Control method for improving steam temperature control effect of coal-fired unit by coupling medium and low temperature energy storage system

Abstract

The application provides a control method for improving the steam temperature control effect of a coal-fired unit by coupling a medium-low temperature energy storage system; a load cooperative matching control method is designed, so that the medium-low temperature energy storage system and a boiler-turbine coordination system of the coal-fired unit jointly bear the whole unit load; in the process of load reduction, the work amount of high-pressure cylinder exhaust steam is obtained by an equivalent enthalpy drop method, the load instruction of the medium-low temperature energy storage system is calculated, the load instruction of the boiler-turbine coordination system of the coal-fired unit is obtained by using parameters such as the originally set load change rate, the initial load and the target load of the coal-fired unit, and the reheated steam temperature regulation mode is corrected; in the process of load increase, the load instruction of the medium-low temperature energy storage system is obtained by the energy storage capacity of the medium-low temperature system, the load instruction of the boiler-turbine coordination system of the coal-fired unit is obtained by using parameters such as the originally set load change rate, the initial load and the target load of the coal-fired unit, the load change pressure of the coal-fired unit is relieved, the parameter fluctuation range of the coal-fired unit is reduced, and the load change performance of the coal-fired unit is improved.

Description

Technical Field

[0001] This invention belongs to the field of coupling control technology of energy storage system and coal-fired unit, and specifically relates to a control method for improving the steam temperature control effect of coal-fired unit by coupling a low-temperature energy storage system. Background Technology

[0002] Against the backdrop of low-carbon energy transition, my country's energy structure continues to optimize, with the proportion of non-fossil energy consumption gradually increasing. However, adjustments to the energy structure directly affect the safe and stable supply of electricity in my country. Non-fossil energy sources such as wind and solar power are characterized by intermittency and randomness. Effectively and economically absorbing these unpredictable new energy sources is crucial for maintaining the balance between power supply and demand. Coal-fired power units, as economically efficient and "controllable" power sources, will be in a state of variable load transients for extended periods. However, the significant fluctuations in the main and reheat steam temperatures during these transients reduce equipment lifespan and impact unit safety. Reducing parameter fluctuations during variable load transients and improving unit performance are key to enhancing operational safety. Using load coordination and matching control methods to reduce the load change rate of the boiler-turbine coordination system can effectively improve parameter control at the same load change rate, thereby enhancing the operational safety of coal-fired power units. Summary of the Invention

[0003] This invention addresses system safety issues caused by parameter fluctuations during transient processes in coal-fired power units. From the perspective of improving steam temperature control in coal-fired power units, it aims to find a control method that reduces parameter fluctuations. The purpose of this invention is to provide a control method that couples a low-temperature energy storage system to improve steam temperature control in coal-fired power units. It comprehensively considers issues such as boiler reheat steam temperature control and load matching between the energy storage system and the boiler-turbine coordination system, proposing a system load coordination and matching control method after coupling the low-temperature energy storage system with the coal-fired power unit. This improves the steam temperature control effect of the coal-fired power unit, reduces the range of parameter fluctuations, and enhances the safety of the coal-fired power unit during operation.

[0004] The technical solution adopted by this invention to solve its technical problem is:

[0005] A control method for improving steam temperature control in coal-fired power units by coupling a low-temperature energy storage system with the coal-fired power unit is proposed. This method couples the low-temperature energy storage system with the coal-fired power unit and designs a load coordination and matching control method. The overall load command is jointly borne by the low-temperature energy storage system and the coal-fired power unit's boiler-turbine coordination system, reducing the parameter fluctuation amplitude of the coal-fired power unit and improving its variable load performance. The calculation steps and adjustment amounts of the load coordination and matching control method differ during load increases and decreases, as detailed below:

[0006] (1) The steps of the load coordination and matching control method during the load reduction process of coal-fired power units are as follows:

[0007] ① Input the high-pressure cylinder exhaust steam extraction ratio to obtain the high-pressure cylinder exhaust steam extraction amount;

[0008] ② The load command of the cryogenic energy storage system during the load reduction process is obtained by using the steam extraction volume of the high-pressure cylinder and the work done by the high-pressure cylinder exhaust per unit mass flow rate.

[0009] ③ Obtain the initial load of the coal-fired unit after load coordination and matching control based on the load command of the medium and low temperature energy storage system and the initial load of the coal-fired unit;

[0010] ④ Based on the initial load and target load of the coal-fired unit and the original set load change rate, obtain the time required for the unit load command to reach the target load;

[0011] ⑤ Based on the initial load of the coal-fired unit after adopting load coordination matching control, the time required for the overall unit load command to reach the target load, and the initial load and target load of the coal-fired unit, the load command of the coal-fired unit boiler-machine coordination system is obtained;

[0012] ⑥ The design opening degree of the high-pressure cylinder exhaust steam extraction valve is obtained based on the high-pressure cylinder exhaust steam extraction volume;

[0013] ⑦ Based on the load command of the medium and low temperature energy storage system, the real-time value of the whole unit load, and the load command of the coal-fired unit boiler coordination system, the corrected opening of the high-pressure cylinder exhaust steam extraction valve is obtained, and the real-time opening of the high-pressure cylinder exhaust steam extraction valve is obtained by adding it to the design opening of the high-pressure cylinder exhaust steam extraction valve.

