Thermal energy storage system and method having a heat recovery steam generator - Patents.com

Abstract

A method and system of retrofit and operation for a heat recovery steam generator (HRSG) and a steam / media heat exchanger in communication with the flow of a heat storage medium. The steam / media heat exchanger receives heat from the HRSG steam and transfers the heat to the storage medium. A first tank in fluid communication with the steam / media heat exchanger receives and stores the heated storage medium. A second tank is fluidly connected to supply the medium to the heat exchanger. The HRSG can include superheaters, attemperators, reheaters, and reheater attemperators, which can be retrofitted to the steam / media exchanger to reduce or eliminate the attemperator. A water / media exchanger exchanges heat with the medium flowing between the tanks, and a heater can add heat to the medium flowing to the first tank.

Description

[Technical field]

[0001] This application claims the benefit of the filing date of U.S. Patent Application Serial No. 63 / 316,169, filed March 3, 2022. [Background technology]

[0002] Many existing power plants for electricity generation were built with the intention of base load operation (e.g., having a fixed electrical output) and, as the impact of renewable energy sources increases, they often operate outside of their design conditions, at least during the day when a large amount of renewable energy is available. In other words, many of the existing power plants were designed and built to operate at base load operation without significant deviations in order to maximize efficiency through operation within their design operating parameters (e.g., gas turbine firing rate, input air ratio, etc.). As energy generation from renewable energy sources increases and power demand from fossil fuel-fired power plants decreases, these fossil fuel-based power plants need to operate in a reduced generation mode resulting in reduced thermal efficiency. However, when renewable energy sources do not operate at peak output (e.g., during low wind times, at night), non-renewable energy power plants are still needed to meet the energy demand. Thus, a solution is needed to increase the efficiency of renewable energy power plants, since non-renewable energy power plants are still required even when renewable energy generation decreases.

[0003] Many existing power plants also have additional problems when operating outside their design conditions. For example, during periods of low power demand, it is desirable to operate a fossil fuel fired (FFF) combined cycle power plant (e.g., one that has both a gas fired turbine and a steam driven turbine that uses heat from the gas fired turbine) at very low load conditions to save on fuel costs (power demand is met, for example, by renewable generation). However, because the steam turbine typically has a minimum steam generation requirement, the associated gas turbine must operate at a higher load than desired in reduced load mode. Therefore, what is needed is a system that can reduce the gas turbine to a low load while maintaining a level of steam generation to meet the steam turbine demand, thereby saving fuel and reducing absolute emissions.

[0004] Low load operation associated with increased renewable energy generation adversely affects the efficiency and performance of various types of power plants, including, but not limited to, gas turbine power plants, combined cycle gas and steam power plants, coal-fired power plants, or other power plants that experience reduced performance when not operating at base load, through the resulting low load operation. The impact of the resulting, at least in part, inefficient low load operation of renewable energy sources particularly affects combined cycle gas power plants.

[0005] A combined cycle power plant basically consists of a combustion power plant combined with a steam power plant. For example, it consists of a combustion turbine that supplies power to a first generator combined with the steam power plant. Such combined cycle gas power plants usually utilize a heat recovery steam generator (HRSG) system. Such HRSG systems use the hot exhaust gases generated by the combustion turbine by directing them through a heat recovery boiler or heat recovery steam generator to generate steam from the heat of the exhaust gases. The generated steam is sent to a steam turbine to drive the steam turbine.

[0006] Combined cycle power plants using HRSGs are particularly affected by low load operation because, at off-design operating conditions of the combined cycle power plant, the temperature of the steam at the HRSG outlet expanding from the HRSG superheater is typically much higher than the temperature of the steam the HRSG steam turbine or other system can accommodate unless some means of regulating or reducing the temperature of the steam is employed. The increased steam temperature results from the way in which the gas turbine achieves part-load operation. To sustain the highest possible efficiency, it is desirable for the gas turbine to burn to the highest temperature in the combustion chamber. This temperature is typically limited by the metal temperature of the first stage turbine blades just downstream of the combustor. During part-load operation, fuel flow is reduced and less available energy is delivered to the system. The reduced fuel flow alone can create problems in the combustor, such as flame stability issues resulting from the velocity of the fuel flow and the oxidizer (i.e., air) velocity in the burner nozzle area. This imbalance can lead to unstable combustion, which can lead to pressure pulsations, noise generation, and in extreme cases, flame blow-out. A cooler flame (i.e. more air passing through) can increase carbon dioxide emissions, and at the same time, regulated turbine emissions are also affected, since an unstable flame can have hot areas that increase the formation of nitrous oxide. To avoid the aforementioned problems, when the turbine reduces load and reduces fuel flow, the inlet guide vanes at the compressor inlet are throttled, so that the air flow through the machine is reduced at the same time. The reduced air flow also reduces the cooling efficiency, which causes higher exhaust temperatures. As the turbine load continues to decrease, maintaining acceptable emissions and flame stability, selected burners are no longer used. At a certain point in the load reduction, the turbine inlet guide vanes are throttled to a minimum opening, and the subsequent reduction in turbine load causes a significant reduction in the gas turbine exhaust temperature, since the reduction in fuel flow is the only remaining means of reducing power generation. For at least these reasons, a system is needed that allows power plants to operate at design conditions, even when the demand for electricity (from renewable energy sources) is reduced, and that can reduce or eliminate such control measures and their associated adverse effects.Unless some active means to control the temperature of the steam is employed, in extreme cases outside the design operation of a combined cycle power plant, the temperature rise of the steam from part-load operation may exceed some of the metal design temperature limits of the boiler.

[0007] In existing combined cycle power plants and power plants with HRSG systems, the steam temperature leaving the HRSG and before entering the turbine, boiler, tank, or similar can be controlled using a direct contact desuperheater (DSHTR) to reduce the steam temperature to within design parameters.

[0008] A common approach for high pressure HRSG systems is the use of a direct contact attemperator in the system. A direct contact attemperator introduces a cooling water stream into the HRSG where it is used to reduce the required set point of operation. However, the introduction of cooling water through a direct contact attemperator reduces the efficiency of the HRSG system because the cooling water introduced into the HRSG does not pass through all of the same heating surfaces of the HRSG and therefore does not extract as much heat energy from the combustion turbine exhaust gas compared to an HRSG that does not employ an attemperator. In other words, even though the cooling water is evaporated into steam and discharged from the HRSG, the increased level of subcooling for this steam production is still higher than if the same amount of water could pass through preheating surfaces upstream of the evaporator and then have a lower level of subcooling, thus reducing efficiency. Attemperators may be used in this manner in both superheater loops that use reheaters and in high pressure loops with reheaters. Attemperators used in conjunction with reheat loops have the additional disadvantage of directly reducing the production of higher pressure, more valuable steam due to the introduction of the reheater attemperator spray stream. In any event, using a desuperheater to cool the steam has a detrimental effect on efficiency.

[0009] Another approach used in some HRSG systems for steam temperature control is the use of a steam bypass. In a steam bypass, steam is routed around the heat exchangers of the HRSG system to produce a cooler final steam compared to passing the steam through all of the heat exchangers of the HRSG system. The cooler bypass steam is reintroduced into the main steam flow routed through the HRSG to control the final destination steam temperature. This reduces efficiency because not all of the heat that can be captured using the HRSG system is captured.

[0010] In power plants utilizing existing attemperators, such use can cause additional undesirable effects. For example, during periods of low power demand in an FFF combined cycle facility, the temperature of the gas turbine exhaust increases and exhaust mass flow is reduced. This results in increased steam temperatures in the heat recovery steam generators (HRSGs). This is due to increased exhaust gas temperatures and reduced steam production due to the low exhaust gas mass flow. Because steam temperatures must be regulated, a significant increase in cooling water is often required for use in the attemperator(s). The cooling water can be introduced directly into the steam, and large amounts of cooling water can create adverse and undesirable effects in the HRSGs, such as introduction of water to hot heating surfaces that can be damaged by thermal shock stresses or poor process control due to poor temperature measurement. A system is needed that provides for steam temperature control that mitigates such adverse effects.

[0011] A typical combined cycle power plant faces additional problems that affect efficiency. For example, when the ambient temperature rises above the combined cycle power plant's design ambient conditions, mass flow from the gas turbine, a low volume machine, is reduced. This reduction in mass flow creates conditions similar to those experienced during part-load operation (i.e., higher exhaust gas temperatures and reduced mass flow). Thus, a system is needed that allows additional steam to be generated during such conditions to address the production "deficit" resulting from off-design conditions, and thus allow the steam turbine to generate more power than is achievable under the plant's conditions.

[0012] What is needed are 1) systems and methods for improving the efficiency of fossil fuel power plants, including combined cycle power plants, when operating in conditions that include periods of below baseload operation; 2) systems and methods for turning part-load inefficiencies into power plant benefits during periods of high demand; 3) systems and methods for improving power plant flexibility by allowing lower load reductions to be achieved; and 4) systems and methods for maximizing power plant production at hotter ambient conditions compared to design conditions. [Brief description of the drawings]

[0013] [Figure 1] 1 is a diagrammatic representation of a heat recovery steam generation system of a combined cycle power plant having an attemperator system for controlling the temperature of steam exiting the heat recovery steam generation system before entering a steam turbine system or component thereof. [Diagram 2] FIG. 2 is a diagrammatic representation of a thermal energy storage system that recovers and stores heat from an HRSG system of the type shown in FIG. 1, reducing or eliminating the need for the use of attemperators to improve power plant efficiency. [Diagram 3]FIG. 3 is a schematic representation of a thermal energy storage system of the type shown in FIG. 2 according to an alternative embodiment adapted and configured, in part, to provide reheated steam to an intermediate pressure steam drum and / or other processes as well and / or to provide high pressure steam to a process or return to the high pressure steam drum. [Figure 4] FIG. 4 is a diagrammatic representation of a thermal energy storage system of the type shown in FIGS. 2 and 3 according to an alternative embodiment adapted and configured in part to store thermal energy from multiple reheaters and superheaters of an HRSG and / or provide the same to other processes or pressure specific steam drums within the HRSG. [Diagram 5] FIG. 5 is a diagrammatic representation of a thermal energy storage system of the type shown in FIG. 4 according to an alternative embodiment adapted and configured, in part, to store thermal energy extracted in series from multiple reheater heat exchangers and multiple superheater heat exchangers of an HRSG and / or to provide other processes or pressure specific steam drums within the HRSG. [Figure 6] FIG. 6 is a diagrammatic representation of a thermal energy storage system of the type shown in FIG. 5 according to an alternative embodiment including one or more electric heaters adapted and configured to further control the temperature of the working fluid used to store the stored thermal energy extracted from the multiple reheat and superheater heat exchangers and / or provide the same to other processes or pressure specific steam drums within the HRSG. [Figure 7] 3 is a diagrammatic representation of a thermal energy storage system of the type shown in FIG. 2 with bypass(s) for supplying steam to a combined cycle power plant and / or for further control of other process(es) and the thermal energy storage system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Corresponding reference numbers indicate corresponding parts throughout the many views of the drawings. Similar numbered parts also have the same or similar characteristics unless otherwise specified. For example, hot tank 194 is the same as hot tank 294. Components shown in dashed lines are optional and may be omitted according to different embodiments and different uses. Components shown and not otherwise described should be given their ordinary meaning as understood by those skilled in the art (e.g., valves, temperature sensors, etc. drawn according to industry standard symbols). Components connected by lines are in fluid communication with each other and may be connected via intervening components in other embodiments not shown, either directly coupled. The drawings use the letters "TE" in circles at various points to indicate the location of temperature sensors that sense fluid temperature at various points.

