A thermal power unit retrofit molten salt heat storage power station and electric-thermal collaborative scheduling method

Abstract

This invention relates to a method for retrofitting thermal power units into molten salt thermal storage power plants and a county-level power-heat coordinated dispatching method. First, it proposes a method for flexibly retrofitting thermal power units into molten salt thermal storage power plants. This involves adding high-temperature molten salt tanks, low-temperature molten salt tanks, heat exchangers, and electric heaters to shut-down or decommissioned thermal power units, and utilizing the thermal cycle system and turbine of the thermal power unit to construct a power-heat coordinated molten salt thermal storage power plant. Second, it proposes a county-level power-heat coordinated dispatching architecture. This utilizes county-wide photovoltaic curtailment and surplus electricity from the county power grid to heat the heat transfer medium for thermal storage, or directly stores waste heat from the county heating network. The thermal cycle system and turbine of the thermal power unit are then used for thermal storage power generation or direct heating, improving both photovoltaic absorption rate and the flexibility of county-level power and heating supply. Finally, it proposes a county-level power-heat coordinated economic dispatching method based on molten salt thermal storage power plants. This method aims to minimize the power generation cost of the county power system, comprehensively considering the constraints of the power system and the thermal system to formulate an optimal dispatching plan.

Description

Technical Field

[0001] This invention relates to the field of thermal power plant retrofitting and thermal energy storage, specifically to a method for retrofitting thermal power units into molten salt thermal energy storage power plants and for coordinated power and heat dispatching. Background Technology

[0002] Currently, promoting the large-scale utilization of renewable energy sources such as wind and solar power, and accelerating the clean transformation of coal-fired power are important trends in energy development. The National Development and Reform Commission and the National Energy Administration have put forward opinions on improving the institutional mechanisms and policy measures for the green and low-carbon transformation of energy, pointing out that while accelerating the grid connection of renewable energy, it is necessary to first establish new systems and then dismantle old ones, and to fully implement the flexibility transformation of thermal power plants. In recent years, energy storage technology has developed rapidly, breaking the traditional power system's "on-demand" characteristic and enabling the coordination of power system supply and demand balance in time. However, energy storage systems still have limitations such as high cost and short lifespan. The transformation method of coupling thermal power units with energy storage systems can not only solve the problem of decommissioning high-energy-consuming thermal power units to the greatest extent and improve resource utilization efficiency, but also reduce the construction cost of energy storage and promote the further development of energy storage in the power sector.

[0003] To support the achievement of the "dual carbon targets," in June 2021, the National Energy Administration issued the "Notice on Submitting Pilot Programs for Rooftop Distributed Photovoltaic Development in Entire Counties (Cities, Districts)," officially launching the large-scale development of distributed photovoltaic power in counties. However, the large-scale grid connection of distributed photovoltaic power has led to difficulties in local consumption and serious curtailment issues, which not only restrict the development of county-wide photovoltaic power but also pose a significant threat to the safety and stability of the power grid. Currently, the configuration of thermal storage in centralized photovoltaic power plants has become an important power generation technology with flexible operation and good regulation performance. While significantly improving the photovoltaic consumption level, it breaks the rigid constraint of traditional heating "determining electricity based on heat," improving the flexibility of system power supply. However, to reduce construction costs, most existing centralized photovoltaic power plants with thermal storage are planned only for photovoltaic consumption, with limited thermal storage capacity. If the photovoltaic power plant is subsequently expanded, high costs will be incurred for thermal storage retrofitting, and the peak-shaving, backup, and other flexible regulation potential of thermal storage cannot be fully utilized.

