Patent Application
20110226780
1. Field of the Invention
The inventions disclosed herein relate generally to energy storage and, more particularly, to thermal energy storage systems and methods thereof.
2. Description of Related Art
Worldwide, there are ever-growing demands for electricity due to increasing populations, technology advancements requiring the use of electricity, and the proliferation of such technology to more and more countries around the world. At the same time, there is an increasing push to harness reusable sources of energy to help meet these increasing electricity demands and offset and/or replace traditional carbon-based generators which continue to deplete natural resources around the world.
Many solutions have been developed to collect and take advantage of reusable sources of energy, such as solar cells, solar mirror arrays, and wind turbines. Solar cells produce direct current energy from sunlight using semiconductor technology. Solar mirror arrays focus sunlight on a receiver pipe containing a heat transfer fluid which absorbs the sun's radiant heat energy. This heated transfer fluid is then pumped to a turbine which heats water to produce steam, thereby driving the turbine and generating electricity. Wind turbines use one or more airfoils to transfer wind energy into rotational energy which spins a rotor coupled to an electric generator, thereby producing electricity when the wind is blowing. All three solutions produce electricity when their associated reusable power sources (sun or wind) are available, and many communities have benefited from these clean and reusable forms of power.
Unfortunately, when the sun or wind is not available, such solutions are not producing any power. In the case of solar solutions, non-reusable energy solutions are often employed during nighttime hours. Similar issues arise for wind turbines during calm weather. Therefore, some form of energy storage is needed to store excess energy from the reusable power sources during power generation times to support energy demands when the renewable power source is unavailable or unable to meet peak demands for energy.
Solar mirror arrays generate and transfer heat as an inherent part of their operation. Solar cells and wind turbines which typically generate electricity can also selectively be used to drive heaters to generate heat and/or transfer heat from windings to a heat transfer fluid. Several solutions have been developed to store heat from these renewable energy sources for use in non-energy-generating times. In particular, one or more large vessels of a liquid may be used to temporarily contain the sensible heat contained by oil heated in a solar field, and delivered to the liquid in the vessels by heat exchangers disposed therein. Hot oil is delivered to heat exchangers in a vessel containing relatively cold liquid, and the liquid in contact with the heat exchangers is heated up. The liquid may initially be in solid form, with some portion of the energy transfer being in the latent heat of fusion in the solid to liquid transition.
During nighttime, or on overcast days when the solar field is down, the flow through the heat exchangers in the thermal energy storage vessel is directed to a steam generator which drives a turbine, which in turn is connected to an electrical generator. Heat is transferred from the heated liquid back into the oil in the heat exchangers, which is pumped to the steam turbine, to drive the turbine and generate electrical power.
One suitable energy storage medium is a molten inorganic salt, with a liquid phase temperature range from about 400 to 750 degrees Fahrenheit (° F.). This temperature range is effective for providing high pressure steam to drive large scale steam turbines for electrical power generation. Additionally, inorganic salts typically have a substantially higher specific gravity than water or organic heat transfer oils, in the range of about two to about four times that of water. On a volumetric basis, a molten inorganic salt can contain more sensible heat than an equal volume of a typical organic heat transfer oil, and is thus preferred in this regard.
Thermal energy storage systems which use molten salt are known, such as the “Solar Two” system which was built near Barstow, Calif., and was operational from about 1994 to 1999. This system used molten salt comprised of a combination of about 60% sodium nitrate and about 40% potassium nitrate as an energy storage medium, which was circulated from a cold storage tank, through the solar field where it was heated, to a hot storage tank. A summary of a similar system is described and shown in
Another known thermal energy storage system is the single-tank thermocline energy storage system, which is also described in the aforementioned patent application Ser. No. 12/033,604 of Geiken et al., and shown in
It is therefore preferable to have a thermal energy storage system in which the molten salt is simply contained within a vessel as the thermal storage medium, and not pumped throughout the overall system. Instead, the thermal energy is transferred from the solar field to the vessel of molten salt by the circulation of a heat transfer fluid, such as an organic heat transfer oil, from the solar field through one or more heat exchangers immersed in the molten salt in the vessel. In like manner, during nighttime or overcast days, the thermal energy is transferred from the vessel of molten salt to the power generator by the circulation of the heat transfer fluid therebetween. The handling of heat transfer fluid by standard pumps, valves and piping is much simpler than the equivalent handling of a molten inorganic salt, which is corrosive, and which is abrasive if some portion of solid phase salt (crystals) is present, and which can solidify in the pumps, valves, and piping at temperatures lower than 400° F., thus requiring a disruptive thawing process step to restart the system.