[0015] With general reference to Figures 1-7, the systems and methods disclosed herein provide improved efficiency and / or flexibility in power generation applications, including, but not limited to, combined cycle power plants. The systems and methods disclosed herein are applicable to any system / method in which the temperature of the steam is to be controlled and may involve a cooling system to maintain the input steam within design parameters (e.g., using a steam attemperator). In general, the disclosed systems and methods are provided to maintain the input steam within design parameters by using a thermal transfer medium to remove heat from steam that exceeds design parameters and storing the thermal transfer medium to be used to heat the steam or other fluid for later use in power generation and / or other processes. By using a thermal transfer medium to cool the input steam and storing the removed heat for later use, in addition to or instead of using a steam attemperator, heat that would otherwise be wasted or recovered with low efficiency is recovered and stored for later use. This improves the efficiency and / or flexibility of the power generation system or other system / method in which the steam temperature is controlled.

[0016] More specifically, in some embodiments of the energy storage device of the present disclosure, the high temperature steam that would normally be cooled by passing through a desuperheater is instead passed through a steam / heat medium heat exchanger. In the steam / heat medium heat exchanger, the steam temperature is reduced while heat is released to a heat storage medium, such as molten salt or any other suitable equivalent medium, flowing through the steam / heat medium heat exchanger. The cooled steam is returned to the HRSG, e.g., output from the HRSG to a high pressure steam turbine or drum, while the heated heat medium is sent to a hot storage tank for later use (e.g., for power generation above base, peak, or other loads). In the HRSG, the desuperheater is left in place and the steam flow through the HRSG can be split between the desuperheater and the thermal energy storage system, with all steam flow passing through the thermal energy storage system or, if the thermal energy storage system is offline, all steam flow passing through the desuperheater.

[0017] Referring to FIG. 1, a heat recovery steam generation system 12 according to one embodiment is shown. Such a system may be modified or retrofitted to include a thermal energy storage system 100 of the type described herein. Alternatively, a complete system including both the heat recovery steam generation system 12 and the thermal energy storage system 100 may be built as a single facility rather than retrofitting an existing system. It should be understood that the heat recovery steam generation system 12 (and thermal energy storage system 100) described herein is for illustrative purposes only. The thermal energy storage system 100 disclosed herein and its variations, as well as other consistent embodiments, may be used with the heat recovery steam generation system 12 or other equivalent systems. For example, the heat recovery steam generation system 12 is depicted as a system for use in a combined cycle gas power plant to recover heat for steam generation from exhaust gases from a gas combustion turbine. However, the thermal energy storage system 100 may be used in any other suitable recovery system (e.g., as used in coal-fired power plants, industrial processes using steam, etc.) or other systems in which the temperature of the recovered heat is controlled.

[0018] Referring to FIG. 1, in the depicted embodiment, a heat recovery steam generation system 12 is part of a combined cycle power plant that includes a gas-fired turbine. The HRSG 12 includes an exhaust duct or a housing 14 for receiving exhaust gas and passing the exhaust gas through heat recovery elements. The housing 14 has an exhaust gas opening 16 at one end of the housing 14, shown at the left end of the housing 14 in FIG. 1. The housing 14 also has an exhaust gas outlet or stack 18 at the opposite end of the housing 14, or at the right end of the housing shown in FIG. 1. The exhaust gas inlet or opening 16 is in operative communication with a burner or other power generating device, such as a gas-fired turbine (not shown), of the power plant to receive hot exhaust gas emitted by, for example, a source for heat recovery of the combined cycle power plant. The hot exhaust gas flows through the housing 14 from the exhaust gas inlet or opening 16 to the exhaust gas outlet or stack 18 from left to right as shown in FIG. 1. Passing the exhaust gases through the housing 14 is used to remove heat from the exhaust gases and use the recovered heat for steam generation. The generated steam may be used, for example, in a combined cycle power plant for power generation using a steam turbine (i.e., to complement power generation from a gas combustion turbine). Typically, heat is extracted from the exhaust gases using one or more heat exchangers in which heat is transferred to a working fluid (e.g., water) for steam generation.

[0019] In the depicted embodiment, the HRSG 12 includes multiple heat exchangers for this purpose. The heat exchangers may be of any suitable type including one or more of a tube field supported within the gas stream, a shell-and-tube heat exchanger, a double tube heat exchanger, a plate heat exchanger, or any other suitable heat exchanger known to those skilled in the art. In the depicted embodiment, the high pressure evaporator heat exchanger 22 is disposed and supported in the housing 14. It should be noted that other equipment may be disposed between the high pressure evaporator heat exchanger 22 and the exhaust stack 18, such as, for example, high pressure economizer(s), intermediate pressure operating systems and / or low pressure operating systems each having their own superheater, evaporator, economizer, preheater, and / or other equipment. Examples of heat recovery steam generator systems and such devices include the heat recovery steam generator system described in U.S. Patent No. 6,508,206, the entireties of which are incorporated herein by reference, and the heat recovery steam generator system described in U.S. Patent No. 10,180,086, the entireties of which are incorporated herein by reference. The high pressure evaporator heat exchanger 22 is in fluid communication with the high pressure steam drum 24. As used herein, the term "fluid communication" should be understood to mean that two components in fluid communication can receive fluid therebetween, either directly or through an intermediate component, in one or two directions, unless expressly described otherwise, e.g., fluid may pass through a conduit, tube, pipe, duct, etc. The high pressure evaporator heat exchanger 22 is in fluid communication with the high pressure drum 24 by a pipe, tube, duct, etc., and in some embodiments is directly connected. The high pressure drum 24 is adapted and configured to store high pressure steam for feeding other components of the HRSG system 12 and / or for use in directly or indirectly driving a steam turbine.

[0020] In the depicted embodiment, the high pressure steam drum 24 is supplied with water from an economizer (not shown) in fluid communication with the high pressure steam drum 24. The economizer is adapted and configured to preheat the feed water to the HRSG (e.g., as a feed water heater). In other words, the high pressure steam drum 24 is supplied with water from an economizer in fluid communication with a feed water source, and the received water is then heated using the high pressure evaporator heat exchanger 22 and then stored in the high pressure steam drum 24 as steam for supplying steam to additional components of the heat recovery steam generation system 12. It should be understood that the high pressure steam drum 24 is connected in fluid communication with any water input source 26. For example, the water input source 26 may be fresh water or condensed steam returning from a steam turbine for reuse.

[0021] In some embodiments, the water in the high pressure steam drum 24 is sent to the high pressure evaporator 22, which heats the water to boiling point and generates steam. The steam / water mixture passes through the high pressure evaporator 22 and is fed to the high pressure drum 24, where the water and steam are separated. The water in the high pressure drum 24 is returned to the high pressure evaporator 22, while the steam collected in the high pressure drum 24 is directed to a first high pressure superheater 32, which is in fluid communication with the high pressure steam drum 24. The first high pressure superheater 32 is a heat exchanger adapted and configured to remove heat from the exhaust gas in the housing 14 and transfer the heat to the steam from the high pressure steam drum 24. High pressure steam can be provided to the first high pressure superheater 32 from the high pressure steam drum 24 through piping 28. In some embodiments, the high pressure steam drum 24 feeds the first high pressure superheater 32 directly. In alternative embodiments, there may be one or more intermediate components (e.g., control devices such as valves, bypasses, additional heat transfer components such as heat exchangers, take offs and / or other components, as the term is used throughout).

[0022] The first high pressure superheater 32 feeds indirectly and through line 34 to the second high pressure superheater 36. The second high pressure superheater 36 feeds indirectly and through line 38 to the high pressure section of a steam turbine (not shown) (such as in a combined cycle power plant). A first high pressure attemperator 44 is disposed between the first high pressure superheater 32 and the second high pressure superheater 36. A second high pressure attemperator 40 is disposed downstream of the second high pressure superheater 36. In an alternative embodiment, the second high pressure attemperator 40 is omitted.