[0004] For county-wide photovoltaic (PV) projects, the widespread distribution of building rooftops, dispersed resources, and small individual unit scale make it difficult, costly, and inefficient to configure thermal storage for all distributed PV systems. However, as county-wide PV projects progress, many high-energy-consuming thermal power units in these areas face decommissioning. If flexible retrofitting technology combining unit coupling with thermal storage can be implemented, these decommissioned or aging thermal power units can be flexibly converted into centralized molten salt thermal storage power plants to serve the county's power and heating systems. This would not only solve the problem of distributed PV integration but also provide an important solution for the flexible retrofitting of thermal power units in the construction of new power systems, improving regional energy supply stability, fully leveraging the flexibility of thermal storage regulation, and achieving a win-win situation for power generation, grid, load, and storage. Summary of the Invention

[0005] This invention addresses the challenges of retrofitting traditional thermal power plants and integrating distributed photovoltaic power in county-level areas by proposing a method for retrofitting thermal power units into molten salt thermal power plants and a coordinated power-heat dispatching system. This invention enables flexible retrofitting of decommissioned thermal power units in county-level areas, promotes the integration of photovoltaic power across the entire county, improves the flexibility and stability of power and heat supply in the county, and achieves multi-energy complementarity of electricity and heat.

[0006] This invention is achieved using the following technical solution: a method for converting thermal power units into molten salt thermal power plants and a method for coordinated power and heat dispatch. First, it proposes a method for flexibly converting shut-down thermal power units into molten salt thermal power plants by adding molten salt tanks. Second, it proposes a county-level coordinated power and heat dispatch architecture. Finally, it proposes a county-level coordinated economic dispatch method for power and heat based on molten salt thermal power plants, with the goal of minimizing operating costs. The method consists of the following three steps:

[0007] Step 1: Install high-temperature molten salt tanks, low-temperature molten salt tanks, a first heat exchanger, a second heat exchanger, and electric heaters in decommissioned or aging thermal power units. Utilize the thermal cycle system and turbine of the thermal power unit to form a centralized molten salt thermal energy storage power station. The specific workflow is as follows: First, within the maximum allowable storage capacity of the molten salt tanks, the electric heaters of the molten salt thermal energy storage power station use surplus solar power or off-peak electricity from the grid to heat the low-temperature heat transfer medium. Alternatively, the second heat exchanger of the molten salt thermal energy storage power station uses waste heat from the county's heating network to exchange heat with the low-temperature heat transfer medium, generating a high-temperature heat transfer medium. The high-temperature heat transfer medium then exchanges heat with the low-temperature heat transfer medium. The molten salt undergoes heat exchange in the first heat exchanger, producing high-temperature molten salt and low-temperature heat transfer medium. The high-temperature molten salt enters a high-temperature molten salt tank for heat storage, while the low-temperature heat transfer medium returns to the electric heater and the second heat exchanger for reuse. In the thermodynamic cycle system, the high-temperature molten salt generates high-temperature steam, which drives a steam turbine to generate electricity, or the high-temperature molten salt, after heat exchange, directly supplies heat to the county's heating network, producing low-temperature molten salt which is stored in a low-temperature molten salt tank. This achieves the recovery of surplus electricity and heat from the county's power grid and heating network, promotes photovoltaic power consumption, and simultaneously provides electricity and heat to the county, improving the stability of the county's energy supply.

[0008] Step Two: Establish a county-level electricity and heat coordinated dispatch architecture, including county-wide photovoltaic and thermal power unit retrofitted with molten salt thermal storage power plants, combined heat and power (CHP) units, heat load, electricity load, power grid, and heating network. In this dispatch architecture, the county-wide photovoltaic, molten salt thermal storage power plants, and CHP units generate electricity to balance the county's electricity load. Simultaneously, when electricity supply exceeds demand, the molten salt thermal storage power plants can absorb curtailed photovoltaic power or off-peak electricity from the grid, converting it into heat energy for storage. When electricity supply is less than demand, the stored heat energy is released and used to generate electricity through a thermal cycle system and steam turbines. The CHP units and molten salt thermal storage power plants provide heat to balance the county's heat load. The molten salt thermal storage power plants can also store waste heat from the heating network and convert this heat energy into electricity or release it at other times, thereby improving the flexibility of electricity and heat supply in the county.