[0014] ⑧ Input the load command of the coal-fired unit boiler-turbine coordination system into the boiler-turbine coordination control system of the coal-fired unit to obtain boiler command and turbine command;

[0015] ⑨ Obtain the correction value for the reheat steam temperature regulation effect based on the high-pressure cylinder exhaust steam extraction rate and boiler commands;

[0016] (2) The steps of the load coordination and matching control method during the load increase process of coal-fired power units are as follows:

[0017] ① Calculate the energy storage capacity of medium and low temperature energy storage systems;

[0018] ②Based on the energy storage capacity of the medium and low temperature energy storage system and the initial and target loads of the coal-fired unit, the maximum duration of energy release during the medium and low temperature energy storage system is obtained;

[0019] ③ Based on the initial load and target load of the coal-fired unit and the original set load change rate, obtain the time required for the unit load command to reach the target load;

[0020] ④ Obtain the load command of the coal-fired unit boiler-machine coordination system based on the initial load and target load of the coal-fired unit, the time required for the overall unit load command to reach the target load, and the maximum duration of energy release during the medium and low temperature energy storage system;

[0021] ⑤ Input the load command of the coal-fired unit boiler-turbine coordination system into the boiler-turbine coordination control system of the coal-fired unit to obtain boiler command and turbine command;

[0022] ⑥ Obtain the load command for the medium and low temperature energy storage system based on the initial load and target load of the coal-fired unit and the maximum duration of energy release during the medium and low temperature energy storage system;

[0023] ⑦ The opening degree of the feedwater pumping valve and the opening degree of the condensate pumping valve are obtained according to the load command of the medium and low temperature energy storage system and the work done by the unit mass flow rate of feedwater and condensate, respectively.

[0024] The method for coupling the low-temperature energy storage system with the coal-fired unit is as follows: During the load reduction process, which is also the energy storage process, the low-temperature energy storage system is connected to the outlet of the high-pressure cylinder through the exhaust steam extraction valve of the high-pressure cylinder. The exhaust steam extraction from the high-pressure cylinder is used as the heat release working fluid. After the heat release working fluid is depressurized, it is sent to the condenser. During the load increase process, which is also the energy release process, the low-temperature energy storage system is connected to the outlet of the condenser through the condensate pumping valve. The pumping water from the condenser outlet is used as the heat absorption working fluid. After the heat absorption working fluid is sent to the deaerator. The medium-temperature energy storage system is connected to the outlet of the deaerator through the feedwater pumping valve. The pumping water from the deaerator outlet is used as the heat absorption working fluid. After the heat absorption working fluid is sent to the outlet of the high-pressure regenerative heater.

[0025] The medium- and low-temperature energy storage system is composed of multi-stage phase change materials.

[0026] The calculation method for the physical quantities in steps ① to ⑨ of the load coordination and matching control method during the load reduction process of the coal-fired unit is as follows:

[0027] ① Calculate the steam extraction volume of the high-pressure cylinder exhaust. G h

[0028]

[0029] In the formula: G h,s The setpoint for high-pressure cylinder exhaust, kg / s; Ra The high-pressure cylinder exhaust / extraction ratio is set by the operator based on the temperature fluctuation range and the minimum flow rate of the low-pressure cylinder.

[0030] ② Calculate the work done by the high-pressure cylinder exhaust steam per unit mass flow rate Pe h

[0031]

[0032] In the formula: h h The enthalpy of the high-pressure cylinder exhaust steam is expressed in kJ / kg. h n The enthalpy of the low-pressure cylinder exhaust is expressed in kJ / kg. The heat absorbed by a reheat steam boiler per unit mass flow rate is expressed in kJ / kg. i This refers to the serial number of the regenerator; m This refers to the number of regenerative heaters; A i For the first i The heat released by the condensate or absorbed by the water side of a regenerative heater, when the regenerative heater is a partitioned heater. A i Extracting the heat released by the hydrophobic layer; when the regenerative heater is a hybrid heater, this heater and subsequent heaters... A i All are heat absorbed on the water side, kJ / kg; q i For the first i Heat release from steam extraction of each regenerative heater, kJ / kg; For steam extraction efficiency;

[0033] ③ Calculate the load command of the cryogenic energy storage system during the load reduction process fh h,d

[0034]

[0035] In the formula: Pe The rated load of the coal-fired unit is kW;

[0036] ④ Calculate the load command of the coal-fired unit boiler-generator coordination system during the load reduction process. fh 0,d

[0037]

[0038]

[0039]

[0040]

[0041]

[0042] In the formula: Pe 1,n The initial load of the coal-fired unit after adopting the load matching control method is kW; Pe 1 represents the initial load of the coal-fired unit, in kW; Pe 2 represents the target load of the coal-fired unit, in kW; t s0 The time, in seconds, for the load command to reach the target load. rate 0 represents the original set variable load rate, in kW / min; rate0,1 The variable load rate (kW / min) of the boiler-generator coordination system of the coal-fired power unit after adopting the load coordination control method; t s0,1 The time, in seconds, for the load command to reach the target load in the boiler-generator coordination system of a coal-fired power unit after adopting the load coordination control method;

[0043] ⑤ Calculate the real-time opening degree of the high-pressure cylinder exhaust and extraction valves.

