System and control method for improving variable load capacity of coal-fired unit by integrated molten salt energy storage

Abstract

This invention discloses a system and control method for enhancing the variable load capacity of coal-fired power units through integrated molten salt energy storage. The system comprises a coal-fired power unit and a molten salt energy storage system. The molten salt energy storage system heats feedwater after steam preheating, and the resulting superheated steam is injected into the intermediate-pressure cylinder to perform work. The corresponding control method is as follows: First, determine the load commands for the coal-fired power unit and the molten salt energy storage system; second, formulate a control strategy for the molten salt energy storage system; next, determine the key parameter setpoints for the integrated molten salt energy storage system to enhance the variable load capacity of the coal-fired power unit; then, calculate the superheated steam flow setpoint for the molten salt energy storage system; finally, iteratively determine the PID controller parameters under optimal conditions. This control method is compatible with the existing control system of the coal-fired power unit, reduces the system's computational complexity and retrofitting costs, and significantly improves variable load capacity and operational control quality.

Description

Technical Field

[0001] This invention belongs to the field of molten salt energy storage technology, specifically relating to a system and control method for integrating molten salt energy storage to enhance the variable load capacity of coal-fired power units. Background Technology

[0002] While the installed capacity of renewable energy is increasing year by year, its time-varying and intermittent nature means that large-scale grid connection can have a significant impact on grid operation, hindering its safe and stable operation. Coal-fired power units, as the main regulating power source in the power industry, play a crucial role in ensuring power supply. Coupled with external energy storage devices, the load-changing capacity of coal-fired units can be effectively improved to cope with the uncertainties brought about by the grid connection of new energy sources. Molten salt energy storage technology, as a new type of energy storage technology with advantages such as long duration, large capacity, safety, and environmental friendliness, can significantly improve the flexibility of coal-fired units. To achieve effective integration of molten salt energy storage systems with coal-fired units, collaborative research on system configuration design and control strategies is needed to provide theoretical basis and technical support for engineering applications. Summary of the Invention

[0003] This invention addresses the problem of insufficient load change rate in coal-fired power units by proposing a system and control method for enhancing the load change capacity of coal-fired power units through integrated molten salt energy storage. In this system, the molten salt energy storage system utilizes preheated feedwater to generate superheated steam, which is then injected into the intermediate-pressure cylinder (4) of the unit to perform work. This invention clarifies the calculation method for load commands, formulates the control strategy for the molten salt energy storage system, and, based on the concept of dominant factors, determines the calculation method for the setpoint values ​​of key system parameters for enhancing the load change capacity of coal-fired power units through integrated molten salt energy storage. This system and control method are compatible with the existing control system of the coal-fired power unit, have low implementation costs, and can effectively improve the load change rate and operational control quality of the unit.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A system for enhancing the variable load capacity of coal-fired power units by integrating molten salt energy storage includes a coal-fired power unit and a molten salt energy storage system; The coal-fired unit includes a boiler 1, a main steam valve 2, a high-pressure cylinder 3, an intermediate-pressure cylinder 4, a low-pressure cylinder 5, a generator 6, a high-pressure heater 7, a feedwater pump 8, a deaerator 9, a low-pressure heater 10, a condensate pump 11, and a condenser 12. The main steam outlet of the boiler 1 is connected to the inlet of the high-pressure cylinder 3. The extraction steam outlet of the high-pressure cylinder 3 is connected to the steam inlet of the high-pressure heater 7 and the steam inlet of the preheater 13 of the molten salt energy storage system. The exhaust steam outlet of the high-pressure heater 7 is connected to the inlet of the deaerator 9. The exhaust steam outlet of the preheater 13 is connected to the inlet of the deaerator 9. The exhaust steam outlet of the high-pressure cylinder 3 is connected to the reheat steam inlet of the boiler 1. The reheat steam outlet of the boiler 1 and the superheat steam outlet of the superheater 15 of the molten salt energy storage system are connected to the inlet of the intermediate-pressure cylinder 4. The extraction steam outlet of the intermediate-pressure cylinder 4 is connected to the inlet of the deaerator 9. The exhaust outlet of cylinder 4 is connected to the inlet of low-pressure cylinder 5; the extraction steam outlet of low-pressure cylinder 5 is connected to the steam inlet of low-pressure heater 10; the exhaust steam outlet of low-pressure heater 10 is connected to the inlet of condenser 12; the exhaust steam outlet of low-pressure cylinder 5 is connected to the inlet of condenser 12; the outlet of condenser 12 is connected to the inlet of condensate pump 11; the outlet of condensate pump 11 is connected to the condensate inlet of low-pressure heater 10; the condensate outlet of low-pressure heater 10 is connected to the inlet of deaerator 9; the outlet of deaerator 9 is connected to the inlet of feedwater pump 8; the pump outlet of a certain stage of feedwater pump 8 is connected to the feedwater inlet of preheater 13; the outlet of feedwater pump 8 is connected to the feedwater inlet of high-pressure heater 7; the feedwater outlet of high-pressure heater 7 is connected to the feedwater inlet of boiler 1; high-pressure cylinder 3, intermediate-pressure cylinder 4, and low-pressure cylinder 5 are connected to generator 6 via drive shafts. The molten salt energy storage system includes a preheater 13, an evaporator 14, a superheater 15, a hot molten salt tank 16, a molten salt pump 17, and a cold molten salt tank 18. The water outlet of the preheater 13 is connected to the water inlet of the evaporator 14, the steam outlet of the evaporator 14 is connected to the steam inlet of the superheater 15, the outlet of the hot molten salt tank 16 is connected to the inlet of the molten salt pump 17, the outlet of the molten salt pump 17 is connected to the molten salt inlet of the superheater 15, the molten salt outlet of the superheater 15 is connected to the molten salt inlet of the evaporator 14, and the molten salt outlet of the evaporator 14 is connected to the inlet of the cold molten salt tank 18.

