EP2458165A2

EP2458165A2 - Heat-Driven Power Generation System

Info

Publication number: EP2458165A2
Application number: EP12156971A
Authority: EP
Inventors: Peter Jeffrey
Original assignee: E-Energy International Ltd
Current assignee: SAMUEL BANNER & CO. LTD
Priority date: 2009-07-31
Filing date: 2010-07-30
Publication date: 2012-05-30
Also published as: WO2011012907A2; WO2011012907A3; GB0913369D0

Abstract

The invention concerns a method of operating an engine (18) having a variable volume working chamber (24, 26), e.g. a piston engine. According to the invention, working fluid driving the engine comprises any of a halocarbon, a halo-hydrocarbon, a partially halogenated carbon compound, a fluorocarbon, a perfluorocarbon, a hydrofluorocarbon, a hydrochlorofluorocarbon, a fluorinated ether, a fluorinated ketone, or a functional derivative of any of the aforegoing.

Description

The present invention is concerned with a system for using heat energy to do useful work, with an engine for the same purpose, and with a working fluid for use in an engine. The invention is particularly but not exclusively applicable to exploitation of heat sources which are low grade, in the sense that the temperatures they provide are moderate.
There is an increasing need in modem society to exploit "alternative" energy sources such as solar and geothermal sources, and an increasing focus on making efficient use of existing energy sources such as nuclear power and burning of fossil fuels.
The infra-red spectrum of solar radiation deposits more power onto relatively small areas of the World's surface than could possibly be used but no economic means of harnessing this power has been devised until now. There is also a massive waste of heat from industrial activities including combustion and nuclear power generation. In generation of power in existing power stations, industrial installations etc., very high temperatures are used and lower temperature heat energy carried e.g. by exhaust gases at temperatures up to 450 degrees Centigrade is wasted by discharge into the atmosphere. Where carbon capture is attempted, exhaust gases must first be significantly cooled at high cost.
It is an object of the present invention to provide a practical means for using low grade heat energy to do useful work. An additional or alternative object to the present invention is to provide an improved means of converting heat energy into usable power. An additional or alternative object of the present invention is to provide a superior working fluid for an engine.
In accordance with a first aspect of the present invention there is a heat-driven power generation system comprising an engine having a variable volume working chamber which is connectable to

(a) a working fluid inlet for supply of pressurised, vaporised working fluid to the working chamber,
(b) a condensing fluid injection port for injection of condensing fluid to the working chamber, and
(c) an exhaust,

The engine may take any of a range of different forms. For example the working chamber may be defined within a cylinder by a reciprocally driven piston. In such an embodiment the working chamber expands and contracts with the piston movement. The working fluid expands throughout one piston stroke, doing useful work in the process. Around the end of the stroke the working fluid is condensed, creating a partial vacuum in the working chamber so that on the return stroke a net force on the piston urging it to return is increased. The arrangement may be double acting. That is, working chambers capable of being pressurised may be formed on both sides of the piston, each having its own working fluid inlet, condensing fluid injection port and exhaust. In such an engine one working chamber can be pressurised while the other suffers a partial vacuum, maximising the force on the piston.
Because the condensing fluid which causes the collapse of the working fluid is injected into the working chamber, cyclical heating and cooling of the engine parts during the engine's operating cycle can be minimised, improving thermal efficiency. An external condenser is not required.
Valves controlling (a) supply of the pressurised, vaporised working fluid to the working chamber; (b) injection of the condensing fluid to the working chamber; and (c) exhaustion of the mixture of the working fluid and the condensing fluid from the working chamber are provided in some embodiments and some or all of these valves typically need to be controlled in synchronism with piston movement. This may be provided for by a mechanical arrangement. Preferably, however, an electronic controller receives signals indicative of piston position and controls some or all of the said valves accordingly, in synchronism with piston movement.
The mechanism through which the expansion and contraction of the working chamber is used to do useful work may take a variety of forms and may for example be mechanical, hydraulic, hydro-mechanical or electric. In the case of a reciprocating piston engine, a crank could for example be used to provide rotary motion to drive an electric generator. However, in a preferred embodiment the piston has a piston rod drivingly connected to a reciprocal action pump and the pump's output is used to do work. In such an embodiment, lacking a crank, some means is preferably provided to assist reversal of the direction of piston movement at the end of each piston stroke. This may take form of a spring arranged to engage the piston assembly at the end of its stroke. The spring may absorb the piston's kinetic energy as it arrests the piston's motion, then return it to the piston as the piston rebounds.
Other engines suitable for use in the system according to the present invention are of rotary type. In these, the working chamber is typically defined between a rotor and an adjacent surface of a housing part and its volume varies as the rotor turns. Vane motors and lobe motors are examples and both may be used in implementing the invention. The working fluid inlet, exhaust and in some embodiments the condensing fluid injections port may be opened and closed by the rotor as it turns.
The condensing fluid is preferably injected into the working chamber in the form of a spray or aerosol. Droplets of condensing fluid can provide nucleation sites for condensation of the working fluid. Resultant condensation can be rapid. A pump is preferably provided to receive the condensing fluid from the separation device output and to provide it to the condensing fluid injection port.
Preferably the system further comprises a cooler arranged to receive the condensing fluid and to cool it prior to its injection into the working chamber.
The working fluid preferably has a low latent heat of vaporisation. Preferably its latent heat of vaporisation is between 88 and 100 kJ/kg. Preferably the working fluid has a boiling point at atmospheric pressure of less than 100 degrees Centigrade. Wherever the term "atmospheric pressure" is used herein it shall be understood to refer to an average atmospheric pressure at sea level. Preferably the latent heat of vaporisation of the condensing fluid is significantly greater than that of the working fluid. Still more preferably, the former is at least five times the latter, yet more preferably at least ten times. The condensing effect of the condensing fluid can thereby be improved. Preferably the working fluid is a hydrocarbon, still more preferably a halocarbon, halo-hydrocarbon, halo-ether, halo-ketone, or functional derivative. Fluorocarbons, perfluorocarbons, fluorinated ethers and ketones may be used. The most preferred compounds are fluorocarbons, hydrofluorocarbons, hydrochloroflurocarbons, perfluorocarbons, fluorinated ethers, fluorinated ketones and any such derivative.
In accordance with a second aspect of the present invention, there is an engine having a variable volume working chamber, a working fluid outlet for supply of pressurised, vaporised working fluid to the working chamber, a condensing fluid injection port for injection of condensing fluid to the working chamber, an exhaust for exhaustion of fluid from the working chamber, and an arrangement for opening and closing the working fluid inlet and the exhaust such that in use pressurised, vaporised working fluid is supplied to the working chamber causing the working chamber to expand, after which condensing fluid is injected into the working chamber causing the working fluid to condense and creating a partial vacuum in the working chamber whose volume then contracts, the engine being provided with a mechanism through which the expansion and contraction of the working chamber is used to do useful work.
The engine preferably makes use of working fluid of one of the types described above. The injection of condensing fluid into the working chamber is advantageous in that it causes the working fluid to condense without need of an external condenser and without any need to cool the relevant parts of the engine itself (e.g. the cylinder and piston of a reciprocating piston engine). Condensation can be achieved very quickly - in as little as fiftieth of a second. The condensing fluid is preferably injected in the form of a spray or aerosol. The condensing fluid preferably has a significantly higher latent heat of vaporisation than the working fluid, again assisting condensation of the working fluid. The condensing and working fluids may be the same, merely being chilled to serve the condensing function, or may be different fluids. The condensing fluid may be water but other liquids can alternatively be used.
A third aspect of the present invention comprises the use in an engine having a variable volume working chamber of a working fluid which comprises any of a hydrocarbon, a halocarbon, a halo-hydrocarbon, a halo-ether, a halo-ketone, or any functional derivative thereof.
A fourth aspect of the present invention is a method of driving an engine having a variable volume working chamber, the method comprising the use of a working fluid which comprises any of a hydrocarbon, a halocarbon, a halo-hydrocarbon, a halo-ether, a halo-ketone, or a functional derivative of any of the aforegoing.
Specific embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:-

