Coupled system and control method for load change of medium-temperature energy storage assisted double reheat unit

Abstract

This invention proposes a coupled system and control method for load change of a secondary reheat unit assisted by intermediate-temperature energy storage. During load reduction, the outlet of the high-pressure cylinder is connected to the intermediate-temperature energy storage system via an extraction steam regulating valve, and the intermediate-temperature energy storage system is connected to the inlet of the low-pressure cylinder via a pressure relief valve. During load increase, the feedwater from the deaerator outlet is connected to the intermediate-temperature energy storage system via a feedwater regulating valve, and the intermediate-temperature energy storage system is connected to the inlet of the low-pressure cylinder via a pipeline. A control method for the load change process of the coupled system is designed, which completes the load change process by assisting the secondary reheat unit with intermediate-temperature energy storage: during load reduction, the power output of the unit is reduced by extracting part of the exhaust steam from the high-pressure cylinder; during load increase, steam is generated by heating part of the feedwater from the deaerator outlet and sent to the low-pressure cylinder to increase the power output of the unit, thereby reducing the response time of the secondary reheat unit and improving its load change performance.

Description

Technical Field

[0001] This invention belongs to the field of thermal control technology for reheat units, specifically relating to a coupling system and control method for reheat units that uses medium-temperature energy storage to assist in load changes. Background Technology

[0002] With the construction of new power systems and the continuous grid connection of large-scale new energy sources, however, new energy sources such as wind and solar power are highly intermittent. To absorb these low-energy-density new energy sources and maintain the power system's supply-demand balance, coal-fired power units bear a crucial peak-shaving responsibility. Double reheat units, typical high-efficiency and advanced coal-fired units, also face the pressure of frequent and rapid peak-shaving. However, double reheat units have numerous components and complex processes, and the inertia differences among the various subsystems within the unit significantly increase the unit's response time. Coupled with external energy storage devices to assist double reheat units in load changes is an important means of reducing unit response time. Therefore, it is urgent to vigorously develop system configurations and control methods for coupling double reheat units with external energy storage devices to promote the construction of new power systems. Summary of the Invention

[0003] This invention addresses the problem of long response time in double reheat units. Starting from the perspective of working fluid flow and temperature matching, it aims to find systems and control methods that can shorten the response time of double reheat units. The purpose of this invention is to provide a coupled system and control method for double reheat units under varying loads, assisted by medium-temperature energy storage. It proposes a coupled system between a medium-temperature energy storage system and the double reheat unit through temperature matching, and proposes a control method for the double reheat unit coupled with medium-temperature energy storage based on the coordinated work of multiple systems, thereby shortening the response time of the double reheat unit.

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

[0005] A coupling system for a secondary reheat unit with load variation is implemented via a medium-temperature energy storage system. This coupling system comprises the secondary reheat unit and a medium-temperature energy storage system. In the secondary reheat unit, the superheated steam outlet of boiler 1 is connected to the steam inlet of the ultra-high pressure cylinder 2 via a pipeline; the exhaust outlet of the ultra-high pressure cylinder 2 is connected to the primary cold reheat steam inlet of boiler 1 via a pipeline; the primary hot reheat steam outlet of boiler 1 is connected to the steam inlet of the high-pressure cylinder 3 via a pipeline; the exhaust outlet of the high-pressure cylinder 3 is connected to the secondary cold reheat steam inlet of boiler 1 via a pipeline; and the secondary hot reheat steam outlet of boiler 1 is connected to the medium-temperature energy storage system. The steam inlet of the intermediate-pressure cylinder 4 is connected to the steam inlet of the low-pressure cylinder 5 via a pipeline. The steam outlet of the low-pressure cylinder 5 is connected to the steam inlet of the condenser 6 via a pipeline. The condensate outlet of the condenser 6 is connected to the condensate inlet of the low-pressure regenerative heater 8 via a condensate pump 7. The condensate outlet of the low-pressure regenerative heater 8 is connected to the condensate inlet of the deaerator 9 via a pipeline. The feedwater outlet of the deaerator 9 is connected to the feedwater inlet of the high-pressure regenerative heater 11 via a feedwater pump 10. The feedwater outlet of the high-pressure regenerative heater 11 is connected to the boiler... The feedwater inlet of furnace 1 is connected via a pipeline. The steam extraction port of ultra-high pressure cylinder 2 is connected via a pipeline to the steam extraction inlet of high-pressure regenerative heater 11. The steam extraction port of high-pressure cylinder 3 is connected via a pipeline to the steam extraction inlet of high-pressure regenerative heater 11. The first-stage steam extraction port of intermediate-pressure cylinder 4 is connected via a pipeline to the steam extraction inlet of high-pressure regenerative heater 11. The second-stage steam extraction port of intermediate-pressure cylinder 4 is connected via a pipeline to the steam extraction inlet of deaerator 9. The remaining stages of steam extraction ports of intermediate-pressure cylinder 4 are connected via pipelines to the steam extraction inlet of low-pressure regenerative heater 8. The steam extraction port of low-pressure cylinder 5 is connected via a pipeline to the low-pressure regenerative heater. The extraction steam inlet of cylinder 8 is connected via a pipeline; the medium-temperature energy storage system consists of extraction steam regulating valve 13, energy storage tank 12, pressure relief valve 14 and feedwater regulating valve 15. During energy storage, the exhaust steam outlet of high-pressure cylinder 3 is connected to the steam inlet of energy storage tank 12 via extraction steam regulating valve 13, and the steam outlet of energy storage tank 12 is connected to the steam inlet of low-pressure cylinder 5 via pressure relief valve 14. During energy release, the feedwater outlet of deaerator 9 is connected to the water medium inlet of energy storage tank 12 via feedwater regulating valve 15, and the steam outlet of energy storage tank 12 is connected to the steam inlet of low-pressure cylinder 5 via a pipeline.