[0005] The system described above, which integrates molten salt energy storage to enhance the variable load capacity of coal-fired power units, has a main steam valve 2 located on the main steam pipeline between the main steam outlet of boiler 1 and the steam inlet of high-pressure cylinder 3.

[0006] The control method for the integrated molten salt energy storage system for enhancing the variable load capacity of coal-fired power units is as follows: 1) Determine the load command for the coal-fired power unit and the load command for the molten salt energy storage system. Upon receiving system load commands to enhance the load-changing capacity of coal-fired power units through integrated molten salt energy storage. Then, considering the operating status and multiple constraints of the molten salt energy storage system, the feasible load commands for the molten salt energy storage system are determined. Simultaneously, the system load command will integrate molten salt energy storage to enhance the variable load capacity of coal-fired units. With the set load command of the molten salt energy storage system The difference serves as the load command for coal-fired power units. : In the formula: This indicates the load command for the coal-fired power unit; This indicates a system load command that integrates molten salt energy storage to enhance the variable load capacity of coal-fired power units; This indicates the load command for the molten salt energy storage system.

[0007] 2) Develop control strategies for molten salt energy storage systems. The superheated steam parameters of the molten salt energy storage system are controlled by coordinating the regulation of multiple valves and flow rates: adjusting the valve opening between the inlet of the intermediate-pressure cylinder 4 and the superheater 15 of the molten salt energy storage system to control the evaporation rate entering the intermediate-pressure cylinder 4; adjusting the steam extraction flow rate of the preheater 13 to stabilize the feedwater temperature; adjusting the hot molten salt flow rate to control the evaporator pressure; adjusting the cold molten salt mixing rate to control the superheated steam temperature; and adjusting the feedwater flow rate to stabilize the water level in the evaporator 14. The real-time calculation formulas for the valve opening between the inlet of the intermediate-pressure cylinder 4 and the outlet of the superheater 15 of the molten salt energy storage system, the preheater steam extraction rate, the hot molten salt flow rate, the cold molten salt mixing rate, and the feedwater flow rate are as follows: In the formula: This indicates the real-time values ​​of valve opening between the inlet of the intermediate pressure cylinder 4 and the outlet of the superheater 15 of the molten salt energy storage system, preheater steam extraction rate, hot molten salt flow rate, cold molten salt mixing rate, and feedwater flow rate. This indicates the valve opening degree between the inlet of the intermediate pressure cylinder 4 and the outlet of the superheater 15 of the molten salt energy storage system, the steam extraction rate of the preheater, the flow rate of hot molten salt, the mixing amount of cold molten salt, and the set value of the feedwater flow rate. This indicates the valve opening degree between the inlet of the intermediate-pressure cylinder 4 and the outlet of the superheater 15 of the molten salt energy storage system, the steam extraction rate of the preheater, the flow rate of hot molten salt, the mixing amount of cold molten salt, and the correction value of the feedwater flow rate, as determined by the PID controller. This indicates the evaporation rate entering the intermediate pressure cylinder 4, the feed water temperature, the evaporator pressure, the superheated steam temperature, and the real-time value of the evaporator water level; This indicates the evaporation rate entering the intermediate pressure cylinder 4, the feed water temperature, the evaporator pressure, the superheated steam temperature, and the evaporator water level setting.

[0008] 3) Determine the key system parameter settings for integrating molten salt energy storage to enhance the load-changing capacity of coal-fired power units. The correction to the key parameter setpoints of the integrated molten salt energy storage system for existing coal-fired units is established through linear fitting based on operating data from multiple steady-state design conditions. In the formula: This indicates the amount of correction that the integrated molten salt energy storage system brings to the set values ​​of key parameters of the original coal-fired power unit; This indicates the maximum load of the molten salt energy storage system; This indicates the amount of correction that the integrated molten salt energy storage system brings to the original key parameter settings of the coal-fired unit when the molten salt energy storage system is under maximum load conditions and under different coal-fired unit loads. This indicates the load corresponding to the standby operating condition of the molten salt energy storage system; This indicates the amount of correction to the key parameter settings of the original coal-fired unit when the molten salt energy storage system is integrated under standby operating conditions and different coal-fired unit loads.

[0009] The system key parameter setpoints for retaining the original coal-fired unit control logic and integrating molten salt energy storage to enhance the variable load capacity of the coal-fired unit are as follows: The key parameter settings of the original coal-fired power units will be used. The adjustment of key parameter setpoints of existing coal-fired power units due to the integrated molten salt energy storage system Sure: In the formula: These represent the key system parameter settings for enhancing the variable load capacity of coal-fired power units through integrated molten salt energy storage. This indicates the key parameter settings of the existing coal-fired power units.

[0010] 4) Calculate the setpoint for superheated steam flow rate of the molten salt energy storage system. Work done by superheated steam in a molten salt energy storage system per unit mass flow rate Defined as: the power increment of an integrated molten salt energy storage system that enhances the load-changing capacity of a coal-fired unit due to the superheated steam generated by the molten salt energy storage system per unit mass flow rate entering the turbine to perform work, under constant boiler load. The system load command for enhancing the variable load capacity of coal-fired power units based on integrated molten salt energy storage can be determined by the following fitting formula for the superheated steam work per unit mass flow rate of the molten salt energy storage system: In the formula: This indicates that when the load of the coal-fired unit is At that time, the amount of work done by the superheated steam with a unit mass flow rate generated by the molten salt energy storage system after entering the intermediate pressure cylinder (4) is kJ / kg; N represents the number of terms in the prefitted polynomial; This represents the polynomial number calculated based on multiple design condition data. i The coefficient before the term; i The first polynomial represents the polynomial. i item.

