Large-scale long-term high-temperature heat storage

Abstract

Concepts, methodologies and structures for long-term high-temperature heat storage in firebrick are presented. Heat storage times can be from hours to many months or longer. A thermal energy storage system includes an insulated chamber, and a plurality of insulating firebrick layers disposed horizontally in the insulated chamber. Each insulating firebrick layer includes a plurality of insulating firebricks and defines a vertical channel at an opposite end from a previous insulating layer. A plurality of flow-through firebrick layers is alternatingly disposed between the plurality of insulating firebrick layer. Each flow-through firebrick layer includes a plurality of conductive firebricks defining a horizontal channel. The plurality of flow-through firebrick layers and the vertical channels define a serpentine flow path from a first side of the insulated chamber to a second side of the insulated chamber. The firebrick can be heated by external hot air or internally heated using electrically conductive firebrick.

Description

LARGE-SCALE LONG-TERM HIGH-TEMPERATURE HEAT STORAGESTATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0001] Not Applicable.FIELD

[0002] One or more aspects described herein relate to managing energy storage.BACKGROUND

[0003] The modern energy generation and distribution network (the “power grid”) includes many different power generation sources. While some generators can operate at a relatively continuous output (e.g., traditional power plants such as coal, oil, natural gas, nuclear, etc.), other power sources such as solar or wind may vary in generation capability, for example, based on environmental factors. The addition of wind and solar energy generation has greatly increased the quantities of low-price electricity — but only at certain times. Solar energy varies on a daily to yearly basis while wind is much less predictable. Customer demands for heat vary from steady state for many industrial applications to large changes in demand with time for some heating applications and production of electricity.

[0004] As increasing solar and wind generators are brought online to reduce greenhouse gas emissions, there are economic incentives for expansion of the power storage capabilities of the power grid to match production with demand. However, present energy storage technologies have proven to be unsatisfactory and are very costly to implement. Attempts have been made to use other types of energy storage systems, such as pumped hydroelectric storage. However, these other systems are site-limited and not readily available or deployable.SUMMARY

[0005] One or more aspects described herein provide an improved energy storage system and method which may be used for a variety of applications, not the least of which includes storing power in a power grid.

[0006] According to one aspect, a system may include an insulated chamber and a plurality of insulating firebrick layers disposed horizontally in the insulated chamber. Each insulating firebrick layer may include a plurality of insulating firebricks. Each insulating firebrick layer may further define a vertical flow-through channel. A plurality of flow-through firebrick layers may be alternatingly disposed between the plurality of insulating firebrick layers. Each flow-through firebrick layer may include a plurality of conductive firebricks defining a horizontal channel. The plurality of flow-through firebrick layers and the vertical flow-through channels may define a flow path from a first side of the insulated chamber to a second side of the insulated chamber.

[0007] In another aspect, a thermal energy storage system may include an insulated chamber and a plurality of insulating firebrick layers disposed horizontally in the insulated chamber. Each insulating firebrick layer may include a plurality of insulating firebricks. Each insulating firebrick layer may further define a vertical channel at an opposite end from a previous insulating layer. A plurality of flow-through firebrick layers may be alternatingly disposed between the plurality of insulating firebrick layers. Each flow-through firebrick layer may include a plurality of conductive firebricks defining a horizontal channel. The plurality of flow-through firebrick layers and the vertical channels may define a serpentine flow path from a first side of the insulated chamber to a second side of the insulated chamber.

[0008] The systems and methods disclosed herein may include, alone or in combination, one or more of the following features. Each vertical flow-through channel may be defined at an opposite end from a previous insulating layer. The flow path may include a serpentine flow path through the insulated chamber. The first side of the insulated chamber may be a bottom side and the second side of the insulated chamber is a top side. The flow path may be a discharge flow path. The first side of the insulated chamber may be a top side and the second side of the insulated chamber may be a bottom side. The flow path may be a charging flow path. At least one compressor and an electric heater may be disposed in an external flow path between the first side and the second side of the insulated chamber. A first compressor may be in fluid communication with one or more first exit ports of the insulated chamber and the electric heater and a second compressor may be in fluid communication with one or more second exit ports of the insulated chamber and the electric heater. The one or more second exit ports may be disposed in a transition zone defined by one or more flow-through firebrick layers. The transition zone may be defined by one or more middle flow-through firebrick layers. The plurality of conductive firebrick may comprise electrically conductive firebricks configured to be heated by an electrical current. The electrical current may be supplied at a time of reduced electricity cost. The electrical current supplied at the time of reduced electricity cost may be selectively chosen from at least one of a solar energy source and a wind-powered energy source. The flow path may be over 100 meters.

[0009] In another aspect, a method of storing thermal energy may include providing a plurality of insulating firebrick layers disposed horizontally in an insulated chamber. Each insulating firebrick layer may include a plurality of insulating firebricks. A plurality of flow-through firebrick layers may be alternatingly disposed between the plurality of insulating firebrick layers. Each flow-through firebrick layer may include a plurality ofconductive firebricks. A flow path may be defined through the plurality of flow-through firebrick layers and around the plurality of insulating firebrick layers from a first side of the insulated chamber to a second side of the insulated chamber. A fluid may be supplied at a first temperature to an inlet port at the first side of the insulated chamber. The fluid may be extracted at a second temperature at an outlet port at the second side of the insulated chamber.

[0010] The systems and methods described herein may further include, alone or in combination, one or more of the following features. The first temperature may be lower than the second temperature and the fluid may be heated as it flows through the flow path. The first temperature may be higher than the second temperature and the conductive firebricks may be heated by the fluid. The plurality of conductive firebricks may include electrically conductive firebricks. An electrical current may be supplied to heat the electrically conductive firebricks.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The foregoing and other objects, features and advantages will be apparent from the following more particular description of the embodiments, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the embodiments.

