WO1997016629A1 - Method and apparatus for driving a rotor - Google Patents

Abstract

Rotor driving system (10) comprises chambers (12, 14) partly filled with water and liquidly connected by pipe network (16) having a rotor (30) therewithin. Alternate displacement of the liquid from one chamber to the other through said pipe network (16) drives rotor (30). The chambers (12, 14) are connected by valves (40, 42) to a pressurised gas source whereby alternate introduction of pressurised gas into one chamber (12) with corresponding pressure reduction in the other chamber (14) effects displacement of water therebetween. System (10) further comprises a valve arrangement to seal one chamber (12) from the gas source whilst continuing pressure reduction in the other chamber (14) to provide isentropic expansion of heated gas within chamber (12). A further method of driving rotor (30) uses displacement of liquid between the first (12) and second (14) chambers in which additional displacement of liquid is effected by sealing chamber (12) from the gas pressure source and effecting isentropic expansion of the heated gas within chamber (12) as pressure in chamber (14) is further reduced.

Description

METHOD AND APPARATUS FOR DRIVING A ROTOR

The present invention is directed towards a system and a method for driving a mechanical rotor, whereby the rotation of such a rotor may be used to drive an electrical generator for the production of electricity. More particularly this invention is directed towards a liquid displacement system whereby the displacement of liquid is used to drive the rotor. The present invention is also directed to a method and apparatus for converting a low grade heat source, such as low pressure flash steam, geothermal steam, a hot water supply (whereby such heat sources may be obtained as industrial by products) or solar radiation to electrical energy. Electrical generators are well known, including hydroelectric generators which use a flow of water to rotate large turbines or rotors, the rotational movement of which is used to generate electricity. However, a drawback of such hydroelectric generators is the need for a constant flow of water which, at present, must be generated by feeding such water from an elevated position to a low position. Conveniently, this flow of water is regenerated by the earth's natural rainfall replenishing reservoirs and lakes in elevated positions. To gain most effective use of such generators they must be situated near the base of upland areas where the flow of water may be the greatest or they must be situated underground, Iower than the relevant water source. These conditions are necessary to obtain the desired head of water needed to create sufficient water flow to drive the turbines, therefore requiring pumping stations to recycle the water from a iower position to an elevated position for maintaining the water cycle.

An alternative method of driving a turbine rotor is the use of conventional steam powered generators whereby water is boiled to produce steam which is then used to drive the rotor in a conventional manner. However, a drawback of such an electrical generator is the requirement of a high energy heat source to boil the water to create the steam. Existing technology incorporates the burning of fossil fuels or the use of nuclear fission reactors to generate the required heat. The use of such methods has environmental drawbacks such as the production of harmful gases which must be released into the atmosphere causing pollution during the burning of fossil fuels or the production of radioactive waste which requires careful handling, storage and ultimately disposal to prevent harmful radiation leaks into the environment.

It is therefore an object of the present invention to provide a system and a method for driving a rotor for the ultimate purpose of generating electricity, which system and method alleviate the aforementioned problems and operate in an environmentally friendly manner.

According to the present invention there is provided a method of driving a rotor within a liquid system having two chambers each partially filled with liquid and liquidly connected by a liquid flow system, which method comprises displacing at least part of the liquid between a first and second chamber whereby liquid flow between the chambers drives the rotor, the liquid displacement being effected by a gaseous pressure source being directed to the first chamber whilst pressure in the second chamber is reduced to a first reduced pressure, the gaseous pressure being provided by heated gas, with additional displacement of the liquid being effected by sealing the first chamber from the gas pressure source and effecting isentropic expansion of the gas within the first chamber as pressure in the second chamber is further reduced to a second reduced pressure.

Usually, the method will comprise alternating displacement of the liquid between the first and second chambers by alternately directing gaseous pressure from the gas pressure source to one of the first and second chambers whilst pressure in the other of said first or second chambers is reduced to a first reduced pressure with additional displacement of the liquid being effected by sealing said one of the first or second chambers from the gas pressure source and effecting isentropic expansion of the gas within said one of he first or second chambers as pressure in said other of the first or second chambers is further reduced to a second reduced pressure. By providing for isentropic expansion of the heated gas, efficiency of the method is significantly increased whereby more work is recovered from the heat of the pressurised gas source. Preferably, each chamber will have a gas inlet valve so that the method of alternately introducing the pressurised gas into each chamber is effected by alternately opening and closing the gas inlet valve of each chamber. The pressure in the other one of the chambers is reduced by reducing the gaseous content within this other chamber, so that the pressure in one chamber is increased whilst the pressure in the other chamber is decreased substantially simultaneously. The reduction of this gaseous content may be effected by partially evacuating the gaseous content from the other chamber or, as an alternative, preferred method, the gaseous content in this other chamber may be reduced by condensing the gas to a liquid state within the chamber. This condensed gas is then usually withdrawn from the respective chambers. The evacuated gaseous content may itself be used as a pressurised gas source within a third chamber.

Usually, this method of driving a rotor may involve maintaining the various pressures within each of the chambers below atmospheric pressure at all times. The pressurised gas will preferably be produced by boiling a liquid within a closed system, usually at a pressure below atmospheric pressure (thereby reducing the boiling point of the liquid), whereby the resulting vapour produced will increase the gaseous pressure in the closed system until saturated vapour pressure is achieved. The liquid may be boiled within a heating vessel which is externally heated, by surrounding it externally with hot fluid, such as steam or hot water produced as a by-product of an industrial process, to boil the liquid therein at a temperature below its boiling temperature at atmospheric pressure. Alternatively, the heating vessel may be heated by direct solar energy to heat the liquid at a reduced boiling temperature. By reducing the pressure within the heating vessel below atmospheriG pressure allows the liquid in the heating vessel, usually water, to be boiled at a temperature below its normal boiling point at atmospheric pressure.

Alternatively, where the invention is used in an industrial or geothermal environment in which excess steam is produced as a by-product, such excess steam may be treated as a direct source of pressurised gas and introduced alternatively into each chamber directly. In such situations the steam may be supplied to the chambers at pressures above atmospheric.

Where saturated vapour pressure is used to generate the pressure within either one of the chambers, this pressure may be lowered by reducing the temperature within this chamber, causing the gaseous vapour to be condensed back to a liquid state, subsequently reducing the pressure in this chamber. This condensed liquid will then increase the liquid content within the chamber, which excess liquid may be recycled back into the heating vessel where it may again be boiled to produce a pressurised gaseous vapour.

Usually, the excess liquid will be drawn off from the fluid flow system and recycled to the heating vessel by means of a pump. Where steam is obtained as a direct source of pressurised gas, the excess liquid is simply drawn off from the system and discarded. Conventional methods of level control can be used for drawing off the excess liquid.