Figure 1 is a schematic representation of a first system embodying the present invention;
Figure 2 is a schematic representation of a second system embodying the present invention;
Figure 3 is a schematic representation of a third system embodying the present invention;
Figure 4 is a schematic representation of an arrangement used to separate a working fluid from a condensing fluid in the Figure 3 system;
Figure 5 is a schematic representation of a fourth system embodying the present invention, which utilises a lobe type engine;
Figures 6a, 6b and 6c illustrate respective arrangements for extracting heat to drive systems of the types depicted in earlier drawings; and
Figure 6d illustrates a fifth system embodying the present invention.

The Figure 1 System

The system 10 illustrated in Figure 1 receives heat energy and converts it to a usable form. The particular example illustrated provides a flow of pressurised fluid (more specifically oil) which can be used to drive an electric generator or other machine, but in other embodiments the system may for example output power through a mechanical arrangement such as a rotating shaft. Typically the system's power output may be used to generate electricity but other possibilities exist. A mechanical output could for example drive another machine directly.
The system is driven by heat energy from a low grade heat source 11, which may for example be geothermal, or solar, or may be waste heat from power generation or an industrial process. Alternatively the heat source may be dedicated to producing heat to drive the system, e.g. by burning bio-fuel or combustible waste. The low grade heat source serves to heat a working fluid by means of a heat exchanger 12 which in this embodiment takes the form of a low pressure (about one atmosphere - 100kPa above ambient pressure) boiler containing the working fluid. Different pressure may be used. In the illustrated embodiment, the heat exchanger 12 is not directly heated by the low grade heat source but instead receives a flow of heated thermal transfer medium through a thermal transfer circuit 14. The thermal transfer medium is heated by the low grade heat source 11. For example the thermal transfer circuit 14 may incorporate a solar collector (not illustrated) in which the thermal transfer medium is heated by solar radiation. Alternatively the thermal transfer medium may for example be heated in the exhaust gases from a combustion power station, or heated by the cooling medium of a nuclear power station, or heated in a geothermal well, or even heated by combustion of fuel such as bio-fuels or combustible waste. In fact any suitable heat source may be utilised. It should preferably be able to heat the thermal transfer medium to 100 to 110 degrees Centigrade or above.
The heated thermal transfer medium is passed through the heat exchanger 12, serving to heat the working fluid, causing it to vaporise and raising its pressure. Note that the term "working fluid" will be used to refer to the relevant fluid in both liquid and vapour forms.
Vaporised, pressurised working fluid output from the heat exchanger 12 is supplied to an input 16 of an engine 18. In Figure 1 the engine 18 has a reciprocating piston 20 running in a cylinder 22, but other suitable types of engine may be used and will be considered below. The particular engine illustrated in Figure 1 is of double-acting type. The piston divides the cylinder into first and second working chambers 24, 26 whose volumes vary as the piston moves and pressure changes in both working chambers drive the piston. The illustrated engine comprises multiple valves:-

