WO2014080164A2 - A heat engine - Google Patents

A heat engine Download PDF

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Publication number
WO2014080164A2
WO2014080164A2 PCT/GB2013/000511 GB2013000511W WO2014080164A2 WO 2014080164 A2 WO2014080164 A2 WO 2014080164A2 GB 2013000511 W GB2013000511 W GB 2013000511W WO 2014080164 A2 WO2014080164 A2 WO 2014080164A2
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WO
WIPO (PCT)
Prior art keywords
reservoir
valve
fluid
heat
pressure
Prior art date
Application number
PCT/GB2013/000511
Other languages
French (fr)
Other versions
WO2014080164A3 (en
Inventor
Mark Trebilcock
Sarah TREBILCOCK
Original Assignee
Mark Trebilcock
Trebilcock Sarah
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Mark Trebilcock, Trebilcock Sarah filed Critical Mark Trebilcock
Publication of WO2014080164A2 publication Critical patent/WO2014080164A2/en
Publication of WO2014080164A3 publication Critical patent/WO2014080164A3/en

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B11/00—Compression machines, plants or systems, using turbines, e.g. gas turbines
    • F25B11/02—Compression machines, plants or systems, using turbines, e.g. gas turbines as expanders
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01K—STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES
    • F01K25/00—Plants or engines characterised by use of special working fluids, not otherwise provided for; Plants operating in closed cycles and not otherwise provided for
    • F01K25/08—Plants or engines characterised by use of special working fluids, not otherwise provided for; Plants operating in closed cycles and not otherwise provided for using special vapours
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22D—PREHEATING, OR ACCUMULATING PREHEATED, FEED-WATER FOR STEAM GENERATION; FEED-WATER SUPPLY FOR STEAM GENERATION; CONTROLLING WATER LEVEL FOR STEAM GENERATION; AUXILIARY DEVICES FOR PROMOTING WATER CIRCULATION WITHIN STEAM BOILERS
    • F22D11/00—Feed-water supply not provided for in other main groups
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B23/00—Machines, plants or systems, with a single mode of operation not covered by groups F25B1/00 - F25B21/00, e.g. using selective radiation effect
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B30/00—Heat pumps
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B41/00—Fluid-circulation arrangements
    • F25B41/20—Disposition of valves, e.g. of on-off valves or flow control valves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B41/00—Fluid-circulation arrangements
    • F25B41/40—Fluid line arrangements

Definitions

  • the present invention relates to a heat engine.
  • the Rankine cycle is well known and is often used to convert heat energy from a heat source (often referred to as waste heat) to produce useful work.
  • An organic Rankine cycle converts heat energy from a low heat energy source.
  • a Rankine cycle uses water as a working fluid and a source of heat energy above 100°C (degrees centigrade).
  • An organic Rankine cycle is typically used to produce useful work, using an organic working fluid, from a heat source at less than 100°C.
  • the Rankine cycle operates by generating a high pressure in the working fluid in one region of a closed circuit, which is usually used to drive an expander, such as a steam turbine.
  • the high pressure is generated by a generator or boiler which transfers heat, from the heat source, to the working fluid principally with the intention of increasing the pressure of the working fluid but in practical systems the heat energy also causes an increase in enthalpy of the working fluid.
  • Downstream of the expander is a condenser which reduces the pressure of the fluid and transfers heat to a low temperature source.
  • a mechanical pump drives the working fluid around the system.
  • US Patent Application US-A-2004/221579 discloses a two-phase thermodynamic power system including a capillary device, an inline turbine and a condenser for generating output power as a generator or receiving input power as a refrigerator.
  • the capillary device such as a heat loop pipe or a capillary pumped loop, is coupled to the inline turbine for generating output power for power generation or for receiving input power for powered refrigeration.
  • the refrigeration system is well suited for removing waste heat from a spacecraft at a low temperature and rejecting that heat into space at a higher temperature.
  • US-A2012125019 discloses a self sustaining energy system for a building and utilises geothermal energy.
  • the energy system includes a ground source heat engine for heating and cooling a building airspace and an organic Rankine cycle.
  • An object of the present invention is to provide an improved heat engine which is suitable for recovering low grade waste heat.
  • a heat engine comprising a fluid circuit for a working fluid, the fluid circuit including: a heat exchanger for receiving heat energy from a first external source for supply to the working fluid; an expander downstream from the heat exchanger for generating work from the supplied heat energy; a condenser downstream from the expander for transferring heat energy from the working fluid to a second external source at a lower temperature than the first external source; and a pressure transfer region downstream of the condenser and upstream of the heat exchanger for conveying fluid around the fluid circuit and comprising: a first reservoir arranged to receive fluid from the condenser; a second reservoir arranged to receive fluid from the first reservoir and to convey it downstream towards the heat exchanger; and a valve arrangement for controlling conveying of fluid from the first and the second reservoirs; wherein the valve arrangement is configured for selectively filling the second reservoir from the first reservoir, isolating the first reservoir from the second reservoir and discharging the second reservoir at high pressure to the heat exchanger.
  • the valve arrangement may comprise a second valve having an open condition for conveying fluid from the second reservoir towards the heat exchanger and a closed condition for resisting the conveyance of fluid.
  • valve arrangement may comprise a third valve for conveying fluid pressure from a location downstream of the second valve to a location downstream of the first valve between the first reservoir and the second reservoir.
  • valve arrangement may comprise a fourth valve for conveying fluid pressure from a location downstream of the second reservoir and upstream of the second valve to a location between the expander and the condenser.
  • a heat engine comprising a fluid circuit for a working fluid, the fluid circuit including: a heat exchanger for receiving heat energy from a first external source for supply to the working fluid; an expander downstream from the heat exchanger for generating work from the supplied heat energy; a condenser downstream from the expander for transferring heat energy from the working fluid to a second external source at a lower temperature than the first external source; and first and second heat exchangers located downstream of the condenser and upstream of the heat exchanger for conveying fluid around the fluid circuit, a common heat transfer circuit enables heat transfer between the first and second heat exchangers, so that they are adapted to receive fluid from the pressure chamber; a valve arrangement for controlling fluid flow from the first and the second reservoirs; characterised in that the valve arrangement is configured for selectively filling the second reservoir from the first reservoir, isolating the first reservoir from the second reservoir and discharging the second reservoir at high pressure to the heat exchanger and selectively filling the first reservoir from the
  • the first valve is operable to convey working fluid from the first reservoir for filling the second reservoir when the liquid level in the second reservoir is reduced below a predetermined level
  • the second valve is operable to convey fluid from the second reservoir to the heat exchanger when the liquid level in the second reservoir is increased above a predetermined level
  • the third valve is operable to equalise the pressure in the second reservoir with the pressure in the heat exchanger generally prior to conveying working fluid from the second reservoir
  • the fourth valve is operable to equalise the pressure in the second reservoir with the pressure upstream of the condenser generally prior to conveying working fluid from the first reservoir to the second reservoir.
  • a third reservoir is located downstream of the second reservoir and upstream of the heat exchanger for receiving liquid from the second reservoir at a first pressure and discharging liquid to the heat exchanger at a second higher pressure.
  • a boiler vessel may be provided for receiving heat energy from an external heat source and transferring the heat energy to liquid being conveyed from the second reservoir to the third reservoir.
  • a second valve arrangement is provided for selectively conveying liquid from the boiler vessel to the third reservoir and from the third reservoir to the heat exchanger.
  • the second valve arrangement may comprise a fifth valve having an open condition for allowing fluid communication between the boiler vessel and the third reservoir and a closed condition for resisting said fluid communication.
  • the second valve arrangement may comprise a sixth valve having an open condition for conveying fluid from the third reservoir towards the heat exchanger and a closed condition for resisting the conveyance of fluid.
  • the second valve arrangement may comprise a seventh valve for conveying fluid pressure from a location downstream of the sixth valve to a location downstream of the fifth valve between the boiler vessel and the third reservoir.
  • the second valve arrangement may comprise an eighth valve for conveying fluid pressure from a location downstream of the third reservoir and upstream of the sixth valve to a flow path extending between the boiler vessel and the heat exchanger.
  • expanded working fluid exhausts from the expander passes to the condenser and subsequently as condensate passes to the first reservoir at a low pressure; when a first predetermined condition is met the second valve opens and drains condensate from the first reservoir to the second reservoir at an intermediate pressure; when a second predetermined condition is met the second valve closes, so as to isolate the first and second reservoirs one from another; when a third predetermined condition is met, the third valve opens and condensate drains from the second reservoir to a third reservoir at a high pressure; when a fourth predetermined condition is met the second valve closes, so as to isolate the second and third reservoirs one from another; when a fifth predetermined condition is met, the fourth valve opens and condensate is returned to the heat exchanger, where it is reheated from an external heat source to repeat the cycle.
  • a heat engine comprising a fluid circuit for a working fluid, the fluid circuit including: a first and a second heat exchangers for receiving heat energy from a first external source for supply to the working fluid; an expander downstream from the first and a second heat exchangers for generating work from the supplied heat energy; a condenser downstream from the expander for transferring heat energy from the working fluid to a second external source at a lower temperature than the first external source; and a pressure transfer region downstream of the condenser and upstream of the first and a second heat exchangers for conveying fluid around the fluid circuit and comprising: a first reservoir arranged to receive fluid from the condenser; and a second reservoir arranged to receive fluid from the condenser and to convey it downstream towards the first and a second heat exchangers; characterised in that a valve arrangement controls the transfer of the working fluid from and to the first and the second heat exchangers wherein the valve arrangement is configured to permit selective filling of the second
  • the fluid circuit is closed; the working fluid is organic and has a boiling temperature at atmosphere of less than 100°C, preferably less than 80°C and more preferably less than 60°C; and the heat engine is configured for use with a low temperature heat source less than 100°C, preferably less than 80°C and more preferably less than 60°C.
