Heat pump cascaded energy storage system coupled with a thermal power plant

Abstract

The present application relates to the field of new energy consumption and thermal power peak shaving technology, and provides a heat pump cascade type energy storage system coupled with a thermal power plant. Based on the commonly used "Brayton cycle" heat pump and traditional two-tank molten salt heat storage, the system proposes to use the "reverse Brayton cycle" heat pump unit to generate heat and combine with the electric heater to increase the temperature, and the cold energy generated by the heat pump is used to cool the condensate water of the power plant. The heat storage and heat exchange parts are designed in a cascade type, and the method of sealing and introducing protective atmosphere is used in the super-high temperature salt tank to improve the decomposition temperature and stability of the molten salt. The system comprises a heat pump and electric heater combined system, a cascade type heat exchange system, a cold storage system and an atmosphere protection system, wherein the heat pump and electric heater combined system comprises a cascade type heat storage system. The cascade type energy storage system widens the temperature range of molten salt, balances the economic decline caused by the upgrading of high-temperature and high-corrosion driven steel materials, and improves the electric-thermal-electric round-trip efficiency and the safety and reliability of system operation.

Description

Technical Field

[0001] This invention relates to the field of new energy consumption and thermal power peak shaving technology, and in particular to a heat pump cascaded energy storage system coupled with a thermal power plant. Background Technology

[0002] With the construction of a clean, low-carbon, safe, and reliable new power system, coal-fired power is transforming from a primary power source to a basic, guaranteed, and system-regulating power source. Currently, many thermal power plants are attempting to leverage thermal energy storage systems to enhance the emergency peak-shaving capabilities of their units and improve their flexibility, for example, through steam extraction for thermal storage and surplus power-to-heat conversion for storage. However, the current thermal energy storage peak-shaving systems coupled with thermal power plants still have relatively low thermoelectric conversion efficiency, and cannot achieve independent peak-shaving through thermal energy storage. Coal combustion remains the primary source of power, with thermal energy storage only playing a supplementary role in peak shaving.

[0003] In related technologies, Vinnemeier et al. (Integration of heat pumps into thermal plants for creation of large-scale electricity storage capacities, 2016) proposed integrating heat pumps into thermal power plants to create large-scale electricity storage capacity. With reasonable heat pump working fluid and process configuration, the maximum round-trip efficiency of the integrated system based on different types of thermal power plants can be between 50% and 60%. Xue et al. (Multi-criteria thermodynamic analysis of pumped-thermal electricity storage with thermal integration and application in electric peak shaving of coal-fired power plant, 2022) proposed an organic Rankine cycle heat pump system incorporating waste heat from a 300MW coal-fired power plant. The heat pump unit absorbs the power plant's electricity and waste heat into the thermal storage system during off-peak hours, and generates electricity during peak hours. This system has advantages in assisting power plants with deep peak shaving, but its limitation lies in the need to obtain additional low-grade industrial waste heat from outside the plant when the power plant's waste heat is insufficient, and its ability to consume excess wind / solar power is limited. The German Aerospace Center (DLR) (Jorge et al., 2019) and a large German utility company studied the conversion of existing coal-fired power plants into energy storage plants, finding that using supercritical steam (24–26 MPa) cycles to increase the main steam pressure improves efficiency compared to subcritical steam (16–19 MPa) cycles. When the heat pump energy storage system is coupled with a supercritical coal-fired power plant with both high main steam pressure (25 MPa) and temperature (600–620°C), the efficiency is high, but the coupling temperature of the heat storage needs to be increased to above 620°C. Using molten salt above 620°C also presents corrosion problems, increasing system costs, and high-temperature compressors also face challenges.

[0004] A patent application (CN111964035A) from Xi'an Thermal Power Research Institute Co., Ltd. proposes a high-efficiency compression heat pump energy storage peak-shaving system and method coupled to thermal power plants. This system uses a heat pump to extract and store heat from flue gas, and heats the condenser circulating water and the heating network return water during heat release. However, this type of heat pump energy storage system cannot achieve a large-scale capacity. A patent application (CN103842744A) from Siemens proposes an energy storage device and method for storing energy. This device converts compressed air from a heat pump unit into high-grade heat energy, which is stored in a thermal energy storage device. During peak electricity demand periods, the stored heat energy is released to the gas to power an expander and generate electricity. Siemens' patent application CN103987925A proposes an energy storage device with an open energy storage loop for storing seasonally excess electrical energy. It converts compressed air from a heat pump unit into high-grade heat energy, which is stored in a thermal energy storage device. During peak electricity demand, part of the heat energy is released to steam for Rankine cycle power generation, and another part is released to the heat pump unit for Brayton cycle power generation, while the cold air is directly discharged into the atmosphere. Siemens' patent application CN103930653A proposes a high-temperature energy storage device with a recovery unit, which stores heat energy through multi-stage air compression and releases the heat energy to steam for Rankine cycle power generation when needed. Siemens' patent concept is to utilize excess electrical energy for large-scale thermal storage and release it for power generation through power plant steam turbines during peak electricity demand. However, its system design is relatively crude. The application of thermal storage materials that meet the high-temperature steam requirements of power plants, such as 566℃, is crucial for the core of the system. Siemens patents utilize sand, rock, concrete, water, or salt. However, in practical applications, sand, rock, and concrete typically have low heat transfer coefficients when transferring heat with steam, resulting in large heat transfer areas, poor economic efficiency, and significant pressure losses. Water-based thermal storage requires high container pressure. Salt-based thermal storage, whether nitrate, chloride, or carbonate, offers advantages over solid thermal storage materials due to its fluidity, leading to higher heat transfer coefficients and faster thermal response. However, it faces the challenge of accelerated corrosion of stainless steel in molten salt above 580°C. Nickel-based alloys offer corrosion resistance, but are expensive. Without specialized design for the thermal storage and exchange systems, it is difficult to guide practical applications. Summary of the Invention

[0005] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, this invention provides a cascaded heat pump energy storage system coupled to a thermal power plant. It proposes a cascaded design for the heat storage and heat exchange components, and employs a closed-loop protective atmosphere in the ultra-high temperature molten salt tank to improve the molten salt decomposition temperature and stability. This design broadens the operating temperature range of the molten salt, balances the economic decline caused by the upgrading of steel materials due to high temperature and high corrosion, and enhances the safety and reliability of the system operation.

[0006] This invention provides a heat pump cascaded energy storage system coupled to a thermal power plant, comprising a heat pump electric heater combined system, a cascaded heat exchange system, and an atmosphere protection system. The heat pump electric heater combined system includes an electric motor, a compressor, an expander, a regenerator, a cascaded thermal storage system, and a cold storage system. The cascaded thermal storage system includes a first heat exchanger, a hot salt tank, a cold salt tank, an ultra-high temperature molten salt heating tank, an electric heater, an ultra-high temperature salt tank, and a high temperature salt tank. The electric heater is located within the ultra-high temperature molten salt heating tank and is suitable for connection to a new energy power generation system. The cold storage system includes a second heat exchanger, a low-temperature coolant tank, and a normal temperature coolant tank. The cascaded heat exchange system includes a multi-stage heat exchanger, comprising a first-stage heat exchanger and a second-stage heat exchanger.