An alternative method of recycling this excess liquid may be effected by connecting the fluid flow system to a first liquid reservoir, which is held at atmospheric pressure, whereby the excess condensed liquid in the other chamber may be removed by forcing this excess liquid into the first liquid reservoir during the displacement cycle of the liquid from one chamber to the other chamber. This first liquid reservoir will usually have an overflow, such as a pipe, connected to a liquid source which is also held at atmospheric pressure and which liquid source is fluidly connected to the heating vessel to provide a liquid source therefor, whereby the excess fluid that is forced into the reservoir may overflow into the liquid source so as to be recycled into the heating vessel as the existing liquid within the heating vessel is vaporised and drawn off, resulting in reduction pressure within the heating vessel drawing water from the liquid source.

Preferably, the method of the present invention involves positioning the liquid reservoir and liquid source substantially on the same horizontal base plane and then positioning the chambers at a predetermined height above the base plane so that the head of liquid, under a complete vacuum, within each of the chambers will not exceed the height of the inlet valve of each chamber above the base plane. This is a fail-safe measure to prevent the possibility of the liquid within the chambers being forced through the inlet valves into the pressurised gas source. The efficiency of this method of driving a rotor may be further increased by directing the displaced liquid through the fluid flow system in a manner such as to drive the rotor in a single direction only irrespective of the direction of liquid flow from one chamber to the other chamber. This may be effected by an arrangement of automatic or non-return flow restriction valves positioned in the fluid flow system. Preferably, the rotation of the rotor is used to generate electricity in a conventional manner by the use of conventional electrical generators.

Further according to the present invention there is provided a rotor driving system comprising two chambers each partially filled with liquid and liquidly connected by a liquid flow system having a rotor positioned for actuation by flow of liquid through the liquid flow system and means for increasing gaseous pressure in a first chamber whilst reducing gaseous pressure in a second chamber to a first reduced pressure to partially displace the liquid from the first chamber to the second chamber, a gas source providing the gaseous pressure, with additional displacement means being provided to effect sealing of the first chamber from the gas pressure source and to reduce pressure in the second chamber to a second reduced pressure to allow isentropic expansion of the gas within the first chamber.

Preferably, the means for increasing gaseous pressure in the first chamber whilst reducing gaseous pressure in the second chamber to a first reducing pressure comprises alternating means for alternating displacement of the liquid between the first and second chambers, further including means for alternately directing gaseous pressure from the gas pressure source to one of the first or second chambers and means for alternately reducing the pressure in the other of said first or second chambers, with the additional displacement means including means for alternatively sealing said one of the first and second chambers from the gas pressure source and for reducing pressure in said other of the first and second chambers to a second reduced pressure to allow isentropic expansion of the heated gas within said one of the first or second chambers.

The means for alternately increasing the gaseous pressure in one of the chambers whilst reducing gaseous pressure in the other one of the chambers may comprise a gas inlet valve assembly associated with each chamber, whereby both of these associated inlet valves are connected to a source of pressurised gas, and also comprise means in each chamber for decreasing the gaseous content within each chamber. The means for decreasing the gaseous content within each chamber will usually comprise a gas cooling system to effect condensation of the gas within the chamber to a liquid, thereby reducing the gaseous pressure therein. Such a gas cooling system will usually comprise a fluid cooled heat exchanger extending into the chamber. Alternatively, the gas cooling system may comprise a direct cooling liquid spray, for spraying a relatively cold liquid directly through the pressurised gas to cool it directly, thereby causing condensation. The liquid spray joins and mixes with the driving fluid system and the excess liquid is drawn off from the fluid flow system by methods previously explained. Alternatively, a system may be installed to recover the cooling liquid spray, whereby the cooling liquid spray is collected into a collection tray and each chamber is provided with additional valve means to allow removal of the cooling liquid accumulated in the collection tray and to facilitate recovery of some of the heat contained therein.

Another, simpler, means for decreasing the gaseous content within each chamber may comprise an outlet valve in the chamber connected to a reduced pressure system at a pressure substantially less than the gas pressure of the chamber, the gas within the chamber being partly evacuated when such an outlet valve is opened. The aforesaid reduced pressure system may take the form of a condensing system whereby the heat obtained from the condensing gas is used for domestic or industrial heating thus providing the high energy usage efficiencies inherent with a combined power and heating system. In the preferred embodiment, the system will be sealed from the atmosphere and operated at pressures substantially below atmospheric pressure, with the pressurised gas providing a gas pressure below atmospheric pressure. Such a system would comprise means for reducing the pressure to below atmospheric pressure.

Preferably, the pressurised gas source will comprise a sealed, pressurised heating vessel in which a liquid may be heated. This vessel is held at a pressure substantially less than atmospheric pressure and the liquid heated therein is heated to a boiling temperature which is substantially less than that required at atmospheric pressure, the subsequent vaporisation producing an increasing gas pressure within the vessel. The heating vessel may be externally heated by direct solar energy. Alternatively, such a heating vessel may be externally heated by a pre-heated fluid, such as hot water or steam produced as a by product of an industrial process. The heating vessel will usually be fluidly connected to a liquid source held at atmospheric pressure, this liquid source replacing the liquid in the vessel removed by vaporisation as liquid is boiled off and the pressurised gas drawn off. As the pressurised gas is removed, the subsequent reduction of pressure within the heating vessel will serve to draw liquid from the liquid source into the vessel.

The system may also comprise a liquid reservoir held at atmospheric pressure and fluidly connected to the fluid flow system for removing from the chambers excess liquid formed by condensation of the gas during the displacement of the liquid from one of the chambers to the other. This liquid reservoir will usually comprise an overflow leading to the liquid source to enable excess liquid collected in the liquid reservoir to flow back to said liquid source for recycling to the pressurised heating vessel.

Usually, the liquid source and liquid reservoir will be positioned on the same horizontal base plane and the chambers will be positioned at a predetermined height above this base plane so that the head of liquid within the chambers, under a complete vacuum, does not exceed the height of the inlet valve assemblies of each chamber above the base plane. This predetermined height of the chamber inlet valve above the base plane is calculated as the barometric height of liquid at atmospheric pressure.

In order to increase the efficiency of the invention the inlet gas valve may be closed before all the liquid has been displaced from the chamber, thereby ensuring isentropic expansion of the gas within the chamber. Furthermore, the elevation of the chambers may be configured to reduce the hydraulic back head at the end of the cycle thereby increasing the potential for expansion within the chamber and providing a more even load on the turbine.

In an alternative arrangement, where the invention is used in an industrial environment in which excess steam is produced as a by-product, such excess steam may be treated as a direct source of pressurised gas and introduced alternatively into each chamber directly. In such situations it may not be necessary to reduce the pressure in the chambers below atmospheric pressure.

Preferably, the liquid used in the system of the present invention is water and the pressurised gas is preferably steam.