[0023] The first high pressure superheater 32 raises the temperature of the steam to a superheated condition. As mentioned above, when the combined cycle power plant operates at low load operating conditions, the temperature of the exhaust gas in the housing 14 may be higher than when operating at base load operation. As a result, the amount of heat transferred to the steam by the first high pressure superheater 32 can cause the temperature of the steam to exceed design parameters. The same is true for the second high pressure superheater 36 and / or any other superheater sections described in detail below. (For example, any number of additional high pressure superheaters can be used, and in the case of more than one such superheater, a corresponding attemperator is typically, but not necessarily, located between the superheater closest to the evaporator and the next superheater located in series with that superheater). The increase in exhaust gas temperature at low load operating conditions can, for example, cause the gas turbine engine to operate at a lower air throughput, which, as mentioned above, does not cool the exhaust gas as much as when the turbine operates at the higher air throughput of base load operation. To reduce the temperature of the steam within design parameters, steam exiting the first high pressure superheater 32 is passed through a first high pressure attemperator 44. The first high pressure attemperator 44 is selectively controlled to use cooling water to reduce the temperature of the steam passing therethrough. For example, the flow of cooling water to the first high pressure attemperator 44 is controlled using a valve 45, which is upstream of the first high pressure attemperator 44 and in fluid communication with both the source of cooling water and the first high pressure attemperator 44. The valve is opened to provide additional cooling water when the temperature of the steam needs to be reduced, and is partially or completely closed to increase the temperature of the steam (e.g., by reducing cooling through the first high pressure attemperator 44).The first high pressure attemperator 44 can be any suitable attemperator, such as, for example, a multi-nozzle spray desuperheater, a tube bundle type desuperheater, a water bath type attemperator, a water spray type attemperator, a single point radial injection spray desuperheater, a multiple point radial injection spray desuperheater, an axial injection spray desuperheater, a counterflow type axial attemperator, a multiple nozzle axial injection attemperator, a variable area type multiple nozzle attemperator, or any other suitable direct contact or indirect contact attemperator. In other embodiments, the first high pressure attemperator 44 is controlled based on the temperature of the steam. In some embodiments, the first high pressure attemperator 44 is controlled based on temperature sensors located downstream of the second high pressure superheater 36 and upstream of the second high pressure attemperator 40. The steam temperature immediately downstream of the DSHTR may also be used to control the cooling water flow.

[0024] Steam exiting the first high pressure desuperheater 44 enters, directly or indirectly, the second high pressure superheater 36, which is in fluid communication with the second high pressure superheater 36. For example, the first high pressure desuperheater 44 is coupled to the second high pressure superheater 36 by piping 34. The second high pressure superheater 36 is a superheater of the same or similar configuration as the first high pressure superheater 32. The second high pressure superheater 36 is a heat exchanger. The second high pressure superheater 36 is adapted and configured to remove heat from the exhaust gas 16 passing through the housing 14 and transfer the heat to the steam to increase the temperature of the steam (e.g., to a superheated state).

[0025] Steam exiting the second high pressure superheater 36 is sent, directly or indirectly, to the second high pressure attemperator 40, which is in fluid communication with the second high pressure attemperator 40. For example, the second high pressure superheater 36 is coupled to the second high pressure attemperator 40 by piping 39. The second high pressure attemperator 40 is typically of the same or similar construction as the first high pressure attemperator 44. In alternative embodiments, the construction of the second high pressure attemperator 40 differs from the first high pressure attemperator 44 in construction and / or operation. The second high pressure attemperator 40 is supplied with cooling water from a suitable source and is configured to maintain the temperature of the steam exiting the second high pressure attemperator 40 within design parameters. For example, the flow of cooling water to the second high pressure attemperator 40 can be controlled to cool the steam based on a temperature sensor located downstream of the second high pressure attemperator 40. The one or more control valves that control the steam admission in FIG.

[0026] Steam exiting the second high pressure attemperator 40 is fed directly or indirectly to the high pressure section of a steam turbine for power generation. Alternatively, additionally or partially, some or all of the steam may be sent to a bypass that bypasses the steam turbine. Such a bypass may be controlled by any suitable technique and / or hardware known to those skilled in the art. Steam may also be directed in parallel to a process and / or to both a steam turbine and a process.

[0027] In some embodiments, the HRSG 12 also includes a first reheater 52 disposed within the housing 14. The first reheater 52 is a heat exchanger, of any suitable type, adapted and configured to transfer heat from the exhaust gas 16 passing through the housing 14 to steam provided to the first reheater 52, as previously described herein. The first reheater 52 can be any suitable reheater. In some embodiments, the first reheater 52 is in direct or indirect fluid communication with a source of intermediate pressure steam and / or cold reheat steam. For example, the cold reheat steam can be steam exiting a high pressure section of a steam turbine, and the intermediate steam can be steam exiting an intermediate pressure section of the HRSG. For example, cooled steam that has passed through a high pressure section of the steam turbine (not shown) is delivered by piping 54 from the steam turbine to the first reheater 52 in the boiler housing 14. Similarly, intermediate pressure steam from an intermediate pressure system of the HRSG can be delivered by piping 54 to the first reheater 52. The first reheater 52 increases the temperature of the intermediate pressure steam or a mixture of intermediate pressure steam and cold reheat steam received from the steam turbine. The steam exiting the first reheater 52 is then routed, for example, by piping 56, directly or indirectly to a first reheater attemperator 64 and then directly or indirectly to a second reheater 58. The steam exiting the reheater 58 can be routed directly or indirectly via a conduit, for example, piping 65 to a second reheater attemperator 60. The steam exiting the second reheater attemperator 60 is routed to a steam turbine (not shown) (e.g., a high pressure section of the steam turbine) as hot reheat steam. In some embodiments, the steam exiting the second reheater 58 is routed to another portion of the steam turbine.

[0028] The first reheater attemperator 64 is disposed downstream of the first reheater 52 and in fluid communication therewith (e.g., by additional piping or tubing 56 in communication with the first reheater 52 along with the second reheater 58). In some embodiments, the first reheater attemperator 64 is disposed immediately after the first reheater 52. In alternative embodiments, additional components may be disposed between the first reheater 52 and the first reheater attemperator 64. In further embodiments, the first reheater attemperator may be disposed upstream of the first reheater. The first reheater attemperator 64 is any suitable type of attemperator (e.g., one of the types described above with respect to the first high pressure attemperator 44). In operation, the first reheater attemperator 64 cools steam such that the steam temperature in the piping or tubing 56 is reduced to a desired temperature. The first reheater attemperator 64 can be controlled using one or more temperature sensors (TE) located downstream of the first reheater attemperator 64 (e.g., located downstream of the second reheater 58). The first reheater attemperator 64 can be any suitable attemperator type (e.g., the type described above in connection with the high pressure attemperator 44). The second reheater attemperator 60 is located downstream of the second reheater 58 and in fluid communication with the second reheater 58 (e.g., by additional piping or tubing 62). In some embodiments, the second reheater attemperator 60 is located immediately after the second reheater 58. In alternative embodiments, additional components can be located between the reheater 58 and the second reheater attemperator 60 (e.g., temperature sensors, control valves, bypasses, etc.). The second reheater attemperator 60 may be controlled using one or more temperature sensors, control valves, or other devices (e.g., temperature sensors upstream and / or downstream of the second reheater attemperator 60). The second reheater attemperator 60 is controlled to maintain the temperature of the exhaust steam within the design parameters of the HRSG 12. Steam exiting the second reheater attemperator 60 is provided to a steam turbine (not shown).

[0029] In some embodiments, the HRSG 12 includes a steam bypass 66, shown in dashed lines in FIG. 1 . In an alternative embodiment, the steam bypass 66 is omitted. The steam bypass 66 is controllable (e.g., using one or more valves and / or temperature sensors TE) so that the steam bypasses the first reheater 52 and the second reheater 58 to control the final steam temperature exiting the HRSG. When the steam bypass 66 is set to bypass, a portion or all of the cold reheat steam and / or intermediate pressure steam bypasses the first reheater 52, the first reheater attemperator 64, and the second reheater 58, and the steam exits the bypass 66 upstream of the second reheater attemperator 60.

[0030] As previously mentioned, the use of attemperators 40, 44, 60, 64 (or any subset thereof in alternative embodiments with different numbers of attemperators) and / or the use of steam bypass 66 reduces the efficiency of the HRSG because steam is either cooled and wastes heat, or in the case of steam bypass 66 is never heated at all and also wastes heat. The low efficiency of heat recovery during low load operation reduces the overall efficiency of the HRSG 12. Furthermore, the ability of the attemperator, as a control mechanism, to sufficiently cool the steam is limited because the amount of attemperator water that can be introduced (e.g., in the case of a direct contact attemperator) is limited by the saturation temperature of the steam at the water injection point (water cannot be injected below its saturation temperature), the amount of injected water relative to the steam flow, and the piping configuration. While the piping configuration can usually be accommodated in new plants, existing plants that are forced to operate off-design have limitations.

[0031] Another approach used for steam temperature control is the steam bypass. This system is more commonly employed in low pressure systems where the margin between the tube / piping design pressure and the code-defined allowable stresses is more easily addressed / provided. In a steam bypass, the steam bypasses the heating surface (partially or fully) and the cooler bypass steam is reintroduced into the main steam to control the final destination steam temperature. For these reasons, attemperators and / or steam bypasses pose significant drawbacks in efficiency and temperature control.

[0032] 2-7 generally, a thermal energy storage system 100 is depicted in accordance with a number of embodiments that improve the efficiency and / or control of the HRSG 12. The disclosed embodiments of the thermal energy storage system 100 enable thermal energy storage (TES) in combined cycle power plants by replacing or augmenting the typical steam temperature controller (attemperator) with a heat exchange system that removes excess heat from the steam during off-design / low load periods of operation and returns energy (via steam generation) during periods of high steam / power demand.

[0033] Thermal energy storage system 100 is a heat storage system in which hot steam, which would normally pass through a attemperator and be cooled, instead passes through a heat exchanger where the steam temperature is reduced while releasing heat to a heat storage medium, preferably molten salt, or any other suitable medium (such as water, thermal oil, etc.). Salt is an exemplary heat storage medium, but other media can be used in alternative embodiments. The cooled steam is returned immediately downstream of the attemperator, while the heated medium is returned to the hot storage tank. The attemperator can be left in place and the steam flow split between the attemperator and a thermal energy storage (TES) heat exchanger, allowing either all flow to pass through the TES, or all flow to pass through the attemperator if the TES is offline or if there is no excess steam temperature at the terminal.

[0034] When the steam / power demand for the plant is high, or when increased plant flexibility is desired, the hot storage medium is pumped through a water / salt heat exchanger to produce saturated or heated steam which is then introduced into any of the operating steam systems, with the high pressure drum outlet piping being the preferred introduction point. The salt leaving the water / salt exchanger is sent to a cold storage tank which acts as a reservoir to feed the steam / salt exchanger(s).

[0035] The thermal energy storage system 100 system can also be used to provide heat to any other industrial heat user, such as, for example, district heating or power plant conditioning.