[0009] Step 3: Establish a county-level economic dispatch model for coordinated power and heat supply based on molten salt thermal power plants, including the objective function and constraints:

[0010] The objective function comprehensively considers the operation and maintenance costs of photovoltaic systems. The cost of abandoning light The cost of generating electricity from combined heat and power units Cost of flexible retrofitting of thermal power plants And the construction and operation and maintenance costs of molten salt thermal power plants The details are as follows:

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[0017] In the formula, t represents the operating period, T represents the total cycle duration, and V represents the total number of photovoltaic power generation systems within the county. Let v be the operation and maintenance cost coefficient of the v-th photovoltaic power generation system. Let v be the power generation of the photovoltaic system during time period t; Let v be the curtailment penalty coefficient for the v-th photovoltaic power generation system. Let v be the amount of solar power curtailed by the photovoltaic system during time period t. R represents the predicted output of the v-th photovoltaic system in time period t; R is the total number of combined heat and power units. , , These are the coefficients of the quadratic, linear, and constant terms of the operating cost of the r-th cogeneration unit. Let r be the electrical output of the r-th cogeneration unit during time period t. Let be the heating power supplied by the r-th combined heat and power unit during time period t. The decrease in electrical power when a unit amount of steam is extracted under a fixed steam inlet for the r-th cogeneration unit; The surplus value utilization coefficient. To improve the investment coefficient, For the flexible retrofit capacity of shut-down thermal power units, the flexible retrofit capacity is the maximum equivalent power of the thermal storage power station; M represents the total number of molten salt thermal storage power stations. Let m be the average annual cost of the m-th molten salt thermal power plant. Let m be the maximum thermal storage capacity of the m-th molten salt thermal power plant. For the discount rate, The service life of the m-th molten salt thermal power plant; Let m be the operation and maintenance cost coefficient for the m-th molten salt thermal power plant. Let m be the electrical output of the m-th molten salt thermal power plant during time period t. The heating power of the m-th molten salt thermal power plant during time period t;

[0018] The constraints must satisfy both power system constraints and thermal system constraints, specifically power balance, thermal power balance, molten salt thermal power plant operation constraints, photovoltaic output constraints, and combined heat and power unit constraints, as follows:

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[0023]

[0024] In the formula, Let t be the total electrical load of the system during time period t. The total heat load of the system during time period t. For the m-th molten salt thermal power plant, the amount of heat stored in time period t is... and These represent the heat storage and heat release power of the m-th molten salt thermal power plant during time period t. and Let be the maximum heat storage and heat release power of the m-th thermal storage power station, respectively. A product of 0 indicates that heat storage and heat release cannot occur simultaneously. A sum of 0 indicates that the constraint of constant periodic heat capacity of the thermal storage system is satisfied. This represents the maximum thermal storage capacity of the m-th thermal storage power station. and These represent the maximum and minimum power generation of the v-th photovoltaic power generation system during normal operation, respectively. and Let be the maximum and minimum allowable electrical output power of the r-th combined heat and power unit, respectively. and These represent the upward and downward ramp rate limits for the r-th cogeneration unit, respectively.

[0025] The features and beneficial effects of this invention are as follows: This invention proposes a method for converting thermal power units into molten salt thermal power plants and a method for coordinated power and heat dispatching, including a method for flexibly converting thermal power units into molten salt thermal power plants, which reduces the construction cost of molten salt thermal power plants and improves the operational flexibility and production efficiency of decommissioned and aging thermal power units; it proposes a county-level coordinated power and heat dispatching architecture, applying the molten salt thermal power plants converted from thermal power plants to the entire county's photovoltaic area, reducing the cost of distributed photovoltaic curtailment penalties, improving regional functional stability, and improving the efficiency of power and heat energy utilization; and it establishes a county-level coordinated economic dispatching model for power and heat based on molten salt thermal power plants, reducing system energy supply costs. Attached Figure Description

[0026] Figure 1 A simplified structural diagram of a thermal power unit being converted into a molten salt thermal storage power plant for flexible modification.

[0027] Figure 2 This is a county-level electricity and heat collaborative scheduling architecture.

[0028] Figure 3 This is a flowchart for solving the county-level power and heat coordinated economic dispatch model based on molten salt thermal power plants.