  • Figure 1 is an overall schematic of a closed Rankine cycle with a waste heat source, a heat engine, an expander and a condenser;
  • Figure 2 is a modification of the Figure 1 arrangement
  • FIG. 3 is schematic drawing of an alternative embodiment and shows in greater detail: a heat source, heat exchangers, a heat engine, an expander a condenser, as well as valves and intermediate sealed vessels;
  • Figure 4 is a modification of the Figure 3 arrangement
  • Figure 5 shows schematic drawing of an alternative embodiment which includes double pressure exchanger
  • Figure 6 shows schematic drawing of an alternative embodiment which includes double heat exchanger.
  • a heat engine 10 comprising a fluid circuit 12 shown in bold arrows for a working fluid.
  • the fluid circuit includes a heat exchanger arrangement for receiving heat energy from a first external source 16 for supply to the working fluid.
  • the heat engine 10 is particularly but not exclusively for use in a so-called organic Rankine cycle with a low heat energy source at a temperature of less than 100°C, or depending on application less than 80°C or less than 60°C, such as waste heat or solar heating.
  • the working fluid may be for example carbon dioxide, n- pentane, toluene, HC hydrocarbon gasses, HFC hydro-flouro-carbon gasses (such as R134a) HF hydro-flouro and HFO refrigerants or ammonia (ammonia has a high specific heat capacity and makes a good heat transfer fluid) in place of water as used in higher temperature applications.
  • the heat exchanger arrangement comprises a boiler 18 and heat exchanger 20. Fluid is circulated about a circuit 14 including the external heat energy source 16, the boiler and the heat exchanger thereby transferring heat energy to fluid conveyed along the fluid circuit 12. Working fluid enters the heat exchanger arrangement as a liquid at high pressure where it is heated at generally constant pressure by the external heat source to become a dry saturated vapour.
  • the boiler is intended to elevate pressure, temperature and enthalpy of received working fluid to a saturated vapour condition. However, if the working fluid conveyed from the boiler contains some liquid it may damage the expander. Therefore in the illustrated arrangement, a second heat exchanger 18 is provided for ensuring that the working liquid is in a saturated vapour state.
  • An expander 22 is located on the fluid circuit 12 downstream from the heat exchanger arrangement 18, 20.
  • the expander receives vaporised fluid at high pressure and generates useful work.
  • the expander may be a turbine, or other mechanical mechanism such as a rotary vane compressor.
  • the working fluid loses energy as it passes through the expander as work energy is extracted causing a drop in working fluid pressure to a low pressure. However, the working fluid still retains sufficient heat energy to remain a vapour.
  • a condenser 24 is located in the fluid circuit 12 downstream from the expander for transferring heat energy from the working fluid to a second external source 26 at a lower temperature than the first external source 16.
  • the condenser may be a heat exchanger for transferring heat energy to a fluid circulated about a cold or ambient temperature fluid circuit 28 including the external source 26.
  • the external source may be a source of cold water and for example may be the sea if the heat energy source is a marine propulsion unit of a ship.
  • Working fluid transferred through the condenser is reduced in heat energy and returns to its liquid state.
  • a pump is located downstream of the condenser for increasing the pressure of the liquid and pumping it round the circuit.
  • the present embodiment does not require a pump and instead uses a pressure transfer region 30 downstream of the condenser and upstream of the heat exchanger for conveying fluid around the fluid circuit.
  • the pressure transfer region 30 comprises a first reservoir 32 arranged to receive fluid from the condenser 24, a second reservoir 34 arranged to receive fluid from the first reservoir and to convey it downstream towards the heat exchanger arrangement 18, 20; and a valve arrangement for controlling conveying of fluid from the first and the second reservoirs.
  • the volumetric capacity required in each of the reservoirs is dependent on the capacity of the system for example a larger capacity system will typically require larger capacity reservoirs.
  • the amount of work that can be generated by the system is dependent on the mass flow rate of working fluid through the system, the specific heat capacity of the working fluid and the difference in temperature between the source of heat and the cold, or ambient, temperature sink. For example, in a 10 kW system reservoir 34 may hold a full charge of 2kg and in a 100 kW system the reservoir may hold 20kg.
  • Elevation of the reservoirs is ideally required to harness gravity for supplying working fluid to the heat exchangers. Additionally or alternatively, pressure difference may induce flow and overcome gravity.
  • the valve arrangement comprises a first valve 36 having an open condition for allowing fluid communication between the first reservoir 32 and the second reservoir 34 and a closed condition for resisting said fluid communication.
  • the first valve is located on the fluid circuit 12 downstream of the first reservoir and upstream of the second reservoir.
  • the first valve may comprise any suitable valve mechanism such as motorised ball valves, solenoid valves and in a preferred embodiment, non-return valves.
  • the valve arrangement also comprises a second valve 38 having an open condition for conveying fluid from the second reservoir 34 towards the heat exchanger arrangement 18, 20 and a closed condition for resisting the conveyance of fluid.
  • the second valve is located on the fluid circuit downstream of the second reservoir and upstream of the heat exchanger arrangement.
  • the second valve may comprise any suitable valve mechanism such as motorised ball valves and in a preferred embodiment, non-return valves.
  • valve arrangement comprises a third valve 40 for conveying fluid pressure from a location downstream of the second valve 38 to a location downstream of the first valve 36 between the first reservoir 32 and the second reservoir 34.
  • the third valve may comprise any suitable valve mechanism and in the present embodiment the valve comprises a solenoid valve in combination with a flow reducing orifice 42.
  • valve arrangement comprises a fourth valve 44 for conveying fluid pressure from a location downstream of the second reservoir 34 and upstream of the second valve 38 to a location between the expander 22 and the condenser 24.
  • the fourth valve may comprise any suitable valve mechanism and in the present embodiment the valve comprises a solenoid valve in combination with a flow reducing orifice 46.
  • a first flow path 48 is provided including the third valve 40 and a second flow path 50 is provided including the fourth valve 44.
  • the valve arrangement is configured for selectively preventing fluid being conveyed from the first reservoir 32 to the second reservoir 34 and allowing the second reservoir to convey fluid downstream towards the heat exchanger arrangement 18, 20 and subsequently to allow fluid in the first reservoir to be conveyed to the second reservoir.
  • the valve arrangement prevents the conveyance of fluid from the first reservoir to the second reservoir for increasing the pressure of fluid in the first reservoir.
  • liquid working fluid flows from the condenser into the first reservoir 32 generally continuously throughout the cycle.
  • the fluid charged into the first reservoir is at low pressure.
  • the first reservoir is principally provided for periodic charging of the second reservoir.
  • the second reservoir is charged from the first reservoir and then connected to the high pressure region of the cycle for increasing the pressure in the second reservoir. At the selected time the contents of the second reservoir are released and their pressure together with gravity is sufficient to drive the heat exchanger arrangement and circulate fluid around the circuit 12.
  • a first stage in the cycle the fluid level in the second reservoir 34 is reducing.
  • the first valve 36 is closed
  • the second valve 38 is open
  • the third valve 40 is energised (i.e. open if the solenoid valve is a normally closed valve)
  • the fourth valve 44 is de- energised (i.e. closed if the solenoid valve is a normally closed valve).
  • a float switch (not shown) energises a fill relay which causes the second valve 38 to start to close.
  • a cam switch de-energises the third valve 40 and energises the fourth valve 44.
  • the first valve 36 is closed, the second valve 38 is closed, the third valve 40 is de-energised and the fourth valve 44 is energised.
  • first valve 36 When the fourth valve 44 is energised the pressure in the second reservoir 34 will reduce until it is generally the same as the pressure at the inlet of the condenser 24.
  • a differential pressure switch opens first valve 36. At this stage, first valve 36 is open, second valve 38 is closed, third valve 40 is de-energised and fourth valve 44 is energised. With the first valve 36 open and the fourth valve 44 energised fluid in the first reservoir 32 can drain into the second reservoir 34.
  • a drain relay causes closing of the first valve 36.
  • a cam switch enables the fourth valve 44 to de- energise and the third valve 40 to energise.
  • the pressure in the second reservoir equalises with the pressure in the heat exchanger arrangement 18, 20.
  • a differential pressure switch senses when the pressure has equalised and causes the second valve 38 to open to allow the content of the second reservoir to drain into the heat exchanger arrangement 18, 20 with the assistance of gravity. Since the third valve 40 is open gas locking is avoided. The cycle then repeats.
  • FIG. 2 A modification of the Figure 1 embodiment is shown in Figure 2 comprising a regenerator vessel 51 and a further reservoir 52.
  • the regenerator vessel is arranged to receive or exchange heat energy exhausted from the expander 22 for pre-heating pressurised working fluid conveyed downstream from the second reservoir 34.
  • the reservoir 52 receives the working fluid from the regenerator vessel 51 prior to it being conveyed to the boiler 20 to ensure a substantially constant or regular feed to the boiler, although in some modifications the reservoir 52 may be omitted.
  • the provision of the regenerator improves the efficiency of the cycle.
  • FIG. 3 A second embodiment of the invention is shown in Figure 3 which is a two-stage modification of the first embodiment and the same reference numerals will be used for similar components.
  • the second embodiment 58 comprises a second stage 60 of the pressure transfer region comprising a similar pressure step- up arrangement as in the first embodiment.
  • the second stage 60 is located downstream of second valve 38 and upstream of boiler 20.
  • the operation of the first stage 30 of the pressure transfer region is the same as described above and will not be repeated. More than two pressure transfer regions may be provided as required.
