator 305. The refrigerant circuit 3103 may replace the refrigerant circuit 2102 of the heat pump 2200. The heat exchanger 315 may be the only component in the working fluid circuit which is not found in a standard vapour compression refrigeration cycle.

This embodiment is preferably based on a pre-existing air-conditioning installation and may allow the use of the heat rejected from the circuit 3103 with the minimum of modification to the original refrigeration equipment. Control means (not shown) may be used to control the speed of the compressor 301 as described above with reference to control of compressors 101 and 201.

Referring next to Figure 4, in one embodiment the second circuit 2102, 3102 may be replaced by an alternative second working fluid circuit 4102a, which may differ from those shown in Figures 2 and 3 in that it includes multiple turbines 412 in parallel connection between the evaporator/boiler 411 and the condenser 413. Higher efficiencies may be realised by using multiple turbines with reduced wire length in each generator, as the decreased load electrical load on each turbine may allow the rotors of each turbine to rotate at a higher, and therefore more efficient, speed, than would be achieved by a single turbine attached to a generator having the same total wire length.

Referring next to Figure 5, in some embodiments a still further alternative second circuit 5102a may be provided with more than one turbine 512 in series. The applicant envisages that in one embodiment six turbines 512 may be utilised in series, although more or fewer than this may be used as required, for example two as illustrated.

Turbines in parallel may be preferred where the mass flow rate of working fluid provided by the pump is greater than the preferred mass flow rate through a single turbine. Turbines in series may be preferred when the pump is capable of creating a greater pressure drop than can be most efficiently utilised by a single turbine.

In a still further embodiment (not shown) a combination of series and parallel turbines may be used as required.

Referring next to Figure 6 a power generation apparatus is generally referenced 6100. The apparatus 6100 includes a working fluid circuit which includes, in order of flow of the working fluid, an evaporator/boiler means 601 , a turbine means 602, a condenser means 603 and a pumping means 604. A receiver 605 is preferably also provided in order to ensure that the working fluid entering the pumping means 604 is in a substantially liquid phase. The turbine means 602 preferably includes a nozzle substantially as described below with reference to Figure 10.

The evaporator means 601 may absorb heat from any suitable source, or from more than one source. In one embodiment the evaporator means 601 may include a heat exchanger for absorbing low temperature heat, such as heat rejected from a refrigeration/airconditioning circuit such working fluid circuits 1101 or 3103, or those described below, and a second heat exchanger for absorbing higher temperature heat, for example from waste steam. In some embodiments the low temperature heat may not evaporate the working fluid, but may merely preheat it, while in other embodiments the working fluid may be evaporated or vaporized by the low temperature heat and may be superheated by the higher temperature heat. Those skilled in the art will appreciate that the evaporation temperature of the working fluid will be a function of the working fluid selected and the pressure it is held at. Preferred embodiments use refrigerant as the working fluid, with R245 and R406 being preferred options.

Similarly the condenser 603 may also include one or more heat exchanger means as required.

A first portion of the working fluid exits the condenser 603 and flows through the receiver 605 if provided, the pumping means 604, the evaporator means 601 and then to the turbine means 602, as generally indicated by arrow 606. However, a second portion of the working fluid exiting the condenser 603 travels through a bypass 607 and enters the turbine means 602 without passing through the evaporator 601, as generally indicated by arrow 608. The flow of working fluid which does not flow through the evaporator means 601 may be controlled by a suitable valve means 609.

In some embodiments a small capacity pump (not shown) may be provided upstream of the receiver 605 in addition to the main pump downstream of the receiver.

At least some of the liquid second portion 608 is vaporised by heat from the vapour portion 606 before it impinges on a rotor (not shown) of the turbine 602, for example by use of the nozzle described further below. Figure 7 shows one preferred embodiment of a refrigeration apparatus, generally referenced 7200 which includes a power generation apparatus 7100 substantially the same as the power generation apparatus 6100 described above.

The refrigeration apparatus 7200 includes a heat pump generally referenced 7201 with a second evaporator means 7201a to absorb heat from a medium to be cooled and a second condenser means 7201b which rejects heat. The heat pump 7201 is preferably a standard refrigeration or air conditioning apparatus and further includes a compressor means 7201c and a throttling valve 7201 d.

