WO2017130010A2 - Power production at low temperatures - Google Patents

Power production at low temperatures Download PDF

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Publication number
WO2017130010A2
WO2017130010A2 PCT/HU2017/050003 HU2017050003W WO2017130010A2 WO 2017130010 A2 WO2017130010 A2 WO 2017130010A2 HU 2017050003 W HU2017050003 W HU 2017050003W WO 2017130010 A2 WO2017130010 A2 WO 2017130010A2
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WO
WIPO (PCT)
Prior art keywords
working fluid
liquid phase
nitrogen
heat
pressing
Prior art date
Application number
PCT/HU2017/050003
Other languages
French (fr)
Other versions
WO2017130010A3 (en
Inventor
Gabriella KÖBLÖ
Gábor KOVÁCS
Ferenc ZETTISCH
Original Assignee
Spacevital Kft.
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 Spacevital Kft. filed Critical Spacevital Kft.
Publication of WO2017130010A2 publication Critical patent/WO2017130010A2/en
Publication of WO2017130010A3 publication Critical patent/WO2017130010A3/en

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Classifications

    • 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
    • F01K25/10—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 the vapours being cold, e.g. ammonia, carbon dioxide, ether

Definitions

  • the object of the invention is a method and system to convert heat energy into useful mechanical energy and the latter into electrical energy, preferably at low temperatures.
  • Utilizing heat energy originating from any source to generate electrical energy is a particularly difficult technical problem in cases where the heat energy is present in a relatively low temperature medium, which cannot be used directly for boiling water and thus for driving steam turbines.
  • a lot of such heat energy (even as much as 75% of the heat power of the power plant) is discharged in the form of waste heat, which firstly reduces the efficiency of the power plant and secondly raises environmental problems, especially in the case of larger power plants.
  • Solar energy, geothermal energy and the heat energy of ambient media, soil, water and air are also heat sources that are similarly difficult to utilize for generating electricity and thus are used mainly for heating purposes, however solutions for generating electricity are also known.
  • the object of the present invention is providing a method and a system suitable for generating electricity from the aforementioned heat sources with greater efficiency than other known solutions.
  • the European Publication Pamphlet No. EP1989400 discloses an energy storage system with liquid nitrogen working fluid, which produces cryogenic liquid nitrogen from ambient air when low cost electricity is available, stores it, then when the energy requirement of the network increases, the working fluid is boiled by a heating medium of ambient temperature or by waste heat, the working fluid expands in a known manner and does work on a suitable turbine which drives an electric generator and thus electrical energy is generated.
  • Said system is open, i.e. the nitrogen serving as a working fluid is obtained from atmospheric air at the beginning of the working process, and then the nitrogen is released back to the atmosphere at the end of the working process, which causes significant losses.
  • An object of the present invention is providing a method and a system, which are firstly suitable for sustained and autonomous energy conversion by utilizing low temperature heat sources, secondly its working fluid is used in a closed cycle, thus the losses that would occur at the points of the system open to the surroundings are avoided, thirdly which harnesses the ability of the volume increase occurring during the freezing of water to do work, and is also capable of operating in a wide range of ambient temperatures.
  • such a material is used as working fluid, whose boil- ing point at a given pressure is lower than the temperature of the heat source, particularly a cooling medium used in cooling systems, known to a person skilled in the art, preferably nitrogen, whose boiling point is 77.35 K, i.e. -195.8 °C at a pressure of 1 bar, which makes the solution suitable to utilize practically any low temperature heat sources, even ambient air.
  • a cooling medium used in cooling systems known to a person skilled in the art, preferably nitrogen, whose boiling point is 77.35 K, i.e. -195.8 °C at a pressure of 1 bar, which makes the solution suitable to utilize practically any low temperature heat sources, even ambient air.
  • practically any material can also be used as working fluid, which is a cooling medium used as a working fluid in air conditioning devices widely used in industrial and domestic environments nowadays.
  • the system according to the invention comprises a working fluid storage tank for storing working fluid; one or more compressing apparatuses; a first flow control device in fluid communication with the storage tank and with at least one of the one or more compressing apparatuses for introducing working fluid to one or more compressing apparatuses; a second flow control device in fluid communication with the outlet of the compressing apparatus for controlling the outflow of the working fluid exiting the compressing apparatus; an engine suitable for doing work by the working fluid and for converting the work done by the working fluid to rotary movement, e.g.
  • a pneumatic motor such as a piston-type or a rotary vane pneumatic motor, or a turbine, preferably a turbine having external bearings
  • an electric generator that is in mechanical connection with the engine, is driven by the engine and is suitable for converting the rotary motion created by the engine to electricity
  • a third flow control device in fluid communication with the outlet of the engine and controlling the outflow of working fluid exiting the engine
  • a device for converting back the working fluid to the state it is in the working fluid storage tank preferably an expansion device
  • an electronic control unit configured to control the system.
  • the compressing apparatus comprises a housing, preferably made of a heat insulating material having high mechanical strength; a compressing chamber within the housing, having a variable volume, into which the working fluid is introduced through a working fluid inlet; the compressing chamber preferably having rigid walls and its volume is variable by moving a compressing piston; a device for producing a pressing force for reducing the volume of the compression chamber, preferably for moving the compressing piston in a direction resulting in the reduction of the volume of the compressing chamber; a first heat exchanger for heating the compressing chamber; a working fluid outlet for allowing the working fluid to exit the compressing chamber.
  • the production of pressing force in the pressing force producing device is preferably carried out by transferring heat to or extracting heat from a medium (from now on: pressing medium) which changes its volume when absorbing or loosing heat.
  • the compressing unit comprises a second heat exchanger for heating and cooling the pressing medium, which is preferably a phase changing medium, particularly preferably water.
  • the pressing medium is contained in a sealable chamber with variable volume, which is configured to facilitate the heat loss or heat absorption of the pressing medium, preferably having a heat exchanger.
  • the chamber containing the pressing medium having a shape preferably tapering towards at least one of its ends, particularly preferably having a conical shape.
  • the device further comprises a portion configured for chang- ing the temperature of the pressing medium, preferably an element for facilitating the heat exchange with a heating-cooling fluid while it flows through, a pressing force applying piston abutting on or being integrally formed with the compressing piston, and an element contacting the pressing medium abutting on or being integrally formed with the pressing force applying piston, having a surface which is preferably tapering towards the compressing chamber, particularly preferably having a conical shape, where the cone angle of the conical surface is preferably an obtuse angle.
  • the pressing force producing device can also be a mechanical, e.g. screw-type or a hydraulic device known to a person skilled in the art.
  • the working fluid whose pressure and temperature have been increased in the one or more compressing apparatuses, is guided from an outlet of the compressing apparatus to the inlet of an engine, where the working fluid does work on suitable movable elements of the engine during expansion.
  • the engine may be any piston-type or rotary vane pneumatic motor or turbine of any design known to a person skilled in the art and available commercially.
  • the engine is a turbine, whose blades are supported in external bearings, thus there are less fluidic obstacles in the path of the expanding working fluid, which in the case of nitrogen working fluid could result in the unde sired conversion to liquid of the working fluid cooled by its expansion due to the disturbance of the flow and the local pressure drop caused thereby.
  • the preferably rotary motion generated by the engine is delivered to an electric generator known to a person skilled in the art via physical connections, e.g. by a transmission or by integrating their shafts in a manner also known to a person skilled in the art, which converts the motion to electricity.
  • the rotor of the electric generator is integrally formed with the rotor of the turbine, which is surrounded by the stator of the generator, characterized in that the iron-core coils of the stator provide the electric output, the coils of the stator are excited by electromagnets of the rotor, the electromagnets of the rotor are supplied with electricity by the current induced in iron-core coils located in the rotor by at least one electromagnet located in the stator.
  • Magnetic field strength of the electromagnets of the rotor may thus be controlled externally, thus the electrical energy production and the effect decelerating the rotor at a given rotation speed (frequency) may be regulated.
  • the method according to the invention comprises: providing a working fluid, preferably a liquid working fluid, preferably liquid nitrogen, preferably transporting it from a working fluid storage tank to a compressing apparatus; increasing the pressure of the working fluid located in the compressing apparatus by compressing it and by supplying heat thereto from outside either directly or indirectly. Compression is carried out preferably before the heat exchange.
  • the amount of electrical energy produced in the method exceeds the amount of electrical energy consumed in the method, and the amount of heat energy consumed in the method exceeds the amount of heat energy produced in the method.
  • the medium is guided through a filter before guiding it to the (first or second) heat exchanger of the compressing apparatus.
  • the ambient air used as a heat source may be subjected to preheating, e.g. by compressing it or by supplying heat thereto from a different heat source.
