Multi-mode control method for bypass system of thermal power unit in response to power grid load demand

Abstract

The bypass system multi-mode control method of the thermal power generating unit responding to the power grid load demand comprises: a bypass control mode is a normal starting mode, and the normal starting mode is used when the unit is normally started. When the unit is normally started, the boiler resets the MFT and then the high bypass automatic is put into use, the minimum pre-opening degree of the high-pressure bypass valve is 6%, and the minimum pre-opening degree of the low-pressure bypass valve is 10%. The method specifically comprises: 1) high bypass pressure reducing valve control, 2) bypass valve control, 3) low bypass pressure reducing valve control, and 4) high and low bypass temperature reducing valve control. The application creates a control strategy for intelligent adaptation of the whole process of the bypass system, implements flexible and efficient operation of the bypass system as the main line, ensures the safe and stable operation of the steam turbine bypass, and is suitable for all thermal power generating units with daily starting and peak shaving.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of intelligent control of thermal power generating units, and particularly relates to a multi-mode control method for a bypass system of a thermal power generating unit in response to load demand of a power grid. BACKGROUND

[0002] As the leading power plant in the conventional power industry, the installed capacity of the thermal power plant is gradually decreasing, and the growth rate continues to decrease. The installed capacity of clean energy units such as wind power, solar power, and solar-thermal power continues to increase. However, as the installed capacity of clean energy units increases, the rate of abandoned wind, light, and water also continues to increase year by year. In order to further reduce the rate of abandoned light, wind, and water in the power grid, according to the current power source structure in the power grid, while ensuring the safe and stable operation of the power grid, the thermal power generating unit, especially the large-capacity unit, must have a deep peaking capacity. That is, during the process of power grid peaking, the unit load must be reduced to below 50%, and the safe and stable operation of the unit must be ensured, and the full load can be received at any time. The above requirements have brought many difficulties and dangers to coal-fired power plants, for example: unstable low-load combustion of the boiler, insufficient water power in the water-cooled wall, possible wet-state operation of the unit, uncontrollable or even exceeding environmental protection parameters, and single-sided operation of auxiliary equipment. The above series of safety problems must be solved, therefore, the research on the flexible peaking of the thermal power generating unit has far-reaching significance for the development of the thermal power industry in the future.

[0003] The power grid has increasingly high requirements for the peaking capacity of the operating unit. Compared with new energy and other power sources, coal power has good peaking performance. The increasingly significant peak-valley difference of the power grid requires large-capacity units to have strong peaking capacity, therefore, the role of the unit bypass system is increasingly prominent. Continuous optimization of the bypass system is required to adapt to the requirements of peaking, meet deep peaking operation, and improve the safety of the unit operation, which is of great significance to the safe and stable operation of the power grid. SUMMARY

[0004] In view of the above problems, the purpose of the present application is to provide a multi-mode distribution control method for a bypass system in response to flexible peaking requirements.

[0005] The present application is realized by adopting the following technical solutions:

[0006] The multi-mode control method for the bypass system of the thermal power generating unit in response to the load demand of the power grid comprises:

[0007] The bypass control mode is a normal starting mode, and the normal starting mode is used when the unit is normally started;

[0008] When normally started, the boiler resets the MFT and inputs the high bypass automatic, and the minimum pre-opening degree of the high-pressure bypass valve is 6%, and the minimum pre-opening degree of the low-pressure bypass valve is 10%;

[0009] The method specifically comprises: 1) high bypass pressure reducing valve control, 2) bypass valve control, 3) low bypass pressure reducing valve control, and 4) high and low bypass temperature reducing valve control.

[0010] The further improvement of the application is that the steam turbine to which the method is applied is a super-supercritical, once intermediate reheated, four-cylinder four-steam, single-shaft, double-back pressure and extraction condensing steam turbine.

[0011] The further improvement of the application is that the unit startup bypass system is composed of two-stage series bypass systems of high pressure bypass and low pressure bypass.