  • the second stage 60 comprises an additional boiler vessel 62 for receiving relatively high pressure liquid from the second reservoir 34.
  • the boiler vessel is arranged to receive heat energy from the heat energy source 16 or possibly an additional or different heat energy source.
  • the heat energy elevates the temperature, pressure and enthalpy of the working liquid towards that of the heat exchanger arrangement 18, 20 and that in the second reservoir.
  • the second stage 60 steps up the temperature in addition to the pressure between the condenser 24 and the boiler 20.
  • the cold or ambient temperature heat sink condenses the vapour exhaust from the expander to form a liquid.
  • the boiler vessel provides heating of the working fluid from a cold or ambient temperature at which it is conveyed from the condenser to a temperature at which it is exhausted from the heat exchangers 18, 20 on the hot side of the system.
  • the boiler vessel 62 elevates the temperature of the working fluid to between the temperature of the hot source 16 and cold source 26.
  • the effective temperature in boiler vessel 62 may be mid way between those temperatures at 52.5°C, although other temperatures are envisaged.
  • the boiler vessel may exchange heat with a different heat source from source 16 or the heat exchanger arrangement itself may be configured to transfer less heat to the working fluid passing through vessel 6.
  • a flow path 64 is provided for conveying heated liquid directly to the heat exchanger 18 to provide a pressure relief line.
  • a third reservoir 66 is arranged to receive fluid from the boiler vessel 62 and to convey it downstream towards the heat exchanger arrangement 18, 20.
  • a second valve arrangement selectively conveys fluid from the boiler vessel and the third reservoir.
  • a non-return valve 61 is located upstream of the boiler vessel 62 to ensure fluid is not conveyed upstream from the boiler vessel to a lower pressure region.
  • a non-return valve 63 may be located in duct 64 for resisting the flow of fluid from the heat exchanger 18 to the boiler vessel 62 when the pressure between the boiler and the heat exchanger is higher than the pressure in the boiler vessel.
  • the second valve arrangement comprises a fifth valve 68 having an open condition for allowing fluid communication between the boiler vessel 62 and the third reservoir 66 and a closed condition for resisting said fluid communication.
  • the fifth valve is located on the fluid circuit 12 downstream of the boiler vessel and upstream of the third reservoir.
  • the fifth valve may comprise any suitable valve mechanism such as a motorised ball valve.
  • the valve arrangement also comprises a sixth valve 70 having an open condition for conveying fluid from the third reservoir 66 towards the heat exchanger arrangement 18, 20 and a closed condition for resisting the conveyance of fluid.
  • the sixth valve is located on the fluid circuit downstream of the third reservoir and upstream of the heat exchanger arrangement.
  • the sixth valve may comprise any suitable valve mechanism such as a motorised ball valve.
  • valve arrangement comprises a seventh valve 72 for conveying fluid pressure from a location downstream of the sixth valve 70 to a location downstream of the fifth valve 68 between the boiler vessel and the third reservoir.
  • the seventh valve may comprise any suitable valve mechanism and in the present embodiment the valve comprises a solenoid valve in combination with a flow reducing orifice 74.
  • the second valve arrangement comprises an eighth valve 76 for conveying fluid pressure from a location downstream of the third reservoir 66 and upstream of the sixth valve 70 to the flow path 64 and to the heat exchanger 18.
  • the fourth valve may comprise any suitable valve mechanism and in the present embodiment the valve comprises a solenoid valve in combination with a flow reducing orifice 78.
  • Flows paths 80, 82 include respectively seventh and eighth valves 72, 76 for conveying fluid as required.
  • the second stage 60 of the pressure transfer region is arranged such that the third reservoir 66 is selectively charged from the boiler vessel 62 at a relatively high pressure (i.e. that pressure between low pressure and high pressure discharged from the second reservoir 34).
  • the liquid pressure in the reservoir is then increased by connection to the high pressure region in the boiler 20 and then subsequently the high pressure liquid is discharged to the boiler 20.
  • the second valve arrangement is functionally equivalent to the first valve arrangement and the fifth, sixth, seventh and eighth valves 68, 70, 72, 76 are operable in the same way as respective first, second, third and fourth valves 36, 38, 40 and 44. Therefore as operation of the first to fourth valves has already been described operation of the fifth to eighth valves need not be described again.
  • expanded working fluid exhausts from the expander, passes to the condenser and subsequently as condensate passes to the first reservoir at a low pressure; when a first predetermined condition is met the second valve opens and drains condensate from the first reservoir to the second reservoir at an intermediate pressure; when a second predetermined condition is met the second valve closes, so as to isolate the first and second reservoirs one from another; when a third predetermined condition is met, the third valve opens and condensate drains from the second reservoir to a third reservoir at a high pressure; when a fourth predetermined condition is met the second valve closes, so as to isolate the second and third reservoirs one from another; when a fifth predetermined condition is met, the fourth valve opens and condensate is returned to the heat exchanger, where it is reheated from an external heat source to repeat the cycle.
  • FIG 4 A modification of the two-stage embodiment of Figure 3 is shown in Figure 4 and comprises a regenerator 84 for receiving or exchanging heat energy with fluid exhausted from the expander 22.
  • the regenerator is located to pre-heat fluid conveyed downstream from the reservoir 34.
  • An additional reservoir 86 is located upstream of the boiler 20 and provides a generally regular or constant flow of fluid to the boiler.
  • a pressure regulating valve is located in duct 64 to ensure that the vessel 62 is not exposed to excess pressure from the fluid being conveyed between the boiler 20 and the heat exchanger 18.
  • Double chamber with two pressure exchanging vessels (or double ' ⁇ ' version, as shown in Figure 5 or more than 2 PX eg triple PX or quad PX
  • SV2 energised 2 The level of working fluid in the chamber reaches a low level limit and a float switch or level sensor energises the fill relay. This initiates a change in motorised valve and solenoid valve status.
  • MV1 starts to close, when the valve is almost closed a cam switch enables SV1 to de-energise and SV2 to energise. This in turn causes the pressure in the now closed pressure change chamber to rise, until the pressure is sufficiently close to the boiler pressure that a differential pressure switch allows MV2 to start opening. So that the following occurs:
  • this embodiment has a pressure transfer region 530 comprising two pressure chambers 531 and 532, similar in many respects to the pressure step-up arrangement as in the embodiment shown in Figure 1 , except in this embodiment there are two pressure chambers.
  • the second stage is located downstream of valves 536 and 538 and upstream of boiler 520.
  • the operation of the first stage 530 of the pressure transfer region is described in greater detail below with reference to a valve control sequence.
  • Two pressure change chambers 531 and 532 are shown but it is appreciated that more may be provided as required.
  • the second stage comprises an additional boiler vessel 520 for receiving relatively high pressure liquid from the second pressure change chamber 532.
  • Boiler vessel 520 is arranged to receive heat energy from a heat energy source 516 or possibly an additional or different (not shown) heat energy source. The heat energy received elevates the temperature, pressure and enthalpy of the working liquid as it is pumped towards a heat exchanger. Likewise working fluid that is in a second reservoir is pumped and heated.
  • the second stage 560 steps up the temperature of the working fluid in addition to the pressure between the condenser 524 and the boiler 520.
  • the cold or ambient temperature heat sink condenses exhaust vapour from the expander 522 to form a liquid.
  • the boiler vessel 520 provides heating of the working fluid from a cold, or ambient temperature, at which it is conveyed from the condenser 524 to a temperature at which it is exhausted from the heat exchangers on the hot side of the system.
  • the boiler vessel 520 elevates the temperature of the working fluid to between the temperature of the hot source 516 and a cold sink.
  • the effective temperature in boiler vessel 520 is typically mid way between those temperatures, that is at 52.5°C.
  • other intermediate temperatures are envisaged.
  • the boiler vessel 520 exchanges heat with a different heat source to heat source 516.
  • the heat exchanger is configured to transfer less heat to the working fluid passing through vessel.
  • a float level switch or other sensor makes or closes to indicate that they are full and empty respectively and initiates a change in the valve positions, as follows:
  • the level float switch initiates another change in valves to prepare PX1 to drain and PX2 to fill again. In order for this to happen the following needs to occur:
  • SV4 de-energised 5. With SV2 and SV3 energised, the pressures in PX1 and PX2 change. PX1 becomes the same pressure as the boiler and PX2 becomes the same pressure as the condenser. Once the pressures have stabilised a pressure switch or other sensor detects this and allows MV3 to open and MV2 to open, so that the following occurs:
  • the second stage 658 comprises an additional heat exchanger arrangement 618 and 620 and that in the second reservoir.
  • the second stage 660 steps up the temperature in addition to the pressure between the condenser 624 and the boiler 620.
  • the cold or ambient temperature heat sink condenses the vapour exhaust from the expander 622 to condense to form a liquid.
  • the boiler vessel provides heating of the working fluid from a cold or ambient temperature at which it is conveyed from the condenser to a temperature at which it is exhausted from the heat exchangers 618 and 619 on the hot side of the system.
  • the boiler vessel 620 elevates the temperature of the working fluid to one that is intermediate the temperature of the hot source 616 and cold source.
  • the effective temperature in boiler vessel 620 may be mid way between those temperatures at 52.5°C, although other intermediate temperatures are envisaged.
  • the boiler vessel may exchange heat with a different heat source from the heat source 616 or the heat exchanger arrangement itself may be configured to transfer less heat to the working fluid.
  • HWSV1 Hot Water Solenoid Valve 1
  • HWSV2 Hot Water Solenoid Valve 2
  • HWSV1 prevents hot water flowing in HX1 whilst filling occurs and HWSV2 ensures water flows through HX2 to assist driving the fluid out of HX2 and ensures hot water continues to flow through to the boiler.