  • the volume changing medium is preferably a substance, whose volume increases during liquid- to-solid phase change, i.e. it can do work during phase change.
  • a material is for example iron or water.
  • water is used as phase changing medium, whose volume increases by about 10% when enough free space is available. The smaller the available space for the expansion of water, the larger the pressure it generates - if the volume change is completely prevented, the pressure of the ice may increase as high as about 10000 bar. This equals the pressure required to compress the about 1.1 volume units of ice obtained by freezing 1 volume unit of water to a volume of 1 volume unit.
  • the expansion of the water ice does work via the pistons on the working fluid, preferably nitrogen, located in the compressing chamber, which is thus compressed - its volume reduces, its pressure and temperature increases.
  • the product of the volume- and pressure change of the working fluid equals the product of the volume- and pressure change of the water during its freezing.
  • the maximum pressure generated in the working fluid may be controlled by changing the ratio of the initial amounts of working fluid and water (and by corresponding dimensioning of the chambers hold- ing them): greater working fluid:water ratio results in smaller pressure, smaller working flu- id:water ratio results in greater pressure.
  • a further possibility for pressure regulation is, espe- cially at a given dimensioning of the apparatus, to fill the chamber holding the phase changing medium with phase changing medium only partially.
  • a seal is arranged between the piston and the housing, which is preferably a commercially available seal designed for cryogenic temperatures (under -150°C) and great pressure (prefera- bly at least 400 bar), for example a seal made of indium or a seal available from the Trelleborg company (Sweden), e.g. a variant of the Turcon Variseal.
  • the housing of the compressing apparatus may be a single, integrally formed element, which is made of a high strength thermally insulating material or a composite material having thermally insulating and load bearing layers.
  • the chamber of the phase changing material is preferably coated with an anti-sticking coating, such as Teflon, which prevents the sticking of the phase changing material to the wall of the chamber, thus it reduces the potential losses arising therefrom and improves the efficiency of the work done by the phase change.
  • FIG. 1 is the schematic representation of an exemplary embodiment of the system according to the invention.
  • FIG. 2 shows schematically in exploded perspective view a preferable exemplary embodiment of the compressing apparatus forming a part of the system according to the invention
  • FIG. 3 is the side view [ Figure (a)] of the apparatus according to Figure 2, an A-A longitudinal section [Figure (b)] of the former and a B-B longitudinal section [ Figure (c)] of the former in a plane perpendicular to the plane of the A-A longitudinal section;
  • FIG. 4 is an A-A longitudinal section of the possible exemplary embodiment of the compressing apparatus according to the invention shown in Figures 2 and 3 in the assembled and sealed state of the apparatus;
  • FIG. 5 shows in perspective view a preferable exemplary embodiment of the heat exchanger unit, with spiral ribs, forming a part of the compressing apparatus shown in Figures 2 and 3;
  • FIG. 7 shows the side view [Figure (a)], A-A section [Figure (b)] and top view [ Figure (c)] of a preferable embodiment of the heat exchanger for facilitating the heat exchange of the pressing medium, forming a part of the compressing apparatus shown in Figures 2 and 3;
  • - Figure 8 shows schematically in exploded perspective view a preferable exemplary embodiment of the engine integrally formed with the electric generator and formed as a turbine with external bearings, forming a part of the system according to the invention;
  • Figure 9 is the side view [Figure (a)] of the turbine according to Figure 8, and the A-A longi- tudinal section [Figure (b)] of the former;
  • FIG. 10 is the side view [Figure (a)] of the turbine center according to Figure 8, and the A-A longitudinal section [ Figure (b)] of the former;
  • FIG. 11 and 12 are exemplary circuit diagrams of the electric generator forming a part of the system according to the invention.
  • T-S temperature-entropy
  • Figure 1 shows schematically the system according to the invention, comprising working fluid storage tank 100, storing the working fluid, preferably nitrogen, at a relatively low pressure, e.g. 1 bar, at low temperature, e.g. -196°C, in liquid state, which working liquid storage tank 100 having a thermal insulation 101; a first flow control device 200, comprising a valve and/or a pump, in fluid communication with the working fluid storage tank 100; one or more compressing apparatuses 300 in fluid communication with the flow control device 200; a second flow control device 400 comprising at least a valve, in fluid communication with the outlet 399 of the compressing apparatus 300; an engine 500 in fluid communication with the outlet side of the flow control device 400, which engine may be a motor operating on a pneumatic principle (either piston-type or rotary vane) known to a person skilled in the art, or a turbine known to a person skilled in the art, preferably a turbine, whose part comprising the turbine blades is supported in external bearings; an electric generator 800, which is mechanical
  • the system preferably further comprises a heat exchanger 1 lOOpreferably having a heat insulation 1101 in (thermal) radiation and/or flow connection with an external heat source 1000, where heat is transferred from the heat source to a heat transport medium.
  • a heat exchanger 1210 located in a heating medium storage 1200 preferably having a heat insulation 1201, is in fluid communica- tion with the outlet of the heat exchanger 1100, optionally through a valve 1110 and if the heat transport medium is gaseous, through a compressor 1120 for the further heating thereof.
  • the heating medium storage 1200 is in fluid communication with the heat exchanger 311 of the compressing apparatus 300 optionally through a first heating medium valve 1220, a second heating medium valve 1230, a heating pump 1240 and cooling pump 1250.
  • the heat exchanger 1100 is in fluid communication with the heat exchanger 330 in the compressing chamber 304 of the compressing apparatus 300.
  • the heat exchanger 311 of the compressing apparatus 300 is in fluid communication with a cooling medium storage 1300 preferably having heat insulation 1301 through a heating pump 1240 and a cooling pump 1250, and a first cooling medium valve 1260 and a second cooling medium valve 1270.
  • a heat exchanger 1310 is located in the cooling medium storage 1300, which is in fluid communication with the heat exchanger 110 of the working fluid storage tank 100 through a third cooling medium valve 1320 and a circulating pump 1330.
  • the tube sections with filled (black) headed arrows accommodate fluid flow only in the direction indicated by the arrow.
  • the flow direction in the tube sections with empty (white) headed arrows depends on the work phase in which the compressing apparatus connected to the given tube section is - during the heating of the pressing medium, flow in the direction of the black arrows is present, during the cooling of the pressing medium, flow in the direction of the white arrows is present.
  • the system preferably comprises more than one compressing apparatus 300, which are connected with each other in parallel regarding the working fluid flow, and are operated in either the same phase or preferably with a phase shift so that together they produce a medium flow on the inlet of the engine, which is less pulsating, preferably substantially constant.
  • the compressing apparatus 300 comprises a housing, which is preferably made of a high mechanical strength heat insulating material and comprises at least a first housing part 301a and a second housing part 301b, and means for securing the housing parts together, preferably screws 302 located in the threaded bores 303a of the first housing part 301a and into the threaded bores 303b of the second housing part 301b.
  • the function of the one or more housing parts is to maintain the high pressure difference, about 100-10000 bar, between the high pressure space created inside the housing and the environment with so little deformation that does not affect significantly the operation of the device.
  • a com- pressing chamber 304 is formed, whose volume may be changed by the movement of a compressing piston 306, where a heat exchanger unit 330 is arranged to facilitate the heat exchange between the working fluid and the heating medium.
  • the first housing part 301a comprises through holes for passage of the working fluid and the heat transport medium, preferably the housing part 301a comprises at least one bottom through hole 391 on its side farther from the pressing chamber and at least one lateral through hole 392 formed in the lateral side of the housing part 301a for the inlet and/or outlet of the working fluid and/or the heating medium; and a pressing device 310 for applying a pressing force on the compressing piston 306 in a direction that results in the volume decrease of the compressing chamber 304.
  • the pressing device 310 is preferably a device having a sealable pressing chamber 311 with variable volume, comprising a medium (pressing medium), which changes its volume during heat transfer, preferably a phase changing medium, most preferably water.
  • the pressing device 310 comprises a pressing piston 307 for transferring a pressing force on the compressing piston 306 and for allowing the volume change of the chamber.
  • the pressing chamber 311 is prefera- bly delimited from one side by the second heat exchanger 312 located in the second housing part 301b in a fixed manner, and from the other side by either the pressing piston 307 or an intermediate element 308 abutting on the pressing piston or integrally formed therewith.
  • the pressing device 310 comprises a second heat exchanger 312.
  • the pressing chamber 311 having a shape preferably tapering toward at least one of its ends, particularly preferably a conical shape, where the cone angle of the conical surface is preferably obtuse angle, preferably 100° to 170°, more preferably 120°to 150°, most preferably about 133°.
  • the second housing part 301b comprises at least two, preferably four passages for the passage of the heating and cooling medium, which are respectively, according to the exemplary embodiment shown in the figure, a cooling medium inlet 395, a cooling medium outlet 396, a heating medium inlet 397 and a heating medium outlet 398.
  • inlets and outlets are interchangeable, and also the heating and the cooling medium (and the inlets and outlets thereof) are also interchangeable.
  • a sealable pressing medium inlet 313 is formed on the second housing part 301b.