[0012] The further improvement of the application is that 1) high bypass pressure reducing valve control comprises:

[0013] (1) minimum pressure control stage: high bypass is automatic, the minimum pre-opening degree of the high pressure bypass valve is 6%, as the evaporation capacity of the boiler increases, when the high bypass front pressure reaches 0.6 MPa, the high bypass valve is gradually increased from the minimum opening degree to 10% after being put into automatic opening, when the main steam pressure is less than 1 MPa, the bypass operation mode is minimum pressure control, at this time, the main steam pressure set value is 1 MP;

[0014] (2) pressure increasing control mode: when the high bypass front pressure is greater than 1.0 MPa, the pressure increasing control mode is entered, as the main steam pressure increases, the high bypass valve is gradually opened, and the main steam pressure is basically maintained at 1 MPa, when the high pressure bypass opening degree is greater than 40%, the main steam pressure set value is gradually increased, and the main steam pressure is basically maintained at 8.5 MPa to increase the rotation pressure;

[0015] (3) constant pressure control mode: when the main steam pressure reaches the rotation pressure 8.5 MPa, the constant pressure control mode is entered, at this time, the valve is automatically maintained at the rotation pressure set value; before reaching the rotation pressure, the constant pressure control mode is switched by the operator;

[0016] restarting mode: when the boiler MFT and the high bypass valve is closed, the restarting mode is entered, when any oil gun is put into operation or any coal feeder is operated, the restarting mode is switched to the normal starting mode;

[0017] In the unit rotation and grid-connected initial load stage, the high bypass pressure reducing valve controls the main steam pressure to ensure the stability of the steam turbine inlet pressure, as the unit load increases and the steam turbine inlet flow increases, the high bypass valve is gradually closed until it is fully closed, and the high bypass valve enters the following mode, at this time, the pressure set value is the actual pressure value plus a 0.5 MPa bias to ensure that the valve is fully closed.

[0018] The further improvement of the application is that when the valve is automatically maintained at the rotation pressure set value, the operator can also set the pressure value.

[0019] The further improvement of the present application is that 2) bypass valve control comprises:

[0020] Meanwhile, the organic group pressure relief function is designed, if the bypass valve is in the automatic state, when the main steam pressure exceeds the set pressure, the high bypass valve will be automatically opened to control the main steam pressure not to exceed the pressure; in the automatic state, if the generator is tripped but the boiler is not tripped, the minimum opening degree of the bypass valve after the tripping is automatically set to 50%, the bypass valve is kept in the opened state to protect the reheater, and if the steam turbine is not tripped, the steam turbine speed or the non-boiler shutdown operation condition can be maintained.

[0021] The further improvement of the present application is that the set pressure value of the main steam pressure exceeds 26.5 MPa.

[0022] The further improvement of the present application is that 3) low bypass pressure reducing valve control comprises:

[0023] In the automatic condition of the low bypass input, when the MFT is reset, the low bypass valve is opened to 10% minimum opening degree, after the boiler is ignited, with the rise of the reheated steam pressure, the low bypass valve is gradually opened and the reheated steam pressure is maintained as the reheated steam pressure set value, when the high bypass is in the pressure rising stage, the reheated steam pressure set value is automatically set according to the reheated steam pressure demand corresponding to the superheated steam pressure;

[0024] When the high bypass pressure rising stage is over, the reheated steam pressure set value is automatically set according to the reheated steam pressure demand corresponding to the unit load;

[0025] After the unit is connected to the grid, with the gradually increased load of the steam turbine, the intermediate regulating valve is gradually opened, in order to maintain the reheated steam pressure, the low pressure bypass valve is gradually closed, when both sides of the low bypass valve are closed, the low bypass control is converted into the following mode, at this time, the reheated steam pressure set value is "actual reheated steam pressure+0.5" to ensure that the low bypass valve is in the closed state, at the same time, when the actual reheated steam pressure exceeds "reheated steam pressure corresponding to the unit load+0.5 MPa", the low bypass valve is gradually opened through the regulating loop to prevent the reheater from overpressure;

[0026] When the generator is tripped or the steam turbine is tripped, if the MFT does not occur, the low bypass valve will be quickly opened to 50% through the regulating loop and converted into pressure regulation, the pressure set value is the reheated steam pressure before the generator is tripped or the steam turbine is tripped, and when the low bypass is quickly opened, the high bypass desuperheating water is also quickly opened to 50% and converted into temperature regulation.