[0044]

[0045]

[0046] In the formula: K h Design opening of the high-pressure cylinder exhaust and extraction valve; k v,h s is the resistance coefficient of the pipeline connecting the high-pressure cylinder outlet and the cryogenic energy storage system. 2 ·MPa / (kg·m 3 ); The exhaust gas density of the high-pressure cylinder is kg / m³. 3 ; The pressure difference between the high-pressure cylinder outlet and the cryogenic energy storage system is expressed in MPa. K h,rt This refers to the real-time opening degree of the exhaust and extraction valve of the high-pressure cylinder. f PID To utilize the correction value of the high-pressure cylinder exhaust steam extraction valve obtained by PID through real-time load deviation, the real-time load deviation is the real-time load of the coal-fired unit minus the load command of the boiler-turbine coordination system minus the load command of the medium-low temperature energy storage system. fh rt This refers to the real-time load of the entire coal-fired power unit.

[0047] ⑥ Calculate the correction value for the reheat steam temperature regulation effect.

[0048]

[0049] In the formula: BA xz This is a correction value for the reheat steam temperature regulation effect. BA The amount of reheat steam temperature regulation effect before correction; f ( Ra ) is a correction factor related to the extraction ratio of the exhaust steam from the high-pressure cylinder.

[0050] The calculation method for the physical quantities in steps ① to ⑦ of the load coordination and matching control method during the load increase process of the coal-fired unit is as follows:

[0051] ① Calculate the energy storage capacity of medium and low temperature energy storage systems

[0052]

[0053]

[0054] In the formula: E m The low-temperature energy storage capacity is used to heat the condensate at the condenser outlet, in kJ. E h The medium-temperature energy storage capacity is used to heat the deaerator outlet feedwater, kJ; C p The specific heat capacity of the phase change material is expressed in kJ / kg / °C. m The mass of the phase change material is expressed in kg. T 2 represents the hot-end temperature of the phase change material, in °C; T 1 represents the cold end temperature of the phase change material, in °C; T 0 represents the melting temperature of the phase change material, in °C. L Latent heat, kJ; hj The number of phase change materials for medium-temperature energy storage. mj The number of phase change materials for low-temperature energy storage;

[0055] ② Calculate the maximum duration of energy release during the cryogenic energy storage system.

[0056]

[0057]

[0058] In the formula: t h The maximum duration, in seconds, is the energy release process of the medium-temperature energy storage system. t m The maximum duration, in seconds, is the energy release process of a cryogenic energy storage system. Pe 2 represents the target load of the coal-fired unit, in kW; Pe 1 represents the initial load of the coal-fired unit, in kW;

[0059] ③ Calculate the load command of the coal-fired unit boiler-generator coordination system during the load increase process. fh 0,u

[0060]

[0061]

[0062]

[0063]

[0064] In the formula:t s0 The time, in seconds, for the load command to reach the target load. rate 0 represents the original set variable load rate, in kW / min; t s1 The time, in seconds, for the load command of the coal-fired unit boiler-generator coordination system to reach the target load after adopting the load coordination control method; rate 1 represents the new variable load rate (kW / min) of the boiler-generator coordination system of the coal-fired unit after adopting the load coordination control method; t The time s is the real-time recording time.

[0065] ④ Calculate the load command of the cryogenic energy storage system during the load increase process.

[0066]

[0067]

[0068]

[0069]

[0070]

[0071]

[0072]

[0073] In the formula: fh old This is the load command for the entire machine under the original variable load rate; fh mh Load command for medium and low temperature energy storage system; t sh The time required, in seconds, for the sum of load commands from the coal-fired power plant boiler-generator coordination system and the medium-temperature energy storage system to reach the target load; rate sh The combined load rate (kW / min) of the coal-fired unit boiler-generator coordination system and the medium-temperature energy storage system; fh sh This is the sum of the load commands from the coal-fired power unit's boiler-generator coordination system and the medium-temperature energy storage system. fh h,u Load command for medium-temperature energy storage system; fh m,u Load command for cryogenic energy storage system;

[0074] ⑤ Calculate the opening degree of the water supply and pumping valves K m

[0075]

[0076] In the formula: The change in power of the coal-fired unit when the unit water flow rate changes, expressed in kW / (kg / s); k v,m The resistance coefficient of the pipeline connecting the water supply outlet and the medium-temperature energy storage system, s 2 ·MPa / (kg·m 3 ); For water supply density, kg / m³ 3 ; The pressure difference between the deaerator outlet and the economizer inlet is expressed in MPa.

[0077] ⑥ Calculate the opening degree of the condensate pumping valve K l

[0078]

[0079] In the formula: The increase in unit power when the condensate flow rate changes per unit is expressed in kW / (kg / s). k v,l s is the resistance coefficient of the pipe connecting the condensate outlet and the cryogenic energy storage system. 2 ·MPa / (kg·m 3 ); The density of condensate is kg / m³ 3 ; ρ represents the pressure difference between the condenser outlet and the deaerator inlet, in MPa.

[0080] Compared with the prior art, the advantages of the present invention are as follows:

[0081] (1) The present invention uses a load coordination matching control method, in which the load of the whole unit is jointly borne by the medium and low temperature energy storage system and the coal-fired unit boiler coordination system, which alleviates the load change pressure of the coal-fired unit boiler coordination system, reduces the parameter fluctuation range of the coal-fired unit during transient processes, and improves the operating safety of the coal-fired unit.