[0006] The energy storage tank 12 uses phase change energy storage material. The selection method for phase change energy storage material comprehensively considers the outlet temperature of the high-pressure cylinder, the inlet temperature of the low-pressure cylinder, and the melting temperature of the phase change energy storage material.

[0007] The control method for the coupled system of the secondary reheat unit with load change assisted by medium-temperature energy storage, as described above, involves the medium-temperature energy storage system in the energy storage process during load reduction. By controlling the opening of the extraction steam regulating valve 13, a portion of the high-pressure cylinder exhaust steam is sent to the energy storage tank 12 for heat release. The working fluid after heat release is sent to the low-pressure cylinder inlet through the pressure relief valve 14, thereby reducing the work done by the secondary reheat unit. That is, the real-time work done by the entire unit is the difference between the original planned overall work done by the secondary reheat unit and the work reduction caused by steam extraction, thus shortening the time required for load change. The actual time for the secondary reheat unit to reach the target load; during the load increase process, the medium-temperature energy storage system is in the energy release process. By controlling the opening of the feedwater regulating valve 15, part of the deaerator outlet feedwater is sent into the energy storage tank 12, and the heat-absorbing working fluid is sent into the low-pressure cylinder inlet, thereby increasing the work done by the secondary reheat unit. That is, the real-time work done by the whole unit is the sum of the original planned overall work done by the secondary reheat unit and the steam work done by the energy storage tank 12, which shortens the actual time for the secondary reheat unit to reach the target load.

[0008] The calculation process for the opening degree of the extraction steam regulating valve 13 during the load reduction process is as follows:

[0009] ① The operator designs the extraction ratio Ra of the high-pressure cylinder exhaust based on the axial thrust and variable load requirements. h ;

[0010] ② Calculate the exhaust steam extraction rate G of the high-pressure cylinder h

[0011] G h =G h,s ·Ra h

[0012] Where: G h,s The high-pressure cylinder exhaust setting value, kg / s, is related to the original overall work output of the secondary reheat unit.

[0013] ③ Calculate the decrease in work Pe caused by steam extraction. h

[0014] Pe h =G h ·f(Pe 0,d )

[0015] In the formula: Pe 0,d The original total power output of the secondary reheat unit during load reduction is kW; f(Pe) 0,d ) represents the change in the work done by the secondary reheat unit after the high-pressure cylinder exhaust steam is cooled and sent to the low-pressure cylinder inlet, which is related to the original overall work done by the boiler and turbine of the secondary reheat unit, in kW / (kg / s).

[0016] ④ Calculate the real-time value K of the opening degree of the extraction steam regulating valve 13. h,13,rt

[0017]

[0018] K h,13,rt =K h,13 +f PID (Pe 0,d Pe rt Pe h )

[0019] Where: K h,13 k is the design value for the opening degree of the extraction steam regulating valve 13. v,13 The resistance coefficient s is the connecting pipe between the outlet of high-pressure cylinder 3 and energy storage tank 12. 2 ·MPa / (kg·m 3 );ρ h The exhaust gas density of the high-pressure cylinder is kg / m³. 3 ;Δp 13 The pressure difference between high-pressure cylinder 3 and energy storage tank 12 is expressed in MPa and K. h,13,rt f is the real-time value of the opening degree of the extraction steam regulating valve 13; PID To correct the opening value of extraction steam regulating valve 13 obtained by PID control using real-time work deviation, where real-time work deviation is the sum of the real-time work output of the secondary reheat unit and the work reduction caused by extraction steam, minus the original planned overall work output of the secondary reheat unit; Pe rt Real-time power output of the secondary reheat unit, kW; Pe 0,d The original total power output of the secondary reheat unit during load reduction is kW.