[0029] In the diagram: 1-Electric heater, 2-High temperature molten salt tank, 3-Low temperature molten salt tank, 4-First heat exchanger, 5-Second heat exchanger, 6-Thermal cycle system, 7-Drive turbine, 8-County photovoltaic system, 9-Molten salt thermal power station, 10-Combined heat and power unit, 11-Heat load, 12-Electric load, 13-Heating network, 14-Power grid. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of application of the present invention.

[0031] like Figure 1As shown, in a first aspect of the present invention, a method for flexibly converting a thermal power unit into a molten salt thermal power plant is provided. A high-temperature molten salt tank 2, a low-temperature molten salt tank 3, a first heat exchanger 4, a second heat exchanger 5, and an electric heater 1 are installed in a decommissioned or aging thermal power unit. The thermal cycle system 6 and the turbine 7 of the thermal power unit are used to construct a centralized molten salt thermal power plant. The specific workflow is as follows: First, within the maximum allowable storage capacity of the molten salt tank, the electric heater 1 of the molten salt thermal power plant uses surplus solar power or off-peak electricity from the grid to heat the low-temperature heat transfer medium. Alternatively, the second heat exchanger 5 of the molten salt thermal power plant uses waste heat from the county-level heating network to exchange heat with the low-temperature heat transfer medium, generating a high-temperature heat transfer medium. The high-temperature heat transfer medium then exchanges heat with the low-temperature... Molten salt undergoes heat exchange in the first heat exchanger 4, producing high-temperature molten salt and low-temperature heat transfer medium. The high-temperature molten salt enters the high-temperature molten salt tank 2 for heat storage, while the low-temperature heat transfer medium returns to the electric heater 1 and the second heat exchanger 5 for reuse. In the thermal cycle system 6, the high-temperature molten salt generates high-temperature steam, which drives the turbine 7 to rotate and generate electricity, or the high-temperature molten salt directly supplies heat to the county's heating network after heat exchange, producing low-temperature molten salt which is stored in the low-temperature molten salt tank 3. This achieves the recovery of surplus electricity and heat from the county's power grid and heating network, promotes photovoltaic power consumption, and simultaneously provides electricity and heat to the county, improving the stability of the county's energy supply.

[0032] like Figure 2 As shown, in a second aspect of this invention, a county-level electricity and heat coordinated dispatch architecture is constructed, including a county-wide photovoltaic system 8, a molten salt thermal power plant 9 converted from a thermal power unit, a combined heat and power (CHP) unit 10, a heat load 11, an electrical load 12, a heat network 13, and a power grid 14. Regarding regional system power balance, the county-wide photovoltaic system 8, the molten salt thermal power plant 9, and the CHP unit 10 generate electricity through the grid 14 to balance the county-level electrical load 12. Simultaneously, the molten salt thermal power plant 9 can absorb surplus photovoltaic power or off-peak electricity from the grid when power supply exceeds demand, converting it into heat energy for storage; when power supply is less than demand, it releases the stored heat energy to generate electricity through a steam turbine. Regarding regional system heat balance, the CHP unit 10 and the molten salt thermal power plant 9 supply heat through the heat network 13 to balance the county-level heat load 11. The molten salt thermal power plant can also store waste heat from the heat network and convert the heat energy into electricity or release it at other times, thereby achieving complementary thermoelectric coupling and improving the flexibility of county-level power and heat supply while promoting photovoltaic absorption.

[0033] like Figure 3 As shown, in a third aspect of this invention, a county-level molten salt thermal energy storage power station's electricity and heat coordinated economic dispatch model is established, including an objective function and constraints. The model is solved in MATLAB using the commercial optimization software CPLEX, which is called via YALMIP. The objective function comprehensively considers the photovoltaic operation and maintenance costs. The cost of abandoning light The cost of generating electricity from combined heat and power units Cost of flexible retrofitting of thermal power plants And the construction and operation and maintenance costs of molten salt thermal power plants The details are as follows:

