EP2780555A1 - Thermal energy storage system - Google Patents
Thermal energy storage systemInfo
- Publication number
- EP2780555A1 EP2780555A1 EP12849192.5A EP12849192A EP2780555A1 EP 2780555 A1 EP2780555 A1 EP 2780555A1 EP 12849192 A EP12849192 A EP 12849192A EP 2780555 A1 EP2780555 A1 EP 2780555A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- steam
- energy
- working fluid
- engine
- energy storage
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01K—STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES
- F01K3/00—Plants characterised by the use of steam or heat accumulators, or intermediate steam heaters, therein
- F01K3/12—Plants characterised by the use of steam or heat accumulators, or intermediate steam heaters, therein having two or more accumulators
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01K—STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES
- F01K3/00—Plants characterised by the use of steam or heat accumulators, or intermediate steam heaters, therein
- F01K3/006—Accumulators and steam compressors
Definitions
- the present invention relates generally to thermal energy storage systems. More particularly, it relates to systems that store thermal energy making use of a phase change such as liquid water / steam.
- the turbine When demand for power is low, and there is an excess of supply from other power sources at low cost, the turbine can be reversed to pump water from the lower reservoir to the upper reservoir, thereby storing energy as gravitational potential energy. At a later time, when the demand for power is higher, the water stored in the upper reservoir can be used to drive the turbine to generate electrical power.
- Other medium and large scale energy storage systems have utilized mechanisms such as thermal energy, compressed air, flywheels, electrical capacitors and chemical energy as the energy storage mechanisms. Although such conventional energy storage systems have a number of benefits, there are continuing efforts to develop cost effective energy storage systems having relatively high round trip energy recovery efficiencies. Such devices can make it practical to acquire or purchase electricity and store the associated energy when energy availability is higher than demand and its price and/or value is low, and to retrieve and utilize or sell such energy when energy availability is less than demand and its price and/or value is high.
- the "hot” thermal reservoir is arranged to hold a working fluid in both a liquid phase and a saturated vapor phase state.
- the “cold” thermal reservoir is arranged to hold the working fluid in a second state having a lower temperature than the working fluid in the hot thermal reservoir.
- a heat engine/heat pump unit is arranged to: (a) extract energy from working fluid passing from the hot reservoir to the cold reservoir via expansion of the working fluid in a manner that generates mechanical energy to facilitate retrieval of energy from the energy storage and retrieval system; and (b) compress working fluid passing from the cold thermal reservoir to the hot thermal reservoir to facilitate the storage of energy in the energy storage and retrieval system.
- water is used as the working fluid.
- the heat engine/heat pump unit may take the form of a steam engine.
- the heat engine/heat pump may take the form of a reversible heat engine that can act as both an expander and a compressor or separate devices may be used as the expander and compressor.
- a reversible positive displacement heat engine e.g. a piston steam engine
- the heat engine includes adjustable valves and a controller arranged to vary the timing of the opening and closing of the valves relative to a crankshaft angle.
- an electric motor/generator unit may be mechanically coupled to the heat engine/heat pump unit.
- the electric motor/generator is arranged to drive the heat engine/heat pump unit during the compression of working fluid and to generate electricity during the expansion of the working fluid.
- the electric motor/generator may be implemented as a single reversible unit or as separate motor and generator devices.
- the hot and cold reservoirs may take the form of pressure vessels or unpressurized reservoirs.
- a sub-atmospheric pressure chamber may be provided to facilitate sub-atmospheric flashing of working fluid to vapor (e.g., liquid water to steam) and/or sub-atmospheric condensation of vapor to a liquid.
- working fluid in the hot reservoir may be stored at a pressure substantially above ambient atmospheric pressure.
- the cold store may be replaced by the combination of a condenser arranged to condense steam and a separate low temperature thermal energy source arranged to provide steam having a lower temperature than the hot reservoir.
- FIG. 1 is a schematic diagram of a heat engine/heat pump based energy storage and retrieval system in accordance with one embodiment of the invention.
- FIG. 2(a) is a schematic diagram of an energy storage and retrieval system having a pressurized hot reservoir and an unpressurized cold reservoir with a sub- atmospheric pressure flashing chamber operating in an energy storage mode.