[0020] The calculation process for the original total work done by the secondary reheat unit during the load reduction process is as follows:

[0021] t s0 =(Pe2-Pe1) / rate0.60

[0022]

[0023] In the formula: t s0 Pe1 is the time (in seconds) for the secondary reheat unit to reach the target load from the initial load under the original variable load rate; Pe2 is the initial load of the secondary reheat unit (kW); Pe3 is the target load of the secondary reheat unit (kW); and rate0 is the original variable load rate of the secondary reheat unit (kW / min).

[0024] The calculation process for the actual time it takes for the secondary reheat unit to reach the target load during the load reduction process is as follows:

[0025]

[0026] In the formula: t s,downThe time, in seconds, is the actual time for the secondary reheat unit to reach the target load during the load reduction process.

[0027] The reduction in the time Δt of the secondary reheat unit to actually reach the target load during the load reduction process. down for:

[0028] Δt down =t s0 -t s,down .

[0029] The calculation process for the opening degree of the water supply regulating valve 15 during the load increase process is as follows:

[0030] ① Calculate the extraction flow rate G of the deaerator outlet feedwater based on the extraction ratio during the load reduction process. d

[0031]

[0032] Where: G h,o The setpoint for high-pressure cylinder exhaust steam under a certain operating condition, kg / s; h h,o h l,o h d,o , respectively, are the enthalpy values ​​of the high-pressure cylinder exhaust steam, the low-pressure cylinder inlet working fluid, and the deaerator outlet working fluid under a certain operating condition, in kJ / kg; f1 is a correction coefficient less than 1 related to the heat exchange efficiency and heat loss of the energy storage tank;

[0033] ② Calculate the correction value G for condensate flow rate cond,xz

[0034] G cond,xz =G cond,s +G d

[0035] Where: G cond,s The condensate flow rate setpoint, kg / s, is related to the original overall work output of the secondary reheat unit.

[0036] ③ Calculate the increase in work Pe caused by the steam generated by energy storage tank 12. d

[0037] Pe d =G d ·(f d (Pe 0,u )-f c (Pe 0,u ))

[0038] In the formula: f d (Pe 0,u ) represents the increase in work done by the working fluid entering the low-pressure cylinder per unit mass flow rate, related to the original overall work done by the boiler and turbine, expressed in kW / (kg / s); fc (Pe 0,u ) represents the reduction in the power output of the secondary reheat unit after the increase in the unit mass flow rate of condensate related to the original overall power output of the boiler and turbine, expressed in kW / (kg / s).

[0039] ④ Calculate the real-time value of the water supply regulating valve opening at 15 degrees.

[0040]

[0041] K h,15,rt =K h,15 +g PID (Pe 0,u Pe rt Pe d )

[0042] Where: K h,15 k is the design value for the opening of the water supply regulating valve (15); v,15 The resistance coefficient of the connecting pipe between the deaerator (9) and the energy storage tank (12) is s. 2 ·MPa / (kg·m 3 );ρ d The feedwater density at the deaerator outlet is kg / m³. 3 ;Δp 15 The pressure difference between the deaerator (9) and the energy storage tank (12) is expressed in MPa and K. h,15,rt The real-time value of the opening degree of the water supply regulating valve (15); g PID The correction value for the opening of the feedwater regulating valve (15) obtained by PID control using real-time work deviation; wherein the real-time work deviation is the real-time work of the secondary reheat unit minus the original planned overall work of the secondary reheat unit minus the increase in work caused by the steam generated by the energy storage tank (12); Pe 0,u The total power output of the secondary reheat unit during the load increase process is the original total power output of the boiler and turbine, in kW.

[0043] The calculation process for the original overall work done by the secondary reheat unit during the load increase process is as follows:

[0044] t s0 =(Pe2-Pe1) / rate0.60

[0045]

[0046] In the formula: t s0 Pe1 is the time (in seconds) for the secondary reheat unit to reach the target load from the initial load under the original variable load rate; Pe2 is the initial load of the secondary reheat unit (kW); Pe3 is the target load of the secondary reheat unit (kW); and rate0 is the original variable load rate of the secondary reheat unit (kW / min).

[0047] The calculation process for the actual time it takes for the secondary reheat unit to reach the target load during the load increase process is as follows:

[0048]

[0049] In the formula: t s,up The time, in seconds, is the actual time for the secondary reheat unit to reach the target load during the load increase process.

[0050] The reduction in the time Δt of the secondary reheat unit actually reaching the target load during the load increase process. up for:

[0051] Δt up =t s0 -t s,up .