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[0040] In the formula, t represents the operating period, T represents the total cycle duration, and V represents the total number of photovoltaic power generation systems within the county. Let v be the operation and maintenance cost coefficient of the v-th photovoltaic power generation system. Let v be the power generation of the photovoltaic system during time period t; Let v be the curtailment penalty coefficient for the v-th photovoltaic power generation system. Let v be the amount of solar power curtailed by the photovoltaic system during time period t. R represents the predicted output of the v-th photovoltaic system in time period t; R is the total number of combined heat and power units. , , These are the coefficients of the quadratic, linear, and constant terms of the operating cost of the r-th cogeneration unit. Let r be the electrical output of the r-th cogeneration unit during time period t. Let be the heating power supplied by the r-th combined heat and power unit during time period t. The decrease in electrical power when a unit amount of steam is extracted under a fixed steam inlet for the r-th cogeneration unit; The surplus value utilization coefficient. To improve the investment coefficient, For the flexible retrofit capacity of shut-down thermal power units, the flexible retrofit capacity is the maximum equivalent power of the thermal storage power station; M represents the total number of molten salt thermal storage power stations. Let m be the average annual cost of the m-th molten salt thermal power plant. Let m be the maximum thermal storage capacity of the m-th molten salt thermal power plant. For the discount rate, The service life of the m-th molten salt thermal power plant; Let m be the operation and maintenance cost coefficient for the m-th molten salt thermal power plant. Let m be the electrical output of the m-th molten salt thermal power plant during time period t. The heating power of the m-th molten salt thermal power plant during time period t.

[0041] The constraints must satisfy both power system constraints and thermal system constraints, specifically power balance, thermal power balance, molten salt thermal power plant operation constraints, photovoltaic output constraints, and combined heat and power unit constraints, as follows:

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[0043]

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[0047] In the formula, Let t be the total electrical load of the system during time period t. The total heat load of the system during time period t. For the m-th molten salt thermal power plant, the amount of heat stored in time period t is... and These represent the heat storage and heat release power of the m-th molten salt thermal power plant during time period t. and Let be the maximum heat storage and heat release power of the m-th thermal storage power station, respectively. A product of 0 indicates that heat storage and heat release cannot occur simultaneously. A sum of 0 indicates that the constraint of constant periodic heat capacity of the thermal storage system is satisfied. This represents the maximum thermal storage capacity of the m-th thermal storage power station. and These represent the maximum and minimum power generation of the v-th photovoltaic power generation system during normal operation, respectively. and Let be the maximum and minimum allowable electrical output power of the r-th combined heat and power unit, respectively. and These represent the upward and downward ramp rate limits for the r-th cogeneration unit, respectively.