[0027] The further improvement of the present application is that 4) high and low bypass desuperheating valve control comprises:

[0028] The high bypass desuperheating valve controls the high bypass outlet temperature, the set value is 360 DEG C, and the operator can bias; the low bypass desuperheating valve controls the low bypass outlet temperature, which is set by the operator.

[0029] The present application has at least the beneficial technical effects:

[0030] The present invention discloses a multi-mode control method for the bypass system of thermal power units that responds to grid load demand. By creating a control strategy that is intelligently adapted to the entire process of the bypass system, it adheres to the principle of flexible and efficient operation of the bypass system as the main line, ensuring the safe and stable operation of the turbine bypass, and is applicable to all thermal power units that "start up and shaving within the day". Attached Figure Description

[0031] Figure 1 A flowchart of a multi-mode control method for a thermal power unit bypass system in response to grid load demand.

[0032] Figure 2 The load increase curve is shown in the embodiment of the present invention, which is 330MW→380MW→520MW→660MW, at 12MW / min.

[0033] Figure 3 The load reduction curves for 660MW→520MW→380MW→330MW at 12MW / min are shown in this embodiment of the invention. Detailed Implementation

[0034] Exemplary embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the invention to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0035] like Figure 1 As shown, the multi-mode control method for a thermal power unit bypass system responding to grid load demand provided by the present invention includes:

[0036] The application scope is for ultra-supercritical, single-stage reheat, four-cylinder, four-exhaust, single-shaft, dual-backpressure, extraction condensing steam turbines. The unit startup bypass system consists of a two-stage series bypass system: a high-pressure bypass and a low-pressure bypass, with two low-pressure bypasses. The high-pressure bypass system consists of a high-pressure bypass valve, a water spray regulating valve, and a water spray isolation valve, while the low-pressure bypass system consists of low-pressure bypass valves on both sides (A and B), a water spray regulating valve, and a water spray isolation valve. The bypass capacity is designed for a 37% BMCR main steam flow rate to meet the unit startup requirements.

[0037] The bypass control mode is the normal start-up mode. The normal start-up mode is used during normal unit startup.

[0038] Normal start-up, boiler reset MFT after the high bypass automatic, high pressure bypass valve minimum pre-opening 6%, low pressure bypass valve minimum pre-opening 10%.

[0039] 1) High bypass pressure reducing valve control

[0040] (1) Minimum pressure control phase: high bypass automatic, high pressure bypass valve minimum pre-opening 6%, as the boiler evaporation capacity increases, when the high bypass front pressure reaches 0.6 MPa, the high bypass valve is automatically opened after the opening is also gradually increased from the minimum opening (6%) to 10%, when the main steam pressure is less than 1 MPa, the bypass operation mode is the minimum pressure control, at this time the main steam pressure set value is 1 MP.

[0041] (2) Pressure increasing mode: when the high bypass front pressure is greater than 1.0 MPa, enter the pressure increasing mode, as the main steam pressure rises, the high bypass valve gradually opens, basically maintaining the main steam pressure at 1 MPa, when the high pressure bypass opening > 40%, the main steam pressure set value gradually increases, basically maintaining the high bypass opening at about 40% to increase the main steam pressure to 8.5 MPa.

[0042] (3) Constant pressure control mode: when the main steam pressure reaches the 8.5 MPa, enter the constant pressure mode, at this time, the valve automatically maintains the pressure set value at the rated pressure (or the operator sets the pressure value). Before reaching the rated pressure, it can also be switched to constant pressure mode by the operator.