[0011] Furthermore, the required superheated steam flow rate for the molten salt energy storage system was calculated: In the formula: This indicates the setpoint for the superheated steam flow rate of the molten salt energy storage system, in kg / s. This indicates the rated load of the unit, in kW.

[0012] 5) Iteratively determine the controller parameters for the optimal effect. Based on control principles and engineering experience, the PID controller parameters are initially set; the control process is executed under a given variable load command, and key performance indicators such as overshoot, settling time, and steady-state deviation of the integrated system response are collected and recorded; with maximizing the variable load rate as the optimization objective, under clear safety and operational constraints, a "performance index" is constructed. The closed-loop feedback mechanism of "parameter adjustment" iteratively corrects the PID parameters; the above steps are repeated until the optimal parameter set of the PID controller that satisfies the safety constraints and maximizes the variable load rate is obtained.

[0013] Furthermore, to ensure the safe operation of the molten salt energy storage system during load changes, it is necessary to comprehensively consider factors such as the steam temperature at the boiler 3 outlet, the heat exchange terminal difference of superheater 15, and the steam temperature fluctuation at the superheater 15 outlet, to rationally select the type of molten salt and determine the hot molten salt temperature and the steam temperature at the superheater 15 outlet, while retaining necessary safety margins. At the same time, the feedwater temperature at the preheater 13 outlet should be higher than the molten salt freezing point to prevent condensation, and the superheated steam outlet pressure should be higher than the corresponding inlet pressure of the intermediate pressure cylinder 4 to ensure smooth flow of the working fluid. Both should also retain sufficient safety operation and control margins.

[0014] Furthermore, when determining the load command change curve of the molten salt energy storage system, several constraints must be met: the total amount of molten salt used during the load change process must be less than the available capacity of the storage tank; the load change rate of the load command should be within the range of the system's dynamic response capability, and a minimum rate lower limit should be set to fully utilize its peak-shaving capability; the system's heat release must not exceed the design upper limit; the difference between the total load change rate of the system and the rate on the molten salt side must be less than the maximum load change rate on the boiler side to ensure the safe and stable operation of boiler 1.

[0015] Furthermore, an incremental PID controller is used to determine the valve opening between the inlet of the intermediate-pressure cylinder 4 and the outlet of the superheater 15 of the molten salt energy storage system, the preheater steam extraction rate, the hot molten salt flow rate, the cold molten salt mixing rate, and the feedwater flow rate correction value. : In the formula: This indicates the proportional coefficient of the PID controller that needs to be tuned; express k The deviation signal corresponding to the time; kIndicates the sampling sequence number; express k The deviation signal corresponding to time -1; This represents the integral coefficient of the PID controller that needs to be tuned; Indicates the sampling time, in seconds; This represents the derivative coefficient of the PID controller that needs to be tuned; express k The deviation signal corresponding to time -2.

[0016] Furthermore, the signals output by the PID controller, such as the valve opening between the inlet of the intermediate-pressure cylinder 4 and the outlet of the superheater 15 of the molten salt energy storage system, the steam extraction rate of the preheater, the flow rate of hot molten salt, the mixing amount of cold molten salt, and the correction value of the feedwater flow rate, are all subjected to amplitude limiting processing to suppress large fluctuations. This ensures that key parameters such as the evaporation rate, feedwater temperature, evaporator pressure, superheated steam temperature, and evaporator water level entering the intermediate-pressure cylinder 4 remain stable within the set range, thus ensuring the smooth operation of the system.

[0017] Furthermore, in the process of iteratively determining the optimal PID controller parameters, the fluctuation range of key operating parameters during the load change process is constrained in accordance with national or industry standards to ensure the safe operation of coal-fired power unit equipment.

[0018] Compared with the prior art, the present invention has the following beneficial technical effects: 1) By preheating the feedwater with steam to increase its temperature, fluctuations in the evaporator inlet water temperature are effectively mitigated. This design significantly alleviates the coupling relationship between internal pressure, temperature, and flow rate of the evaporator, improving the independence of system control and operational stability.

[0019] 2) This invention achieves system integration through setpoint correction, avoiding changes to the control logic; simultaneously, it employs a simplified model to calculate the work done per unit mass of steam. Both methods reduce the computational complexity and modification costs of the control system while ensuring accuracy and reliability.

[0020] 3) The proposed integrated system design and control method can significantly enhance the variable load capacity of coal-fired units and effectively optimize the control quality of key operating parameters such as main steam pressure and unit power. Attached Figure Description

[0021] Figure 1. Schematic diagram of a coal-fired power system with integrated molten salt energy storage.

[0022] Figure 2. Comparison of cumulative power deviation of the unit during the load increase process.

[0023] Figure 3. Comparison of cumulative deviations in main steam pressure during the load increase process. Detailed Implementation

[0024] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0025] Example This invention provides a system and control method for integrating molten salt energy storage to enhance the variable load capacity of coal-fired power units. A 660 MW ultra-supercritical unit is selected as the object, with main steam and reheat steam temperatures of 600℃ and 620℃, respectively.

[0026] The present invention provides a system for enhancing the variable load capacity of coal-fired power units by integrating molten salt energy storage, comprising a coal-fired power unit and a molten salt energy storage system.