The fluid flow system may also comprise an arrangement of automatic or non-return valves to direct liquid flow between the two chambers in a single direction across the rotor to actuate the rotor in a single direction of rotation, irrespective of the direction of liquid flow into or out of each chamber. The system may further comprise an electrical generator connected to said rotor whereby the rotation of the rotor is used to generate electricity.

Usually, this system will comprise an inertial flywheel connected to the rotor to maintain smooth operation of the rotor when subject to intermittent liquid flow through the fluid flow system. The invention will now be described, by way of an example only, with reference to the drawings, in which:-

Figure 1 is a schematic diagram of a hydroelectric power generating system;

Figure 1 a is a schematic diagram of an alternative pipe network of the system of Figure 1 ;

Figure 2 is a schematic diagram of a heat exchanger system;

Figure 3 is a schematic diagram of an alternative heat exchanger; Figure 4 is a schematic diagram of an alternative hydroelectric power generating system, and

Figure 5 is a schematic diagram of an alternative embodiment of a hydroelectric power generating system.

Referring now to Figure 1 , a hydroelectric power generating system 10 comprises apparatus for driving a rotor, primarily having two liquid chambers

12 and 14 which are fluidly connected by a pipe network 16 leading from the base 13 and 15 of each chamber 12 and 14, respectively. The pipe network 16 comprises an array of automatic or non-return valves 20, 21 , 22, 23 which are arranged so as to direct fluid flow through the pipe 25 in a single direction indicated by the arrow 26. The pipe 25 contains a fluid driven rotor 30 of conventional design which is connected to an electricity generator 32, whereby rotation of said rotor by the fluid flow in the pipe 25 drives the generator 32 to create electricity. An inertial flywheel (not shown) and bypass valve 80 may be connected to the rotor to ensure smooth rotation of said rotor when subjected to intermittent changes in fluid flow through the pipe 25, thereby maintaining smooth operation of the generator 32. The generator 32 may be in the form of a hydroelectric turbine generator. The bypass valve 80 may be used to direct flow away from the rotor 30 if necessary.

In use, fluid flow from chamber 12 to chamber 14 is directed through the open valve 20 along pipe 25, through open valve 23 and into chamber 14. In a reverse direction, fluid flow from chamber 14 to chamber 12 is effected through open valve 21 along the pipe 25 then through open valve 22 into chamber 12. Irrespective of the direction of fluid flow between the chambers, fluid flow 26 along pipe 25 is thus maintained in a single direction.

At the respective upper parts 35 and 36 of said chambers 12 and 14, fluid inlet pipes 37 and 38 are provided, each having a valve assembly 40, 42 connecting said chambers 12 and 14 with a pressurised gas source 48 by means of a pipe network 49. The pressurised gas source 48 comprises a sealed heating vessel 50 fluidly connected to a liquid source tank 52 by a pipe 53. The liquid held in the source tank 52 is exposed to atmospheric pressure.

A liquid reservoir 54 is liquidly connected by a means of a pipe 55 to the pipe network 16 to connect the chambers 12 and 14 with this reservoir. The liquid contained in the reservoir 54 is also exposed to atmospheric pressure. The liquid source tank 52 and the liquid reservoir 54 are positioned substantially on the same horizontal plane with an overflow pipe 57 leading from the liquid reservoir to the liquid source tank 52.

Each of the chambers 12 and 14 further comprise a respective fluid controlled heat exchanger 60 and 62, each of which comprise a coiled tube inserted through the wail of the chamber into the chamber interior. A cooled fluid is forced through this coiled pipe to cool any gas within the chamber. Each of the two heat exchangers 60 and 62 has a respective control valve 63 and 64 for controlling the operation of the heat exchanger by regulating the flow of cooled fluid.

In use, the system 10 is initially filled with the operating liquid which, in this particular embodiment, is water. The liquid source and liquid reservoirs 52 and 54 are respectively filled with water at atmospheric pressure. At this time the pipe network 16 is also completely filled with water. Furthermore, if the pipe networks 53 and 49 are held at atmospheric pressure by opening valves 40 and 42, the water from the water source 52 flows freely into the heating vessel 50 whereby the liquid levels within the liquid source 52 and the heating vessel 50 will be at the same level since there is no difference in pressure between the liquid source 52 and the heating vessel 50. A vacuum pump 68 is further connected to the pipe 49 via a valve 69.

The valve 69 is opened and the pipe work 49 and heating vessel 50 are partially evacuated by the pump 68 to a pressure substantially below atmospheric pressure. The chambers 12 and 14 will also filled with water under a vacuum if valves 40 and 42 are kept open, since both of the chambers 12 and 14 are fluidly connected to the liquid reservoir 54 containing water at atmospheric pressure. More water is added to the liquid source tanks 52 as required. The valve 69 is then closed to maintain the internal reduced pressure of the pipe 49 and the heating vessel 50 below atmospheric pressure.

The height of the chambers above the water reservoir 54 is carefully selected such that the respective valves 40 and 42 of chambers 12 and 14 respectively are at a predetermined height (indicated at 70 in Figure 1 ) above the water level of the liquid reservoir. If this height 70 is calculated to be the barometric height of water under a vacuum, conveniently being 10.36 metres (or 34 feet), when the chambers are completely evacuated, the water level in such chambers will not exceed the height of the valves 40, 42 above that of the water reservoir 54. In use, the minimum pressure reached within the chambers 12 and 14 (although substantially below atmospheric pressure) will be equivalent to the water vapour pressure at the cooled temperature.

The water level within the liquid reservoir 54 is maintained substantially the same as the water level in the liquid source tank 52. Thus, when the heating vessel 50 is partially evacuated by the vacuum pump 68 the resulting pressure differential between the heating vessel and the water in the liquid source tank 52 under atmospheric pressure results in the water level 72 within the heating vessel 50 having a height generally indicated at 72 in Figure 1 above the water level within the liquid source tank. Generally, this height may be calculated using the simple physical formula:-

Δ P = h Q g where:

Δ P = the pressure differential between atmospheric pressure and the internal pressure of the heating vessel; h = the difference in height between the water level in the heating vessel and the water level in the liquid source tank 52; Q = the density of water, and g = acceleration due to gravity, 9.8 m.s^'2 Thus, following the initial evacuation of the heating vessel 50, the height

72 will be governed by the pressure differential between the vessel 50 and atmosphere. Since the pressure from the heating vessel 50 is below atmospheric pressure, this greatly reduces the boiling point of the water within the vessel 50.

The vessel 50 is then heated by an external heat source such as solar energy, collected and used to heat the vessel in a conventional manner using known solar collectors. Alternatively, heated water or steam, for example from a conventional hot water system, can be used to heat the external surface of heating vessel 50 and thus the internal contents. The heat provided by these low energy heat sources will then raise the temperature of the water within the heating vessel 50 above its reduced boiling temperature thus effectively boiling the water therein to generate steam. Since the steam produced is within a sealed system, this will increase the pressure within the heating vessel 50 and this increase in pressure will subsequentiy increase the boiling temperature of the water therein.