By using a heat transfer fluid to perform the energy transfer from the solar field to the thermal storage vessel, and from the vessel to the power generator, the problems to be addressed are simplified to those relating to containment of the molten salt, and heat transfer to and from the molten salt. This simplification notwithstanding, the problems of containing the molten salt, and transferring thermal energy to and from it are significant, particularly at the scale needed by a public utility for an economically viable thermal energy storage process. The main problems are summarized briefly as follows:
It is further noted that at minimum, for any thermal energy storage system that comprises a molten inorganic salt as a thermal storage medium, the above problems 1-4 must be simultaneously addressed or otherwise rendered inconsequential by the features and capabilities of the system. A system that further addresses problems 5, 6, and/or 7 will be further advantageous.
In accordance with the present disclosure, the problem of containing a large mass of molten salt, which undergoes repeated extreme thermal cycling in a thermal energy storage system is solved by providing a vessel comprising a bottom wall joined to a surrounding side wall, and an inner liner disposed within the bottom wall and side wall and comprising an inner liner bottom and an inner liner side wall. One aspect of the inner liner bottom and side wall is that they are configured to repeatedly expand and contract during the thermal cycling of the storage system in a manner that avoids stress concentrations within the liner, which could otherwise cause fractures and leaks in the liner. The liner bottom and side wall are both comprised of means for expanding radially outwardly when heated, and contracting radially inwardly when cooled, without producing stress concentrations.
The inner liner bottom may be comprised of a central plate surrounded by an array of radially arranged sector-shaped plates. Each of the sector-shaped plates may be joined at a radial portion of its perimeter to a radial portion of the perimeter of an adjacent sector-shaped plate by a radial flexible joint and joined at an inner portion of its perimeter to the central plate by an inner flexible joint. The inner liner side wall is joined to the inner liner bottom and may be comprised of a plurality of panels. Each of the panels may be joined at a lateral portion of its perimeter to a lateral portion of the perimeter of an adjacent panel by a lateral flexible joint. The vessel may be cylindrical, with the bottom wall of the vessel correspondingly being circular.
The inner liner contained within the vessel is constructed so as to be able to expand and contract under the loading thereof with the molten salt, and in particular, due to the thermal expansion and contraction caused by contact with the molten salt at temperatures up to about 750° F. During thermal cycling, the radial and inner flexible joints of the liner bottom and the lateral flexible joints of the liner side wall flex and accommodate the thermal expansion and contraction of the sector shaped plates and arcuate panels, so as to prevent localized stress concentrations in the liner. The central plate may be circular, or the central plate may be a polygon. The number of sides of the polygon may be equal to the number of sector-shaped plates. The number of radially arranged sector-shaped plates may be between three and twelve, or more, depending upon the size of the vessel. A flexible joint which joins a sector shaped plate at a radial portion of its perimeter to a radial portion of the perimeter of an adjacent plate may be comprised of an arcuate shaped member formed and joined to the adjacent plates.
Depending upon the particular molten salt, the inner liner may be made of a material selected from, but not limited to, plain carbon steels; steels alloyed with copper, manganese, molybdenum, nickel, silicon, tungsten, titanium, vanadium and chromium, individually or in any combination thereof such as chromium-molybdenum, or nickel-chromium-molybdenum; and stainless steels. In one embodiment, the inner liner is made of 316 stainless steel.
The vessel may further include an outer liner comprising an outer liner bottom and an outer liner side wall joined to the outer perimeter of the outer liner bottom. The outer liner contains the inner liner within it, and is separated from the inner liner by thermal insulation.
The vessel may further include thermal insulation disposed between the bottom wall of the vessel and the inner liner bottom. The bottom thermal insulation may be comprised of a plurality of support members of a first insulating material interspersed within a second insulating material. The support members of the first insulating material provide structural support to the liner bottom, thereby enabling the second insulating material to have a higher R-value without needing to provide significant structural support. Hence the combination of the first and second insulating materials provided in this manner solves the problem of having insulation that has the required structural strength and the required high R-value insulating capability. In embodiments in which an outer liner is provided, the thermal insulation is disposed between the bottom wall of the vessel and the outer liner bottom.
The bottom wall of the vessel may be made of concrete, and preferably, steel-reinforced concrete. The bottom wall of the vessel may be formed upon a mud slab that is formed in the supporting ground. The side wall of the vessel may be comprised of a network of structural members. A plurality of insulating support members may be disposed between the network of structural members and the inner liner side wall. In embodiments in which an outer liner is provided, the insulating support members may be disposed between the network of structural members and the outer liner side wall. The vessel may further include thermal insulation covering the plurality of insulating support members and the network of structural members.
In accordance with the invention, a thermal energy storage system may include the instant vessel comprising a bottom wall joined to a surrounding side wall, and an inner liner disposed within the bottom wall and side wall as described above; a roof structure disposed on the surrounding side wall; and a heat exchanger assembly comprising a heat exchanger comprised of an upper region, a central region, and a lower region, a central support hanger connected to the central region of the heat exchanger and suspended from the roof structure, a spring loaded upper hanger connected to the upper region of the heat exchanger and suspended from the roof structure, and a lower hanger suspended from the central support hanger and connected to the lower region of the heat exchanger. The heat exchanger assembly may include an array of heat exchangers disposed in the vessel and arranged so as to enclose a volume within the vessel. Each of the heat exchangers may be comprised of an upper manifold connected to a lower manifold by a plurality of heat exchanger tubes. The heat exchangers of the array may be connected in series. The system may be further comprised of a mixer comprising a shaft and at least one impeller disposed within the volume enclosed by the array of heat exchangers.