  • the compressing apparatus 300 comprises - where sealing is necessary - sealing ele- ments arranged between corresponding elements, operating at the pressure and temperature ranges occurring at the given locations during operation.
  • cryogenic high pressure sealing ring 321 a cryogenic high pressure sealing ring 321, a first cryogenic sealing ring 322 (not high pressure), a second cryogenic sealing ring 323 (not high pressure), a third cryogenic sealing ring 324 (not high pressure), a fourth cryogenic sealing ring 325 (not high pressure), a fifth cryogenic sealing ring 326 (not high pressure), a seal hold-down sleeve 327, a high pressure sealing ring 328 (non-cryogenic), a sealing ring 329 (not high pressure, non-cryogenic).
  • Cryogenic sealing rings may be commercially available conventional indium sealing rings commonly used in cryogenic systems known to a person skilled in the art, while non-cryogenic sealing rings may be formed by conventional sealing rings commonly used in non-cryogenic fluid systems.
  • the pressing device 310 may optionally be formed by a mechanical, e.g. screw-type, or hydraulic pressure applying device known to a person skilled in the art.
  • Figures 5 and 6 show a particularly preferable embodiment of the heat exchanger unit 330 forming a part compressing apparatus 300, which is suitable for carrying out efficient heat exchange of a relatively large amount of working fluid relatively quickly.
  • the heat exchanger has a substantially cylindrical body 331, comprising a mantle portion 332 and a base 333.
  • Helical ribs 334 are arranged on the outer side of the mantle portion 332, providing large active surface for the heat exchange between the heat exchanger body 331 and the heating fluid.
  • a spine 340 is formed, whose height is preferably at least 50%, particularly preferably at least 70% of the height of the body.
  • Heat exchanging ribs 341 are formed parallel with each other and substantially perpendicular to the spine 340, and heating medium passages 342 are formed inside the spine, substantially parallel with the spine.
  • the spine 340 and the ribs 341 increase the contact area of the working fluid and the heat exchanger, while the heating medium passages 342 increase the contact area of the heating medium and the heat exchanger to facilitate more efficient heat exchange.
  • a working fluid inlet tube 337a, a working fluid outlet tube 337b and a heating medium inlet tube 338a opening into the heating medium passages 342 are formed on the bottom 333 of the body 331.
  • the heating medium enters the heat exchanger 330 in the compressing chamber 304 (in which the heat exchanger 330 is located) through a heating medium inlet tube 338a placed into a bottom through-hole 391 formed in the wall of the housing part 301a, it passes through the passages 342 and between the helical ribs 334 of the mantle 332, then leaves the chamber 304 through the heating medium outlet tube 338b located in the lateral through -hole 392.
  • the heating medium outlet tube 338b is secured to the first housing part 301a by an outlet tube hold-down screw 338c. Outlets and inlets are interchangea- ble.
  • FIG. 7 illustrates a preferable embodiment of the heat exchanger 312, forming a part of the compressing apparatus 300, facilitating the heat transfer of the pressing medium.
  • the heat exchanger 312 comprises a wall 361 delimiting the pressing chamber 311, and curved heat ex- changing ribs 362 in a spiral arrangement, providing large contact area for the heat exchanger and the heating and cooling medium.
  • the heat exchanger 312 further comprises a pressing medium passage 363 for guiding the pressing medium into the pressing chamber 311.
  • the heat exchanger 312 comprises a sealing ring socket 364 for the sealing ring 328, and the end 365 of the part of the pressing chamber 311 which is inside the heat exchanger 312 on the side of the pressing piston 307 is formed so that the pressing piston 307 or the intermediate element 308 may enter thereto and create a tight seal with the sealing ring 328.
  • Figures 8, 9 and 10 illustrate a preferable exemplary embodiment of the engine 500 used in the system according to the invention, where it is a turbine with external bearings integrated with an electric generator 800.
  • the working fluid whose pressure and temperature has been increased in the compressing apparatus 300 is guided through an outlet 399 of the compressing apparatus 300 to an inlet 502a of the turbine 500, optionally through a flow control device 400.
  • the working fluid flows preferably substantially in an unobstructed manner from inlet 502a of the turbine 500 to the turbine blades 541, it applies a pressure thereon, thus does work thereon by rotating them, then flows to the outlet 502b of the turbine 500 preferably in unobstructed manner.
  • the rotor preferably comprises a plurality of rows of turbine blades.
  • the rotor 540 comprises the rotor 840 of the generator 800, comprising armature coils 841 and a coil 849 having an iron core 850 arranged in a comb-like manner.
  • the stationary armature part 814 - preferably formed as a ring-like element - of the generator 800 surrounded by a generator housing 801, and the station- ary exciting unit 830 of the generator, and dielectric rings 550 therebetween are arranged in the stator of the turbine 500.
  • the rotor 540 of the turbine is supported by bearings 560 formed at its two ends in bearing housings 501, which also receive the one or more stationary exciting units 830. Between the bearing housings 501 a stator housing 813 is arranged, which receives the stationary armature 814.
  • the bearing housings 501 and the stator housing 813 are preferably held together by screws 570 screwed into threaded bores formed therein.
  • a further flow control device is situated at the outlet 502b of the turbine, from where the working fluid is guided into the expansion device 700. Due to the external bearing assembly, there are fewer obstacles in the flow path of the expanding working fluid which would disturb the flow (and would create a local pressure drop), which in the case of nitrogen working fluid could cause undesired transition into liquid due to the excessive cooling caused by the excessive expansion.
  • the turbine body is preferably made of a high strength heat insulating material or a composite material.
  • FIG 11 illustrates the circuit diagram of an exemplary embodiment of the electric generator 800, where the rotor 840 of the generator is integrally formed with the rotor of turbine which is supported in external bearings.
  • the rotor 840 is surrounded by the stator of the generator.
  • the stator of the generator comprises armature coils 811, wherein electric current is induced by at least one field coil 849 of the generator when the rotor is rotated. If the number of the armature coils 811 of the stator is e.g.
  • the stator further comprises a field coil 831, which is preferably supplied by direct current obtained by rectifying the three-phase power generated in the armature coils 811 of the stator by a three-phase diode bridge 812 (i.e. a Graetz bridge).
  • the field coil 831 of the stator induces current in the armature coils 841 of the rotor 840.
  • the number of the armature coils 841 is three or dividable by three, they produce three-phase electric power in wye or delta connection, which may be converted to direct current by e.g. a three-phase diode bridge 842.
  • the thus produced direct current supplies power to the field coil 849 of the rotor, having an iron core 850 in a comb-like arrangement.
  • a great advantage of this configuration versus the prior art solutions is firstly that it does not contain sliding/frictional electrical contacts, which would require maintenance; secondly the performance of the generator at a given rotational speed may be externally controlled by controlling the current of the field coil 831.
  • Figure 12 illustrates the circuit diagram of a further exemplary embodiment of the electric generator 800, where the field coils 83 ⁇ of the stationary exciting unit 830' and the armature coils 84 ⁇ of the rotor 840' are arranged - in a manner known to a person skilled in the art - so that direct current is induced in the armature coils 84 ⁇ when the rotor is rotated.
  • the electronic unit 888 controlling the excitation is also shown in the figure.
  • the same reference numbers denote the same elements.
  • the generator is optionally connected to a converting device (e.g. a diode bridge or a transformer) known to a person skilled in the art for converting the output of the generator to a form having desired parameters (voltage, frequency).
  • a converting device e.g. a diode bridge or a transformer
  • the system further comprises a control unit in operating connection with the valves and pumps for controlling the operation thereof, and temperature- and pressure measuring devices for providing temperature- and pressure data to the control unit, particularly at the inlet and the outlet of the turbine, and in the heating medium-, working fluid-, and cooling medium storage tanks.
  • the subu- nits may be connected fluidly or electrically in parallel to identical subunits, and the subunits may be substituted by other subunits having the same function.
  • the method according to the invention comprises the following steps: a) providing a working fluid preferably by pumping a working fluid from a working fluid storage tank; b) compressing the working fluid; c) heating the working fluid, preferably while maintaining it in the closed space used for the compression; d) the working fluid is released from the closed space; e) doing work with the working fluid during its expansion; f) the working fluid is liquefied again and preferably guided back to the working fluid storage tank; and optionally g) converting the work done by the working fluid to electric power.
  • nitrogen working fluid is used, compressing is carried out by the compressing apparatus 300 while using water as pressing medium.
  • Figure 13 illustrates the state changes of nitrogen during the cyclical process.
  • the cycle starts from point A by filling the liquid nitrogen into the compressing chamber. From there, the system is brought (step I.) to the state represented by point B by compressing the nitrogen, while pres- sure and temperature is increased, and entropy is decreased. After this, the temperature of the system is increased while its entropy is decreased and the system is brought (step II.) to a state represented by point C, while transferring heat to the nitrogen. Following the sufficient extent of heating, the nitrogen is released in a controlled manner to an engine, while the nitrogen does work, its temperature is decreased and its entropy is increased, the system is brought (step III.) to the state represented by point D.
  • the temperature of the nitrogen is further decreased by its expansion without doing work, its entropy increases and the gas liquefies, thus (and after the liquefied gas is filled into the compressing chamber again without doing work) the system is brought (step IV.) back to the state represented by point s.

