JP2015503048A - Thermal energy storage system - Google Patents

Abstract

Various energy storage and recovery systems are described. In general, “hot” and “cold” heat stores are provided. A “hot” reservoir holds both liquid and saturated vapor phase working fluids. A “cold” reservoir holds the working fluid at a lower temperature than the hot reservoir. The heat engine / heat pump unit (a) extracts energy from the steam traveling from the hot reservoir to the cold reservoir by expansion of the working fluid vapor in a manner that generates mechanical energy to facilitate energy recovery. And (b) compress the vapor traveling from the cold store to the hot store to facilitate energy storage. In some embodiments, the heat engine / heat pump takes the form of a reversible positive displacement heat engine that can act as both an expander and a compressor. In order to facilitate the storage and recovery of electrical energy, an electric motor / generator unit may be mechanically coupled to a heat engine / heat pump unit. [Selection] Figure 1

Description

  The present invention relates generally to thermal energy storage systems. More particularly, the present invention relates to a system for storing thermal energy using phase changes such as liquid water / water vapor.

  There are many situations where it is desirable to store electrical energy in order to resolve the temporal discrepancy between energy supply and demand. For example, the availability of any alternative energy sources, such as solar energy and wind energy, can vary widely throughout the day, and the device (eg photovoltaic concentrator or wind turbine) that collects such energy The output often does not match the demand for electrical energy generated by such devices. Another example of supply and demand discrepancies is embodied in baseline power generation facilities such as nuclear power plants, which are generally designed to produce a substantially stable electrical output, Demand tends to change over time.

  Supply and demand discrepancies may make bulk electrical energy storage desirable and over the years various systems and devices have been proposed and / or used to facilitate the storage and recovery of such electrical energy. ing. One of the most familiar examples of devices designed to store electrical energy is a battery. Batteries tend to work well for relatively small energy storage applications, but tend to be prohibitively expensive in larger energy storage systems. An example of a larger energy storage system used in grid scale electrical energy storage applications is pumped hydropower generation and storage. In a pumped hydropower generation and storage system, power is generated by a turbine that extracts the potential energy of water flowing from the upper reservoir to the lower reservoir. When the demand for power is low and there is surplus 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, energy is stored as gravitational potential energy. Later, when the demand for power becomes higher, the water stored in the upper reservoir can be used to drive the turbine to generate power.

  Other media and large-scale energy storage systems utilize mechanisms such as thermal energy, compressed air, flywheels, condensers, and chemical energy as energy storage mechanisms. While such conventional energy storage systems have several benefits, efforts continue to develop cost effective energy storage systems with relatively high round trip energy recovery efficiency. Such devices acquire or purchase electricity to store related energy when energy availability is higher than demand and energy price and / or value is low, and energy availability is lower than demand. When the price and / or value of energy is high, it can be practical to recover and use or sell such energy.

  Various energy storage and recovery systems are described. In general, “hot” and “cold” heat stores are provided. A “hot” heat reservoir is configured to hold the working fluid in both a liquid phase state and a saturated vapor phase state. The “cold” heat store is configured to hold the working fluid in a second state having a lower temperature than the working fluid in the hot heat store. The heat engine / heat pump unit is: (a) from a high temperature reservoir to a low temperature storage by expansion of working fluid vapor in a manner that generates mechanical energy to facilitate recovery of energy from the energy storage and recovery system. Extracting energy from the working fluid going to (b), and (b) configured to compress the working fluid going from the cold store to the hot store to facilitate storage of energy within the energy storage and recovery system .

  A variety of different materials can be used as the working fluid. In some preferred embodiments, water is used as the working fluid. When water is used as the working fluid, the water passes through the heat engine / heat pump unit as water vapor. In such embodiments, 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. . In some embodiments, a reversible positive displacement heat engine (eg, a piston steam engine) is used as a heat engine / heat pump. As an example, uniflow, universal-uniflow, and counter-flow steam engines work well. In some preferred implementations, the heat engine includes an adjustable valve and a controller that is configured to vary the timing of opening and closing the valve relative to the crankshaft angle.

  In order to facilitate the storage and recovery of electrical energy, an electric motor / generator unit may be mechanically coupled to a heat engine / heat pump unit. The electric motor / generator is configured to drive the heat engine / heat pump unit during compression of the working fluid and to generate electricity during expansion of the working fluid. The electric motor / generator can 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 non-pressurized reservoirs. When a non-pressurized reservoir is used, a sub-atmospheric pressure chamber is provided to provide a sub-atmospheric pressure flush of the working fluid to the vapor (eg, liquid water to water vapor) and / or the vapor to the liquid Atmospheric pressure condensate can be promoted. When the pressurized container is used as a high temperature reservoir, the working fluid in the high temperature reservoir can be stored at a pressure substantially higher than ambient atmospheric pressure.

  In some alternative embodiments, the cold storage device is a condenser configured to condense steam and a separate steam configured to provide steam having a lower temperature than the hot storage. It can be replaced by a combination with a low temperature thermal energy source.

  The invention and its advantages are best understood by referring to the following description, taken in conjunction with the accompanying drawings.

1 is a schematic diagram of a heat engine / heat pump based energy storage and recovery system according to one embodiment of the invention. FIG.

1 is a schematic diagram of an energy storage and recovery system having a pressurized hot storage and a non-pressurized cold storage with a sub-atmospheric pressure flushing chamber operating in an energy storage mode. FIG.

It is the schematic of the energy storage system of Fig.2 (a) which operate | moves in energy recovery mode.

1 is a schematic diagram of an energy storage and recovery system having a non-pressurized hot and cold storage.

1 is a schematic diagram of an energy storage and recovery system having a pressurized hot and cold storage.

1 is a schematic diagram of an energy storage and recovery system having a cold source and another cold sink. FIG.

  In the drawings, the same reference numbers are sometimes used to represent similar structural elements. It should also be understood that the illustrations in the drawings are schematic and are not drawn to scale.

  Several thermal energy based energy storage and recovery systems are described. In general, the storage system described utilizes a working fluid having a substantial heat capacity and utilizes a phase change (eg, liquid water / water vapor phase change) to help improve the storage capacity of the system.