[0036] It should be understood that the examples disclosed herein are merely examples and that the thermal energy storage system 100 may be used in additional or alternative examples (e.g., 200-600). For example, the thermal storage medium can be any material that meets the process needs. Molten salt is one example and is a preferred medium due to its low cost, solubility, and safety, but any suitable medium may be used. The disclosed embodiments are for use with at least an "intermediate" attemperator or possibly a bypass or both. However, there are many plants that also employ end-stage attemperators where the attemperator is located on the terminal steam line. Although this is a less likely application area than the intermediate location, the thermal energy storage system 100 may be arranged to operate with such attemperators. In other words, the general use of a steam / storage medium heat exchanger to replace or supplement the attemperator allows the thermal energy storage system 100 to be used in any number or configuration of power plants or other systems that use attemperators. For example, in the case of a HRSG / boiler with multiple pressure levels (e.g., high pressure, reheater medium pressure, low pressure, etc.), attemperators are typically employed only in the high pressure and reheater sections. However, multiple attemperators can be used. In the case of a boiler / heat recovery steam generator with only one pressure system, the one pressure system may require an attemperator by default. The thermal energy storage system 100 described herein is not limited or restricted based on the number of pressure levels of a single boiler / HRSG or any designation of high pressure, medium pressure, low pressure. Any suitable number of attemperators can be used with any suitable number of steam / heat storage medium heat exchanger combinations to achieve the functionality of the thermal energy storage system described herein with reference to the depicted embodiment or other embodiments.

[0037] The thermal energy storage system 100 provides benefits to the combined cycle power plants (and other operations) described throughout herein, including increased efficiency by storing excess heat generated in part-load power plant operation, higher power generation during peak demand periods by utilizing stored heat, increased plant flexibility by allowing lower loads to be achieved, and reduced concerns regarding higher off-design ambient condition steam generation and high levels of water injection (e.g., erosion / stress failure, corrosion) by reducing the need for attemperator operation. Elimination or reduction of attemperator use is also a desirable feature in that potential damage and wear to the HRSG and / or steam turbine is reduced when less water is introduced into the steam (e.g., in the case of direct contact / injection attemperators). Damage from attemperator use can occur in a variety of ways, including thermal fatigue, erosion, and / or chemical imbalances in the steam chemistry.

[0038] More simply stated, power plants are increasingly being forced into off-design operating modes to accommodate the influx of power from renewable energy sources. These off-design modes can cause inefficient plant operation, shortened plant life, and create safety concerns. The thermal energy storage system 100 described herein provides benefits by allowing power plants to operate more efficiently and flexibly, by storing energy generated in unusable / undesirable off-design conditions, and by returning energy to the system, or to another user, when the energy is more useful (e.g., baseload operation).

[0039] While it is desirable to assist in improving efficiency at part load and is accomplished using the systems and methods described herein, such systems and methods also provide an additional benefit by addressing inefficiencies that occur during part load operation in a manner that allows for this inefficiency to be turned into a lever for improved plant operation during times of increased power demand and the need for fossil fuel fired (FFF) plants to operate at base load. The systems and methods described herein allow for operation at performance levels beyond the original base load operation by drawing energy from stored energy during peak demand / part load operation. This performance improvement may take many forms, including but not limited to increased steam generation and thus generating more power for the power cycle, increased process steam so that other steam generators do not need to operate or can be drawn from a thermal energy storage system, reducing fuel costs for the plant by reducing fuel burn for the heat source while still achieving normal base load steam generation rates, and potentially improving the heat sink of the plant. An additional benefit provided by the systems and methods described herein is that the gas turbine can be turned down to a low load to conserve fuel and reduce absolute emissions while drawing energy from the thermal energy storage system to maintain steam production at a level that meets the steam turbine demand (e.g., the gas turbine can run at a low load to conserve fuel and emissions while supplying the minimum amount of steam required to the steam turbine, which load cannot generate enough on its own to supply the minimum amount of steam required to the steam turbine). The systems and methods described herein also reduce or eliminate some of the adverse effects that result from the use of superheater(s) by replacing such components with thermal energy storage systems to control the temperature of the steam exiting the heat recovery steam generator. For example, reducing or eliminating the use of cooling water injected by attemperator(s) reduces or eliminates the thermal shock and associated wear that result from the injected cooling water.Another benefit of the systems and methods described herein is that such systems and methods address inefficiencies resulting from off-design operating conditions (e.g., operating at ambient temperature conditions above the design conditions). For example, the systems and methods described herein use stored energy (in an energy storage system) to create steam and address production "deficiencies" resulting from off-design conditions (e.g., operating at ambient temperatures above the ambient temperature the plant was designed for), thereby allowing the steam turbine to make more power than would otherwise be achievable under the plant conditions.

[0040] Now, with particular reference to FIG. 2, the general principles and components of the energy storage system 100 described above will be described in more detail. The thermal energy storage system 100 of the present disclosure is shown within the dashed boundary 172 of FIG. 2. The thermal energy storage system 100 is combined with the HRSG 12 to replace or augment the steam temperature control provided by the attemperator 40, 44, 60, 64. This combination can be performed as either a retrofit or a ground-up design / build. It should be understood that one skilled in the art can use the disclosure herein in a manner to retrofit an existing HRSG 12 with the thermal energy storage system 100 by coupling the components of the energy storage system 100 to the existing heat recovery steam generator 12 in the locations described herein. Additionally, any necessary temperature sensors, valves, control systems, and the like may be added to achieve the functionality described herein, as would be understood by one skilled in the art.

[0041] One or more of the attemperators 40, 44, 60, 64 are replaced or supplemented with a heat exchanger system 176, 184 (ie, a steam / TES heat exchanger) that removes excess heat therefrom (eg, brings the temperatures therefrom within design parameters).

[0042] The thermal energy storage system 100 includes a cold tank 174 that stores a flowable thermal storage medium (e.g., hot salt, molten salt, thermal oil, etc.). Preferably, the thermal storage medium is molten salt. The cold tank 174 is sufficiently insulated to keep the thermal storage medium stored in the cold tank in a flowable condition. In some embodiments, additional heaters, heating elements, steam, or other heat sources can be used to keep the thermal storage medium pumpable. During periods when the TES does not need to charge or discharge, a continuous flow of salt can pass through the flow paths and exchangers to maintain the metal temperature above the freezing point of the salt(s). This recirculation freeze protection can also be employed in other embodiments of the system described herein.

[0043] The thermal energy storage system 100 includes a first high pressure steam / heat medium heat exchanger 176 adapted and configured to remove heat from the steam in the HRSG 12. The steam / heat medium heat exchangers and such devices described herein can be any suitable heat exchanger (e.g., of the type described above with respect to the first high pressure superheater 32) suitable for transferring heat from steam to a heat medium (e.g., molten salt). The first high pressure steam / heat medium heat exchanger 176 is in direct or indirect fluid communication with the cold tank 174 and receives a heat storage medium (e.g., a heat medium) from the cold tank 174. The first high pressure steam / heat medium heat exchanger 176 is positioned such that it can be supplied with steam from the first high pressure superheater 32 and is in direct or indirect fluid communication with the first high pressure superheater 32. For example, the first high pressure steam / heat medium heat exchanger 176 is coupled to the piping or tubes 34 and 178 and selectively bypasses the first high pressure attemperator 44 coupled between the first high pressure superheater 32 and the second high pressure superheater 36. The temperature of the steam entering the second high pressure superheater 36 may be controlled by selectively bypassing the first high pressure attemperator 44, in whole or in part, using the depicted control valve and based on data from one or more temperature sensors (e.g., temperature sensors upstream of the first high pressure attemperator 44 and / or downstream of the first high pressure attemperator 44). For example, if cooling of the steam is required, the first high pressure attemperator 44 can be completely bypassed using the control valve and heat removed from the steam by the first high pressure steam / heat medium heat exchanger 176 and the steam returned downstream of the first high pressure attemperator 44 (and upstream of the second high pressure superheater 36). If additional cooling is required, a portion of the steam may be passed to the first high pressure attemperator 44 and selectively cooled using cooling water (e.g., the first high pressure steam / heat medium heat exchanger 176 and the first high pressure attemperator 44 work in conjunction to cool the steam exiting the first high pressure superheater 32). In this example, if cooling of the steam is not required, the steam may be passed entirely through the first attemperator 44, but no cooling water is provided to the first attemperator 44 and no cooling occurs. In this manner, the steam may be cooled or uncooled to a desired temperature (e.g., within design parameters) using one or more of the high pressure attemperators 44 and the first high pressure steam / heat medium heat exchanger 176, alone or in combination.Steam exiting the first high pressure steam / heat medium heat exchanger 176 and / or the first high pressure attemperator 44 is supplied to the second high pressure superheater 36. The heat storage medium heated by the first high pressure steam / heat medium heat exchanger 176 and exiting the first high pressure steam / heat medium heat exchanger 176 is supplied, directly or indirectly, to a hot tank 194 (e.g., for storage or use).

[0044] The heat storage medium entering the first high pressure steam / heat medium heat exchanger 176 is supplied, directly or indirectly, from a cold tank 174, and the inlet of the first high pressure steam / heat medium heat exchanger 176 is in fluid communication with the cold tank 174 (e.g., fluid communication is provided by piping or tubing 182, which includes a supply line). The cold tank 174, the first high pressure steam / heat medium heat exchanger 176, and the hot tank 194 form a superheater cooling loop that selectively extracts heat from steam heated by one or more high pressure superheaters of the HRSG 12. The heat storage medium moving from the cold tank to the first high pressure steam / heat medium heat exchanger 176 is heated and then moves to the hot tank 194 (as described below, the heat storage medium is selectively moved from the hot tank 194 to the cold tank 174 as heat is extracted for use in steam generation or other processes).