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  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
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Abstract

The invention relates to a method and system for converting heat energy to useful mechanical work and the latter to electrical energy, preferably at low temperature. The method comprises arranging a liquid phase working fluid and a liquid phase pressing medium in a storage vessel having constant volume so as to be separated from each other by a separating element in a thermally insulated, gastight and sealed manner, the pressing medium having a negative coefficient of thermal expansion, where the separating element is configured to allow the volume change of the pressing medium accompanying the phase change of the pressing medium; inducing phase change of the pressing medium by extracting heat from the pressing medium, thus increasing the pressure of the liquid phase working fluid through compressing it by the separating element, where the pressure increase is carried out so that the Joule-Thomson coefficient of the working fluid is kept at positive values at all times; supplying heat to the increased pressure liquid phase working fluid in an amount sufficient for inducing at least partial transition of the working fluid to gas phase, while maintaining the Joule-Thomson coefficient of the working fluid at positive values; cooling the at least partially gas phase working fluid having increased pressure and a temperature lower than the inversion temperature of the working fluid to liquid phase working fluid by expanding it through a throttle, the expansion of the working fluid is carried out at a continuously controlled expansion rate for maintaining the expanded working fluid in liquid phase; doing mechanical work with the working fluid during the expansion of the working fluid, which mechanical work is converted to electrical energy by an electric machine, and coupling out the thus obtained electrical energy for later use in a known manner; guiding the expanded liquid phase working fluid back to the storage vessel after doing mechanical work; supplying heat to the pressing medium to induce phase change of the pressing medium; and repeating the preceding steps.