[0027] The coal-fired unit includes a boiler 1, a main steam valve 2, a high-pressure cylinder 3, an intermediate-pressure cylinder 4, a low-pressure cylinder 5, a generator 6, a high-pressure heater 7, a feedwater pump 8, a deaerator 9, a low-pressure heater 10, a condensate pump 11, and a condenser 12. The main steam outlet of the boiler 1 is connected to the inlet of the high-pressure cylinder 3. The extraction steam outlet of the high-pressure cylinder 3 is connected to the steam inlet of the high-pressure heater 7 and the steam inlet of the preheater 13, respectively. The exhaust steam outlet of the high-pressure heater 7 is connected to the inlet of the deaerator 9. The exhaust steam outlet of the preheater 13 is connected to the inlet of the deaerator 9. The exhaust steam outlet of the high-pressure cylinder 3 is connected to the reheat steam inlet of the boiler 1. The reheat steam outlet of the boiler 1 and the superheat steam outlet of the superheater 15 are connected to the inlet of the intermediate-pressure cylinder 4. The extraction steam outlet of the intermediate-pressure cylinder 4 is connected to the inlet of the deaerator 9. The exhaust steam outlet of the intermediate-pressure cylinder 4 is connected to... The inlet of low-pressure cylinder 5 is connected to the steam outlet of low-pressure cylinder 5, which is connected to the steam inlet of low-pressure heater 10. The exhaust outlet of low-pressure heater 10 is connected to the inlet of condenser 12. The exhaust outlet of low-pressure cylinder 5 is connected to the inlet of condenser 12. The outlet of condenser 12 is connected to the inlet of condensate pump 11. The outlet of condensate pump 11 is connected to the condensate inlet of low-pressure heater 10. The condensate outlet of low-pressure heater 10 is connected to the inlet of deaerator 9. The outlet of deaerator 9 is connected to the inlet of feedwater pump 8. The pump outlet of a certain stage of feedwater pump 8 is connected to the feedwater inlet of preheater 13. The outlet of feedwater pump 8 is connected to the feedwater inlet of high-pressure heater 7. The feedwater outlet of high-pressure heater 7 is connected to the feedwater inlet of boiler 1. High-pressure cylinder 3, intermediate-pressure cylinder 4, and low-pressure cylinder 5 are connected to generator 6 via drive shafts. The molten salt energy storage system includes a preheater 13, an evaporator 14, a superheater 15, a hot molten salt tank 16, a molten salt pump 17, and a cold molten salt tank 18. The water outlet of the preheater 13 is connected to the water inlet of the evaporator 14, the steam outlet of the evaporator 14 is connected to the steam inlet of the superheater 15, the outlet of the hot molten salt tank 16 is connected to the inlet of the molten salt pump 17, the outlet of the molten salt pump 17 is connected to the molten salt inlet of the superheater 15, the molten salt outlet of the superheater 15 is connected to the molten salt inlet of the evaporator 14, and the molten salt outlet of the evaporator 14 is connected to the inlet of the cold molten salt tank 18.

[0028] The system described above, which integrates molten salt energy storage to enhance the load-changing capacity of coal-fired power units, has a main steam valve 2 located on the main steam pipeline between the main steam outlet of boiler 1 and the steam inlet of high-pressure cylinder 3. During load adjustment, adjusting the main steam valve can achieve precise control of the output power of the coal-fired power unit, which is beneficial for the rapid load-changing process of the coal-fired power unit. When the coal-fired power unit participates in the primary frequency regulation process, adjusting the main steam valve can achieve a rapid response to the frequency, which is beneficial for maintaining the safety of the power grid.

[0029] The control method for the integrated molten salt energy storage system for enhancing the variable load capacity of coal-fired power units is as follows: 1) Determine the load command for the coal-fired power unit and the load command for the molten salt energy storage system. Upon receiving system load commands to enhance the load-changing capacity of coal-fired power units through integrated molten salt energy storage. Then, considering the operating status and multiple constraints of the molten salt energy storage system, the feasible load commands for the molten salt energy storage system are determined. Simultaneously, the system load command will integrate molten salt energy storage to enhance the load-changing capacity of coal-fired units. With the set load command of the molten salt energy storage system The difference serves as the load command for coal-fired power units. : In the formula: This indicates the load command for the coal-fired power unit; This indicates a system load command that integrates molten salt energy storage to enhance the variable load capacity of coal-fired power units; This indicates the load command for the molten salt energy storage system.

[0030] 2) Develop control strategies for molten salt energy storage systems. The superheated steam parameters of the molten salt energy storage system are controlled by coordinating the regulation of multiple valves and flow rates: adjusting the valve opening between the inlet of the intermediate-pressure cylinder 4 and the superheater 15 of the molten salt energy storage system to control the evaporation rate entering the intermediate-pressure cylinder 4; adjusting the steam extraction flow rate of the preheater 13 to stabilize the feedwater temperature; adjusting the hot molten salt flow rate to control the evaporator pressure; adjusting the cold molten salt mixing rate to control the superheated steam temperature; and adjusting the feedwater flow rate to stabilize the water level in the evaporator 14. The real-time calculation formulas for the valve opening between the inlet of the intermediate-pressure cylinder 4 and the outlet of the superheater 15 of the molten salt energy storage system, the preheater steam extraction rate, the hot molten salt flow rate, the cold molten salt mixing rate, and the feedwater flow rate are as follows: In the formula: This indicates the real-time values ​​of valve opening between the inlet of the intermediate pressure cylinder 4 and the outlet of the superheater 15 of the molten salt energy storage system, preheater steam extraction rate, hot molten salt flow rate, cold molten salt mixing rate, and feedwater flow rate. This indicates the valve opening degree between the inlet of the intermediate pressure cylinder 4 and the outlet of the superheater 15 of the molten salt energy storage system, the steam extraction rate of the preheater, the flow rate of hot molten salt, the mixing amount of cold molten salt, and the set value of the feedwater flow rate. This indicates the valve opening degree between the inlet of the intermediate-pressure cylinder 4 and the outlet of the superheater 15 of the molten salt energy storage system, the steam extraction rate of the preheater, the flow rate of hot molten salt, the mixing amount of cold molten salt, and the correction value of the feedwater flow rate, as determined by the PID controller. This indicates the evaporation rate entering the intermediate pressure cylinder 4, the feed water temperature, the evaporator pressure, the superheated steam temperature, and the real-time value of the evaporator water level; This indicates the evaporation rate entering the intermediate pressure cylinder 4, the feed water temperature, the evaporator pressure, the superheated steam temperature, and the evaporator water level setting.