[0012] FIG. l is a block diagram of an illustrative industrial system employing a conductive firebrick system, according to aspects of the present disclosure;

[0013] FIG. 2 is a diagram of an illustrative vessel system for containing an electrically heated thermal energy storage system, according to aspects of the present disclosure;

[0014] FIG. 3A shows a sectional view of an example heat storage system core in discharge mode, according to aspects of the present disclosure;

[0015] FIG. 3B shows a sectional view of an example heat storage system core in charge mode, according to aspects of the present disclosure;

[0016] FIG. 3C shows a sectional view of an example heat storage system core with electrically conductive firebrick, according to aspects of the present disclosure

[0017] FIG. 4 is a sectional view of a thermocline heat storage system;

[0018] FIG. 5 is a sectional view of an example heat storage system core with intermediate fluid extraction, according to aspects of the present disclosure;

[0019] FIG. 6 is a flow diagram of a method of storing thermal energy, according to aspects of the present disclosure.DETAILED DESCRIPTION

[0020] Aspects of the present disclosure include concepts, techniques and structures for long-term, high-temperature heat storage in firebrick. A heat storage system core may be provided with alternating layers of insulating firebricks and conductive firebricks, including traditional firebricks and / or electrically conductive firebricks. A flow path may be defined through the conductive firebricks and around the insulating firebricks such that the fluid either conditions (e.g., heats) the firebricks, or is conditioned by heat stored in the firebricks. In one aspect, the fluid may also or instead be heated directly through the application of an electrical current to the conductive firebricks. Electrically conductive firebrick include a set of technologies where electric resistance heating occurs within the firebrick that is storing the heat.

[0021] Storing heat at high temperatures in a firebrick for short periods of time (e.g., hours) is known in the art. The design challenge for longer-term storage at high temperatures includes keeping hot firebrick hot and cold firebrick cold for extended periods of time. When dealing with high temperatures, (e.g., above 700 °C) radiative heat transfer and heat conduction transfers heat from hot firebrick to colder firebrick rapidly, therebypreventing the ability of known systems to store high-temperature heat for long periods of time. At these temperatures, much of the heat transfer may be radiative heat transfer that increases as the fourth power of the absolute temperature. Aspects of the present disclosure provide firebrick heat storage systems configured to slow this heat transfer process to maintain firebrick at high and low temperatures in a heat storage system for long periods of time.

[0022] According to one or more aspects of the present disclosure, concepts, techniques, and structures for performing electrically heated thermal energy storage are provided. As increasing numbers of renewable energy generators are deployed into the power grid, it may be desirable for abundant and affordable energy storage technologies to cover cycles in power generation, for example, in solar or wind energy generation. Aspects of the energy storage systems and methods described herein may satisfy these goals. Moreover, these and / or other aspects may be used in various industrial processes that generate and / or consume heat, such as furnaces, kilns, refineries, nuclear power plants, and so on. As described herein, some aspects of the energy storage systems may employ electrically heated firebricks (e.g., electrically conductive firebricks) to store heat energy for use as heat or conversion to electricity, as described in U.S. Patent No. 11,877,376, issued on January 16, 2024 and entitled “Electrically Conductive Firebrick System”, the entire contents of which are hereby incorporated by reference in their entirety.

[0023] According to one aspect, energy storage systems, like those described herein, may be built of firebrick, a low-cost material available for operation at these temperatures. Heat may be added directly to the system as high-temperature air or other fluid, or using electrically conductive firebrick, depending upon the application. Heat may be extracted by blowing a fluid, such as air or another gas, through the firebrick and heating the fluid tohigh temperatures. According to one aspect, electrically conductive firebrick heaters, if used, may enable the system to heat up to about 1800° C.

[0024] In known energy storage systems, multiple insulated chambers with firebricks use conventional electrical heaters that can heat to about 1100° C. With multiple insulated chambers, the known systems may sequentially heat each pile of firebrick and sequentially remove heat from piles of firebrick to provide variable heat to the customer. At such temperatures radiative heat transfer is a major mode of heat transport. According to one aspect of the present disclosure, as described below, systems may use electrically-conductive firebrick to provide the practical advantage of increasing peak temperatures to potentially as high as 1800° C. Higher temperatures may reduce the cost of the firebrick used for sensible heat storage (e.g. larger hot to cold temperature swing) and more provide a more feasible system for potential customers.

[0025] Much of the capital cost of storing high-temperature heat is in the insulation system. The heat storage capacity of any storage system may be directly proportional to the volume that increases as the cube of the dimensions. The insulation and its cost increase as the surface area that increases as the square of the dimensions. Low-cost high-temperature storage systems may need to be large to be cheap to reduce insulation cost and heat loss per unit of heat stored. Ideally, a design would be simple if a fixed quantity of heat could be stored for a fixed time. The firebrick is heated, the heat is stored, and the heat is recovered over a short period of time. However, this ideal operational scenario is hampered by the heat inputs and outputs varying over time.

[0026] Aspects of the storage system described herein may include increased efficiency (e.g. lower energy losses) and a decrease in the cost per unit of stored heat with storage capacity, strongly favoring large storage capacities measured in gigawatt hours. According to one aspect, storage temperatures may approach 1800° C. Accordingly, such systems mayenable the use of generated heat by high-temperature power cycles such as gas turbines and by industries producing products such as glass and cement.