The inner liner of the vessel and the heat exchanger suspension system of the thermal energy storage system may be separately useful in other applications involving high temperature material processing. Accordingly, there is provided an expandable liner for a vessel comprising a liner bottom comprising a central plate surrounded by an array of radially arranged sector-shaped plates, each of the sector-shaped plates joined at a radial portion of its perimeter to a radial portion of the perimeter of an adjacent sector-shaped plate by a radial flexible joint and joined at an inner portion of its perimeter to the central plate by an inner flexible joint; and a liner side wall joined to the liner bottom and comprising a plurality of panels, each of the panels joined at a lateral portion of its perimeter to a lateral portion of the perimeter of an adjacent panel by a lateral flexible joint.
There is also provided a heat exchanger assembly comprising a heat exchanger comprising an upper region, a central region, and a lower region, and a suspension system suspendable from a structure and connected to the heat exchanger. The suspension system may be comprised of a central support hanger proximate to the central region of the heat exchanger and suspendable from the structure, a spring loaded upper hanger connected to an upper region of the heat exchanger and suspendable from the structure, and a lower hanger suspended from the central support hanger and connected to a lower region of the heat exchanger. The heat exchanger may be comprised of an upper manifold connected to a lower manifold by a plurality of heat exchanger tubes.
In accordance with the invention, methods for using thermal energy are also provided. The methods may include storing the thermal energy received from a source and delivering the thermal energy to a power generating station. In one embodiment, a method comprises providing a thermal energy storage system as recited above, connecting at least one heat exchanger of the system to a thermal energy source, and delivering heated heat transfer fluid from the thermal energy source to the heat exchangers, thereby heating a thermal energy storage substance contained in the vessel. The method may further comprise connecting the heat exchanger to a power generating station and delivering heated heat transfer fluid from the heat exchanger to the power generating station.
In another embodiment, a method comprises providing a thermal energy storage system comprised of a vessel containing a heat exchanger, connecting the heat exchanger to a first thermal energy source, charging the vessel with a solid thermal energy storage substance, and delivering heated heat transfer fluid from the first thermal energy source to the heat exchanger, thereby heating and melting the thermal energy storage substance contained in the vessel. The charging of the vessel with a solid thermal energy storage substance and delivering heated heat transfer fluid from the first thermal energy source to the heat exchanger may be performed simultaneously. The first thermal energy source may be a solar array. The thermal energy storage substance may be an inorganic salt. The method may be further comprised of mixing the thermal energy storage substance. The method may be further comprised of connecting the heat exchanger to a second thermal energy source and delivering heated heat transfer fluid from the second thermal energy source to the heat exchanger. The second thermal energy source may be a solar array.
The present disclosure will be provided with reference to the following drawings, in which like numerals refer to like elements, and in which:
The present invention will be described in connection with a preferred embodiment, however, it will be understood that there is no intent to limit the invention to the embodiment described. On the contrary, the intent is to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.
For a general understanding of the present invention, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate identical elements.
In daytime operation of the system 100, the control valves of the liquid transfer unit 490 are positioned such that heat transfer oil is recirculated by the pump 492 from the solar field 10, through the heat exchanger array 400 in the vessel 101, and back out to the solar field 10. In the solar field 10, the heat transfer fluid passes through piping in the solar collectors, which collect and concentrate the solar radiation by suitable means such as mirrors and/or lenses onto the piping. The heat transfer fluid passing therethrough is heated to a high temperature of as much as 800° F. This hot heat transfer fluid is then pumped through the heat exchanger array 400 in the containment vessel 101. Heat from the hot heat transfer fluid is transferred into the molten salt contained in the vessel 101, and the heat transfer oil is cooled. The relatively cold heat transfer oil is recirculated back to the solar field 10 for reheating. During a startup condition, the solid salt in the vessel is heated and melted into a liquid (molten) state, and is then further heated up beyond its melting point. The molten salt thus contains energy in the form of the latent heat of fusion of the salt, as well as the sensible heat of the heated liquid. It is also noted that during the delivery of hot oil from the solar field 10 to the system 100, some portion of the hot oil may be routed directly to a power generating station 20 by pumps, piping, and valving (not shown) for driving the power generating station 20.
