Classifications

• • 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
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
  • F24S20/00—Solar heat collectors specially adapted for particular uses or environments
  • F24S20/20—Solar heat collectors for receiving concentrated solar energy, e.g. receivers for solar power plants
• • 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
• • 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
  • F24—HEATING; RANGES; VENTILATING
  • F24S—SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS
  • F24S60/00—Arrangements for storing heat collected by solar heat collectors
  • F24S60/30—Arrangements for storing heat collected by solar heat collectors storing heat in liquids
• • 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
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F21/00—Constructions of heat-exchange apparatus characterised by the selection of particular materials
  • F28F21/02—Constructions of heat-exchange apparatus characterised by the selection of particular materials of carbon, e.g. graphite
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F21/00—Constructions of heat-exchange apparatus characterised by the selection of particular materials
  • F28F21/04—Constructions of heat-exchange apparatus characterised by the selection of particular materials of ceramic; of concrete; of natural stone
• • 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
• • 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
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P90/00—Enabling technologies with a potential contribution to greenhouse gas [GHG] emissions mitigation
  • Y02P90/50—Energy storage in industry with an added climate change mitigation effect

Definitions

• Thermal energy storage may be accomplished by storing the energy in the form of heat, either as sensible heat or latent heat (or a combination thereof).
• Current solar collectors utilize heliostats, parabolic troughs or liner Fresnel reflectors to concentrate sunlight on solar receivers. These receivers are heated by the concentrated sunlight and utilize steam, oil, liquid salt, liquid alkali metal or gas as the heat collection and transfer fluid. This fluid may be used as the heat storage medium itself or the heat may be transferred to another medium to provide the storage.
• Thermal storage may be provided by the sensible heat in tanks of oil, oil and rock, liquid salts, or liquid alkali metals as discussed by Geyer in Winter et. al..
• the fluids heated by the concentrated sunlight are used to generate steam, heat a working fluid for energy conversion or they may be stored at high temperatures (or in combination). After giving up their heat for energy conversion the cooled fluids are stored separately from the hot fluids. This may be accomplished in separate hot and cold tanks or by using a thermocline configuration. In the thermocline system, the colder (denser) fluid forms the bottom layer with the hotter (less dense) fluid forms the upper layer. In any of these configurations, when the sun is not providing heat, the stored hot liquid may be pumped through the heat exchanger to heat the working fluid for power production and then to the cold side of the storage to complete the cycle.
• the latent heat of fusion may be used to store thermal energy.
• Liquid salts or alkali metals that undergo a phase change to store or release heat at their melting temperature have been used in thermal storage systems.
• An advantage of this form of heat storage is that the heat is released at a nearly constant temperature, providing the optimum operating conditions for the energy conversion cycle.
• Another advantage to the use of latent heat energy storage occurs because the amount of storage material can be significantly decreased.
• the amount of energy stored in specific heat is determined by the product of the specific heat and the temperature change. For example; the specific heat of water is 1 cal/gm, if the temperature is lowered by 1 ° C, one gram of the water releases 1 calorie of heat.
• the latent heat of fusion of water is about 80 cal/gm so that the energy released in freezing or solidifying one gram of ice is 80 calories of heat at a nearly constant temperature.
• the amount of water needed to store the same amount of heat that is provided by freezing one gram of ice is 80 times greater than that to change the temperature of the water by 1 ° C.
• Embodiments of the invention relate to the use of melting and solidifying or freezing metals and metal alloys to store and release the high latent heat of fusion of certain metals and alloys to store large amounts of heat energy at very high temperatures suitable for operating a gas turbine or other purposes.
• the alloy may consist of two or more metals with melting and eutectic temperatures in the range that is compatible with the energy conversion device to be used.
• the metal or alloy is contained in an array of tubes located in an insulated channel through which the high temperature gas is circulated.
• the system is charged by passing gas, from the solar receiver or other heat source, past the tubes in order to heat and melt the metal/alloy contained within the tubes.
• the system is discharged by passing the air to be heated through the same channel until the metal or alloy has changed phase (liquid to solid) and the temperature has dropped to the optimum operating temperature for the system.