[0027] The systems, concepts, and methodologies described herein provide several practical and advantageous applications to energy generation and storage systems. For one, the large-scale addition of wind and solar has resulted in very low and sometimes negative electricity prices at certain times of day, providing a low-cost primary input to the heat storage system. Second, firebrick is made of earth-abundant elements such as aluminum oxide and magnesium oxide that are cost-effective. These types of firebricks have been used on a large industrial scale for over a century in the production of glass, cement and steel. Third, higher peak temperatures may increase the hot to cold temperature swing (e.g. sensible heat storage) and thus reduce capital costs. Fourth, there may be a large demand for high-temperature heat, but that heat may need to be dispatchable, thus the need for the storage system to supply heat when needed (e.g. on demand). Fifth, the high temperatures may match natural gas combustion temperatures. Accordingly, if storage is depleted, the system may use natural gas or biofuels to provide high-temperature heat without impacting the customer. According to one aspect, the system may be a drop-in replacement for fossil fuels.

[0028] According to one aspect, as described herein, a primary source of heat may include electricity purchased at times of low prices and converted to high-temperature heat. The addition of wind and solar energy generation has greatly increased the quantities of low-price electricity, however, only at certain times. Solar energy varies on a daily to yearly basis while wind generation is much less predictable. Customer demands for heat may vary from steady state for many industrial applications to large fluctuations in demand over time for some heating applications and production of electricity.

[0029] Referring now to FIG. 1, one or more aspects of an illustrative deployment of an energy storage system employing heated firebricks in a power grid or industrial system is shown. A heated firebricks 108 may receive electricity input 104 to heat the firebricks, and may also receive air input 102. For example, air input 102 may be “cold” air, ambient temperature air, exhaust air from an industrial process, and the like. The input air may be heated by the heated firebrick 108, and may be output as hot air 110. In some aspects, the temperature of output hot air 110 may be adjusted by a temperature adjustment 114, which may include air provided by an air bypass 106 from the input air 102. For example, the temperature of the output air might be adjusted by providing cooler air (e.g., via the bypass 106) if the temperature of heated firebricks 108 is greater than the temperature desired for the output hot air 110 provided to the output user 112, which may be, for example, a kiln, furnace or the like. Alternatively, in one aspect, if the temperature of the heated firebricks 108 is less than the desired temperature for the output air 110, additional fuel, such as natural gas, might be provided via the temperature adjustment 114 to increase the temperature of the output hot air 110.

[0030] In some aspects, the output user 112 may be a natural gas power cycle plant. In accordance with one or more aspects, a predetermined efficiency may be achieved, e.g., a roundtrip electrical efficiency of 55-60%. In other aspects, output user 112 may be a nuclear power plant (e.g., a generation IV nuclear reactor), and the energy storage system may achieve, for example, a roundtrip electrical efficiency of 65-70% when coupled to a thermodynamic topping cycle. The nuclear reactor may heat the working fluid in the power cycle and the heat storage system may provide added higher-temperature heat to increase peak power cycle temperatures. In one embodiment, the energy storage system (e.g., the firebricks 108) may be collocated proximately with the user 112.

[0031] Existing systems do not achieve high enough temperature ranges and / or suffer dramatically short lifetimes due to high temperature required. For example, existing heaters provide limited temperature ranges (e.g., Tpeak of the heater < Tpeak of the firebricks), limited charge rates (e.g., limited ability to transfer heat from the heater to the firebrick due to surface wattage loading of the heaters and / or temperature gradients and thermal stresses of the firebrick), and heater lifetimes dramatically shortened by high temperature, which may incur high replacement costs.

[0032] As described herein, thermal heat storage may be generated and managed using a combination of thermally conductive firebricks and insulating firebricks, and a defined flow path therebetween. The energy storage system may be charged and discharged with conditioned fluid based on the given state of the firebricks. Additionally, one or more aspects of the disclosure may provide for direct resistance heating of the firebricks 108. For example, one or more embodiments may electrically heat an insulated mass of firebrick to very high temperatures (e.g., ~1000°C to ~2000°C, although higher temperature ranges are possible).

[0033] The heat stored in the firebricks 108 may be delivered as the output air 110 by blowing air through a flow path defined by one or more horizontal and vertical channels in the system to deliver the stored heat for industrial heat applications (e.g., kilns, furnaces, refineries) or electricity generation applications (e.g., power plants).

[0034] Similarly, the firebricks 108 may be heated by blowing pre-heated air through the flow path, transferring thermal energy from fluid to the firebricks, where the energy may be stored for a significant duration.

[0035] The firebrick energy storage system may eliminate the wattage loading constraints of existing heaters, and designing the firebricks to provide near-uniform heat generationthroughout the firebrick system reduces stress on the system, which, in turn, reduces repair costs and provides for more reliable operation.

[0036] Referring now to FIG. 2, a diagram of an illustrative regenerator vessel that may be used to contain a firebrick energy storage system is shown. A vessel system 200 may include air inlet 210, lower plenum 208, body 212, upper plenum 204, and hot air outlet 202. Collectively, plenums 204 and 208 and body 212 may form vessel 214. In general, vessel 214 may be an insulated steel vessel that is collocated at an industrial facility or power plant. In some embodiments having higher air pressures, vessel 214 may be prestressed concrete. As described herein, vessel 214 might contain a pattern of firebricks, shown generally as firebricks 206, and which may be implemented such as described in regard to FIGS. 3A-B.

[0037] As shown, the lower plenum 208 may be a hemispherical entrance of an air stream into the vessel 214, and the upper plenum 204 may be a hemispherical exit of an air stream through the vessel 214. The air stream may be provided from the inlet 210 and flows through the firebricks 206 as indicated by the dashed arrow 216 and which then exits through the hot air outlet 202. In some aspects, the lower plenum 208 includes support structures for the vessel 214 (e.g. corrosion-resistant steel, ceramic archways or dome structure, etc.) to support the vessel 214 as a standing structure. Additionally, in some aspects, the lower plenum 208 may be maintained at a lower temperature than the rest of the vessel 214 by employing an insulation layer between lower plenum 208 and the firebricks 206, and / or by employing one or both of passive and active cooling. Although shown in FIG. 2 as being generally cylindrical, the vessel 214 may have a specific size and shape that varies based on its use and application.

