Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
  • F24S60/00—Arrangements for storing heat collected by solar heat collectors
  • F24S60/10—Arrangements for storing heat collected by solar heat collectors using latent heat
• • 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
  • F01K3/00—Plants characterised by the use of steam or heat accumulators, or intermediate steam heaters, therein
  • F01K3/12—Plants characterised by the use of steam or heat accumulators, or intermediate steam heaters, therein having two or more accumulators
• • 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
  • F01K7/00—Steam engine plants characterised by the use of specific types of engine; Plants or engines characterised by their use of special steam systems, cycles or processes; Control means specially adapted for such systems, cycles or processes; Use of withdrawn or exhaust steam for feed-water heating
  • F01K7/16—Steam engine plants characterised by the use of specific types of engine; Plants or engines characterised by their use of special steam systems, cycles or processes; Control means specially adapted for such systems, cycles or processes; Use of withdrawn or exhaust steam for feed-water heating the engines being only of turbine type
  • F01K7/22—Steam engine plants characterised by the use of specific types of engine; Plants or engines characterised by their use of special steam systems, cycles or processes; Control means specially adapted for such systems, cycles or processes; Use of withdrawn or exhaust steam for feed-water heating the engines being only of turbine type the turbines having inter-stage steam heating
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F22—STEAM GENERATION
  • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
  • F22B1/00—Methods of steam generation characterised by form of heating method
  • F22B1/006—Methods of steam generation characterised by form of heating method using solar heat
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
  • F28D20/00—Heat storage plants or apparatus in general; Regenerative heat-exchange apparatus not covered by groups F28D17/00 or F28D19/00
  • F28D20/02—Heat storage plants or apparatus in general; Regenerative heat-exchange apparatus not covered by groups F28D17/00 or F28D19/00 using latent heat
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
  • F28D20/00—Heat storage plants or apparatus in general; Regenerative heat-exchange apparatus not covered by groups F28D17/00 or F28D19/00
  • F28D20/02—Heat storage plants or apparatus in general; Regenerative heat-exchange apparatus not covered by groups F28D17/00 or F28D19/00 using latent heat
  • F28D20/021—Heat storage plants or apparatus in general; Regenerative heat-exchange apparatus not covered by groups F28D17/00 or F28D19/00 using latent heat the latent heat storage material and the heat-exchanging means being enclosed in one container
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/40—Solar thermal energy, e.g. solar towers
  • Y02E10/46—Conversion of thermal power into mechanical power, e.g. Rankine, Stirling or solar thermal engines
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/14—Thermal energy storage
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E70/00—Other energy conversion or management systems reducing GHG emissions
  • Y02E70/30—Systems combining energy storage with energy generation of non-fossil origin

Definitions

• This invention relates to a thermal storage facility that is especially suitable for use in storing thermal energy and especially, although not exclusively, thermal energy that has been derived from the sun using a concentrating solar power installation.
• thermal energy storage is made possible.
• Thermal storage is required in order to buffer the power generating cycle of sunny, clear days so that a solar power plant is enabled to supply electrical energy at night time and during bad weather.
• Current thermal storage systems mostly operate in the sensible heat mode, and either store thermal energy in a molten salt of some kind, or store the heat in solid bodies, like concrete.
• the use of molten salt has the disadvantages that solidification of the salt may occur in the receiver loop at night; trace heating is therefore needed to keep salts in a liquid form during non operational times such as night time and in auxiliary piping; and this may lead to maintenance problems.
• phase change concepts have been noted but they are all based on low conductivity salts, and require extensive heat transfer modification to improve their thermal conductivity.
• Solid storage materials such as concrete bodies, also have limited power output and, furthermore, may suffer from thermal stress that limits the useful life of such media. Modifications to the solid storage elements makes them expensive.
• oil may be used as a storage medium and heat transfer fluid.
• One of the primary problems with this is the fact that the maximum operating temperature of oil is about 400 °C. This seriously limits the maximum receiver temperature, and curbs the maximum efficiency of the power plant.
• thermal energy storage As far as applicant is aware all of the current modes of thermal storage have limitations. Generally there are two limitations to thermal energy storage, one is a temperature limitation, and the other is high melting point heat transfer fluids that causes a inherent blockage problem.
• a thermal storage facility for storing thermal energy at elevated temperature
• the facility comprising an enclosure for retaining a thermal storage medium, primary heat transfer surfaces for transferring heat from a circulating heat transfer fluid, and secondary heat transfer surfaces for transferring heat from the thermal storage medium to steam pipes associated with a power generation facility
• the thermal storage facility being characterized in that the thermal storage medium is a metallic phase change material (PCM) that is interposed between the primary heat transfer surfaces and the secondary heat transfer surfaces and in that the heat transfer fluid is a liquid metal.