[0007] The system comprises a motor, compressor, expander, and regenerator connected to form a closed heat pump circuit. The working gas in the hot gas pipe of the heat pump circuit can exchange heat with the working gas in the feedback pipe of the heat pump circuit within the regenerator. The first heat exchanger, the cold salt tank, the primary heat exchanger, and the hot salt tank are sequentially connected to form a first heat storage circuit. The first heat exchanger is positioned on the heat pump circuit, allowing the molten salt in the first heat storage circuit to absorb the heat energy of the working gas in the heat pump circuit. The high-temperature salt tank, the ultra-high-temperature molten salt heating tank, the ultra-high-temperature salt tank, and the secondary heat exchanger are sequentially connected to form a second heat storage circuit. The primary and secondary heat exchangers are connected in series via steam pipes and coupled to the power plant to form a heat release circuit. The molten salt in the first and second heat storage circuits releases heat energy to the water and / or steam in the heat release circuit through the primary and secondary heat exchangers to generate steam for the turbine.

[0008] The atmosphere protection system is used to introduce protective gas into the ultra-high temperature salt tank, the ultra-high temperature molten salt heating tank, and the high temperature salt tank, enabling them to operate under protected atmosphere conditions. When Hitec salt is used, the protective gas comprises a mixture of nitrogen and oxygen. When the molten salt temperature in the ultra-high temperature salt tank and the ultra-high temperature molten salt heating tank reaches a set temperature, protective gas is introduced into them via the atmosphere protection system. The atmosphere protection system can also be used to control the rate, pressure, and composition ratio of the protective gas introduced.

[0009] The second heat exchanger is disposed on the heat pump circuit and connected between the inlet of the low-temperature coolant tank and the outlet of the normal-temperature coolant tank. The outlet of the low-temperature coolant tank and the inlet of the normal-temperature coolant tank are adapted to be connected to the condenser in the thermal power plant to form a first cooling circuit. The second heat exchanger is used for the coolant flowing in the first cooling circuit to absorb the cold energy of the working gas in the heat pump circuit so that the condenser can condense the exhaust steam output by the steam turbine.

[0010] This invention, based on the commonly used Brayton cycle heat pump and traditional two-tank molten salt thermal storage, proposes to utilize a "reverse Brayton cycle" heating system for the heat pump unit. This system preheats the low-temperature working gas before it enters the compressor inlet using a regenerator, achieving a low pressure ratio and ensuring the working gas reaches the desired high temperature. A cascaded thermal storage system stores the heat energy generated by the heat pump unit in stages, and a corresponding cascaded heat exchange system transfers this stored heat energy to the power plant. An electric heater is used to raise the temperature before the ultra-high temperature salt tank, widening the operating temperature range of the molten salt, offsetting the economic decline caused by the upgrading of steel materials due to high temperature and high corrosion, and improving the efficiency of the electricity-heat-electricity cycle and the safety and reliability of the system operation. Atmosphere protection for the ultra-high temperature and high temperature salt tanks ensures that the molten salt in the second thermal storage loop reaches a temperature sufficient to obtain supercritical steam, enabling clean, low-carbon, and flexibly adjustable power output from the power plant. The cold energy generated by the heat pump loop is used to cool the exhaust steam output from the power plant, improving the cycle efficiency of the heat pump peak-shaving system and the Rankine cycle efficiency of the power plant. This heat pump energy storage peak-shaving system not only meets the flexible and deep peak-shaving requirements of thermal power plants, but also improves the power generation efficiency of thermal power plants, which is conducive to the large-scale, high-proportion, and efficient consumption of random new energy sources.

[0011] Furthermore, the ultra-high temperature salt tank has a nickel-based alloy body, while the high-temperature salt tank, the hot salt tank, and the cold salt tank are made of stainless steel. This reduces the volume of the ultra-high temperature salt tank, thereby lowering the cost of the nickel-based alloy body. The required protective gas for the ultra-high temperature salt tank is also reduced, and control is relatively easier. In this four-tank cascade storage design, the volume of the ultra-high temperature salt tank using the nickel-based alloy is only 40% of the volume of the high-temperature salt tank containing binary nitrate solar salt. Due to the minimal use of nickel-based alloy, the four-tank cascade storage design has a cost advantage. In addition, when the tanks are smaller, the control of the internal protective gas is also easier.

[0012] Furthermore, the multi-stage heat exchanger includes a first multi-stage heat exchanger and a second multi-stage heat exchanger. The first multi-stage heat exchanger is connected between the boiler's feedwater pipe and the high-pressure cylinder main steam input pipe to form a first heat release circuit. The second multi-stage heat exchanger is connected between the high-pressure cylinder steam output pipe and the intermediate-pressure cylinder reheat steam input pipe of the turbine to form a second heat release circuit. Both the first and second multi-stage heat exchangers include a first-stage heat exchanger and a second-stage heat exchanger connected in series. The first-stage heat exchanger of the first multi-stage heat exchanger and the first-stage heat exchanger of the second multi-stage heat exchanger are connected in parallel to the first heat storage circuit. The second-stage heat exchanger of the first multi-stage heat exchanger and the second-stage heat exchanger of the second multi-stage heat exchanger are connected in parallel to the second heat storage circuit.

[0013] In this system, water from the feedwater pipeline sequentially absorbs the heat energy stored in the two stages of the cascaded thermal energy storage system before being fed into the high-pressure cylinder of the power plant. Steam from the high-pressure cylinder outlet sequentially absorbs the heat energy stored in the two stages of the cascaded thermal energy storage system before being fed into the medium-pressure cylinder of the power plant. Furthermore, the first thermal energy storage loop and its primary heat exchanger are used for primary heat exchange between the water and steam, followed by secondary heat exchange using the second thermal energy storage loop and its secondary heat exchanger. Thus, this cascaded heat pump energy storage system achieves staged heat exchange between water and steam, improving energy efficiency while broadening the operating temperature range of molten salt.

[0014] Furthermore, the first heat exchanger and / or regenerator is a micro shell-and-tube heat exchanger, which can achieve a high heat transfer area to volume ratio.

[0015] Furthermore, the heat exchange tubes of the second multi-stage heat exchanger are made of Haynes 230. When this cascaded energy storage system is applied to a supercritical power plant, the second multi-stage heat exchanger serves as a molten salt-supercritical water / steam heat exchanger, and the use of Haynes 230 for its heat exchange tubes helps to reduce the wall thickness of the heat exchange tubes.

[0016] Furthermore, the heat exchange system also includes: a third heat exchanger; the outlet of the low-temperature coolant tank and the inlet of the normal-temperature coolant tank are connected to both ends of the third heat exchanger via a second coolant pipe, forming a second cooling release circuit; wherein, the third heat exchanger is adapted to be connected to refrigeration equipment, and the coolant flowing in the second cooling release circuit can absorb heat from the refrigeration equipment through the third heat exchanger to realize the utilization of cold energy. The refrigeration equipment can be a refrigerator, ice maker, freezer, etc. The refrigeration equipment can also be part of the heat exchange system. A third regulating valve is provided on the second cooling release circuit, and the cooling release operation of the second cooling release circuit can be started by activating the third regulating valve.

[0017] The present invention also provides an operation method for a heat pump cascaded energy storage system coupled to a thermal power plant, comprising:

[0018] If it is determined that there is surplus electrical energy in the new energy power generation system, the heat pump electric heater combined system is started to convert the surplus electrical energy into heat energy and cold energy, and the heat energy is stored in the cascaded thermal storage system and the cold energy is stored in the cold storage system.

[0019] If the power generation demand of the thermal power plant is determined to be less than a set threshold, the boiler and the regulating valve group between the boiler's steam outlet and the steam input pipeline of the steam turbine are closed, and the heat release circuit and the first cold release circuit are started, so that the heat energy stored in the cascaded thermal storage system is released to the water and / or steam in the heat release circuit, and the cold energy stored in the cold storage system is released to the coolant in the cold release circuit.