[0038] As will be described, the arrangement of the vessel 214, the air inlet 210, the air outlet 202, and the air flow (e.g. arrow 216) may be reversed to support a charging state ofoperation for the energy storage system. In such a system, the air may be input to the firebricks to “charge” or heat the firebricks 206. Resulting cold air may be output for reheating or other such purpose. Additional details of charging an energy storage system are described below in connection with FIG. 3B.

[0039] FIGS. 3A-C show a heat storage system core 300 for enabling efficient storage of high-temperature heat over time with stored quantities of heat changing over time. FIG. 3 A shows the system 300 in a discharge mode. FIG. 3B shows the system 300 in a charging mode with an external heating system, including a heater 314 and a compressor 312. FIG.3C shows the system 300 including electrically conductive firebricks with an electricity source 328 supplying a current 332.

[0040] In one aspect, storage system 300 may be built of firebrick surrounded by firebrick insulation that is within a metallic shell (e.g., an insulated chamber 302) to provide a gastight system. The firebrick may include two types of horizontal layers across the width of the insulated chamber. A first set of horizontal layers may include solid firebricks (e.g., as insulating firebrick) that prevent fluid flow through the layer and have a low thermal conductivity. A second set of horizontal layers of thermally conductive firebrick (e.g., as flow-through firebrick layers) may include or define holes or channels that enable horizontal fluid flow therethrough. Insulating firebricks with vertical flow channels may connect the flow-through firebrick layers of firebrick at the opposite ends of the storage system. As described herein, thermally conductive firebricks may include, according to one or more aspects, one of, or a combination of, traditional industrial firebrick used for heat storage, electrically conductive firebrick that can store heat and be used as electric resistance heaters and / or other materials. Known firebrick may be made from alumina, silica or other materials, as is known in the art. The thermally conductive firebricks of theflow-through firebrick layers may be chosen to maximize heat capacity (stored heat) per unit volume.

[0041] As shown in FIGS. 3A-B, the energy storage system 300 is shown including the insulated chamber 302 and a plurality of insulating firebrick layers 304A-E (generally referred to as insulating firebrick layers 304), arranged or disposed horizontally in the insulated chamber 302. Each of the insulating firebrick layers 304 may include a plurality of insulating firebricks and define a vertical channel 306 at an opposite end from a previous insulating layer. A plurality of flow-through firebrick layers 308A-D (generally referred to as flow-through firebrick layers 308) are alternatingly disposed between the plurality of insulating firebrick layers 304. Each flow-through firebrick layer 308 may include a plurality of thermally conductive firebricks defining a horizontal channel 310A-D (generally referred to as horizontal channels 310). In one aspect, the thermally conductive firebricks may include traditional firebricks (e.g., fireclay). In another aspect, as further described below and shown in FIG. 3C, the thermally conductive firebricks may include electrically conductive firebricks. In yet another aspect, the flow-through firebrick layers may include a combination of traditional firebricks and electrically conductive firebricks. In one aspect, electrically conductive firebrick includes technologies where electric resistance heat is generated within heat storage firebrick; thus, no fluid flow is required when charging the heat storage system. This includes implementations in which the firebrick is electrically conductive and is the resistance heater and when some of the firebrick has a geometry and other features allowing incorporation of other types of electric resistance heating elements as part of the firebrick.

[0042] In known energy storage systems, multiple insulated chambers with firebricks use conventional electrical heaters that can heat to about 1100° C. With multiple insulated chambers, the known systems may sequentially heat each pile of firebrick and sequentiallyremove heat from piles of firebrick to provide variable heat to the customer. At such temperatures radiative heat transfer is a major mode of heat transport. According to one aspect of the present disclosure, using electrically-conductive firebrick, where the firebrick is the resistance heater, may provide the practical advantage of increasing peak temperatures to potentially as high as 1800° C. Higher temperatures may reduce the cost of the firebrick used for sensible heat storage (e.g. larger hot to cold temperature swing) and provide a more feasible system for potential customers.

[0043] In one aspect, the plurality of flow-through firebrick layers 308 and the vertical channels 306 may define a flow path from a first side (e.g., at arrow 301) of the insulated chamber to a second side (e.g., at arrow 305) of the insulated chamber 302. According to one aspect, the flow path may be defined as an ‘S’ shape or serpentine shape, in which the air flows through the thermally conductive firebricks horizontally from one side of the insulating chamber 302 to the other where it may pass through a vertical channel 306 and flow back to the other side in the next layer of thermally conductive firebricks, and so forth until the fluid reaches the outlet. According to one aspect, as described herein, the energy storage system 300 may define the flow path from the bottom to the top (FIG. 3A), or from the top to the bottom (FIG. 3B).

[0044] In one aspect, the system 300 may operate in a discharge mode, as shown in FIG.3 A. If, for example, the firebrick is initially hot or already in a charged state, cold air or other fluid from a heat user can enter the storage system 300 at the bottom (e.g., 301) and flow through the serpentine flow path upward. As the fluid flows through the extended flow path, heat from the thermally conductive firebricks in the flow-through layers 310 may be transferred to the fluid, gradually heating the fluid as it flows across and upward (as indicated by the temperature scale 350). Eventually the fluid may exit (305) the storage system 300 as hot fluid and return to the heat user.