  Referring now to FIG. 1, the basic architecture of a heat engine / heat pump based electrical energy storage and recovery according to one embodiment of the present invention will be described. The storage system 100 includes a “high temperature” heat store 105 and a “cold” heat store 110. A heat engine / heat pump 120 is used to carry working fluid between the two heat stores 105 and 110. In the illustrated embodiment, the heat engine / heat pump 120 is coupled to a generator / motor 130 that is further coupled to a power source and, if appropriate, an electrical load. When operating the system 100 in a manner that stores energy, electricity from the power source powers the motor 130, which drives (activates) the heat pump 120. The heat pump compresses the working fluid in vapor form drawn from the cryogenic heat reservoir 110, which also inherently heats the working fluid. The compressed working fluid is then stored in the high temperature heat reservoir 105.

  When operating system 100 in a manner that recovers energy, heat engine / heat pump 120 is operated in a heat engine mode. The heat engine 120 drives (activates) the generator 130, which generates electricity (electric power) that can be used to power an electrical load and send it to the power grid. Or can be utilized in any other desired manner. Although a system for receiving and delivering electrical energy is illustrated, in alternative embodiments, mechanical energy (such as a rotating shaft driven by a wind turbine or other device) can drive a heat pump, and / or If desired, the mechanical output of the heat engine can be used directly.

  Although the high temperature heat reservoir 105 holds the working fluid at a higher temperature than the low temperature heat reservoir 110, the actual temperature of the reservoir can vary widely. Thus, as used herein, the names “hot” and “cold” are not relative to the specific temperature of the working fluid inside the reservoir, but to the relative temperature of the reservoir, or ambient or any specific reference temperature. It is only intended to indicate the temperature of the reservoir. As will be described in more detail below, heat reservoirs 105 and 110 may take a variety of forms and may store pressurized or non-pressurized working fluid.

  In the described embodiment, steam is used as the working fluid in the heat engine / heat pump 120, and thus water / steam is stored in the heat reservoirs 105 and 110. However, it should be understood that in alternative embodiments, a variety of other working fluids can be used in place of water. By way of example, in alternative embodiments, use various water-based mixtures (eg, water / ammonia mixtures), fluorocarbons, ammonia, hydrocarbons, and refrigerants, and / or mixtures containing any of these fluids. Can do. In general, it is desirable to store the working fluid primarily in the liquid phase so that phase change can be advantageously used to improve the storage capacity of the system.

  To facilitate the description of the operation of the energy storage and recovery system 100, FIGS. 2 (a) and 2 (b) schematically illustrate the operation of one suitable configuration of the system 100. In this embodiment, low temperature heat reservoir 110 (also referred to as “cold storage device”) holds non-pressurized water, while high temperature heat reservoir 105 (also referred to as “high temperature storage device”) holds pressurized water. FIG. 2 (a) schematically illustrates the operation of the energy storage system in the energy storage mode, and FIG. 2 (b) illustrates the operation of the system in the energy recovery mode. In the energy storage mode illustrated in FIG. 2A, water vapor is drawn from the low temperature storage device 110 and compressed by the heat pump 120 (a). Pressurized water vapor is injected into the high temperature storage device 105 where it is condensed by contacting the water inside the high temperature storage device. The introduction and condensate of compressed steam has the effect of warming the high temperature storage device, thereby facilitating the storage of thermal energy. As will be appreciated by those skilled in the art, adiabatic compression of a gas (eg, water vapor) has the effect of significantly warming the gas, so the compressed water vapor is generally supplied to the heat pump 120 (a). It is much hotter than the water vapor from the cold storage device 110 that served as the source.

  Since the high temperature storage device 105 is a pressurized type, saturated water vapor and pressurized water are inherently present inside the high temperature storage device. There may be some thermal stratification inside the reservoir, but generally there is a thermodynamic equilibrium between saturated water vapor and liquid water at the liquid / vapor interface (ie, the water surface). When compressed water vapor is introduced into a high temperature storage device, both the temperature and pressure of the high temperature storage device increase, while generally maintaining thermodynamic equilibrium at the liquid / vapor interface. To help reduce temperature stratification within the high temperature storage device, it is often desirable to inject water vapor from near the bottom of the high temperature storage device, as illustrated in FIG. Contact with liquid water as it rises through the reservoir, thereby facilitating condensate of the injected steam. Illustrated here, the injection of incoming steam into liquid water works well to promote condensate and reduce temperature stratification, but other mechanisms may be used to achieve the same function. This is not mandatory as it can.

  Since the high temperature heat reservoir is a substantially closed system, the actual operating pressure of the high temperature storage device at any given time is highly dependent on the current temperature of the high temperature storage device (ie, higher temperature = higher pressure). As more compressed water vapor is added to the high temperature storage device, both the temperature and pressure of the high temperature storage device continue to rise. However, it is desirable to set some limit on the maximum operating temperature / pressure for high temperature storage devices. In fact, the maximum operating temperature / pressure tends to be dictated by economic constraints, the main constraint being the cost of the container used as the high temperature heat store. Currently, there are several commercially available pressure vessels (tanks) rated at a pressure of about 17 or 18 bar (gauge pressure) (ie, about 17 or 18 atmospheres). At a pressure of 17 bar (gauge pressure) (about 250 psig (gauge pressure)), the temperature of water and water vapor inside the high temperature storage device is about 207 ° C. Since such pressure vessels are commercially available at a relatively low cost, it may be desirable to design the system such that the maximum operating pressure of the high temperature storage device 105 is within that range. However, this is not a requirement at all and the maximum operating pressure of the high temperature storage device can be varied widely to meet the requirements of any particular application.

  As described above, the cold storage device 110 serves as a water vapor source for the heat pump 120 (a). In the embodiment of FIG. 2 (a), the low temperature storage device 110 is non-pressurized. The water volume in the cold storage device 110 is not pressurized, but a column 112 is provided to facilitate subatmospheric pressure flushing (boiling) of water vapor. As is well known, water boils at a temperature of about 100 ° C. at standard atmospheric pressure (normal pressure). However, at lower pressures, water flashes (boils) at lower temperatures and becomes steam (naturally water boils at higher temperatures at higher pressures). For example, water boiled at a temperature of about 46 ° C. at a pressure of 0.1 bar (absolute pressure), boiled at a temperature of about 33 ° C. at a pressure of 0.05 bar (absolute pressure), and 0.02 bar (absolute At a temperature of about 17.5 ° C. Using this property of water, water vapor can be generated at temperatures well below 100 ° C. even when the water inside the associated storage device is not pressurized.