- FIG. 2(b) is a schematic diagram of the energy storage system of Fig. 2(a) operating in an energy retrieval mode.
- FIG. 3 is a schematic diagram of an energy storage and retrieval system having unpressurized hot and cold reservoirs.
- FIG. 4 is a schematic diagram of an energy storage and retrieval system having pressurized hot and cold reservoirs.
- FIG. 5 is a schematic diagram of an energy storage and retrieval system having a low temperature source and a separate low temperature sink.
- thermo energy based energy storage and retrieval systems utilize a working fluid having a substantial heat capacity and make use of a phase change to help improve the storage capacity of the system (e.g. a liquid water/steam phase change).
- the storage system 100 includes a "hot" thermal reservoir 105 and a "cold” thermal reservoir 110.
- a heat engine/heat pump 120 is used to convey a working fluid between the two thermal reservoirs 105 and 110.
- the heat engine/heat pump 120 is coupled to a generator/motor 130 which in turn is coupled to an electric source and the electric load as appropriate.
- electricity from an electrical source powers motor 130 which in turn drives heat pump 120.
- the heat pump compresses a vapor form of the working fluid drawn from the cold thermal reservoir 110 which inherently heats the working fluid as well. The compressed working fluid is then stored in the hot thermal reservoir 105.
- the heat engine/heat pump 120 When operating system 100 in a manner that retrieves energy, the heat engine/heat pump 120 is operated in a heat engine mode.
- the heat engine 120 drives generator 130 which in turn generates electricity which can be used to power an electrical load, delivered to the power grid, or utilized in any other desired manner.
- generator 130 which in turn generates electricity which can be used to power an electrical load, delivered to the power grid, or utilized in any other desired manner.
- mechanical energy such as a rotating shaft driven by a wind turbine or other device
- the hot thermal reservoir 105 holds working fluid at a higher temperature than the cold thermal reservoir 110 although the actual temperatures of the reservoirs may vary widely.
- the labels "hot” and “cold” are merely intended to indicate the relative temperatures of the reservoirs as opposed to the specific temperatures of the working fluid within the reservoirs or their temperatures relative to ambient temperatures or any specific reference temperature.
- the thermal reservoirs 105 and 110 may take a wide variety of forms and may store either pressurized or unpressurized working fluid.
- steam is used as the working fluid within the heat engine/heat pump 120 and therefore water/steam is stored in the thermal reservoirs 105 and 110.
- water/steam is stored in the thermal reservoirs 105 and 110.
- other working fluids could be used in place of water.
- various water based mixtures e.g., water/ammonia mixtures
- fluorocarbons e.g., ammonia
- hydrocarbons and other refrigerants and/or mixtures that include any of these fluids can be used in alternative embodiments.
- Figs. 2(a) and 2(b) schematically illustrate the operation of one suitable configuration of system 100.
- the cold thermal reservoir 110 also referred to as a "cold store” holds unpressurized water
- hot thermal reservoir 105 hot store
- Fig. 2(a) schematically illustrates the operation of an energy storage system in an energy storage mode
- Fig. 2(b) illustrates the operation of the system in an energy retrieval mode.
- steam is drawn from the cold store 110 and compressed by heat pump 120(a).
- the pressurized steam is injected into the hot store 105 where it is condensed by its contact with water within the hot store.
- the introduction and condensation of the compressed steam has the effect of warming the hot store thereby facilitating the storage of thermal energy.
- an adiabatic compression of a gas e.g. steam
- the compressed steam will generally be much warmer than the steam from the cold store 110 that served as the source for the heat pump 120(a).
- the hot store 105 Since the hot store 105 is pressurized, there will inherently be both saturated steam and pressurized water within the hot store. Although there may be some temperature stratification within the reservoir, there will generally be a thermodynamic equilibrium between the saturated steam and the liquid water at the liquid/vapor boundary (i.e., the water surface). As compressed steam is introduced to the hot store, both the temperature and the pressure of the hot store will increase while generally maintaining a thermodynamic equilibrium at the liquid/vapor boundary. To help reduce temperature stratification within the hot store, it is often desirable to inject the steam near the bottom of the hot store as illustrated in Fig. 2(a) so that the injected steam will contact the liquid water as it rises through the reservoir, thereby facilitating condensation of the injected steam. Although the illustrated injection of incoming steam into the liquid water works well to facilitate condensation and reduce temperature stratification, it is not required as other mechanisms can be used to accomplish the same function(s).