[0031] 3) Determine the key system parameter settings for integrating molten salt energy storage to enhance the load-changing capacity of coal-fired power units. The correction to the key parameter setpoints of the integrated molten salt energy storage system for existing coal-fired units is established through linear fitting based on operating data from multiple steady-state design conditions. In the formula: This indicates the amount of correction that the integrated molten salt energy storage system brings to the set values ​​of key parameters of the original coal-fired power unit; This indicates the maximum load of the molten salt energy storage system; This indicates the amount of correction that the integrated molten salt energy storage system brings to the original key parameter settings of the coal-fired unit when the molten salt energy storage system is under maximum load conditions and under different coal-fired unit loads. This indicates the load corresponding to the standby operating condition of the molten salt energy storage system; This indicates the amount of correction to the key parameter settings of the original coal-fired unit when the molten salt energy storage system is integrated under standby operating conditions and different coal-fired unit loads.

[0032] The system key parameter setpoints for retaining the original coal-fired unit control logic and integrating molten salt energy storage to enhance the variable load capacity of the coal-fired unit are as follows: The key parameter settings of the original coal-fired power units will be used. The adjustment of key parameter setpoints of existing coal-fired power units due to the integrated molten salt energy storage system Sure: In the formula: These represent the key system parameter settings for enhancing the variable load capacity of coal-fired power units through integrated molten salt energy storage. This indicates the key parameter settings of the existing coal-fired power units.

[0033] 4) Calculate the setpoint for superheated steam flow rate of the molten salt energy storage system. Work done by superheated steam in a molten salt energy storage system per unit mass flow rate Defined as: the power increment of an integrated molten salt energy storage system that enhances the load-changing capacity of a coal-fired unit due to the superheated steam generated by the molten salt energy storage system per unit mass flow rate entering the turbine to perform work, under constant boiler load. The system load command for enhancing the variable load capacity of coal-fired power units based on integrated molten salt energy storage can be determined using the following fitting formula for the superheated steam work per unit mass flow rate of the molten salt energy storage system: In the formula: This indicates that when the load of the coal-fired unit is At that time, the amount of work done by the superheated steam with a unit mass flow rate generated by the molten salt energy storage system after entering the intermediate pressure cylinder (4) is kJ / kg; N represents the number of terms in the prefitted polynomial; This represents the polynomial number calculated based on multiple design condition data. i The coefficient before the term; i The first polynomial represents the polynomial. i item.

[0034] Furthermore, the required superheated steam flow rate for the molten salt energy storage system was calculated: In the formula: This indicates the setpoint for the superheated steam flow rate of the molten salt energy storage system, in kg / s. This indicates the rated load of the unit, in kW.

[0035] 5) Iteratively determine the controller parameters for the optimal effect. Based on control principles and engineering experience, the PID controller parameters are initially set; the control process is executed under a given variable load command, and key performance indicators such as overshoot, settling time, and steady-state deviation of the integrated system response are collected and recorded; with maximizing the variable load rate as the optimization objective, under clear safety and operational constraints, a "performance index" is constructed. The closed-loop feedback mechanism of "parameter adjustment" iteratively corrects the PID parameters; the above steps are repeated until the optimal parameter set of the PID controller that satisfies the safety constraints and maximizes the variable load rate is obtained.

[0036] Furthermore, to ensure the safe operation of the molten salt energy storage system during load changes, it is necessary to comprehensively consider factors such as the boiler 3 outlet steam temperature, the heat exchange terminal difference of superheater 15, and the fluctuation of superheater 15 outlet steam temperature to rationally select the molten salt type and determine the hot molten salt temperature and the superheater 15 outlet steam temperature, while retaining necessary safety margins. At the same time, the preheater 13 outlet feedwater temperature should be higher than the molten salt freezing point to prevent condensation, and the superheated steam outlet pressure should be higher than the corresponding intermediate pressure cylinder 4 inlet pressure to ensure smooth working fluid flow. Both should also retain sufficient safety and control margins. By comprehensively considering factors such as boiler outlet steam temperature, superheater heat exchange terminal difference, and outlet steam temperature fluctuations to select the molten salt type and operating temperature, the system's operational stability during rapid load adjustment is enhanced. Necessary safety margins are maintained between the hot molten salt temperature and the superheater outlet temperature, and between the feedwater temperature and the molten salt freezing temperature, which prevents superheater overheating or underheating and eliminates the risk of molten salt solidification and blockage in the low-temperature range.

[0037] Specifically, the molten salt type is selected as solar salt, the hot tank molten salt temperature is set at 559℃, the cold tank temperature at 284.5℃, and the outlet superheated steam temperature of the molten salt energy storage system is set at 555℃. The preheater outlet feedwater temperature is set at 248℃, the superheated steam outlet pressure under rated operating conditions is 6.321MPa, and the flow rate is 377t / h.