  In the embodiment illustrated in FIG. 2 (a), a flushing column 112 is provided in conjunction with a cryogenic heat reservoir. The flushing column 112 is open at a height below the water level line inside the low-temperature heat reservoir 110 and extends above the surface of the water inside the reservoir 110. When air is evacuated from the column, a vacuum (relative to ambient pressure) is generated inside the column, which has the effect of raising the surface of the water inside the column to a higher water level than the ambient water at ambient pressure. When the column height is sufficient and the evacuation of the air is complete, some of the water inside the column is flushed (boiling), thereby filling the column with saturated water vapor above the level line. The chamber formed by the portion of the column above the water level is sometimes referred to herein as the flushing chamber 113. The saturated water vapor inside the flushing chamber is equal to the temperature and pressure at which the water level inside the column 112 equilibrates with water. Therefore, as in the high temperature storage device 105, the temperature and pressure of the water vapor inside the flushing chamber 113 change according to the temperature of the adjacent water. The actual height of the flushing column 112 can vary widely based on the design goals of any particular heat storage system, but when water vapor is used as the working fluid, the desired sub-atmosphere inside the flushing chamber 113 A column height of at least about 9.4 meters is generally preferred for generating water vapor pressure.

  In the energy storage mode, as illustrated in FIG. 2A, water vapor is drawn from the flushing chamber 113 and compressed by the heat pump 120 (b). As water vapor is withdrawn from the flushing chamber, the pressure inside the flushing chamber drops, which causes more water to evaporate (flush), returning the chamber 113 to equilibrium. Since the latent heat of evaporation of water (and other working fluids) is relatively high, some evaporation of water into water vapor extracts heat from the surrounding water, thereby effectively cooling the surrounding water. Therefore, when water vapor is withdrawn from the flushing chamber 113, the temperature of the water inside the low-temperature heat reservoir 110 gradually decreases.

  When a flushing column is used, the actual design of the column can be varied widely to meet the requirements of any application. Typically, providing sufficient water surface area within the flushing chamber to ensure that water vapor can be generated at a flow rate high enough to supply heat pump 120 (b) at the desired flow rate. Is important. In some applications, it may also be desirable to provide a mechanism for circulating water around the cryogenic heat storage 110 and the flushing column 112. This mixing of water helps reduce the risk of temperature stratification within the flushing column 112. In particular, when a considerable amount of water vapor is generated, the water on the flushing surface cools relatively quickly, and the thermosiphon effect alone changes the temperature of the water on the flushing surface to the water body body inside the cold storage device 110. It should be understood that it may not be sufficient to maintain approximately the same temperature. This is especially the case when the column diameter or width (and hence the flushing surface area) is small compared to the column height. In general, it is undesirable for the water at the surface of the flushing chamber to be at a much lower temperature than the temperature of the underlying water body. This is because the temperature and pressure of the water vapor supplied to the heat pump 120 (b) will be reduced, reducing the overall efficiency of the system.

  Various mechanisms can be used to improve the circulation of water within the cryogenic storage and flushing chamber. For example, to improve circulation and mixing, impellers, propellers, and other mixing devices can be used with proper positioning within the cryogenic storage (eg, within column 112). In various other embodiments, more than one column can be used to improve circulation.

  Next, the operation of the energy storage system 100 in the energy recovery mode will be described with reference to FIG. During energy recovery, water vapor is withdrawn from the high temperature storage device 105 and passed to the steam engine 120 (b), as illustrated in FIG. 2 (b). The steam engine expands the steam and extracts energy from the steam to produce useful mechanical work such as rotation of the drive shaft. The drive shaft can then be used in any desired manner, for example, to power generator 130 (b) and generator 130 (b) generates electricity to drive the pump, or otherwise Drive the machinery. The water vapor supplied to the steam engine 120 (b) is typically drawn from a location near the top of the high temperature storage device, but this is not a requirement.

  As water vapor is withdrawn from the hot storage device 105, the pressure inside the storage device decreases, which further evaporates (flushes) more water and returns the hot storage device 105 to equilibrium. Such evaporation of some water into water vapor extracts heat from the surrounding water, thereby effectively cooling the surrounding water. Thus, when water vapor is withdrawn from the high temperature storage device 105, the water / water vapor temperature and pressure inside the high temperature storage device gradually drop.

  As will be appreciated by those skilled in the art of heat engines, adiabatic expansion of a gas significantly reduces the temperature of the gas during the expansion process. Therefore, the expanded water vapor exhausted by the steam engine 120 (b) may be considerably lower than the water vapor at the time of inhalation and returned to the low-temperature storage device 110. In general, it is desirable to exhaust the steam at the lowest possible pressure so that the steam engine can extract the maximum amount of work from the steam (and thus operate most efficiently). Therefore, it is often desirable to exhaust water vapor from a steam engine at a pressure below atmospheric pressure. Since the pressure inside the flushing chamber 113 is below atmospheric pressure, the flushing chamber is a preferred location for receiving exhaust from the steam engine.

  Conceptually, when water vapor is delivered to the flushing chamber 113, the pressure inside the flushing chamber increases, which condenses some of the water vapor inside the chamber 113 and returns the chamber 113 to equilibrium. Therefore, in the energy recovery mode, the flushing chamber 113 effectively works as a sub-atmospheric pressure condensate chamber. Some steam condensate into liquid water adds heat to the cold storage device, thereby effectively warming the surrounding water. Accordingly, when water vapor is introduced into the flushing chamber 113, the temperature of the water inside the low-temperature heat reservoir 110 gradually increases.

  When steam is injected into the cold storage device, it preferably helps to ensure efficient condensate of the steam and good thermal mixing of the condensate and water in the cold storage device. Measures are taken. One way to improve the condensate inside the chamber 113 is to spray water droplets into the chamber when water vapor is introduced into the chamber. Since water vapor tends to condense on water droplets, water droplets improve the condensate of water vapor. Such spraying can be accomplished by the sprayer 114, which draws water from the cold storage and sprays a shower of water from the top (or near the top) of the column, thereby condensing chamber 113. Effectively produce a water shower inside. A simple pump (not shown) can be used to draw water from any suitable location inside the cold storage device and spray water into the condensate chamber, thereby improving condensate. Other conventional condensation enhancement mechanisms such as drip trays and Raschig rings, trays, or other structures configured to increase the exposed surface area of water (not shown) can also be used.