[0020] If the power generation demand of the thermal power plant is determined to be greater than or equal to the set threshold, then the boiler is started and the regulating valve group is opened;

[0021] After starting the boiler and opening the regulating valve group, once the boiler load reaches a stable value, the heat release circuit is shut off.

[0022] When the power generation demand of a thermal power plant is less than a set threshold, it indicates that the plant is under low load. At this time, the boiler enters a self-protection, self-circulation state, and the heat release circuit is activated. This allows the water output from the boiler or the steam output from the high-pressure cylinder of the turbine to absorb the heat energy stored in the cascaded thermal energy storage system before entering the turbine. The first cold release circuit is then activated, allowing the coolant in the cold storage system to flow through the condenser and condense the steam inside.

[0023] When the power generation demand of a thermal power plant is greater than or equal to a set threshold, it indicates that the power plant is under high load and the thermal energy stored in the cascaded thermal energy storage system is insufficient. At this time, a boiler hot start-up is performed, causing the main steam in the first heat release loop to mix with the main steam directly output from the boiler before entering the high-pressure cylinder. The reheat steam in the second heat release loop mixes with the reheat steam directly output from the boiler before entering the intermediate-pressure cylinder.

[0024] After the boiler is started up, the load gradually increases. When the load reaches the set value and remains within the set fluctuation range for a set time period, the boiler load is considered to have reached a stable state. At this point, the first and second heat release circuits are shut down, and the boiler operates independently to generate electricity.

[0025] Furthermore, it also includes: if it is determined that the steam thermal energy in the condenser is insufficient to heat the coolant in the cold storage system to the set temperature, then the second cooling release circuit is activated, so that part of the coolant in the cold storage system flows through the condenser through the first cooling release circuit, and the other part flows through the third heat exchanger through the second cooling release circuit, so as to utilize the excess cold energy and improve the economy of the system. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the coupling structure between the heat pump cascaded energy storage system coupled to a thermal power plant provided by the present invention and the thermal power plant.

[0028] Figure 2 The Ts diagram is for a reverse Brayton cycle with and without a regenerator;

[0029] Figure 3 These are the efficiency variation curves of the compressor and turboexpander under variable input load;

[0030] Figure 4 This is a comparison chart of the electrothermal conversion efficiency of the heat pump electric heater combined system and the pure electric heater under variable input load in this invention;

[0031] Figure 5 This is a comparison chart of the round-trip efficiency of the integrated system formed by the original power plant system coupled with the heat pump electric heater system and the original power plant system under different output loads.

[0032] Figure 6 This is a flowchart illustrating the operation method of the heat pump cascaded energy storage system coupled with a thermal power plant provided by the present invention.

[0033] Figure label:

[0034] 1. Electric motor; 2. Compressor; 3. Expander; 6. Regenerator;

[0035] 101. Hot air pipeline; 102. Feedback pipeline; 200. Steam pipeline; 201. First steam pipeline; 202. Second steam pipeline; 301. First coolant pipeline; 302. Second coolant pipeline; 401. First molten salt pipeline; 402. Second molten salt pipeline;

[0036] 4. Cascaded thermal storage system; 41. First heat exchanger; 42. Hot salt tank; 43. Cold salt tank; 44. Ultra-high temperature salt tank; 45. Electric heater; 46. High temperature salt tank; 47. Ultra-high temperature molten salt heating tank;

[0037] 5. Cold storage system; 51. Second heat exchanger; 52. Low-temperature coolant tank; 53. Normal temperature coolant tank;

[0038] 71. Multistage heat exchanger; 711. First multistage heat exchanger; 712. Second multistage heat exchanger; 721. First regulating valve; 722. Second regulating valve; 73. Third heat exchanger; 74. Refrigeration equipment; 75. Third regulating valve. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0040] In the description of the embodiments of the present invention, it should be noted that, unless otherwise expressly specified and limited, the terms "first" to "fifth" are numbered to clearly describe product components and do not represent any substantial difference. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention according to the specific circumstances.

[0041] The heat pump cascaded energy storage system coupled to a thermal power plant provided in this embodiment of the invention comprises the following five systems:

[0042] The combined heat pump electric heater system includes an electric motor 1, a compressor 2, an expander 3, a regenerator 6, a cascaded thermal storage system 4, and a cold storage system 5.

[0043] Cascaded thermal storage system 4: includes a first heat exchanger 41, a hot salt tank 42, a cold salt tank 43, an ultra-high temperature salt tank 44, an ultra-high temperature molten salt heating tank 47, an electric heater 45, and a high temperature salt tank 46.

[0044] The cold storage system 5 includes a second heat exchanger 51, a low-temperature coolant tank 52, and a normal-temperature coolant tank 53.

[0045] Cascaded heat exchange system: includes a multi-stage heat exchanger 71 and a third heat exchanger 73. The multi-stage heat exchanger 71 includes a first multi-stage heat exchanger 711 and a second multi-stage heat exchanger 712. Both the first multi-stage heat exchanger 711 and the second multi-stage heat exchanger 712 include a first-stage heat exchanger 71a and a second-stage heat exchanger 71b.

[0046] Atmosphere protection system: used to introduce protective gas into the ultra-high temperature salt tank 44, the ultra-high temperature molten salt heating tank 47 and the high temperature salt tank 46.

[0047] The heat pump energy storage peak-shaving system for thermal power plants provided in this embodiment of the invention is coupled to the thermal power plant to form the following four loops:

[0048] The first heat release circuit is formed by connecting the two ends of the first multi-stage heat exchanger 711 to the feedwater pipeline of the boiler and the main steam input pipeline of the high-pressure cylinder of the steam turbine in the thermal power plant through the first steam pipeline 201.

[0049] The second heat release circuit is formed by connecting the two ends of the second multi-stage heat exchanger 712 to the high-pressure cylinder steam output pipeline and the intermediate-pressure cylinder reheat steam input pipeline of the steam turbine in the thermal power plant through the second steam pipeline 202 respectively.

[0050] The first cooling circuit is formed by connecting the second heat exchanger 51, the low-temperature coolant tank 52, the condenser of the thermal power plant, and the normal temperature coolant tank 53 in sequence through the first coolant pipeline 301.

[0051] The second cooling circuit is formed by connecting the second heat exchanger 51, the low-temperature coolant tank 52, the third heat exchanger 73, and the normal-temperature coolant tank 53 sequentially through the second coolant pipe 302.

[0052] The following is combined Figure 1 Figure 6 The present invention describes a cascaded energy storage system coupled with a thermal power plant for new energy consumption using a heat pump heating system.

[0053] The cascaded heat pump heating system coupled to a thermal power plant, provided in this embodiment of the invention, can be coupled to a thermal power plant for energy storage and peak shaving. For example... Figure 1 As shown, the cascaded energy storage system includes a heat pump electric heater combined system, a cascaded heat exchange system, and an atmosphere protection system.

[0054] The heat pump electric heater combined system includes an electric motor 1, a compressor 2, an expander 3, a regenerator 6, a cascaded thermal storage system 4, and a cold storage system 5. The electric motor 1, compressor 2, and expander 3 are connected sequentially via a drive shaft. The electric motor 1 is suitable for electrical connection to a new energy power generation system. The outlet of compressor 2 and the inlet of expander 3 are connected via a hot gas pipe 101, and the inlet of expander 3 and the inlet of compressor 2 are connected via a feedback pipe 102, thus forming a closed heat pump loop.