first and second engine inlet valves 28, 30 which are each supplied with vaporised fluid from the engine input 16 and communicate respectively with the first and second working chambers 24, 26 to selectively input vaporised working fluid to the working chambers via working fluid inlets 29, 31 communicating respectively with the first and second working chambers 24, 26;
first and second start-up valves 32, 34 which serve to selectively vent pressure in the working chambers to facilitate engine start-up, as will be explained below;
first and second condensing fluid supply valves 36, 38 which control supply of a condensing fluid to condensing fluid supply ports 40, 42 communicating respectively with the first and second working chambers 24, 26. The condensing fluid supply valves 36, 38 are supplied with chilled condensing fluid from a cooler 44 by respective condensing fluid pumps 46, 48. When opened they cause a spray of condensing fluid to be injected into their respective working chambers 24, 26; and
first and second drain valves 50, 52 which communicate with respective working chambers 24, 26 via exhausts 33, 35 and serve when opened to permit condensed fluid to be drained from the chambers by means of respective drain pumps 54, 56.

The opening and closing of the valves must be coordinated with the movement of the piston 20. This may be done by mechanical means such as cams attached to the exposed part of a piston rod 58 but in the present embodiment the valves are electrically operated by means of a suitable electronic controller (not illustrated), which may take the form of a suitably programmed microprocessor based device. The electronic controller needs to receive a signal indicative of piston position in order to coordinate the valves' action with the piston movement, and this may for example be achieved by means of markers on the piston rod which are detected as they move past a predetermined point.
The operation of the engine is as follows. Under electronic control and based on sensor information, start-up valves 32 and 34 may be opened to allow air to be exhausted from the working fluid. Upon start-up, and once the working fluid in the heat exchanger/boiler 12 has been heated sufficiently to reach an operating pressure (which in the present embodiment is approximately 1 atmosphere - 100 kPa - above ambient, although other pressures could be selected in other embodiments and in fact a value of 700 kPa is chosen in certain preferred embodiments) the start-up valve 32 or 34 associated with whichever of the working chambers 24, 26 currently has the largest volume (due to the position in which the piston 20 happens to have come to rest) is opened. For purposes of this discussion we will take it that the relevant working chamber is the first (item 24) and the first start-up valve 32 is therefore opened.
In this case the second inlet valve 30 associated with the second working chamber 26 is opened to supply vaporised working fluid from the heat exchanger 12 to the second working chamber, raising its pressure to the operating pressure (about 100 kPa in the present example). Since the second working chamber is pressurised while pressure in the first working chamber is relieved, the piston is subject to a force causing it to move along the cylinder, its direction of travel being to the left in Figure 1. As the piston approaches the end of its travel:-

the second inlet valve 30 is closed;
the first inlet valve 28 is opened to raise pressure in the first working chamber 24 to the operating pressure;
the first start-up valve 32 is closed (and the start-up valves remain closed after this initial piston stroke);
the second condensing fluid supply valve 38 is momentarily opened causing the cooled condensing fluid to be sprayed into the second working chamber 26, which is at that point in time filled with working fluid vapour, causing the vapour to condense and so to create a partial vacuum in the second working chamber 26.

The effect is to reverse the pressure difference on the piston, which is thus urged to reverse its direction of travel (the piston moves to the right, as viewed in Figure 1).
When the piston approaches the opposite end of its travel, the valves are again controlled to drive the piston back along the cylinder by:-

closing the first inlet valve 28 to cut off supply of working fluid to the first working chamber;
opening the second inlet valve 30 to pressurise the second working chamber 26;
momentarily opening the first condensing fluid supply valve 36, collapsing the vapour in the first working chamber and creating a partial vacuum in it.