[0043] Restart mode: when the boiler MFT and the high bypass valve is closed, enter the restart mode. When any oil gun is in operation or any coal feeder is running, the restart mode is converted to the normal start-up mode.

[0044] During the unit's start-up and synchronization with initial load, the high bypass pressure reducing valve controls the main steam pressure to ensure the stability of the turbine inlet pressure. As the unit load increases and the turbine inlet flow increases, the high bypass valve gradually closes until it is fully closed, and the high bypass valve enters the following mode, at this time the pressure set value is the actual pressure value plus a 0.5 MPa bias to ensure that the valve is fully closed.

[0045] 2) Bypass valve control

[0046] At the same time, the unit pressure relief function is designed. If the bypass valve is in automatic state, when the main steam pressure exceeds 26.5 MPa (which can be modified according to the actual needs of the power plant), the high bypass valve will automatically open to control the main steam pressure not to overpressure; in the automatic state, if the generator is de-energized but the boiler is not tripped, the minimum opening of the bypass valve is automatically set to 50% after de-energization to keep the bypass valve open to protect the reheater, and if the turbine is not tripped, it can assist in maintaining the turbine speed or operating in the condition of stopping the boiler.

[0047] 3) Low bypass pressure reducing valve control

[0048] In the case of low bypass input automatically, when MFT is reset, the low bypass valve opens to 10% minimum opening, after the boiler is ignited, with the rise of the reheated steam pressure, the low bypass valve gradually opens and maintains the reheated steam pressure as the reheated steam pressure set value, when the high bypass is in the pressure rising stage, the reheated steam pressure set is automatically set according to the reheated steam pressure requirement corresponding to the superheated steam pressure, see Table 1 as follows.

[0049] Table 1 reheated steam pressure set value corresponding to superheated steam pressure

[0050] Superheated steam pressure (unit: MPa) 0 8.5 Reheated steam pressure (unit: MPa) 0 1.2

[0051] When the high bypass pressure rising stage is over, the reheated steam pressure set is automatically set according to the reheated steam pressure requirement corresponding to the unit load, see Table 2.

[0052] Table 2 reheated steam pressure set value corresponding to superheated steam pressure

[0053]

[0054] After the unit is connected to the grid, with the gradual increase of the turbine load, the intermediate regulating valve gradually opens, in order to maintain the reheated steam pressure, the low pressure bypass valve gradually closes, when both sides of the low bypass valve are closed, the low bypass control turns to the following mode, at this time the reheated steam pressure set value is "actual reheated steam pressure + 0.5" to ensure that the low bypass valve is in the closed state, at the same time, when the actual reheated steam pressure exceeds "reheated steam pressure corresponding to unit load + 0.5 MPa", the low bypass valve gradually opens through the regulating loop to prevent the reheater from overpressure.

[0055] When the generator is out of step or the turbine is tripped, if MFT does not occur, the low bypass valve will quickly open to 50% through the regulating loop and turn to pressure regulation, the pressure set is the reheated steam pressure before the generator is out of step or the turbine is tripped. When the low bypass is quickly opened, the high bypass desuperheating water is also quickly opened to 50% and turns to temperature regulation.

[0056] 4) High and low bypass desuperheating valve control

[0057] The high bypass desuperheating valve controls the high bypass outlet temperature, the set value is 360℃, and the operator can bias; the low bypass desuperheating valve controls the low bypass outlet temperature, which is set by the operator.

[0058] It should be noted that when the high and low bypass valves are closed, the corresponding desuperheating valve is closed and locked open, the low bypass desuperheating valve override signal needs to be changed to pulse command, that is, after the low bypass pressure reducing valve is closed, the low bypass desuperheating valve can still be opened to prevent the condenser from overtemperature.

[0059] In this example, the unit uses a load change rate of 12 MW / min to increase the load, with load change amplitudes of 50 MW, 140 MW, and 140 MW respectively. During the load change process, the maximum deviation of the main steam pressure is 0.84 MPa, and the maximum deviation of the unit load is -4.2 MW. Other control parameters are shown in Table 3, and the load change process curve is shown in [Table 3]. Figure 2 .