On overcast days and during nighttime, this sensible and latent heat is available to be transferred back into the heat transfer oil, and delivered to an electrical power generating station or “power block” 20. During this portion of the operation, the control valves of the liquid transfer unit 490 are positioned such that heat transfer oil is recirculated by the pump 492 from the power block 20, through the heat exchanger array 400 in the vessel 101, and back out to the power block 20. In the power block 20, the heat transfer fluid passes through a steam generator, which produces high pressure steam that is used to drive a turbine, which drives an electrical generator. The heat transfer fluid passing therethrough is cooled substantially as its thermal energy is transferred to produce steam. This relatively cold heat transfer fluid is then pumped through the heat exchanger array 400 in the containment vessel 101, where it is reheated and delivered back to the power block 20. This cycle may continue, with the thermal energy contained in the molten salt that was transferred from the solar field being used to generate electrical power during nighttime or overcast days, for as long as the molten salt contains enough thermal energy to heat the heat transfer fluid to a temperature suitable for producing steam in the steam turbines of the power block 20.
The salt used for thermal energy storage may be a salt mixture, or a eutectic salt mixture. Suitable salts include, without limitation, lithium nitrate, potassium nitrate, sodium nitrate, sodium nitrite, calcium nitrate, lithium carbonate, potassium carbonate, sodium carbonate, rubidium carbonate, magnesium carbonate, lithium hydroxide, lithium fluoride, beryllium fluoride, potassium fluoride, sodium fluoride, calcium sulfate, barium sulfate, lithium sulfate, lithium chloride, potassium chloride, sodium chloride, iron chloride, tin chloride, and zinc chloride, and mixtures and solutions thereof.
A thermal energy storage system containing a molten salt will be particularly useful in the commercial generation of electrical power if it can contain a minimum of 3,400 MMBTU (million British Thermal Units) for transfer to the power block 20 during nighttime or overcast days. Such a system would have the capacity to maintain generating operation of a 50 megawatt power block for about 6 hours.
This need for large thermal capacity in a thermal energy storage system results in the previously recited problems of vessel size, related structural loads, high operating temperatures, and repeated thermal cycling. These problems are solved in the thermal energy storage system, containment vessel, heat exchanger array, and related suspension system.
The containment vessel is comprised of a bottom wall joined to a surrounding containment side wall, and an expandable liner disposed within the bottom wall and side wall and comprising a liner bottom and a liner side wall. The expandable liner bottom may be comprised of a central plate surrounded by an array of radially arranged sector-shaped plates. Each of the sector-shaped plates may be joined at a radial portion of its perimeter to a radial portion of the perimeter of an adjacent sector-shaped plate by a radial flexible joint and joined at an inner portion of its perimeter to the central plate by an inner flexible joint. The liner side wall is joined to the outer perimeter of the liner bottom and may be comprised of a plurality of arcuate panels. Each of the panels may be joined at a lateral portion of its perimeter to a lateral portion of the perimeter of an adjacent arcuate panel by a lateral flexible joint. An array of heat exchangers is contained within the vessel. The heat exchangers are suspended from a roof structure by a suspension system configured to accommodate the thermal expansion of the heat exchangers resulting from the large temperature fluctuations that occur during the thermal process. The vessel may further include a second, outer liner comprising an outer liner bottom and an outer liner side wall joined to the outer perimeter of the outer liner bottom. In such an embodiment, the outer liner contains the inner liner within it, and is separated from the inner liner by thermal insulation.
In the following disclosure, the containment vessel, liners, and thermal insulation of the thermal energy storage system 100 will be described first, followed by descriptions of the heat exchanger array and mixer. The respective relationships between these components and sub-assemblies to form the overall thermal storage system 100, and methods for making and assembling the system 100, vessel, liners, and heat exchanger array will also be provided.
Turning first to
The bottom wall 110 may be formed upon a mud slab 112, which in turn is formed in the ground. The mud slab 112 may be comprised of an engineered fill. For simplicity of illustration, the outer edge 116 of the mud slab 112 is shown as being terminated at the same location as the outer edge 114 of the bottom wall 110 in
The containment side wall 120 may be comprised of a network of structural members. The structural members may be structural steel members, such as steel I-beams and steel channels. In the embodiment depicted in
The roof structure 140 may further include a bottom sheet covering 142 which provides a protective barrier to prevent personnel from falling into the containment vessel during inspection and service, and also provides a structural support, upon which thermal insulation 330 (
In another embodiment depicted in
In order to contain the liquid molten salt within the containment vessel 101, a liner 200 is provided within the bottom wall 110 and containment side wall 120. The liner 200 is comprised of a liner bottom 201 and a liner side wall 230, both of which may be configured to repeatedly expand and contract during the thermal cycling of the storage system 100. Referring again to
The number of radially arranged sector-shaped plates may be between three and twelve, or more, depending upon the size of the vessel. In the embodiment depicted in
Referring to
Referring again to
The inner flexible joint 210, radial flexible joints 206A-206H, and lateral flexible joints 234A-234H are means for the liner to expand radially outwardly when heated, and contract radially inwardly when cooled, without producing stress concentrations. The radially arranged sector-shaped plates of the liner bottom 201 and the panels of the liner side wall 230 may be provided in substantially greater numbers than shown, with corresponding flexible joints between them, to the point where the liner side wall 230 and liner bottom 201 are provided essentially as corrugated structures.