[0082] (2) The control method proposed in this invention extracts part of the high-pressure cylinder exhaust steam during the load reduction process, which affects the ratio of main and reheat steam flow and optimizes the boiler steam temperature control method, so as to control the steam temperature more accurately. Attached Figure Description

[0083] Figure 1 This is a load coordination and matching control method.

[0084] Figure 2 This is a schematic diagram illustrating the coupling method between the medium-low temperature energy storage system and the case unit.

[0085] Figure 3 This is a comparison chart of main steam temperatures after adopting the load-coordinated matching control method. (Taking the load reduction process as an example)

[0086] Figure 4 This is a comparison chart of reheat steam temperatures after adopting the load coordination and matching control method. (Taking the load increase process as an example) Detailed Implementation

[0087] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0088] This invention discloses a control method for improving steam temperature control in coal-fired power units by coupling a low-temperature energy storage system. A 660 MW coal-fired power unit is selected as a case study, and the specific implementation method is as follows:

[0089] 1. Case Unit Introduction

[0090] Figure 2 The diagram shows a schematic of the unit in the case study. The outlet of the high-pressure heater 11 is connected to the feedwater inlet of boiler 1 via a feedwater pipe. The main steam outlet of boiler 1 is connected to the inlet of the ultra-high pressure cylinder 2 via a main steam pipe. The outlet of the ultra-high pressure cylinder 2 is connected to the primary reheat steam inlet of boiler 1 via a pipe. The primary reheat steam outlet of boiler 1 is connected to the inlet of the high-pressure cylinder 3 via a pipe. The outlet of the high-pressure cylinder 3 is connected to the secondary reheat steam inlet of boiler 1 via a pipe. The secondary reheat steam outlet of boiler 1 is connected to the inlet of the intermediate-pressure cylinder 4 via a pipe. The outlet of the intermediate-pressure cylinder 4 is connected to the inlet of the low-pressure cylinder 5 via a pipe. The outlet of the low-pressure cylinder 5 is connected to the inlet of the condenser 6 via a pipe. The outlet of the condenser 6 is connected to the condensate pump 7. The outlet of condensate pump 7 is connected to the inlet of low-pressure regenerative heater 8 via a pipeline. The outlet of low-pressure regenerative heater 8 is connected to the inlet of deaerator 9. The outlet of deaerator 9 is connected to the inlet of condensate pump 10. The outlet of condensate pump 10 is connected to the inlet of high-pressure heater 11. The extraction ports of ultra-high-pressure cylinder 2 and high-pressure cylinder 3 are connected to the extraction port of high-pressure heater 11. The first-stage extraction port of intermediate-pressure cylinder 4 is connected to the extraction port of high-pressure heater 11. The second-stage extraction port of intermediate-pressure cylinder 4 is connected to the extraction port of deaerator 9. The third and fourth-stage extraction ports of intermediate-pressure cylinder 4 are connected to the extraction port of low-pressure regenerative heater 8. The extraction port of low-pressure cylinder 5 is connected to the extraction port of low-pressure regenerative heater 8.

[0091] 2. Coupling methods between medium- and low-temperature energy storage systems and coal-fired power units

[0092] like Figure 2As shown, during the energy storage process, the energy storage tank 12 serves as a medium-low temperature energy storage system. The medium-low temperature energy storage system is connected to the exhaust outlet of the high-pressure cylinder through the high-pressure cylinder exhaust valve 16. After the heat is released, the working fluid is depressurized through the pressure relief valve 17 and then sent to the condenser 6. During the energy release process, the low temperature energy storage system is connected to the outlet of the condenser 6 through the condensate pump valve 18. After the heat is absorbed, the working fluid is sent to the deaerator 9. The medium temperature energy storage system is connected to the outlet of the deaerator 9 through the feedwater pump valve 19. After the heat is absorbed, the working fluid is sent to the outlet of the high-pressure heater 11.

[0093] 3. Material selection for medium and low temperature energy storage systems

[0094] The temperature range of the high-pressure cylinder exhaust steam of the case unit is 446 ~ 455 °C. The energy storage tank 12 is composed of three layers of phase change materials. The first layer of phase change material 13 is KNO3 with a melting temperature of 330 °C. The second layer of phase change material 14 is LiCl(37)-63LiOH with a melting temperature of 262 °C. The third layer of phase change material 15 is LiNO3(55.4)-4.5NaNO3-40.1 KCl with a melting temperature of 160 °C.

[0095] 4. Load coordination and matching control methods during load reduction

[0096] ① The operator sets the high-pressure cylinder exhaust / extraction ratio based on the temperature fluctuation range and the minimum flow rate of the low-pressure cylinder. Ra ,calculate G h For the high-pressure cylinder exhaust steam extraction volume

[0097]

[0098] In the formula: G h,s This is the setpoint for the high-pressure cylinder exhaust, in kg / s.

[0099] ② Obtain the pressure and temperature of the high-pressure cylinder exhaust, low-pressure cylinder exhaust, and inlet / outlet working fluid of the regenerator from the heat balance diagram of the case unit. Obtain the enthalpy values ​​of each working fluid from the steam property table. Calculate the work done per unit flow rate of high-pressure cylinder exhaust using the equivalent enthalpy drop method. Pe h .