[0045] Thermal energy storage system 100 also includes a first reheat steam / thermal media heat exchanger 184 adapted and configured to remove heat from the steam in HRSG 12. First reheat steam / thermal media heat exchanger 184 is any suitable type of steam / thermal media heat exchanger, such as those described above with respect to first high pressure steam / thermal media heat exchanger 176. Similarly, first reheat steam / thermal media heat exchanger 184 operates and is controlled with reference to / in conjunction with first reheat attemperator 64 in the manner described above with respect to first high pressure steam / thermal media heat exchanger 176 and high pressure attemperator 44 (e.g., using one or more valves and / or temperature sensors to operate in conjunction with the attemperator, instead of the attemperator, or not at all with steam passing through a non-cooled attemperator). The first reheat steam / heat medium heat exchanger 184 is in direct or indirect fluid communication with the cold tank 174 and receives a heat storage medium (e.g., heat medium) from the cold tank 174. For example, the first reheat steam / heat medium heat exchanger 184 is connected by piping, tubing, conduits 186 (as are other components described herein) to selectively bypass the first reheater attemperator 64, which is connected between the first reheater 52 and the second reheater 58. Through control of the first reheat steam / heat medium heat exchanger 184 and the first reheater attemperator 64 using control valves and temperature sensors as previously described, steam may or may not be cooled to a desired temperature (e.g., within design parameters) using one or more of the first reheat steam / heat medium heat exchanger 184 and / or the reheater attemperator 64. The first reheat steam / heat medium heat exchanger 184 is positioned to be supplied with steam from the first reheater 52 and is in fluid communication, directly or indirectly, with the first reheater 52. Steam exiting the first reheat steam / heat medium heat exchanger 184 and / or the first reheater attemperator 64 is supplied to the second reheater 58. The heat storage medium heated by the first reheat steam / heat medium heat exchanger 184 and exiting the first reheat steam / heat medium heat exchanger 184 is supplied, directly or indirectly, to a hot tank 194 (e.g., for storage or use).

[0046] The heat storage medium entering the first reheat steam / heat medium heat exchanger 184 is supplied, directly or indirectly, from the cold tank 174, and the inlet of the first reheat steam / heat medium heat exchanger 184 is in fluid communication with the cold tank 174 (e.g., fluid communication is provided by piping or tubing 185 that constitutes a supply line).

[0047] The cold tank 174, the first reheat steam / heat medium heat exchanger 184, and the hot tank 194 form a reheat cooling loop that selectively extracts heat from steam heated by one or more high reheaters of the HRSG 12. A heat storage medium moves from the cold tank 174 to the first reheat steam / heat medium heat exchanger 184, is heated, and then moves to the hot tank 194 (as described later herein, the heat storage medium selectively moves from the hot tank 194 to the cold tank 174 as heat is extracted for use in steam generation or other processes).

[0048] It should be understood that the cold tank 174 and / or the hot tank 194 can function as a buffer such that a process can take place without requiring the transfer of heat storage medium from the hot tank 194 to the cold tank 174. In other words, the entire thermal energy storage system 100 includes sufficient heat storage medium to provide a buffer. The heating of the heat storage medium (and cooling of the steam) using the superheater cooling loop and / or the reheat loop can operate (to some extent) independently of any process that uses the heated heat storage medium from the hot tank 194. For example, the thermal energy storage system 100 includes sufficient buffer heat storage medium such that the superheater cooling loop and / or the reheat loop can operate during anticipated periods of off peak / low load operation of any particular power plant.

[0049] A pump 192 provides a flow of a heat storage medium (e.g., heat medium) from the cold tank 174 to the first high pressure steam / heat medium heat exchanger 176. The pump 192 is any suitable pump for pumping a heat medium used by the thermal energy storage system 100 (e.g., a salt pump for a molten salt heat medium). The flow provided by the pump 192 causes the heated heat medium exiting the first high pressure / heat medium heat exchanger 176 to move to the hot tank 194. Similarly, a pump 198 provides a flow of a heat storage medium (e.g., heat medium) from the cold tank 174 to the first reheat steam / heat medium heat exchanger 184. The flow provided by the pump 198 causes the heater heat medium exiting the first reheat steam / heat medium heat exchanger 184 to move to the hot tank 194.

[0050] The thermal energy storage system 100 also includes a water / heat medium heat exchanger 187 connected in fluid communication between the cold tank 174 and the hot tank 194. The water / heat medium heat exchanger 187 is any suitable type of heat exchanger (e.g., as described with reference to the high pressure evaporator 22) or multiple heat exchangers in parallel or series for transferring heat from a heat medium (e.g., molten salt) to water to generate, at least in part, steam. The water / heat medium heat exchanger 187 is also connected in fluid communication with a water source 189 (e.g., water provided by a feed pump or an economizer). The water source 189 provides water to the thermal energy storage system 100 for generating steam using the heat medium from the hot tank 194 when the steam demand of the power plant increases (e.g., when the power plant returns to base load operation from off-peak operation). The water / heat medium heat exchanger 187 can also, or alternatively, be used to generate hot water, high quality steam, saturated steam, superheated steam, supercritical steam, or to heat any other fluid in a similar physical phase. The water / heat medium heat exchanger can be used in this manner with any of the embodiments described herein.

[0051] During high steam / power demands of the combined cycle power plant, the heat storage medium (e.g., heat transfer medium or thermal storage medium) is pumped by pump 191 (e.g., any suitable pump including a salt pump for a hot salt heat transfer medium) from hot tank 194 through water / heat transfer medium heat exchanger 187 to cold tank 174. Pump 193 can pump water through water / heat transfer medium heat exchanger 187 from a water source 189, or the water source 189 can be provided under pressure (e.g., from a pump not shown). The heat storage medium pumped through water / heat transfer medium heat exchanger 187 produces saturated or heated steam from water pumped through water / heat transfer medium heat exchanger 187 by water pump 193 (in any embodiment described herein, water / heat transfer medium heat exchanger 187 can also be used to generate hot water, high quality steam, saturated steam, superheated steam, supercritical steam, or alternatively used to generate these or heat any other fluid in a similar physical phase). The steam produced by the water / heat medium heat exchanger 187 passes through a separator 195 that separates the residual water from the steam. The residual water is returned to the water / heat medium heat exchanger 187 by a pump 193. The produced steam is supplied as additional produced steam to the HRSG 12, for example, downstream of the high pressure drum 24. Alternatively, or in addition, the produced steam is supplied to another process (e.g., district heating or power plant conditioning). This may be controlled using one or more control valves (not shown). Alternatively, the heat exchanger 187 of this embodiment, or any other, may be configured to produce superheated steam that may then be supplied to the steam system (e.g., in the HRSG or steam turbine) or elsewhere in the facility. The heat storage medium leaving the water / heat medium heat exchanger 187 is sent to a cold storage tank 174, which serves as a reservoir of cooled heat storage medium for heating and cooling steam using the first high pressure steam / heat medium heat exchanger 176 and the first reheat steam / heat medium heat exchanger 184.

[0052] The cold tank 174, hot tank 194, and pump 191 may be run based on the temperature of the stored medium in the cold tank 174 and / or hot tank 194 (based on corresponding temperature sensors). For example, the flow of heat transfer medium from the hot tank 194 to the cold tank 174 may ensure that the heat transfer medium in the cold tank remains in a molten state.

[0053] Thus, the thermal energy storage system 100 stores energy generated during off-design conditions, where it cannot be used or is not needed, in a hot tank of thermal storage medium, allowing the energy to be returned to the system in the form of additional steam or returned to another user when the energy is more useful (e.g., during base load operation). The thermal energy storage system may also generate steam for any suitable use using the water / heat medium heat exchanger 187. The steam generated by the thermal energy storage system in any embodiment described herein may be sent to an existing heat recovery steam generator system or any other potential steam user, including, but not limited to, an existing steam turbine, a new steam turbine / expander (e.g., one added in a retrofit of an existing power plant that includes the addition of a thermal energy storage system), a drive system for mechanical equipment (e.g., pumps), and / or any other process that uses steam.

[0054] Referring now to FIG. 3, an alternative embodiment thermal energy storage system 100 is depicted. The thermal energy storage system 200 depicted in FIG. 3 differs from the embodiment 100 described with reference to FIG. 2 in that the thermal energy storage system 200 includes two additional controllable steam outputs for use in other processes and / or to supply an intermediate steam drum. In particular, the thermal energy storage system 200 includes a steam take-off downstream of the first high pressure steam / heat medium heat exchanger 276 that takes off steam or a portion of the steam that would otherwise be supplied to the second high pressure superheater 36 (e.g., control is provided by one or more control valves and one or more temperature sensors). The taken off steam is supplied to a compressor 277. The compressor 277 is any suitable compressor for increasing the pressure of the steam. The compressor selectively supplies one or more additional processes (e.g., district heating or power plant conditioning) and / or the high pressure steam drum 24 and is in fluid communication, directly or indirectly, with other process equipment and the high pressure steam drum 24. Using steam take-off, compressor 277 and / or process take-off controlled by appropriate valves and temperature sensors, steam may be directed from the first high pressure steam / heat medium heat exchanger 276 to one or more of the second high pressure superheater 36, additional processes, and / or high pressure steam drum 24 in any combination or amount.

[0055] The thermal energy storage system 200 further includes a steam take-off downstream of the first reheat steam / heat medium heat exchanger 284 that selectively removes steam or a portion of the steam that would otherwise be provided to the second reheater 58 (e.g., control provided by one or more control valves and one or more temperature sensors). The removed steam is provided to a compressor 279. The compressor 279 is any suitable processor for increasing the pressure of the steam. The compressor selectively supplies one or more additional processes (e.g., district heating or power plant conditioning) and / or an intermediate pressure steam drum (not shown) for supplying a steam turbine of a power plant, and is in fluid communication, directly or indirectly, with other process equipment and the intermediate pressure steam drum. Using steam take-off, compressor 279, and / or process take-off, controlled using appropriate valves and temperature sensors, steam may be directed from the first reheat steam / heat medium heat exchanger 284 to one or more, in any combination or quantity, of the second reheater 58, additional process and / or intermediate pressure steam drums.