  It is also desirable to ensure that good mixing of the water on the surface of the flushing chamber and the water in the cold storage device below occurs. If good mixing does not occur, the energy from the steam that condenses heats the water near the surface, thus increasing the temperature at the surface compared to the pool below. The higher temperature at the water / steam interface has the effect of increasing the pressure inside the chamber 113. The increased pressure inside the chamber 113 means that the water vapor cannot be expanded much in the steam engine, which reduces the work that can be extracted from the water vapor and thereby the energy storage and recovery process. Reduce overall round trip efficiency. The same mixing mechanism that is used to improve the circulation of water inside the cold storage device during steam generation can also be used to circulate water in the condensate.

  The described energy storage and recovery system 100 is well suited to facilitate thermal storage of energy. When surplus electrical or mechanical energy is available, such energy is used to store working fluid (eg, water vapor) drawn from the low temperature heat storage 110 in the high temperature heat storage 105. Heat pump 120 (a) can be driven to compress and heat for this purpose. When it is desirable to recover energy from the storage system, hot high pressure steam is withdrawn from the high temperature storage device and expanded in heat engine 120 (b) to extract useful work from the steam, It can be used to generate electricity or for any other desired purpose. In an ideal system where the heat engine / heat pump 120 and motor / generator 130 are not lossy and there is no heat loss or pressure loss (or gain) in the heat store, the energy storage round trip efficiency is 100%. Can be. That is, in theory, the amount of useful energy that can be recovered from the system is the same as the amount of energy used to drive the system. Of course, 100% round trip storage / recovery efficiency (RTE) is not possible in an actual system, but electricity is used to power the system and the form of power ultimately output by the system is electrical. Even at times, using existing technology (eg, using positive displacement steam engines / compressors in combination with motors / generators, as described in more detail below), rounds as high as 60-80% Trip storage / recovery efficiency is considered easily achievable, and even higher round trip efficiency may be possible. Any inefficiency of the motor / generator 130 in systems that directly supply the mechanical power that drives (actuates) the heat engine / heat pump and / or directly utilizes the mechanical power output by the heat engine / heat pump Since efficiency is omitted, higher efficiencies are possible. As will be apparent to those skilled in grid scale energy storage applications, there are several applications where round trip storage and recovery efficiencies in the range of 60-80% are economically feasible.

Other Heat Store Configurations In the embodiment illustrated in FIGS. 2 (a) and 2 (b), the high temperature heat store 105 is pressurized while the low temperature heat store is not pressurized. However, this is not a requirement and both reservoirs may utilize pressurized or non-pressurized reservoirs. As an example, FIG. 3 shows a configuration in which both the high temperature storage device 105 (a) and the low temperature storage device 110 (a) are non-pressurized containers including a quantity of water and a space for moisture-containing water. Indicates. In this embodiment, the high temperature storage device 105 (a) also includes a mechanism (eg, column 107) that promotes the generation of water vapor at sub-atmospheric pressure, similar to the water vapor generation column 112 described above with respect to FIG. The cold storage device can operate in the same manner as described above with respect to FIG. Thus, both the high temperature storage device and the low temperature storage device have a mechanism for generating water vapor at sub-atmospheric pressure.

  An advantage of a system of the type illustrated in FIG. 3 is that the cost of the non-pressurized water container is in some cases much lower than the cost of the pressurized container, which can help reduce the overall system cost. The disadvantage is that the temperature and pressure differences between the high temperature storage device and the low temperature storage device are considerably reduced in the configuration of FIG. Due to the smaller temperature / pressure difference, the volume of water vapor that must pass through the heat engine / heat pump 120 is much larger for a given system energy storage capacity. Thus, typically a fairly large heat engine / heat pump and a large heat storage are required, both of which require additional expense. Which configuration is more cost effective in any particular implementation depends on the relative costs of the various components and the space available.

  Yet another embodiment is illustrated in FIG. In this embodiment, both the high temperature storage device 105 (b) and the low temperature storage device 110 (b) are pressure vessels. The high temperature storage device 105 (b) functions in the same manner as described above with respect to the pressurized high temperature storage device 105 of FIG. The cold storage device 110 (b) generally operates in a similar manner, but typically there is no longer a need for a separate flushing column. Accordingly, during energy storage, water vapor for the heat pump can be drawn from the water vapor chamber region 111 of the low temperature storage device 110 (b), and during energy recovery, water vapor exhausted from the steam engine can be extracted from the water vapor chamber. It can be moved back into region 111. As with the previously described embodiments, it is typically desirable to spray water into the water vapor chamber region 111 when water vapor is added to the cold storage device to improve water vapor condensate.

  From the foregoing, it will be apparent that the size, geometry, and layout of the heat reservoirs 105 and 110 can vary widely within the scope of the present invention. In practice, many tanks and containers have a circular cross section, but this is not essential. In a pressurized high temperature storage device, it is often preferred to orient the tank generally horizontally (ie, the tank length is greater than the tank height), as illustrated in FIGS. This may be desirable because it provides a greater surface area of water, and a larger surface area of water improves the phase transition between the gas phase and the liquid phase of water. The horizontal orientation also reduces the pressure difference between the top and bottom of the tank in some cases, which means that water vapor is injected into the liquid water near the bottom of the tank, as illustrated for example in FIG. It may be useful when It should be understood that the pressure inside the water column increases with depth, and therefore a higher pressure is generated at the bottom of the tank than at the top of the tank and inside the water vapor chamber. Therefore, injecting water vapor from a lower position in the tank inside the water column compresses the inhaled water vapor than when water vapor is injected into the water vapor chamber region 111 above the water level line. Need. Overcompression has the disadvantage of reducing the overall round trip efficiency of the system, so the advantage of using a shallower and wider tank is that overcompression is due to injecting water vapor from near the bottom of the shallower tank. It can be smaller. Of course, in other embodiments, compressed water vapor can be introduced into the water vapor chamber region 111 and other mechanisms can be used as needed to ensure good condensate of the water vapor, Thermal stratification can be minimized.

  When a closed tank is used as a cold storage device, the tank should be able to withstand the vacuum pressure of the flushing chamber (eg, negative pressure up to 1 atmosphere). In some applications, the use of such a vacuum resistant tank may be more cost effective than providing a non-pressurized tank with a flushing column 112. As an example, a cylindrical tank having a height of at least 10 meters (eg, 12 meters to fit the length of the shipping container) works well in many applications.