[0100]

[0101] In the formula: h h The enthalpy of the high-pressure cylinder exhaust steam is expressed in kJ / kg. h n The enthalpy of the low-pressure cylinder exhaust is expressed in kJ / kg. The heat absorbed by a reheat steam boiler per unit mass flow rate is expressed in kJ / kg. iThis refers to the serial number of the regenerator; m This refers to the number of regenerative heaters; A i For the first i The heat released by the condensate or absorbed by the water side of a regenerative heater, when the regenerative heater is a partitioned heater. A i Extracting the heat released by the hydrophobic layer; when the regenerative heater is a hybrid heater, this heater and subsequent heaters... A i All are heat absorbed on the water side, kJ / kg; q i For the first i Heat release from steam extraction of each regenerative heater, kJ / kg; This refers to the extraction efficiency.

[0102] ③ Calculate the load command of the cryogenic energy storage system during the load reduction process based on the high-pressure cylinder exhaust steam extraction rate in step ① and the work done by the high-pressure cylinder exhaust steam per unit flow rate in step ②. fh h,d .

[0103]

[0104] In the formula: Pe The rated load of the coal-fired unit is kW; Pe = 660,000 kW.

[0105] ④ Based on the boiler-turbine coordination control system of the case unit, obtain the initial load, target load, and original set load change rate of the case unit, and calculate the load command of the boiler-turbine coordination system of the case unit during the load reduction process. fh 0,d

[0106]

[0107]

[0108]

[0109]

[0110]

[0111] In the formula: Pe 1,n The initial load of the coal-fired unit after adopting the load matching control method is kW; Pe 1 represents the initial load of the coal-fired unit, in kW; Pe 2 represents the target load of the coal-fired unit, in kW; t s0 The time, in seconds, for the load command to reach the target load.rate 0 represents the original set variable load rate, in kW / min; rate 0,1 The variable load rate (kW / min) of the boiler-generator coordination system of the coal-fired power unit after adopting the load coordination control method; t s0,1 The time, in seconds, for the load command to reach the target load in the boiler-generator coordination system of a coal-fired power unit after adopting the load coordination control method; fh 0,d Load commands for the boiler-generator coordination system of coal-fired power units;

[0112] ⑤ Calculate the real-time opening degree of the high-pressure cylinder exhaust steam extraction valve based on the high-pressure cylinder exhaust steam extraction volume in step ① and the load command of the cryogenic energy storage system during the load reduction process in step ③.

[0113]

[0114]

[0115] In the formula: K h Design opening of the high-pressure cylinder exhaust and extraction valve; k v,h s is the resistance coefficient of the pipeline connecting the high-pressure cylinder outlet and the cryogenic energy storage system. 2 ·MPa / (kg·m 3 ); The exhaust gas density of the high-pressure cylinder is kg / m³. 3 ; The pressure difference between the high-pressure cylinder outlet and the cryogenic energy storage system is expressed in MPa. K h,rt This refers to the real-time opening degree of the exhaust and extraction valve of the high-pressure cylinder. f PID To utilize the correction value of the high-pressure cylinder exhaust steam extraction valve obtained through PID using the real-time load deviation, the real-time load deviation is the real-time load of the unit in the case study minus the load command of the boiler-turbine coordination system minus the load command of the medium-low temperature energy storage system. fh rt This refers to the real-time load of the entire coal-fired power unit.

[0116] ⑥ The case unit uses the flue gas recirculation rate as a variable to regulate the reheat steam temperature, and corrects the flue gas recirculation rate as follows:

[0117]

[0118] In the formula: BA xz This is a correction value for the amount of flue gas recirculation. BA This represents the flue gas recirculation rate before correction. f (Ra ) is a correction factor related to the extraction ratio of the exhaust steam from the high-pressure cylinder.

[0119] ⑦ Load command for coal-fired unit boiler-generator coordination system fh 0,d The commands are sent to the boiler-turbine coordination control system of the case unit to obtain boiler commands and turbine commands.

[0120] 5. Load coordination and matching control methods during load increase process

[0121] ① Based on the specific heat capacity, latent heat, and melting temperature of the phase change material obtained in step 3, calculate the energy storage capacity of the medium- and low-temperature energy storage system.

[0122]

[0123]

[0124] In the formula: E m The low-temperature energy storage capacity is used to heat the condensate at the condenser outlet, in kJ. E h The medium-temperature energy storage capacity is used to heat the deaerator outlet feedwater, kJ; C p The specific heat capacity of the phase change material is expressed in kJ / kg / °C. m The mass of the phase change material is expressed in kg. T 2 represents the hot-end temperature of the phase change material, in °C; T 1 represents the cold end temperature of the phase change material, in °C; T 0 represents the melting temperature of the phase change material, in °C. L Latent heat, kJ; hj The number of phase change materials for medium-temperature energy storage. mj This refers to the number of phase change materials used in cryogenic energy storage; in the case unit, hj =2, mj =1.

[0125] ② Calculate the maximum duration of energy release during the cryogenic energy storage system.

[0126]

[0127]

[0128] In the formula: t h The maximum duration, in seconds, is the energy release process of the medium-temperature energy storage system. t m The maximum duration, in seconds, is the energy release process of a cryogenic energy storage system. Pe 2 represents the target load of the coal-fired unit, in kW;Pe 1 represents the initial load of the coal-fired unit, in kW;

[0129] ③ Based on the boiler-turbine coordination control system of the case unit, obtain the initial load, target load, and original set load change rate of the case unit, and calculate the load command of the boiler-turbine coordination system during the load increase process, denoted as: fh 0,u

[0130]

[0131]

[0132]

[0133]

[0134] In the formula: t s0 The time, in seconds, for the load command to reach the target load. rate 0 represents the original set variable load rate, in kW / min; t s1 The time, in seconds, for the load command of the coal-fired unit boiler-generator coordination system to reach the target load after adopting the load coordination control method; rate 1 represents the new variable load rate (kW / min) of the boiler-generator coordination system of the coal-fired unit after adopting the load coordination control method; t s represents the real-time recording time.