[0056] Referring now to FIG. 4, an alternative embodiment of the thermal energy storage system 200 is depicted. The thermal energy storage system 300 depicted in FIG. 4 differs from the embodiment 200 depicted in FIG. 3 in that the thermal energy storage system 300 includes two additional steam / heat medium heat exchangers to support a compressor. Specifically, the thermal energy storage system 200 includes a second high pressure steam / heat medium heat exchanger 375 that is the same as or similar to the first high pressure steam / heat medium heat exchanger 376. In parallel with the heat medium flow, the second high pressure steam / heat medium heat exchanger 375 is supplied with heat medium from a cold tank 374 and from a take-off on the line that feeds the first high pressure steam / heat medium heat exchanger 376, and the heated heat medium exits the second high pressure steam / heat medium heat exchanger 375 and is supplied to a hot tank 394 at a supply port that joins the output from the first high pressure steam / heat medium heat exchanger 376. The second high pressure steam / heat medium heat exchanger 375 is selectively (e.g., through control valve and temperature sensor control) supplied with steam from a take-off between the second high pressure superheater 36 and the second high pressure attemperator 40. The second high pressure steam / heat medium heat exchanger 375 outputs steam downstream of the second high pressure attemperator 40. This allows the second high pressure steam / heat medium heat exchanger 375 to operate in a similar manner to the first high pressure steam / heat medium heat exchanger 376 as the first high pressure steam / heat medium heat exchanger 376 does for steam exiting the first high pressure superheater 32, to control the steam temperature of the steam exiting the second high pressure superheater 36, allowing the need for cooling from the second high pressure attemperator 40 to be partially or completely avoided. Steam exiting second high pressure steam / heat medium heat exchanger 375 is supplied to the high pressure steam section of the steam turbine and / or selectively (all, none, or some) supplies the take-off and compressor 373 in a manner similar to compressor 377 and first high pressure steam / heat medium heat exchanger 376. Steam exiting compressor 373 is provided to high pressure drum 24. Thermal energy storage system 200 also includes a water / heat medium heat exchanger 287 connected in fluid communication between cold tank 274 and hot tank 294, which components operate and are connected in a manner similar to that described for corresponding components 187, 174, and 194 of system 100 of FIG. 2.

[0057] The thermal energy storage system 300 further includes a second reheat steam / heat medium heat exchanger 383 that is the same as or similar to the first reheat steam / heat medium heat exchanger 384. The first reheat steam / heat medium heat exchanger 384 and the second reheat steam / heat medium heat exchanger 383 are supplied with heat medium from the cold tank 374 and from a take-off on the line that feeds the first reheat steam / heat medium heat exchanger 384 allowing the two exchangers (e.g. 383 and 384) to operate in parallel with respect to heat medium flow, where the heat medium exits the second reheat steam / heat medium heat exchanger 383 and is supplied to a hot tank 394 at a supply port that joins the output from the first reheat steam / heat medium heat exchanger 384. The second reheat steam / heat medium heat exchanger 383 is selectively (e.g., through control valve and temperature sensor control) supplied with steam from a take-off between the second reheater 58 and the second reheater attemperator 60. The second reheat steam / heat medium heat exchanger 383 outputs steam downstream of the second reheater attemperator 60. This allows the second reheat steam / heat medium heat exchanger 383 to operate in a similar manner to the first reheat steam / heat medium heat exchanger 384, controlling the steam temperature of the steam exiting the second reheater 58 in a manner similar to that which the first heat exchanger 384 does for the steam exiting the first reheater 52, thereby allowing the need for cooling from the second reheater attemperator 60 to be partially or completely avoided. Steam exiting the second reheat steam / heat medium heat exchanger 383 is supplied as hot reheat steam to a turbine or bypass and / or selectively (all, none, or part) to a take-off and compressor 381 in a manner similar to compressor 379 and first reheat steam / heat medium heat exchanger 384. Steam exiting compressor 381 is supplied to an intermediate pressure steam drum and / or to another process. Thermal energy storage system 300 also includes a water / heat medium heat exchanger 387 connected in flow communication between the cold tank 374 and the hot tank 394, which components operate and are connected in a manner similar to that described for corresponding components 187, 174, and 194 of system 100 of FIG. 2.

[0058] Referring to FIG. 5, an alternative embodiment of the thermal energy storage system 300 is depicted. The thermal energy storage system 400 depicted in FIG. 5 differs from the embodiment 300 depicted in FIG. 4 in that the thermal energy storage system 400 has a heat medium that feeds the high pressure steam / heat medium heat exchanger in series and feeds the reheat steam / heat medium heat exchanger in series. More specifically, the steam flows of the first high pressure steam / heat medium heat exchanger 476, the second high pressure steam / heat medium heat exchanger 475, the first reheat steam / heat medium heat exchanger 484, and the second reheat steam / heat medium heat exchanger 483 remain the same. The heat medium flows are different from the thermal energy storage system 300. The heat medium from the cold tank 474 is pumped to the first high pressure steam / heat medium heat exchanger 476, where it is heated, and exits the first high pressure steam / heat medium heat exchanger 476 and is fed (e.g., directly or indirectly) to the second high pressure steam / heat medium heat exchanger 475. The heated heat transfer medium then returns to the hot tank 494. The heat transfer medium from the cold tank 474 is also pumped to the first reheat steam / heat transfer medium heat exchanger 484 where it is heated and exits the first reheat steam / heat transfer medium heat exchanger 484 and is supplied (e.g., directly or indirectly) to the second reheat steam / heat transfer medium heat exchanger 483. The heater heat transfer medium then returns to the hot tank 494. The thermal energy storage system 400 further includes a water / heat transfer medium heat exchanger 487 connected in fluid communication between the cold tank 474 and the hot tank 494, the components of which operate and are connected in a similar manner as described for the corresponding components 187, 174 and 194 of the system 100 of FIG. 2.

[0059] Referring now to Figure 6, an alternative embodiment of thermal energy storage system 400 is depicted. Thermal energy storage system 500 depicted in Figure 6 differs from embodiment 400 depicted in Figure 5 in that thermal energy storage system 500 includes an electric heater for controlling the temperature of the heat medium and omits the compressor of thermal energy storage system 400. Specifically, thermal energy storage system 500 omits compressors 477, 473, 481, and 479 of thermal energy storage system 400. In thermal energy storage system 500, steam exiting first high pressure steam / heat medium heat exchanger 576 is provided to second high pressure superheater 36, and steam exiting second high pressure steam / heat medium heat exchanger 575 is provided to the high pressure section of the steam turbine (or bypass). Similarly, steam exiting first reheat steam / heat medium heat exchanger 584 is provided to second reheater 58, and steam exiting second reheat steam / heat medium heat exchanger 583 is provided to a steam turbine (or bypass) as hot reheat steam. Thermal energy storage system 500 differs from other embodiments in that steam generated using hot heat medium and water / heat medium heat exchanger 587 is not provided to high pressure steam drum 24, but instead is supplied to HRSG 12 upstream of second high pressure attemperator 40.

[0060] The thermal energy storage system 500 also includes a first electric heater 503 and a second electric heater 505. Each electric heater is any suitable electric heater for heating a heat carrier (e.g., molten salt). The electric heaters 503, 505 are controlled to manage the temperature of the heat carrier (e.g., based on temperature sensors measuring the temperature of the heat carrier in the hot tank 505 and / or the cold tank 574). For example, the electric heaters 503, 505 can maintain the temperature of the heat carrier so that it is pumpable. Alternatively or additionally, the electric heaters 503, 505 can allow the temperature of the heat carrier (e.g., the temperature of the salt) to be further increased if it is desired to increase the steam temperature entering the downstream process (i.e., the process supplied by the steam generated using the water / heat carrier heat exchanger 587). If the downstream process is a steam turbine, a higher temperature of the steam increases the efficiency of the plant and helps minimize condensation formation in the final stage of the steam turbine at part-load operation. Similarly, the electric heaters 503, 505 can be used to further increase (compared to an embodiment without electric heaters) the temperature of the steam exiting the water / heat medium heat exchanger 587 provided to the HRSG 12 upstream of the second high pressure attemperator 40 for use in providing high pressure steam to the steam turbine of the power plant. The electric heaters 503, 505 can be used in combination with any of the embodiments described herein. Similarly, an arrangement of steam / heat medium heat exchangers (parallel or series) can be used in combination with any of the embodiments described herein. The thermal energy storage system 500 further includes a water / heat medium heat exchanger 587 connected in flow communication between the cold tank 574 and the hot tank 594, which components operate and are connected in a similar manner as described for the corresponding components 187, 174, and 194 of the system 100 of FIG. 2, except that the heaters 503 and 505 operate as described.

[0061] Referring to FIG. 7, an embodiment of a thermal energy storage system 600 is depicted that includes various controllable bypasses (e.g., controlled based on steam / process needs, temperature sensors, pressure sensors, etc.). It should be understood that the type of bypasses shown and described corresponding to the thermal energy storage system 600 can be used in connection with any of the embodiments described herein. Specifically, the thermal energy storage system 600 is similar to the thermal energy storage system 100 described with reference to FIG. 2, except that the thermal energy storage system 600 includes multiple bypasses. The thermal energy storage system 600 includes a bypass 607 that allows the heat medium to selectively and controllably bypass the first reheat steam / heat medium heat exchanger 684. A similar bypass can be used in embodiments that include a second reheat steam / heat medium heat exchanger. A bypass 609 allows the heat medium to selectively and controllably bypass the first high pressure steam / heat medium heat exchanger 676. A similar bypass can also be used in embodiments that include a second high pressure steam / heat medium heat exchanger. The thermal energy storage system 600 also includes a bypass 611 that allows the heat medium to be transferred from the hot tank 694 to the cold tank 674 without heat being extracted by the water / heat medium heat exchanger 687. Any other such bypasses can be used with respect to any of the components of the embodiments shown herein.

[0062] In the alternative embodiment of Figures 3-7, elements are numbered similarly to the embodiment of Figure 2, with the last two digits corresponding to the numbering of elements with the same or similar function. For example, while the illustration of Figure 2 shows that the heat storage medium enters the first high pressure steam / heat medium heat exchanger 176, which is supplied, directly or indirectly, from the cold tank 174, and the inlet of the first high pressure steam / heat medium heat exchanger 176 is in fluid communication with the cold tank 174 (e.g., fluid communication is provided by piping or tubing 182 that constitutes the supply line), in Figures 3-7, the numbers 276, 376, 476, 576, and 676 correspond to the high pressure steam / heat medium heat exchanger 176, and the numbers 282, 382, ​​482, 582, and 682 correspond to the piping or tubing 182 for the heat medium flow.