  In most of the examples described above, heat stores are described primarily in the context of various tanks and pressure vessels. Although tanks and pressure vessels function fairly well, it should be understood that a variety of different structures can be used as heat stores, if appropriate. By way of example, lakes, ponds, or other defined water bodies can be used as unpressurized heat stores (especially as cold storage devices) if available. When readily available, the use of such water bodies can have several possible advantages. For example, if the total mass of water in a lake or pond is significantly greater than the amount used by the energy storage system, the overall temperature of the lake used as a cold storage will be significantly increased throughout the energy storage and recovery cycle. May not fluctuate. Cold storage devices that maintain a relatively constant temperature tend to facilitate more efficient storage. In other embodiments, water reservoirs and various underground water storage devices can be used as one or both of the heat reservoirs.

  In most illustrated embodiments, each heat reservoir takes the form of a single water reservoir. However, it should be understood that one or both of the reservoirs may be formed from any number of individual water storage structures. In fact, for some applications, a modular water reservoir may be preferred. For example, in one particular application, several modular tanks, each sized to fit inside a shipping container, can be used to form one of the heat stores (eg, a cold storage device). .

  Typically, it is desirable to insulate the high temperature storage device to avoid heat loss in the main energy storage device. Depending on the location and operating conditions, it may or may not be desirable to insulate the cold storage device. Insulation may be less desirable for cold storage devices because the inefficiency of the storage and recovery process typically adds heat to the system and tends to transfer such heat to the cold storage device. That is. More specifically, during the charge / discharge cycle, some of the energy lost due to compressor and heat engine inefficiencies appears as a net heat flow into the cold storage device. This amount of heat typically needs to be removed from the system to prevent the temperature of the cold storage device from rising to an inefficient level over time. Various conventional mechanisms can be used to adjust the temperature of the cold storage device 110. Thus, some natural cooling of the cold storage device may be desirable to help maintain system balance.

  With reference now to FIG. 5, yet another alternative energy storage system configuration is described. In this embodiment, the function of the cold storage device 110 described in the previous embodiment is effectively divided into two separate components: a cold sink 175 and a cold energy source 185. This type of configuration may be advantageous when there are heat sources available, such as waste heat from industrial processes or thermal power plants. In other aspects, the system may be substantially the same as any of the previously described embodiments.

  In the illustrated configuration, the high temperature storage device 105 (c) is an adiabatic pressure vessel that includes water and a saturated water vapor space and operates in the same manner as described above. The cryogenic energy source may take the form of a non-pressurized water container that is heated by any suitable heat source. The cold sink 175 is a condenser that is cooled by an available heat sink. The heat sink can take any suitable form, and the most suitable heat sink may vary from location to location. As an example, a water stream or other water body, an evaporative cooler, a fin-fan cooler, or various other heat exchangers may be used to cool the condenser.

  In general, the cold energy source 185 is maintained at a higher temperature than the sink 175. When storing energy, the water in the cryogenic energy source 185 is flushed into water vapor, similar to that described above for the cryogenic storage device 110. As described above, a column or other suitable vessel structure can be used to facilitate water vapor subatmospheric flushing. The temperature of the water, and thus the saturated water vapor supplied by the energy source 185, is generally higher than when a cold storage device is used. Since the temperature of the water is higher, the pressure of the water vapor drawn into the heat pump 120 (a) is higher, which requires less energy to compress the water vapor for storage in the high temperature storage device 105. Means that.

  When recovering energy, the steam engine 120 (b) exhausts water vapor to the cold sink 175 (not the energy source 185). The sink 175 condenses water vapor and is cooled by an available heat sink. Similar to the cold storage device, the sink 175 includes a sub-atmospheric condenser 177 that facilitates condensing exhaust water vapor at sub-atmospheric pressure. In general, the temperature of the sink 175 is lower than the temperature of the energy source 185. Since the temperature of the water inside the sink condensate chamber is lower than the temperature of the energy source, the pressure inside the condenser 177 (and thus the pressure at which condensate occurs) is also lower. Thus, the steam can be exhausted from the steam engine 120 (b) at a lower pressure than is possible when the steam is returned to the energy 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 recovery system.

  In an ideal system operating in the configuration of FIG. 5, it is shown that more energy is available for extraction from water vapor in the high temperature storage device 105 than is required to compress the water vapor during energy storage. Should be understood. Thus, from the perspective of an electrical system that drives a heat pump and uses electrical energy from a steam engine, in theory, the electrical system can draw more electricity during recovery than it was used during storage. This suggests a round trip efficiency greater than 100% from an electrical system perspective. Of course, this is not free energy, and the system effectively converts thermal energy from the low temperature heat source 185 into electrical energy. However, if such thermal energy is waste heat and therefore substantially free (free), it can be utilized in a manner that improves the apparent round trip efficiency of the energy storage system 100.

  Optionally, the condensate from the condenser in the sink 175 can be recycled to the low temperature heat source 185, where the condensate is heated before being used to generate steam. The The advantage of such recirculation is that in some cases the overall water consumption of the system is reduced.

  It will be apparent that there are several industrial and power generation processes that generate waste heat that can be utilized in a system of the type illustrated in FIG. If such waste heat is carried by water, such water can optionally be stored directly in the cold heat source 185. Alternatively, one or more suitable heat exchangers can be used to warm the water stored in the heat source 185.

  Suitable storage sizes for use as the high temperature heat storage 105 and the low temperature heat storage 110 are the desired energy storage capacity of the system, containers, tanks, or other used as storage and / or flushing columns. It may vary with the pressure rating of the structure, the operating temperature range (which may be determined in part by the allowable operating pressure range), etc. As an example, a system designed to deliver 1 megawatt (MW) of power over 10 hours (thus having a storage capacity of over 10 megawatt hours) to give a rough size of the appropriate system size Can be implemented using a 170000 gallon hot storage device that can be pressurized to about 17 bar (about 250 psi) and a 500,000 gallon non-pressurized cold storage device. In this particular example, the cold storage device has a volume approximately three times that of the cold storage device. However, the actual relative volume of the high temperature storage device and the low temperature storage device can vary widely, and the relative price of the container available for use as a heat storage can vary depending on any particular storage capacity. It should be understood that this may have a significant impact on the final reservoir size selected.