• the metal or alloy is contained in an insulated container equipped with heat transfer elements or tubes that thermally communicate with the heat source.
• the system is charged by transferring heat from a high temperature gas circulating in a channel or passageway through a wall into the chamber containing the solid/liquid metal or alloy until it melts.
• the system is discharged by passing heat out of the chamber with the same or different heat transfer elements or tubes that communicate with the channel carrying the gas to be heated.
• alloys there is a wide choice of alloys to be used.
• two elements are combined to form an alloy with a melting temperature determined by the fraction of each metal present, which is in turn chosen by the desired operating temperature.
• the alloy composed of aluminum and silicon is chosen.
• the operating point may be chosen from about 600° C to 141 1 ° C. This very wide temperature range provides for the operation of a variety of turbine inlet temperatures including the upper range of Rankine steam cycles.
• the tubes containing the metal or metal alloy in the first embodiment may be made from ceramic, metal, or clad graphite.
• the graphite must be clad in metal or ceramic in the case of air or other oxidizing gas (e.g., carbon dioxide) in the heat exchanger as otherwise the graphite would be subject to oxidation at the operating temperatures considered here.
• the tubes may be composed of solid metal of suitably high melting temperature e.g. copper, steel, nickel, or high temperature alloys of these or other metals.
• the elements may also be composed of graphite in direct contact with the molten metal if there is minimum chemical reaction with the heat storage metal or metal alloy, but with appropriate cladding in the sections that they may be exposed to an oxidizing atmosphere.
• these heat transfer elements or tubes may also be closed hollow tubes composed of a high temperature metal ceramic or graphite containing a relatively small amount of an element or compound with a boiling temperature that is above that of the melting point of the metal or metal alloy storage material.
• the element or compound is boiled within the lower end of the tube by the gas passing through the channel below the storage tank with the upper end imbedded in the metal or metal alloy storage material.
• This heat pipe arrangement is very effective as a heat exchanger.
• the thermal storage is discharged by similar tubes, but that contain an element or compound with a lower boiling temperature than the melting point of the metal or metal alloy storage material.
• the lower end of the heat pipe is in the metal or alloy storage material while the upper end passes through the upper side of the storage chamber and into a separate gas carrying channel. In this case the storage is discharged by passing a gas through the upper channel.
• Figure 1 a is a schematic illustration of the top view of an embodiment of a heat exchanger of an embodiment of the invention.
• Figure 1 b is a schematic illustration of the side view of an embodiment of a heat exchanger of an embodiment of the invention.
• Figure 1 c is a schematic illustration one of the tubes containing the metal or metal alloy of an embodiment of the invention.
• Figure 1 d is a schematic of an embodiment of the invention using a vertical flow configuration wherein the gas is moving parallel to the alignment of the storage tubes.
• Figures 1 e and 1f depict alternative embodiments of the tubes of the invention.
• Figure 2 is a schematic of another embodiment of the invention showing the charging plenum at the bottom and the discharging plenum above the metal or metal alloy storage container.
• Figure 3a is a schematic illustration how an embodiment of the invention is implemented with a gas turbine generator in solar only mode.
• Figure 3b is a schematic illustration how an embodiment of the invention is implemented with a gas turbine generator during thermal discharging.
• Figure 3c is a schematic illustration how an embodiment of the invention is implemented with a gas turbine generator during hybrid operation wherein power for the turbine is supplied from storage and the solar receiver.
• Liquid Metal Thermal Storage system also know as a Liquid Metal Thermal Storage system (LIMETS) consists of substantially four items ; the metal or metal alloy thermal storage material, the tubes or a compartment containing the metal or metal alloy, the insulated cavity enclosing the tubes, and the heat transfer medium (gas).
• Figure la is a top view of a schematic drawing of the system showing the insulated cavity 100, the ceramic or clad graphite tubes 101 containing the metal or metal alloy and the insulated container 102.
• Figure lb is a side view of the same components.
• Figure 1 c is a cross sectional view of the tube and metal showing one tube 101 and metal 103 with the open top.
• Figure 1 d depicts a perspective view of this embodiment.
• tubes 101 can include fins or other appendages or structures that increase the surface area of the tubes and the rate of heat transfer to and/or from the tubes (Figure 1 e).