  • HWSV1 energised
  • HX1 now continue to feed to the boiler via NRV1 and with the aid of HWSV1 to drive heat into the fluid and on to the boiler.
  • HX2 is almost empty, having fed its contents through NRV2 and HWSV2 are de-energised.
  • HWSV1 energised
  • Boiler continues to be fed by HX1 , with the aid of heat from HWSV .
  • HWSV1 energised
  • HWSV 1 de-energised
  • HWSV2 energised Then PX starts to refill HX2 in readiness for it to provide continual feed for the boiler as HX1 level gets lower. This is accompanied by the change in HWSV as follows:
  • HWSV1 de-energised as HX1 will be low and HWSV2 uses the heat to drive out the fluid in HX2 and ensure constant hot water flow to the boiler.
  • HWSV2 energised
  • the pressure in PX reduces to condenser pressure and the pressure switch once again detects this and initiates a further change.
  • HWSV2 energised The cycle has now run it full cycle and both HX1 and HX2 have been alternatively filled.
  • pressure vessels and heat exchangers downstream from item 32 up to and including item 18 may all be enclosed in one pressure vessel to reduce manufacturing cost, although some valves and actuators may need to be externally mounted on this vessel.
  • the illustrated heat engines can be used in any of the following applications which are listed by way of example only. They may be used to: recover waste heat from marine propulsion units, such as diesel engines or any internal combustion engines in combination with a cold heat source of the sea; to recover waste heat from refineries; processing plants and factories (such as sugar mills and other industrial processes) that generate low grade waste heat.
  • marine propulsion units such as diesel engines or any internal combustion engines in combination with a cold heat source of the sea
  • refineries to recover waste heat from refineries
  • processing plants and factories such as sugar mills and other industrial processes
  • Supermarkets and food process factories using large amounts of vapour compression cycle refrigeration can also harvest low grade waste heat from the high temperature discharge gas, by acting as a de-super heater before using the existing condensers;
  • Power stations the higher quality low grade waste heat being returned to the ambient condensers can be used to further generate more electricity from the cycle.
  • sources of waste heat suitable for use with the present invention include: large scale district heating and cooling plants generating low grade waste heat, geothermal heat sources and solar ponds.
  • Solar heating arrangements, particularly in warm climates, can also be used as a means to transfer or store a potential energy source such as hydro electric, batteries and flywheels
  • the invention may also be used in the recovery of waste heat from power stations - such as nuclear power stations - and conventional coal and gas fired power stations.

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Abstract

The present invention provides a heat engine (10) comprising a fluid circuit (12) for a working fluid. The fluid circuit includes: a heat exchanger (18, 20) for receiving heat energy from a first external source (16) for supply to the working fluid. An expander (22) downstream from the heat exchanger generates work from the supplied heat energy. A condenser (24) downstream from the expander transfers heat energy from the working fluid to a second external source (26) at a lower temperature than the first external source; and a pressure transfer region (30) downstream of the condenser and upstream of the heat exchanger conveys fluid around the fluid circuit and comprises: a first reservoir (32) arranged to receive fluid from the condenser. A second reservoir (34) is arranged to receive fluid from the first reservoir and to convey it downstream towards the heat exchanger; and a valve arrangement (36, 38, 40, 44) for controlling conveyance of fluid from the first and the second reservoirs. The valve arrangement is configured for selectively filling the second reservoir from the first reservoir, isolating the first reservoir from the second reservoir and discharging the second reservoir at high pressure to the heat exchanger.

Description

A HEAT ENGINE
Field of the Invention
The present invention relates to a heat engine. Background of the Invention
The Rankine cycle is well known and is often used to convert heat energy from a heat source (often referred to as waste heat) to produce useful work. An organic Rankine cycle converts heat energy from a low heat energy source. Typically, a Rankine cycle uses water as a working fluid and a source of heat energy above 100°C (degrees centigrade). An organic Rankine cycle is typically used to produce useful work, using an organic working fluid, from a heat source at less than 100°C.
The Rankine cycle operates by generating a high pressure in the working fluid in one region of a closed circuit, which is usually used to drive an expander, such as a steam turbine. The high pressure is generated by a generator or boiler which transfers heat, from the heat source, to the working fluid principally with the intention of increasing the pressure of the working fluid but in practical systems the heat energy also causes an increase in enthalpy of the working fluid. Downstream of the expander is a condenser which reduces the pressure of the fluid and transfers heat to a low temperature source. A mechanical pump drives the working fluid around the system.
There are continued attempts to improve the Rankine cycle and aspects of it and generally these attempts have been aimed at improving the efficiency of the expander.
Prior Art
US Patent Application US-A-2004/221579 (The Aerospace Corporation) discloses a two-phase thermodynamic power system including a capillary device, an inline turbine and a condenser for generating output power as a generator or receiving input power as a refrigerator. The capillary device, such as a heat loop pipe or a capillary pumped loop, is coupled to the inline turbine for generating output power for power generation or for receiving input power for powered refrigeration. The refrigeration system is well suited for removing waste heat from a spacecraft at a low temperature and rejecting that heat into space at a higher temperature.
US-A2012125019 (Sami) discloses a self sustaining energy system for a building and utilises geothermal energy. The energy system includes a ground source heat engine for heating and cooling a building airspace and an organic Rankine cycle.
An object of the present invention is to provide an improved heat engine which is suitable for recovering low grade waste heat.
Summary of Invention
According to a first aspect of the present invention, there is provided a heat engine comprising a fluid circuit for a working fluid, the fluid circuit including: a heat exchanger for receiving heat energy from a first external source for supply to the working fluid; an expander downstream from the heat exchanger for generating work from the supplied heat energy; a condenser downstream from the expander for transferring heat energy from the working fluid to a second external source at a lower temperature than the first external source; and a pressure transfer region downstream of the condenser and upstream of the heat exchanger for conveying fluid around the fluid circuit and comprising: a first reservoir arranged to receive fluid from the condenser; a second reservoir arranged to receive fluid from the first reservoir and to convey it downstream towards the heat exchanger; and a valve arrangement for controlling conveying of fluid from the first and the second reservoirs; wherein the valve arrangement is configured for selectively filling the second reservoir from the first reservoir, isolating the first reservoir from the second reservoir and discharging the second reservoir at high pressure to the heat exchanger. The valve arrangement may comprise a first valve having an open condition for allowing fluid communication between the first reservoir and the second reservoir and a closed condition for resisting said fluid communication.
The valve arrangement may comprise a second valve having an open condition for conveying fluid from the second reservoir towards the heat exchanger and a closed condition for resisting the conveyance of fluid.
In an alternative arrangement the valve arrangement may comprise a third valve for conveying fluid pressure from a location downstream of the second valve to a location downstream of the first valve between the first reservoir and the second reservoir.
In a further alternative arrangement the valve arrangement may comprise a fourth valve for conveying fluid pressure from a location downstream of the second reservoir and upstream of the second valve to a location between the expander and the condenser.
According to a second aspect of the present invention, there is provided a heat engine comprising a fluid circuit for a working fluid, the fluid circuit including: a heat exchanger for receiving heat energy from a first external source for supply to the working fluid; an expander downstream from the heat exchanger for generating work from the supplied heat energy; a condenser downstream from the expander for transferring heat energy from the working fluid to a second external source at a lower temperature than the first external source; and first and second heat exchangers located downstream of the condenser and upstream of the heat exchanger for conveying fluid around the fluid circuit, a common heat transfer circuit enables heat transfer between the first and second heat exchangers, so that they are adapted to receive fluid from the pressure chamber; a valve arrangement for controlling fluid flow from the first and the second reservoirs; characterised in that the valve arrangement is configured for selectively filling the second reservoir from the first reservoir, isolating the first reservoir from the second reservoir and discharging the second reservoir at high pressure to the heat exchanger and selectively filling the first reservoir from the second reservoir, isolating the second reservoir from the first reservoir and discharging the first reservoir at high pressure to the heat exchanger.
Preferably, in each aspect of the invention the first valve is operable to convey working fluid from the first reservoir for filling the second reservoir when the liquid level in the second reservoir is reduced below a predetermined level, the second valve is operable to convey fluid from the second reservoir to the heat exchanger when the liquid level in the second reservoir is increased above a predetermined level, the third valve is operable to equalise the pressure in the second reservoir with the pressure in the heat exchanger generally prior to conveying working fluid from the second reservoir, and the fourth valve is operable to equalise the pressure in the second reservoir with the pressure upstream of the condenser generally prior to conveying working fluid from the first reservoir to the second reservoir.
In one embodiment, a third reservoir is located downstream of the second reservoir and upstream of the heat exchanger for receiving liquid from the second reservoir at a first pressure and discharging liquid to the heat exchanger at a second higher pressure.
A boiler vessel may be provided for receiving heat energy from an external heat source and transferring the heat energy to liquid being conveyed from the second reservoir to the third reservoir.
Preferably, a second valve arrangement is provided for selectively conveying liquid from the boiler vessel to the third reservoir and from the third reservoir to the heat exchanger.
The second valve arrangement may comprise a fifth valve having an open condition for allowing fluid communication between the boiler vessel and the third reservoir and a closed condition for resisting said fluid communication.
The second valve arrangement may comprise a sixth valve having an open condition for conveying fluid from the third reservoir towards the heat exchanger and a closed condition for resisting the conveyance of fluid. The second valve arrangement may comprise a seventh valve for conveying fluid pressure from a location downstream of the sixth valve to a location downstream of the fifth valve between the boiler vessel and the third reservoir.
The second valve arrangement may comprise an eighth valve for conveying fluid pressure from a location downstream of the third reservoir and upstream of the sixth valve to a flow path extending between the boiler vessel and the heat exchanger.