  It should be understood that the size of the high temperature storage device can generally be reduced if the container used as the high temperature storage device can withstand higher operating temperatures and pressures. Conversely, if the container used can only withstand lower operating temperatures and pressures, or if the high temperature storage device is non-pressurized, the size of the high temperature storage device must increase. In addition, it should be understood that the volume of the cold storage can also have a significant effect on the required volume of the high temperature storage. More specifically, as described above, during operation in the energy storage mode, thermal energy is drawn from the cold storage device 110, thereby cooling the cold storage device and adding thermal energy to the hot storage device 105; Thereby, the high-temperature storage device is heated. Thus, the temperature of the heat reservoir converges during energy storage. Conversely, during energy recovery, thermal energy is drawn from the high temperature storage device 105, thereby cooling the high temperature storage device, and thermal energy is added to the low temperature storage device 110, thereby heating the low temperature storage device. Thus, the temperature of the heat store will diverge during energy recovery. As the temperature converges, the amount of energy that can be recovered from the water vapor drawn from the high temperature storage device decreases.

  It should be understood that the temperature of a cold storage device of the same size as the hot storage device varies more than the temperature of a cold storage device having a volume three times (3X) that of the hot storage device. Thus, assuming the same high temperature storage device, a system with three times the low temperature storage device has the ability to extract more energy than a system with a low temperature storage device of the same size as the high temperature storage device. If expanded and larger cold storage devices are used (eg 10 times lower temperature storage devices), it is possible to extract more energy from the same size hot storage device. If a relatively large body of water is used, such as a lake having a volume many times larger than a high temperature storage device, the low temperature storage device can maintain substantially the same temperature throughout the energy storage and recovery cycle. Such a system has the ability to extract more energy assuming the same high temperature storage device, which provides a larger usable energy storage capacity. Thus, it will be apparent that the selection of the relative size of the hot and cold reservoirs is often based primarily on cost-benefit analysis, assuming available reservoirs, tanks, and pressure vessels.

  Either the high-temperature and low-temperature heat stores may be implemented as a single tank, container, or reservoir, or may be implemented as multiple tanks, containers, and / or reservoirs is there. As an example, a 500,000 gallon (2273.045 cubic meter) high temperature storage device can be implemented as seventeen 30,000 gallon (136.3827 cubic meter) pressure vessels, each pressure vessel approximately 40 feet (12.192 m) in length. ), 12 feet (3.6576 m) in diameter.

Steam Engine The heat engine / heat pump 120 can be implemented in a variety of different ways. Although a variety of heat pumps and heat engines may be used, including steam turbines, one class of heat engines that are particularly well suited for use as heat engine / heat pump 120 are positive displacement piston steam engines. One advantage that piston steam engines have over turbines and other conventional heat pumps and heat engines is their relatively high operating efficiency over a wide range of intake and exhaust pressures and temperatures. This is particularly useful in the energy storage and recovery system described. This greatly changes the temperature and pressure of both the hot and cold heat stores over the course of the energy storage and recovery cycle without significantly reducing the system's round trip energy storage and recovery efficiency. It is because it becomes possible to make it.

  Another advantage of a piston steam engine is that it can operate relatively efficiently over a range of water vapor mass flow rates so that the system can efficiently deliver energy even when faced with fluctuating energy supplies and demands. Is to be able to withdraw or feed. This performance is particularly suitable for applications where the energy available for storage can vary significantly at any given time during the day, as is inherent in solar and wind farms. It is also very well suited for applications where the demand for energy changes during recovery (many such uses).

  Many piston steam engines can operate both as a heat engine (expander) and as a heat pump (compressor), so that they can move backwards. This can be advantageous because it allows a single machine to be used as both a heat pump and a heat engine. A reversible device is useful in many applications, but is not essential. When desired, separate devices can be used as the heat pump and heat engine, and the heat pump / heat engine shown in the drawings is intended to represent both approaches. This may be desirable, for example, when separate expanders and compressors are cheaper and / or more efficient than reversible devices. Furthermore, it should be understood that multiple steam engines (or other devices) can be used in parallel as heat engines / heat pumps to provide the desired throughput.

  It should also be understood that, although positive displacement piston steam engines are not widely used today, piston steam engines are a very mature technology. In fact, piston steam engines were the mainstream power source in the 20th century. Thus, there are several existing piston steam engine designs that can be used as a heat engine / heat pump. These include single steam engines and dual (multiple expansion stage) steam engines. In some specific applications, single or double uniflow, universal-uniflow, or counterflow piston steam engines may be used. One such engine has been developed by the applicant and is based on the Skinner Universal-Uniflow steam engine from the 1930s.

  The actual number of continuous stages desirable and appropriate for any particular application, including the expected temperature difference between the heat reservoirs, the availability of steam separators and water jets, costs, and other factors It varies according to several factors. In some applications, only one expansion stage may be preferred, while in other applications, multiple stages (typically continuous stages in the range of 2-5) are preferred.

  Uniflow and universal-uniflow steam engines are piston-based steam engines that utilize poppet valves to control the introduction of water vapor into a cylinder that serves as an expansion chamber. Conventionally, the valve timing is controlled by a camshaft. However, it should be understood that other known valve timing control mechanisms may be used. For example, an electronic solenoid can be used to open and close the valve, which facilitates electronic control of valve opening and closing timing, if desired. Regardless of the mechanism used, there are several advantages that provide extensive control over the relative timing of valve opening and closing. For example, in order to maximize efficiency, it is generally preferred that the compression ratio of the steam engine / heat pump be relatively closely matched to the pressure ratio of the hot storage device pressure to the cold storage device pressure. Changing the timing of opening and closing the intake valve and the exhaust valve is a suitable method for accurately controlling the compression ratio of the engine. Changing the intake valve cutoff timing also provides a good mechanism for controlling the mass flow rate of water vapor through the steam engine, which allows for better control of the power generated by the steam engine during expansion. .