Description

POWER PRODUCTION AT LOW TEMPERATURES
The object of the invention is a method and system to convert heat energy into useful mechanical energy and the latter into electrical energy, preferably at low temperatures.
Utilizing heat energy originating from any source to generate electrical energy is a particularly difficult technical problem in cases where the heat energy is present in a relatively low temperature medium, which cannot be used directly for boiling water and thus for driving steam turbines. In the cases of fossil fuel and nuclear power plants, a lot of such heat energy (even as much as 75% of the heat power of the power plant) is discharged in the form of waste heat, which firstly reduces the efficiency of the power plant and secondly raises environmental problems, especially in the case of larger power plants. Solar energy, geothermal energy and the heat energy of ambient media, soil, water and air, are also heat sources that are similarly difficult to utilize for generating electricity and thus are used mainly for heating purposes, however solutions for generating electricity are also known. The object of the present invention is providing a method and a system suitable for generating electricity from the aforementioned heat sources with greater efficiency than other known solutions.
The European Publication Pamphlet No. EP1989400 discloses an energy storage system with liquid nitrogen working fluid, which produces cryogenic liquid nitrogen from ambient air when low cost electricity is available, stores it, then when the energy requirement of the network increases, the working fluid is boiled by a heating medium of ambient temperature or by waste heat, the working fluid expands in a known manner and does work on a suitable turbine which drives an electric generator and thus electrical energy is generated.
Said system is open, i.e. the nitrogen serving as a working fluid is obtained from atmospheric air at the beginning of the working process, and then the nitrogen is released back to the atmosphere at the end of the working process, which causes significant losses.
In the publication entitled„Ice power" published in the magazine entitled„ Popular Science" in the issue of April, 1989, in page 154, a method and apparatus is described for utilizing the volume increase occurring during the freezing of water for doing work. In the apparatus, the water to be frozen fills about 90% of the volume of a tank, the rest of the volume is filled with oil serving as intermediary and working fluid. The volume increase occurring during the freezing of water is transmitted to an energy storage tank containing nitrogen, where the work done by the freezing water is stored until later use through the compression of the nitrogen. After this, the oil pressurized by the nitrogen is guided through a hydraulic motor for driving a vehicle, and the used (low pressure) oil is stored until later use. In the apparatus according to the publication, ambient cold is used for freezing the water and ambient heat is used for melting it, therefore due to the relatively large size and the shape of the tank, the apparatus can only be operated in quite long cycles of several hours or about 1 day. Furthermore each operation cycle of the apparatus requires the availability of ambient temperatures both under and above 0°C, otherwise the apparatus does not work, and each work phase also needs manual operation, thus the apparatus in the form described in the publication is not suitable for sustained energy production (conversion).
An object of the present invention is providing a method and a system, which are firstly suitable for sustained and autonomous energy conversion by utilizing low temperature heat sources, secondly its working fluid is used in a closed cycle, thus the losses that would occur at the points of the system open to the surroundings are avoided, thirdly which harnesses the ability of the volume increase occurring during the freezing of water to do work, and is also capable of operating in a wide range of ambient temperatures.
In one aspect, the aforementioned object is achieved by elaborating the method according to claim 1; preferable exemplary embodiments of the method are set forth in claims 2 to 10.
In a further aspect, the aforementioned object is achieved by elaborating a system according to claim 11 for carrying out the method according to the invention; preferable exemplary embodiments of the system are set forth in claims 12 to 16.
In the solution according to the invention, such a material is used as working fluid, whose boil- ing point at a given pressure is lower than the temperature of the heat source, particularly a cooling medium used in cooling systems, known to a person skilled in the art, preferably nitrogen, whose boiling point is 77.35 K, i.e. -195.8 °C at a pressure of 1 bar, which makes the solution suitable to utilize practically any low temperature heat sources, even ambient air. In the solution according to the invention, practically any material can also be used as working fluid, which is a cooling medium used as a working fluid in air conditioning devices widely used in industrial and domestic environments nowadays.
The system according to the invention comprises a working fluid storage tank for storing working fluid; one or more compressing apparatuses; a first flow control device in fluid communication with the storage tank and with at least one of the one or more compressing apparatuses for introducing working fluid to one or more compressing apparatuses; a second flow control device in fluid communication with the outlet of the compressing apparatus for controlling the outflow of the working fluid exiting the compressing apparatus; an engine suitable for doing work by the working fluid and for converting the work done by the working fluid to rotary movement, e.g. a pneumatic motor, such as a piston-type or a rotary vane pneumatic motor, or a turbine, preferably a turbine having external bearings; an electric generator that is in mechanical connection with the engine, is driven by the engine and is suitable for converting the rotary motion created by the engine to electricity; optionally a third flow control device in fluid communication with the outlet of the engine and controlling the outflow of working fluid exiting the engine; a device for converting back the working fluid to the state it is in the working fluid storage tank, preferably an expansion device; an electronic control unit configured to control the system.
The function of the compressing apparatus is to bring the working to a state suitable for doing work, namely to increase its pressure and temperature. To this end, the compressing apparatus comprises a housing, preferably made of a heat insulating material having high mechanical strength; a compressing chamber within the housing, having a variable volume, into which the working fluid is introduced through a working fluid inlet; the compressing chamber preferably having rigid walls and its volume is variable by moving a compressing piston; a device for producing a pressing force for reducing the volume of the compression chamber, preferably for moving the compressing piston in a direction resulting in the reduction of the volume of the compressing chamber; a first heat exchanger for heating the compressing chamber; a working fluid outlet for allowing the working fluid to exit the compressing chamber.
The production of pressing force in the pressing force producing device is preferably carried out by transferring heat to or extracting heat from a medium (from now on: pressing medium) which changes its volume when absorbing or loosing heat. The compressing unit comprises a second heat exchanger for heating and cooling the pressing medium, which is preferably a phase changing medium, particularly preferably water. The pressing medium is contained in a sealable chamber with variable volume, which is configured to facilitate the heat loss or heat absorption of the pressing medium, preferably having a heat exchanger. The chamber containing the pressing medium having a shape preferably tapering towards at least one of its ends, particularly preferably having a conical shape. The device further comprises a portion configured for chang- ing the temperature of the pressing medium, preferably an element for facilitating the heat exchange with a heating-cooling fluid while it flows through, a pressing force applying piston abutting on or being integrally formed with the compressing piston, and an element contacting the pressing medium abutting on or being integrally formed with the pressing force applying piston, having a surface which is preferably tapering towards the compressing chamber, particularly preferably having a conical shape, where the cone angle of the conical surface is preferably an obtuse angle. The pressing force producing device can also be a mechanical, e.g. screw-type or a hydraulic device known to a person skilled in the art. The working fluid, whose pressure and temperature have been increased in the one or more compressing apparatuses, is guided from an outlet of the compressing apparatus to the inlet of an engine, where the working fluid does work on suitable movable elements of the engine during expansion. The engine may be any piston-type or rotary vane pneumatic motor or turbine of any design known to a person skilled in the art and available commercially. In a preferable em- bodiment of the system according to the invention, the engine is a turbine, whose blades are supported in external bearings, thus there are less fluidic obstacles in the path of the expanding working fluid, which in the case of nitrogen working fluid could result in the unde sired conversion to liquid of the working fluid cooled by its expansion due to the disturbance of the flow and the local pressure drop caused thereby. The preferably rotary motion generated by the engine is delivered to an electric generator known to a person skilled in the art via physical connections, e.g. by a transmission or by integrating their shafts in a manner also known to a person skilled in the art, which converts the motion to electricity. In a preferred embodiment of the system according to the invention, where the engine is a turbine with external bearings, the rotor of the electric generator is integrally formed with the rotor of the turbine, which is surrounded by the stator of the generator, characterized in that the iron-core coils of the stator provide the electric output, the coils of the stator are excited by electromagnets of the rotor, the electromagnets of the rotor are supplied with electricity by the current induced in iron-core coils located in the rotor by at least one electromagnet located in the stator. Magnetic field strength of the electromagnets of the rotor may thus be controlled externally, thus the electrical energy production and the effect decelerating the rotor at a given rotation speed (frequency) may be regulated.
The method according to the invention comprises: providing a working fluid, preferably a liquid working fluid, preferably liquid nitrogen, preferably transporting it from a working fluid storage tank to a compressing apparatus; increasing the pressure of the working fluid located in the compressing apparatus by compressing it and by supplying heat thereto from outside either directly or indirectly. Compression is carried out preferably before the heat exchange. Bringing the working fluid partially or completely into gas phase and/or supercritical state by supplying heat thereto, then guiding it from the compressing chamber through a first regulating valve to the input of the engine; at least partially converting the kinetic energy produced by the engine from the work done by the working fluid to electrical energy by an electric generator; guiding the working fluid from the output of the engine to the input of an expansion device, where it is cooled by increasing its volume and optionally by additional heat extraction and is converted back to liquid state. The liquid state working fluid is guided back to the working fluid storage tank, and using the electrical energy produced by generator partially to operate the parts of the system demanding electricity.
The amount of electrical energy produced in the method exceeds the amount of electrical energy consumed in the method, and the amount of heat energy consumed in the method exceeds the amount of heat energy produced in the method.