[0045] Alternatively, according to one aspect, the system may operate in a charge mode, as shown in FIG. 3B. If the firebrick is initially cold, for example, hot air 322 or other fluid, from the heater 314, may enter the storage system 300 at the top and flow through the S-shaped, or serpentine, flow pattern downward. As the heated fluid flows through the extended flow path, heat from the fluid in the flow-through layers 310 may be transferred to the conductive firebricks of the flow-through firebrick layers, gradually heating the firebricks as the fluid flows across and downward. As the heat is transferred to the firebricks, the fluid may be cooled (as indicated by the temperature scale 352) and eventually exit the storage system as cold fluid 318. A compressor 312 may receive the cold fluid and return the cold fluid to the heater 314, where it can be reheated and reintroduced to the system 300 to continue to charge the firebricks. In one aspect, the heater 314 may include electrically conductive firebrick, or another electrical heating source.Advantageously, electrically conductive firebrick, as used in the external heater 314 may the only technology capable of providing sufficiently high temperatures to provide hot air to the system 300.

[0046] The above-described charge mode may provide one of two strategies for heating the energy storage system. As described above, a cold fluid may be taken, heated to very high temperatures and injected into the top of the storage pile where it heats the firebrick from top to bottom. The fluid can be heated outside the storage system using the heater 314. The heater 314 may supply heated fluid using, for example, electrically conductive firebrick, burning combustible gases, or other electric heating methods. In some aspects, there may be at certain times excess hydrogen or other fuels that can be burned to provide high-temperature heat.

[0047] Alternatively, in a second heating strategy according to one or more aspects, as shown in FIG. 3C, the system 300 may include electrically conductive firebricks that maybe charged directly by supplying an electrical current to the electrically conductive firebricks where the supplied current may be converted to thermal energy and stored.

[0048] In one aspect, flow-through firebrick layers 324A-D, collectively referred to as flow-through firebrick layers 324, may include a plurality of electrically conductive firebricks. The electrically conductive firebricks may define horizontal flow-through channels 326A-D, collectively referred to herein as flow-through channels 326. In one aspect, use of electrically conductive firebrick may provide numerous advantages, including but not limited to, enabling heating the flow-through firebrick layers 324 while also providing heated fluid to an output user at the same time. Electrically conductive firebrick may allow independent sizing of the rate of heat addition inside the heat storage system versus the rate of heat extraction that is controlled by fluid flow rates through the firebrick. Because, low-price electricity may be available for limited times it may be desireable to have large heat input rates when low-price electricity is available. If there are lower peak heat demands, smaller fluid flow channels may be desired to minimize flow channel volume in the heat storage system and heat losses out of the system via the fluid flow channels. Internal heating of the firebrick may avoid thermal losses associated with external loops with heaters. Additionally, the use of electrically conductive firebrick may be a most cost-effective system to build, operate and maintain.

[0049] In one aspect, the electrically conductive firebricks may be or include electrically conductive semiconductor-doped metal-oxide firebricks made by mixing a powder form of a bulk material (e.g., chromium oxide) with a desired amount of a dopant material (e.g., nickel oxide). In some aspects, the dopant material may be between approximately 2% and 5% of the mixture. In one or more aspects, the electrically conductive firebricks may be, or include, chromium oxide doped with nickel, chromium oxide doped with magnesium, nickel oxide doped with lithium, nickel oxide doped with copper, zinc oxide doped withaluminum, stabilized zirconium oxide doped with cerium, titanium oxide doped with niobium, or other high temperature metal oxides doped with metals of a different valency, which may also be blended with electrically inactive oxides such as alumina, magnesia, or silica. For example, in some aspects, some alumina (e.g., aluminum oxide) may be blended in with chromia (e.g., chromium oxide) doped with nickel, which could make the firebrick cheaper and / or stronger, without significantly altering the electrical properties of the firebrick.

[0050] In one aspect, an electricity source 328 may be supply the electrically conductive firebrick with a current 332, such that the flow-through firebrick layers 324 may act as a resistive heat source when electricity is supplied. As the supplied current heats the electrically conductive firebrick, thermal energy 330 may be transferred to the fluid in the flow-through channels 326. Accordingly, the heat generation of the system 300 is accomplished inside the insulated chamber 302. In one aspect, the flow-through firebrick layers 324 may include a combination of traditional firebricks and electrically conductive firebricks, in which the fluid in the system 300 may be heated by both an external heater (heater 314, FIG. 3B) and electrically conductive firebrick with a supplied current.

[0051] In any of the example systems shown in FIGS. 3 A-C, with hot firebrick on top of cold firebrick, there may be no convective fluid flow to transfer heat from hot firebrick to cold firebrick. Hot fluid is less dense than cold fluid. However, there may be thermal conduction through the firebrick and radiation heat transfer from a hot to cold zone. Heat movement over time may eliminate or reduce the high temperatures. Heat flow may be minimized by multiple mechanisms, as described herein, having alternating layers of insulative firebrick and high-heat-capacity firebrick with horizontal flow channels.

[0052] According to one aspect, the thermal energy system 300 may reduce or stop direct downward flow of heat. The solid horizontal layers of low thermal conductivity firebrickmay minimize downward heat transfer from hot to cold firebrick. There may be small openings in these layers (e.g., vertical channels) for the fluid to flow through. The fluid flow channel size in the insulating firebrick layers may be minimized to reduce radiation heat transfer in the downward direction. A tradeoff, however, may be presented. Larger flow channels in the vertical direction may minimize fluid pumping power but they may increase radiative heat transfer in the downward direction. In one aspect, curved (e.g., half circle) or other geometries within the system may reduce radiation heat transfer in the downward direction via the fluid flow channels. Radiative heat transfer may be from surface to surface in a straight line. The downward flow channels may be made of low-thermal-conductivity firebrick to minimize heat transfer by conduction from the layers of firebrick with high thermal conductivity.