- the temperature of the water and steam within the hot store would be about 207°C. Since such pressure vessels are commercially available at relatively low costs, it may be desirable to design a system such that the maximum operational pressure of the hot store 105 is in that range. However, that is by no means a requirement and the maximum operational pressure of the hot store may be widely varied to meet the needs of any particular application.
- the cold store 110 serves as a source of steam for the heat pump 120(a).
- the cold store 110 is unpressurized.
- a column 112 is provided to facilitate sub- atmospheric flashing (boiling) of steam.
- water boils at a temperature of about 100°C at normal atmospheric pressures. However, at lower pressures, water will flash (boil) into steam at lower temperatures (and of course water boils at higher temperatures at higher pressures).
- water will boil at a temperature of about 46°C
- water will boil at a temperature of about 33°C
- water will boil at a pressure of 0.02 bar absolute
- water will boil at a temperature of about 17.5°C. This property of water can be used to generate steam at temperatures well below 100°C even when the water within an associated store is unpressurized.
- a flashing column 112 is provided in conjunction with the cold thermal reservoir.
- the flashing column 112 opens at a level below the waterline within the cold thermal reservoir 110 and extends above the surface of the water within the reservoir 110.
- a vacuum relative to ambient pressure
- the column When air is evacuated from the column, a vacuum (relative to ambient pressure) is generated within the column, which has the effect of drawing the surface of the water within the column to a higher level than the surrounding water at ambient pressure. If the height of the column is sufficient and the evacuation of air complete, some of the water within the column will flash (boil) such that saturated steam fills the column above the waterline.
- the chamber formed by the portion of the column above the waterline is sometimes referred to herein as a flashing chamber 113.
- the saturated steam within the flashing chamber will equalize to a temperature and pressure that is in equilibrium with the water at the water surface within the column 112. Therefore, like in the hot store 105, the temperature and pressure of the steam within flashing chamber 113 will vary as a function of the temperature of the adjacent water.
- the actual height of the flashing column 112 may be widely varied based on the design goals of any particular thermal storage system, but when steam is used as the working fluid, column heights of at least about 9.4 meters are generally preferred to generate the desired sub-atmospheric steam pressures within the flashing chamber 113.
- the actual design of the column may be widely varied in order to meet the needs of any application. Typically, it will be important to provide sufficient water surface area within the flashing chamber(s) to ensure that steam can be generated at a rate high enough to supply the heat pump 120(b) at the desired flow rates. In some applications it will also be desirable to provide a mechanism for circulating water around the cold thermal reservoir 110 and the flashing column 112. This mixing of the water helps reduce the risk of temperature stratification within the flashing column 112.
- the water at the flashing surface will cool relatively quickly and thermosiphoning alone may not be sufficient to maintain the temperature of the water at the flashing surface at close to the same temperature as the main body of water within the cold store 110 - especially if the diameter or width of the column (and thus the flashing surface area) is small relative to the column height. It is generally undesirable for water at the surface of the flashing chamber to be at a temperature that is significantly below the temperature of underlying body of water since that would cause a reduction in the temperature and pressure of the steam being supplied to the heat pump 120(b) which would reduce the overall efficiency of the system.
- a variety of mechanism can be used to enhance circulate of the water within the cold store and flashing chamber.
- impellers, propellers and other mixing devices can be appropriately positioned within the cold store (e.g. in the column 112) and used to enhance circulation and mixing.
- two or more columns may be used to enhance circulation.
- Fig. 2(b) operation of the energy storage system 100 in an energy retrieval mode will be described.
- steam is drawn from the hot store 105 and passed through steam engine 120(b) as illustrated in Fig. 2(b).
- the steam engine expands the steam extracting energy from the steam in a manner that produces useful mechanical work such as the rotation of a drive shaft.
- the drive shaft can then be used in any desired manner, as for example, to power a generator 130(b) that generates electricity, to drive a pump or to drive other machinery.
- the steam supplied to the steam engine 120(b) is typically drawn from a location near the top of the hot store, although this is not a requirement.
- the adiabatic expansion of a gas will cause the temperature of the gas to drop significantly during the expansion process.