Preferably, in use; expanded working fluid exhausts from the expander, passes to the condenser and subsequently as condensate passes to the first reservoir at a low pressure; when a first predetermined condition is met the second valve opens and drains condensate from the first reservoir to the second reservoir at an intermediate pressure; when a second predetermined condition is met the second valve closes, so as to isolate the first and second reservoirs one from another; when a third predetermined condition is met, the third valve opens and condensate drains from the second reservoir to a third reservoir at a high pressure; when a fourth predetermined condition is met the second valve closes, so as to isolate the second and third reservoirs one from another; when a fifth predetermined condition is met, the fourth valve opens and condensate is returned to the heat exchanger, where it is reheated from an external heat source to repeat the cycle.
According to a third aspect of the present invention, there is provided a heat engine comprising a fluid circuit for a working fluid, the fluid circuit including: a first and a second heat exchangers for receiving heat energy from a first external source for supply to the working fluid; an expander downstream from the first and a second heat exchangers for generating work from the supplied heat energy; a condenser downstream from the expander for transferring heat energy from the working fluid to a second external source at a lower temperature than the first external source; and a pressure transfer region downstream of the condenser and upstream of the first and a second heat exchangers for conveying fluid around the fluid circuit and comprising: a first reservoir arranged to receive fluid from the condenser; and a second reservoir arranged to receive fluid from the condenser and to convey it downstream towards the first and a second heat exchangers; characterised in that a valve arrangement controls the transfer of the working fluid from and to the first and the second heat exchangers wherein the valve arrangement is configured to permit selective filling of the second heat exchanger at substantially the same time as the first heat exchanger is draining; and at a subsequent time the valve arrangement permits selective filling of the first heat exchanger at substantially the same time as the second heat exchanger is draining.
In the embodiments illustrated, the fluid circuit is closed; the working fluid is organic and has a boiling temperature at atmosphere of less than 100°C, preferably less than 80°C and more preferably less than 60°C; and the heat engine is configured for use with a low temperature heat source less than 100°C, preferably less than 80°C and more preferably less than 60°C.
Brief Description of the Drawings
In order that the invention may be well understood, an embodiment thereof, which is given by way of example only, will now be described with reference to the accompanying drawings, in which:
Figure 1 is an overall schematic of a closed Rankine cycle with a waste heat source, a heat engine, an expander and a condenser;
Figure 2 is a modification of the Figure 1 arrangement;
Figure 3 is schematic drawing of an alternative embodiment and shows in greater detail: a heat source, heat exchangers, a heat engine, an expander a condenser, as well as valves and intermediate sealed vessels;
Figure 4 is a modification of the Figure 3 arrangement;
Figure 5 shows schematic drawing of an alternative embodiment which includes double pressure exchanger; and Figure 6 shows schematic drawing of an alternative embodiment which includes double heat exchanger.
Detailed description of an Embodiment of the Invention
Referring to Figure 1 , a heat engine 10 is shown comprising a fluid circuit 12 shown in bold arrows for a working fluid. The fluid circuit includes a heat exchanger arrangement for receiving heat energy from a first external source 16 for supply to the working fluid. The heat engine 10 is particularly but not exclusively for use in a so-called organic Rankine cycle with a low heat energy source at a temperature of less than 100°C, or depending on application less than 80°C or less than 60°C, such as waste heat or solar heating.
In an organic Rankine cycle the working fluid may be for example carbon dioxide, n- pentane, toluene, HC hydrocarbon gasses, HFC hydro-flouro-carbon gasses (such as R134a) HF hydro-flouro and HFO refrigerants or ammonia (ammonia has a high specific heat capacity and makes a good heat transfer fluid) in place of water as used in higher temperature applications.
In this embodiment, the heat exchanger arrangement comprises a boiler 18 and heat exchanger 20. Fluid is circulated about a circuit 14 including the external heat energy source 16, the boiler and the heat exchanger thereby transferring heat energy to fluid conveyed along the fluid circuit 12. Working fluid enters the heat exchanger arrangement as a liquid at high pressure where it is heated at generally constant pressure by the external heat source to become a dry saturated vapour.
The boiler is intended to elevate pressure, temperature and enthalpy of received working fluid to a saturated vapour condition. However, if the working fluid conveyed from the boiler contains some liquid it may damage the expander. Therefore in the illustrated arrangement, a second heat exchanger 18 is provided for ensuring that the working liquid is in a saturated vapour state.
An expander 22 is located on the fluid circuit 12 downstream from the heat exchanger arrangement 18, 20. The expander receives vaporised fluid at high pressure and generates useful work. The expander may be a turbine, or other mechanical mechanism such as a rotary vane compressor. The working fluid loses energy as it passes through the expander as work energy is extracted causing a drop in working fluid pressure to a low pressure. However, the working fluid still retains sufficient heat energy to remain a vapour.
A condenser 24 is located in the fluid circuit 12 downstream from the expander for transferring heat energy from the working fluid to a second external source 26 at a lower temperature than the first external source 16. The condenser may be a heat exchanger for transferring heat energy to a fluid circulated about a cold or ambient temperature fluid circuit 28 including the external source 26. The external source may be a source of cold water and for example may be the sea if the heat energy source is a marine propulsion unit of a ship. Working fluid transferred through the condenser is reduced in heat energy and returns to its liquid state.
In known Rankine cycles a pump is located downstream of the condenser for increasing the pressure of the liquid and pumping it round the circuit. The present embodiment does not require a pump and instead uses a pressure transfer region 30 downstream of the condenser and upstream of the heat exchanger for conveying fluid around the fluid circuit.
The pressure transfer region 30 comprises a first reservoir 32 arranged to receive fluid from the condenser 24, a second reservoir 34 arranged to receive fluid from the first reservoir and to convey it downstream towards the heat exchanger arrangement 18, 20; and a valve arrangement for controlling conveying of fluid from the first and the second reservoirs.
The volumetric capacity required in each of the reservoirs is dependent on the capacity of the system for example a larger capacity system will typically require larger capacity reservoirs. The amount of work that can be generated by the system is dependent on the mass flow rate of working fluid through the system, the specific heat capacity of the working fluid and the difference in temperature between the source of heat and the cold, or ambient, temperature sink. For example, in a 10 kW system reservoir 34 may hold a full charge of 2kg and in a 100 kW system the reservoir may hold 20kg.
Elevation of the reservoirs is ideally required to harness gravity for supplying working fluid to the heat exchangers. Additionally or alternatively, pressure difference may induce flow and overcome gravity.
The valve arrangement comprises a first valve 36 having an open condition for allowing fluid communication between the first reservoir 32 and the second reservoir 34 and a closed condition for resisting said fluid communication. The first valve is located on the fluid circuit 12 downstream of the first reservoir and upstream of the second reservoir. The first valve may comprise any suitable valve mechanism such as motorised ball valves, solenoid valves and in a preferred embodiment, non-return valves.
The valve arrangement also comprises a second valve 38 having an open condition for conveying fluid from the second reservoir 34 towards the heat exchanger arrangement 18, 20 and a closed condition for resisting the conveyance of fluid. The second valve is located on the fluid circuit downstream of the second reservoir and upstream of the heat exchanger arrangement. The second valve may comprise any suitable valve mechanism such as motorised ball valves and in a preferred embodiment, non-return valves.
Additionally, the valve arrangement comprises a third valve 40 for conveying fluid pressure from a location downstream of the second valve 38 to a location downstream of the first valve 36 between the first reservoir 32 and the second reservoir 34. The third valve may comprise any suitable valve mechanism and in the present embodiment the valve comprises a solenoid valve in combination with a flow reducing orifice 42.
Further, the valve arrangement comprises a fourth valve 44 for conveying fluid pressure from a location downstream of the second reservoir 34 and upstream of the second valve 38 to a location between the expander 22 and the condenser 24. The fourth valve may comprise any suitable valve mechanism and in the present embodiment the valve comprises a solenoid valve in combination with a flow reducing orifice 46.
A first flow path 48 is provided including the third valve 40 and a second flow path 50 is provided including the fourth valve 44.
The valve arrangement is configured for selectively preventing fluid being conveyed from the first reservoir 32 to the second reservoir 34 and allowing the second reservoir to convey fluid downstream towards the heat exchanger arrangement 18, 20 and subsequently to allow fluid in the first reservoir to be conveyed to the second reservoir.
The valve arrangement prevents the conveyance of fluid from the first reservoir to the second reservoir for increasing the pressure of fluid in the first reservoir. In this regard, liquid working fluid flows from the condenser into the first reservoir 32 generally continuously throughout the cycle. The fluid charged into the first reservoir is at low pressure. The first reservoir is principally provided for periodic charging of the second reservoir. The second reservoir is charged from the first reservoir and then connected to the high pressure region of the cycle for increasing the pressure in the second reservoir. At the selected time the contents of the second reservoir are released and their pressure together with gravity is sufficient to drive the heat exchanger arrangement and circulate fluid around the circuit 12.
The use of heat engine 10 will now be described in more detail. In a first stage in the cycle the fluid level in the second reservoir 34 is reducing. At this stage, the first valve 36 is closed, the second valve 38 is open, the third valve 40 is energised (i.e. open if the solenoid valve is a normally closed valve) and the fourth valve 44 is de- energised (i.e. closed if the solenoid valve is a normally closed valve). When the level in the second reservoir reaches a predetermined low level limit, a float switch (not shown) energises a fill relay which causes the second valve 38 to start to close. When the valve is almost or substantially closed a cam switch de-energises the third valve 40 and energises the fourth valve 44. At this stage, the first valve 36 is closed, the second valve 38 is closed, the third valve 40 is de-energised and the fourth valve 44 is energised.