[0038] Furthermore, when determining the load command change curve of the molten salt energy storage system, several constraints must be met: the total amount of molten salt used during the load change process must be less than the available capacity of the storage tank; the load change rate of the load command should be within the range of the system's dynamic response capability, and a minimum rate lower limit should be set to fully utilize its peak-shaving capability; the system's heat release must not exceed the design upper limit; the difference between the total load change rate of the system and the rate on the molten salt side must be less than the maximum load change rate on the boiler side to ensure the safe and stable operation of boiler 1.

[0039] Furthermore, an incremental PID controller is used to determine the valve opening between the inlet of the intermediate-pressure cylinder 4 and the outlet of the superheater 15 of the molten salt energy storage system, the preheater steam extraction rate, the hot molten salt flow rate, the cold molten salt mixing rate, and the feedwater flow rate correction value. : In the formula: This indicates the proportional coefficient of the PID controller that needs to be tuned; express k The deviation signal corresponding to the time; k Indicates the sampling sequence number; express k The deviation signal corresponding to time -1; This represents the integral coefficient of the PID controller that needs to be tuned; Indicates the sampling time, in seconds; This represents the derivative coefficient of the PID controller that needs to be tuned; express k The deviation signal corresponding to time -2.

[0040] Furthermore, the signals output by the PID controller, such as the valve opening between the inlet of the intermediate-pressure cylinder 4 and the outlet of the superheater 15 of the molten salt energy storage system, the steam extraction rate of the preheater, the flow rate of hot molten salt, the mixing amount of cold molten salt, and the correction value of the feedwater flow rate, are all subjected to amplitude limiting processing to suppress large fluctuations. This ensures that key parameters such as the evaporation rate, feedwater temperature, evaporator pressure, superheated steam temperature, and evaporator water level entering the intermediate-pressure cylinder 4 remain stable within the set range, thus ensuring the smooth operation of the system.

[0041] Furthermore, in the process of iteratively determining the optimal PID controller parameters, the fluctuation range of key operating parameters during the load change process is constrained in accordance with national or industry standards to ensure the safe operation of coal-fired power unit equipment.

[0042] Specifically, this includes: main steam temperature fluctuation not exceeding 8℃, reheat steam temperature fluctuation not exceeding 10℃, main steam pressure fluctuation not exceeding 3% of the rated value, and unit power fluctuation not exceeding 2% of the rated value.

[0043] Table 1 shows a comparison of the optimization effects of the integrated molten salt energy storage system on improving the load-changing capacity of coal-fired units at a load increase rate of 2.0% Pe / min, in terms of cumulative deviation of unit power, main steam pressure, and maximum deviation of unit power. As can be seen from Table 1, compared to the original system, the integrated molten salt energy storage system reduced the cumulative deviation of unit power by 55.84%, the maximum deviation of unit power by 11.28%, and the cumulative deviation of main steam pressure by 33.74% at a load increase rate of 2.0% Pe / min. The maximum load increase rate also increased from 2.0% Pe / min to 2.6% Pe / min, significantly improving the load-changing capacity of the coal-fired unit.

[0044] Table 1. Optimization effect of key parameters during load increase process Before the integrated molten salt energy storage system After integrating molten salt energy storage system Improvement range 2.0% Pe / min load increase rate unit power cumulative deviation 6260.12 MJ 2764.54 MJ -55.84% Maximum power deviation of unit at a load increase rate of 2.0% Pe / min 12.89 MW 11.43 MW -11.28% 2.0% Pe / min load increase rate, cumulative deviation of main steam pressure 333.82 MPa·s 221.19 MPa·s -33.74% Maximum load increase rate 2.0% Pe / min 2.6% Pe / min 30.00% like Figure 2 , Figure 3 The figure shows a comparison of the effects of the original coal-fired unit (the original system) and the integrated system at different load increase rates. As can be seen from the figure, after integrating the molten salt energy storage system, the maximum load increase rate increased from 2.0% Pe / min to 2.6% Pe / min; at the same time, the cumulative deviations of unit power and main steam pressure decreased significantly, by 55.84% and 33.74%, respectively.

[0045] In summary, the integrated molten salt energy storage system and control method proposed in this invention can enhance the variable load capacity of coal-fired power units, while also improving the control quality of key parameters such as unit power and main steam pressure.