In addition the second drain valve 52 is opened allowing the condensed working fluid in the second working chamber to be drawn from it by the second drain pump 56. Once more, the pressure difference across the piston is reversed and the piston is urged back along the cylinder. This process continues, driving the piston back and forth along the cylinder in a reciprocating motion.
Note that in each piston stroke after the first, the pressure difference across the piston is provided not only by the raised pressure (above ambient) of the working fluid in one working chamber, but also by the reduced pressure (below ambient) of the condensed fluid in the other. The operating pressure of the boiler/heat exchanger 12 may for example be one atmosphere (100 kPa) above ambient but the pressure difference created across the piston can approach two atmospheres (200 kPa).
Working fluid drained from the cylinder is returned to the heat exchanger 12 for re-heating but it should be noted that as additional, cooled condensing fluid was injected into the cylinder to cause the collapse of the vapour, the volume of fluid drained from the cylinder will exceed the replacement volume demanded to keep the liquid level at the heat exchanger 12 at the optimum level. It is therefore necessary to meter the volume of working fluid returned to the heat exchanger 12 and to direct the surplus to a working fluid header tank 57, which feeds both the heat exchanger 12 and the cooler 44.
Note that the system provides a closed circuit for circulation of the working fluid/condensing fluid. No fluid need be lost and if the fluid used is inflammable then danger of its combustion is avoided.
Some means is required to use the reciprocating motion of the piston 20 to do useful work. This could be achieved in well known manner by connecting the piston rod 58 to a crank mechanism to provide rotary motion. However in the embodiment illustrated in Figure 1 a different approach is taken, using the piston 20 to drive a reciprocating pump 70 to provide a flow of pressurised pump fluid which in turn is used to do work. In the present embodiment the reciprocating pump 70 is a high pressure oil pump. It has a pump piston 72 which is coupled to and driven by the engine's piston rod 58 and which moves in a pump cylinder 74 to draw in oil through one-way pump inlet valves 76, 78 and expel it under pressure through one-way pump outlet valves 80, 82.
The diameter of the pump piston 72 is typically smaller than the diameter of the engine piston 20 so that the pump is able to output oil pressure considerably higher than the operating pressure of the engine 18. For example the pump piston 72 may be one tenth the diameter of the engine piston 20. As much as 20,000 kPa can be achieved.
Upon start-up of the engine 18, particularly during the first stroke of the piston 20, the reciprocating pump 70 may be disabled to relieve the engine's load. This may for example be achieved by opening the pump inlet and outlet valves 76-82.
The output of the reciprocating pump 70 is in this embodiment supplied to an accumulator 84 which has a smoothing effect, providing a continuous supply of pressurised oil despite breaks and variations in the flow out of the pump. The pressurised oil is then supplied to a hydraulic motor 86 to drive an electric generator or any other machine. The illustrated arrangement, using coupled pistons to supply power and to pressurise oil, is advantageous in the reduction of initial cost, high efficiency and reduced maintenance costs. Oil is circulated via an oil header tank 92.
Reversal of the direction of motion of the assembly comprising the engine and pump pistons 20, 72 and the piston rod 58 may be assisted, in the absence of a crank, by springs 88, 90. These may be placed in the engine cylinder 22, as shown in Figure 1, although they could be positioned elsewhere, e.g. acting on the exposed part of the piston rod 58. Simple helical springs are schematically represented in the drawing but any suitable spring mechanism may be used and in this context "spring" should be understood to encompass for example gas springs or other mechanisms not necessarily reliant on deformation of a solid spring member. Hydraulic rams with remote energy storage and/or transfer could be utilised.
The diameter of the engine's piston can be large and the speed of its reciprocating movement low. A piston of 2 metre diameter subject to a two atmosphere (200 kPa) pressure difference can exert a force in excess of 60 tonnes and with a stroke length of 4 metres can output a calculated power of 5,000 kW. Note however that smaller or larger engines may be used in embodiments of the invention.
The engine cylinder 22 need not withstand excessively large pressures or temperatures and may be constructed from a spun reinforced concrete pipe, (as used in the construction of sewers) or other low-cost tubular formation of adequate strength, with a low friction lining e.g. formed of epoxy resin, PTFE, silico-silicate etc., or stainless steel tube. The piston 20 and end caps needed to close the cylinder 22 can be made from composite resin materials, high strength metal alloys or any other suitable material. The piston 20 incorporates one or more grooves in its circumference (not shown) to accommodate sealing ring(s) (such as O-rings) and an attachment in its centre to which the piston rod 58 is secured. The end caps incorporate the engine's valves and one of them has a seal for engagement with the piston rod 58.
Several engines may be coupled to the same accumulator/hydraulic motor to power larger generators or groups of generators. The use of several engines to feed into a single pressurised oil system is particularly advantageous where some of the engines are working at lower efficiency due to carbon capture activity (to be described below).

The Figure 2 System

The system illustrated in Figure 2 is similar to that of Figure 1. Corresponding parts are given the same reference numerals in Figure 2 as in Figure 1 and will not be described in detail again. The engine 18 of Figure 2 is once more a reciprocating piston engine and has an arrangement of valves similar to that described with reference to Figure 1, although the start-up valves 32, 34 are dispensed with. Like the Figure 1 system, that of Figure 2 has a high pressure reciprocating oil pump 70 driving a hydraulic motor 86 via an accumulator 84. Figure 2 additionally shows an oil header tank 92 which receives oil output from the hydraulic motor 86, the oil being drawn from the header tank 92 by the reciprocating pump 70 and thereby recirculated.
Figure 2 includes a schematic representation of an arrangement for extracting heat from exhaust gases in a chimney or flue 94. This comprises an arrangement of heat exchange tubes 96 which are arranged in the flue 94 to be heated by the exhaust gases, and through which the heat transfer medium is circulated. Heat transfer medium is circulated from a heat transfer circuit header tank 98, through the heat exchange tubes 96 and then to an inlet 100 of the heat exchanger 12. The heat exchanger 12 incorporates thermal transfer pipework 102 which is in thermal contact with the working fluid 104 used to drive the engine 18, so as the heat transfer medium passes through the heat exchanger 12 to reach its outlet 106, it transfers heat energy to the working fluid. The heat transfer medium may be passed through the heat exchanger upwards, downwards or from side-to-side. From the heat exchanger outlet 106, the heat transfer medium returns to the heat transfer circuit header tank 98 for recirculation.
Figure 2 also provides more detail than Figure 1 of the arrangement of the working fluid header tank 57. As in Figure 1, drain valves 50, 52 allow condensed working fluid to be exhausted from the cylinder 22 and returned to the working fluid header tank 57. The header tank 57 has two outlets. A cooler pump 110 draws working fluid into the cooler 44 whence it is supplied to the condensing fluid supply valves 36, 38 for use in condensing working fluid in the working chambers 24, 26, as described above. A heat exchanger supply pump 112 draws working fluid from the working fluid header tank 57 and supplies it to the heat exchanger 12 for vaporisation therein.
The embodiments illustrated in Figures 1 and 2 use the thermal transfer circuit 14 and the thermal transfer medium circulating in it to receive heat from the heat source and transfer it, in the heat exchanger 12, to the working fluid. However in other embodiments the thermal transfer circuit 14 may be dispensed with, the heat exchanger 12 being more directly exposed to the heat source. For example the heat exchanger could be formed as a thermal collector through which the working fluid is circulated, or as a set of heat exchange tubes through which the working fluid is circulated and which are directly heated by exhaust gases from a combustion process.