[0063] Throughout this disclosure, control of various equipment and / or processes is described. It should be understood that such control is performed using any suitable technique known to those of skill in the art. The valves can be of a type controllable by control circuits, computer controls, programmable logic controllers, or the like. For example, the valves can be solenoid, pneumatic, or other motor controlled valves. The control can be based on temperature sensors, pressure sensors, power output sensors, and / or any other suitable sensors and / or algorithms using sensor data or such data known to those of skill in the art. Components connected by lines are in fluid communication with each other and can be directly connected or connected through intervening components of other embodiments not depicted. It should be understood that the preferred embodiment is as depicted and in direct fluid communication to avoid both thermal and pumping losses.

[0064] Since various changes may be made in the above construction methods without departing from the broad scope of the present disclosure, it is intended that all matter contained in the above description or shown in the accompanying drawings be interpreted in an illustrative and not a limiting sense.

Claims

1. a steam / medium heat exchanger operable to receive steam from a heat recovery steam generator, receive a flow of a heat storage medium, and transfer heat from the steam to the heat storage medium to heat the heat storage medium; a storage hot tank in fluid communication with the vapor / media heat exchanger and operable to receive the heated thermal storage medium from the vapor / media heat exchanger and to store the heated thermal storage medium; Including, Thermal energy storage systems.

2. a water / medium heat exchanger operable to receive a flow of water, receive the heated heat storage medium stored in the hot tank from the hot tank, transfer heat from the heated heat storage medium to the water to generate steam, and deliver the steam to the heat recovery steam generator or process.

10. The thermal energy storage system of claim 1.

3. The thermal energy storage system is adapted and configured to reduce the temperature of the steam generated by the heat recovery steam generator and increase the temperature of the heat storage medium when the power plant served by the heat recovery steam generator operates at low load or off-design conditions, and to utilize the stored heated heat storage medium in the hot tank to generate steam using the water / media heat exchanger and supply the generated steam to the heat recovery steam generator when the power plant served by the heat recovery steam generator operates at peak load or higher than peak load.

3. The thermal energy storage system of claim 2.

4. the heat recovery steam generator includes a superheater and a attemperator; the steam / medium heat exchanger receiving steam from a heat recovery steam generator is adapted and configured to cool steam generated by the heat recovery steam generator in a manner that replaces or reduces the operation of the attemperator of the heat recovery steam generator; 3. The thermal energy storage system of claim 2.

5. the heat recovery steam generator includes at least a first reheater and a first reheater attemperator; the steam / media heat exchanger includes a plurality of steam / media heat exchangers including a first high pressure steam / media heat exchanger replacing or reducing the operation of the first attemperator and a first reheat steam / media heat exchanger replacing or reducing the operation of the first reheat attemperator; 5. The thermal energy storage system of claim 4.

6. the heat recovery steam generator includes a second attemperator, a second reheat steam / medium heat exchanger, and a second reheater attemperator; the plurality of steam medium heat exchangers including a second steam / heat medium heat exchanger replacing or reducing the operation of the second attemperator and a second reheat steam / medium heat exchanger replacing or reducing the operation of the second reheat attemperator; 6. The thermal energy storage system of claim 5.

7. the first high pressure steam / medium heat exchanger is in fluid communication with the heat recovery steam generator downstream of the first superheater and downstream of the first attemperator; 6. The thermal energy storage system of claim 5.

8. the first reheat steam / media heat exchanger is in fluid communication with the heat recovery steam generator downstream of the first reheater and downstream of the first reheater attemperator; 6. The thermal energy storage system of claim 5.

9. the second steam / heat medium heat exchanger is in fluid communication with the heat recovery steam generator downstream of the second superheater and downstream of the second attemperator.

7. The thermal energy storage system of claim 6.

10. the second reheat steam / media heat exchanger is in fluid communication with the heat recovery steam generator downstream of the second reheater and downstream of the second reheater attemperator; 7. The thermal energy storage system of claim 6.

11. a storage cold tank for storing the heat medium received from the water / medium heat exchanger, the storage cold tank operable to transfer heat from the heated heat storage medium to the water to generate steam and deliver the steam to the heat recovery steam generator; The cold tank supplies a heat medium to one or more steam / medium heat exchangers.

7. The thermal energy storage system of claim 6.

12. The cold tank supplies heat medium to the first and second high pressure steam / medium heat exchangers in parallel.

12. The thermal energy storage system of claim 11.

13. The cold tank supplies heat medium to the first and second steam / heat medium heat exchangers in series.

12. The thermal energy storage system of claim 11.

14. The cold tank supplies heat medium to the first and second reheat steam / heat medium heat exchangers in parallel.

12. The thermal energy storage system of claim 11.

15. The cold tank supplies heat medium to the first and second reheat steam / heat medium heat exchangers in series.

12. The thermal energy storage system of claim 11.

16. The heat transfer medium is a molten salt.

10. The thermal energy storage system of claim 1.

17. the system is adapted and configured to be operated to transfer heat from the heated storage medium to the water to generate steam, and to generate steam at a rate sufficient for use by the steam turbine while transferring the steam to the heat recovery steam generator to enable a reduction in gas turbine load; the gas turbine and the steam turbine are part of a combined cycle power plant.

3. The thermal energy storage system of claim 2.

18. the system is adapted and configured to transfer heat from the heated storage medium to the water to generate steam, such that additional steam can be generated during periods of elevated ambient temperature; 3. The thermal energy storage system of claim 2.

19. the water / media heat exchanger is operable to transfer heat from the heated storage medium to the water to generate steam and deliver the steam to one or more of an existing heat recovery steam generator, an existing steam turbine of the existing heat recovery steam generator, an additional steam turbine or additional expander that is not part of the existing heat recovery steam generator, a steam driven pump, or a drive system for mechanical equipment; 3. The thermal energy storage system of claim 2.

20. 1. A method for operating a thermal energy storage system in combination with a heat recovery steam generator, comprising: transferring heat from steam from the heat recovery steam generator to a heat storage medium and heating the heat storage medium using a steam / medium heat exchanger operable to receive steam from the heat recovery steam generator and a flow of a heat storage medium and transfer heat from the steam to the heat storage medium to heat the heat storage medium; storing the heated heat storage medium using a storage hot tank in fluid communication with the vapor / media heat exchanger and operable to receive the heated storage medium from the vapor / media heat exchanger and store the heated storage medium; Including, method.

21. generating steam using a water / media heat exchanger operable to receive a flow of water, receive from the hot tank the heated heat storage medium stored in the hot tank, transfer heat from the heated heat storage medium to the water to generate steam, and deliver the steam to the heat recovery steam generator or process; 21. The method of claim 20.

22. further comprising the steps of: reducing the temperature of steam generated by the heat recovery steam generator and increasing the temperature of the heat storage medium when the power plant supplied by the heat recovery generator operates at low load or off-design conditions using the steam / media heat exchanger; and generating steam using the stored heated heat storage medium in the hot tank and the water / media heat exchanger and supplying the generated steam to the heat recovery steam generator when the power plant supplied by the heat recovery steam generator operates at peak load or above peak load.

22. The method of claim 21.

23. the steam / medium heat exchanger receiving steam from a heat recovery steam generator is adapted and configured to cool steam generated by the heat recovery steam generator in a manner that replaces or reduces the operation of a desuperheater of the heat recovery steam generator; 22. The method of claim 21.

24. the steam / medium heat exchanger includes a plurality of steam medium heat exchangers including a first high pressure steam / heat medium heat exchanger replacing or reducing the operation of a first high pressure attemperator of the heat recovery steam generator, and a first reheat steam / heat medium heat exchanger replacing or reducing the operation of a first reheater attemperator of the heat recovery steam generator; 24. The method of claim 23.

25. the plurality of steam medium heat exchangers including a second high pressure steam / heat medium heat exchanger replacing or reducing the operation of a second high pressure attemperator of the heat recovery steam generator, and a second reheat steam / heat medium heat exchanger replacing or reducing the operation of a second reheater attemperator of the heat recovery steam generator; 25. The method of claim 24.

26. the first high pressure steam / heat medium heat exchanger is in fluid communication with the heat recovery steam generator downstream of the first high pressure superheater and downstream of the first high pressure attemperator; 25. The method of claim 24.

27. the first reheat steam / heat medium heat exchanger is in fluid communication with the heat recovery steam generator downstream of the first reheater and downstream of the first reheater attemperator; 25. The method of claim 24.

28. the second high pressure steam / heat medium heat exchanger is in fluid communication with the heat recovery steam generator downstream of the second high pressure superheater and downstream of the second high pressure attemperator.

26. The method of claim 25.

29. the second reheat steam / heat medium heat exchanger is in fluid communication with the heat recovery steam generator downstream of the second reheater and downstream of the second reheater attemperator; 26. The method of claim 25.

30. and supplying a heat medium to one or more steam / media heat exchangers using a storage cold tank for storing the heat medium received from the water / media heat exchanger, the storage cold tank being operable to transfer heat from the heated heat storage medium to the water to generate steam and deliver the steam to the heat recovery steam generator.

26. The method of claim 25.

31. The cold tank supplies heat medium to the first and second high pressure steam / heat medium heat exchangers in parallel.

31. The method of claim 30.

32. The cold tank supplies heat medium to the first and second high pressure steam / heat medium heat exchangers in series.

31. The method of claim 30.

33. The cold tank supplies heat medium to the first and second reheat steam / heat medium heat exchangers in parallel.

31. The method of claim 30.

34. The cold tank supplies heat medium to the first and second reheat steam / heat medium heat exchangers in series.

31. The method of claim 30.

35. The heat storage medium is a molten salt.

21. The method of claim 20.

36. transferring heat from the heated heat storage medium to the water to generate steam and delivering the steam to the heat recovery steam generator to reduce a gas turbine load while generating steam at a rate sufficient for use by the steam turbine; the gas turbine and the steam turbine are part of a combined cycle power plant.

22. The method of claim 21.

37. and transferring heat from the heated thermal storage medium to the water to generate steam, allowing for additional steam generation during periods of high ambient temperature, and in this manner enhancing power generation of the heat recovery steam generator.

22. The method of claim 21.

38. The water / media heat exchanger is operable to transfer heat from the heated thermal storage medium to the water to generate steam and deliver the steam to one or more of an existing heat recovery steam generator, an existing steam turbine of the existing heat recovery steam generator, an additional steam turbine or additional expander that is not part of the existing heat recovery steam generator, a steam driven pump, or a drive system for mechanical equipment.