Eventually, an equilibrium will be reached whereby the pressure within the heating vessel 50 has reached a saturated vapour pressure P1 which is dependent on the external temperature of the heating vessel 50. Since the pressure P1 is greater than that of the originally evacuated system the height

72 between the water level within the heating vessel and the fluid source 52 will have decreased accordingly. The saturated vapour pressure of the boiled water from the pipe 49 may now be considered as a pressurised gas source

Valve 40 is then opened and valve 42 closed, usually by a computer controlled operation system of a type conventionally known. The control of all the valves within this system may be conducted automatically by the use of such conventional computer operated valve systems. Such technology is well know and will not be discussed further in this specification.

When the valve 40 is opened, the pressurised gas source will force the water level within the chamber 12 to be displaced through the pipe network 16. On initial operation of the system 10 the chamber 14 will be full of water and the water displaced from the chamber 12 is forced through the pipe 55 into the fluid reservoir 54 from which the excess is discarded.

The operation of the system can then be started by sealing valve 40 and opening valve 42 thus subjecting the water within the chamber 14 to a pressurised gas source of pressure P1 , causing displacement of the water within chamber 14 through pipe network 16. At the same time, the valve 63 is opened to allow a cooled liquid source to flow through the heat exchanger 60 within chamber 12 which serves to condense the saturated vapour within chamber 12, converting the steam therein to water which then mixes with the original water within the chamber 12. Condensation of the steam within chamber 12 will thus cause a significant reduction of the pressure therein, causing the water level within chamber 12 to rise relative to the water level within the liquid reservoir 54.

Thus, the water displaced from chamber 14 by the application of pressure P1 is forced through the pipe network 16 through valve 21 through pipe 25 subsequently to drive the rotor 30 and then passes through the valve 22 into chamber 12. The liquid in chamber 12 will then rise to an operating height dependent on the pressure P2 within this chamber which is to be considered as the condensed vapour pressure. Simple mathematical extrapolation indicates that the height of the water within the vessel 12, at a pressure P2, will result in the water level rising to a height above the water level at atmospheric pressure, which may be considered as being so many metres below the height 70 of the liquid in a vacuum. This height is generally indicated at 76 on Figure 1. Due to the resulting pressure in chamber 12 this height 76 will maintain the water level of chamber 12 below the valve 40.

The application of pressure P1 to chamber 14 causes displacement of the water level within chamber 14 to the height indicated at 74 in a manner similar to that described for displacement of the water within chamber 12. Any excess water from the chambers 12 and 14 is removed by forcing it through the pipe 55 into the liquid reservoir 54. The cycle is then repeated by opening valve 40 to increase the pressure in chamber 12 to P1 whilst closing valve 42 opening valve 64 and thus condensing the vapour pressure within chamber 14 to P2 causing resultant water flow from chamber 12 to 1 through the pipe network 16 through valve 20 on pipe 25 and through valve 23. Thus, by alternately opening and closing valves 40 and 42, and valves 63 and 64 on the heat exchangers the liquid may be alternately displaced between chambers 12 and 14 through pipe 25 to drive the rotor 30 in a single direction. An inertial flywheel (not shown) may be used to maintain a smooth rotation load applied to the electricity generator 32, when the alternate cycles of the fluid displacement occur.

Due to the condensation of the saturated vapour within the chambers 12 and 14, excess water enters the system 10 and is displaced into the fluid reservoir 54. It will be appreciated that the water level within the reservoir 54 will vary slightly due to the adjustments in pressure within the system. As excess water is forced into the reservoir 54 this will reach an overflow pipe 57 and drain into the liquid source 52. The opening of valves 40 and 42 will obviously result in a decrease in pressure within the heating vessel 50 during operation of the system 10. The subsequent reduction in pressure within chamber 50 will decrease the boiling temperature of the water therein and thus boiling will resume until saturated pressure P1 is again achieved. However, the pressure within the vessel 50 is maintained beiow atmospheric pressure at all times and thus a substantially constant level 72 of water is maintained within the vessel 50. Thus, according to simple fluid dynamics, the excess water drained through the overflow 57 into the liquid source 52 is recycled into the heating vessel 50. The entire system 10 therefore operates in a closed system manner. Since the reservoir 54 and liquid source 52 are open to atmosphere it will be appreciated however, that liquid loss due to evaporation may need to be occasionally replaced.

In the particular embodiment shown in Figure 1 , the pipe network 16 and the rotor 30 must be maintained at a height below that determined. by 74 to prevent the formation of vacuums within the pipe network. Thus, in practice, it is envisaged that the heating vessel 50, fluid reservoir 54 and fluid source 52 are maintained on a base level within a building with the chambers 12 and 14 positioned at a sufficient height above this to ensure that the valves 40 and 42 are at a level 70 above the base level, the pipe network 16 and rotor 30 being maintained at a level below the base level.

The shaft seal on the hydroelectric turbine 32 should be below the minimum water level of the reservoir 54 to ensure that there is no possibility of sucking air into the low pressure system. Alternatively, the shaft seal should be flushed with water to avoid this problem. In addition, the pressurised gas source isolation valves 40 and 42 and non-return valves 20, 21 , 22 and 23 are preferably glandless or of a design which avoids the possibility of sucking air into the low pressure system. It will be appreciated that pressures P1 and P2 are dependent on temperature whereby P1 may be increased by increasing the heat source to the heating vessel 50 and P2 may be varied by varying the temperature of the heat exchangers 60 and 62. If the temperature of the liquid applied through the heat exchangers 60 and 62 is decreased, greater condensation will occur within the chambers, thus decreasing the vapour pressure therein. However, a residual vapour pressure P2 will be maintained within the vessels 12, 14.

In one envisaged use, the system 10 will be operated by the use of solar energy to heat the vessel 50 during the day such that hot water, previously heated and stored, is used to boil the water within the heating vessel 50 during the night or during periods when there is insufficient solar energy to generate steam within the heating vessel 50. In this way, intermittently available natural energy, such as that provided by solar and wind energy, may be stored by heating water which may be considered as a low grade heat source that can be stored within conventional insulation tanks and used to generate electric power at a later time.

The non return valves (or automatic valves) 20, 21 , 22 and 23 are of a conventional design and will not be discussed further in this description.