- the expanded steam exhausted by the steam engine 120(b) will be substantially cooler than the input steam and may be returned to the cold store 110.
- flashing chamber 113 when steam is delivered to the flashing chamber 113, the pressure within the flashing chamber increases, which causes some of the steam within chamber 113 to condense to bring the chamber 113 back into equilibrium.
- flashing chamber 113 effectively acts as a sub- atmospheric condensation chamber. The condensation of some of the steam back into liquid water adds heat to the cold store thereby effectively warming the surrounding water. Therefore, as steam is introduced to the flashing chamber 113, the temperature of the water within the cold thermal reservoir 110 will gradually rise.
- One way to enhance condensation within the chamber 113 is to spray water droplets into the chamber as steam is introduced to the chamber.
- the water droplets enhance condensation of the steam since steams tends to condense on the droplets.
- Such spraying can be accomplished by a sprayer 114 which draws water from the cold store and sprays a shower of water from the top (or near the top) of the column, thereby effectively creating a shower of water within the condensation chamber 113.
- a simple pump may be used to draw water from any suitable location in the cold store and spray it into the condensation chamber to thereby enhance condensation.
- Other conventional condensation enhancing mechanisms such as drip trays and Raschig rings, trays or other structures arranged to enhance the exposed surface area of water (not shown) can be used as well.
- the described energy storage and retrieval system 100 is well suited to facilitate thermal storage of energy.
- excess electrical or mechanical energy can be used to drive the heat pump 120(a) in a manner that compresses and heats working fluid (e.g. steam) drawn from the cold thermal reservoir 110 for storage in the hot thermal reservoir 105.
- working fluid e.g. steam
- hot, high pressure steam is drawn from the hot store and expanded in heat engine 120(b) to extract useful work from the steam that can be used to generate electricity or for any other desired purposes.
- the Round Trip Efficiency of the energy storage can be 100%. That is, the amount of useful energy that could be retrieved from the system would theoretically be the same as the amount of energy used to drive the system.
- round trip storage/retrieval efficiency is not possible in a practical system, however even when the electricity is used to power the system and electricity is the form of the power ultimately output by the system, round trip storage/retrieval efficiencies on the order of 60-80% are believed to be readily obtainable using existing technology (e.g., using a positive displacement steam engine/compressor in conjunction with a motor/generator as described in more detail below) and even higher round trip efficiencies may be possible. Higher efficiencies are also possible in systems that would directly supply and/or utilize the mechanical power that drives and/or is output by the heat engine/heat pump since any inefficiencies of the motor/generator 130 would be eliminated. As will be apparent to those familiar with grid scale energy storage applications, there are a number of applications where round trip storage and retrieval efficiencies in the 60-80% range are economically viable.
- the hot thermal reservoir 105 is pressurized, whereas the cold thermal reservoir is not.
- both reservoirs may utilize either pressurized or unpressurized reservoirs.
- Fig. 3 illustrates an arrangement in which both the hot store 105(a) and the cold store 110(a) are unpressurized vessels containing a quantity of water and space for humid air.
- the hot store 105(a) also includes a mechanism (e.g. column 107) that facilitates the generation of steam at sub-atmospheric pressures like the steam generating column 112 described above with respect to Fig. 2.
- the cold store may operate in the same fashion as described above with respect to Fig. 2.
- both the hot and cold stores have mechanisms for generating steam at sub-atmospheric pressures.
- An advantage of the type of system illustrated in Fig. 3 is that the cost of an unpressurized water vessel is potentially much cheaper than the cost of pressurized vessel which can help reduce overall system costs.
- a disadvantage is that the temperature and pressure difference between the hot and cold stores will be substantially less in the configuration of Fig. 3. With a smaller temperature/pressure differential the volume of steam that must pass through the heat engine/heat pump 120 is much larger for a given system energy storage capacity. Thus a substantially larger heat engine/heat pump and larger thermal reservoirs would typically be required, both of which involve additional expense.
- Which configuration is more-cost effective in any particular implementation will be a function of the relative costs of the various components, the available space, etc.
- both the hot store 105(b) and the cold store 110(b) are pressure vessels.
- the hot store 105(b) works in the same manner described above with respect to the pressurized hot store 105 of Fig. 2.