When the fourth valve 44 is energised the pressure in the second reservoir 34 will reduce until it is generally the same as the pressure at the inlet of the condenser 24. A differential pressure switch opens first valve 36. At this stage, first valve 36 is open, second valve 38 is closed, third valve 40 is de-energised and fourth valve 44 is energised. With the first valve 36 open and the fourth valve 44 energised fluid in the first reservoir 32 can drain into the second reservoir 34.
As the fluid level in the second reservoir 34 increases the float switch rises, and once a predetermined level is reached, a drain relay causes closing of the first valve 36. When the first valve is almost closed a cam switch enables the fourth valve 44 to de- energise and the third valve 40 to energise. At this stage the pressure in the second reservoir equalises with the pressure in the heat exchanger arrangement 18, 20. A differential pressure switch senses when the pressure has equalised and causes the second valve 38 to open to allow the content of the second reservoir to drain into the heat exchanger arrangement 18, 20 with the assistance of gravity. Since the third valve 40 is open gas locking is avoided. The cycle then repeats.
A modification of the Figure 1 embodiment is shown in Figure 2 comprising a regenerator vessel 51 and a further reservoir 52. In this modification the regenerator vessel is arranged to receive or exchange heat energy exhausted from the expander 22 for pre-heating pressurised working fluid conveyed downstream from the second reservoir 34. The reservoir 52 receives the working fluid from the regenerator vessel 51 prior to it being conveyed to the boiler 20 to ensure a substantially constant or regular feed to the boiler, although in some modifications the reservoir 52 may be omitted. The provision of the regenerator improves the efficiency of the cycle.
A second embodiment of the invention is shown in Figure 3 which is a two-stage modification of the first embodiment and the same reference numerals will be used for similar components. Referring to Figure 3 in greater detail, the second embodiment 58 comprises a second stage 60 of the pressure transfer region comprising a similar pressure step- up arrangement as in the first embodiment. The second stage 60 is located downstream of second valve 38 and upstream of boiler 20. The operation of the first stage 30 of the pressure transfer region is the same as described above and will not be repeated. More than two pressure transfer regions may be provided as required.
The second stage 60 comprises an additional boiler vessel 62 for receiving relatively high pressure liquid from the second reservoir 34. The boiler vessel is arranged to receive heat energy from the heat energy source 16 or possibly an additional or different heat energy source. The heat energy elevates the temperature, pressure and enthalpy of the working liquid towards that of the heat exchanger arrangement 18, 20 and that in the second reservoir.
Accordingly, the second stage 60 steps up the temperature in addition to the pressure between the condenser 24 and the boiler 20. The cold or ambient temperature heat sink condenses the vapour exhaust from the expander to form a liquid. However, once condensed it is desirable to increase the temperature (and pressure of the liquid) prior to it entering the boiler. Therefore, the boiler vessel provides heating of the working fluid from a cold or ambient temperature at which it is conveyed from the condenser to a temperature at which it is exhausted from the heat exchangers 18, 20 on the hot side of the system.
In a currently preferred arrangement, the boiler vessel 62 elevates the temperature of the working fluid to between the temperature of the hot source 16 and cold source 26. For example if the hot source is at 80°C and the cold source is at 25°C, the effective temperature in boiler vessel 62 may be mid way between those temperatures at 52.5°C, although other temperatures are envisaged. In order to elevate the temperature of the working fluid in this way, the boiler vessel may exchange heat with a different heat source from source 16 or the heat exchanger arrangement itself may be configured to transfer less heat to the working fluid passing through vessel 6. A flow path 64 is provided for conveying heated liquid directly to the heat exchanger 18 to provide a pressure relief line. A third reservoir 66 is arranged to receive fluid from the boiler vessel 62 and to convey it downstream towards the heat exchanger arrangement 18, 20. A second valve arrangement selectively conveys fluid from the boiler vessel and the third reservoir.
A non-return valve 61 is located upstream of the boiler vessel 62 to ensure fluid is not conveyed upstream from the boiler vessel to a lower pressure region. Similarly a non-return valve 63 may be located in duct 64 for resisting the flow of fluid from the heat exchanger 18 to the boiler vessel 62 when the pressure between the boiler and the heat exchanger is higher than the pressure in the boiler vessel.
The second valve arrangement comprises a fifth valve 68 having an open condition for allowing fluid communication between the boiler vessel 62 and the third reservoir 66 and a closed condition for resisting said fluid communication. The fifth valve is located on the fluid circuit 12 downstream of the boiler vessel and upstream of the third reservoir. The fifth valve may comprise any suitable valve mechanism such as a motorised ball valve.
The valve arrangement also comprises a sixth valve 70 having an open condition for conveying fluid from the third reservoir 66 towards the heat exchanger arrangement 18, 20 and a closed condition for resisting the conveyance of fluid. The sixth valve is located on the fluid circuit downstream of the third reservoir and upstream of the heat exchanger arrangement. The sixth valve may comprise any suitable valve mechanism such as a motorised ball valve.
Additionally, the valve arrangement comprises a seventh valve 72 for conveying fluid pressure from a location downstream of the sixth valve 70 to a location downstream of the fifth valve 68 between the boiler vessel and the third reservoir. The seventh valve may comprise any suitable valve mechanism and in the present embodiment the valve comprises a solenoid valve in combination with a flow reducing orifice 74.
Furthermore the second valve arrangement comprises an eighth valve 76 for conveying fluid pressure from a location downstream of the third reservoir 66 and upstream of the sixth valve 70 to the flow path 64 and to the heat exchanger 18. The fourth valve may comprise any suitable valve mechanism and in the present embodiment the valve comprises a solenoid valve in combination with a flow reducing orifice 78.
Flows paths 80, 82 include respectively seventh and eighth valves 72, 76 for conveying fluid as required. The second stage 60 of the pressure transfer region is arranged such that the third reservoir 66 is selectively charged from the boiler vessel 62 at a relatively high pressure (i.e. that pressure between low pressure and high pressure discharged from the second reservoir 34). The liquid pressure in the reservoir is then increased by connection to the high pressure region in the boiler 20 and then subsequently the high pressure liquid is discharged to the boiler 20.
The second valve arrangement is functionally equivalent to the first valve arrangement and the fifth, sixth, seventh and eighth valves 68, 70, 72, 76 are operable in the same way as respective first, second, third and fourth valves 36, 38, 40 and 44. Therefore as operation of the first to fourth valves has already been described operation of the fifth to eighth valves need not be described again.
Briefly however in use, expanded working fluid exhausts from the expander, passes to the condenser and subsequently as condensate passes to the first reservoir at a low pressure; when a first predetermined condition is met the second valve opens and drains condensate from the first reservoir to the second reservoir at an intermediate pressure; when a second predetermined condition is met the second valve closes, so as to isolate the first and second reservoirs one from another; when a third predetermined condition is met, the third valve opens and condensate drains from the second reservoir to a third reservoir at a high pressure; when a fourth predetermined condition is met the second valve closes, so as to isolate the second and third reservoirs one from another; when a fifth predetermined condition is met, the fourth valve opens and condensate is returned to the heat exchanger, where it is reheated from an external heat source to repeat the cycle.
A modification of the two-stage embodiment of Figure 3 is shown in Figure 4 and comprises a regenerator 84 for receiving or exchanging heat energy with fluid exhausted from the expander 22. The regenerator is located to pre-heat fluid conveyed downstream from the reservoir 34. An additional reservoir 86 is located upstream of the boiler 20 and provides a generally regular or constant flow of fluid to the boiler.
In the Figure 4 arrangement a pressure regulating valve is located in duct 64 to ensure that the vessel 62 is not exposed to excess pressure from the fluid being conveyed between the boiler 20 and the heat exchanger 18.
The following describe examples of cycles shown in the Figures and are indeed to be read in conjunction with the appropriate flow schematic.
1. Single chamber or basic heat engine, as shown in Figures 1 to 4.
2. Double chamber with two pressure exchanging vessels, (or double 'ΡΧ' version, as shown in Figure 5 or more than 2 PX eg triple PX or quad PX
3. Double chamber with two heat exchangers, (or double ΉΧ' as shown in Figure 6 or more than 2 HX eg triple HX quad HX
Cycle Description of a single chamber as depicted in Figures 1 to 4.
Key
MV1 = Motorised Valve 1
MV2 = Motorised Valve 2
SV1 = Solenoid Valve 1
SV2 = Solenoid Valve 2
1. At this stage in the cycle the fluid level in the pressure change chamber is reducing. The following conditions occur.
MV1 closed
MV2 open
SV1 de-energised
SV2 energised 2. The level of working fluid in the chamber reaches a low level limit and a float switch or level sensor energises the fill relay. This initiates a change in motorised valve and solenoid valve status.
3. When the fill relay energises motorised valve MV2 starts to close, at the 'almost closed' position a cam switch de-energises SV2 and energises SV1 , so that:
MV1 closed
MV2 closed
SV1 energised
SV2 de-energised
4. With SV1 energised the pressure in the pressure change chamber reduces, until the pressure is close to the pressure in the condenser portion of the system. At this point a differential pressure switch allows MV1 to start opening, so that:
MV1 open
MV2 closed
SV1 energised
SV2 de-energised
5. With MV1 open and SV1 energised working fluid in the receiver drains there from into the pressure change chamber, so that:
MV1 open
MV2 closed
SV1 energised
SV2 de-energised
6. As the level of the chamber increases a float switch rises in the chamber, once the maximum level has been reached; the maximum level switch closes. This in turn de-energises the fill relay and energises the drain relay to bring about a change in status of the valves and solenoids. 7. With the drain relay energised the following occurs: MV1 starts to close, when the valve is almost closed a cam switch enables SV1 to de-energise and SV2 to energise. This in turn causes the pressure in the now closed pressure change chamber to rise, until the pressure is sufficiently close to the boiler pressure that a differential pressure switch allows MV2 to start opening. So that the following occurs:
MV1 closed
MV2 open
SV1 de-energised
SV2 energised
8. With MV2 open and SV2 energised (to ensure no gas locking can occur) the fluid with the aid of gravity then drains into the boiler.