The Working Fluid

For systems designed to utilise low grade heat sources, a careful selection is made of the working fluid in accordance with the present invention. It should preferably have one or more of the following properties:-

a. a low boiling point, to enable its use with heat energy sources providing moderate temperatures. Preferably the boiling point is below 100 degrees Centigrade at atmospheric pressure.
b. low latent heat of vaporisation, so that phase change from liquid to vapour takes place with minimal heat energy. A latent heat of vaporisation between 88 and 250 kJ/kg is preferred.
c. low surface tension, to evaporate and change from liquid to vapour (gas) with low energy demand.
d. non-flammability, for safety and ease of handling.
e. low solubility, an advantage when a different liquid is used to condense the working fluid.
f. high chemical stability, making the fluid resistant to degradation and safe if it should leak into the environment.

One possibility is a mixture of water and alcohol, but the preferred working fluids are hydrocarbons, more specifically halocarbons, halo-hydrocarbons, halo-ethers, halo-ketones or functional derivatives. The most favoured fluids are fluorocarbon monomers, which can provide all of the properties listed above. The boiling point of the fluid is preferably between 30 degrees Centigrade and 210 degrees Centigrade at atmospheric pressure.
A fluid with high pentane content can be made to boil and produce pressurised vapour at a temperature as low as 30 degrees Centigrade and is suitable.
A highly suitable fluid is a fluorocarbon sold under the trade mark Electronic Fluid by 3M. It was conceived as a refrigerant. It has a latent heat of vaporisation of 88 kJ/kg (compared for example with water whose latent heat of vaporisation is 2150 kJ/kg). It is immiscible and is approximately twice as dense as water, so that it is easy to separate from water - when a mixture of the two is collected in a tank, Electronic Fluid sinks to the lower part of the tank leaving the water floating on top and a clear line of demarcation between the two liquids. Its boiling point can be a low as 31 degrees Centigrade and a usable pressure can be generated using temperatures as low as 50 degrees Centigrade.
Because the present system provides an essentially closed circuit for circulation of the working fluid, the fact that many of the options for the working fluid are highly flammable is not necessarily problematic but the preferred working fluids are not flammable. Where the evaporation fluid employed is of a highly flammable nature the seal where the piston-rod emerges from its cylinder may be doubled (two adjacent seals) with a pressure change detector in the space between the two seals. If any leak of potentially flammable material occurs past the first seal, the pressure detector activates an alarm which results in the engine being closed down so that the failed seal can be replaced without any discharge of the evaporation fluid to the outside. All of the valves and pumps employed in the system are preferably of the closed type so that no seal failure can result in any discharge of the working fluid in such embodiments.

The Condensing Fluid

In certain embodiments the system embodying the invention may use two different fluids in relation to the engine. Working fluid, e.g. of the type referred to in the section above, is used to drive the engine. The working fluid circulates through the heat exchanger 12 and through the engine 18 where its expansion and condensation serves to drive the engine. A condensing fluid of different composition from the working fluid is used to cause the working fluid to condense in the engine. It is the condensing fluid that is injected into the engine's working chambers 24, 26 through the condensing fluid supply ports 40, 42. In such a system the working fluid and the condensing fluid are passed through respective, largely separate circuits but note that the two fluids are mixed in the engine. Hence some means is needed to subsequently separate them. This function may for example be achieved by use of a separation tank in which one fluid floats upon the other. Figure 3 shows a system having suitable arrangement. It is closely similar to Figure 2, but note that in place of the header tank 57 of Figure 2, the Figure 4 system has a separator tank 57a which has an upper outlet 120 to the cooler 44 which is higher than a lower outlet 122 which supplies the heat exchanger 12.
In the separator tank 57a the condensing fluid 104 floats upon the working fluid, which is indicated at 124. The line 126 of separation of the two fluids is between the levels of the upper and lower outlets 120, 122. Hence the heat exchanger 12 receives the working fluid 104 and the condensing circuitry including the cooler 44 receives the condensing fluid.
Note also that in this embodiment the cooler 44 supplies a condensing fluid header tank 127 from which the condensing fluid is supplied to the engine. Also in Figure 3 the hydraulic motor 86 is shown driving a generator 87 which supplies an electric load 89.
A float may be provided with an intermediate density so that it tends to remain at the interface of the two fluids in the separator tank, and may be connected to some form of sensor to provide information on the level of the fluids in the tank. This sensor may be electrical or mechanical and the information provided may be used to moderate the extraction of one or both of the fluids.
To enable separation of the fluids in this manner, the working fluid and the condensing fluid are in this example chosen to be immiscible and of significantly different densities, the working fluid being more dense in the present example. Water can be used as the condensing fluid along with working fluids of the types disclosed above.
Figure 4 illustrates in more detail a practical arrangement for separating the working fluid from the condensing fluid. The separator tank is again indicated at 57a. A conduit 400 supplies the working fluid 124 to the heat exchanger (which is not seen in Figure 4) via the lower outlet 122 and a non-return valve 402. Sensor arrays 404a-e are seen at various locations and each serves to pass data representing flow, temperature and pressure in a respective fluid conduit to an electronic controller, preferably in the form of a computer, and still more preferably in the form of a PLC (Programmable Logic Controller), serving to control operation of the system. Input conduit 406 receives the mixed fluid exhausted from the engine (which is not seen in Figure 4) and supplies it to a settling tank 408 provided with a level sensor 410. A pump 412 transfers the mixed fluid to the separator tank 57a via a non-return valve 414. The condensing fluid 104 is drawn from the separator tank 57a via the upper outlet 120 and a non-return valve 416 by a pump 418, and thereby supplied to the chiller 44. In this embodiment the chiller uses a liquid coolant in a reservoir 418, the condensing fluid being passed through coils 420 in the reservoir 418 to cool the fluid and then being output via a conduit 422 to the condensing fluid header tank 127 (not seen in Figure 4 but see Figure 3).
In other embodiments the working and condensing fluids may be separated by other means including, without limitation, filtration, separation in a centrifuge, or any other suitable process.
The condensation of the working fluid by the condensing fluid can be very rapid. The condensing fluid is injected in the form of an aerosol and droplets of it cause nucleation of the vaporised working fluid. Condensation can be achieved in a fiftieth of a second. To this end the condensation fluid preferably has a high latent heat of vaporisation compared to the working fluid.