Claims

1. A system for integrating molten salt energy storage to enhance the variable load capacity of coal-fired power units, characterized in that: This includes coal-fired power units and molten salt energy storage systems; The coal-fired unit includes a boiler (1), a main steam valve (2), a high-pressure cylinder (3), a medium-pressure cylinder (4), a low-pressure cylinder (5), a generator (6), a high-pressure heater (7), a feedwater pump (8), a deaerator (9), a low-pressure heater (10), a condensate pump (11), and a condenser (12). The main steam outlet of the boiler (1) is connected to the inlet of the high-pressure cylinder (3). The extraction steam outlet of the high-pressure cylinder (3) is connected to the steam inlet of the high-pressure heater (7) and the steam inlet of the preheater (13) of the molten salt energy storage system. The exhaust steam outlet of the high-pressure heater (7) is connected to the inlet of the deaerator (9). The exhaust steam outlet of the preheater (13) is connected to the inlet of the deaerator (9). The exhaust steam outlet of the high-pressure cylinder (3) is connected to the reheat steam inlet of the boiler (1). The reheat steam outlet of the boiler (1) and the superheat steam outlet of the superheater (15) of the molten salt energy storage system are connected to the inlet of the medium-pressure cylinder (4). The extraction steam outlet of the medium-pressure cylinder (4) is connected to the inlet of the deaerator (9). The exhaust outlet of the intermediate-pressure cylinder (4) is connected to the inlet of the low-pressure cylinder (5). The extraction steam outlet of the low-pressure cylinder (5) is connected to the steam inlet of the low-pressure heater (10). The exhaust outlet of the low-pressure heater (10) is connected to the inlet of the condenser (12). The exhaust outlet of the low-pressure cylinder (5) is connected to the inlet of the condenser (12). The outlet of the condenser (12) is connected to the inlet of the condensate pump (11). The outlet of the condensate pump (11) is connected to the condensate inlet of the low-pressure heater (10). The condensate outlet of the device (10) is connected to the inlet of the deaerator (9), the outlet of the deaerator (9) is connected to the inlet of the feed water pump (8), the pump outlet of a certain stage of the feed water pump (8) is connected to the feed water inlet of the preheater (13), the outlet of the feed water pump (8) is connected to the feed water inlet of the high-pressure heater (7), and the feed water outlet of the high-pressure heater (7) is connected to the feed water inlet of the boiler (1); the high-pressure cylinder (3), the medium-pressure cylinder (4), and the low-pressure cylinder (5) are connected to the generator (6) through the drive shaft; The molten salt energy storage system includes a preheater (13), an evaporator (14), a superheater (15), a hot molten salt tank (16), a molten salt pump (17), and a cold molten salt tank (18). The water outlet of the preheater (13) is connected to the water inlet of the evaporator (14), the steam outlet of the evaporator (14) is connected to the steam inlet of the superheater (15), the outlet of the hot molten salt tank (16) is connected to the inlet of the molten salt pump (17), the outlet of the molten salt pump (17) is connected to the molten salt inlet of the superheater (15), the molten salt outlet of the superheater (15) is connected to the molten salt inlet of the evaporator (14), and the molten salt outlet of the evaporator (14) is connected to the inlet of the cold molten salt tank (18).

2. The system for integrating molten salt energy storage to enhance the variable load capacity of coal-fired power units according to claim 1, characterized in that, The main steam valve (2) is located on the main steam pipeline between the main steam outlet of the boiler (1) and the steam inlet of the high-pressure cylinder (3).

3. The control method for a system for enhancing the variable load capacity of a coal-fired power unit using integrated molten salt energy storage as described in claim 1 or 2, characterized in that: 1) Determine the load command for the coal-fired power unit and the load command for the molten salt energy storage system. Upon receiving system load commands to enhance the load-changing capacity of coal-fired power units through integrated molten salt energy storage. Then, considering the operating status and multiple constraints of the molten salt energy storage system, the feasible load commands for the molten salt energy storage system are determined. Simultaneously, the system load command will integrate molten salt energy storage to enhance the variable load capacity of coal-fired units. With the set load command of the molten salt energy storage system The difference serves as the load command for coal-fired power units. : In the formula: This indicates the load command for the coal-fired power unit; This indicates a system load command that integrates molten salt energy storage to enhance the variable load capacity of coal-fired power units; This indicates a load command for the molten salt energy storage system; 2) Develop control strategies for molten salt energy storage systems. The superheated steam parameters of the molten salt energy storage system are controlled by coordinating the adjustment of multiple valves and flow control: adjusting the valve opening between the inlet of the intermediate pressure cylinder (4) and the superheater (15) of the molten salt energy storage system to control the evaporation rate entering the intermediate pressure cylinder (4); adjusting the steam extraction flow rate of the preheater (13) to stabilize the feedwater temperature; adjusting the hot molten salt flow rate to control the evaporator pressure; adjusting the cold molten salt mixing amount to control the superheated steam temperature; and adjusting the feedwater flow rate to stabilize the water level of the evaporator (14). The calculation formulas for the valve opening between the inlet of the intermediate pressure cylinder (4) and the outlet of the superheater (15) of the molten salt energy storage system, the preheater steam extraction rate, the hot molten salt flow rate, the cold molten salt mixing amount, and the feedwater flow rate are as follows: In the formula: The real-time values ​​of valve opening between the inlet of the medium-pressure cylinder (4) and the outlet of the superheater (15) of the molten salt energy storage system, preheater steam extraction rate, hot molten salt flow rate, cold molten salt mixing rate, and feedwater flow rate are indicated. The valve opening between the inlet of the medium-pressure cylinder (4) and the outlet of the superheater (15) of the molten salt energy storage system, the steam extraction rate of the preheater, the flow rate of hot molten salt, the amount of cold molten salt mixed, and the set value of the feedwater flow rate are indicated. The values ​​represent the valve opening between the inlet of the medium-pressure cylinder (4) and the outlet of the superheater (15) of the molten salt energy storage system, the preheater steam extraction rate, the hot molten salt flow rate, the cold molten salt mixing rate, and the feedwater flow rate correction value determined by the PID controller. The values ​​indicate the evaporation rate, feed water temperature, evaporator pressure, superheated steam temperature, and real-time evaporator water level entering the intermediate pressure cylinder (4). The values ​​indicate the evaporation rate, feedwater temperature, evaporator pressure, superheated steam temperature, and evaporator water level setting in the intermediate pressure cylinder (4). 3) Determine the key system parameter settings for integrating molten salt energy storage to enhance the load-changing capacity of coal-fired power units. The correction to the key parameter setpoints of the integrated molten salt energy storage system for existing coal-fired units is established through linear fitting based on operating data from multiple steady-state design conditions. In the formula: This indicates the amount of correction that the integrated molten salt energy storage system brings to the set values ​​of key parameters of the original coal-fired power unit; This indicates the maximum load of the molten salt energy storage system; This indicates the amount of correction that the integrated molten salt energy storage system brings to the original key parameter settings of the coal-fired unit when the molten salt energy storage system is under maximum load conditions and under different coal-fired unit loads. This indicates the load corresponding to the standby operating condition of the molten salt energy storage system; This indicates the amount of correction to the key parameter settings of the original coal-fired unit when the molten salt energy storage system is integrated under standby operating conditions and different coal-fired unit loads. The system key parameter setpoints for retaining the original coal-fired unit control logic and integrating molten salt energy storage to enhance the variable load capacity of the coal-fired unit are as follows: The key parameter settings of the original coal-fired power units will be used. The adjustment of key parameter setpoints of existing coal-fired power units due to the integrated molten salt energy storage system Sure: In the formula: These represent the key system parameter settings for enhancing the variable load capacity of coal-fired power units through integrated molten salt energy storage. This indicates the set values ​​of key parameters for existing coal-fired power units; 4) Calculate the setpoint for superheated steam flow rate in the molten salt energy storage system. Work done by superheated steam in a molten salt energy storage system per unit mass flow rate Defined as: the power increment of an integrated molten salt energy storage system that enhances the load-changing capacity of a coal-fired unit due to the superheated steam generated by the molten salt energy storage system per unit mass flow rate entering the turbine to perform work, under constant boiler load. Based on the system load command for enhancing the variable load capacity of coal-fired power units through integrated molten salt energy storage, the work done by superheated steam per unit mass flow rate of the molten salt energy storage system is determined by the following fitting formula: In the formula: This indicates that when the load of the coal-fired unit is At that time, the amount of work done by the superheated steam with a unit mass flow rate generated by the molten salt energy storage system after entering the intermediate pressure cylinder (4) is kJ / kg; N represents the number of terms in the prefitted polynomial; This represents the polynomial number calculated based on multiple design condition data. i The coefficient before the term; i The first polynomial represents the second polynomial. i item; The required superheated steam flow rate for the molten salt energy storage system is calculated as follows: In the formula: This indicates the setpoint for the superheated steam flow rate of the molten salt energy storage system, in kg / s. Indicates the rated load of the unit, in kW; 5) Iteratively determine the controller parameters for the optimal effect. Based on control principles and engineering experience, the PID controller parameters are initially set; the control process is executed under a given variable load command, and the overshoot, settling time, and steady-state deviation performance indicators of the integrated system response are collected and recorded; with maximizing the variable load rate as the optimization objective, under clear safety and operational constraints, a performance index is constructed. The closed-loop feedback mechanism of "parameter adjustment" iteratively corrects the PID parameters; the above steps are repeated until the optimal parameter set of the PID controller that satisfies the safety constraints and maximizes the variable load rate is obtained.