[0135] ④ Based on the boiler-turbine coordination control system of the case unit, obtain the initial load and target load of the case unit, the original set load change rate, and calculate the load command of the cryogenic energy storage system during the load increase process.

[0136]

[0137]

[0138]

[0139]

[0140]

[0141]

[0142]

[0143] In the formula: fh old This is the load command for the entire machine under the original variable load rate; fh mhLoad command for medium and low temperature energy storage system; t sh The time required, in seconds, for the sum of load commands from the coal-fired power plant boiler-generator coordination system and the medium-temperature energy storage system to reach the target load; rate sh The combined load rate (kW / min) of the coal-fired unit boiler-generator coordination system and the medium-temperature energy storage system; fh sh This is the sum of the load commands from the coal-fired power unit's boiler-generator coordination system and the medium-temperature energy storage system. fh h,u Load command for medium-temperature energy storage system; fh m,u This is a load command for a cryogenic energy storage system.

[0144] ⑤ Calculate the opening degree of the water supply and pumping valves K m

[0145]

[0146] In the formula: The change in unit power of the case unit when the unit water flow rate changes, expressed in kW / (kg / s); k v,m The resistance coefficient of the pipeline connecting the water supply outlet and the medium-temperature energy storage system, s 2 ·MPa / (kg·m 3 ); For water supply density, kg / m³ 3 ; The pressure difference between the deaerator outlet and the economizer inlet is expressed in MPa.

[0147] ⑥ Calculate the opening degree of the condensate pumping valve K l

[0148]

[0149] In the formula: The increase in unit power when the condensate flow rate changes per unit is expressed in kW / (kg / s). k v,l s is the resistance coefficient of the pipe connecting the condensate outlet and the cryogenic energy storage system. 2 ·MPa / (kg·m 3 ); The density of condensate is kg / m³ 3 ; ρ represents the pressure difference between the condenser outlet and the deaerator inlet, in MPa.

[0150] ⑦ Load command of the unit's boiler-turbine coordination system in the case study fh 0,uThe commands are sent to the boiler-turbine coordination control system of the coal-fired unit to obtain boiler commands and turbine commands.

[0151] 6. Optimization effect of the case unit

[0152] Figure 3 The paper presents a comparison of the main steam temperature curves before and after the application of load coordination matching control method during load reduction in the case unit. It can be seen that the maximum main steam temperature decreased by 7.3 °C after adopting the load coordination matching control method during load reduction.

[0153] Figure 4 The paper presents a comparison of the reheat steam temperature curves before and after the application of load coordination matching control method during the load increase process of the case unit. It can be seen that the maximum reheat steam temperature decreased by 1.8 °C after adopting the load coordination matching control method during the load increase process.

[0154] In summary, after adopting the control method of the present invention, which uses a coupled low-temperature energy storage system to improve the steam temperature control effect of a coal-fired power unit, the steam temperature fluctuation range is significantly reduced, thus improving the variable load performance of the coal-fired power unit.

Claims

1. A control method for improving steam temperature control in coal-fired power units by coupling a low-temperature energy storage system, characterized in that: A load coordination and matching control method is designed by coupling a low-temperature energy storage system with a coal-fired power unit. The overall load command is jointly borne by the low-temperature energy storage system and the coal-fired power unit's boiler-turbine coordination system, reducing the parameter fluctuation amplitude of the coal-fired power unit and improving its variable load performance. The calculation steps and adjustment amounts of the load coordination and matching control method differ during load increases and decreases, as detailed below: (1) The steps of the load coordination and matching control method during the load reduction process of coal-fired power units are as follows: ① Input the high-pressure cylinder exhaust steam extraction ratio to obtain the high-pressure cylinder exhaust steam extraction amount; ② The load command of the cryogenic energy storage system during the load reduction process is obtained by using the steam extraction volume of the high-pressure cylinder and the work done by the high-pressure cylinder exhaust per unit mass flow rate. ③ Based on the load command of the medium-low temperature energy storage system and the initial load of the coal-fired unit, the initial load of the coal-fired unit after adopting the load coordination matching control method is obtained; ④ Based on the initial load and target load of the coal-fired unit and the original set load change rate, obtain the time required for the unit load command to reach the target load; ⑤ Based on the initial load of the coal-fired unit after adopting load coordination matching control, the time required for the overall unit load command to reach the target load, and the initial load and target load of the coal-fired unit, the load command of the coal-fired unit boiler-machine coordination system is obtained; ⑥ The design opening degree of the high-pressure cylinder exhaust steam extraction valve is obtained based on the high-pressure cylinder exhaust steam extraction volume; ⑦ Based on the load command of the medium and low temperature energy storage system, the real-time value of the whole unit load, and the load command of the coal-fired unit boiler coordination system, the corrected opening of the high-pressure cylinder exhaust steam extraction valve is obtained, and the real-time opening of the high-pressure cylinder exhaust steam extraction valve is obtained by adding it to the design opening of the high-pressure cylinder exhaust steam extraction valve. ⑧ Input the load command of the coal-fired unit boiler-turbine coordination system into the boiler-turbine coordination control system of the coal-fired unit to obtain boiler command and turbine command; ⑨ Obtain the correction value for the reheat steam temperature regulation effect based on the high-pressure cylinder exhaust steam extraction rate and boiler commands; (2) The steps of the load coordination and matching control method during the load increase process of coal-fired power units are as follows: ① Calculate the energy storage capacity of medium and low temperature energy storage systems; ②Based on the energy storage capacity of the medium and low temperature energy storage system and the initial and target loads of the coal-fired unit, the maximum duration of energy release during the medium and low temperature energy storage system is obtained; ③ Based on the initial load and target load of the coal-fired unit and the original set load change rate, obtain the time required for the unit load command to reach the target load; ④ Obtain the load command of the coal-fired unit boiler-machine coordination system based on the initial load and target load of the coal-fired unit, the time required for the overall unit load command to reach the target load, and the maximum duration of energy release during the medium and low temperature energy storage system; ⑤ Input the load command of the coal-fired unit boiler-turbine coordination system into the boiler-turbine coordination control system of the coal-fired unit to obtain boiler command and turbine command; ⑥ Obtain the load command for the medium and low temperature energy storage system based on the initial load and target load of the coal-fired unit and the maximum duration of energy release during the medium and low temperature energy storage system; ⑦ The opening degree of the feedwater pumping valve and the opening degree of the condensate pumping valve are obtained according to the load command of the medium and low temperature energy storage system and the work done by the unit mass flow rate of feedwater and condensate, respectively.