[0052] Compared with the prior art, the advantages of the present invention are as follows:

[0053] (1) Based on the concept of temperature matching, this invention proposes a coupling system for medium-temperature energy storage to assist the secondary reheat unit in changing load. By using medium-temperature energy storage, the power change of the secondary reheat unit during the changing load process is increased, and the response time is shortened.

[0054] (2) The control method proposed in this invention overcomes the safety limit of the deaerator water level by using the condensate correction value, which shortens the unit response time and improves the unit operation safety. Attached Figure Description

[0055] Figure 1 A schematic diagram of a coupling system for a medium-temperature energy storage auxiliary secondary reheat unit under varying loads.

[0056] Figure 2 This is a control method for variable load in medium-temperature energy storage auxiliary secondary reheat units.

[0057] Figure 3 This is a comparison chart of the response time of the secondary reheat unit during the load reduction process.

[0058] Figure 4 This is a comparison chart of the response time of the secondary reheat unit during the load increase process. Detailed Implementation

[0059] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0060] This invention relates to a coupling system and control method for a double reheat unit under varying load conditions, assisted by medium-temperature energy storage. A 660MW double reheat unit is selected as the case study. The specific implementation method is as follows:

[0061] 1. A coupling system for load changes in secondary reheat units assisted by medium-temperature energy storage, such as... Figure 1The coupling system includes a secondary reheat unit and a medium-temperature energy storage system. In the secondary reheat unit, the superheated steam outlet of boiler 1 is connected to the steam inlet of ultra-high pressure cylinder 2 via a pipeline; the exhaust outlet of ultra-high pressure cylinder 2 is connected to the primary cold reheat steam inlet of boiler 1 via a pipeline; the primary hot reheat steam outlet of boiler 1 is connected to the steam inlet of high-pressure cylinder 3 via a pipeline; the exhaust outlet of high-pressure cylinder 3 is connected to the secondary cold reheat steam inlet of boiler 1 via a pipeline; and the secondary hot reheat steam outlet of boiler 1 is connected to the steam inlet of intermediate-pressure cylinder 4 via a pipeline. The exhaust outlet of the high-pressure cylinder 4 is connected to the steam inlet of the low-pressure cylinder 5 via a pipeline. The exhaust outlet of the low-pressure cylinder 5 is connected to the exhaust inlet of the condenser 6 via a pipeline. The condensate outlet of the condenser 6 is connected to the condensate inlet of the low-pressure regenerative heater 8 via a pipeline through the condensate pump 7. The condensate outlet of the low-pressure regenerative heater 8 is connected to the condensate inlet of the deaerator 9 via a pipeline. The feedwater outlet of the deaerator 9 is connected to the feedwater inlet of the high-pressure regenerative heater 11 via the feedwater pump 10 via a pipeline. The feedwater outlet of the high-pressure regenerative heater 11 is connected to the feedwater inlet of the boiler 1. The inlets are connected via pipelines. The extraction port of the ultra-high pressure cylinder 2 is connected to the extraction inlet of the high-pressure regenerative heater 11 via a pipeline. The extraction port of the high-pressure cylinder 3 is connected to the extraction inlet of the high-pressure regenerative heater 11 via a pipeline. The first-stage extraction port of the intermediate-pressure cylinder 4 is connected to the extraction inlet of the high-pressure regenerative heater 11 via a pipeline. The second-stage extraction port of the intermediate-pressure cylinder 4 is connected to the extraction inlet of the deaerator 9 via a pipeline. The remaining extraction ports of the intermediate-pressure cylinder 4 are connected to the extraction inlet of the low-pressure regenerative heater 8 via pipelines. The extraction port of the low-pressure cylinder 5 is connected to the low-pressure regenerative heater 8. The extraction steam inlet is connected via a pipeline; the medium-temperature energy storage system consists of an extraction steam regulating valve 13, an energy storage tank 12, a pressure relief valve 14, and a feedwater regulating valve 15. During energy storage, the exhaust outlet of the high-pressure cylinder 3 is connected to the steam inlet of the energy storage tank 12 via the extraction steam regulating valve 13, and the steam outlet of the energy storage tank 12 is connected to the steam inlet of the low-pressure cylinder 5 via the pressure relief valve 14. During energy release, the feedwater outlet of the deaerator 9 is connected to the water inlet of the energy storage tank 12 via the feedwater regulating valve 15, and the steam outlet of the energy storage tank 12 is connected to the steam inlet of the low-pressure cylinder 5 via a pipeline.

[0062] 2. Material selection for energy storage tank 12

[0063] The exhaust temperature range of the high-pressure cylinder of the case unit is 446~455℃, the inlet steam temperature range of the low-pressure cylinder is 317~333℃, and the selected phase change energy storage material is KNO3, whose melting temperature is 330℃.