4. The control method for a system for enhancing the variable load capacity of a coal-fired power unit through integrated molten salt energy storage according to claim 3, characterized in that: To ensure the safe operation of the molten salt energy storage system during load changes, it is necessary to comprehensively consider the boiler (3) outlet steam temperature, the heat exchange end difference of the superheater (15) and the fluctuation of the superheater (15) outlet steam temperature, select the type of molten salt and determine the hot molten salt temperature and the superheater (15) outlet steam temperature, and retain the necessary safety margin. At the same time, the preheater (13) outlet feedwater temperature should be higher than the molten salt freezing point to prevent condensation, and the superheated steam outlet pressure should be higher than the corresponding intermediate pressure cylinder (4) inlet pressure to ensure smooth flow of working fluid. Both should also retain safety operation and control margins.

5. The control method for a system for enhancing the variable load capacity of a coal-fired power unit through integrated molten salt energy storage according to claim 3, characterized in that: When determining the load command change curve of a molten salt energy storage system, several constraints must be met: the total amount of molten salt used during the load change process must be less than the available capacity of the storage tank; the load change rate of the load command should be within the dynamic response capability of the system, and a minimum rate lower limit should be set to fully utilize its peak-shaving capability; the heat release of the system must not exceed the design upper limit. The difference between the total load rate of the system and the rate on the molten salt side must be less than the maximum load rate on the boiler side in order to ensure the safe and stable operation of the boiler (1).

6. The control method for a system for enhancing the variable load capacity of a coal-fired power unit through integrated molten salt energy storage according to claim 3, characterized in that: An incremental PID controller is used to determine the valve opening between the inlet of the intermediate-pressure cylinder (4) and the outlet of the superheater (15) of the molten salt energy storage system, the preheater steam extraction rate, the hot molten salt flow rate, the cold molten salt mixing rate, and the feedwater flow rate correction value. : In the formula: This indicates the proportional coefficient of the PID controller that needs to be tuned. express k The deviation signal corresponding to the given time; k Indicates the sampling sequence number; express k The deviation signal corresponding to time -1; This represents the integral coefficient of the PID controller that needs to be tuned; Indicates the sampling time, in seconds; This represents the derivative coefficient of the PID controller that needs to be tuned; express k The deviation signal corresponding to time -2. Furthermore, the valve opening, preheater steam extraction rate, hot molten salt flow rate, cold molten salt mixing rate, and feedwater flow rate correction signals output by the PID controller between the inlet of the medium-pressure cylinder (4) and the outlet of the superheater (15) of the molten salt energy storage system are all subjected to amplitude limiting processing to suppress large fluctuations, thereby ensuring that the key parameters of evaporation rate, feedwater temperature, evaporator pressure, superheated steam temperature, and evaporator water level entering the medium-pressure cylinder (4) remain stable within the set range, ensuring the smooth operation of the system.

7. The control method for a system for enhancing the variable load capacity of a coal-fired power unit through integrated molten salt energy storage according to claim 3, characterized in that: In the process of iteratively determining the optimal PID controller parameters, the fluctuation range of key operating parameters during load changes is constrained in accordance with national or industry standards to ensure the safe operation of coal-fired power unit equipment.

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