[0055] The cascaded thermal energy storage system 4 includes a first heat exchanger 41, a hot salt tank 42, a cold salt tank 43, an ultra-high temperature salt tank 44, an ultra-high temperature molten salt heating tank 47, an electric heater 45, and a high temperature salt tank 46. The electric heater 45 is located within the ultra-high temperature molten salt heating tank 47 and is suitable for connection to a new energy power generation system. The electric heater 45 can be an electric heating rod-type resistance heater or an electrode heater with positive and negative electrodes. The cascaded heat exchange system includes a multi-stage heat exchanger 71, which includes a first-stage heat exchanger 71a and a second-stage heat exchanger 71b. The cold storage system 5 includes a second heat exchanger 51, a cryogenic coolant tank 52, and a normal temperature coolant tank 53.

[0056] The first heat exchanger 41, cold salt tank 43, primary heat exchanger 71a, and hot salt tank 42 are sequentially connected via a first molten salt pipe 401 to form a first heat storage circuit. The first heat exchanger 41 is mounted on the hot gas pipe 101, allowing the molten salt in the first heat storage circuit to absorb the heat energy of the working gas in the heat pump circuit through the first heat exchanger 41. The high-temperature salt tank 46, ultra-high-temperature molten salt heating tank 47, ultra-high-temperature salt tank 44, and secondary heat exchanger 71b are sequentially connected via a second molten salt pipe 402 to form a second heat storage circuit. Both the ultra-high-temperature salt tank 44 and the ultra-high-temperature molten salt heating tank 47 are enclosed.

[0057] The primary heat exchanger 71a and the secondary heat exchanger 71b are connected in series via a steam pipe 200 and are adapted to be coupled to the power plant via the steam pipe 200 to form a heat release loop. Molten salt in the first and second heat storage loops releases heat energy to the water and / or steam in the heat release loop through the primary and secondary heat exchangers 71a and 71b respectively, forming steam supplied to the turbine in the power plant. The steam pipe 200 is used to circulate water transported from the boiler feedwater pipe and / or steam output from the high-pressure cylinder of the turbine.

[0058] The working gas in the heat pump circuit is one of air, nitrogen, helium, or argon. Hot salt tank 42 and cold salt tank 43 contain binary nitrate solar salt, which is composed of 60% NaNO3 and 40% KNO3. Ultra-high temperature salt tank 44 and high temperature salt tank 46 contain one of Hitec salt, chloride salt, and carbonate salt. Hitec salt is composed of 7% NaNO3, 53% KNO3, and 40% NaNO2; chloride salt is composed of 7.5% NaCl, 23.9% KCl, and 68.6% ZnCl2, or 37.5% MgCl2 and 62.5% KCl; carbonate salt is composed of 33.4% Na2CO3, 34.5% K2CO3, and 32.1% Li2CO3. The operating temperature of cold salt tank 43 and hot salt tank 42 is 300℃~500℃, and the operating temperature of high temperature salt tank 46 and ultra-high temperature salt tank 44 is 500℃~660℃.

[0059] An atmosphere protection system is connected to the ultra-high temperature salt tank 44, the ultra-high temperature molten salt heating tank 47, and the high temperature salt tank 46, respectively. This system is used to introduce protective gas into these tanks, ensuring they operate under a protected atmosphere. When using Hitec salt, the protective gas consists of a mixture of nitrogen and oxygen. When the molten salt temperature in the ultra-high temperature salt tank 44 and the ultra-high temperature molten salt heating tank 47 reaches a set temperature, the atmosphere protection system introduces protective gas into them. The atmosphere protection system can also be used to control the rate, pressure, and composition of the introduced protective gas.

[0060] The second heat exchanger 51 is mounted on the feedback pipe 102 and connected between the inlet of the cryogenic coolant tank 52 and the outlet of the ambient temperature coolant tank 53. The outlet of the cryogenic coolant tank 52 and the inlet of the ambient temperature coolant tank 53 are adapted to be connected to both ends of the cooling channel of the condenser via the first coolant pipe 301, forming a first cooling release circuit. The coolant flowing in the first cooling release circuit can absorb the cold energy of the working gas in the heat pump circuit through the second heat exchanger 51 to supply the condenser with the exhaust steam output from the turbine. The coolant flowing in the first cooling release circuit is brine with a phase change temperature between 0°C and -21.2°C.

[0061] The regenerator 6 is located on the hot gas pipe 101 between the first heat exchanger 41 and the air inlet of the expander 3, and on the feedback pipe 102 between the second heat exchanger 51 and the air inlet of the compressor 2, so that the working gas in the hot gas pipe 101 can exchange heat with the working gas in the feedback pipe 102 in the regenerator 6.

[0062] The new energy power generation system in this embodiment of the invention may include wind power and / or photovoltaic power stations. When there is random, unabsorbable electrical energy in the wind power and / or photovoltaic power station, or when the thermal power plant itself cannot connect to the grid, on the one hand, a portion of the electrical energy is converted into mechanical energy by the motor 1 into the compressor 2 and expander 3, and the compressor 2 converts the mechanical energy into heat energy, which is then stored in the hot salt tank 42 of the first thermal storage circuit; the expansion work is recovered by the cold storage system 5, and the cold energy is stored in the low-temperature coolant tank 52 of the first cold release circuit. On the other hand, another portion of the electrical energy is converted into heat energy by the electric heater 45 and stored in the ultra-high temperature salt tank 44 of the second thermal storage circuit for use by the thermal power plant during peak shaving.

[0063] The heat pump cascaded energy storage system coupled to a thermal power plant provided in this embodiment of the invention comprises a cascaded thermal storage system 4 and a cold storage system 5 set up on the heat pump loop. The thermal energy in the heat pump loop is stored in the hot salt tank 42 of the cascaded thermal storage system 4, the thermal energy converted by the electric heater 45 is stored in the ultra-high temperature salt tank 44 of the cascaded thermal storage system 4, and the cold energy in the heat pump loop is recovered in the cold salt tank 43 of the cold storage system 5. The cascaded thermal storage system 4 can be coupled to the thermal power plant through a cascaded heat exchange system to form a heat release loop, and the cold storage system 5 can be coupled to the thermal power plant to form a first cold release loop. When needed, the heat energy is released through the heat release loop and coupled into the thermal power plant for power generation, realizing frequency regulation and peak shaving of the thermal power plant and the absorption of new energy sources; the exhaust steam output from the turbine is cooled through the first cold release loop.

[0064] This invention, based on the commonly used Brayton cycle heat pump and traditional two-tank molten salt thermal storage, proposes a "reverse Brayton cycle" heating system for the heat pump unit. The thermal storage and heat exchange sections are cascaded, with four molten salt tanks storing heat energy in stages. An electric heater 45 raises the temperature before the ultra-high temperature salt tank 44, and a sealed protective atmosphere is used in the ultra-high temperature salt tank 44 to improve the molten salt decomposition temperature and stability. This system broadens the operating temperature range of molten salt, balances the economic decline caused by the upgrading of steel materials due to high temperature and high corrosion, and improves the electricity-heat-electricity round-trip efficiency and the safety and reliability of system operation. The cold energy generated by the heat pump loop is used to cool the exhaust steam output from the power plant, improving the cycle efficiency of the heat pump peak-shaving system and the Rankine cycle efficiency of the thermal power plant. When the thermal power plant requires deep peak shaving, the stored heat energy can be used to generate electricity independently. This heat pump energy storage peak-shaving system not only meets the flexible deep peak-shaving requirements of thermal power plants but also improves the power generation efficiency of thermal power plants, which is conducive to the large-scale, high-proportion, and efficient absorption of random new energy sources.