Depending upon the particular molten salt, the liner 200 may be made of a material selected from, but not limited to, plain carbon steels; steels alloyed with copper, manganese, molybdenum, nickel, silicon, tungsten, titanium, vanadium and chromium, individually or in any combination thereof such as chromium-molybdenum, or nickel-chromium-molybdenum; and stainless steels. In one embodiment, the liner is made of 316 stainless steel.
The containment vessel may further include a second, outer liner comprising an outer liner bottom and an outer liner side wall joined to the outer perimeter of the outer liner bottom. The outer liner contains the first, inner liner within it, and is separated from the inner liner by thermal insulation. The outer liner serves to provide secondary containment of the molten salt in the event that the inner liner develops a leak and allows molten salt to pass through it.
The outer liner 260 may be provided with flexible joints in the bottom wall 261 and side wall 270 in a manner similar to that described for the inner liner 200. Referring to
Although not shown, corresponding flexible joints may be provided in the outer liner bottom 261, which follow the respective contours of the flexible joints 206 of the inner liner bottom 201. In such an embodiment, the outer liner bottom 261 is comprised of a plurality of sector-shaped plates having substantially the same shape as the sector shaped plates 202A-202H of the inner liner bottom 201. Additionally, referring to
Referring to
The containment vessel may further include thermal insulation disposed between the bottom wall of the vessel and the inner liner bottom. In embodiments in which an outer liner is provided, the thermal insulation is disposed between the bottom wall of the vessel and the outer liner bottom. The bottom thermal insulation may be comprised of a plurality of support members of a first insulating material interspersed within a second insulating material. This is best understood with reference to
The side wall of the liner (or liners, if an inner and outer liner are provided) may be supported by the network of structural members of the containment vessel so as to prevent expansion and contraction of the liner(s) during thermal cycling. However, it is preferable that the liner(s) not be in direct contact with the structural members; because the structural members are made of steel or another high thermal conductivity material, any such contact would cause a substantial heat loss through the vessel side wall 120. To address this problem, a plurality of insulating support members may be disposed between the network of structural members and the inner liner side wall. In embodiments in which an outer liner is provided, the insulating support members may be disposed between the network of structural members and the outer liner side wall. The vessel may further include a second thermal insulation material covering the plurality of insulating support members, the network of structural members, and the portions of the exterior of the liner wall that are not covered by the insulating support members. In a manner similar to the thermal insulation of the bottom of the vessel liner, the insulating support members of the first insulating material provide structural support to the liner side wall, thereby enabling the second insulating material to be selected from a higher R-value material, without the need for the second material to provide significant structural support.
This is best understood with reference to
Referring now to
Each of the lower and middle arcuate channel sections (e.g. sections 131A and 132A of
Referring again to FIGS. 11 and 12A-12D, a second thermal insulation material 324 is provided, which covers the plurality of insulating support members, the network of structural members, and the portions of the exterior of the liner wall that are not covered by the insulating support members. As can be seen particularly in
A wire mesh 326, or other supporting material may be attached to the network of structural members to provide support to the second thermal insulation material 324 during fabrication of the vessel 101 and operation of the thermal storage system 100. The second thermal insulation material 324 may be covered with a layer of waterproof and weather-resistant protective material 328 to keep the insulation material 324 dry, thereby maintaining its high R-value.
The liners within the vessel, and the inner liner in particular are constructed so as to be able to expand and contract under the loading thereof with the molten salt, and in particular, due to the thermal expansion and contraction caused by contact with the molten salt at temperatures up to about 750° F. During thermal cycling, the radial and inner flexible joints of the liner bottom and the lateral flexible joints of the liner side wall flex and accommodate the thermal expansion and contraction of the sector shaped plates and arcuate panels. Having described the construction of the vessel walls, liners, and insulation, the manner in which the vessel liners expand and contract during thermal cycling will now be explained.
The network of structural members, and the solid substantially incompressible thermal insulation members disposed between the structural members and the liner side wall serve to dimensionally constrain the liner side wall and prevent substantial radial thermal expansion of the vessel liner(s) during the heating portion of thermal cycling. Accordingly, each of the sector-shaped plates 202A-202H of the inner liner bottom 201 is prevented from significant expansion radially outwardly along its outer arcuate perimeter portion. Thus during heating, each sector-shaped plate is free to expand along the radial portions of its perimeter, and radially inwardly at its inner perimeter portion. Along the radial portions of the perimeters of the sector-shaped plates, a radial flexible joint accommodates the circumferential or angular thermal expansion by flexing. At the inner perimeter portions of the sector-shaped plates, the flexible joint 210 which borders the central circular plate 204 accommodates the radially inward thermal expansion by flexing as well.