2. The control method for improving steam temperature control effect of a coupled low-temperature energy storage system in a coal-fired power unit according to claim 1, characterized in that: The method for coupling the low-temperature energy storage system with the coal-fired unit is as follows: During the load reduction process, which is also the energy storage process, the low-temperature energy storage system is connected to the outlet of the high-pressure cylinder through the exhaust steam extraction valve of the high-pressure cylinder. The exhaust steam extraction from the high-pressure cylinder is used as the heat release working fluid. After the heat release working fluid is depressurized, it is sent to the condenser. During the load increase process, which is also the energy release process, the low-temperature energy storage system is connected to the outlet of the condenser through the condensate pumping valve. The pumping water from the condenser outlet is used as the heat absorption working fluid. After the heat absorption working fluid is sent to the deaerator. The medium-temperature energy storage system is connected to the outlet of the deaerator through the feedwater pumping valve. The pumping water from the deaerator outlet is used as the heat absorption working fluid. After the heat absorption working fluid is sent to the outlet of the high-pressure regenerative heater.

3. The control method for improving the steam temperature control effect of a coal-fired power unit by coupling a low-temperature energy storage system according to claim 1, characterized in that: The medium- and low-temperature energy storage system is composed of multi-stage phase change materials.

4. The control method for improving the steam temperature control effect of a coal-fired unit using a coupled low-temperature energy storage system according to claim 1, characterized in that: The calculation method for the physical quantities in steps ① to ⑨ of the load coordination and matching control method during the load reduction process of the coal-fired power unit is as follows: ① Calculate the steam extraction rate G of the high-pressure cylinder exhaust. h G h =G h,s ·Ra Where: G h,s The set value for high-pressure cylinder exhaust steam is kg / s; Ra is the high-pressure cylinder exhaust steam extraction ratio set by the operator based on the temperature fluctuation range and the minimum flow rate of the low-pressure cylinder. ② Calculate the work done by the high-pressure cylinder exhaust per unit mass flow rate, Pe. h Where: h h The enthalpy of the high-pressure cylinder exhaust is expressed in kJ / kg; h. n σ represents the enthalpy of the low-pressure cylinder exhaust steam (kJ / kg); σ represents the heat absorbed per unit mass flow rate in the reheat steam boiler (kJ / kg); i represents the serial number of the regenerator; m represents the number of regenerators; A i For the i-th regenerative heater, A represents the condensate heat release or water-side heat absorption. When the regenerative heater is a partitioned heater, A... i Take the heat released by the hydrophobic condensate; when the regenerative heater is a hybrid heater, the A of this heater and subsequent heaters i All are heat absorbed on the water side, kJ / kg; q i η is the heat release from the extraction steam of the i-th regenerative heater, in kJ / kg; i For steam extraction efficiency; ③ Calculate the load command fh of the cryogenic energy storage system during the load reduction process. h,d In the formula: Pe is the rated load of the coal-fired unit, in kW; ④ Calculate the load command fh of the coal-fired unit boiler-generator coordination system during the load reduction process. 0,d Instead 1,n =For1-G h ·Instead h t s0 =(Pe2-Pe1) / rate0·60 t s0,1 =(Pe2-Pe1) / rate 0,1 ·60 In the formula: Pe 1,n Pe1 is the initial load of the coal-fired unit after load matching control is adopted, kW; Pe2 is the target load of the coal-fired unit, kW; t s0 The time it takes for the load command to reach the target load is 1 second; rate0 is the original set load change rate, kW / min; rate 0,1 The load change rate (kW / min) of the boiler-generator coordination system of a coal-fired power unit after adopting the load coordination control method; t s0,1 The time, in seconds, for the load command to reach the target load in the boiler-generator coordination system of a coal-fired power unit after adopting the load coordination control method; ⑤ Calculate the real-time opening degree of the high-pressure cylinder exhaust and extraction valves. K h,rt =K h +f PID (fh 0,d ,fh rt ,fh h,d ) In the formula: K h The design opening of the high-pressure cylinder exhaust and extraction valve; k v,h s is the resistance coefficient of the pipeline connecting the high-pressure cylinder outlet and the cryogenic energy storage system. 2 ·MPa / (kg·m 3 );ρ h The exhaust gas density of the high-pressure cylinder is kg / m³. 3 ;Δp h The pressure difference between the high-pressure cylinder outlet and the cryogenic energy storage system is expressed in MPa and K. h,rt f represents the real-time opening degree of the high-pressure cylinder exhaust and extraction valve; PID To utilize the correction value of the high-pressure cylinder exhaust steam extraction valve obtained through PID control based on real-time load deviation, the real-time load deviation is calculated as the real-time load of the coal-fired unit minus the load command from the boiler-turbine coordination system minus the load command from the cryogenic energy storage system; fh rt This refers to the real-time load of the entire coal-fired power unit. ⑥ Calculate the correction value for the reheat steam temperature regulation effect. BA xz =BA·f(Ra) In the formula: BA xz 1 is the correction value for the reheat steam temperature regulation effect; BA is the reheat steam temperature regulation effect before correction; f(Ra) is the correction coefficient related to the extraction ratio of the high-pressure cylinder exhaust.