  Adjustable valve timing is also very useful to facilitate reverse operation of the steam engine so that the steam engine can be operated as an expander (conventional steam engine) or as a compressor (heat pump) It may be. Conceptually, many steam engines, including pistons and other positive displacement steam engines, can operate as expanders or compressors. The main difference is that in expander mode, high pressure steam is drawn into the expansion chamber and used to drive the piston, which sends useful work to the crankshaft, while in compressor mode, the electric motor (Or other suitable power source) powers the crankshaft, which drives the piston to compress the water vapor inside the chamber (here it acts as a compression chamber rather than an expansion chamber). If the valve opening / closing timing does not change (relative to the crank angle), the direction of rotation of the crankshaft must be reversed in order to change from expansion to compression. This requires stopping the steam engine and reversing the direction of the steam engine. This is because power is expected to be mainly stored at night when electricity usage is low, and when recovery is expected to occur mainly at other times of the day when electricity usage is higher. It works well in energy storage systems where a rapid shift between consumption and power generation is not required. However, there are also some applications, such as load balancing, where the ability to shift quickly between power storage modes and power transmission modes (ie shifting modes in seconds instead of minutes) is quite beneficial. In piston-based steam engines, this type of rapid shift between power generation mode and storage mode is possible if the crankshaft can continue to rotate in the same direction when shifting modes. This can be achieved by changing the relative timing of opening and closing the valves. Of course, when the operating mode is reversed, the function of the valve (intake and exhaust) is reversed.

  As is well known, conditions close to adiabatic compression of water vapor cause water vapor to overheat. Excessive overheating of water vapor may be undesirable because it can lead to heat loss in the system. Thus, in some embodiments, one or more water injection devices are provided to spray water into water vapor prior to or during compression, thereby providing some of the thermal energy generated during compression. Absorbed by evaporation of the injected water. The injector may be configured to inject water directly into each cylinder during compression, or may be configured to inject water into the water vapor prior to the introduction of water vapor into the compression cylinder. In general, it is desirable to keep the compressed water vapor exiting the steam engine during compression near saturation so that excessive overheating does not occur. However, this is not a requirement. It should be understood that the desired amount of water to be injected depends on several different factors such as the compression ratio currently in use, the mass flow rate of water vapor through the cylinder, the inlet temperature and pressure. 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 with compressed steam exiting the steam engine. If multiple compression stages are used, it may be desirable to inject water for each compression stage, but this is not a requirement.

  Conversely, adiabatic expansion of saturated water vapor may condense some of the water vapor during expansion. In general, it is not desirable to introduce wet steam (i.e., water vapor containing water droplets) into the cylinder because condensate can corrode the inlet valve port. Thus, in dual steam engines, it is often desirable to pass the steam through a steam separator (not shown) between successive stages in order to remove most of the water droplets from the steam. It may also be desirable to pass the steam through a steam separator before the steam enters the first (or just one) expansion chamber (cylinder). The water condensed by the steam separator can be returned to one of the heat stores (typically a cold store) to help capture the energy contained in the water. A variety of different conventional steam separators can be used to remove water droplets from the steam. As an example, a mesh steam separator works well.

  In other embodiments, it may be desirable to superheat the steam before it enters the steam engine and / or reheat the steam between successive stages. This may involve the use of an optional superheater that heats the steam drawn from the high temperature storage device before entering the steam engine, and / or an optional reheater that heats the steam between successive stages of the steam engine. Can be achieved. Although a superheater and / or reheater can be used, the heat source used to supply the superheater and / or reheater is a waste heat source or other very low cost energy source. Unless otherwise, it is often not cost effective.

Further Features It will be apparent that the various energy storage systems described above are well suited to provide low cost bulk energy storage and recovery with high round trip efficiency. The interval between storage and collection may be as short as a few seconds or as long as several hours or days. Discontinuous power sources such as wind and sun tend to exacerbate the mismatch between energy supply and demand, thus increasing the need for such energy storage and recovery systems.

  Although only some embodiments have been described in detail, it should be understood that the invention can be embodied in many other forms without departing from the spirit or scope of the invention. For example, the specific configuration and layout of the high and low temperature heat stores, and the specific devices used as heat pumps and heat engines can vary widely. Each of the high temperature storage device and the low temperature storage device may be implemented as a single tank or a plurality of separate tanks. When multiple tanks are used for one of the storage devices, the working fluids in the different tanks at that storage device can be at substantially the same temperature or at different temperatures. As described above, one or more reversible heat engines / heat pumps may be used as the expander / compressor, or separate devices may be used for expansion and compression. Similarly, reversible motors / generators can be used to drive or be driven by heat engines / heat pumps in electrical storage and recovery applications, or separate motors and generators Machine may be used. The system described above is easily scaleable and can be used in a variety of different energy storage applications, including grid scale energy storage and recovery applications.

  It should also be understood that if low cost heat sources are readily available, such heat can be used to help improve the efficiency of the system. One such configuration is illustrated in FIG. 5, in which waste heat is used to warm (or provide) the water, which is the low-temperature steam used for compression. Work as a source. In other embodiments, a suitable heater or heat exchanger can be used to superheat the steam from the high temperature storage device 105 before the steam is introduced into the heat engine 120 (b) or expand. Water vapor can be reheated between stages. As will be appreciated by those skilled in the art, overheating of steam prior to expansion and / or reheating of steam during the expansion stage is a problem and inefficiency that may be induced by steam condensate during the expansion process Can help eliminate the need to reduce or eliminate the need to use a steam separator. Of course, the maximum use of available heat depends in part on the temperature that can be obtained. Thus, when desired and appropriate, a superheater (not shown) is provided between the high temperature storage device 105 and the heat engine to superheat the steam before it enters the steam engine 120 (b). And / or one or more reheaters (not shown) can be provided to reheat the water vapor at an appropriate stage in the expansion process.

  Using the above approach, an effective round trip efficiency of at least 60, 70, or even 80% can be achieved. Although higher round trip efficiency is generally desired, cost considerations may define the system design and thus the achievable round trip efficiency. However, for some specific applications, it is considered economically feasible to have a system with 60-80% (or more) round trip efficiency.

  The above embodiments are to be considered illustrative rather than limiting, and the present invention is not limited to the details presented herein, but is modified within the scope of the appended claims and the equivalents thereof. can do.