• PCM metallic phase change material
• the metallic phase change material to have high thermal conductivity, high latent heat of fusion with an high melting temperature, preferably above about 500 °C, and high operating temperatures.
• One candidate material is a metallic phase change material that is an alloy of aluminium and silicon, preferably a commercially available alloy such as one containing 87.76% Al and 12.24% Si (AISM 2 which is also known as LM6 casting alloy).
• the invention further provides for the metallic heat transfer fluid to be liquid over an extended range of temperatures from ambient temperature through to a maximum operating temperature in excess of the melting point of the metallic phase change material, with the metallic heat transfer fluid typically being molten alkali metals or alloys of alkali metals and especially an alloy of sodium and potassium such as that known as NaK; and for the heat transfer surfaces to be those of generally parallel pipes extending through or adjacent the enclosure.
• the invention also provides a thermal storage facility as defined above in which the thermal storage facility forms part of a unit selected from a pre- heater, a boiler, a super heater, a re-heater and a combination unit designed to perform the function of any two or more of such units.
• a solar power installation that is typically of a relatively small capacity, may have a single heliostat field and associated solar receiver mounted on a tower forming part of the solar power installation in which instance the thermal storage facility as defined above may be built into the tower.
• a solar power installation may comprise multiple heliostat fields with associated solar receivers carried on towers with each of the solar receivers being connected to one or more common thermal storage facilities as defined above.
• a thermal storage facility may be embodied in any one or more units selected from a pre- heater, a boiler, a super-heater, and a reheater, typically all of these, with the flow of heat transfer fluid to each of the facilities being controlled to achieve the relevant objective of the relevant unit
• suitable molten alkali metal alloys can be employed as heat transfer fluid whilst the presence of the metallic phase change material between the molten hot alkali metal alloy and water or steam prevents contact from being made between the alkali metal and the water or steam, which could otherwise have disastrous results.
• the arrangement enables the particular properties of materials not heretofore used in the relevant situations to be usefully employed and advantage to be taken of their special properties.
• the invention therefore enables the water or steam heater or generator to be combined with the thermal storage unit.
• heat may be transferred from a receiver atop a tower by molten heat transfer fluid, typically in the form of molten alkali metal alloys such as NaK (eutectic or hypoeutectic), to the metallic phase change material that melts to thereby absorb thermal energy by way of the material's latent heat of fusion with the heat being stored and transferred to the secondary heat exchange surfaces to generate steam from water and superheat it for use in a power generation plant, as may be required.
• molten heat transfer fluid typically in the form of molten alkali metal alloys such as NaK (eutectic or hypoeutectic)
• NaK eutectic or hypoeutectic
• FIG. 1 is a schematic illustration of one variation of concentrating solar power installation embodying the facility of the invention wherein a single solar receiver is located atop a tower that carries it;
• Figure 2 is a similar illustration of a another variation of concentrating power installation embodying the facility of the invention in which multiple solar receivers are located atop multiple towers that carry them and heat transfer fluid is fed to multiple thermal storage facilities that utilise the heat to heat water or steam as may be required;
• Figure 3 is a schematic cross-section taken through one form of a storage vessel according to the invention showing the primary and secondary heat transfer pipes distributed through the metallic phase change material.
• the concentrating solar power installation includes a substantially conventional field of heliostat (1 ) with a solar receiver (2) mounted on a tower (3).
• the solar receiver on the tower is to be used to heat a metallic heat transfer fluid in the form of the alkali metal NaK.
• the thermal storage unit, steam generator and circulation system of the heat transfer fluid are all embodied in the tower. It is envisaged that such an arrangement will only be applicable to certain sizes of concentrating solar power installation and not to larger ones that will most likely be more like the embodiment of the invention described with reference to Figure 2.
• the heat transfer fluid is circulated by means of a pump (4) through the receiver and through metallic phase change material (5) contained within the enclosure (6) substantially filling the tower by way of a series of heat transfer pipes (7).
• the heat transfer fluid namely the molten NaK heat transfer fluid, is thus heated in the thermal receiver and circulated through the series of heat transfer pipes (7) that define the primary heat transfer surfaces.
• the steam pipes (8) that define the secondary heat transfer surfaces are also in contact with the metallic phase change material but are spaced apart from the heat transfer pipes (7).
• the steam pipes extend between a lower reservoir (9) and an upper steam chamber (1 0) or there may be an external steam drum.