[0065] In practical applications, the combined heat pump and electric heater system provided by this invention can achieve an electro-thermal conversion efficiency greater than 1.2. The cold storage system 5 provided by this invention can condense the exhaust steam from the low-pressure cylinder of the original power plant into subcooled water at 3℃-5℃, while the subcooled water temperature of the original thermal power plant is approximately 30℃, thereby increasing the heating power. In summary, the cascaded heat pump heating system coupled with a thermal power plant for new energy consumption provided by this invention can increase the overall round-trip efficiency to over 60% under rated operating conditions.

[0066] The following is a detailed description of the heat pump energy storage and peak-shaving system for thermal power plants provided by the present invention.

[0067] See Figure 1When there is surplus electricity in the new energy power generation system, the electricity is supplied to motor 1, and the heat pump circuit starts working. Motor 1 drives compressor 2, which compresses the working gas to obtain high-temperature heat energy, which is stored in the hot salt tank 42 through the first heat exchanger 41. Then the working gas flows through the regenerator 6 and reaches the expander 3, where it expands to obtain low-temperature cold energy, which is stored in the low-temperature coolant tank 52 through the second heat exchanger 51. Then the working gas flows through the regenerator 6 and is reheated before entering compressor 2, starting the next cycle. In this process, the preheating of the low-temperature working gas before it enters the compressor 2 through the regenerator 6 achieves the purpose of a low pressure ratio and enabling the working gas to reach the expected high temperature.

[0068] When the heat pump circuit and the first heat storage circuit are operating, the high-temperature working gas output by the compressor 2 can release its heat energy to the molten salt flowing in the first heat storage circuit within the first heat exchanger 41, and store the heat energy in the hot salt tank 42. When the second heat storage circuit is operating, the high-temperature molten salt in the high-temperature salt tank 46 can be heated to above 566°C by the electric heater 45 before flowing into the ultra-high temperature salt tank 44, and the heat energy is stored in the ultra-high temperature salt tank 46.

[0069] When the heat release circuit, the first heat storage circuit, and the second heat storage circuit are working, the water output from the boiler feedwater pipeline and / or the steam output from the high-pressure cylinder of the steam turbine in the thermal power plant can enter the heat release circuit and flow sequentially through the first-stage heat exchanger 71a and the second-stage heat exchanger 71b. In the first-stage heat exchanger 71a, the heat energy of the molten salt in the first heat storage circuit is absorbed, and in the second-stage heat exchanger 71b, the heat energy of the molten salt in the second heat storage circuit is absorbed. Then, the steam is input into the steam turbine from the steam input pipeline of the steam turbine for Rankine cycle work.

[0070] The first heat storage circuit in this embodiment of the invention has both heat storage and heat release functions. The cold molten salt in the cold salt tank 43 flows through the first heat exchanger 41 and exchanges heat with the working gas before reaching the hot salt tank 42, thus storing thermal energy. The hot molten salt in the hot salt tank 42 flows through the primary heat exchanger 71a and exchanges heat with water and / or steam before returning to the cold salt tank 43, thus releasing thermal energy.

[0071] The second heat storage circuit in this embodiment of the invention also has heat storage and heat release functions. The high-temperature molten salt in the high-temperature salt tank 46 flows through the ultra-high-temperature molten salt heating tank 47 and then reaches the ultra-high-temperature salt tank 44, achieving heat energy storage. The ultra-high-temperature molten salt in the ultra-high-temperature salt tank 44 flows through the secondary heat exchanger 71b, exchanges heat with water and / or steam, and then flows back to the high-temperature salt tank 46, achieving heat energy release.

[0072] The first cooling circuit in this embodiment of the invention has both cooling storage and cooling release functions. Coolant in the ambient temperature coolant tank 53 flows through the second heat exchanger 51, exchanges heat with the working gas, and then reaches the cryogenic coolant tank 52, thus storing cold energy. The cryogenic coolant in the cryogenic coolant tank 52 flows through the condenser tubes in the condenser, exchanges heat with the steam in the condenser, and then flows back to the ambient temperature coolant tank 53, thus releasing cold energy. The steam in the condenser is the exhaust steam from the last stage of the low-pressure cylinder of a steam turbine in a thermal power plant. The first cooling circuit can condense this steam into subcooled water at 3℃-5℃, heating the coolant temperature to approximately 20℃ before returning it to the ambient temperature coolant tank 53.

[0073] Considering the availability of air and the widespread application of air compressor technology (such as aviation gas turbines and compressed air energy storage), air is selected as the working gas in this embodiment of the invention.

[0074] In gas turbines, the highest temperature reached by air compressor technology can be several hundred degrees Celsius. In practice, it is difficult for compressors used for such large energy storage to reach temperatures above 500°C. In this embodiment of the invention, an electric heater 45 is used to raise the molten salt temperature in the high-temperature section (>500°C) of the cascaded thermal storage system 4. Preferably, the lower 80%–90% of the heat in the temperature range is achieved by a heat pump, and the remaining 10%–20% is achieved by the electric heater 45. The response time of the electric heater 45 is shorter than that of the heat pump, and the electric heater 45 can start first during startup.

[0075] In terms of thermal energy storage, inorganic molten salts, granite, and ceramic particles can all meet the requirements. Granite and ceramic particles can be used at temperatures above 600℃, but their thermal conductivity is very low (1.5 W / m²). -1 K -1 This presents a challenge for heat exchanger design. Divalent nitrate solar salts (NaNO3:KNO3 = 60:40, wt%) offer a cost advantage and can be used in a temperature range of 260°C to 565°C. Hitec salts (NaNO3:KNO3:NaNO2 = 7:53:40, wt%) can decompose at temperatures up to 680°C in a closed container under a protective atmosphere, a temperature range sufficient to generate 566°C steam suitable for supercritical turbines.

[0076] Since the outlet temperature of the high-power compressor in grid-level energy storage is difficult to reach above 500°C with current technology, this embodiment of the invention is based on a compressor outlet temperature of 500°C and adopts a four-tank tiered storage method. Specifically, the cold salt tank 43 and hot salt tank 42 in the first thermal storage loop store binary nitrate solar salt at 300°C to 500°C; the high-temperature salt tank 46 and ultra-high-temperature salt tank 44 in the second thermal storage loop store one of Hitec salt, chloride salt, and carbonate salt at 500°C to 660°C, and the thermal storage material is heated by an electric heater 45.

[0077] Nitrates, chlorides, and carbonates, compared to solid thermal storage materials, have the advantage of high heat transfer coefficients and rapid thermal response due to their fluidity. However, molten salts above 580°C exacerbate the corrosion of stainless steel salt tanks. Nickel-based alloy tanks are corrosion-resistant but expensive. Therefore, in this embodiment of the invention, the ultra-high temperature salt tank 44 in the ultra-high temperature section of the cascaded thermal storage system 4 uses a nickel-based alloy tank, such as chromium-nickel-iron alloy. The high-temperature salt tank 46, hot salt tank 42, and cold salt tank 43 use traditional stainless steel tanks. This reduces the volume of the ultra-high temperature salt tank 44, thereby lowering the cost of the nickel-based alloy tank. The required protective gas for the ultra-high temperature salt tank 44 is also reduced, and control is relatively easier. In this four-tank cascaded storage design, the volume of the nickel-based alloy ultra-high temperature salt tank 44 is only 40% of the volume of the high-temperature salt tank 46 containing binary nitrate solar salts. Due to the minimal use of nickel-based alloys, the four-tank cascaded storage design has a cost advantage. Furthermore, when the storage tank is smaller, the control of the protective gas inside is also easier.