- the cold store 110(b) operates in a generally similar manner, but there is typically no longer a need for a separate flashing column.
- steam for the heat pump can be drawn from the steam chamber region 111 of the cold store 110(b) and during the retrieval of energy, steam exhausted from the steam engine can be directed back into the steam chamber region 111.
- thermal reservoirs 105 and 110 may be widely varied within the scope of the invention. In practice, many tanks and vessels have a circular cross section although this is not required. In a pressurized hot stores, it is often preferable to orient the tank(s) in a generally horizontal manner as illustrated in Figs 2-4 (i.e., such that their length is greater than their height). This can be desirable because it gives more water surface area, which enhances transitions between the gas and liquid phases of the water.
- the horizontal orientation also potentially reduces the pressure differential between the top and bottom of the tank, which can be useful when steam is injected into liquid water near the bottom of a tank, as illustrated for example, in Fig. 2(a).
- the pressure within the water column will increase with depth such that there is a higher pressure at the bottom of the tank than the pressure within the steam chamber at the top of the tank.
- injecting steam lower in the tank within the water column requires the input steam to be compressed more than if the steam is injected into the steam chamber region 111 above the waterline.
- Over- compression has the drawback of reducing the overall Round Trip Efficiency of the system and therefore an advantage of using shallower broader tanks is that less over- compression is needed it inject steam near the bottom of a shallower tank.
- the compressed steam can be introduced into the steam chamber region 111 and other mechanisms can be used as necessary to insure good condensation of the steam and to minimize thermal stratification within the tank.
- the tank When a sealed tank is used as the cold store, the tank should be capable of withstanding the vacuum pressure of the flashing chamber (e.g., up to 1 atmosphere of negative pressure). In some applications, the use of such vacuum pressure resistant tanks may be more cost effective than providing a non-pressurized tank with a flashing column 112.
- cylindrical tanks having a height of at least 10 meters (as for example 12 meters to match shipping container length) work well for many applications.
- thermal reservoirs are described primarily in the context of various tanks and pressure vessels. Although tanks and pressure vessels work quite well, it should be appreciated that a wide variety of different structures can be used as the thermal reservoirs when appropriate.
- a lake, pond or other defined body of water could be used as an unpressurized thermal reservoir - and particularly as the cold store.
- the use of such bodies of water may have several potential advantageous. For example, if the total mass of water in a lake or pond it very substantially more than is used by the energy storage system, then the overall temperature of a lake used as a cold reservoir may not fluctuate significantly through the course of an energy storage and retrieval cycle. A cold store that maintains a relatively constant temperature tends to facilitate more efficient storage.
- cisterns and various in-ground containments can be used as one or both of the thermal reservoirs.
- each of the thermal reservoirs takes the form of a single containment.
- either or both of the reservoirs may be formed from any number of individual containment structures. Indeed, in some applications, modular containments may be preferable. For example, in one specific application a number of modular tanks each sized to fit within a shipping container may be used to form one of the thermal reservoirs (e.g., a cold store).
- FIG. 5 yet another alternative energy storage system configuration will be described.
- the functionality of the cold store 110 described in the previous embodiments is effectively divided into two separate components, a low temperature sink 175 and a low temperature energy source 185.
- This type of configuration can be advantageous when there is an available source of heat, such as waste heat from an industrial process or a thermal power plant.
- the system may be substantially the same as any of the previously described embodiments.
- the hot store 105(c) is an insulated pressure vessel containing water and a saturated steam space that operates as described above.
- the low temperature energy source may take the form of an unpressurized water vessel heated by any suitable heat source.
- the low temperature sink 175 is a condenser cooled by an available heat sink.
- the heat sink may take any suitable form and the most appropriate heat sink may vary by location. By way of example, a stream or other body of water, evaporative coolers, fin- fan coolers or a variety of other heat exchangers may be used to cool the condenser.
- the low temperature energy source 185 is maintained at a temperature that is higher than the sink 175.
- water in the low temperature energy source 185 is flashed into steam as previously discussed with respect to the cold store 110.
- a column or other suitable vessel structure may be used to facilitate sub-atmospheric flashing of the steam.
- the temperature of the water and thus the saturated steam supplied by the source 185 is generally higher than it would be if a cold store was used. Since the temperature of the water is higher, the pressure of the steam input to the heat pump 120(a) is higher which means that less energy is required to compress the steam for storage in the hot store 105.