An alternative pipe network 16' is shown in Figure 1 a and may be used to replace the network 16 illustrated in Figure 1. Basically, the pipe network 16' comprises a valve arrangement similar to that of pipe network 16 with the exception that a turbine outlet pipe 25' may discharge directly into an open tank of the system liquid (water) with the water return pipes to the chambers 12' and 14' respectively being fed directly by insertion into the open tank 31 '. The use of such a tank may be used to replace the liquid reservoir as shown in Figure 1 whereby an overflow pipe 57' could be used to flow directly into the liquid source tank 52. It will be appreciated that the system shown in Figure 1a will cause water to be drawn through the pipe network system 16' when one of the chambers is subjected to a reduced pressure. It will also be appreciated that should such a system 16' be employed then the positioning of the tank 13V will define the head of water within the chambers 12' and 14' respectively. The use of the pipe network 16' is primarily envisaged for use with known impulse turbines.

The amount of energy recoverable from the system according to the present invention is determined by the Laws of Thermodynamics whereby the majority of heat input into the system is lost as unavoidable thermodynamic heat rejection. The theoretical maximum work which could be recoverable from an ideal system, as determined by the Carnot Cycle, is 22.8% of the heating input for a heat engine operating between 100 °C and 15 °C. However due to limitations of apparatus and practical measures, it is not possible to obtain ideal maximum heat recovery as seen in the ideal Carnot Cycle.

With the present system, however, it has been discovered that the efficiency can be significantly improved by increasing the extent of the isentropic expansion of the steam within the chambers. Thus, in the present invention, following the opening of valve 40 to allow the pressurised gas into chamber 12 the vaive 40 is closed before the equilibrium position is achieved. Condensation of steam within chamber 14 continues to reduce further the pressure within chamber 14 following closure of the valve 40. In this way, the steam within chamber 12 is allowed to expand isentropically to provide the most efficient method of converting the internal energy of the steam (or hot gas) into work as identified in the ideal Carnot Cycle.

It is submitted here that a man skilled in the art will be fully conversant with the theoretical principles of the Carnot Cycle, so it is not necessary to indulge in further theoretical discussion on thermodynamic principles and the Carnot Cycle. It is sufficient to state that the efficiency of the invention is increased when the gas entering the first chamber is allowed to expand within that chamber while continuing the displacement of the fluid into the second chamber by a contained reduction of pressure therein. This condition is achieved by closing the valve on the first chamber before the chamber is totally full of gas. The work of the expanding gas is used to displace the fluid between the chambers which, in turn, drives a rotor to allow work to be extracted from the gas expansion. Isentropic gas expansion (i.e. at constant entropy) provides the most thermodynamically efficient way of converting the internal energy and heated gas into work as identified in the ideal Carnot Cycle. However, it should be noted that work may only be extracted by the hydraulic piston/rotor system if there is a pressure difference between the two chambers. Pressure in the second chamber is reduced below the pressure in the first chamber by condensing the gas in the second chamber by extracting heat from the system. Since this final pressure reduction is not by isentropic expansion, some thermodynamic efficiency is lost in this part of the process. Therefore, maximum practical efficiency is achieved when the gas in the first chamber is expanded to the minimum practical pressure before condensation, reducing the work loss. Performing such isentropic expansion of the gas within the chamber provides for an increased efficiency of the system and will increase energy recovered from the heat of the gas.

Further improvements to the basic design of this hydroelectric power generating system can be effected in the basic thermal efficiency of the system by improving the heat recovery from the condensation of the steam within the chambers. In its simplest form, this improvement involves using the heat removed in the condensation stage to preheat the water feed to the heating vessel 50. The value of heat recovered can be enhanced by operating the heat exchange to a higher temperature level. If the condensation stage of the cycle described is delayed so that the pressurised steam vapour within one chamber is not condensed as the other chamber 14 is exposed to the pressure P1 , a certain degree of compression of the steam will take place within cylinder 12 before the heat exchanger 60 is operated. In such a situation, the steam in chamber 12 will be condensed at a higher pressure (hence higher temperature) and more of the condensation heat could be used to pre-heat feed water, and even to generate steam.

An example of this is shown in Figure 2 whereby heat exchanger coils 101 and 102 extend in a conventional manner into an area of two chambers 104 and 106, respectively, to operate in a conventional manner. Valves 108 and 1 10 allow a cooling liquid to flow through the heat exchangers 101 and 102. In this case, the heat exchangers 101 and 102 are supplied with heating vessel feed water from a source drum 112 which is alternately fed into chambers 104 and 106 by sequential control of the respective valves 108 and 1 10. The water in the heat exchangers 101 and 102 is then heated, by removing heat from the hot vapour within the chamber, and this water may then be removed through a pipe 1 14 where it may be utilised to preheat the water entering the heating vessel 50 of the previously described system 10. If sufficient heat exchange occurs, the water within the heat exchangers 101 and 102 may be converted to steam and may be withdrawn along the pipe 1 14 as steam itself.

It should be noted that the arrangement described above is a preferred embodiment of heat exchange serving to condense the gas within the chambers. It will be understood by skilled persons that there are many known methods of heat exchange commonly available, any of which may be utilised in the present invention. One example of such a method would be to use external heat exchangers in the form of coils extending externally around the chambers, whereby such coils are used to extract heat from the chambers as a whole and thus indirectly from the gas within.

An alternative method of cooling the gas within the chambers would be to utilise condensation by direct cooler water injection as schematically illustrated in Figure 3. In this case, the cooling water is injected directly into the chamber vapour space 120 through a gas valve 122. The injected cooling water may be allowed to mix with the drawing fluid and then removed from the system by one of the methods described elsewhere. Alternatively, the cooling water may be collected in a collecting tray 124 from which it is recovered through a sequence control valve 126 at a convenient period during the system cycle. Again, the cooling liquid will be heated as a consequence of the heat exchange in condensing the gas within the chamber and this heated water may then be used to pre-heat the water feed for the heating vessel 50.

As a further alternative, the gas may be quenched externally of the chamber by direct water injection in a fluidly connected container. The connected container is held at a pressure below that of the gas which subsequently flows into that chamber in order to reach equilibrium when an appropriate valve is opened. Water quenching of the gas in that container then maintains the required reduced pressure in that container whilst the quenching fluid and condensed gas are collected externally of the chamber.

The embodiment of the present invention described in relation to Figure 1 is considered to be applicable in domestic houses for to taking advantage of low energy heat sources to provide the pressurised gas source. However, the system can be simplified to take advantage of other sources of pressurised gas.

In its simplest form, the present invention can utilize a pressurised gas source such as high pressure steam (e.g. from geothermal energy) whereby the pipe 49 of Figure 1 is connected directly to such a gas source. This alleviates the need for the heating vessel 50 and recycling system 52, 54, 55 and also the need for heat exchangers 60, 62 in each vessel. In a simplified system such as this, high pressure steam is introduced into a first chamber 12 through a first valve 40 whilst the second chamber 14 is simply evacuated (or partly evacuated) by use of a valve (not shown) connecting the second chamber to a low pressure system. This allows the fluid in the first chamber to be forced through the pipe network 16 into the second chamber 14 in the manner previously discussed, thus driving the rotor 30. Valve 40 may then be closed and valve 42 opened to repeat the process in the opposite direction (a valve, not shown, also opened to evacuate chamber 12) to establish the alternating cycle as described with reference to Figure 1. This simplified system may be operated at pressures below atmospheric pressure but could easily be operated at atmospheric pressure provided the gas source is at a pressure greater than atmospheric pressure, the chambers being partly evacuated by opening them to the atmosphere to reduce the pressure therein during the operating cycle. In addition, such a simplified system does not require height differentials of the chambers relative to a reference level (as for the system of Figure 1 ).