[0064] 3. Control methods for the load reduction process, such as Figure 2 As shown

[0065] ① The operator designs the extraction ratio Ra of the high-pressure cylinder exhaust based on the axial thrust and variable load requirements. h ;

[0066] ② Calculate the exhaust steam extraction rate G of the high-pressure cylinder h

[0067] G h =G h,s ·Ra h

[0068] Where: G h,s The high-pressure cylinder exhaust setting value, which is related to the original overall power output of the boiler and turbine in the secondary reheat unit, was obtained from the design document of the case unit, and is kg / s.

[0069] ③ Calculate the decrease in work Pe caused by steam extraction. h

[0070] Pe h =G h ·f(Pe 0,d )

[0071] Where: Pe0 is the original total work done by the secondary reheat unit during the load reduction process, f(Pe 0,d The value represents the change in the overall work done by the secondary reheat unit after the high-pressure cylinder exhaust steam is cooled and sent to the low-pressure cylinder inlet, which is related to the original overall work done by the boiler and turbine. It is obtained through the high-pressure cylinder exhaust steam disturbance test, kW / (kg / s).

[0072] ④ Calculate the real-time value K of the opening degree of the extraction steam regulating valve 13. h,13,rt

[0073]

[0074] K h,13,rt =K h,13 +f PID (Pe 0,d Pe rt Pe h )

[0075] Where: K h,13 k is the design value for the opening degree of the extraction steam regulating valve 13. v,13 The resistance coefficient s is the connecting pipe between the outlet of high-pressure cylinder 3 and energy storage tank 12. 2 ·MPa / (kg·m 3 );ρ h The exhaust gas density of the high-pressure cylinder is kg / m³. 3 ;Δp 13 The pressure difference between high-pressure cylinder 3 and energy storage tank 12 is expressed in MPa and K. h,13,rt f is the real-time value of the opening degree of the extraction steam regulating valve 13; PIDThis is the correction value for the opening of the extraction steam regulating valve 13 obtained through PID control using real-time work deviation; where the real-time work deviation is the sum of the real-time work output of the secondary reheat unit and the work reduction caused by steam extraction, minus the original planned overall work output of the secondary reheat unit and boiler; Pe rt Real-time power output of the secondary reheat unit, kW; Pe 0,d The original total power output of the secondary reheat unit during load reduction is kW.

[0076] ⑤ The calculation process for the original total work done by the secondary reheat unit during load reduction is as follows:

[0077] t s0 =(Pe2-Pe1) / rate0.60

[0078]

[0079] In the formula: t s0 Pe1 is the time (in seconds) for the secondary reheat unit to reach the target load from the initial load under the original variable load rate; Pe2 is the initial load of the secondary reheat unit (kW); Pe3 is the target load of the secondary reheat unit (kW); and rate0 is the original variable load rate of the secondary reheat unit (kW / min).

[0080] ⑥ The calculation process for the actual time for the double reheat unit to reach the target load is as follows:

[0081]

[0082] In the formula: t s,down This refers to the actual time it takes for the unit to reach the target load during the load reduction process.

[0083] ⑦ The reduction in time Δt of the actual time for the secondary reheat unit to reach the target load during the load reduction process. down for:

[0084] Δt down =t s0 -t s,down .

[0085] 4. Control methods for the load increase process, such as Figure 2 As shown

[0086] ① Calculate the extraction flow rate G of the deaerator outlet feedwater based on the extraction ratio during the load reduction process. d The enthalpy of the working fluid involved in the calculation process is obtained by measuring the temperature and pressure of the working fluid at the corresponding temperature and pressure measuring points of the case unit and then processing it through a steam property program.

[0087]

[0088] Where: Gh,o The setpoint for high-pressure cylinder exhaust steam under a certain operating condition, kg / s; h h,o h l,o h d,o , respectively, are the enthalpy values ​​of the high-pressure cylinder exhaust steam, the low-pressure cylinder inlet working fluid, and the deaerator outlet working fluid under a certain operating condition, in kJ / kg; f1 is a correction coefficient less than 1 related to the heat exchange efficiency and heat dissipation loss of the energy storage tank.

[0089] ② Calculate the correction value G for condensate flow rate cond,xz

[0090] G cond,xz =G cond,s +G d

[0091] Where: G cond,s The condensate flow rate setpoint, which is related to the original overall power output of the boiler and turbine of the secondary reheat unit, was obtained from the design document of the case unit, in kg / s.

[0092] ③ Calculate the increase in work Pe caused by the steam generated by the energy storage tank (12). d

[0093] Pe d =G d ·(f d (Pe 0,u )-f c (Pe 0,u ))

[0094] In the formula: f d (Pe 0,u ) represents the increase in work done by the working fluid entering the low-pressure cylinder per unit mass flow rate, related to the original overall work done by the boiler and turbine, expressed in kW / (kg / s); f c (Pe 0,u ) represents the reduction in the power output of the secondary reheat unit after the increase in the unit mass flow rate of condensate related to the original overall power output of the boiler and turbine, expressed in kW / (kg / s).