The evaporator means 701 includes a first heat exchanger 701a for preheating the working fluid with heat rejected from a first standard refrigeration/air conditioning cycle 7201, and a second heat exchanger 701b which heats the working fluid to a superheated vapour with waste heat from a suitable process, for example heat from a boiler or waste steam. A non-return valve (not shown) may be used immediately upstream of the second heat exchanger 701b. In one embodiment oil may be used as a medium to transfer heat from the process to the heat exchanger 701b. However, in a preferred embodiment the second heat exchanger 701b includes a conduit through which the medium carrying the waste heat flows. A plurality of tubes carry the working fluid extend into the conduit so as to be in contact with the heating medium. The working fluid tubes may be arranged in substantially straight parallel rows or may be helical in shape. In one embodiment the second heat exchanger 701b forms part of a flue from a boiler.

The heat exchangers 701a and 701b may be in a common housing, or may be separate.

The condenser means 703 preferably includes a heat exchanger 703a which rejects heat to a suitable heat absorption means, for example a heat pump 7202, and at least partially condenses the working fluid. A further heat exchanger 703b may also be provided, if required, to further cool the working fluid. The further heat exchanger 703b may be air or water cooled as required.

The heat exchangers 703a, 703b may be in a common housing or may be separate. In a preferred embodiment at least one of the heat exchangers 703a, 703b may have one or more thermoelectric generators (not shown) embedded in the partition between the hot and cold fluids. The thermoelectric generators generate electricity from a temperature differential, typically using the well known Seebeck effect. The working fluid exiting the turbine heats the hot junction of the thermoelectric generator and the cold junction is cooled using any suitable cooling means.

In some embodiments the heat rejected through the thermoelectric generators may be sufficient to maintain the heat balance in the system, and further heat exchangers may not be required.

A first portion of the working fluid exiting the condenser 703 flows through the receiver 705, if provided, the pumping means 704, the evaporator means 701 and then to the turbine means 702. However, a second portion of the working fluid exiting the condenser 703 travels through a bypass 707 and enters the turbine means 702 without passing through the evaporator 701. In one embodiment (not shown) a power generation apparatus may have the same components as the power generation apparatus 7100, but may omit the bypass between the pump and the turbine.

A control means (not shown) may monitor the power generated by the turbine 702, the power used by the pump 704 and/or other suitable variables such as the rate of heat being absorbed by the second evaporator 7201 a of the heat pump 7201 , and may vary the setting of the valve means 709 and/or the amount of heat input into or rejected by the apparatus 7100, for example by controlling the speed of cooling fans (not shown) operating on the second evaporator 7201a to optimise a selected variable, for example power consumption, or heat absorbed by the second evaporator 7201a.

Figure 8 shows an alternative embodiment of the power generation apparatus 7100 of Figure 7, and is generally referenced 8101. In this embodiment a portion of the fluid exiting the turbine 802, but upstream of the pump 804, flows through a further heat exchanger 801c downstream of the pump 804, but upstream of the turbine 802. In a preferred embodiment the further heat exchanger 801 c is between the first heat exchanger 801a and second heat exchanger 801b which receives higher temperature heat, for example waste heat as described above with reference to Figure 6. The position of the further heat exchanger 801 c may be selected so that the fluid downstream of the pump 804 is being heated, rather than cooled, by the fluid exiting the turbine 802. A valve means 810 may be used to vary the flow through of working fluid through the further heat exchanger 801c, although in other embodiments substantially all of the flow from the turbine 802 may flow to the further heat exchanger 801 c. A control means may control the flow through the valve means 810.

Referring next to Figure 9, another power generation apparatus 9102 is shown, which could be substituted for the power generation apparatus 7100 shown in Figure 7. Apparatus 9102 has substantially the same features as the power generation apparatus 8101 shown in Figure 8, but does not a have a bypass to allow working fluid to be directed to the turbine 902 without passing through the evaporator 901.

Figure 10 shows a turbine nozzle, generally referenced 10300, which may be used with any of the apparatus 1100, 2200, 6100, 7200, or 8100 described above. The nozzle may be used with any suitable turbine and turbine rotor configuration.