• the remainder of the concentrating solar power installation is substantially conventional and includes the usual steam treatment equipment, high pressure, medium pressure, and low pressure turbines (1 1 , 1 2, 1 3), and condensation recycling equipment generically indicated by numeral (14).
• a re-heater (1 5) for reheating steam leaving the high-pressure turbine (1 1 ) and preparatory to it entering the medium pressure turbine (1 2) can be constructed in a similar manner and have its own heliostat field (1 6), receiver, tower and thermal storage facility.
• thermal storage units that form part of water and steam heating and generating units.
• thermal storage and water and steam heating and generating units include a pre-heater (24), a boiler (25), a super-heater (26) and a re-heater (27) that is interposed between the high- pressure turbine (28) and medium pressure turbine (29).
• the relevant unit has its own enclosure that is composed of heat transfer pipes and steam pipes that have not been separately shown as they are arranged in substantially the same way as those described below with reference to Figure 3.
• a preferred general type of arrangement of steam pipes (31 ) and heat transfer fluid pipes (32) is achieved by distributing the pipes throughout the interior of a containment enclosure (33) that is filled with metallic phase change material (34) in a suitable pattern, such as on a series of concentric circles.
• the desirable properties of the metallic heat transfer fluid include low melting point (preferably below room temperature) ; high thermal conductivity; high density; and high specific heat capacity.
• a low melting point is very important for a reliable concentrating solar power plant, as the receivers will be cold for at least half of their life cycle.
• a high melting point heat transfer fluid in the receivers would reduce the reliability of the installation since solidification of the heat transfer fluid may pose significant problems.
• NaK is a eutectic mixture of sodium and potassium and its eutectic composition is 78% potassium and 22% sodium (by mass). It is a liquid between -12.6°C and 785 °C. Compositions between 40% and 90% potassium (by mass) are liquid at room temperatures. Mixtures with more sodium are preferred, since the specific heat capacity of sodium is more than that of potassium.
• the properties of NaK include high reactivity with water; if it is stored in air, it forms a potassium super oxide that can ignite and is highly reactive with organics which makes it dangerous to store in organic solvents and mineral oil.
• Eutectic NaK has a very high surface tension ; a density of 0.855 g/mL at 100°C; and a thermal conductivity of 23.2 W.m "1 .K "1 @ 100°C
• the metallic phase change material two good contenders are an alloy composed of 87.76% Al and 12.24% Si that has a melting temperature of 557 °C and a heat of fusion of 498 J/g; and an alloy composed of 83.14% Al, 1 1 .7%Si and 5.16% Mg that has a melting temperature of 555 °C and a heat of fusion of 485 J/g.
• the former was chosen because it is a common and low cost casting alloy with high thermal conductivity. It is non toxic, readily available, and there are prospects of improving its latent heat of fusion through further alloying.
• the upper receiver temperature of over 770 °C, and the melting temperature of the AISi alloy at 557 °C makes the use of a steam cycle possible. Superheated steam can therefore be produced directly from heat stored in the metallic phase change material.
• the containment enclosure does not need to be cylindrical, but in the instance of a tower, a cylindrical form makes sense.
• a regards possible pipe layouts associated with the containment enclosure more specific geometries may be suitable for particular applications.
• One factor that needs to be considered is the heat to be transferred by way of the primary heat transfer surfaces being those of the heat transfer fluid pipes.
• Another factor is the distance between those heat transfer fluid pipes and the secondary heat transfer surfaces being those of the steam pipes in order to provide for the required heat flux.
• Another factor is the volume of the metallic phase change heat storage material present. Naturally the heat transfer requirements are size dependant.
• the invention therefore provides an effective thermal storage facility that is especially suitable for use in conjunction with heliostat field receiver plants.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Life Sciences & Earth Sciences (AREA)
• Sustainable Energy (AREA)
• Sustainable Development (AREA)
• Engine Equipment That Uses Special Cycles (AREA)

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• 2012
  • 2012-03-06 EP EP12757909.2A patent/EP2683983A1/de not_active Withdrawn
  • 2012-03-06 WO PCT/IB2012/051038 patent/WO2012123853A1/en not_active Ceased
  • 2012-03-06 US US14/004,661 patent/US20140000583A1/en not_active Abandoned
  • 2012-03-06 AP AP2013007169A patent/AP2013007169A0/xx unknown
  • 2012-03-06 JP JP2013558538A patent/JP2014513260A/ja active Pending
• 2013
  • 2013-10-07 ZA ZA2013/07450A patent/ZA201307450B/en unknown

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