[0095] ④ Calculate the real-time value of the water supply regulating valve opening at 15 degrees.

[0096]

[0097] K h,15,rt =K h,15 +g PID (Pe 0,u Pe rt Pe d )

[0098] Where: K h,15 This is the design value for the water supply regulating valve opening of 15 degrees; kv,15 The resistance coefficient, s, is the connecting pipe between the deaerator 9 (outlet) and the energy storage tank 12. 2 ·MPa / (kg·m 3 );ρ d The feedwater density at the deaerator outlet is kg / m³. 3 ;Δp 15 The pressure difference between deaerator 9 and energy storage tank 12 is expressed in MPa and K. h,15,rt This is the real-time value of the water supply regulating valve opening at 15 degrees; g PID This is a correction value for the opening of the feedwater regulating valve 15 obtained through PID control using real-time work deviation; where the real-time work deviation is the real-time work of the secondary reheat unit minus the original planned overall work of the secondary reheat unit and the increase in work caused by the steam generated by the energy storage tank 12; Pe 0,u The total power output of the secondary reheat unit during the load increase process is the original total power output of the boiler and turbine, in kW.

[0099] ⑤ The calculation process for the original total work done by the secondary reheat unit during the load increase process is as follows:

[0100] t s0 =(Pe2-Pe1) / rate0.60

[0101]

[0102] In the formula: t s0 Pe1 is the time (in seconds) for the secondary reheat unit to reach the target load from the initial load under the original variable load rate; Pe2 is the initial load of the secondary reheat unit (kW); Pe3 is the target load of the secondary reheat unit (kW); and rate0 is the original variable load rate of the secondary reheat unit (kW / min).

[0103] ⑥ The calculation process for the actual time for the secondary reheat unit to reach the target load during the load increase process is as follows:

[0104]

[0105] In the formula: t s,up The time, in seconds, is the actual time for the secondary reheat unit to reach the target load during the load increase process.

[0106] ⑦ The reduction in the actual time Δt for the secondary reheat unit to reach the target load during the load increase process. up for:

[0107] Δt up =t s0 -t s,up .

[0108] 5. Optimization effect of the case unit

[0109] Figure 3This is a comparison chart of the response time of the secondary reheat unit during load reduction. It can be seen that the unit response time decreased by 204 seconds.

[0110] Figure 4 This is a comparison chart of the response time of the secondary reheat unit during load increase. It can be seen that the unit response time has been reduced by 44 seconds.

[0111] In summary, the coupling system and control method for variable load operation of secondary reheat units proposed in this invention through medium-temperature energy storage can significantly shorten the unit response time and greatly improve the variable load performance of secondary reheat units.

Claims

1. A coupling system for load change of a secondary reheat unit assisted by medium-temperature energy storage, characterized in that: The coupling system includes a secondary reheat unit and a medium-temperature energy storage system; in the secondary reheat unit, the superheated steam outlet of boiler (1) is connected to the steam inlet of ultra-high pressure cylinder (2) through a pipeline, the exhaust outlet of ultra-high pressure cylinder (2) is connected to the primary cold reheat steam inlet of boiler (1) through a pipeline, the primary hot reheat steam outlet of boiler (1) is connected to the steam inlet of high pressure cylinder (3) through a pipeline, the exhaust outlet of high pressure cylinder (3) is connected to the secondary cold reheat steam inlet of boiler (1) through a pipeline, the secondary hot reheat steam outlet of boiler (1) is connected to the steam inlet of intermediate pressure cylinder (4) through a pipeline, and the intermediate pressure cylinder (4)... The exhaust outlet is connected to the steam inlet of the low-pressure cylinder (5) via a pipeline. The exhaust outlet of the low-pressure cylinder (5) is connected to the exhaust inlet of the condenser (6) via a pipeline. The condensate outlet of the condenser (6) is connected to the condensate inlet of the low-pressure regenerative heater (8) via a condensate pump (7). The condensate outlet of the low-pressure regenerative heater (8) is connected to the condensate inlet of the deaerator (9) via a pipeline. The feedwater outlet of the deaerator (9) is connected to the feedwater inlet of the high-pressure regenerative heater (11) via a feedwater pump (10). The feedwater outlet of the high-pressure regenerative heater (11) is connected to the feedwater inlet of the boiler (1) via a pipeline. The extraction port of the ultra-high pressure cylinder (2) is connected to the extraction inlet of the high-pressure regenerative heater (11) through a pipe; the extraction port of the high-pressure cylinder (3) is connected to the extraction inlet of the high-pressure regenerative heater (11) through a pipe; the first-stage extraction port of the intermediate-pressure cylinder (4) is connected to the extraction inlet of the high-pressure regenerative heater (11) through a pipe; the second-stage extraction port of the intermediate-pressure cylinder (4) is connected to the extraction inlet of the deaerator (9) through a pipe; the remaining extraction ports of the intermediate-pressure cylinder (4) are connected to the extraction inlet of the low-pressure regenerative heater (8) through a pipe; and the extraction port of the low-pressure cylinder (5) is connected to the extraction inlet of the low-pressure regenerative heater (8) through a pipe. The medium-temperature energy storage system consists of a steam extraction regulating valve (13), an energy storage tank (12), a pressure relief valve (14), and a feedwater regulating valve (15). During the energy storage process, the exhaust outlet of the high-pressure cylinder (3) is connected to the steam inlet of the energy storage tank (12) through the steam extraction regulating valve (13), and the steam outlet of the energy storage tank (12) is connected to the steam inlet of the low-pressure cylinder (5) through the pressure relief valve (14). During the energy release process, the feedwater outlet of the deaerator (9) is connected to the water inlet of the energy storage tank (12) through the feedwater regulating valve (15), and the steam outlet of the energy storage tank (12) is connected to the steam inlet of the low-pressure cylinder (5) through a pipeline.