[0060] Table 3. Load variation test data at 12MW / min for 330MW→380MW→520MW→660MW.

[0061]

[0062] like Figure 2 As shown: 1-Load command: 0MW~700MW; 2-Actual power generation: 0MW~700MW; 3-Main steam pressure setpoint: 2MPa~28MPa; 4-Main steam pressure: 2MPa~28MPa; 5-Load change rate: 0MW / min~100MW / min; 6-Superheated steam temperature: 0℃~600℃; 7-Separator outlet superheat: 0℃~200℃; 8-Reheated steam temperature: 0℃~600℃; 9-Oxygen content: 0%~21%; 10-Total fuel quantity: 50t / h-400t / h; 11-Boiler feedwater flow rate: 800t / h~2500t / h; 12-Furnace pressure: -1000Pa~2000Pa.

[0063] The unit adopted a load change rate of 12 MW / min to reduce load, with load change ranges of 140 MW, 140 MW, and 50 MW. During the load change process, the maximum deviation of the main steam pressure was 0.91 MPa, and the maximum deviation of the unit load was +10.8 MW. Other control parameters are shown in Table 4, and the load change process curves are shown in [Table 4]. Figure 3 .

[0064] Table 4. Test data for load variation at 12MW / min from 660MW to 520MW to 380MW to 330MW.

[0065]

[0066] like Figure 3As shown: 1-Load command: 0MW~700MW; 2-Actual power generation: 0MW~700MW; 3-Main steam pressure setpoint: 2MPa~28MPa; 4-Main steam pressure: 2MPa~28MPa; 5-Load change rate: 0MW / min~100MW / min; 6-Superheated steam temperature: 0℃~600℃; 7-Separator outlet superheat: 0℃~200℃; 8-Reheated steam temperature: 0℃~600℃; 9-Oxygen content: 0%~21%; 10-Total fuel quantity: 50t / h-400t / h; 11-Boiler feedwater flow rate: 800t / h~2500t / h; 12-Furnace pressure: -1000Pa~2000Pa.