5. The control method for improving the steam temperature control effect of a coal-fired unit using a coupled low-temperature energy storage system according to claim 1, characterized in that: The calculation methods for the physical quantities in steps ① to ⑦ of the load coordination and matching control method during the load increase process of the coal-fired unit are as follows: ① Calculate the energy storage capacity of medium and low temperature energy storage systems In the formula: E m This refers to the low-temperature energy storage capacity used to heat the condensate at the condenser outlet, in kJ / E. h The medium-temperature energy storage capacity is used to heat the deaerator outlet feedwater, in kJ / C. p denoted as , where is the specific heat capacity of the phase change material (T2), kJ / kg / ℃; is the mass of the phase change material (m), kg; is the hot-end temperature of the phase change material (T2), ℃; is the cold-end temperature of the phase change material (T1), ℃; is the melting temperature of the phase change material (T0), ℃; is the latent heat (L), kJ; is the number of phase change materials for medium-temperature energy storage; and is the number of phase change materials for low-temperature energy storage. ② Calculate the maximum duration of energy release during the cryogenic energy storage system. In the formula: t h The maximum duration, in seconds, is the energy release process of the medium-temperature energy storage system. t m Pe1 represents the maximum duration of energy release during the cryogenic energy storage system, in seconds; Pe2 represents the target load of the coal-fired unit, in kW; Pe1 represents the initial load of the coal-fired unit, in kW. ③ Calculate the load command fh of the coal-fired unit boiler-generator coordination system during the load increase process. 0,u t s0 =(Pe2-Pe1) / rate0·60 t s1 =t s0 -t m -t h rate1=(Pe2-Pe1) / t s1 ·60 In the formula: t s0 The time for the total load command to reach the target load is 1 second; rate0 is the original set load change rate, kW / min; t s1 The time (s) for the load command of the coal-fired power unit's boiler-unit coordination system to reach the target load after adopting the load coordination control method; rate1 is the new variable load rate of the coal-fired power unit's boiler-unit coordination system after adopting the load coordination control method, kW / min; t is the real-time recording time, s; ④ Calculate the load command of the cryogenic energy storage system during the load increase process. fh mh =fh old -fh 0,u t sh =t s0 -t m rate sh =(Pe2-Pe1) / t sh ·60 fh m,u =fh old -fh sh fh h,u =fh mh -fh m,u In the formula: fh old This is the load command for the entire unit under the original variable load rate; fh mh For medium and low temperature energy storage system load command; t sh The time required, in seconds, for the sum of load commands from the coal-fired power plant's boiler-generator coordination system and the medium-temperature energy storage system to reach the target load; rate sh The combined load change rate (kW / min) of the coal-fired unit boiler-generator coordination system and the medium-temperature energy storage system; fh sh The sum of load commands from the coal-fired power plant boiler coordination system and the medium-temperature energy storage system; fh h,u For medium-temperature energy storage system load command; fh m,u Load command for cryogenic energy storage system; ⑤ Calculate the opening degree K of the water supply and pumping valve. m In the formula: The change in power of a coal-fired unit when the unit feedwater flow rate changes, expressed in kW / (kg / s); k v,m The resistance coefficient of the pipeline connecting the water supply outlet and the medium-temperature energy storage system, s 2 ·MPa / (kg·m 3 );ρ m For water supply density, kg / m³ 3 ;Δp m The pressure difference between the deaerator outlet and the economizer inlet is expressed in MPa. ⑥ Calculate the opening degree K of the condensate pumping valve. l In the formula: The increase in unit power per unit change in condensate flow rate, expressed in kW / (kg / s); k v,l s is the resistance coefficient of the pipe connecting the condensate outlet and the cryogenic energy storage system. 2 ·MPa / (kg·m 3 );ρ l The density of condensate is kg / m³ 3 ;Δp l ρ represents the pressure difference between the condenser outlet and the deaerator inlet, in MPa.

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