- the steam engine 120(b) When retrieving energy, the steam engine 120(b) exhausts steam into the low temperature sink 175 (as opposed to the source 185).
- the sink 175 condenses the steam and is cooled by the available heat sink.
- the sink 175 includes a sub-atmospheric condenser 177 that facilitates condensation of the exhaust steam at sub-atmospheric pressures.
- the temperature of the sink 175 is cooler than the temperature of the source 185. Since the temperature of water within the sink's condensation chamber is lower than the temperature of the source, the pressure within the condenser 177 (and thus the pressure at which condensation occurs) is lower as well. Therefore, steam can be exhausted from the steam engine 120(b) at a lower pressure than it could if the steam was returned to source 185. This allows the steam engine to extract more energy from the expansion of the steam, thereby improving the efficiency of the storage and retrieval system.
- condensate from the condenser in sink 175 can be recirculated to low temperature heat source 185 where it is heated before being used to generate steam.
- An advantage of such recirculation is that it potentially reduces the system's overall consumption of water.
- waste heat there are a number of industrial and power generation processes that generate waste heat which could be utilized in the type of system illustrated in Fig. 5. If such waste heat is carried by water, such water can potentially be stored directly in the low temperature heat source 185. Alternatively, one or more appropriate heat exchangers may be used to warm the water stored in the source 185.
- the size of the reservoirs that are suitable for use as the hot and cold thermal reservoirs 105, 110 can vary with the desired energy storage capacity of the system, the pressure ratings of the vessels, tanks or other structures used as the reservoirs and/or flashing columns, the operating temperatures ranges (which may be dictated in part by the permissible operating pressure ranges), etc.
- a system designed to deliver 1 Megawatt (MW) of power for 10 hours (and thus has over 10MW hours of storage capacity) could be implemented using a 170,000 gallon hot store that can be pressurized to about 17 bar (about 250 psi) and a 500,000 gallon unpressurized cold store.
- the cold store has about 3 times the volume of the cold store.
- the actual relative volumes of the hot and cold store may vary widely and that the relative prices of the vessels that are available for use as the thermal reservoirs may strongly influence the ultimate reservoir sizes selected for any particular power storage capacity.
- the size of the hot store can generally be reduced if the vessel used as the hot store can withstand higher operating temperatures and pressures. Conversely, the size of the hot store will have to increase if the vessel used can only withstand lower operating temperatures and pressures or if the hot store is unpressurized. Furthermore, it should be appreciated that the volume of the cold reservoir can significantly affect the required volume of the hot reservoir as well. More specifically, as indicated above, during operation in the energy storage mode, thermal energy is withdrawn from the cold store 110 thereby cooling the cold store and thermal energy is added to the hot store 105 thereby heating the hot store. Thus, the temperatures of the thermal reservoirs will diverge during energy storage.
- thermal energy is withdrawn from the hot store 105 thereby cooling the hot store and thermal energy is added to the cold store 110 thereby heating the cold store.
- thermal energy is added to the cold store 110 thereby heating the cold store.
- the temperature of a cold store that is the same size as the hot store will vary significantly more than the temperature of a cold store that has three times (3X) the volume of the hot store.
- 3X three times
- a system that has a 3X cold store will have the ability to extract more energy than a system with a cold store that is the same size as the hot store.
- a still larger cold store e.g. a 10X cold store
- a relatively large body of water such as a lake that has many, many times the volume of the hot store, then the cold store may stay substantially the same temperature throughout an energy storage and retrieval cycle.
- Either of the hot and cold thermal reservoirs may be implemented as single tank, vessel or reservoir, or may be implemented as multiple tanks, vessels and/or reservoirs.
- a 500,000 gallon hot store could be implemented as seventeen 30,000 gallon pressure vessels which might each be about 40 feet long and 12 feet in diameter.
- the heat engine/heat pump 120 can be implemented in a variety of different manners. Although a variety of heat pumps and heat engines including steam turbines may be used, one class of heat engines that is particularly well suited for use as the heat engine/heat pump 120 are positive displacement piston steam engines.