If the heating is carried out with ambient water or air, the medium is guided through a filter before guiding it to the (first or second) heat exchanger of the compressing apparatus. Optionally, the ambient air used as a heat source may be subjected to preheating, e.g. by compressing it or by supplying heat thereto from a different heat source.
The volume changing medium is preferably a substance, whose volume increases during liquid- to-solid phase change, i.e. it can do work during phase change. Such a material is for example iron or water. In the present invention preferably water is used as phase changing medium, whose volume increases by about 10% when enough free space is available. The smaller the available space for the expansion of water, the larger the pressure it generates - if the volume change is completely prevented, the pressure of the ice may increase as high as about 10000 bar. This equals the pressure required to compress the about 1.1 volume units of ice obtained by freezing 1 volume unit of water to a volume of 1 volume unit. The expansion of the water ice does work via the pistons on the working fluid, preferably nitrogen, located in the compressing chamber, which is thus compressed - its volume reduces, its pressure and temperature increases. The product of the volume- and pressure change of the working fluid equals the product of the volume- and pressure change of the water during its freezing. Accordingly, the maximum pressure generated in the working fluid may be controlled by changing the ratio of the initial amounts of working fluid and water (and by corresponding dimensioning of the chambers hold- ing them): greater working fluid:water ratio results in smaller pressure, smaller working flu- id:water ratio results in greater pressure. A further possibility for pressure regulation is, espe- cially at a given dimensioning of the apparatus, to fill the chamber holding the phase changing medium with phase changing medium only partially.
A seal is arranged between the piston and the housing, which is preferably a commercially available seal designed for cryogenic temperatures (under -150°C) and great pressure (prefera- bly at least 400 bar), for example a seal made of indium or a seal available from the Trelleborg company (Sweden), e.g. a variant of the Turcon Variseal.
The housing of the compressing apparatus may be a single, integrally formed element, which is made of a high strength thermally insulating material or a composite material having thermally insulating and load bearing layers. The chamber of the phase changing material is preferably coated with an anti-sticking coating, such as Teflon, which prevents the sticking of the phase changing material to the wall of the chamber, thus it reduces the potential losses arising therefrom and improves the efficiency of the work done by the phase change.
In what follows, the invention is described in detail with reference to the accompanying draw- ings, wherein
- Figure 1 is the schematic representation of an exemplary embodiment of the system according to the invention;
- Figure 2 shows schematically in exploded perspective view a preferable exemplary embodiment of the compressing apparatus forming a part of the system according to the invention; - Figure 3 is the side view [Figure (a)] of the apparatus according to Figure 2, an A-A longitudinal section [Figure (b)] of the former and a B-B longitudinal section [Figure (c)] of the former in a plane perpendicular to the plane of the A-A longitudinal section;
- Figure 4 is an A-A longitudinal section of the possible exemplary embodiment of the compressing apparatus according to the invention shown in Figures 2 and 3 in the assembled and sealed state of the apparatus;
- Figure 5 shows in perspective view a preferable exemplary embodiment of the heat exchanger unit, with spiral ribs, forming a part of the compressing apparatus shown in Figures 2 and 3;
- Figures 6 (a) and 6 (b) respectively show the A-A and B-B sections of the heat exchanger unit shown in Figure 5;
- Figure 7 shows the side view [Figure (a)], A-A section [Figure (b)] and top view [Figure (c)] of a preferable embodiment of the heat exchanger for facilitating the heat exchange of the pressing medium, forming a part of the compressing apparatus shown in Figures 2 and 3; - Figure 8 shows schematically in exploded perspective view a preferable exemplary embodiment of the engine integrally formed with the electric generator and formed as a turbine with external bearings, forming a part of the system according to the invention;
- Figure 9 is the side view [Figure (a)] of the turbine according to Figure 8, and the A-A longi- tudinal section [Figure (b)] of the former;
- Figure 10 is the side view [Figure (a)] of the turbine center according to Figure 8, and the A-A longitudinal section [Figure (b)] of the former;
- Figures 11 and 12 are exemplary circuit diagrams of the electric generator forming a part of the system according to the invention;
- Figure 13 is a temperature-entropy (T-S) diagram showing the energy conversion cycle according to the invention.
Figure 1 shows schematically the system according to the invention, comprising working fluid storage tank 100, storing the working fluid, preferably nitrogen, at a relatively low pressure, e.g. 1 bar, at low temperature, e.g. -196°C, in liquid state, which working liquid storage tank 100 having a thermal insulation 101; a first flow control device 200, comprising a valve and/or a pump, in fluid communication with the working fluid storage tank 100; one or more compressing apparatuses 300 in fluid communication with the flow control device 200; a second flow control device 400 comprising at least a valve, in fluid communication with the outlet 399 of the compressing apparatus 300; an engine 500 in fluid communication with the outlet side of the flow control device 400, which engine may be a motor operating on a pneumatic principle (either piston-type or rotary vane) known to a person skilled in the art, or a turbine known to a person skilled in the art, preferably a turbine, whose part comprising the turbine blades is supported in external bearings; an electric generator 800, which is mechanically connected to at least one part of the engine 500 and is driven by the engine 500; optionally a third flow control device in fluid communication with the outlet of the engine; an expansion device 700 downstream of the engine 500 and optionally downstream of the third flow control device, where the used working fluid is guided into the expansion device, there it expands on a relatively low pressure, and optionally with additional heat extraction returns to liquid phase (condenses), then in liquid phase it is guided back to the working fluid storage tank 100; an electronic control unit (not shown on the drawings) connected to the flow control devices and the generator. The system preferably further comprises a heat exchanger 1 lOOpreferably having a heat insulation 1101 in (thermal) radiation and/or flow connection with an external heat source 1000, where heat is transferred from the heat source to a heat transport medium. A heat exchanger 1210 located in a heating medium storage 1200, preferably having a heat insulation 1201, is in fluid communica- tion with the outlet of the heat exchanger 1100, optionally through a valve 1110 and if the heat transport medium is gaseous, through a compressor 1120 for the further heating thereof. The heating medium storage 1200 is in fluid communication with the heat exchanger 311 of the compressing apparatus 300 optionally through a first heating medium valve 1220, a second heating medium valve 1230, a heating pump 1240 and cooling pump 1250. The heat exchanger 1100 is in fluid communication with the heat exchanger 330 in the compressing chamber 304 of the compressing apparatus 300. The heat exchanger 311 of the compressing apparatus 300 is in fluid communication with a cooling medium storage 1300 preferably having heat insulation 1301 through a heating pump 1240 and a cooling pump 1250, and a first cooling medium valve 1260 and a second cooling medium valve 1270. A heat exchanger 1310 is located in the cooling medium storage 1300, which is in fluid communication with the heat exchanger 110 of the working fluid storage tank 100 through a third cooling medium valve 1320 and a circulating pump 1330.
In the figure the tube sections with filled (black) headed arrows accommodate fluid flow only in the direction indicated by the arrow. The flow direction in the tube sections with empty (white) headed arrows depends on the work phase in which the compressing apparatus connected to the given tube section is - during the heating of the pressing medium, flow in the direction of the black arrows is present, during the cooling of the pressing medium, flow in the direction of the white arrows is present. The system preferably comprises more than one compressing apparatus 300, which are connected with each other in parallel regarding the working fluid flow, and are operated in either the same phase or preferably with a phase shift so that together they produce a medium flow on the inlet of the engine, which is less pulsating, preferably substantially constant.
The function of the compressing apparatus 300 shown in Figures 2, 3 and 4 is to bring the work- ing fluid into a state suitable for doing work, namely to increase its pressure and temperature. To this end, the compressing apparatus 300 comprises a housing, which is preferably made of a high mechanical strength heat insulating material and comprises at least a first housing part 301a and a second housing part 301b, and means for securing the housing parts together, preferably screws 302 located in the threaded bores 303a of the first housing part 301a and into the threaded bores 303b of the second housing part 301b. The function of the one or more housing parts is to maintain the high pressure difference, about 100-10000 bar, between the high pressure space created inside the housing and the environment with so little deformation that does not affect significantly the operation of the device. Inside the first housing part 301a a com- pressing chamber 304 is formed, whose volume may be changed by the movement of a compressing piston 306, where a heat exchanger unit 330 is arranged to facilitate the heat exchange between the working fluid and the heating medium. The first housing part 301a comprises through holes for passage of the working fluid and the heat transport medium, preferably the housing part 301a comprises at least one bottom through hole 391 on its side farther from the pressing chamber and at least one lateral through hole 392 formed in the lateral side of the housing part 301a for the inlet and/or outlet of the working fluid and/or the heating medium; and a pressing device 310 for applying a pressing force on the compressing piston 306 in a direction that results in the volume decrease of the compressing chamber 304. The pressing device 310 is preferably a device having a sealable pressing chamber 311 with variable volume, comprising a medium (pressing medium), which changes its volume during heat transfer, preferably a phase changing medium, most preferably water. The pressing device 310 comprises a pressing piston 307 for transferring a pressing force on the compressing piston 306 and for allowing the volume change of the chamber. The pressing chamber 311 is prefera- bly delimited from one side by the second heat exchanger 312 located in the second housing part 301b in a fixed manner, and from the other side by either the pressing piston 307 or an intermediate element 308 abutting on the pressing piston or integrally formed therewith. In order to facilitate heat transfer between the pressing medium and a heating/cooling medium, the pressing device 310 comprises a second heat exchanger 312. The pressing chamber 311 having a shape preferably tapering toward at least one of its ends, particularly preferably a conical shape, where the cone angle of the conical surface is preferably obtuse angle, preferably 100° to 170°, more preferably 120°to 150°, most preferably about 133°. The second housing part 301b comprises at least two, preferably four passages for the passage of the heating and cooling medium, which are respectively, according to the exemplary embodiment shown in the figure, a cooling medium inlet 395, a cooling medium outlet 396, a heating medium inlet 397 and a heating medium outlet 398. As it is known to a person skilled in the art, inlets and outlets are interchangeable, and also the heating and the cooling medium (and the inlets and outlets thereof) are also interchangeable. A sealable pressing medium inlet 313 is formed on the second housing part 301b. The compressing apparatus 300 comprises - where sealing is necessary - sealing ele- ments arranged between corresponding elements, operating at the pressure and temperature ranges occurring at the given locations during operation. In the embodiment shown in the figure, these are: a cryogenic high pressure sealing ring 321, a first cryogenic sealing ring 322 (not high pressure), a second cryogenic sealing ring 323 (not high pressure), a third cryogenic sealing ring 324 (not high pressure), a fourth cryogenic sealing ring 325 (not high pressure), a fifth cryogenic sealing ring 326 (not high pressure), a seal hold-down sleeve 327, a high pressure sealing ring 328 (non-cryogenic), a sealing ring 329 (not high pressure, non-cryogenic). Cryogenic sealing rings may be commercially available conventional indium sealing rings commonly used in cryogenic systems known to a person skilled in the art, while non-cryogenic sealing rings may be formed by conventional sealing rings commonly used in non-cryogenic fluid systems. The pressing device 310 may optionally be formed by a mechanical, e.g. screw-type, or hydraulic pressure applying device known to a person skilled in the art.