The turbine nozzle 10300 defines a first fluid path 1011 having a first inlet 1012 and a first outlet 1013 and a second fluid path 1014 having a second inlet 1015 and a second outlet 1016.

A first fluid 1017 passes through the first fluid path 1011 and is preferably substantially gaseous. A second fluid 1018 passes through the second fluid path 1014 and is preferably substantially liquid. The first and second fluid paths 1011 , 1014 are preferably substantially circular or annular in cross-section, and in a particularly preferred embodiment are substantially coaxial, with the first fluid path 1011 substantially surrounding the second fluid path 1014.

The nozzle 10300 is adapted to mix the two streams of working fluid before they impinge on a rotor of a turbine. In the embodiment shown the mixing is achieved by turbulence in the two fluid streams.

By mixing the streams, the heat from the working fluid vapour stream 1017 heats vaporises at least part of the substantially liquid vapour stream 1018. Some turbines may require that substantially all of the liquid working fluid is vaporised prior to impinging on the blades. The volume flow rate of the second fluid 1018 is preferably much lower than that of the first fluid 1017. In a preferred embodiment the cross-sectional area of the second fluid path 1014 is much smaller than that of the first fluid path 1011.

The first fluid path 1011 of the nozzle 10300 illustrated in Figure 10 has a converging/diverging cross-section suitable for accelerating the first fluid 1017 beyond the local speed of sound. However, this is not essential, and in embodiments where subsonic fluid flows are required the diverging section 1019 may be omitted. If a converging/diverging section is used then a further section 1020 having a substantially constant cross-section is preferably provided immediately downstream of the diverging section 1019. The exit 1016 of the second fluid path is preferably provided within or at the entrance to the constant cross-section area section 1020.

By mixing liquid working fluid with gaseous working fluid, the mass flow exiting the nozzle 10300 may be increased and the combined density of the first and second fluids may be greater than that of the first fluid alone.

It is envisaged that in some cases a turbine, in conjunction with the nozzle 10300, may reduce the temperature and pressure of the gas sufficiently that they can be used to replace the throttling or Tx valve in heat pump apparatus such as a refrigeration or air conditioning cycle. In some embodiments the turbine may remove sufficient energy from the stream of gas and liquid that the fluid is mainly liquid at its outlet. In these embodiments the turbine may also perform the function of a condenser, although some further heat rejection may be required in order to maintain heat balance in the cycle.

In some embodiments sensors (not shown) may be positioned at suitable points in the nozzle to provide feedback on the conditions of the working fluid, in order to allow a control means to monitor whether the required flow rates and velocities are being achieved. In one embodiment sensors measuring temperature and pressure may be provided at the inlets 1012, 1015 outlets 1013, 1016, and in the case of a converging/diverging nozzle, the throat 1023. The control means may vary the conditions at one or both of the inlets 1012, 1015 in order to keep the flow at the outlets 1013, 1016 within a required range. In one embodiment the size of the nozzle throat may be varied. Alternatively the turbine may be provided with a plurality of nozzles (not shown), each having different geometry, and the control means may direct the working fluid to the nozzle which provides the best performance. Referring next to Figure 11 , a turbine is generally referenced 11200.

The turbine includes a housing 1110 divided into a first chamber 1110a and a second chamber 1110b. A first rotor 1111 is rotatably connected to the first chamber 1110a and is rotatable independently of a second rotor 1112 which is rotatably connected to the second chamber 1110b. The rotors 1111, 1112 are preferably substantially identical.

The housing 1110 is provided with at least one first inlet nozzle 1113 for supplying a working fluid (not shown) to the first rotor 1111. The working fluid exits the housing 1110 via at least one outlet 1114 and moves through a conduit 1115 to a second nozzle 1116 which supplies fluid to the second rotor 1112.

The turbine rotors 1111 , 1112 may be of any suitable design, and are preferably radial flow turbine rotors. The working fluid from the nozzles 1113, 1116 preferably approaches the respective rotor 1111 , 1112 substantially radially and exits the rotor 1111 , 1112 substantially axially.

Each turbine rotor 1111 , 1112 is connected to a separate electrical energy generator means such as a generator 1117, 1118, an alternator or the like. Because the rotors 1111 , 1112 are independently rotatable they are able to operate at different rotational speeds. This may provide a more efficient use of the pressure available than if the two rotors were constrained to rotate at the same speed.