[0078] For cold energy storage, inexpensive and safe coolants are preferred. Some organic liquids can operate at low vapor pressures below 200K (close to or below 0.1MPa), such as butane and heptane, but they are highly flammable and neurotoxic. The phase transition of the NaCl-water mixture occurs between 0℃ and -21.2℃, corresponding to the eutectic point (NaCl mass ratio in water is 23.3%).

[0079] In practical applications, the main irreversible energy conversion in the heat pump system is through compressor 2. The isentropic efficiencies of compressor 2 and expander 3 vary depending on their type and conditions. In this embodiment, the compressor efficiency is 0.8 and the expander efficiency is 0.9. Based on the solar salt operating temperature, the regeneration temperature is set to 280℃. Figure 2 As shown, this is the Ts diagram for the reverse Brayton cycle (energy charging process) with and without a regenerator under ideal operating conditions, without considering the actual efficiency of compressor 2 and expander 3. Figure 2 As can be seen from this, when the regenerator 6 is added, the inlet temperature of compressor 2 increases (T0). + '→T c The inlet temperature of expander 3 decreased (T). c + →T0'), thereby reducing the pressure ratio.

[0080] Calculations show that the coefficient of performance (COP) of the heat pump system with regenerator 6 is 2.8, and the electrothermal conversion efficiency (η) is... e-h =1.9. The coefficient of performance (COP) of the heat pump system without a regenerator 6 is 2.2, and the electrothermal conversion efficiency η is... e-h =1.6. It can be seen that the COP and η of the heat pump system with regenerator 6 are... e-h All have been significantly improved.

[0081] During the charging process of the heat pump system, when the input power changes, the compressor 2 or expander 3 experiences a rapid decrease in efficiency when the input load is less than 0.4, due to significant local eddy current losses. For example... Figure 3 As shown, the compressor efficiency curve has an extreme point at a rate of 0.8, and then decreases slightly after reaching a rate of 0.8. Under ideal conditions, the efficiency of a reciprocating compressor can reach up to 0.91, and that of a turbine compressor can reach up to 0.96. With current technology, the efficiency of compressors (axial or centrifugal compressors) used for large energy storage may not reach such high levels, but the efficiency trends under different operating conditions can serve as a reference.

[0082] The present invention adopts a combined heating scheme of heat pump and electric heater 45, and takes the outlet temperature of compressor 2 as 500°C and the regeneration temperature as 280°C as an example.

[0083] Depend on Figure 4 The comparison of heating efficiency of heat pump + electric heater 45 and pure electric heater 45 under variable input load shows that when the electric input load is greater than 60%, the heat pump electric heater combined system can obtain a higher heating efficiency (1.39~1.426), and when the input load is low, the efficiency of compressor 2 and expander 3 drops sharply.

[0084] Depend on Figure 5 The comparison of the round-trip efficiency of the integrated system (formed by coupling a heat pump system to the original power plant system) and the original power plant system under different output loads shows that the round-trip efficiency of the integrated system is generally higher than that of the original power plant. When the output load is greater than 80%, the round-trip efficiency of the integrated system can reach 0.55–0.56; when the output load is 40%, the round-trip efficiency of the integrated system is 0.47, while the round-trip efficiency of the original power plant is 0.36. When the output load is 20%, the efficiency of the integrated system is only 0.38.

[0085] See Figure 1 In some embodiments of the present invention, the multi-stage heat exchanger 71 includes a first multi-stage heat exchanger 711 and a second multi-stage heat exchanger 712. Both the first multi-stage heat exchanger 711 and the second multi-stage heat exchanger 712 include a first-stage heat exchanger 71a and a second-stage heat exchanger 71b. The first-stage heat exchanger 71a of the first multi-stage heat exchanger 711 and the first-stage heat exchanger 71a of the second multi-stage heat exchanger 712 are connected in parallel to the first molten salt pipe 401. The second multi-stage heat exchanger 712 of the first multi-stage heat exchanger 711 and the second multi-stage heat exchanger 712 are connected in parallel to the second molten salt pipe 402. The steam pipe 200 includes a first steam pipe 201 and a second steam pipe 202.

[0086] The heat release loop includes a first heat release loop and a second heat release loop. Specifically, the first-stage heat exchanger 71a and the second-stage heat exchanger 71b of the first multi-stage heat exchanger 711 are adapted to be connected in series via a first steam pipe 201 between the boiler feedwater pipe and the main steam input pipe of the high-pressure cylinder of the steam turbine in a thermal power plant, thereby forming the first heat release loop. Similarly, the first-stage heat exchanger 71a and the second-stage heat exchanger 71b of the second multi-stage heat exchanger 712 are adapted to be connected in series via a second steam pipe 202 between the high-pressure cylinder steam output pipe and the intermediate-pressure cylinder reheat steam input pipe of the steam turbine in a thermal power plant, thereby forming the second heat release loop.

[0087] Both the primary heat exchanger 71a and the secondary heat exchanger 71b are equipped with molten salt channels and steam channels. In the first multi-stage heat exchanger 711, the molten salt channel of the primary heat exchanger 71a is allocated to the first heat storage loop for the flow of solar salt; the molten salt channel of the secondary heat exchanger 71b of the first multi-stage heat exchanger 711 is allocated to the second heat storage loop for the flow of Hitec salt. In the second multi-stage heat exchanger 712, the molten salt channel of the primary heat exchanger 71a is allocated to the first heat storage loop for the flow of solar salt; the molten salt channel of the secondary heat exchanger 71b of the second multi-stage heat exchanger 712 is allocated to the second heat storage loop for the flow of Hitec salt.

[0088] When the heat release function of the first and second heat storage circuits is activated and the heat release circuits are working, the water output from the boiler feedwater pipe flows through the first steam pipe 201 sequentially through the first-stage heat exchanger 71a and the second-stage heat exchanger 71b of the first multi-stage heat exchanger 711. After absorbing the heat energy of the molten salt, it is sent to the high-pressure cylinder of the steam turbine. The steam output from the high-pressure cylinder steam output pipe of the steam turbine flows through the second steam pipe 202 sequentially through the first-stage heat exchanger 71a and the second-stage heat exchanger 71b of the second multi-stage heat exchanger 712. After absorbing the heat energy of the molten salt, it is delivered to the intermediate-pressure cylinder of the steam turbine.

[0089] The first heat release circuit is equipped with a first regulating valve 721, and the second heat release circuit is equipped with a second regulating valve 722. The first heat release circuit is started or stopped by opening or closing the first regulating valve 721. The second heat release circuit is started or stopped by opening or closing the second regulating valve 722.

[0090] A regulating valve assembly is installed between the boiler's steam outlet and the turbine's steam inlet pipe. Specifically, this regulating valve assembly includes a fourth regulating valve and a fifth regulating valve. The fourth regulating valve is located on the pipe between the boiler's steam outlet and the high-pressure cylinder's main steam inlet pipe. The fifth regulating valve is located on the pipe between the boiler's steam outlet and the intermediate-pressure cylinder's reheat steam inlet pipe.

[0091] The cascaded energy storage system for renewable energy consumption, coupled with a thermal power plant, requires variable load output, causing the heat exchangers to operate under varying conditions. This presents challenges to the metal materials of the heat exchangers, including creep and fatigue. To address this, in this embodiment, the first heat exchanger 41 and / or the regenerator 6 employ compact heat exchangers, such as micro-shell-and-tube heat exchangers, to achieve a high heat transfer area to volume ratio. The heat exchange tubes of the first multi-stage heat exchanger 711 have a straight-through structure. The heat exchange tubes of the second multi-stage heat exchanger 712 are made of Haynes 230. When this cascaded energy storage system is applied to a supercritical power plant, the second multi-stage heat exchanger 712 serves as a molten salt-supercritical water / steam heat exchanger, and the use of Haynes 230 heat exchange tubes helps reduce the tube wall thickness.