By way of illustration, referring to
In a similar manner, the thermal expansion of the arcuate panels 232A-232H is accommodated by the lateral expansion joints provided between them. Again by way of illustration, referring to
Referring also to
It will be apparent that the thermal expansion of the outer liner 260, constructed similarly with sector-shaped plates in the bottom 261 thereof, and arcuate panels in the side wall 270 thereof, is accommodated in a similar manner by its respective radial and lateral flexible joints.
Referring back to
An exemplary heat exchanger array and heat exchanger suspension system will now be described with reference to FIGS. 5 and 13-16B. Referring first to FIGS. 5 and 13-14B, a heat exchanger array 401 is suspended in the containment vessel 102. The heat exchangers are arranged so as to enclose a volume within them and within the vessel. In the embodiment depicted in
Referring to
The suspension system 420 is comprised of a central support hanger 422 suspended from the roof structure 141 proximate to the central region 441 of the heat exchanger 416, a spring loaded upper hanger 424 suspended from the roof structure 141 and connected to an upper region 443 of the heat exchanger 416, and a lower hanger 426 suspended from the central support hanger 422 and connected to a lower region 445 of the heat exchanger 416. The central support hanger 422 may be comprised of a horizontal support member 428 that is suspended from the roof structure 141 by threaded rods 429 and nuts 430. The lower hanger 426 may be comprised of a threaded rod 427 secured to the horizontal support member 428 by nuts 421.
Referring also to
In the embodiment depicted in
When the heat exchanger array 401 is installed in the containment vessel 102, each of the heat exchangers 412-418 is provided with a support system 420. During installation, when the heat exchanger 416 is first suspended from the central and lower support hangers 422 and 426, all of the weight of the heat exchanger is supported by those hangers. But when the spring loaded upper hanger 424 is added to the support system 420, and the nut 436 is turned down on the support rod 434, then the spring 432 begins to compress, and an increasing amount of the weight of the heat exchanger 416 becomes carried by spring loaded upper hanger 424. The nut 436 may be turned down sufficiently such that approximately half, or slightly more than half of the weight of the heat exchanger 416 is borne by the spring loaded upper hanger 424, with the remainder of the weight being borne by the central and lower support hangers 422 and 426. The container 431 of the spring loaded upper hanger 424 may be provided with indicia 439 of a compression scale of the spring 432, and the retainer plate 435 may be provided with a pointer 440 proximate to the indicia, so that adjustment of the spring 432 can be made quantitatively. In that manner, when the weights of the heat exchangers 412-418, spring constant of the springs 432, and dimensions of the heat exchangers 412-418 and suspension system 420 are known, the adjustments of spring compression can be made according to the indicia, without the need for individual tension measurements of the support hangers 422, 424, and 426.
In operation of the thermal energy storage system 100, when the molten salt is thermally cycled, the heat exchanger suspension systems 420 provide for expansion of the heat exchangers in both vertical directions, and also prevent stress of the heat exchangers due to any difference in thermal expansion coefficients of the heat exchanger tubes and the hanger rods 427, 429, and 434. Some of the thermal expansion of the heat exchangers 412-418 will be in downward from the horizontal support member 428, and some of the expansion will be in upward from the horizontal support member 428 by the action of the spring loaded upper hanger 424.
The system 100 or 102 may be further comprised of a mixer comprising a shaft and at least one impeller disposed within the volume enclosed by the array of heat exchangers. In the embodiment depicted in
Details of one exemplary design of the applicants' thermal energy storage system and containment vessel will now be provided. These details are to be considered as exemplary only, and not limiting. Many other designs of the system and vessel are possible, and are within the scope of the present invention. In this embodiment, the side wall 120 of the vessel may be about 23 feet in diameter and about 22 feet high. The bottom wall 110 of the vessel may be of steel rebar reinforced concrete about 24 inches thick. The mud slab 112 beneath the bottom wall 110 may also be about 24 inches thick. The concrete used in the bottom wall 110 may be 4000 psi (pounds per square inch) concrete. The vertical I-beams 121 of the vessel wall 120 may be 8-inch×8-inch steel I-beams, and the ring channels 131, 132, and 133 may be formed from 8-inch wide steel channel.
The plates of the inner liner bottom 210 and the arcuate panels of the side wall 230 of the liner 200 are preferably made of metal, which provides sufficient structural strength at high temperatures, and which is joinable at the job site by suitable means such as welding. The particular metal must also be resistant to corrosion by the molten salt. Suitable metals include stainless steel, titanium, and other metals and metal alloys previously cited herein with regard to the liner. In one embodiment, the inner liner 200 may be made of 304 stainless steel having a thickness of about ¼ inch. The outer liner, which serves as secondary containment in the event of a leak through the inner liner, is not directly exposed to the molten salt. In one embodiment, the outer liner is made of carbon steel.