2. The coupling system for load change of a secondary reheat unit assisted by medium-temperature energy storage as described in claim 1, characterized in that: The energy storage tank (12) uses phase change energy storage material. The selection method for phase change energy storage material comprehensively considers the outlet temperature of the high-pressure cylinder, the inlet temperature of the low-pressure cylinder, and the melting temperature of the phase change energy storage material.

3. The control method for a coupled system of a secondary reheat unit with variable load assisted by medium-temperature energy storage as described in claim 1 or 2, characterized in that: During the load reduction process, the medium-temperature energy storage system is in the energy storage process. By controlling the opening of the extraction steam regulating valve (13), part of the high-pressure cylinder exhaust steam is sent into the energy storage tank (12) for heat release. The working fluid after heat release is sent into the low-pressure cylinder inlet through the pressure relief valve (14), thereby reducing the work done by the secondary reheat unit. That is, the real-time work done by the whole unit is the difference between the original planned overall work done by the secondary reheat unit and the work reduction caused by steam extraction, which shortens the time for the secondary reheat unit to actually reach the target load. During the load increase process, the medium-temperature energy storage system is in the energy release process. By controlling the opening of the feedwater regulating valve (15), part of the deaerator outlet feedwater is sent into the energy storage tank (12), and the working fluid after heat absorption is sent into the low-pressure cylinder inlet, thereby increasing the work done by the secondary reheat unit. That is, the real-time work done by the whole unit is the sum of the original planned overall work done by the secondary reheat unit and the steam work done by the energy storage tank (12), which shortens the time for the secondary reheat unit to actually reach the target load.

4. The control method for a coupled system of a secondary reheat unit with variable load assisted by medium-temperature energy storage as described in claim 3, characterized in that: The calculation process for the opening degree of the extraction steam regulating valve (13) during the load reduction process is as follows: ① The operator designs the extraction ratio of the high-pressure cylinder exhaust based on the axial thrust and variable load requirements. Ra h ; ② Calculate the exhaust steam extraction rate of the high-pressure cylinder G h In the formula: G h,s The high-pressure cylinder exhaust setting value, kg / s, is related to the original overall work output of the boiler and turbine. ③ Calculate the decrease in work caused by steam extraction. Pe h In the formula: Pe 0,d The original total power output of the secondary reheat unit during load reduction is kW; f ( Pe 0,d ) represents the change in the work done by the secondary reheat unit after the high-pressure cylinder exhaust steam is cooled and sent to the low-pressure cylinder inlet, which is related to the original overall work done by the boiler and turbine of the secondary reheat unit, in kW / (kg / s). ④ Calculate the real-time value of the opening degree of the extraction steam regulating valve (13). K h,13,rt In the formula: K h,13 The design value for the opening of the extraction steam regulating valve (13); k v,13 The resistance coefficient of the pipe connecting the outlet of the high-pressure cylinder (3) and the energy storage tank (12) is s. 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 (3) and the energy storage tank (12) is expressed in MPa. K h,13,rt This is the real-time value of the opening degree of the extraction steam regulating valve (13); f PID The correction value of the opening of the extraction steam regulating valve (13) obtained by PID control using the real-time work deviation is the sum of the real-time work of the secondary reheat unit and the work reduction caused by extraction, minus the original total work of the secondary reheat unit. Pe rt The real-time power output of the secondary reheat unit is expressed in kW. Pe 0,d The original total power output of the secondary reheat unit during load reduction is kW.