9. The system has now completed a full cycle and returns to step 1.
Referring now to Figure 5 in greater detail, this embodiment has a pressure transfer region 530 comprising two pressure chambers 531 and 532, similar in many respects to the pressure step-up arrangement as in the embodiment shown in Figure 1 , except in this embodiment there are two pressure chambers.
The second stage is located downstream of valves 536 and 538 and upstream of boiler 520. The operation of the first stage 530 of the pressure transfer region is described in greater detail below with reference to a valve control sequence. Two pressure change chambers 531 and 532 are shown but it is appreciated that more may be provided as required.
The second stage comprises an additional boiler vessel 520 for receiving relatively high pressure liquid from the second pressure change chamber 532. Boiler vessel 520 is arranged to receive heat energy from a heat energy source 516 or possibly an additional or different (not shown) heat energy source. The heat energy received elevates the temperature, pressure and enthalpy of the working liquid as it is pumped towards a heat exchanger. Likewise working fluid that is in a second reservoir is pumped and heated.
The second stage 560 steps up the temperature of the working fluid in addition to the pressure between the condenser 524 and the boiler 520. The cold or ambient temperature heat sink condenses exhaust vapour from the expander 522 to form a liquid. However, once condensed it is desirable to increase the temperature (and pressure of the liquid) prior to it entering the boiler 520. Therefore, the boiler vessel 520 provides heating of the working fluid from a cold, or ambient temperature, at which it is conveyed from the condenser 524 to a temperature at which it is exhausted from the heat exchangers on the hot side of the system.
In a currently preferred arrangement, the boiler vessel 520 elevates the temperature of the working fluid to between the temperature of the hot source 516 and a cold sink. For example if the hot source is at 80°C and the cold sink is at 25°C, the effective temperature in boiler vessel 520 is typically mid way between those temperatures, that is at 52.5°C. However, other intermediate temperatures are envisaged.
In order to elevate the temperature of the working fluid in this way, the boiler vessel 520 exchanges heat with a different heat source to heat source 516. Alternatively the heat exchanger is configured to transfer less heat to the working fluid passing through vessel.
It is understood that the embodiment shown in Figure 5 therefore offers the advantage that a larger quantity of heat can be extracted from the working fluid than in the embodiment shown in Figure 1.
The cycle description 'Double PX' (Pressure Exchanger) as depicted in Figure 5 will now be described with reference to the following detailed valve control and flow summary.
Key MV1 = Motorised valve 1
MV2 = Motorised valve 2
MV3 = Motorised valve 3
MV4 = Motorised valve 4
SV1 = Solenoid Valve 1
SV2 = Solenoid Valve 2
SV3 = Solenoid Valve 3
SV4 = Solenoid Valve 4
PX1 = Pressure change chamber 1
PX2 = Pressure change chamber 2
1. At this stage in the cycle the fluid level in pressure change chamber 1 (PX1 ) is lowering and the pressure in pressure change chamber 2 (PX2) is rising. The valve configuration will be as follows:
MV1 = closed
MV2 = open
MV3 = open
MV4 = closed
SV1 = de-energised
SV2 = energised
SV3 = energised
SV4 = de-energised
2. Once PX 1 is emptied and PX 2 is full, a float level switch or other sensor makes or closes to indicate that they are full and empty respectively and initiates a change in the valve positions, as follows:
MV1 = closed
MV2 = closed
MV3 = closed
MV4 = closed
SV1 = energised
SV2 = de-energised SV3 = de-energised
SV4 = energised
With SV 1 energises the pressure in PX1 lowers from boiler pressure to match the condenser pressure. SV 4 is energised and the pressure in PX2 increases to the pressure in the boiler.
3. Once the pressure in PX 1 matches condenser pressure, MV1 opens to start refilling PX 1. Simultaneously, once the pressure in PX 2 matches the pressure in the boiler, MV 4 opens to start draining PX 2 and as such refills the boiler, so that the following configuration is achieved:
MV1 = open
MV2 = closed
MV3 = closed
MV4 = open
SV1 = energised
SV2 = de-energised
SV3 = de-energised
SV4 = energised
4. Once PX1 has filled and PX2 has drained, the level float switch initiates another change in valves to prepare PX1 to drain and PX2 to fill again. In order for this to happen the following needs to occur:
MV1 = closed
MV2 = closed
MV3 = closed
MV4 = closed
SV1 = de-energised
SV2 = energised
SV3 = energised
SV4 = de-energised 5. With SV2 and SV3 energised, the pressures in PX1 and PX2 change. PX1 becomes the same pressure as the boiler and PX2 becomes the same pressure as the condenser. Once the pressures have stabilised a pressure switch or other sensor detects this and allows MV3 to open and MV2 to open, so that the following occurs:
MV1 = closed
MV2 = open
MV3 = open
MV4 = closed
SV1 = de-energised
SV2 = energised
SV3 = energised
SV4 = de-energised
At this point, the cycle in Figure 5, has run full circuit and the valves are in the same position as stage 1.
Referring now to Figure 6 in greater detail, in this embodiment a second stage 658 pressure transfer region is described. This is in many respects similar to the pressure step-up arrangement in the first embodiment described above with reference to Figure 1.
The second stage 658 comprises an additional heat exchanger arrangement 618 and 620 and that in the second reservoir.
The second stage 660 steps up the temperature in addition to the pressure between the condenser 624 and the boiler 620. The cold or ambient temperature heat sink condenses the vapour exhaust from the expander 622 to condense to form a liquid. However, once condensed it is desirable to increase the temperature (and pressure of the liquid) prior to it returning to the boiler 620. Therefore, the boiler vessel provides heating of the working fluid from a cold or ambient temperature at which it is conveyed from the condenser to a temperature at which it is exhausted from the heat exchangers 618 and 619 on the hot side of the system. In a currently preferred arrangement, the boiler vessel 620 elevates the temperature of the working fluid to one that is intermediate the temperature of the hot source 616 and cold source. For example if the hot source is at 80°C and the cold source is at 25°C, the effective temperature in boiler vessel 620 may be mid way between those temperatures at 52.5°C, although other intermediate temperatures are envisaged. In order to elevate the temperature of the working fluid in this way, the boiler vessel may exchange heat with a different heat source from the heat source 616 or the heat exchanger arrangement itself may be configured to transfer less heat to the working fluid.
The cycle description of a double heat exchanger, as depicted in Figure 6 will now be described with reference to the following detailed valve control and flow summary.
Key
MV1 = Motorised valve 1
MV2 = Motorised valve 2
MV3 = Motorised valve 3
SV1 = Solenoid Valve 1
SV2 = Solenoid Valve 2
SV3 = Solenoid Valve 3
HX1 = Heat exchanger 1
HX2 = Heat exchanger 2
HWSV1 = Hot Water Solenoid Valve 1
HWSV2 = Hot Water Solenoid Valve 2
NRV = Non Return Valve
1. At the start point of this cycle the pressure change chamber (PX) is reducing in level as it fills HX1. At the same time HX2 is draining into the boiler through NRV2
MV1 = closed
MV2 = open
MV3 = closed SV1 = de-energised
SV2 = energised
SV3 = de-energised
HWSV1 de-energised
HWSV2 energised
HWSV1 prevents hot water flowing in HX1 whilst filling occurs and HWSV2 ensures water flows through HX2 to assist driving the fluid out of HX2 and ensures hot water continues to flow through to the boiler.
2. Once the pressure change chamber (PX) has emptied a float switch or other sensor registers the low level and initiates a change of the valves as follows:
MV1 = closed
MV2 = closed
MV3 = closed
SV1 = energised
SV2 = de-energised
SV3 = de-energised
HWSV1 = energised
HWSV2 = de-energised
HX1 now continue to feed to the boiler via NRV1 and with the aid of HWSV1 to drive heat into the fluid and on to the boiler. HX2 is almost empty, having fed its contents through NRV2 and HWSV2 are de-energised.
3. With SV1 energised the pressure in the PX reduces to the same pressure as the condenser. Once the pressure in PX is the same as the condenser, a pressure switch or other sensor detects this and initiates a further change in valve positions as follows:
MV1 = open
MV2 = closed
MV3 = closed SV1 = energised
SV2 = de-energised
SV3 = de-energised
HWSV1 = energised
HWSV2 = de-energised
Boiler continues to be fed by HX1 , with the aid of heat from HWSV .
4. Once the PX is full a level switch detects this and initiates a further change as follows:
MV1 = closed
MV2 = closed
MV3 = closed
SV1 = de-energised
SV2 = de-energised
SV3 = energised
HWSV1 = energised
HWSV2 = de-energised
With SV3 energised the pressure in PX increases to the same pressure as the boiler via vent line associated with SV3.
5. Once PX has reached boiler pressure, a pressure switch detects this and allows MV3 to open
MV1 = closed
MV2 = closed
MV3 = open
SV1 = de-energised
SV2 = de-energised
SV3 = energised
HWSV 1 = de-energised
HWSV2 = energised Then PX starts to refill HX2 in readiness for it to provide continual feed for the boiler as HX1 level gets lower. This is accompanied by the change in HWSV as follows:
HWSV1 de-energised as HX1 will be low and HWSV2 uses the heat to drive out the fluid in HX2 and ensure constant hot water flow to the boiler.
6. Once the level of PX has reached the lowest level, the float switch detects this and initiates a change in valve positions.