In some embodiments nozzle 10300 may be used as the first nozzle 1113.

In a preferred embodiment the turbine 11200 is provided with a lubrication circuit and cooling circuit. Cool liquid refrigerant, which contains lubricating oil in accordance with normal air conditioning/refrigeration practice, is supplied to a lubrication system inlet 1119. Capillary tubes 1120 run from the inlet 1119 to positions immediately adjacent the generator windings 1121 , outer bearings 1122 and the first rotor inner bearing. When the liquid refrigerant reaches the end of the capillary tubes 1120 it flashes to vapour, carrying oil with it. This spray cools and lubricates the bearings and windings, and in particular the magnets. Some of the oil on the outer bearings 1122 is thrown off by centrifugal force and assists in cooling the generators 1117, 1118. OiI and refrigerant from the inner bearing 1123 bleeds through a small orifice in a plate 1124 which separates the first rotor 1111 from the second rotor 1112 and assists in lubricating the cooling the second rotor inner bearing 1125.

Any refrigerant which does not flash is collected in a sump 1126 and is drained to the accumulator.

In a preferred embodiment, each generator 1117, 1118 includes two sets of ten stationary windings positioned side by side so as to be energised by rare earth magnets which are mounted on the shaft of each turbine rotor so as to rotate with the turbine. The alternating current outputs from each of the 20 coils of each generator are grouped into five sets of four coils (which are hereinafter referred to as quads). Each quad is connected in a phase synchronised pattern as shown in Figure 12. Each coil is paired with a diametrically opposite coil on the other set of windings. Referring to Figure 12, four selected coils 1201 , 1202, 1203 and 1204 are connected in a phase synchronised manner so as to generate an alternating current across outputs 1205. It will be seen that other quad combinations, or even individual coils, may be selected so as to provide an alternating current output.

Turning now to Figure 13 each quad (substantially according to figure 12) is shown as a single winding marked 1301 to 1305 respectively. As mentioned above, individual windings or other combinations of windings may be used rather than the quad arrangement illustrated in Figure 13. The alternating current output of each quad is provided to a step up transformer 1306 to 1310 respectively. In a preferred embodiment, each step up transformer has a turns ratio of approximately 1 :5. This increases the voltage of the AC output, having the advantage of providing a more manageable voltage as will be described further below for inversion to produce an alternating current output which is viable for provision to the mains power supply. The transformers also have the advantage of providing a means of power matching the generator output to its load, and providing isolation between quads.

The output of each transformer is rectified, preferably using a bridge rectifier 1301 to 1305 respectively and filtered using one or more capacitors 1316 to 1320. In a preferred embodiment a circuit breaker 1321 to 1325 is also provided in case an overload condition occurs. The rectified outputs i.e. the outputs from each quad, are cumulatively connected together so that the output voltage adds cumulatively i.e. they are connected in series rather than parallel, so that the voltage of each output is cumulatively combined to produce a cumulative DC output voltage which is then inverted by an inverter unit 1326 to provide alternating current electric power, being three phase alternating current in the preferred embodiment. This alternating output may then be provided to a mains supply, or be used for other purposes. In a preferred embodiment, the inversion unit comprises of variable speed drive with a regenerative front end, manufactured by Control Techniques Ltd of the United Kingdom. Those skilled in the art to which the invention relates will appreciate that other suitable apparatus may be used.

The AC to DC interface used with the invention has a number of advantages. The use of direct current simplifies the phasing problem between generator coils and produces an output which is independent of any speed variations or differences between the turbines or turbine stages. The direct current output produces a higher voltage output per ampere-turn on the generator windings and therefore lowers the number ampere-turns required to provide a given voltage output. The DC output is also easily summed to produce a higher voltage output. It will be seen that each generator can be used to provide a separate DC output, and the output of each generator can be cumulatively combined to provide an overall DC output which can then be inverted to produce a required alternating current output. Furthermore, the direct current output means that known inverter apparatus can be used to provide a range of different alternating current outputs at varying voltages as required.

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 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.