The flexible joints of the liner bottom 201 and liner side wall 230 may be made by suitable forming means such as a metal brake, or by stamping with a die. The flexible joints may be made of the same material as the sector shaped plates 202A-202H and the arcuate panels 232A-232H.
The Applicants have determined that modularity of the instant thermal storage system is preferred. In construction of the vessel and overall thermal energy storage system, a system that is of a modular design is more cost effective. In a modular system, a major portion of the system components can be fabricated in a shop environment, which is better equipped and controlled, and then shipped to the job site. Final construction and assembly can then be done on the job site.
Accordingly, one aspect of the liner 200 of the containment vessel 101 is that it may be designed in a modular manner, i.e. such that the various pieces of the liner bottom 210 and liner side wall 230 may be cut and formed in a workshop or factory, and then transported to the job site to be assembled. The panels of the side wall 230 may be formed from upper and lower arcuate panels that are pre-formed in a shop and welded together at the job site. In one embodiment, the lower panels may be thicker than the upper panels to contain the higher fluid pressures near the bottom of the containment vessel 101. The respective sector plates 202A-202H, center plate 204, radial flexible joints 206A-206H, and center plate perimeter joints 210 may also all be pre-cut and formed in a shop.
Other configurations of the sectoral portions of the liner bottom 201 are also possible. In one embodiment, each sectoral section 202A-202H may be provided with a flexible joint formed along one radial edge, with the other radial edge being a simple straight edge. In that manner, when the sectoral plates are joined together, a flexible joint is provided between each of them. Additionally, the center plate 204 could be formed with its perimeter flexible joint 210 integrally formed therewith. Many other configurations are possible, with the operative requirement being that the respective adjacent plates are separated by flexible joints to accommodate the expansion and contraction of the liner 200 during thermal cycling.
The thermal insulation of the containment vessel 101 will now be described. Referring first to
The insulating support members or piers 320 beneath the liner bottom walls 201 and 261 may also be made of MARINITE® I insulation. In one embodiment, the piers 320 are 12 inches in diameter, 16 inches high, and are distributed as shown in
The heat exchangers 402 of the system 100 may be made of “2¼ Cr-1 Mo alloy,” (also known as ASME SA-213-T22 tubing), a steel alloy containing molybdenum and chromium, which is particularly suitable for high temperature pressure vessels in corrosive environment. The upper and lower manifolds of the heat exchangers may be 8-inch diameter pipes, with 31 rows of five tubes connecting them. The tubes may be ¾-inch diameter and have twelve fins each.
A method of making the applicants' thermal energy storage system 100 may be substantially as described in the aforementioned U.S. Provisional Patent Application No. 61/228,351 of Bell et al., except that the preparation of the system site such that the system my be partially submerged in the ground would likely not be performed.
One aspect of the instant system 100 and method 500 is that the latent heat contained in the system 100 will be extracted in an optimal manner. In transferring thermal energy out of the system 100, when most of the sensible heat has been removed from the molten salt and the salt is near its freezing point, the salt will begin to freeze on the outside of the heat exchanger tubes 411. The molten salt will be agitated by the mixer 450 to bring hotter molten salt in contact with the cooler solidified salt on or near the heat exchanger tubes 411, thus allowing maximum heat removal from the salt bath. The heat transfer oil within the heat exchangers will have a lower temperature rise across the salt bath, but can still be utilized overnight to heat oil in the solar field 10 or to preheat components in the power generating station 20.
From calculations, it is estimated that approximately 15% of the latent heat in the salt bath can be recovered for producing power, and the oil temperature from thermal storage will be below 520° F. The low grade heat that is not hot enough to produce steam in the power generating station 20 can be used to preheat the oil in the solar field 10 and to preheat feed water in the power generating station 20. This will enable a faster daily startup of the power generating station 20, which will bring the turbine cycle of the station 20 to full load sooner and increase the daily energy production of the station 20.
A method for storing thermal energy using the applicants' thermal energy storage system will now be described. Referring in particular to
To facilitate the startup process of the thermal energy storage system 100, the Applicants have determined that it is desirable that the initial melting of the salt be performed in the containment vessel, rather than melting the salt at a remote location and pumping it to the containment vessel, as is widely practiced in the art currently. Accordingly, in step 540, the vessel 101 is charged with solid phase salt. The solid salt is typically in a coarse granular state, and is delivered through a charging port (not shown) in the top of the vessel 101. The salt may be delivered manually, or the system may be provide with a temporary or permanent hopper and/or auger, or other conveying means (not shown) to deliver the granular salt into the vessel 101. In one embodiment, as the incoming granular salt contacts the lower regions of the heat exchangers 412-418, the melting process can be started. Valves 495 and 497 of heater loop 494 are positioned to circulate heat transfer fluid through heater 496, and through the heat exchanger array 400, and back to the heater loop 494. The heat transfer oil is heated to above the melting point of the salt by the heater 496, and then circulated through the heat exchanger array 400, such that the initial granular salt contacting the heat exchangers 412-418 is melted early in the charging process. As the liquid salt level rises, it submerges the lower impeller 458, such that the mixer functions to circulate a slurry of liquid salt and solid granules as the melting process proceeds. With mixing and therefore enhanced heat transfer occurring during almost the entire salt melting process, the initial salt melting process is accelerated. This melting process is also beneficial in that if the vessel 101 were fully filled with granular salt and then melted, a second charge of salt would need to be added. This is because the granular salt has a large void volume, and once that first charge of granular salt were melted, the vessel would not be full to capacity, thus requiring a second charge of salt.