MV1 = closed
MV2 = closed
MV3 = closed
SV1 = energised
SV2 = de-energised
SV3 = de-energised
HWSV1 = de-energised
HWSV2 = energised
The pressure in PX reduces to condenser pressure and the pressure switch once again detects this and initiates a further change.
7. MV1 is opened to allow PX to fill and this results in the following:
MV1 = open
MV2 = closed
MV3 = closed
SV1 = energised
SV2 = de-energised
SV3 = de-energised
HWSV1 = de-energised
HWSV2 = energised The cycle has now run it full cycle and both HX1 and HX2 have been alternatively filled.
In another embodiment the pressure vessels and heat exchangers downstream from item 32 up to and including item 18, may all be enclosed in one pressure vessel to reduce manufacturing cost, although some valves and actuators may need to be externally mounted on this vessel.
The illustrated heat engines can be used in any of the following applications which are listed by way of example only. They may be used to: recover waste heat from marine propulsion units, such as diesel engines or any internal combustion engines in combination with a cold heat source of the sea; to recover waste heat from refineries; processing plants and factories (such as sugar mills and other industrial processes) that generate low grade waste heat.
Supermarkets and food process factories using large amounts of vapour compression cycle refrigeration can also harvest low grade waste heat from the high temperature discharge gas, by acting as a de-super heater before using the existing condensers;
Power stations the higher quality low grade waste heat being returned to the ambient condensers can be used to further generate more electricity from the cycle. Other examples of sources of waste heat suitable for use with the present invention include: large scale district heating and cooling plants generating low grade waste heat, geothermal heat sources and solar ponds. Solar heating arrangements, particularly in warm climates, can also be used as a means to transfer or store a potential energy source such as hydro electric, batteries and flywheels
The invention may also be used in the recovery of waste heat from power stations - such as nuclear power stations - and conventional coal and gas fired power stations.
The invention has been described by way of several embodiments, with modifications and alternatives, but having read and understood this description, further embodiments and modifications will be apparent to those skilled in the art. All such embodiments and modifications are intended to fall within the scope of the present invention as defined in the accompanying claims.

Claims

Claims
1. A heat engine comprising a fluid circuit for a working fluid, the fluid circuit including: a heat exchanger for receiving heat energy from a first external source for supply to the working fluid; an expander downstream from the heat exchanger for generating work from the supplied heat energy; a condenser downstream from the expander for transferring heat energy from the working fluid to a second external source at a lower temperature than the first external source; and a pressure transfer region downstream of the condenser and upstream of the heat exchanger for conveying fluid around the fluid circuit and comprising: a first reservoir arranged to receive fluid from the condenser; a second reservoir arranged to receive fluid from the first reservoir and to convey it downstream towards the heat exchanger; and a valve arrangement for controlling conveying of fluid from the first and the second reservoirs; wherein the valve arrangement is configured for selectively filling the second reservoir from the first reservoir, isolating the first reservoir from the second reservoir and discharging the second reservoir at high pressure to the heat exchanger.
2. A heat engine comprising a fluid circuit for a working fluid, the fluid circuit including: a heat exchanger for receiving heat energy from a first external source for supply to the working fluid; an expander downstream from the heat exchanger for generating work from the supplied heat energy; a condenser downstream from the expander for transferring heat energy from the working fluid to a second external source at a lower temperature than the first external source; and first and second heat exchangers located downstream of the condenser and upstream of the heat exchanger for conveying fluid around the fluid circuit, a common heat transfer circuit enables heat transfer between the first and second heat exchangers, so that they are adapted to receive fluid from the pressure chamber; a valve arrangement for controlling fluid flow from the first and the second reservoirs; characterised in that the valve arrangement is configured for selectively filling the second reservoir from the first reservoir, isolating the first reservoir from the second reservoir and discharging the second reservoir at high pressure to the heat exchanger and selectively filling the first reservoir from the second reservoir, isolating the second reservoir from the first reservoir and discharging the first reservoir at high pressure to the heat exchanger.
3. A heat engine comprising a fluid circuit for a working fluid, the fluid circuit including: a first and a second heat exchangers for receiving heat energy from a first external source for supply to the working fluid; an expander downstream from the first and a second heat exchangers for generating work from the supplied heat energy; a condenser downstream from the expander for transferring heat energy from the working fluid to a second external source at a lower temperature than the first external source; and a pressure transfer region downstream of the condenser and upstream of the first and a second heat exchangers for conveying fluid around the fluid circuit and comprising: a first reservoir arranged to receive fluid from the condenser; and a second reservoir arranged to receive fluid from the condenser and to convey it downstream towards the first and a second heat exchangers; characterised in that a valve arrangement controls the transfer of the working fluid from and to the first and the second heat exchangers wherein the valve arrangement is configured to permit selective filling of the second heat exchanger at substantially the same time as the first heat exchanger is draining; and at a subsequent time the valve arrangement permits selective filling of the first heat exchanger at substantially the same time as the second heat exchanger is draining.
4. A heat engine as claimed in any preceding claim, wherein the valve arrangement comprises a first valve having an open condition for allowing fluid communication between the first reservoir and the second reservoir and a closed condition for resisting fluid communication between the first reservoir and the second reservoirs.
5. A heat engine as claimed in any preceding claim, wherein the valve arrangement comprises a second valve having an open condition for conveying fluid from the second reservoir towards the heat exchanger and a closed condition for resisting the conveyance of fluid.
6. A heat engine as claimed in any preceding claim, wherein the valve arrangement comprises a third valve for conveying fluid pressure from a location downstream of the second valve to a location downstream of the first valve between the first reservoir and the second reservoir.
7. A heat engine as claimed in any preceding claim, wherein the valve arrangement comprises a fourth valve for conveying fluid pressure from a location downstream of the second reservoir and upstream of the second valve to a location between the expander and the condenser.
8. A heat engine as claimed in claims 4 to 7, wherein the first valve is operable to convey working fluid from the first reservoir for filling the second reservoir when the liquid level in the second reservoir is reduced below a predetermined level, the second valve is operable to convey fluid from the second reservoir to the heat exchanger when the liquid level in the second reservoir is increased above a predetermined level, the third valve is operable to equalise the pressure in the second reservoir with the pressure in the heat exchanger generally prior to conveying working fluid from the second reservoir, and the fourth valve is operable to equalise the pressure in the second reservoir with the pressure upstream of the condenser generally prior to conveying working fluid from the first reservoir to the second reservoir.
9. A heat engine as claimed in any preceding claim, comprising a third reservoir located downstream of the second reservoir and upstream of the heat exchanger for receiving liquid from the second reservoir at a first pressure and discharging liquid to the heat exchanger at a second higher pressure.
10. A heat engine as claim in claim 9, comprising a boiler vessel for receiving heat energy from an external heat source and transferring the heat energy to liquid being conveyed from the second reservoir to the third reservoir.
11. A heat engine as claimed in claim 9 or 10, comprising a second valve arrangement for selectively conveying liquid from the boiler vessel to the third reservoir and from the third reservoir to the heat exchanger.
12. A heat engine as claimed in claim 11 , wherein the second valve arrangement comprises a fifth valve having an open condition for allowing fluid communication between the boiler vessel and the third reservoir and a closed condition for resisting said fluid communication.
13. A heat engine as claimed in claim 9 or 10, wherein the second valve arrangement comprises a sixth valve having an open condition for conveying fluid from the third reservoir towards the heat exchanger and a closed condition for resisting the conveyance of fluid.
14. A heat engine as claimed in claim 13, wherein the second valve arrangement comprises a seventh valve for conveying fluid pressure from a location downstream of the sixth valve to a location downstream of the fifth valve between the boiler vessel and the third reservoir.
15. A heat engine as claimed in claim 13 or 14, wherein the second valve arrangement comprises an eighth valve for conveying fluid pressure from a location downstream of the third reservoir and upstream of the sixth valve to a flow path extending between the boiler vessel and the heat exchanger.
16. A heat engine as claimed in any of the preceding claims, wherein, in use; expanded working fluid exhausts from the expander, passes to the condenser and subsequently as condensate passes to the first reservoir at a low pressure; when a first predetermined condition is met the second valve opens and drains condensate from the first reservoir to the second reservoir at an intermediate pressure; when a second predetermined condition is met the second valve closes, so as to isolate the first and second reservoirs one from another; when a third predetermined condition is met, the third valve opens and condensate drains from the second reservoir to a third reservoir at a high pressure; when a fourth predetermined condition is met the second valve closes, so as to isolate the second and third reservoirs one from another; when a fifth predetermined condition is met, the fourth valve opens and condensate is returned to the heat exchanger, where it is reheated from an external heat source to repeat the cycle.
17. A heat engine as claimed in any one of the preceding claims, wherein the fluid circuit is closed.
18. A heat engine as claimed in any one of the preceding claims, wherein the working fluid is organic and has a boiling temperature at atmosphere of less than 100°C, preferably less than 80°C and more preferably less than 60°C.
19. A heat pump as claimed in any one of the preceding claims, configured for use with a low temperature heat source less than 100°C, preferably less than 80°C and more preferably less than 60°C.
20. A heat engine as claimed in any one of the preceding claims, arranged when in use such that the elevation of the reservoirs imparts gravitational force to the working fluid when in a liquid state for increasing the pressure of the working fluid prior to entering the boiler.
21. A heat engine as claimed in any of claims 1 to 20 included in a waste heat recovery plant on board a ship.
22. A method of recovering heat energy using the heat engine as claimed in any of claims 1 to 20.
PCT/GB2013/000511 2012-11-23 2013-11-25 A heat engine WO2014080164A2 (en)

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CN110388241B (en) * 2019-07-31 2021-07-20 东北师范大学 Waste heat recovery thermal circulation system of automobile engine

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