[0092] The cascaded heat pump heating energy storage system coupled to a thermal power plant, provided in this invention embodiment, can be applied to supercritical coal-fired power plants, forming a coupled system between the supercritical coal-fired power plant and the heat pump system. According to the thermodynamic analysis results of this system, under a moderate recoil rate (2.6), this coupled system has advantages in thermal efficiency and flexibility compared to the original coal-fired power plant. The round-trip efficiency is 0.53–0.56 when the output load is greater than 60%. Due to the utilization of existing coal-fired power plant infrastructure, this coupled system has a lower equilibrium electricity cost than pump-type hydraulic energy storage, compressed air energy storage, and vanadium redox flow batteries when the discharge time is less than 9 hours. Compared to pure electric thermal storage systems, the heat pump system can provide additional cooling energy. If the cooling energy is sold, the heat pump system will achieve greater economic benefits than the electric thermal storage system. Replacing the boiler with thermal energy storage will also significantly reduce carbon dioxide emissions and various pollutants generated from coal combustion.

[0093] The cascaded energy storage system for new energy consumption coupled with a thermal power plant heat pump heating system provided in this embodiment of the invention also includes a third heat exchanger 73. The outlet of the low-temperature coolant tank 52 and the inlet of the normal-temperature coolant tank 53 are connected to both ends of the third heat exchanger 73 through a second coolant pipe 302, thereby forming a second cooling circuit.

[0094] The third heat exchanger 73 is adapted to be connected to the refrigeration equipment 74. The coolant flowing in the second cooling circuit can absorb heat from the refrigeration equipment 74 through the third heat exchanger 73, realizing the utilization of cold energy. The refrigeration equipment 74 can be a refrigerator, ice maker, freezer, etc. The refrigeration equipment 74 can also be part of a heat exchange system. A third regulating valve 75 is provided on the second cooling circuit, and the cooling operation of the second cooling circuit can be started by activating the third regulating valve 75.

[0095] This invention also provides an operation method for a cascaded energy storage system coupled with a thermal power plant for new energy consumption, as described in any of the above embodiments. Figure 6As shown, the running method includes:

[0096] Step S100: If it is determined that there is surplus electrical energy in the new energy power generation system, the heat pump electric heater combined system is started to convert the surplus electrical energy into heat energy and cold energy, and the heat energy is stored in the cascaded thermal storage system 4 and the cold energy is stored in the cold storage system 5.

[0097] Step S200: If the power generation demand of the thermal power plant is determined to be less than the set threshold, then close the boiler and the regulating valve group between the boiler's steam outlet and the steam input pipeline of the steam turbine, start the heat release circuit and the first cold release circuit, so that the heat energy stored in the cascaded thermal storage system 4 is released to the water and / or steam in the heat release circuit, and the cold energy stored in the cascaded cold storage system 5 is released to the coolant in the first cold release circuit.

[0098] Step S300: If the power generation demand of the thermal power plant is determined to be greater than or equal to the set threshold, then the regulating valve group is activated.

[0099] Step S400: After starting the boiler and opening the regulating valve group, once the boiler load reaches a stable value, the heat release circuit is closed.

[0100] Furthermore, in the above steps S200 to S400, the method further includes: if it is determined that the steam thermal energy in the condenser is insufficient to heat the coolant in the cold storage system 5 to the set temperature, then the second cold release circuit is activated.

[0101] Specifically, when surplus electrical energy is determined to exist, the motor 1, compressor 2, expander 3, cascaded thermal storage system 4, and cold storage system 5 are started. On one hand, the compressor 2 and expander 3 convert a portion of the electrical energy into heat and cold energy. The heat energy is transferred to the hot salt tank 42 of the first thermal storage circuit for storage through the hot gas pipeline 101; the cold energy is transferred to the first heat release circuit through the feedback pipeline 102 and stored in the low-temperature coolant tank 52. On the other hand, the electric heater 45 converts another portion of the electrical energy into heat energy and stores it in the ultra-high temperature salt tank 44.

[0102] When the power generation demand of a thermal power plant is less than a set threshold, it indicates that the plant is under low load. For example, when a thermal power plant requires deep peak shaving, the boiler is shut down, putting it into a self-protection and self-circulation state. Simultaneously, the heat release circuit and the first cold release circuit are activated. The water output from the boiler or the steam output from the high-pressure cylinder steam output pipe of the turbine absorbs the heat energy stored in the cascaded thermal storage system 4 and then enters the steam input pipe of the turbine. The coolant in the cold storage system 5 flows through the condenser via the first cold release circuit, condensing the steam inside the condenser.

[0103] For example, the first and / or second thermal storage loops of the cascaded thermal storage system 4 are started, causing the high-temperature hot salt in the hot salt tank 42 and the ultra-high-temperature hot salt in the ultra-high-temperature salt tank 44 to flow through the first multi-stage heat exchanger 711 and the second multi-stage heat exchanger 712. The water output from the boiler feedwater pipeline flows through the first multi-stage heat exchanger 711, and the steam output from the high-pressure cylinder steam output pipeline of the steam turbine flows through the second multi-stage heat exchanger 712. After absorbing the heat energy of the hot salt, the steam enters the main steam input pipeline of the high-pressure cylinder and the reheat steam input pipeline of the intermediate-pressure cylinder, respectively. At the same time, the cold storage system 5 is also started, causing the low-temperature coolant in the low-temperature coolant tank 52 to flow through the condenser to condense the steam in the condenser.

[0104] When the power generation demand of a thermal power plant is greater than or equal to a set threshold, it indicates that the power plant is under high load and the thermal energy stored in the cascaded thermal storage system 4 is insufficient. At this time, the boiler is started up, and the regulating valve group is opened so that the main steam in the first heat release circuit mixes with the main steam directly output from the boiler and enters the high-pressure cylinder through the main steam input pipe. The reheat steam in the second heat release circuit mixes with the reheat steam directly output from the boiler and enters the intermediate-pressure cylinder through the reheat steam input pipe.

[0105] After the boiler is started up, the boiler load gradually increases. When the load reaches the set value and remains within the set fluctuation range for a set time period, the boiler load is considered to have reached a stable state. The set value is the stable value of the boiler load. At this time, the first regulating valve 721 and the second regulating valve 722 are closed, thereby closing the first heat release circuit and the second heat release circuit, and the boiler operates alone to generate electricity.

[0106] When the steam heat energy in the condenser is insufficient to heat the coolant in the cold storage system 5 to the set temperature, the third regulating valve is opened to start the second cooling circuit, so that part of the coolant in the cold storage system 5 flows through the condenser through the first cooling circuit, and the other part flows through the third heat exchanger 73 through the second cooling circuit.