[0053] In a traditional high-temperature firebrick recuperator, heat travels from top to bottom in the downward direction. According to one aspect, the energy storage systems described herein may leverage a long or extended heat flow path to heat by conduction and radiation following an S-shaped (e.g., serpentine) path defined by the horizontal flow paths in the thermally conductive layers and the vertical fluid flow channels in the insulating layers. The firebrick heat storage system may be, according to one aspect, about 5 to 30 meters tall; but, the fluid flow path may be over about 100 meters long. Heat transfer may follow this extended fluid flow path that has the high-thermal-conductivity firebrick enabling heat transfer by conduction and radiation heat transfer through the open fluid flow channels. With firebrick, high heat capacity (e.g., storage) and high thermal conductivity may be provided in the same firebrick.

[0054] While aspects of the systems shown in FIGS. 3 A-C show fluid flow from left-to-right and right-to-left, there are also other geometries possible. In large circular systems, for example, channels connecting the horizontal flow layers may be provided in the center ofthe system and the outer edge. According to one aspect, the energy storage system may establish a long flow path for heat that slows heat transfer.

[0055] According to one aspect, an operational strategy may be enabled by configuration of the energy storage system. When adding high-temperature heat with flowing fluids to the top (FIG. 3B), a hot to cold zone interface may shrink as warm firebrick is heated up to full temperature. On the other hand, when adding cold fluid to the bottom to obtain hot fluids out the top (FIG. 3 A), the warm firebrick may be cooled down and the hot to cold zone interface may shrink. The dynamic addition and removal of heat can shrink the interface zone. High-temperature heat may be only lost via the outer insulation. In this context, long-duration storage may be different from systems designed for short duration storage. With long-duration storage, the rates of heat addition or removal (fluid flow rates) may be small relative to the quantities of stored heat. In one aspect, large temperature differences between firebrick and the fluid are not required for fast heat transfer. The number of horizontal zones of low-conductivity firebrick may determine how small such a transition zone can be if heat is frequently added or removed. In this manner, the system 300 may act as a dynamic insulation system with very small heat losses out of the bottom where the cold fluid enters.

[0056] FIG. 4 is a sectional diagram of a known thermocline system 400 heating system. The system may include an insulated chamber 402 in fluid communication with a heater 414 and one or more compressors, such as compressor A 412 and compressor B 416. The insulated chamber may include firebricks used to retain thermal energy. Thermocline systems, like the system 400, may include a hot zone 404 with heated fluid at the top of the insulated chamber 402 and cold zone 408 with cooled fluid at the bottom of the insulated chamber 402. A transition zone 406 may be created or formed in which fluid may transition between hot and cooled to an intermediate temperature. Over time, when no heat is being added or removed, the transition zone 406 may grow as the temperature of the fluidchanges. Over an extended period of time, the temperature in the insulated chamber may reach an equilibrium.

[0057] As the transition zone grows, the quantity of hot firebrick at the peak temperature decreases. Accordingly, the quantity of high-quality, hot-stored heat decreases. In some systems the transition zone can be minimized by extracting the intermediate temperature fluid (shown at arrows 420). The intermediate temperature fluid may be pushed by compressor B 416 to the heater 414 where it can be heated to a high temperature. This may occur when low-price electricity or another heat source is available. The system 400 faces a number of complications, however, because the suction from compressor B 416 to extract the intermediate temperature fluid will draw in fluid from above and below the transition zone that is closer to the exit from the storage system to the compressor 416. If using firebrick, the fluid flow resistance slows flow from the far left of the heat storage relative fluid from the closer hot and cold zones. Accordingly, the extraction by compressor B 416 may be an inefficient process that pulls undesired fluid from the hot zone 404 and the cold zone 408, instead of the intermediate temperature fluid in the transition zone, particularly the fluid on the opposite side of the insulation chamber 402 from the outlets to compressor B 416.

[0058] FIG. 5 is a sectional view of an example heat storage system core 500 with intermediate fluid extraction, according to aspects of the present disclosure. The energy storage system 500 may be the same or similar to the system 300 described above and shown in FIGS. 3A-3C, where like reference numbers correspond to like components. In contrast to known thermocline systems, like that shown in FIG. 4, the energy storage system 500, with the addition of alternating layers of firebrick with fluid flow (e.g., flow-through firebrick layers 308) and insulating firebrick layers (e.g., insulating firebrick layers 304), the fluid may follow an S-curve flow path (e.g., serpentine) from top (322) to bottom (318).

[0059] If a buildup of “hot-growing-cold” firebricks occurs in a transition zone (for example at layers 308B, 304C, and 308C), the resulting intermediate temperature fluid may be extracted (320) to compressor B 316. This intermediate temperature fluid may be pumped to the heater 314 heated to a high temperature and returned to the insulated chamber 302. Because the low-conductivity layers (e.g., insulating layers 304) do not allow fluid flow, only the intermediate temperature fluid in that region (e.g., the fluid flowing through the horizontal channels 310B and 310C) may be extracted. In one aspect, multiple outlet ports may be provided on the side of the insulated chamber 302 to pull only the desired intermediate temperature fluid from the system to be reheated.

[0060] According to one aspect, the system 500 may provide additional benefits as charging the firebrick can eliminate substantially all of the hot-to-cold cold transition zone (e.g., flow-through layers 308B, 308C). The system 500 may therefore maximize the amount of firebrick at the maximum temperature storing only high-temperature heat. According to one aspect, the extraction of intermediate temperature fluid may be implemented independently and separately, as a secondary benefit, to system operations as described in connection with the systems of FIGS. 3A-B. If using electrically conductive firebrick in the heat storage system (FIG 3C), the external heater 314 may be eliminated in system 500.

[0061] FIG. 6 is a flow diagram of an example method 600 of storing thermal energy, according to one or more aspects of the present disclosure. As shown in block 602, a plurality of insulating firebrick layers may be provided. The insulating firebrick layers may be disposed horizontally in a fluidically-sealed (e.g., air-tight) insulated chamber. In one aspect, each insulating firebrick layer may include a plurality of insulating (e.g., low thermal conductivity) firebricks. Each insulating firebrick layer may further define one or more vertical flow-through channels.