Claims

1. A turbine nozzle including a first fluid path which includes a first inlet adapted to receive a first working fluid vapour stream, and a first outlet adapted to communicate a jet of said working fluid to a rotor of a turbine, the nozzle further including a second fluid path which includes a second inlet adapted to receive a second substantially liquid working fluid stream and a second outlet adapted to communicate a jet of said second working fluid to the rotor of said turbine, wherein the nozzle is adapted to mix the jets of working fluid so that at least part of the liquid working fluid is vaporised by heat from the working fluid vapour.

2. The nozzle of claim 1 wherein the first working fluid stream and said second working fluid stream are from a common working fluid circuit.

3. The nozzle of claim 1 or 2 wherein substantially all of the substantially liquid working fluid vapour is vaporised by heat from the substantially vapour working fluid jet.

4. The nozzle of any one of the previous claims wherein the first and second fluid paths are preferably substantially circular or annular in cross-section.

5. The nozzle of claim 4 wherein the second outlet is concentric with the first fluid path.

6. The nozzle of any one of the previous claims wherein the first fluid path has a converging/diverging section adapted to accelerate the stream of working fluid vapour to a mean velocity above the local speed of sound.

7. The nozzle of claim 6 wherein a section of the first fluid path immediately downstream of the converging diverging section. has a substantially constant cross-section.

8. The nozzle of claim 7 wherein the second outlet is in the substantially constant cross-section section of the first fluid path.

9. A turbine including the nozzle of any one of claims 1 to 8 operable to supply working fluid to a rotor.

10. The turbine of claim 9 wherein, in use, the second fluid is completely vapourised before impinging on the rotor.

11. A dual stage turbine including a housing including a first chamber provided with a first inlet nozzle for supplying a working fluid to a first turbine rotor rotatably connected to the housing within the first chamber, the first chamber including a first outlet adapted to receive working fluid exiting the first turbine rotor, the first outlet connected to a second inlet nozzle provided in a second chamber, the second nozzle supplying a working fluid to a second turbine rotor which is rotatably connected to the housing, the housing further including a second outlet adapted to receive fluid exiting the second turbine rotor, wherein the first and second turbine rotors are independently rotatable.

12. The dual stage turbine of claim 11 wherein the first and second turbine rotors are substantially identical.

13. The dual stage turbine of claim 11 or 12 wherein the working fluid from the first nozzle is radially incident on the first turbine rotor.

14. The dual stage turbine of claim 11 , 12 or 13 wherein the working fluid from the second nozzle is radially incident on the second turbine rotor.

15. The dual stage turbine of any one of claims 11 to 14 wherein the working fluid exits each said turbine rotor substantially axially.

16. The dual stage turbine of any one of claims 11 to 15 wherein each said turbine rotor is operably connected to an electrical energy generation means.

17. The dual stage turbine of any one of claims 11 to 16 wherein at least one of said first and second nozzles is a nozzle according to any one of claims 1 to 10.

18. A heat pump including a working fluid circuit including, in order, a compressor, a condenser, a throttling means, an evaporator, and a first turbine, wherein the circuit further includes a bypass means operable to transfer a proportion of a working fluid within said working fluid circuit from upstream of said throttling means to said first turbine without passing through throttling means or said evaporator.

19. The heat pump of claim 18 wherein the bypass means includes working fluid pumping means.

20. The heat pump of claim 18 or 19 wherein the working fluid circuit rejects heat to a second working fluid in a second working fluid circuit via first heat exchanger means.

21. The heat pump of claim 20 wherein the second working fluid circuit includes a second turbine.

22. The heat pump of claim 21 wherein the second working fluid circuit includes a second heat exchanger means operable to add further heat to said second working fluid.

23. The heat pump of any one of claims 18 to 22 wherein the first turbine is a turbine according to claim 9, 10 or 17.

24. A power generation apparatus including a working fluid circuit including, in order of fluid flow, an evaporator means, a turbine means, a condenser means, a receiver means and a pumping means, wherein the working fluid circuit is adapted to allow a first portion of a working fluid exiting the condenser means to pass through the evaporator means before entering the turbine means, and a second portion of the working fluid to enter the turbine means without passing through the evaporator means.

25. The power generation apparatus of claim 24 wherein the first turbine is a turbine according to claim 9, 10 or 17.

26. The power generation apparatus of claim 24 or 25 wherein the working fluid circuit may includes valve means for controlling the ratio of the first portion of working fluid to second portion of working fluid entering the turbine.