Figures 5 and 6 show a particularly preferable embodiment of the heat exchanger unit 330 forming a part compressing apparatus 300, which is suitable for carrying out efficient heat exchange of a relatively large amount of working fluid relatively quickly. In order to achieve this, the heat exchanger has a substantially cylindrical body 331, comprising a mantle portion 332 and a base 333. Helical ribs 334 are arranged on the outer side of the mantle portion 332, providing large active surface for the heat exchange between the heat exchanger body 331 and the heating fluid. Inside the body 331, preferably along a diameter thereof, a spine 340 is formed, whose height is preferably at least 50%, particularly preferably at least 70% of the height of the body. Heat exchanging ribs 341 are formed parallel with each other and substantially perpendicular to the spine 340, and heating medium passages 342 are formed inside the spine, substantially parallel with the spine. The spine 340 and the ribs 341 increase the contact area of the working fluid and the heat exchanger, while the heating medium passages 342 increase the contact area of the heating medium and the heat exchanger to facilitate more efficient heat exchange. A working fluid inlet tube 337a, a working fluid outlet tube 337b and a heating medium inlet tube 338a opening into the heating medium passages 342 are formed on the bottom 333 of the body 331. With such a structure of the heat exchanger 330, the heating medium enters the heat exchanger 330 in the compressing chamber 304 (in which the heat exchanger 330 is located) through a heating medium inlet tube 338a placed into a bottom through-hole 391 formed in the wall of the housing part 301a, it passes through the passages 342 and between the helical ribs 334 of the mantle 332, then leaves the chamber 304 through the heating medium outlet tube 338b located in the lateral through -hole 392. The heating medium outlet tube 338b is secured to the first housing part 301a by an outlet tube hold-down screw 338c. Outlets and inlets are interchangea- ble.
Figure 7 illustrates a preferable embodiment of the heat exchanger 312, forming a part of the compressing apparatus 300, facilitating the heat transfer of the pressing medium. The heat exchanger 312 comprises a wall 361 delimiting the pressing chamber 311, and curved heat ex- changing ribs 362 in a spiral arrangement, providing large contact area for the heat exchanger and the heating and cooling medium. The heat exchanger 312 further comprises a pressing medium passage 363 for guiding the pressing medium into the pressing chamber 311. The heat exchanger 312 comprises a sealing ring socket 364 for the sealing ring 328, and the end 365 of the part of the pressing chamber 311 which is inside the heat exchanger 312 on the side of the pressing piston 307 is formed so that the pressing piston 307 or the intermediate element 308 may enter thereto and create a tight seal with the sealing ring 328.
Figures 8, 9 and 10 illustrate a preferable exemplary embodiment of the engine 500 used in the system according to the invention, where it is a turbine with external bearings integrated with an electric generator 800. The working fluid whose pressure and temperature has been increased in the compressing apparatus 300 is guided through an outlet 399 of the compressing apparatus 300 to an inlet 502a of the turbine 500, optionally through a flow control device 400. The working fluid flows preferably substantially in an unobstructed manner from inlet 502a of the turbine 500 to the turbine blades 541, it applies a pressure thereon, thus does work thereon by rotating them, then flows to the outlet 502b of the turbine 500 preferably in unobstructed manner. The rotor preferably comprises a plurality of rows of turbine blades. The rotor 540 comprises the rotor 840 of the generator 800, comprising armature coils 841 and a coil 849 having an iron core 850 arranged in a comb-like manner. The stationary armature part 814 - preferably formed as a ring-like element - of the generator 800 surrounded by a generator housing 801, and the station- ary exciting unit 830 of the generator, and dielectric rings 550 therebetween are arranged in the stator of the turbine 500. The rotor 540 of the turbine is supported by bearings 560 formed at its two ends in bearing housings 501, which also receive the one or more stationary exciting units 830. Between the bearing housings 501 a stator housing 813 is arranged, which receives the stationary armature 814. The bearing housings 501 and the stator housing 813 are preferably held together by screws 570 screwed into threaded bores formed therein. Optionally a further flow control device is situated at the outlet 502b of the turbine, from where the working fluid is guided into the expansion device 700. Due to the external bearing assembly, there are fewer obstacles in the flow path of the expanding working fluid which would disturb the flow (and would create a local pressure drop), which in the case of nitrogen working fluid could cause undesired transition into liquid due to the excessive cooling caused by the excessive expansion. The turbine body is preferably made of a high strength heat insulating material or a composite material. The elements of the turbine 500 coming into contact with the working fluid have equal internal diameter in order to restrict the expansion of the working fluid and thus to prevent the undesired transition thereof to liquid. Figure 11 illustrates the circuit diagram of an exemplary embodiment of the electric generator 800, where the rotor 840 of the generator is integrally formed with the rotor of turbine which is supported in external bearings. The rotor 840 is surrounded by the stator of the generator. The stator of the generator comprises armature coils 811, wherein electric current is induced by at least one field coil 849 of the generator when the rotor is rotated. If the number of the armature coils 811 of the stator is e.g. three or dividable by three, the coils may be arranged in a wye (Y) or delta (Δ) connection to provide three-phase electric power as it is known to a person skilled in the art. The stator further comprises a field coil 831, which is preferably supplied by direct current obtained by rectifying the three-phase power generated in the armature coils 811 of the stator by a three-phase diode bridge 812 (i.e. a Graetz bridge). The field coil 831 of the stator induces current in the armature coils 841 of the rotor 840. If the number of the armature coils 841 is three or dividable by three, they produce three-phase electric power in wye or delta connection, which may be converted to direct current by e.g. a three-phase diode bridge 842. The thus produced direct current supplies power to the field coil 849 of the rotor, having an iron core 850 in a comb-like arrangement. A great advantage of this configuration versus the prior art solutions is firstly that it does not contain sliding/frictional electrical contacts, which would require maintenance; secondly the performance of the generator at a given rotational speed may be externally controlled by controlling the current of the field coil 831. This is particularly advantageous in the arrangement according to the invention, because the extent of deceleration of the turbine by the generator can be controlled this way, thus the amount of power "extracted" from the working fluid, i.e. the work done by the working fluid on the turbine blades per time units can be controlled, which improves the operation of turbine by allowing better control over the physical parameters (pressure, temperature) of the working fluid - it makes it possible to avoid the undesired phase change (transition into liquid phase) of the working fluid inside the turbine.
Figure 12 illustrates the circuit diagram of a further exemplary embodiment of the electric generator 800, where the field coils 83 Γ of the stationary exciting unit 830' and the armature coils 84 Γ of the rotor 840' are arranged - in a manner known to a person skilled in the art - so that direct current is induced in the armature coils 84 Γ when the rotor is rotated. The electronic unit 888 controlling the excitation is also shown in the figure. In Figures 11 and 12 the same reference numbers denote the same elements. The generator is optionally connected to a converting device (e.g. a diode bridge or a transformer) known to a person skilled in the art for converting the output of the generator to a form having desired parameters (voltage, frequency).
The system further comprises a control unit in operating connection with the valves and pumps for controlling the operation thereof, and temperature- and pressure measuring devices for providing temperature- and pressure data to the control unit, particularly at the inlet and the outlet of the turbine, and in the heating medium-, working fluid-, and cooling medium storage tanks.
The parts of the system according to the invention and the complete system can be modularized in manner obvious to a person skilled in the art, i.e. without involving inventive step, the subu- nits may be connected fluidly or electrically in parallel to identical subunits, and the subunits may be substituted by other subunits having the same function.
The method according to the invention comprises the following steps: a) providing a working fluid preferably by pumping a working fluid from a working fluid storage tank; b) compressing the working fluid; c) heating the working fluid, preferably while maintaining it in the closed space used for the compression; d) the working fluid is released from the closed space; e) doing work with the working fluid during its expansion; f) the working fluid is liquefied again and preferably guided back to the working fluid storage tank; and optionally g) converting the work done by the working fluid to electric power. In a preferable embodiment of the method, nitrogen working fluid is used, compressing is carried out by the compressing apparatus 300 while using water as pressing medium.
Figure 13 illustrates the state changes of nitrogen during the cyclical process. The cycle starts from point A by filling the liquid nitrogen into the compressing chamber. From there, the system is brought (step I.) to the state represented by point B by compressing the nitrogen, while pres- sure and temperature is increased, and entropy is decreased. After this, the temperature of the system is increased while its entropy is decreased and the system is brought (step II.) to a state represented by point C, while transferring heat to the nitrogen. Following the sufficient extent of heating, the nitrogen is released in a controlled manner to an engine, while the nitrogen does work, its temperature is decreased and its entropy is increased, the system is brought (step III.) to the state represented by point D. Finally, the temperature of the nitrogen is further decreased by its expansion without doing work, its entropy increases and the gas liquefies, thus (and after the liquefied gas is filled into the compressing chamber again without doing work) the system is brought (step IV.) back to the state represented by point s.