[0062] Shown in block 604, a plurality of flow-through firebrick layers may be alternatingly disposed between the plurality of insulating firebrick layers. Each of the flow-through firebrick layers may include a plurality of thermally conductive firebricks that define a horizontal channel. As described herein, the thermally conductive firebricks may include traditional firebricks (e.g., fireclay) or may include electrically conductive firebricks. As shown in block 606, the plurality of flow-through firebrick layers and the vertical flow-through channels may define a flow path, for example a serpentine flow path, from a first side of the insulated chamber to a second side of the insulated chamber. In one aspect, the first side may be a top of the insulated chamber and the second side may be a bottom of the insulated chamber. In another aspect, first side may be a bottom of the insulated chamber and the second side may be a top of the insulated chamber.

[0063] As shown in block 608 a fluid, such as air or other gas, may be supplied to the insulated chamber. In one aspect, the energy storage system may be in one of a discharge mode or a charging mode, shown in block 610. If, as shown in block 612, the system is in a discharge mode, and the thermally conductive firebricks are already heated, the fluid may flow through the serpentine flow path where it is heated as it flows from bottom to top of the insulated chamber.

[0064] If the system is in a charge mode and the thermally conductive firebricks are not heated, the system may be charged according to at least one of two heating strategies, depending on the makeup of thermally conductive firebricks. In a first strategy, as shown in block 614, in which traditional firebricks may be used, externally heated fluid may flow through the insulated chamber, from top to bottom, transferring heat from the fluid to the conductive firebricks as it flows through the serpentine flow path. The externally heated fluid may be supplied by an electric heater, including additional electrically conductivefirebricks, or other heating sources. Fluid exiting the insulted chamber may be pumped by a compressor back to the heater to reheat the fluid and reintroduce the fluid to the chamber.

[0065] In a second heating strategy, as shown in block 616, if the flow-through firebrick layers include electrically conductive firebricks, the firebricks may be directly heated using an applied current. The electrical current supplied to the firebricks may be converted to thermal energy that may be stored in the electrically conductive firebricks.

[0066] According to one aspect, when in charge mode, the system may additionally extract fluid at an intermediate temperature from one or more middle flow-through layers. The intermediate temperature fluid may be taken by a compressor and sent to the heater to reintroduce the fluid at a high temperature to the insulated chamber.

[0067] As described herein, the exemplary energy storage systems may include a number of firebrick layers, alternating between insulating (low thermal conductivity) firebricks with thermally conductive firebricks having flow-through channels defined therethrough. One skilled in the art will recognize that the numbers of layers are not limited to the example systems described herein. According to one aspect, the number of low and high conductivity firebrick layers and their thicknesses may be optimized depending on the charge and discharge schedule as well as the total system heat storage capacity.

[0068] According to one or more aspects, low-cost, high-temperature storage may be enabled by very large systems that are tens of meters tall with multiple horizontal layers of solid low-conductivity firebrick that limit heat transfer in the vertical direction. Large systems may minimize the total external surface area per unit volume for conductive heat transfer through the external insulation. In one aspect, surface area may increase by the square of the dimensions, while heat storage volume increases by the cube of the dimensions. In one aspect, industrial systems implementing aspects of the energy storage systems described herein may have storage capacities measured in gigawatt hours. Smallsystems with short distances between hot and cold zones may not be capable of storing high-temperature heat for long periods of time.

[0069] According to one aspect, the thermal conductivity of insulative firebrick (e.g., ~0.4 w / mK) may be more than an order of magnitude less than firebrick used to store heat. In one aspect, a solid layer may stop radiative heat transfer. The density of insulative firebrick, and thus the volumetric heat capacity, may be one-fourth or less of firebrick used for heat storage, in one aspect. Considering, for example, a system whereby 20% volume is insulative firebrick, 10% fluid flow channels and 70% heat-storage firebrick (e.g., electrically conductive), the insulative firebrick may be less than 10% of the heat storage capacity.

[0070] Known firebrick recuperators have storage capacities of 0.5 to 1 MWh / m3and daily heat losses of 1 to 3%. Large hot-to-cold temperature swings increase heat storage per unit volume. Reducing heat losses requires internal structures to reduce heat transfer from hot to cold zones and thicker external insulation. The internal structure of the energy storage systems described herein may also minimize heat losses out of the bottom of the system when operating at lower temperatures.

[0071] According to one aspect, higher density firebrick may have greater heat capacity and higher thermal conductivity. For the horizontal fluid flow channels, the energy storage system may use higher-density firebrick to maximize heat storage per unit volume.However, for the solid horizontal insulation layers, the system may use lower thermal conductivity to slow heat transfer in the vertical direction. Such a configuration may be viable because this system may be designed for long-duration storage where the rate of heat removal out of the system is small relative to the heat storage capacity. Industrial firebrick recuperators typically store heat for at most a few hours and thus have large fluid flow channels and designs that enable rapid heat transfer. The energy storage systems describedherein may have very large quantities of stored heat relative to rate of charging or discharging heat storage. This difference may enable the system to use relatively small fluid flow channels. Accordingly, any piece of firebrick may heat up and cool down at a slow rate.

[0072] According to another aspect, in the systems described herein, inefficiencies (e.g., entropy generation) may be minimized by the counter-current flow of the fluid through the firebrick. The hottest heating fluid may be in the top and travel and downward. Heat may be removed by reversing air or other fluid flow.