The Engine

While the above described systems all use engines incorporating a reciprocating piston, other types of engine may be substituted. Favoured engines are of the type in which the working fluid is received in a sealable working chamber and does work due to its pressure by expansion/contraction in and of the chamber. It is of course known to exploit kinetic energy of a fluid to do work, e.g. in a turbine, but engines operating on that principle are not considered suitable. Suitable engines may be characterised as "sealed chamber pressure engines".
Rotary type engines, lacking a reciprocating piston, may be adopted. Suitable engine types include vane engines/motors and lobe engines (note that the terms "engine" and "motor" are used interchangeably herein). Both are in themselves well known. Lobe type engines are particularly suitable, as to which see Figure 5. The lobe engine 18a depicted therein receives vaporised working fluid from a heat exchanger 12 as in the embodiments described above. The mechanism of the lobe motor itself is somewhat modified in accordance with an aspect of the invention and will now be described.
Power is output from the lobe motor through a driven shaft 200 which carries and is driven by a main rotor 202 having recesses 204 at regular intervals around its outer circumference. The main rotor 202 seals against adjacent part-circular portions of a motor housing 203. It also engages with two rotary lobe members 208a, 208b each of which has a central hub 210 and projecting lobes 212, 214 on either side of the central hub. The profiles of the main rotor 202 and the lobe members 208a, 208b are such that they are all able to turn at once while maintaining a respective sealing contact between the main rotor 202 and each lobe member 208a, 208b. The profiles of the components are chosen, in known manner, such that there is little or no slip at these contacts. Also each lobe member is housed in a respective part-circular portion of the motor housing with whose inner wall 216a, 216b the respective lobe member 208a, 208b forms a seal. Fluid inlets 218a, 218b receive pressurised, vaporised working fluid which is thus delivered to working chambers 220a, 220b within the motor housing 203. Pressure in these working chambers urges the main rotor 202 to turn along with the lobe members 208a, 208b, since this turning motion causes the volumes of the working chambers 220a, 220b to increase. The direction of rotation of the main rotor 202 in the drawing is clockwise. The lobe members 208a, 208b turn anticlockwise. At a certain point in the rotation, the working chamber 220a or 220b is closed against input of fluid from the respective inlet 218a, 218b (see lobe member 208b in the drawing) by engagement of lobes 212, 214 with the inner housing wall 216a, b, and further rotation opens the working chamber 220a or 220b to a respective exhaust passage 222a or 222b. Hence at this point the working chamber is defined by the main rotor 202, the relevant load member 208a, 208b, the relevant inner housing wall, and the exhaust itself. The condensing fluid is sprayed into this space through respective condensing fluid supply ports 40a, 40b to condense the working fluid in this region, producing a partial vacuum at the exhausts which increases the torque at the main rotor 202. In this embodiment, the working chamber is automatically opened and closed to the spray of condensing fluid by the movement of the lobe member and it is not necessary to switch the spray of condensing fluid on and off in synchronism with the movement of the motor components - it can instead be a continuous spray.
An alternative is to connect the exhausts 222a, 222b to a separate condenser (not shown) to create a vacuum therein.
The condensed working fluid is injected back into the heat exchanger 12. A solenoid pump controlled by the working fluid level in the separator tank may for example be used. Other types of pressure pump could be substituted. At the outlet of the heat exchanger 12 is a pressure controlled valve which opens fully when a pre-set pressure is achieved during start-up.