- piston steam engines have over turbines and other conventional heat pumps and heat engines is their relatively high operating efficiencies over a wide range of inlet and exhaust pressures and temperatures. This is particularly useful in the described energy storage and retrieval systems because it allows the temperatures and pressures of both the hot and cold thermal reservoirs to vary significantly over the course of an energy storage and retrieval cycle without drastically reducing the system's round trip energy storage and retrieval efficiency.
- piston steam engines can operate relatively efficiently over a range of steam mass flow rates which allows the system to efficiently draw or deliver energy even in the face of variable energy supply and demand.
- This capacity meshes well in applications where the energy available for storage at any given time may vary significantly during the course of a day, such as is inherent in solar and wind farms. It also fits extremely well in applications that have variable demand for energy during retrieval (which are many).
- Many piston steam engines are reversible in that they may be operated as both as a heat engine (expander) and as a heat pump (compressor). This can be advantageous because it allows a single machine to be used as both the heat pump and the heat engine. Although a reversible device is useful in many applications, it is not required. Rather, when desired, separate devices can be used as the heat pump and the heat engine and the heat pumps/heat engines shown in the drawings are intended to represent both approaches. This may be desirable, for example, when separate expanders and compressors are less expensive and/or more efficient than a reversible device. Furthermore, it should be appreciated that more than one steam engine (or other devices) may be used in parallel as the heat engine/heat pump in order to deliver the desired throughput.
- piston steam engines are a very mature technology. Indeed, piston steam engines were the dominant source of power well into the 20 th century. Accordingly, there are a number of existing piston steam engine designs that may be used as the heat engine/heat pump. These include single stage steam engines and multi-stage (multiple expansion stages) steam engines, etc. In some specific applications, a single or multi-stage Unaflow, Universal- Unaflow or counter-flow piston steam engine may be used. One such engine has been developed by the Applicant and is based on the Skinner Universal-Unaflow steam engine from the 1930s.
- Unaflow steam engines and Universal-Unaflow steam engines are piston based steam engines that utilize poppet valves to control the introduction of steam into the cylinder that serves as an expansion chamber.
- the timing of the valves has been controlled by a camshaft.
- other known valve timing control mechanisms can be used as well.
- electronic solenoids may be used to open and close the valves which facilitates electronic control the timing of the opening and closing of the valves if desired. Regardless of the mechanism used, there are several advantages to providing a wide range of control over the relative timing of the opening and closing of the valves.
- the compression ratio of the steam engine / heat pump in order to maximize efficiency, it is generally preferable for the compression ratio of the steam engine / heat pump to relatively closely match the pressure ratio between the pressures of the hot and cold stores. Varying the timing of the opening and closing of the intake and exhaust valves is one good way to accurately control the compression ratio of the engine. Varying the intake valve cutoff timing also provides a good mechanism for controlling the mass flow rate of steam through the steam engine which allows good control of the power generated by the steam engine during expansion.
- Adjustable valve timing can also be very useful in facilitating reversible operation of the steam engine such that the steam engine may be operated as either an expander (a traditional steam engine) or as a compressor (heat pump).
- many steam engines, including piston and other positive displacement steam engines may be operated as either an expander or a compressor.
- the primary difference is that in the expander mode, high pressure steam is drawn into the expansion chamber and is used to drive a piston that delivers useful work to a crankshaft, whereas in the compressor mode, an electric motor (or other suitable power source) powers the crankshaft which drives the pistons to compress steam within the chamber (which now acts as a compression chamber instead of an expansion chamber).
- one or more water injectors are provided to spray water into the steam before or during compression so that some of the thermal energy generated during compression is absorbed by vaporization of the injected water.
- the injector(s) may be arranged to inject water directly into each cylinder during compression or they may be arranged to inject the water into the steam prior to its introduction into a compression cylinder. In general it is desirable to keep the compressed steam that exits the steam engine during compression at a state that is close to saturation so that excess superheating does not occur. However, that is not a requirement.
- the desired amount of water to inject will vary as a function of several different factors such as the compression ratio currently in use, the mass flow rate of steam passing through the cylinder(s), the entrance temperature and pressure, etc. Therefore, it is preferable to control the volume of water injected at any given time based on the operating state of the engine so that a point close to saturation can be achieved in the compressed steam exiting the steam engine. If more than one compression stage is used, then water injection may be desired for each compression stage, although again, this is not a requirement.