[0073] The heat storage system and other embodiments described herein can provide heat to all types of heat users and heat-related applications (e.g., an industrial application, commercial application, residential application, transportation application, etc.). Some of these applications may relate to electricity production, but other applications may relate to other purposes that require heat that are unrelated to electricity production. Thus, while one or more aspects may serve in some cases as an effective replacement for a battery, other aspects may be used in various other contexts such as for providing heat for virtually any purpose.

[0074] Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the claimed subject matter. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. The same applies to the term “implementation.”

[0075] To the extent directional terms are used in the specification and claims (e.g., upper, lower, top, bottom, parallel, perpendicular, etc.), these terms are merely intended toassist in describing various embodiments and are not intended to limit the claims in any way. Such terms do not require exactness (e.g., exact perpendicularity or exact parallelism, etc.), but instead it is intended that normal tolerances and ranges apply. Similarly, unless explicitly stated otherwise, each numerical value and range should be interpreted as being approximate as if the word “about”, “substantially” or “approximately” preceded the value of the value or range. Unless otherwise specified, the terms “about”, “substantially” or “approximately” refer to values that are within ±10%. For example, a first amount that is “substantially” the same as a second value may refer to a first value that is within ±10% of the second value.

[0076] Also, for purposes of this description, the terms “couple,” “coupling,” “coupled,” “connect,” “connecting,” or “connected” refer to any manner in which energy is transferred between two or more elements.

[0077] It should be understood that the steps of the illustrative methods set forth herein are not necessarily required to be performed in the order described. Likewise, additional steps may be included in such methods, and certain steps may be omitted or combined, in methods consistent with various embodiments.

[0078] It will be further understood that various changes in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain the nature of the described embodiments might be made by those skilled in the art without departing from the scope of the following claims.

Claims

CLAIMSWe claim:

1. A thermal energy storage system comprising:an insulated chamber;a plurality of insulating firebrick layers disposed horizontally in the insulated chamber, each insulating firebrick layer including a plurality of insulating firebricks, each insulating firebrick layer further defining a vertical flow-through channel; and a plurality of flow-through firebrick layers alternatingly disposed between the plurality of insulating firebrick layers, each flow-through firebrick layer including a plurality of conductive firebricks defining a horizontal channel;wherein the plurality of flow-through firebrick layers and the vertical flow-through channels define a flow path from a first side of the insulated chamber to a second side of the insulated chamber.

2. The thermal energy storage system of claim 1 wherein each vertical flow-through channel is defined at an opposite end from a previous insulating layer.

3. The thermal energy storage system of claim 1, wherein the flow path comprises a serpentine flow path through the insulated chamber.

4. The thermal energy storage system of claim 1 wherein the first side of the insulated chamber is a bottom side and the second side of the insulated chamber is a top side.

5. The thermal energy storage system of claim 4 wherein the flow path is a discharge flow path.

6. The thermal energy storage system of claim 1 wherein the first side of the insulated chamber is a top side and the second side of the insulated chamber is a bottom side.

7. The thermal energy storage system of claim 6 wherein the flow path is a charging flow path.

8. The thermal energy storage system of claim 1 further comprising at least one compressor and an electric heater disposed in an external flow path between the first side and the second side of the insulated chamber.

9. The thermal energy storage system of claim 8 further comprising:a first compressor in fluid communication with one or more first exit ports of the insulated chamber and the electric heater; anda second compressor in fluid communication with one or more second exit ports of the insulated chamber and the electric heater.

10. The thermal energy storage system of claim 9, wherein the one or more second exit ports are disposed in a transition zone defined by one or more flow-through firebrick layers.

11. The thermal energy storage system of claim 10, wherein the transition zone is defined by one or more middle flow-through firebrick layers.

12. The thermal energy storage system of claim 1 wherein the plurality of conductive firebrick comprises electrically conductive firebricks configured to be heated by an electrical current.

13. The thermal energy storage system of claim 12 wherein the electrical current is supplied at a time of reduced electricity cost.

14. The thermal energy storage system of claim 13 wherein the electrical current supplied at the time of reduced electricity cost is selectively chosen from at least one of a solar energy source and a wind-powered energy source.

15. The thermal energy storage system of claim 1 wherein the flow path is over 100 meters.

16. A method of storing thermal energy comprising:providing a plurality of insulating firebrick layers disposed horizontally in an insulated chamber, each insulating firebrick layer including a plurality of insulating firebricks, providing a plurality of flow-through firebrick layers alternatingly disposed between the plurality of insulating firebrick layers, each flow-through firebrick layer including a plurality of conductive firebricks;defining a flow path through the plurality of flow-through firebrick layers and around the plurality of insulating firebrick layers from a first side of the insulated chamber to a second side of the insulated chamber;supplying a fluid at a first temperature to an inlet port at the first side of the insulated chamber; andextracting the fluid at a second temperature at an outlet port at the second side of the insulated chamber.

17. The method of claim 16 wherein the first temperature is lower than the second temperature and the fluid is heated as it flows through the flow path.

18. The method of claim 16 wherein the first temperature is higher than the second temperature and the conductive firebricks are heated by the fluid.

19. The method of claim 16 further comprising supplying an electrical current to heat the plurality of conductive firebricks, wherein the plurality of conductive firebricks includes electrically conductive firebricks.

20. A thermal energy storage system comprising:an insulated chamber;a plurality of insulating firebrick layers disposed horizontally in the insulated chamber, each insulating firebrick layer including a plurality of insulating firebricks, each insulating firebrick layer further defining a vertical channel at an opposite end from a previous insulating layer; anda plurality of flow-through firebrick layers alternatingly disposed between the plurality of insulating firebrick layers, each flow-through firebrick layer including a plurality of thermally conductive firebricks defining a horizontal channel;wherein the plurality of flow-through firebrick layers and the vertical channels define a serpentine flow path from a first side of the insulated chamber to a second side of the insulated chamber.

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