Once the salt is completely melted, or nearly so, such that the mixer 450 can circulate substantially the entire contents of the vessel 101, the contents may be maintained 550 in the pre-heated state by using the heater loop 494 if necessary until thermal energy is available 555 from the solar field 10 or other thermal source. The various valves of the fluid delivery system 490 are switched, circulating hot heat transfer fluid from the solar field 10 through the heat exchanger array 450 and back, thereby delivering 560 thermal energy to the vessel from the solar field 10. Any remaining solid salt in the vessel is fully melted, and the molten salt is heated further, typically to a temperature of as much as 800° F. When the molten salt is at its maximum operating temperature, the vessel 101 is at its maximum thermal capacity 565. This maximum thermal energy is available to deliver to the power generating station 20.
This is typically needed from evening to morning, or during cloudy periods of the day. The various valves of the fluid delivery system 490 are again switched, circulating hot heat transfer fluid through the heat exchanger array 450 in the vessel 101 to the power generating station 20 and back, thereby delivering 570 thermal energy from the vessel 101 to the power generating station 20. The heat transfer rate from the molten salt to the heat transfer fluid in the heat exchangers 412-418 is enhanced by use of the mixer 450. This may continue until the molten salt in the vessel 101 is cooled to a point where it begins to solidify on the upstream portion of the inlet heat exchanger 414, at which point the available thermal energy in the vessel 101 is substantially depleted. It is preferable that the system 100 not be operated such that the molten salt completely freezes and encloses the heater exchangers 412-418. This is because the enhanced heat transfer provided by the fluid flow caused by the mixer would then no longer be available. After depletion of the thermal energy in the vessel 101, the salt is maintained 550 in a heated state with minimal heat loss by virtue of the substantial amount of thermal insulation surrounding the entire vessel. In the event that it is necessary to completely shut down the process, or to interrupt the process for a prolonged period of time, it is permissible to allow some or all of the entire contents of the vessel to solidify. The solid salt in the vessel can be re-melted by resuming the circulation of hot heat transfer fluid through the heat exchangers 412-418.
It is also noted that it is not necessary to have the vessel fully charged to maximum thermal capacity 565 before delivering 570 thermal energy to the power generating station 20, as indicated by dotted line arrow 568. If conditions warrant, a partial thermal charge may be delivered 570 to the power generating station 20. Additionally, even if the temperature of the molten salt in the vessel 101 is relatively low, and only a small amount of thermal energy is available in the vessel 101, that energy may still be beneficially used. As described previously, the low grade heat that is not hot enough to produce steam in the power generating station 20 can be used to preheat the oil in the solar field 10 and/or to preheat feed water in the power generating station 20. This will enable a faster daily startup of the power generating station 20, which will bring the turbine cycle of the station 20 to full load sooner and increase the daily energy production of the station 20.
It is, therefore, apparent that there has been provided, in accordance with the present invention, a vessel for containing a thermal energy storage liquid, a thermal energy storage system comprising such vessel, and methods for making and using the vessel and thermal energy storage system. Having thus described the basic concept of the invention, it will be rather apparent to those skilled in the art that the foregoing detailed disclosure is intended to be presented by way of example only, and is not limiting. Various alterations, improvements, and modifications will occur and are intended to those skilled in the art, though not expressly stated herein. These alterations, improvements, and modifications are intended to be suggested hereby, and are within the spirit and scope of the invention. Additionally, the recited order of processing elements or sequences, or the use of numbers, letters, or other designations therefore, is not intended to limit the claimed processes to any order except as may be specified in the claims. Accordingly, the invention is limited only by the following claims and equivalents thereto.
This application claims priority from U.S. provisional patent Application No. 61/314,313, filed Mar. 16, 2010, the disclosure of which is incorporated herein by reference. This application is also related to the following copending commonly owned United States patent applications: application Ser. No. 12/033,604 of Geiken et al., filed Feb. 19, 2008; application Ser. No. 12/172,673 of Flynn et al., filed Jul. 14, 2008; and application Ser. No. 12/842,203 of Bell et al., filed Jul. 23, 2010. The disclosures of these United States patent applications are incorporated herein by reference in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| 61314313 | Mar 2010 | US |