27. The power generation apparatus of claim 24, 25 or 26 wherein the working fluid is a refrigerant.

28. A refrigeration apparatus including a heat pump means including an evaporator for cooling a medium to be cooled and a condenser, wherein the condenser rejects heat to an evaporator means of a power generation apparatus according to any one of claims 24 to 27.

29. The refrigeration apparatus of claim 28 wherein the condenser means of the power generation apparatus rejects heat to an evaporator of a second heat pump.

30. A method of supplying working fluid to a turbine means having a rotor means including the steps of:

^■ directing a jet of working fluid vapour towards the rotor; ^■ directing a jet of substantially liquid working fluid towards the rotor;

^■ mixing the jets prior to the substantially liquid working fluid jet impinging on the rotor so that at least part of the substantially liquid working fluid vapour is vaporised by heat from the working fluid vapour jet.

31. The method of claim 30 wherein substantially all of the substantially liquid working fluid vapour is vaporised by heat from the substantially vapour working fluid jet.

32. The method of claim 31 or 32 including the step of directing the jet of working fluid vapour through a fluid path having a converging/diverging section.

33. A heat pump including a working fluid circuit including, in order, a compressor, a condenser, a receiver, a throttling valve, and an evaporator, the heat pump further including heat exchanger means for rejecting heat to a second working fluid cycle.

34. A method of generating power using a pre-existing refrigeration circuit, the method including inserting a heat exchanger upstream of a condenser in the pre-existing refrigeration circuit whereby heat is transferred from the pre-existing refrigeration circuit to working fluid in a heat pump circuit, the heat pump circuit including an evaporator or boiler downstream of the heat exchanger, a turbine generator downstream of the evaporator or boiler, a condenser downstream of the turbine generator and means to circulate the working fluid about said heat pump circuit.

35. A method for generating alternating current electric power from an energy recovery system using a source of waste heat, the system including a turbine unit and a generator having a plurality of windings, the generator being operably associated with the turbine, comprising the steps of: ^■ generating a first alternating current from at least a first of the plurality of windings, and a second alternating current from at least another from the plurality of windings;

^■ increasing the voltage of each alternating current using a transformer, rectifying the output of the transformers to produce a first direct current output and a second current output;

^■ cumulatively adding the first direct current output to the second direct output and;

^■ inverting the cumulative direct current output to produce alternating current electric power.

36. The method of claim 35 wherein the first and second alternating currents are each produced from a plurality of phase synchronised windings.

37. The method of claim 35 or 36 wherein the step of rectifying the output of the transformers includes using a bridge rectifier and filtering the output of the bridge rectifier.

38. Apparatus for generating alternating current electric power in an energy recovery system from waste heat, the apparatus including a turbine unit and a generator operably associated with the turbine, the generator having a plurality of windings arranged to produce a first alternating current and a second alternating current, a first transformer to increase the voltage of the first alternating current and in the second transformer to increase the voltage of the second alternating current, a first and second rectifying means to rectify the output of each transformer, and the rectified outputs being cumulatively added together to produce a cumulative direct current output, and an inverter means to invert the cumulative direct current output to alternating current electric power.

39. A method for generating alternating current electric power in an energy recovery system from waste heat, the system including two turbine rotors, each turbine rotor adapted to operate independently, a generator operably associated with each turbine rotor, comprising the steps of:

^■ generating a first alternating current using each generator;

^■ increasing the alternating current output of each generator using a transformer;

■ rectifying the output of each transformer to produce a direct current output;

^■ cumulatively adding the direct current outputs together; and

^■ inverting the cumulative direct current output to produce alternating current direct power.

40. Apparatus for generating alternating current electric power in a energy recovery system from waste heat, the apparatus including two turbine rotors adapted to independently, each turbine rotor operably associated with a generator, each generator producing an alternating current which is provided to a transformer, each transformer being operable to increase the voltage of each of the alternating currents, rectifying means to rectify the output of each transformer to produce a first direct current output and a second direct current output, the first and second direct current outputs being cumulatively combined, and an inverter means to invert the cumulative direct current output to provide alternating current electric power.