Heat Sources

Figures 6a to c illustrate arrangements for exploiting respectively (a) waste heat in an exhaust flue; (b) waste heat from a hot liquid such as the cooling water or heat transfer oil used to cool a combustion engine or other machinery; and (c) solar radiation. The invention may alternatively be applied to exploitation of any other heat source, be it waste heat or heat deliberately created for conversion into electric power e.g. by burning waste or other combustible material. In Figure 6a a section of an existing flue 300 has been cut and removed, and replaced with a section 302 adapted in accordance with the present invention to receive heat from the exhaust gases in the flue by means of internal heat exchanger tubes 304 through which a fluid heat transfer medium is circulated. Cooler exhaust gases thus emerge from the said flue section 302 at its upper end 304 and the exhaust gases can thus be prepared for carbon capture.
In Figure 6b item 310 is a pipe through which heated waste liquid passes and in accordance with the present invention a section 312 of the pipe is provided with heat exchanger tubes 314 through which the heat transfer medium is circulated.
In Figure 6c a solar collector 316 is heated by the sun 318 and serves in turn to heat a transfer medium which is circulated through a heat exchanger 12.
Figure 6d illustrates a system 600 embodying the present invention in highly schematic form. Vaporised working fluid, e.g. from the devices depicted in any of Figures 6a to c, is received in a manifold 602 for delivery to multiple engines 18, only one of which is shown. The vaporised working fluid in this example may be at a pressure from three to seven Bar (300 to 700 kPa). Pressure difference across the engine, and hence its output power, is increased by virtue of a condenser 604 on the engine output side which creates a partial vacuum. In this example the condenser is air cooled - a fan 606 is schematically illustrated - but other types of condenser, e.g. water cooled devices, may be used. An injector pump 608 returns the condensed working fluid to the heat exchanger to be re-vaporised.
The systems described above all have closed circuits for circulation of the working fluid (and, where relevant, the condensing fluid) so that the fluid(s) do not need to be replenished. Expensive and/or volatile fluids can thus be used. The mechanical, rotary, engine output in the Figure 6 system may for example be used to drive an electric generator 610, a hydraulic pump 612, or an air compressor 614.
Heat exchange devices of the types described above may be used in conjunction with conventional combustion-based power stations, the heat exchange devices being configured to lower the temperature of exhaust gases from the power station in order to economically assist with the process of carbon capture. In this case, heat collection coils are placed in the exhaust gas flues to collect heat in the power station exhaust gases. If carbon capture is to be applied to the power station then the extent of the heat collection coils is extended to collect even much lower temperature heat energy and thus cool the exhaust gases ready for carbon dioxide separation. The heat collection coils closest to the furnace will collect the most useful heat energy and without the requirement for carbon capture it would become progressively less efficient and desirable to collect the heat energy the further the heat collection coil is from the furnace. However, as the cost of carbon capture activity is largely the result of cooling the exhaust gases, it is economically justifiable to use the principle of the present invention to cool the exhaust gases even if only small quantities of electric power result. The heated transfer medium emanating from the heat collection coils closest to the furnace would be connected to heat exchangers 12 supplying pressurised vapour to different engines from those furthest away, so that there is no efficiency reduction in those engines which would be utilised if no carbon capture was to be undertaken.
The foregoing embodiments are presented by way of example only. Numerous variants and other applications will be apparent to the skilled person. For instance, while the above description applies in part to large, high power output systems, the principle underlying the invention may also be applied to smaller systems. Where only small quantities of heat energy are available, for example from a domestic heating furnace, a small geothermal source or a small solar collection array, the boiler/heat exchanger 12 could be eliminated and the vaporisation of the working fluid occur within heat exchange coils. The reciprocating motion of the piston-rod assembly could be used to directly create electric power by attaching it to a magnetised rod passing through an electrical coil.