This simplified system, although practical, may be regarded as inefficient since the power required to produce the pressurised gas source may approach the energy output of the electricity generator. However, such a simplified system may be applied in an industrial environment in which excess steam, produced as an industrial by product, is used as the pressurised gas source. In some circumstances, geothermal steam could be utilised. This excess or natural steam could be pressurised to pressures greater than atmospheric pressure or may simply be used in conjunction with the chambers held at sub- atmospheric pressure, as described with reference to Figure 1. In either situation, the use of heat exchangers in each chamber will be employed to condense the steam and thereby reduce the pressure in the relevant chamber with the excess liquid simply being pumped out of the pipe system 16 for disposal. In this arrangement, the steam is not recycled.

A more efficient system 400, primarily for industrial application, is shown in Figure 4. This system is similar to the system 10 of Figure 1 except the recycling unit 52, 54, 55, 57 of system 10 has been replaced with an electric or hydraulic pump 410. To avoid repetition, the features of the system 400 which correspond to those features of the system 10 have been accorded the same reference numerals with the exception that the prefix "3" has been added, whilst additional features have been accorded new numbers with the prefix "4".

The system 400 employs a similar hydraulic piston arrangement to that of the system 10 whereby water is alternatively forced between a first chamber 312 and a second chamber 314, via a pipe network 316, to drive a rotor 332 in the manner previously described with reference to Figure 1 . The system 400 is evacuated initially by a pump 368 to a pressure substantially below atmospheric pressure and the pressurised gas source comprises steam generated by boiling water in a heating vessel 350 at a reduced pressure in a similar manner to that previously described, resulting in a saturated vapour pressure dependent on the external heat supplied to the heating vessel 350. In many industrial environments, hot water and steam are produced as a by¬ product and this heat source can be utilized to boil the liquid in the heating vessel at a reduced pressure.

This pressurised steam is then alternately admitted to the two chambers 312 and 314 via respective valves 340 and 342 to drive the hydraulic piston arrangement.

However, in the system 400, the excess water obtained by condensing the steam and/or injecting cooling liquid in the respective chambers (in order to reduce the pressure therein) is simply removed from the pipe network 316 by a pump 410. Known fluid measurement techniques may be incorporated in the system 400 to ensure that water levels do not build up within the chambers and cause a reduction in efficiency of the process. Once the predetermined volume of water has entered one of the chambers during the cycle, the pump 410 is activated to remove any excess water and such excess water is pumped back into the heating vessel 350 to complete the recycling process.

The use of the pump 410 (which may be a known electrical pump) ensures that the entire system 400 is closed to the atmosphere and, as such, the positioning of the chambers is not governed by or dependent on the barometric height of the water in the system (as in system 10). Thus, system 400 may to be arranged on a single level if desired, resulting in a more compact design. In addition, no water is lost through evaporation in such a closed system, whilst the energy needed to operate the pump will be minimal compared to that generated by the system 400. Again, it will be appreciated that the efficiency of such systems will be significantly increased by providing for isentropic expansion of the steam when alternately admitted to the two chambers 312 and 314 in the manner described previously. Again, by allowing such isentropic expansion of the gas, more of the energy contained within the steam is converted to work as the temperature of that steam is reduced by such isentropic expansion.

Further embodiments of the present invention may include the use of different fluids within the system having different boiling temperatures at reduced pressures. Water is used in the present invention for convenience and safety. In addition, it will be appreciated that, in order to obtain the greatest efficiency from the embodiment of the invention shown in Figure 1 , the system should be completely evacuated, although in practice a reduced pressure will remain. However, there are obviously operational constraints on creating a complete vacuum, so it is envisaged that there will be a residual amount of air remaining in the system following evacuation. This does not detract greatly from the overall efficiency of the system.

In addition, the efficiency of the system may be improved by designing the chambers to have a minimal thermal capacity to reduce heat loss. To effect this, the thickness of the chamber walls should be as thin as possible while satisfying pressure and vacuum requirements of the system. Such chambers could employ external stiffening rings indirectly attached through insulating means. In addition, the materials of construction for the cylinders and pipe networks should have a low specific heat capacity and, additionally, may incorporate a layer or coating of internal insulation.

It will be appreciated that the systems 10 and 400 shown in Figures 1 and 4, respectively, are of a schematic nature only. The present invention is in no way restricted to the specific layout of these schematic diagrams or to the shapes of the chambers illustrated. The chambers themselves may be cylindrical, spherical, conical or a combination of forms to improve the efficiency of the process.

Although two chambers only are shown in the preferred embodiments, it will be appreciated that the system may incorporate more than two cylinders in sequence. It will also be appreciated that more than one rotor, and thus more than one electrical generator, may also be utilised in this system. In addition, the operational sequence of the valves in systems 10, 310 and 16 may be arranged to achieve expansion of the fluid within the chambers 12 (312) and 14 (314) in order to improve efficiencies further.

Furthermore, it will be appreciated that, whilst the embodiments refer to a closed system operating at a reduced pressure to enable steam to be produced at temperatures below 100°C (and thus to enable exploitation of low energy heat sources), the present invention is equally applicable to a hydraulic system held at atmospheric (or higher) pressure provided that the vaporised gas source produces pressures suitable to effect fluid displacement between the chambers at such higher pressures. For example, if the steam source is waste steam from an industrial process, the necessity to reduce the pressure of the hydraulic system is obviated, provided that the requirement is met that the pressure P1 is sufficient to effect displacement of the fluid from the first chamber to the second chamber. This may be achieved by condensing steam within the second chamber to produce a pressure P2 below that of P1 . The system is equally efficient at such high pressures, since the underlying principles of operation remain the same as for the Iower pressure sealed system.

A further embodiment of the present invention is shown in Figure 5 where the elevations of the chambers are configured to reduce the hydraulic back head, thereby improving the thermodynamic efficiency of the system by increasing the expansion within the chamber and increasing the efficiency of the turbine generator by providing a more even load. In this embodiment, steam (e.g. from an industrial process) enters chamber 12 via valve 40 and displaces water through turbine 30 via valves 20 and 523 into chamber 514 which is at a higher elevation than chamber 12. The pressure in chamber 514 is reduced by the injection of cold water via valve 503 (or by other techniques previously discussed) to cause condensation. Valve 40 may be closed before all the water has been displaced from chamber 12 if a high level of expansion is required whereby such isentropic expansion, as previously discussed, will again further improve the efficiency of the system.