• the tubes also have cross-sections that increase the rate of heat transfer (Figure 1f).
• Such cross-sections increase the surface area of the cross-section by including, for example, a star-shaped cross-section.
• the tubes and enclosure are to be arranged so as to maximize the heat transfer considering the temperature and nature of the gas transfer medium. The Reynolds number is determined by the properties of the gas and the characteristic dimensions of the tubes and the design should be optimized for these factors to maximize the heat transfer to and from the tubes.
• Figure 2 illustrates another embodiment utilizing the tubes.
• a vertical orientation of the tubes is useful so as to utilize the down comer from the solar receiver located at the top of tower and to provide an alternative design to optimize the heat transfer to the tubes.
• Ducting arrangements can allow flow of the gas in either up or down past the vertical tubes. In both of these arrangements the system is charged by passing hot gas from the solar receiver over the tubes until melting takes place. Since most metals and metal alloys expand when melting the lower density melt will rise to the top, leaving the bottom to melt last. This has a consequence of encouraging good mixing to ensure that the metal or metal alloy is nearly isothermal.
• the metal or metal alloy 104 is contained in a separate insulated container 105 that thermally communicates to the heated air via either high conductivity metal or metal clad graphite rods, or preferably by using hollow heat pipes or tubes 106 and 107.
• a separate insulated container 105 that thermally communicates to the heated air via either high conductivity metal or metal clad graphite rods, or preferably by using hollow heat pipes or tubes 106 and 107.
• the hot gas passes through the lower channel 108 and the heat pipes or tubes or rods 106 and carry the heat to the metal or metal alloy to melt the storage material 104.
• a similar set of heat pipes or tubes or rods 107 carries the heat to the upper channel when cooler gas is pumped through the upper channel.
• the heat transfer may be substantially improved by using heat pipes in which an element or compound with a suitable boiling point is encapsulated within the tubes.
• an element or compound with a suitable boiling point can include potassium that may be used from about 500° C to 1000° C, sodium from 500° C to 1000° C, and lithium from 900° C to 1700° C.
• heat pipes carry heat most efficiently in an upward direction
• the element or compound within the lower pipes or tubes 106 is preferably chosen to have an operating point above the melting temperature of the metal or metal alloy storage material.
• the element or compound within the upper pipes or tubes 107 is preferably chosen to have an operating point below the meeting temperatures of the metal or metal alloy storage material.
• the hot gas passing through the lower channel heats the lower end of the tubes and the element or compound in the tubes vaporizes and moves upward and condense at the cooler end in the storage material.
• the gas to be heated is pumped through the upper channel.
• the upper heat pipes contain an element or compound that has an operating temperature below that of the melting temperature of the storage material. Therefore, when cooler air is pumped through the upper channel, the element or compound in the upper heat pipes condenses on the upper end transferring the heat to the gas to operate the turbine.
• the heat transfer is controlled by the flow of gases, moving upwards when heat is needed.
• the choice of the metal or alloy rod or tube is determined by, for example, 1 ) the melting temperature, 2) latent heat of fusion, 3) heat conductivity, 4) its viscosity and thermal convection characteristics, 5) expansion and contraction upon phase change, 5) chemical reactivity with containment and heat transfer elements and 6) effects of contaminants.
• the melting temperature may be determined by the choice of metal, or be more finely tuned by the selection of alloy.
• Other considerations include crystallite size, effects of contaminates and alloy separation during the solidifying or freezing and re-melting. Another consideration is the price of the metal or metal alloy in current metal markets and what its future price will be at the decommissioning of the plant as this is likely to represent a significant investment.
• the other pure metals have impractically high or low melting temperatures, are rare, expensive, radioactive, or toxic.
• alloys of the above mentioned and other metals form a very large class of possible alternatives for thermal storage materials.
• Another embodiment of the invention includes the specific choice of aluminum and silicon as a thermal storage material.