- This can be accomplished through the use of an optional superheater that heats steam drawn from the hot store before it enters the steam engine, and/or an optional reheater that heats steam between sequential stages of the steam engine.
- an optional superheater that heats steam drawn from the hot store before it enters the steam engine
- an optional reheater that heats steam between sequential stages of the steam engine.
- the use of superheaters and/or reheaters is possible, they are often not cost effective unless the heat source(s) used to power the superheaters and/or reheaters are waste heat sources or other very low cost energy sources.
- the hot and cold thermal reservoirs and the specific devices used as the heat pumps and heat engine may be widely varied.
- the hot and cold stores may each be implemented as a single tank or as multiple separate tanks. When multiple tanks are used for one of the stores, the working fluid within the different tanks in the same store may be a substantially the same temperature or at different temperatures.
- one or more reversible heat engine(s)/heat pump(s) may be used as the expander/compressor or separate devices may be used for expansion and compression.
- a reversible motor/generator may be used to drive/be driven by the heat engine/heat pump, or separate motor(s) and generator(s) may be used.
- the described systems are readily scalable and may be used in a variety of different energy storage applications, including grid scale energy storage and retrieval applications.
- a superheater (not shown) may be provided between the hot store 105 and the heat engine to superheat steam before it enters the steam engine 120(b) and/or one or more reheaters (not shown) may be provided to reheat steam at appropriate stage in the expansion process.
- Effective Round Trip Efficiencies of at least 60, 70 and even 80% can be attained using the described approach. Although higher Round Trip Efficiencies are generally desirable, cost considerations may dictate the system design and thus the attainable Round Trip Efficiency. However, systems having 60-80% (or higher) Round Trip Efficiencies are believed to be economically viable in a number of specific applications. [0072]
- the described embodiments should be considered illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Engine Equipment That Uses Special Cycles (AREA)
- Valve Device For Special Equipments (AREA)
Abstract
Description
Claims
Applications Claiming Priority (2)
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US201161559318P | 2011-11-14 | 2011-11-14 | |
PCT/US2012/065120 WO2013074699A1 (en) | 2011-11-14 | 2012-11-14 | Thermal energy storage system |
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EP2780555A1 true EP2780555A1 (en) | 2014-09-24 |
EP2780555A4 EP2780555A4 (en) | 2015-07-22 |
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EP12849192.5A Withdrawn EP2780555A4 (en) | 2011-11-14 | 2012-11-14 | Thermal energy storage system |
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US (1) | US20130118170A1 (en) |
EP (1) | EP2780555A4 (en) |
JP (1) | JP2015503048A (en) |
WO (1) | WO2013074699A1 (en) |
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WO2014052927A1 (en) | 2012-09-27 | 2014-04-03 | Gigawatt Day Storage Systems, Inc. | Systems and methods for energy storage and retrieval |
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DE102013209680A1 (en) | 2013-05-24 | 2014-11-27 | Siemens Aktiengesellschaft | Energy storage arrangement for flexibilization of power plants |
FR3011626B1 (en) | 2013-10-03 | 2016-07-08 | Culti'wh Normands | THERMODYNAMIC SYSTEM FOR STORAGE / ELECTRIC POWER GENERATION |
DE102014202849A1 (en) * | 2014-02-17 | 2015-08-20 | Siemens Aktiengesellschaft | Method and device for loading a thermal stratified storage tank |
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US20180120009A1 (en) * | 2015-05-06 | 2018-05-03 | Trienco Ltd. | System and method for dynamic mechanical power management |
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WO2009044139A2 (en) * | 2007-10-03 | 2009-04-09 | Isentropic Limited | Energy storage |
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WO2010111688A2 (en) * | 2009-03-26 | 2010-09-30 | Solar Storage Company | Intermediate pressure storage system for thermal storage |
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2012
- 2012-11-14 JP JP2014541424A patent/JP2015503048A/en active Pending
- 2012-11-14 EP EP12849192.5A patent/EP2780555A4/en not_active Withdrawn
- 2012-11-14 WO PCT/US2012/065120 patent/WO2013074699A1/en active Application Filing
- 2012-11-14 US US13/677,241 patent/US20130118170A1/en not_active Abandoned
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JP2015503048A (en) | 2015-01-29 |
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