Claims (17)

An energy storage and recovery system,
A first heat reservoir configured to hold the working fluid in a first state that includes a working fluid in a liquid phase and a saturated vapor phase;
A second heat reservoir configured to hold the working fluid in a second state that is at a temperature lower than the temperature of the working fluid in the first heat reservoir;
A heat engine / heat pump unit, and the heat engine / heat pump unit comprises:
(A) the second heat storage from the first heat reservoir by expansion of working fluid vapor in a manner that generates mechanical energy to facilitate recovery of energy from the energy storage and recovery system; Extract the energy from the working fluid vapor going to the vessel,
(B) configured to compress working fluid vapor traveling from the second heat reservoir to the first heat reservoir to facilitate energy storage within an energy storage and recovery system; ,
Energy storage and recovery system. An energy storage and recovery system,
A first heat reservoir configured to hold water and saturated water vapor in a first state;
A second heat reservoir configured to hold water and water vapor in a second state having a lower temperature than the first state;
A reversible positive displacement steam engine, the reversible positive displacement steam engine comprising:
(A) from the first heat reservoir to the second heat reservoir by expansion of water vapor in a manner that generates mechanical energy to facilitate recovery of energy from the energy storage and recovery system; Extract energy from the water vapor,
(B) configured to compress water vapor traveling from the second heat reservoir to the first heat reservoir to facilitate storage of energy within an energy storage and recovery system;
Water and water vapor serve as working fluids for energy storage and recovery systems,
Energy storage and recovery system. An energy storage and recovery system,
A first heat reservoir configured to hold the working fluid in a first state including a liquid phase and a saturated vapor phase working fluid;
A low-temperature thermal energy source configured to provide a vapor phase working fluid in a second state having a lower temperature than the first state;
A condenser configured to condense the vapor phase working fluid;
A heat engine / heat pump unit, and the heat engine / heat pump unit comprises:
(A) advancing from the first heat reservoir to the condenser by expansion of working fluid vapor in a manner that generates mechanical energy to facilitate recovery of energy from the energy storage and recovery system; Extract energy from working fluid vapor,
(B) configured to compress working fluid vapor traveling from the low temperature thermal energy source to the first heat reservoir to facilitate storage of energy within an energy storage and recovery system;
Energy storage and recovery system. The energy storage and recovery system according to any one of claims 1 to 3,
The working fluid is
(A) water or a mixture containing water;
(B) a fluorocarbon or a mixture containing a fluorocarbon;
(C) ammonia or a mixture containing ammonia;
(D) a hydrocarbon or a mixture containing hydrocarbons;
An energy storage and recovery system selected from the group consisting of: The energy storage and recovery system according to any one of claims 1 to 4, further comprising:
An electric motor / generator mechanically coupled to a heat engine / heat pump unit or a steam engine, the electric motor / generator when the heat engine / heat pump unit or steam engine is operated as a heat pump, the heat An energy storage and recovery system configured to drive an engine / heat pump unit or steam engine and configured to generate electricity when the heat engine / heat pump unit or steam engine is operated as a heat engine. The energy storage and recovery system according to any one of claims 1 to 5,
The energy storage and recovery system, wherein the heat engine / heat pump unit or steam engine is selected from the group consisting of a uniflow steam engine, a universal-uniflow steam engine, and a reverse flow steam engine. The energy storage and recovery system according to any one of claims 1 to 6,
The first heat storage includes a pressure vessel configured to hold the working fluid within the first heat storage at a pressure substantially higher than ambient atmospheric pressure, energy storage and recovery system. The energy storage and recovery system according to any one of claims 1 to 7,
The second heat reservoir or the low-temperature thermal energy source is configured to hold a non-pressurized working fluid and includes a sub-atmospheric pressure chamber, the sub-atmospheric pressure chamber being sub-atmospheric for liquid working fluid to vapor. An energy storage and recovery system that facilitates atmospheric pressure flushing and / or quasi-atmospheric condensate of the vapor working fluid into the liquid phase. The energy storage and recovery system according to any one of claims 1 to 8,
The second heat reservoir or the low temperature thermal energy source includes a pressure vessel configured to hold the working fluid vapor at sub-atmospheric pressure, and sub-atmospheric flushing of liquid into the vapor, and / or liquid Energy storage and recovery system that promotes sub-atmospheric condensate of steam into the. The energy storage and recovery system according to any one of claims 1 to 9,
The heat engine / heat pump unit or steam engine is adapted to compress the working fluid vapor before compression from the heat engine / heat pump or steam engine to the first heat reservoir for compression. An energy storage and recovery system comprising a liquid jetting device for adding a liquid phase working fluid to a vapor phase working fluid passing through a unit or steam engine. In the energy storage and recovery system according to any one of claims 1 to 10,
The energy storage and recovery system, wherein the heat engine / heat pump unit or steam engine includes a separator for removing liquid from a partially expanded working fluid passing through the heat engine / heat pump unit or steam engine. The energy storage and recovery system according to any one of claims 1 to 11,
The heat engine / heat pump unit or steam engine includes a crankshaft and at least one working chamber, each working chamber having an associated reciprocating piston coupled to the crankshaft and a plurality of associated valves. The valve facilitates the introduction of the working fluid into the working chamber and the discharge of the working fluid from the working chamber, and the opening and closing timing of the valve can be changed, whereby (a) The heat engine / heat pump unit or steam engine can be operated in both expansion mode and compression mode using the crankshaft rotating in a direction, and (b) expansion of the heat engine / heat pump unit or steam engine / Open / close timing of the valve with respect to the crankshaft angle to facilitate changing the compression ratio It can be varied, the energy storage and recovery system. The energy storage and recovery system according to any one of claims 1 to 12,
The energy storage and recovery system wherein the round trip efficiency of the energy storage and recovery system is at least 70 percent. The energy storage and recovery system according to any one of claims 1 to 13, further comprising:
The vapor phase working fluid drawn from the first heat reservoir is superheated before the working fluid is passed through the heat engine / heat pump unit or steam engine; and the heat engine / heat pump unit or steam engine Reheating the working fluid between expansion stages;
An energy storage and recovery system comprising a heater for at least one of the following. The energy storage and recovery system according to any one of claims 1 and 3 to 14,
The energy storage / recovery system, wherein the heat engine / heat pump unit includes at least one heat engine and at least one heat pump separate from the heat engine. The energy storage and recovery system according to any one of claims 5 to 15,
The energy storage and recovery system, wherein the electric motor / generator includes at least one motor and at least one generator separate from the motor. The energy storage and recovery system according to any one of claims 1 to 16,
The steam engine
A plurality of sequential expansion stages;
An energy storage and recovery system comprising a water vapor separator for removing water from the partially expanded water vapor between a pair of related expansion stages.

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