5. The control method for a coupled system of a secondary reheat unit with load variation assisted by medium-temperature energy storage as described in claim 3, characterized in that: The calculation process for the original overall work done by the secondary reheat unit during the load reduction process is as follows: In the formula: t s0 The time, in seconds, for the secondary reheat unit to reach the target load from the initial load under the original variable load rate; Pe 1 represents the initial load of the double reheat unit, in kW; Pe 2 represents the target load for the secondary reheat unit, in kW; rate 0 represents the original variable load rate of the double reheat unit, in kW / min; Pe 0,d The original total power output of the secondary reheat unit during load reduction is kW.

6. The control method for a coupled system of a secondary reheat unit with load variation assisted by medium-temperature energy storage as described in claim 3, characterized in that: The calculation process for the actual time it takes for the secondary reheat unit to reach the target load during the load reduction process is as follows: In the formula: t s,down The time, in seconds, is the actual time for the secondary reheat unit to reach the target load during the load reduction process.

7. The control method for a coupled system of a secondary reheat unit with load variation assisted by medium-temperature energy storage as described in claim 3, characterized in that: The reduction in the time it takes for the secondary reheat unit to actually reach the target load during the load reduction process. for: 。 8. The control method for a coupled system of a secondary reheat unit with load variation assisted by medium-temperature energy storage as described in claim 3, characterized in that: The calculation process for the opening degree of the water supply regulating valve (15) during the load increase process is as follows: ① Calculate the deaerator outlet feedwater extraction flow rate based on the extraction ratio during the load reduction process. G d In the formula: G h,o The setpoint for high-pressure cylinder exhaust steam under a certain operating condition, in kg / s; h h,o , h l,o , h d,o These are the enthalpy values ​​of the high-pressure cylinder exhaust steam, the low-pressure cylinder inlet working fluid, and the deaerator outlet working fluid under a certain operating condition, respectively, in kJ / kg; f 1 is a correction factor less than 1 related to the heat exchange efficiency and heat loss of the energy storage tank; ② Calculate the correction value for condensate flow rate G cond,xz In the formula: G cond,s The condensate flow rate setpoint, kg / s, is related to the original overall work output of the secondary reheat unit. ③ Calculate the increase in work done caused by the steam generated by the energy storage tank (12). Pe d In the formula: f d ( Pe 0,u The unit mass flow rate of the working fluid entering the low-pressure cylinder represents the additional work done by the working fluid after it enters the low-pressure cylinder, which is related to the original overall work done by the boiler and turbine of the secondary reheat unit. It is expressed as kW / (kg / s). f c ( Pe 0,u ) represents the reduction in the power output of the secondary reheat unit after the increase in the unit mass flow rate of condensate related to the original overall power output of the boiler and turbine, expressed in kW / (kg / s). ④ Calculate the real-time value of the opening degree of the water supply regulating valve (15). In the formula: K h,15 The design value for the opening of the water supply regulating valve (15); k v,15 The resistance coefficient of the pipe connecting the deaerator (9) outlet and the energy storage tank (12) is s. 2 ·MPa / (kg·m 3 ); The feedwater density at the deaerator outlet is kg / m³. 3 ; The pressure difference between the deaerator (9) and the energy storage tank (12) is expressed in MPa. K h,15,rt The real-time value of the opening degree of the water supply regulating valve (15); g PID The correction value of the opening of the feedwater regulating valve (15) obtained by PID control using the real-time work deviation; wherein the real-time work deviation is the real-time work of the secondary reheat unit minus the original planned overall work of the secondary reheat unit minus the increase in work caused by the steam generated by the energy storage tank (12); Pe 0,u The total power output of the secondary reheat unit during the load increase process is the original total power output of the boiler and turbine, in kW.

9. The control method for a coupled system of a secondary reheat unit with load variation assisted by medium-temperature energy storage as described in claim 3, characterized in that: The calculation process for the original overall work done by the secondary reheat unit during the load increase process is as follows: In the formula: t s0 The time, in seconds, for the secondary reheat unit to reach the target load from the initial load under the original variable load rate; Pe 1 represents the initial load of the double reheat unit, in kW; Pe 2 represents the target load for the secondary reheat unit, in kW; rate 0 represents the original variable load rate of the secondary reheat unit, in kW / min.

10. The control method for a coupled system of a secondary reheat unit with load variation assisted by medium-temperature energy storage as described in claim 3, characterized in that: The calculation process for the actual time it takes for the secondary reheat unit to reach the target load during the load increase process is as follows: In the formula: t s,up The actual time (in seconds) for the secondary reheat unit to reach the target load during the load increase process; The reduction in the time it takes for the secondary reheat unit to actually reach the target load during the load increase process. for: 。

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