When all the water has been displaced from chamber 12, the steam remaining in chamber 12 is expanded into chamber 512 by opening valve 540 to displace water from chamber 512 through turbine 30 and into chamber 14 via valves 520 and 23. The pressure in chamber 14 is reduced by the injection of cold water via valve 501. Lower pressure steam is used for the transfer of water from chamber 512 to chamber 14 than for the transfer from chamber 12 to 514 but the transfer from 512 to chamber 14 is assisted by the elevation difference between the chambers whereas the transfer from chamber 12 to chamber 514 is resisted by the elevation difference.

After the transfer from chamber 512 to chamber 14 has been effected, the cycle is completed by transferring water firstly from chamber 14 to chamber 512 and then from chamber 514 to chamber 12. All valves in the process are either operated automatically or are non-return valves which open or close depending upon pressures. The operation of the embodiment has been described as for a steam water system but other gases and liquids could be used. A further embodiment could use several chamber pairs at different elevations to improve efficiencies further.

Yet another embodiment of the present invention is possible by utilising the equipment illustrated in figure 5, producing an alternative valve operation sequence. In this further embodiment, steam enters a low elevation high pressure chamber where it displaces water through the turbine into the second low elevation chamber. Simultaneously, the remaining steam in the second Iower elevation chamber is displaced into one of higher elevation chambers where it is used to displace water, through the turbine, into the second higher elevational chamber, whereby gas is condensed in the second high elevation chamber. This can be explained more clearly with reference to Figure 5. Steam enters chamber 12 via valve 40 and displace water through a turbine 30 via valves 20 and 23 into chamber 14. Simultaneously, steam is displaced from chamber 14 via valve 542 into chamber 514 where it is used to displace water from chamber 514 through turbine 30 via valves 521 and 522 into chamber 512. The pressure in 512 is reduced by an injection of cold water via valve 502 (or by other techniques previously discussed) to effect condensation. Valve 40 may be closed before full water displacement has been achieved from chamber 12 to provide isentropic expansion of the steam within the Iower cylinder 12 to improve the efficiency of the system. It is also envisaged that isentropic expansion can be effected with the steam passing from chamber 14 to chamber 514 if chamber 514 is larger than chamber 14. Thus, yet further efficiency may be achieved from the present invention.

When the displacement of water from chamber 12 to chamber 14 and from chamber 514 to 512 is completed, the cycle may then be completed by switching the valves so that water is subsequently displaced from chambers 14 to 12 and from chambers 512 to 514, respectively. It will also be appreciated that a pump may be used in conjunction with any one of the aforementioned embodiments to counteract the effect of elevational differences of the hydraulic head throughout the cycle, and hence provide a more constant turbine load when displacing water from one chamber to another.

Thus it will be appreciated from the foregoing description that there are many embodiments of the present invention utilising a heated gas source to effect hydraulic displacement of fluid from one chamber to another, such displacement of the fluid being used to drive a turbine to recover energy from the heated gas. Such operation may be achieved at sub-atmospheric pressure or at atmospheric pressure depending on the heat sources available and it has been found that, by allowing isentropic expansion of the heated gas source within one of the chambers, the efficiency of energy recovery from such a system is significantly increased. This is because less heat is lost by subsequent condensation of the heated gas in the return cycle (the necessity to condense such heated gas being to reduce the pressure in that chamber to allow fluid to be displaced back into the chamber).

Claims

1 . A method of driving a rotor within a liquid system having two chambers each partially filled with liquid and liquidly connected by a liquid flow system, which method comprises displacing at least part of said liquid between a first and second chamber whereby liquid flow between the chambers drives the rotor, said liquid displacement being effected by a gaseous pressure from a gas pressure source being directed to the first chamber whilst pressure in the second chamber is reduced to a first reduced pressure, said gaseous pressure being provided by a heated gas, with additional displacement of the liquid being effected by sealing said first chamber from said gas pressure source and effecting isentropic expansion of the gas within the first chamber as pressure in the second chamber is further reduced to a second reduced pressure.

2. A method as claimed in claim 1 comprising alternating displacement of said liquid between said first and second chambers by alternately directing gaseous pressure from the gas pressure source to one of the first or second chambers whilst pressure in the other of the first or second chambers is reduced to said first reduced pressure with additional displacement of the liquid being effected by sealing said one of the first or second chambers from said gas pressure source and effecting isentropic expansion of the heated gas within said one of the first or second chambers as pressure in said other of the first or second chambers is further reduced to a second reduced pressure.

3. A method as claimed in claim 2 in which each chamber has a gas inlet valve and wherein pressurised gas is alternately introduced into each chamber by alternately opening and closing the gas inlet valve of each chamber.

4. A method as claimed in any one of the preceding claims in which the pressure in said other one of the chambers is reduced by reducing the gaseous content within said other one of the chambers.

5. A method as claimed in claim 4 wherein the gaseous content is reduced by at least partially evacuating said gaseous content from said other chamber.

6. A method as claimed in claim 4 wherein the gaseous content is reduced by condensing the gas to a liquid state in said other chamber.

7. A method as claimed in claim 6 in which the liquid state of the condensed gas is withdrawn from the other chamber.

8. A method as claimed in claim 4 including the step of directing the gaseous content within said other one of the chambers to a third chamber to act as a gas pressure source for displacing fluid from said third chamber through said liquid flow system or an additional but similar liquid flow system.

9. A method as claimed in claim 8 wherein said third chamber is larger than said other one of said first and second chambers to allow isentropic expansion of said gaseous contents therein.

10. A method as claimed in any one of the preceding claims in which the pressures employed within the chambers are below atmospheric pressure.

1 1. A method as claimed in any one of the preceding claims comprising producing said pressurised gas by boiling a liquid, in a closed system, with the resulting vapour increasing the gaseous pressure in said closed system.

12. A method as claimed in any one of claims 1 to 10 in which said pressurised gas is provided as steam from an external source.

13. A method as claimed in claim 1 1 when appended to claim 10 in which said closed system is held at a pressure below atmospheric pressure with the resulting vapour increasing the gaseous pressure in said closed system.

14. A method as claimed in claim 1 1 or claim 13 comprising boiling the liquid by directing solar radiation onto a heating vessel containing the liquid.

15. A method as claimed in claim 1 1 or claim 13 comprising boiling said liquid in a heating vessel by raising the external temperature of said vessel with a pre-heated fluid.

16. A method as claimed in claim 14 or claim 15 when appended to claim 7 including recycling the liquid state of the condensed gas to the heating vessel.

17. A method as claimed in claim 7 or in claim 16 when appended to claim 7 comprising connecting said liquid flow system to a first liquid reservoir held at atmospheric pressure such that excess condensed liquid in said other chamber is removed by forcing said excess liquid into said first liquid reservoir during displacement of said liquid from one chamber to said other chamber.