THE FOLLOWING ARE NOT CLAIMS, BUT INSTEAD ARE STATEMENTS CONCERNING PREFERRED FEATURES OF THE INVENTION

A. An engine having a variable volume working chamber, a working fluid inlet for supply of pressurised, vaporised working fluid to the working chamber, a condensing fluid injection port for injection of condensing fluid to the working chamber, an exhaust, and an arrangement for opening and closing the working fluid inlet and the exhaust such that in use pressurised, vaporised working fluid is supplied to the working chamber causing the working chamber to expand, after which condensing fluid is injected into the working chamber causing the working fluid to condense and creating a partial vacuum in the working chamber whose volume then contracts, the engine being provided with a mechanism through which the expansion and contractions of the working chamber is used to do useful work.
B. An engine as in statement A which comprises a reciprocally driven piston which defines the working chamber within a cylinder.
C. An engine as in statement B in which the engine is double acting, variable volume working chambers being formed on two sides of the piston and each having a working fluid in that, a condensing fluid injection port and a exhaust.
D. An engine as in statement B or statement C which comprises at least one spring arranged to engage an assembly comprising the piston as the piston approaches an end of a piston stroke to cause the piston to rebound, reversing its direction of travel.
E. An engine as in statement A which is of rotary type, the working chamber being defined between a rotor and adjacent surface of a housing part, the volume of the working chamber varying as the rotor turns.
F. An engine as in any of statements A to E further comprising working fluid which has a latent heat of vaporisation between 88 and 250 kJ/kg.
G. An engine as in any of statements A to F comprising a working fluid which is any of a hydrocarbon, a halocarbon, a halo-hydrocarbon, a halo-ether, a halo-ketone, or a functional derivative of any of the aforegoing.
H. A heat-driven power generation system comprising an engine having a variable volume working chamber which is provided with
1. (a) a working fluid inlet for supply of pressurised, vaporised working fluid to the working chamber,
2. (b) a condensing fluid injection port for injection of condensing fluid to the working chamber, and
3. (c) an exhaust,
so that in use pressurised, vaporised working fluid supplied to the working chamber through the working fluid inlet causes the working chamber to expand, after which condensing fluid injected to the working chamber through the condensing fluid injection port causes the working fluid to condense, creating a partial vacuum in the working chamber whose volume then contracts, the system comprising a mechanism through which the expansion and contraction of the working chamber is used to do useful work and the exhaust being arranged to permit the resultant mixture of the working fluid and the condensing fluid to be exhausted from the working chamber, the system further comprising
a separation device which is connectable to the engine's exhaust to receive the mixture of the working fluid and the condensing fluid and to separate the two liquids, providing working fluid at a first separation device output and condensing fluid at a second separation device output,
a heat exchanger arranged to receive working fluid from the first separation device output, the heat exchanger being adapted to receive heat energy from an external source and to use the said heat energy to heat the working fluid, vaporising and pressurising it, the heat exchanger having an outlet which is connectable to the working fluid inlet to supply the vaporised, pressurised working fluid thereto, and
a condensing fluid supply arrangement comprising a conduit for conducting condensing fluid from the second separation device output to the condensing fluid injection port.
I. A heat-driven power generation system as in statement H in which the engine comprises a reciprocally driven piston which defines the working chamber within a cylinder.
J. A heat-driven power generation system as in statement I in which the engine is double acting, variable volume working chambers being formed on two sides of the piston and each having a working fluid inlet, a condensing fluid injection port and an exhaust.
K. A heat-driven power generation system as in statement I or statement J in which the engine comprises at least one spring arranged to engage an assembly comprising the piston as the piston approaches an end of a piston stroke to cause the piston to rebound, reversing its direction of travel.
L. A heat-driven power generation system as in statement H in which the engine is a rotary engine in which the working chamber is defined between a rotor and an adjacent surface of a housing part, the volume of the working chamber varying as the rotor turns.
M. A heat-driven power generation system as in statement L in which the working fluid inlet and/or the condensing fluid injection port and/or the exhaust is opened and closed by the rotor as it turns.
N. A heat-driven power generation system as in any of statements H to M further comprising a pump for receiving condensing fluid from the second separation device output and delivering it to the condensing fluid injection port.
O. A heat-driven power generation system as in any of statements H to N further comprising a cooler arranged to receive the condensing fluid and to cool it prior to its injection into the working chamber.
P. A heat-driven power generation system as in any of statements H to O wherein the system comprises the working fluid and the working fluid has a latent heat of vaporisation between 88 and 250 kJ/kg
Q. A heat-driven power generation system as in any of statements H to P wherein the system comprises the working fluid and the working fluid is any of a hydrocarbon, a halocarbon, a partially halogenated carbon, a fluorocarbon, a perfluorocarbon, an ether, a ketone, a fluorinated ether and a fluorinated ketone.
R. A heat-driven power generation system as in any of statements H to Q wherein the system comprises the working fluid and the condensing fluid and the condensing fluid has a greater latent heat of vaporisation than the working fluid.
S. A heat-driven power generation system as in any of statements H to R wherein the system comprises the working fluid and the condensing fluid and the two fluids are immiscible and/or of different densities, so that the said mixture of the two fluids separates when placed in a tank.
T. A heat-driven power generation system as in statement S wherein the separation device comprises a tank, the first and second separation device outputs being at different heights and each communicating with the interior of the tank.
U. A method of driving an engine having a variable volume working chamber, the method comprising the use of a working fluid which comprises any of a hydrocarbon, a halocarbon, a halo-hydrocarbon, a halo-ether, a halo-ketone, or a functional derivative of any of the aforegoing.
V. A method as in statement U in which the working fluid is a fluorocarbon.
W. A heat-driven power generation system substantially as herein described with reference to, and as illustrated in, any of the accompanying drawings.
X. An engine substantially as herein described with reference to, and is illustrated in, any of the accompanying drawings.

Claims

A method of operating an engine having a variable volume working chamber, the method comprising the use of a working fluid which comprises any of a halocarbon, a halo-hydrocarbon, a partially halogenated carbon compound, a fluorocarbon, a perfluorocarbon, a hydrofluorocarbon, a hydrochlorofluorocarbon, a fluorinated ether, a fluorinated ketone, or a functional derivative of any of the aforegoing.
A method as claimed in claim 1 in which the working fluid comprises a fluorocarbon, a hydrochlorofluorocarbon or a functional derivative thereof.
A method as claimed in claim 1 in which the working fluid comprises a fluorinated ether.
A method as claimed in any preceding claim in which the working fluid has a latent heat of vaporisation between 88 and 250 kJ/kg.
A method as claimed in any preceding claim in which the boiling point of the working fluid is below 100°C at atmospheric pressure.
A method as claimed in any preceding claim in which the working fluid is immiscible in water.
A method as claimed in any preceding claim, comprising circulating the working fluid through the engine in a closed circuit.
A method as claimed in claim 7, comprising passing the working fluid through a heat exchanger adapted to receive heat energy from an external source and to use the said heat energy to heat the working fluid, vaporising and pressurising it, and supplying the heated fluid to an input of the engine.
An engine which has a variable volume working chamber and which is provided with a working fluid comprising any of a halocarbon, a halo-hydrocarbon, a partially halogenated carbon compound, a fluorocarbon, a perfluorocarbon, a hydrofluorocarbon, a hydrochlorofluorocarbon, a fluorinated ether, a fluorinated ketone, or a functional derivative of any of the aforegoing.
An engine as claimed in claim 9 in which the working fluid comprises a fluorocarbon, a hydrochlorofluorocarbon or a functional derivative thereof.
An engine as claimed in claim 9 in which the working fluid comprises a fluorinated ether.
An engine as claimed in any of claims 9 to 11 in which the boiling point of the working fluid is below 100°C at atmospheric pressure.
An engine as claimed in any of claims 9 to 12 in which the working fluid is immiscible in water.
Use, in a heat engine having a variable volume working chamber, of a working fluid comprising any of a halocarbon, a halo-hydrocarbon, a partially halogenated carbon compound, a fluorocarbon, a perfluorocarbon, a hydrofluorocarbon, a hydrochlorofluorocarbon, a fluorinated ether, a fluorinated ketone, or a functional derivative of any of the aforegoing.