Claims

1. Method to produce electrical energy using low temperature working fluid, comprising the steps of
(a) arranging a liquid phase working fluid and a liquid phase pressing medium in a storage ves- sel of constant volume so as to be separated from each other by a separating element in a thermally insulated, gastight and sealed manner, said pressing medium having a negative coefficient of thermal expansion, said separating element being configured to allow a volume change of the pressing medium associated with a phase change of said pressing medium;
(b) inducing phase change of the pressing medium by extracting heat from said pressing medi- um, thereby increasing the pressure of the working fluid through the compression of the liquid phase working fluid by means of the separating element, said pressure increase being carried out along with maintaining the Joule -Thomson coefficient of the working fluid continuously at positive values;
(c) supplying heat to the increased pressure liquid phase working fluid in an amount sufficient for inducing at least partial transition of the working fluid to gas phase, while maintaining the Joule-Thomson coefficient of the working fluid at positive values;
(d) cooling the at least partially gas phase working fluid having increased pressure and a temperature lower than the inversion temperature of the working fluid to liquid phase working fluid by expanding it through a throttle, the expansion of the working fluid is carried out at a continuously controlled expansion rate for maintaining the expanded working fluid in liquid phase;
(e) doing mechanical work with the working fluid during the expansion of the working fluid, which mechanical work is converted to electrical energy by an electric machine, and coupling out the thus obtained electrical energy for later use in a known manner;
(f) guiding the expanded liquid phase working fluid back to the storage vessel after doing mechanical work;
(g) supplying heat to the pressing medium to induce phase change of the pressing medium; and
(h) repeating steps (a) to (g).
2. The method according to claim 1, wherein ambient heat is used for supplying heat in step (c).
3. The method according to claim 1, wherein artificially generated heat is used for supplying heat in step (c).
4. The method according to any one of claims 1 to 3, wherein the electric machine is in the form of a generator integrated with a turbine, where the turbine comprises at least one region for doing mechanical work.
5. The method according to claim 4, wherein the turbine is formed with a constant internal cross-section in its at least one region for doing mechanical work.
6. The method according to any one of claims 1 to 5, wherein the separating element is a compressing piston movably arranged in the storage vessel.
7. The method according to any one of claims 1 to 6, wherein the part of the storage vessel on the side of the pressing medium, near the separating element is formed with a truncated cone shape tapering in the direction of the separating element.
8. The method according to any one of claims 1 to 7, wherein the working fluid is nitrogen or a cooling medium commonly used as working fluid in air conditioning apparatuses.
9. The method according to any one of claims 1 to 8, wherein the pressing medium is water.
10. Method for producing electrical energy by using a working fluid at cryogenic temperature, wherein
(a) arranging liquid phase nitrogen and liquid phase water in a storage vessel having constant volume so as to be separated from each other by a separating element in a thermally insulated, gastight and sealed manner, where the separating element is configured to allow the volume change of the water accompanying its phase change by freezing;
(b) inducing the phase change by freezing of water by cooling it, thus increasing the pressure of the liquid phase nitrogen through the separating element, the pressure increase is carried out so as to maintain the Joule-Thomson coefficient of the nitrogen at positive values;
(c) supplying heat to the increased pressure liquid phase nitrogen in an amount sufficient for inducing at least partial transition of the nitrogen into gas phase while maintaining the Joule- Thomson coefficient of the nitrogen at positive values;
(d) cooling the at least partially gas phase nitrogen having increased pressure and a temperature lower than the inversion temperature of nitrogen to liquid phase nitrogen by expanding it through a throttle, the expansion of the nitrogen is carried out at a continuously controlled expansion rate for maintaining the expanded nitrogen in liquid phase; (e) doing mechanical work with the nitrogen during the expansion of the nitrogen, which mechanical work is converted to electrical energy by an electric machine, and coupling out the thus obtained electrical energy for later use in a known manner;
(f) guiding the expanded liquid phase nitrogen back to the storage vessel after doing mechanical work;
(g) inducing phase change of water through melting by heating it; and
(h) repeating steps (a) to (g).
11. System for producing electrical energy at low temperature, comprising
heat exchanger (1100) in thermal connection with an external heat source for heat ex- change between the external heat source and a heat transporting medium; the system further comprising
compressing apparatus (300) for compressing a working fluid, having at least one heat exchanger (330) in fluid communication through one or more intermediate elements with the heat exchanger (1100) which is in thermal connection with the external heat source,
an engine (500) in fluid communication with the compressing apparatus (300);
an electric generator (800) in mechanical connection with the engine;
an expansion device (700) in fluid communication with the engine;
a working fluid storage tank (100) in fluid communication with the expansion device.
12. The system according to claim 11, characterized in that the compressing apparatus is a mechanical, preferably screw-type compressing apparatus.
13. The system according to claim 11, characterized in that the engine is a pneumatic motor, preferably a piston-type pneumatic motor or a rotary vane pneumatic motor.
14. The system according to claim 11, characterized in that the engine is a turbine, preferably a turbine having turbine blades supported in external bearings.
15. The system according to claim 11, characterized in that the compressing apparatus (300) comprises
a housing (301a, 301b), which is made of a material preferably having high mechanical strength and preferably being thermally insulating; a compressing chamber (304) having a variable volume, for receiving a working fluid to be compressed, where the compressing chamber preferably having rigid walls and its volume may be varied by moving a piston (306);
pressing means for reducing the volume of the compressing chamber, preferably by causing a movement of the piston in a direction resulting in the volume reduction of the compressing chamber.
16. The system according to claim 15, characterized in that
comprising a chamber (311) having variable volume, comprising volume changing, preferably phase changing medium, particularly preferably water, the chamber having a shape preferably tapering in the direction of at least one end thereof, particularly preferably a conical shape, where the cone angle of the cone is preferably an obtuse angle, more preferably between 120° and 150°, particularly preferably about 130° to 135°;
comprising a second heat exchanger (312) for changing the temperature of the pressing medium, which is in thermal connection with the chamber (311) comprising the pressing medium;
comprising a pressing piston (307) in contact with the pressing medium and abutting on or being integrally formed with the compressing piston (306).
PCT/HU2017/050003 2016-01-26 2017-01-26 Power production at low temperatures WO2017130010A2 (en)

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US201662287007P 2016-01-26 2016-01-26
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HUP1600044 2016-01-26

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4249378A (en) * 1979-08-31 1981-02-10 Benson Glendon M Thermally actuated heat pump
JP2551067B2 (en) * 1987-12-26 1996-11-06 アイシン精機株式会社 Cooling system
US8683803B2 (en) * 2007-01-24 2014-04-01 Ashraf F. Bastawros Method and apparatus for energy harvesting through phase-change induced pressure rise under cooling conditions
RU2604408C2 (en) * 2010-04-15 2016-12-10 Гершон Машин Лтд. Generator
FR2963644A1 (en) * 2010-08-06 2012-02-10 Jean Francois Chiandetti Mechanical device for e.g. internal or external combustion engine, has triggering or isothermal/autothermal mechanism for utilizing heat from flow or mass of material or fuel, or heat from heat accumulator, to assure compression

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