• Silicon is a common component of aluminum alloys; particularly at the composition of AISM 2 (approximately 88% aluminum and 12% silicon with a small amount of impurities such as iron). This is a particularly advantageous combination of materials, because of the physical properties resulting therein. While aluminum has a melting point of about 660° C, and silicon has a melting point of 141 1 ° C, the melting point at the eutectic mixture of AISM 2 is about 600° C. Thus, it can be seen that by varying the composition, the melting point of the resulting alloy ranges from 600° C at the eutectic point to 141 1 ° C for a pure Si composition. This is illustrated in the graph of melting temperatures vs. compositions shown below. This is a very wide and convenient range for high temperature latent heat storage materials. i
• the latent heat of aluminum is relatively quite high at 95 cal/gm compared to other metals
• the latent heat of fusion of silicon is amongst the highest known at 430 cal/gm.
• the melting temperature of the mixture is about 1000° C.
• the latent heat of the resulting mixture is about 263 cal/gm. This may be compared to value for sodium which has been used for a latent heat storage medium at 27 cal/gm. (about 1/10th that of the mixture - requiring 10 times the storage mass ).
• Another advantage of the combination of silicon and aluminum is the relatively low cost of these materials in the industrial grades sufficient for this purpose compared to other metals with suitable melting temperatures.
• the containment tubes should be chosen to maximize the heat transfer with the gas and optimize the melting rates and patterns of the enclosed metal. In some circumstances radial or axial fins can be added to improve heat transfer to the tubes.
• High temperature ceramic materials are suitable because of the high melting temperatures of the metals involved (600 - 1200 C). However, certain high temperature alloy tubes may be considered for containment in the lower part of that temperature range.
• Another choice of materials is graphite. Graphite has high thermal conductivity and low reactivity with aluminum as discussed by Simensen and is widely used in aluminum refining for electrodes and containment materials.
• graphite may not be used in the presence of oxidization gases such as air or carbon dioxide because it will oxidize to carbon dioxide and fail as a containment or heat transfer means.
• the graphite may be clad with metals or ceramics to prevent its oxidation.
• the choice of the tube material should be guided by the desired operating temperatures and potential metal— containment tube interactions.
• the tubes may be closed or open depending on the choice of gas and metals. If air is the heat transfer medium the tubes should be closed to eliminate possible oxidation or other reactions between the metal and the components of the air. If helium, nitrogen or carbon dioxide is used the tubes may be open at the top if there are no interactions between the metal and gasses. For other gasses the potential interactions must be taken into consideration.
• FIG. 3a illustrates the components of the system without the heat storage system 1 1 1 being connected or in the "pure solar" mode Air enters the turbo compressor 1 12 and is compressed before arriving at the heat source 1 13.
• This may be a high temperature solar receiver heating a gas by direct or indirect of absorption of sunlight or a non-solar high temperature heat source.
• the heat source 1 13 can be a windowed high temperature solar receiver that uses small particles to absorb concentrated sunlight 1 16 and heats the gas in which they are entrained.
• FIG. 3b illustrates the arrangement for charging the storage wherein all the gas is routed through the storage system before passing through the expansion turbine.
• Fig. 3c illustrates operation of the system in "hybrid" mode in which the gas is selectively routed both through the storage and through the turbine, in parallel, adjusted with the controlling valves 1 17 and 1 18.
• Valve 1 17 can divert gasses directly to the solar receiver or heat source 1 13 (for the operation of the embodiment of Fig 3a) or directly to the heat storage system 111 for the operation of the embodiment of Fig 3b).
• Valve 118 can divert gasses to the heat storage system 111 or to the expansion turbine 114.
• Various positions of the valves 117 and 118 can allow the expansion turbine 114 to run directly on energy provided by the receiver or heat source 113, or alternatively on energy provided by the heat storage system 111, or both.

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• Engineering & Computer Science (AREA)
• Thermal Sciences (AREA)
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• Ceramic Engineering (AREA)
• Engine Equipment That Uses Special Cycles (AREA)
• Powder Metallurgy (AREA)

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• 2010
  • 2010-09-09 EP EP10816103A patent/EP2475886A2/de not_active Withdrawn
  • 2010-09-09 CN CN2010800485820A patent/CN102597513A/zh active Pending
  • 2010-09-09 WO PCT/US2010/048312 patent/WO2011031894A2/en active Application Filing
  • 2010-09-09 US US12/878,896 patent/US20110120669A1/en not_active Abandoned

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