[0067] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A multi-mode control method for a thermal power unit bypass system responding to grid load demand, characterized in that, include: The bypass control mode is the normal start-up mode, which is used during normal unit startup. During normal startup, after the boiler resets the MFT (Mechanical Fuel Transfer), the high-pressure bypass valve is automatically activated. The minimum pre-opening degree of the high-pressure bypass valve is 6%, and the minimum pre-opening degree of the low-pressure bypass valve is 10%. This method specifically includes: 1) High-pressure bypass pressure reducing valve control, including: (1) Minimum pressure control stage: High pressure bypass is automatic, and the minimum pre-opening degree of the high pressure bypass valve is 6%. As the boiler evaporation rate increases, when the pressure before the high pressure bypass reaches 0.6MPa, the opening degree of the high pressure bypass valve after automatic operation also gradually increases from the minimum opening degree to 10%. When the main steam pressure is less than 1MPa, the bypass operation mode is minimum pressure control, and the main steam pressure setting value is 1MPa. (2) Pressure boosting control mode: When the pressure before the high pressure bypass is greater than 1.0MPa, the pressure boosting mode is entered. As the main steam pressure increases, the high pressure bypass valve gradually opens, basically maintaining the main steam pressure at 1MPa. When the high pressure bypass opening is greater than 40%, the main steam pressure setting value is gradually increased, basically maintaining the high pressure bypass opening at about 40% to increase the main steam pressure to the starting pressure of 8.5MPa. (3) Constant pressure control mode: When the main steam pressure reaches the starting pressure of 8.5MPa, it enters constant pressure mode. At this time, the regulating valve automatically maintains the pressure set value at the starting pressure. Before the starting pressure is reached, the operator switches to constant pressure mode. Restart mode: When the boiler is in MFT and the high-pressure bypass valve is closed, it enters the restart mode. When any oil gun is put into operation or any coal feeder is running, it switches from the restart mode to the normal start mode. During the initial startup and grid connection phases with initial load, the main steam pressure is controlled by the high-pressure bypass valve to ensure the stability of the turbine inlet steam pressure. As the unit load increases and the turbine inlet steam flow increases, the high-pressure bypass valve gradually closes until it is fully closed. The high-pressure bypass valve enters the following mode, at which time the pressure setpoint is the actual pressure value plus an offset of 0.5 MPa to ensure that the valve is fully closed. 2) Bypass valve control, including: The unit is also designed with a pressure relief function. If the bypass valve is in automatic mode, when the main steam pressure exceeds the set pressure, the high-pressure bypass valve will open automatically to control the main steam pressure from overpressure. In automatic mode, if the generator is disconnected but the boiler does not trip, the minimum opening of the bypass valve will be automatically set to 50% after disconnection to keep the bypass valve open and protect the reheater. If the turbine does not trip, it can help maintain the turbine speed or operate under the condition of shutdown without stopping the boiler. 3) Low-pressure bypass valve control, including: When the low-side bypass is put into automatic mode, after the MFT is reset, the low-side bypass valve opens to 10% of its minimum opening. After the boiler is ignited, as the reheat steam pressure rises, the low-side bypass valve gradually opens and maintains the reheat steam pressure at the reheat steam pressure set value. When the high-side bypass is in the pressure-boosting stage, the reheat steam pressure setting is automatically set according to the reheat steam pressure requirement corresponding to the superheat steam pressure. After the high-pressure bypass boosting stage ends, the reheat steam pressure setting is automatically set according to the reheat steam pressure requirement corresponding to the unit load. After the unit is connected to the grid, as the turbine load gradually increases, the intermediate control valve gradually opens. In order to maintain the reheat steam pressure, the low-pressure bypass valve gradually closes. When both low-pressure bypass valves are closed, the low-pressure bypass control switches to the following mode. At this time, the reheat steam pressure setpoint is "actual reheat steam pressure + 0.5" to ensure that the low-pressure bypass valve is in the closed state. At the same time, when the actual reheat steam pressure exceeds "reheat steam pressure corresponding to the unit load + 0.5MPa", the low-pressure bypass valve gradually opens through the regulating circuit to prevent the reheater from overpressure. When the generator is disconnected or the turbine trips, if no MFT occurs, the low-pressure bypass valve will quickly open to 50% through the regulating circuit and switch to pressure regulation. The pressure is set to the reheat steam pressure before the generator is disconnected or the turbine trips. When the low-pressure bypass valve opens quickly, the high-pressure bypass desuperheating water will also open quickly to 50% and switch to temperature regulation. 4) High and low pressure bypass desuperheating valve control, including: The high-temperature bypass desuperheating valve controls the high-temperature bypass outlet temperature, with a set value of 360℃, and the operator can bias it; the low-temperature bypass desuperheating valve controls the low-temperature bypass outlet temperature, which is set by the operator.

2. The multi-mode control method for a thermal power unit bypass system responding to grid load demand according to claim 1, characterized in that, This method is applicable to ultra-supercritical, single-stage reheat, four-cylinder four-exhaust, single-shaft, double-backpressure, and extraction condensing steam turbines.

3. The multi-mode control method for a thermal power unit bypass system responding to grid load demand according to claim 1, characterized in that, The unit's startup bypass system consists of a two-stage series bypass system consisting of a high-voltage bypass and a low-voltage bypass.

4. The multi-mode control method for a thermal power unit bypass system responding to grid load demand according to claim 1, characterized in that, The regulating valve automatically maintains the pressure setpoint, and the pressure value can also be set by the operator when the pressure is turned on.

5. The multi-mode control method for a thermal power unit bypass system responding to grid load demand according to claim 1, characterized in that, The main steam pressure exceeds the set pressure value of 26.5 MPa.

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