[0107] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A heat pump cascaded energy storage system coupled to a thermal power plant, characterized in that, It includes a heat pump electric heater combined system, a cascaded heat exchange system and an atmosphere protection system. The heat pump electric heater combined system includes: an electric motor, a compressor, an expander, a regenerator, a cascaded thermal storage system and a cold storage system. The electric motor, the compressor, and the expander are connected in sequence via a drive shaft. The electric motor is adapted to be connected to a new energy power generation system. The outlet of the compressor and the inlet of the expander are connected via a hot air pipe, and the inlet of the expander and the inlet of the compressor are connected via a feedback pipe, forming a closed heat pump circuit. The cascaded thermal energy storage system includes a first heat exchanger, a hot salt tank, a cold salt tank, an ultra-high temperature molten salt heating tank, an electric heater, an ultra-high temperature salt tank, and a high temperature salt tank. The electric heater is located inside the ultra-high temperature molten salt heating tank and is suitable for connection to a new energy power generation system. The cold energy storage system includes a second heat exchanger, a low temperature coolant tank, and a normal temperature coolant tank. The cascaded heat exchange system includes a multi-stage heat exchanger, which includes a first-stage heat exchanger and a second-stage heat exchanger. The first heat exchanger, the cold salt tank, the primary heat exchanger, and the hot salt tank are sequentially connected via a first molten salt pipeline to form a first heat storage circuit. The first heat exchanger is mounted on the hot gas pipeline, allowing the molten salt in the first heat storage circuit to absorb the heat energy of the working gas in the heat pump circuit. The high-temperature salt tank, the ultra-high-temperature molten salt heating tank, the ultra-high-temperature salt tank, and the secondary heat exchanger are sequentially connected via a second molten salt pipeline to form a second heat storage circuit. The ultra-high-temperature salt tank and the ultra-high-temperature molten salt heating tank are both sealed. The primary heat exchanger and the secondary heat exchanger are connected in series via a steam pipeline and are adapted to be coupled to a thermal power plant via the steam pipeline to form a heat release circuit. The molten salt in the first heat storage circuit and the second heat storage circuit releases heat energy to the water and / or steam in the heat release circuit through the primary heat exchanger and the secondary heat exchanger, respectively, to form steam supplied to the turbine in the thermal power plant. The working gas in the heat pump circuit is one of air, nitrogen, helium, or argon; the hot salt tank and the cold salt tank store binary nitrate solar salt, which is composed of 60% NaNO3 and 40% KNO3; the ultra-high temperature salt tank and the high temperature salt tank store one of Hitec salt, chloride salt, and carbonate salt, wherein the Hitec salt is composed of 7% NaNO3, 53% KNO3, and 40% NaNO2; the chloride salt is composed of... The salt is composed of 7.5% NaCl, 23.9% KCl, and 68.6% ZnCl2, or 37.5% MgCl2 and 62.5% KCl; the carbonate is composed of 33.4% Na2CO3, 34.5% K2CO3, and 32.1% Li2CO3; the operating temperature of the cold salt tank and the hot salt tank is 300℃~500℃, and the operating temperature of the high-temperature salt tank and the ultra-high-temperature salt tank is 500℃~660℃. The atmosphere protection system is connected to the ultra-high temperature salt tank, the ultra-high temperature molten salt heating tank, and the high temperature salt tank respectively, and is used to introduce protective gas into the ultra-high temperature salt tank, the ultra-high temperature molten salt heating tank, and the high temperature salt tank; wherein, when Hitec salt is used, the protective gas includes a mixture of nitrogen and oxygen. The second heat exchanger is disposed on the feedback pipe and connected between the inlet of the cryogenic coolant tank and the outlet of the ambient temperature coolant tank. The outlet of the cryogenic coolant tank and the inlet of the ambient temperature coolant tank are adapted to be connected to both ends of the cooling channel of the condenser in the thermal power plant through the first coolant pipe to form a first cooling release circuit. The coolant flowing in the first cooling release circuit can absorb the cold energy of the working gas in the heat pump circuit through the second heat exchanger to supply the condenser to condense the exhaust steam output by the turbine. The coolant is brine with a phase change temperature between 0°C and -21.2°C. The regenerator is located on the hot gas pipeline between the first heat exchanger and the air inlet of the expander, and on the feedback pipeline between the second heat exchanger and the air inlet of the compressor, so that the working gas in the hot gas pipeline can exchange heat with the working gas in the feedback pipeline within the regenerator.

2. The heat pump cascaded energy storage system coupled to a thermal power plant according to claim 1, characterized in that, The ultra-high temperature salt tank has a nickel-based alloy body, while the high temperature salt tank, the hot salt tank, and the cold salt tank have stainless steel bodies.

3. The heat pump cascaded energy storage system coupled to a thermal power plant according to claim 1, characterized in that, The multi-stage heat exchanger includes: a first multi-stage heat exchanger and a second multi-stage heat exchanger, each including a first-stage heat exchanger and a second-stage heat exchanger. The first-stage heat exchangers of the first and second multi-stage heat exchangers are connected in parallel to the first molten salt pipeline, and the second-stage heat exchangers of the first and second multi-stage heat exchangers are connected in parallel to the second molten salt pipeline; the steam pipeline includes a first steam pipeline and a second steam pipeline. The heat release circuit includes a first heat release circuit and a second heat release circuit. The first-stage heat exchanger and the second-stage heat exchanger of the first multi-stage heat exchanger are adapted to be connected in series between the feedwater pipeline of the boiler and the main steam input pipeline of the high-pressure cylinder in the thermal power plant through the first steam pipeline to form the first heat release circuit. The first-stage heat exchanger and the second-stage heat exchanger of the second multi-stage heat exchanger are adapted to be connected in series between the steam output pipeline of the high-pressure cylinder and the reheat steam input pipeline of the intermediate-pressure cylinder of the steam turbine through the second steam pipeline to form the second heat release circuit.

4. The heat pump cascaded energy storage system coupled to a thermal power plant according to claim 3, characterized in that, The first heat exchanger and / or regenerator is a miniature shell-and-tube heat exchanger.

5. The heat pump cascaded energy storage system coupled to a thermal power plant according to claim 3, characterized in that, The heat exchange tubes of the second multi-stage heat exchanger are made of Haynes 230.

6. The heat pump cascaded energy storage system coupled to a thermal power plant according to claim 1, characterized in that, The heat exchange system also includes: a third heat exchanger; The outlet of the low-temperature coolant tank and the inlet of the normal-temperature coolant tank are connected to both ends of the third heat exchanger through a second coolant pipe to form a second cooling circuit; wherein, the third heat exchanger is adapted to be connected to a refrigeration device, and the coolant flowing in the second cooling circuit can absorb heat from the refrigeration device through the third heat exchanger.

7. An operation method for a heat pump cascaded energy storage system coupled to a thermal power plant as described in any one of claims 1-6, characterized in that, include: If it is determined that there is surplus electrical energy in the new energy power generation system, the heat pump electric heater combined system is started to convert the surplus electrical energy into heat energy and cold energy, and the heat energy is stored in the cascaded thermal storage system and the cold energy is stored in the cold storage system. If the power generation demand of the thermal power plant is determined to be less than a set threshold, the boiler and the regulating valve group between the boiler's steam outlet and the steam input pipeline of the steam turbine are closed, and the heat release circuit and the first cold release circuit are started, so that the heat energy stored in the cascaded thermal storage system is released to the water and / or steam in the heat release circuit, and the cold energy stored in the cold storage system is released to the coolant in the cold release circuit. If the power generation demand of the thermal power plant is determined to be greater than or equal to the set threshold, then the boiler is started and the regulating valve group is opened; After starting the boiler and opening the regulating valve group, once the boiler load reaches a stable value, the heat release circuit is shut off.

8. The operation method of the heat pump cascaded energy storage system coupled to a thermal power plant according to claim 7, characterized in that, Also includes: If it is determined that the steam heat energy in the condenser is insufficient to heat the coolant in the cold storage system to the set temperature, then the second cold release circuit is activated.

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