18. A method as claimed in claim 17 when appended to claim 14 or claim 15 comprising connecting said heating vessel to a liquid source at atmospheric pressure and providing said first liquid reservoir with an overflow so that said excess liquid overflows from said reservoir into said liquid source to be recycled into the heating vessel.

19. A method as claimed in claim 18 when appended to claim 3 including positioning said liquid reservoir and liquid source substantially on the same horizontal base plane and positioning said chambers a predetermined height above said base plane so that the head of liquid, under a complete vacuum, within said chambers does not exceed the height of the inlet valves of each chamber above said base plane.

20. A method as claimed in any one of the preceding claims including directing said displaced liquid through the liquid flow system to drive the rotor in a single direction irrespective of the direction of liquid flow between the chambers.

21. A method of generating electricity by connecting a rotor to an electricity generator and driving said rotor according to the method of any one of the preceding claims.

22. A rotor driving system comprising two chambers each partially filled with liquid and liquidly connected by a liquid flow system, a rotor positioned for actuation by flow of liquid through the liquid flow system and means for increasing gaseous pressure in a first chamber whilst reducing gaseous pressure in a second chamber to a first reduced pressure to partially displace said liquid from said first chamber to said second chamber, a heated gas source for providing said gaseous pressure, with additional displacement means being provided to effect sealing of said first chamber from said gas pressure source and to reduce pressure in the second chamber to a second reduced pressure to allow isentropic expansion of the gas within the first chamber.

23. A system as claimed in claim 22 in which said means for increasing gaseous pressure in a first chamber whilst reducing gaseous pressure in a second chamber to a first reduced pressure comprises alternating means for alternating displacement of said liquid between said first and second chambers, including means for alternately directing gaseous pressure from the gas pressure source to one of the first or second chambers and means for alternately reducing the pressure in the other of said first or second chambers, with the additional displacement means including means for alternately sealing said one of the first or second chambers from said gas pressure source and for reducing pressure in the other of said first or second chamber to a second reduced pressure to allow isentropic expansion of the heated gas within said one of the first or second chambers.

24. A system as claimed in claim 23 in which said means for alternately increasing gaseous pressure in one of the chambers whilst reducing gaseous pressure in the other one of the chambers comprises a gas inlet valve assembly associated with each chamber, both valves being connected to the source of pressurised gas, and means in each chamber for decreasing the gaseous content within each chamber.

25. A system as claimed in claim 24 in which said means for decreasing the gaseous content within each chamber comprises a gas cooling system for condensing said gas within the chamber to reduce the gaseous pressure therein.

26. A system as claimed in claim 24 in which said gas cooling system comprises a fluid cooled heat exchanger extending into a chamber.

27. A system as claimed in claim 23 in which said gas cooling system comprises a direct cooling liquid spray.

28. A system as claimed in claim 27 further comprising a collection tray and additional valve means in said chamber for collecting and removing said cooling liquid collected from said chamber.

29. A system as claimed in any one of claims 25 to 27 in which each chamber comprises means for external liquid quenching of said gas to condense said gas.

30. A system as claimed in any one of claims 22 to 24 in which said means for decreasing the gaseous content within each chamber comprises an outlet valve in the chamber connected to a reduced pressure system at a pressure substantially less than the pressurised gas of the chamber.

31. A system as claimed in claim 30 comprising a third chamber elevated with respect to the first and second chambers said third chamber being partially filled with liquid and held at a pressure substantially below that of the first and second chambers, whereby said outlet valves of said first and second chambers are alternately connected to said third chamber, so that said decreasing gaseous content within said one of the first or second chambers provides a pressurised gas source for said third chamber to displace the liquid from said third chamber.

32. A system as claimed in claim 31 in which said third chamber is larger than said first and second chambers to allow isentropic expansion of said gas within said third chamber.

33. A system as claimed in any one of claims 20 to 32 which is sealed from the atmosphere and operated at pressures substantially below atmospheric pressure, said pressurised gas source being less than atmospheric pressure.

34. A system as claimed claim 33 comprising means for reducing the pressure within said system below atmospheric pressure.

35. A system as claimed in claim 33 or claim 34 in which said pressurised gas source comprises a sealed, pressurised heating vessel in which said liquid is heated, at a pressure substantially less than atmospheric pressure, to a boiling temperature less than its normal boiling point at atmospheric pressure, with the subsequent vaporisation producing an increase in gas pressure within the vessel.

36. A system as claimed in claim 35 in which said pressurised heating vessel is externally heated by solar energy.

37. A system as claimed in claim 35 or 36 in which said heating vessel is externally heated by pre-heated fluid.

38. A system as claimed in any one of claims 35 to 37 having a liquid source held at atmospheric pressure which is liquidly connected to the heating vessel for replacing the liquid in the vessel removed by vaporisation.

39. A system as claimed in claim 25 or in any one of claims 26 to 38 when appended to claim 25 having a liquid reservoir held at atmospheric pressure and liquidly connected to the liquid flow system for removing excess liquid from the chambers, said excess liquid being formed by condensation of said gas, during displacement of the liquid from one of the chambers to the other one of the chambers.

40. A system as claimed in claim 39 when appended to claim 38 in which said liquid reservoir comprises an overflow leading to the liquid source for excess liquid collected in said liquid reservoir as a result of condensation of said pressurised gas to flow back to said liquid source.

41. A system as claimed in either claim 39 or claim 40 in which the liquid source and liquid reservoir are positioned on a common horizontal base plane and said chambers are positioned a predetermined height above said base plane such that the head of liquid within said chambers, under a complete vacuum, cannot exceed the height of the inlet valve assemblies of each chamber above the base plane.

42. A system as claimed in claim 41 in which said predetermined height is calculated as the barometric height of the liquid at atmospheric pressure.

43. A system as claimed in any one of claims 22 to 28 in which said pressurised gas is provided as the by-product of an industrial process or as geothermal energy.

44. A system as claimed in claim 43 in which said pressurised gas is steam.

45. A system as claimed in any one of claims 22 to 44 in which the liquid is water.

46. A system as claimed in any one of claims 22 to 45 in which said liquid flow system comprises an arrangement of non return valves to direct liquid flow between the two chambers in a single direction across said rotor to actuate said rotor in a single direction, irrespective of the direction of liquid flow into or out of each chamber.

47. A system as claimed in any one of claims 22 to 46 comprising an electric generator driven by rotation of said rotor.

48. A system as claimed in claim 47 comprising an inertial flywheel connected to said rotor to maintain a smooth operation of said rotor when subject to intermittent liquid flow.

49. A system as claimed in claim 30 comprising a second pair of first and second chambers in which said means for decreasing the gaseous content within each chamber of said first pair of first and second chambers provide a pressurised hot gas source for said second pair of chambers.