22. The method of claim 21.

39. retrofitting an existing power plant by coupling the steam / media heat exchanger to an existing heat recovery steam generator system of the existing power plant, and coupling the steam / media heat exchanger to the storage hot tank in fluid communication with the steam / media heat exchanger, such that the steam / media heat exchanger receives steam from the heat recovery steam generator and a flow of a heat storage medium; the vapor / medium heat exchanger is operable to transfer heat from the vapor to the thermal storage medium to heat the thermal storage medium; the storage tank is operable to receive the heated thermal storage medium from the vapor / media heat exchanger and to store the heated thermal storage medium.

21. The method of claim 20.

40. 1. A method for retrofitting a heat recovery steam generator (HRSG) including a plurality of components, comprising: The components include: a housing having an inlet configured to receive exhaust gases from a combustion turbine, the housing having an outlet and an internal gas exhaust flow path between the inlet and the outlet; a superheater coil of heat exchange tubes, the superheater coil being disposed within the housing interior exhaust flow path downstream of the inlet; a high pressure evaporator including a coil disposed within the housing interior exhaust flow path downstream of the housing inlet and a superheater coil; an additional downstream coil within a heat exchanger tube, the additional downstream steam coil being disposed within the housing downstream of the high pressure evaporator coil such that gas coming from the housing inlet can flow downstream through the heater coil, the high pressure evaporator coil, and the downstream coil toward the housing outlet; a attemperator heat exchanger disposed external to the internal gas exhaust flowpath of the HRSG, the attemperator heat exchanger having a low temperature path and a high temperature path; a fluid communication extending between the high pressure evaporator and the heater; a fluid communication extending from the superheater to the high temperature path of the attemperator; Including, The method comprises: providing a steam / medium heat exchanger disposed external to the internal gas exhaust flowpath of the HRSG, configured to receive fluid from the heat recovery steam generator and to receive a flow of a heat storage medium, and configured to transfer heat from steam to the heat storage medium and heat the heat storage medium; providing a first fluid communication path from the superheater to the high temperature path of the steam / media heat exchanger; providing a first storage tank; providing a second fluid communication path from the cold path of the vapor / media heat exchanger to the first storage tank configured to receive the heated thermal storage medium from the vapor / media heat exchanger and to store the heated thermal storage medium; Including, method.

41. directing steam through the first fluid communication path from the superheater to the hot path of the steam / media heat exchanger to heat the thermal storage medium; directing a thermal storage medium to flow through the second fluid communication path from the vapor / medium heat exchanger to the first storage tank; Including, 41. The method of claim 40.

42. providing a second storage tank configured to store a medium that is cooler than the medium stored in the first storage tank; providing a fluid communication path from the second storage tank to the cold path of the vapor / media heat exchanger; Including, 41. The method of claim 40.

43. directing a heat storage medium to flow through the third fluid communication path from the second storage tank to the cold path of the vapor / medium heat exchanger to heat the heat storage medium; 43. The method of claim 42.

44. The fluid communication extending from the superheater to the high temperature path of the attemperator. modifying to reduce the flow of fluid from a superheater to the hot path of the attemperator.

41. The method of claim 40.

45. The elements of the HRSG include: a reheater including a coil disposed within the interior exhaust flow passage of the housing; a reheater attemperator heat exchanger disposed external to the internal gas exhaust flowpath of the HRSG, the attemperator heat exchanger having a low temperature path and a high temperature path; a fluid communication extending from the reheater to the high temperature path of the reheater attemperator; Further comprising: The method comprises: providing a reheat steam / media heat exchanger disposed external to the internal gas exhaust flowpath of the HRSG, configured to receive fluid from the reheater and to receive a flow of a heat storage medium, and configured to transfer heat from steam to the heat storage medium; providing a fluid communication path from the reheater to the high temperature path of the reheat steam / media heat exchanger; providing a fluid communication path from the cold path of the reheat steam / media heat exchanger to the first storage tank configured to receive the heated heat storage medium from the reheat steam / media heat exchanger and to store the heated heat storage medium; Including, 41. The method of claim 40.

46. inducing steam to flow through the fluid communication path from the reheater to the hot path of the reheat steam / media heat exchanger to heat the thermal storage medium; directing a heat storage medium to flow through a fluid communication path from the reheat steam / medium heat exchanger to the first storage tank; Further comprising:

46. ​​The method of claim 45.

47. Providing a water / heat medium heat exchanger; providing a water flow path through the water / heat medium heat exchanger configured to exchange heat between the heat medium and water; providing a heat transfer medium fluid communication path extending from the first storage tank to the water / heat transfer medium heat exchanger, through the water / heat transfer medium heat exchanger, and to the second storage tank configured such that heat transfer medium flows from the first storage tank, through the water / heat transfer medium heat exchanger, and to the second storage tank; Further comprising:

43. The method of claim 42.

48. directing a heat transfer medium to flow through the first heat transfer medium fluid communication path through the water / heat transfer medium heat exchanger, through the medium communication path, and to the first storage tank; Flowing water through the water flow path of the water / heat medium heat exchanger, inducing the heat medium to heat the water, and then inducing the water to flow out of the water / heat medium heat exchanger; Further comprising:

48. The method of claim 47.

49. providing a heater thermally connected to the second fluid communication path from the cold path of the vapor / media heat exchanger to the first storage tank; the heater heating the thermal storage medium before it enters the first storage tank; Further comprising:

41. The method of claim 40.

50. 1. A method for retrofitting a heat recovery steam generator (HRSG) including a plurality of components, comprising: The components include: a housing having an inlet configured to receive exhaust gas from a combustion turbine, the housing having an outlet and an internal gas exhaust flow path between the inlet and the outlet; a superheater coil of a heat exchanger tube, the superheater coil being disposed within the housing interior exhaust flow path downstream of the inlet; a high pressure evaporator including a coil disposed within the housing interior exhaust flow path downstream of the housing inlet and a heater coil; an additional downstream coil of heat exchanger tubes, the additional downstream steam coil being disposed within the housing downstream of the high pressure evaporator coil such that gas coming from the housing inlet can flow through the superheater coil, through the high pressure evaporator coil, and through the downstream coil toward the housing outlet; a attemperator heat exchanger disposed external to the internal gas exhaust flowpath of the HRSG, the attemperator heat exchanger having a low temperature path and a high temperature path; a fluid communication extending between the high pressure evaporator and the superheater; a fluid communication extending from the superheater to the high temperature path of the attemperator; a reheater including a coil disposed within the housing interior exhaust flow passage; a reheat attemperator heat exchanger disposed external to the internal gas exhaust flowpath of the HRSG, the attemperator heat exchanger having a low temperature path and a high temperature path; a fluid communication extending from the reheater to the high temperature path of the reheater attemperator; Including, The method comprises: providing a steam / medium heat exchanger disposed external to the internal gas exhaust flowpath of the HRSG, the steam / medium heat exchanger configured to receive fluid from the heat recovery steam generator and to receive a flow of a heat storage medium, the steam / medium heat exchanger configured to transfer heat from the steam to the heat storage medium and to heat the heat storage medium; providing a first fluid communication path from the superheater to the high temperature path of the steam / media heat exchanger; providing a first storage tank; providing a second fluid communication path from the cold path of the vapor / media heat exchanger to the first storage tank configured to receive the heated thermal storage medium from the vapor / media heat exchanger and store the heated thermal storage medium; providing a reheat steam / media heat exchanger disposed external to the internal gas exhaust flowpath of the HRSG, configured to receive fluid from the reheater and to receive a flow of a heat storage medium, and configured to transfer heat from steam to the heat storage medium; providing a fluid communication path from the reheater to the high temperature path of the reheat steam / media heat exchanger; providing a fluid communication path from the cold path of the reheat steam / media heat exchanger to the first storage tank configured to receive the heated heat storage medium from the reheat steam / media heat exchanger and to store the heated heat storage medium; providing a second storage tank configured to store a medium that is cooler than the medium stored in the first storage tank; providing a fluid communication path from the second storage tank to the cold path of the vapor / media heat exchanger; Including, method.

51. inducing steam to flow through the first fluid communication path from the superheater to the high temperature path of the steam / media heat exchanger to heat the thermal storage medium; directing a thermal storage medium to flow through the second fluid communication path from the vapor / medium heat exchanger to the first storage tank; inducing a thermal storage medium to flow through the fluid communication path from the second storage tank to the cold path of the vapor-to-media heat exchanger to heat the thermal storage medium; modifying the fluid communication extending from the superheater to the hot path of the attemperator configured to reduce the flow of fluid from the superheater to the hot path of the attemperator; inducing steam to flow through the fluid communication from the reheater to the hot path of the reheat steam / media heat exchanger to heat the thermal storage medium; directing a thermal storage medium to flow through the fluid communication path from the reheat steam / medium heat exchanger to the first storage tank; providing a fluid communication path from the second storage tank to the cold path of the reheat steam / media heat exchanger and directing a heat storage medium to flow through the fluid communication path from the second storage tank; Further comprising:

51. The method of claim 50.

52. Providing a water / heat medium heat exchanger; providing a water flow path through the water / heat medium heat exchanger configured to exchange heat between the heat medium and water; providing a heat transfer medium fluid communication path extending from the first storage tank to the water / heat transfer medium heat exchanger, through the water / heat transfer medium heat exchanger, and to a second storage tank configured such that heat transfer medium flows from the first storage tank, through the water / heat transfer medium heat exchanger, and to the second storage tank; directing a heat transfer medium to flow through the first heat transfer medium fluid communication path through the water / heat transfer medium heat exchanger, through the medium communication path, and to the first storage tank; Flowing water through the water flow path of the water / heat medium heat exchanger, inducing the heat medium to heat the water, and then inducing the water to exit the water / heat medium heat exchanger; Further comprising:

52. The method of claim 51.

53. providing a heater in thermal communication with the second fluid communication path from the cold path of the vapor / media heat exchanger to the first storage tank; the heater heating the thermal storage medium before it enters the first storage tank; Further comprising:

51. The method of claim 50.

54. providing a heater in thermal communication with the second fluid communication path from the cold path of the vapor / media heat exchanger to the first storage tank; the heater heating the thermal storage medium before it enters the first storage tank; Further comprising:

41. The method of claim 40.

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