Claims

1. A method for retrofitting thermal power units into molten salt thermal storage power plants and for coordinated power and heat dispatching, characterized in that: Includes the following steps: Step 1: Install a high-temperature molten salt tank (2), a low-temperature molten salt tank (3), a first heat exchanger (4), a second heat exchanger (5), and an electric heater (1) in a decommissioned or aging thermal power unit, and use the thermal cycle system (6) and turbine (7) of the thermal power unit to form a centralized molten salt thermal power station. The specific workflow is as follows: First, within the maximum allowable storage capacity of the molten salt tank, the electric heater (1) of the molten salt thermal power station uses photovoltaic waste or surplus electricity from off-peak hours to heat the low-temperature heat transfer medium, or the second heat exchanger (5) of the molten salt thermal power station uses the waste heat from the county heating network to exchange heat with the low-temperature heat transfer medium to generate a high-temperature heat transfer medium; The medium and low-temperature molten salt exchange heat in the first heat exchanger (4) to produce high-temperature molten salt and low-temperature heat transfer medium. The high-temperature molten salt enters the high-temperature molten salt tank (2) to store heat, and the low-temperature heat transfer medium returns to the electric heater (1) and the second heat exchanger (5) for reuse. In the thermal cycle system (6), the high-temperature molten salt generates high-temperature steam, which drives the steam turbine (7) to rotate and generate electricity, or the high-temperature molten salt directly supplies heat to the county heating network after heat exchange, and the low-temperature molten salt is stored in the low-temperature molten salt tank (3), thereby realizing the recovery of surplus electricity and heat of the county power grid and heating network, promoting photovoltaic consumption, and at the same time providing power and heat to the county, improving the stability of county energy supply. Step 2: Establish a county-level electricity and heat coordinated dispatch architecture, including county-wide photovoltaic (8), molten salt thermal power plant (9) converted from thermal power units, cogeneration units (10), heat load (11), electricity load (12), power grid (14), and heat network (13); In the dispatch architecture, the county-wide photovoltaic (8), molten salt thermal power plant (9), and cogeneration units (10) generate electricity to balance the county's electricity load. At the same time, the molten salt thermal power plant (9) can absorb photovoltaic curtailment or off-peak electricity from the power grid when the power supply exceeds the demand, convert it into heat energy for storage, and release the stored heat energy when the power supply is less than the demand, generating electricity through the thermal cycle system (6) and the steam turbine (7); The cogeneration units (10) and the molten salt thermal power plant (9) provide heat to balance the county's heat load. At the same time, the molten salt thermal power plant (9) can also store waste heat from the heat network and convert the heat energy into electricity or release the heat energy at other times, thereby improving the flexibility of the county's power supply and heating. Step 3: Establish a county-level economic dispatch model for coordinated power and heat supply based on molten salt thermal power plants, including the objective function and constraints: The objective function comprehensively considers the operation and maintenance costs of photovoltaic systems. The cost of abandoning light The cost of generating electricity from combined heat and power units Cost of flexible retrofitting of thermal power plants And the construction and operation and maintenance costs of molten salt thermal power plants The details are as follows: ， ， ， ， ， ， In the formula, t represents the operating period, T represents the total cycle duration, and V represents the total number of photovoltaic power generation systems within the county. Let v be the operation and maintenance cost coefficient of the v-th photovoltaic power generation system. Let v be the power generation of the photovoltaic system during time period t; Let v be the curtailment penalty coefficient for the v-th photovoltaic power generation system. Let v be the amount of solar power curtailed by the photovoltaic system during time period t. R represents the predicted output of the v-th photovoltaic system in time period t; R is the total number of combined heat and power units. , , These are the coefficients of the quadratic, linear, and constant terms of the operating cost of the r-th cogeneration unit. Let r be the electrical output of the r-th cogeneration unit during time period t. Let be the heating power supplied by the r-th combined heat and power unit during time period t. The decrease in electrical power when a unit amount of steam is extracted under a fixed steam inlet for the r-th cogeneration unit; The surplus value utilization coefficient. To improve the investment coefficient, For the flexible retrofit capacity of shut-down thermal power units, the flexible retrofit capacity is the maximum equivalent power of the thermal storage power station; M represents the total number of molten salt thermal storage power stations. Let m be the average annual cost of the m-th molten salt thermal power plant. Let m be the maximum thermal storage capacity of the m-th molten salt thermal power plant. For the discount rate, The service life of the m-th molten salt thermal power plant; Let m be the operation and maintenance cost coefficient for the m-th molten salt thermal power plant. Let m be the electrical output of the m-th molten salt thermal power plant during time period t. The heating power of the m-th molten salt thermal power plant during time period t; The constraints must satisfy both power system constraints and thermal system constraints, specifically power balance, thermal power balance, molten salt thermal power plant operation constraints, photovoltaic output constraints, and combined heat and power unit constraints, as follows: ， ， ， ， ， In the formula, Let t be the total electrical load of the system during time period t. The total heat load of the system during time period t. For the m-th molten salt thermal power plant, the amount of heat stored in time period t is... and These represent the heat storage and heat release power of the m-th molten salt thermal power plant during time period t. and Let be the maximum heat storage and heat release power of the m-th thermal storage power station, respectively. A product of 0 indicates that heat storage and heat release cannot occur simultaneously. A sum of 0 indicates that the constraint of constant periodic heat capacity of the thermal storage system is satisfied. This represents the maximum thermal storage capacity of the m-th thermal storage power station. and These represent the maximum and minimum power generation of the v-th photovoltaic power generation system during normal operation, respectively. and Let be the maximum and minimum allowable electrical output power of the r-th combined heat and power unit, respectively. and These represent the upward and downward ramp rate limits for the r-th cogeneration unit, respectively.

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