A variable parameter nonlinear coal-fired unit control method based on load instruction

Abstract

The application discloses a variable parameter nonlinear coal-fired unit control method based on a load instruction, and belongs to the field of power plant control. The conventional PID controller has a decreased regulation quality in a low load nonlinear region, which results in large fluctuations of main steam pressure and furnace pressure. The application comprises the following steps: when the unit load is reduced to below 30% of the rated load, plasma / micro-oil ignition and combustion stabilization and feedwater dynamic regulation joint control are performed; in a low load working condition, the high-pressure heater emergency drain is closed, and a sliding pressure operation+steam supplement valve regulation mode is adopted; in a deep peak shaving working condition, a few coal mills are operated in a high power mode; when the unit load is below 30% Pe, the flue gas temperature at the economizer outlet is lower than the minimum continuous operation temperature of the SCR catalyst, and a flue gas bypass and feedwater bypass joint temperature rising system is started; and the parameter of the coordinated control system is reconfigured, and a variable parameter nonlinear PID control strategy based on a load instruction is established. The application is used for improving the deep peak shaving capacity of a 660 MW coal-fired unit.

Description

Technical Field

[0001] This invention belongs to the field of flexible operation technology of thermal power generating units, specifically relating to a variable parameter nonlinear coal-fired power generating unit control method based on load commands. Background Technology

[0002] Traditional 660MW coal-fired power units are typically designed with a minimum stable combustion load of 40%-50% of rated load. Under a power grid structure with a high proportion of renewable energy, the units need to frequently perform deep peak shaving tasks, reducing the load to 20%-30% of rated load or even lower.

[0003] However, existing technologies have the following prominent problems under deep peak shaving conditions: Poor boiler combustion stability: The furnace temperature is low at low loads, making it difficult for pulverized coal to ignite. This can easily lead to fire extinguishing or furnace deflagration accidents, requiring the use of large amounts of fuel oil for combustion, resulting in poor economic efficiency.

[0004] Hydrodynamic safety issues: For supercritical / ultra-supercritical once-through boilers, the low feedwater flow rate under low load can easily lead to flow deviation between water-cooled wall tubes and film-like boiling, resulting in tube overheating and tube rupture.

[0005] Denitrification system forced to shut down: Economizer outlet flue gas temperature decreases as load decreases. When it falls below the SCR catalyst operating window, denitrification efficiency drops sharply, ammonia slip rate increases, and the system may even be forced to shut down, resulting in NOx emissions exceeding standards.

[0006] Safety risks of turbine last-stage blades: Under low load, the steam flow is small, and the turbine last-stage blades operate under small volumetric flow, which can easily cause flutter or blow-by friction, threatening the safety of the turbine.

[0007] Deterioration of coordinated control quality: Conventional PID controllers experience a decline in regulation quality in the low-load nonlinear region, resulting in large fluctuations in main steam pressure and furnace pressure, and unstable unit operation. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing technologies by providing a variable parameter nonlinear coal-fired power unit control method based on load commands.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A variable-parameter nonlinear coal-fired power unit control method based on load command includes the following steps: Step 1: When the unit load drops below 30% of the rated load, implement combined control of plasma / micro-oil ignition and stable combustion with dynamic feedwater regulation: Step 2: Optimize the turbine regenerative system. Under low load conditions, shut down the emergency drain of the high-pressure heater and adopt the sliding pressure operation + steam injection valve regulation mode. Step 3: Under deep peak shaving conditions, adopt a high-output operation mode with fewer coal mills, operating only 2-3 coal mills in the bottom and middle layers, maintaining the output of a single coal mill at 60%-80% of its rated output, and controlling the fineness R90 of coal powder at 6%-8% by adjusting the speed of the dynamic separator, shortening the coal powder combustion time and improving the combustion efficiency under low load. Step 4: When the unit load is lower than 30%Pe, causing the economizer outlet flue gas temperature to be lower than the minimum continuous operating temperature of the SCR catalyst, start the combined flue gas bypass and feedwater bypass heating system. Step 5: Reconstruct the parameters of the coordinated control system and establish a variable parameter nonlinear PID control strategy based on load commands. In the 20%-40% load range, adjust the pressure pullback coefficient from 0.8 at high load to 0.3-0.5, reduce the main steam pressure control weight, prioritize the boiler combustion stability, introduce a furnace pressure fluctuation feedforward signal, and adjust the induced draft fan and forced draft fan dampers in advance when the load command changes to suppress furnace pressure fluctuations within ±100Pa.

[0010] The aforementioned variable-parameter nonlinear coal-fired power unit control method based on load commands includes the following steps in step one: (1) The plasma ignition device or micro-oil ignition device is put into the bottom burner (layer A) to maintain the furnace flame center temperature not lower than 1100℃. (2) Based on the characteristics of the once-through boiler or the steam drum boiler, dynamic bias control of feedwater is adopted: when the load is lower than 25%Pe, the feedwater temperature at the economizer inlet is increased to 260℃-280℃, and the superheat at the water-cooled wall outlet is controlled within a narrow range of 5℃-15℃ to prevent the water-cooled wall tube wall from overheating and the hydrodynamic instability.

[0011] The variable parameter nonlinear coal-fired power unit control method based on load command, wherein step two includes the following steps: (1) The unit adopts sliding pressure operation mode, and the main steam pressure decreases linearly with the load. At 20% load, the main steam pressure drops to 6-8 MPa; (2) Open the high-pressure cylinder steam injection valve to introduce a portion of new steam into the middle of the high-pressure cylinder, increase the flow rate of the last stage blades of the high-pressure cylinder, and prevent blade flutter and overheating due to air friction under low load.

[0012] The aforementioned variable-parameter nonlinear coal-fired power unit control method based on load commands includes the following steps in step four: (1) Open the economizer flue gas bypass damper to directly introduce some high-temperature flue gas to the SCR reactor inlet, so that the SCR inlet flue gas temperature is raised to 300℃-320℃; (2) Synchronously adjust the economizer feedwater bypass valve to reduce the heat absorption of the economizer and help increase the flue gas temperature. Beneficial effects

[0013] 1. This invention reduces the minimum technical output of a 660MW unit from the traditional 40%Pe (approximately 264MW) to 20%Pe (approximately 132MW) through multi-system collaborative optimization of the boiler and turbine, significantly improving the grid's ability to absorb new energy.

[0014] 2. This invention solves the problem of unstable hydrodynamics at low load in once-through boilers, and at the same time avoids the risk of last-stage blade flutter by adjusting the turbine make-up steam valve, thus ensuring the safety of the unit during deep peak shaving.

[0015] 3. This invention uses flue gas heating technology to ensure continuous operation of the SCR denitrification system during deep peak shaving, so that NOx emissions always meet the ultra-low emission requirements, avoiding environmental assessment risks. It also uses plasma stable combustion to replace traditional large oil gun combustion, which greatly reduces fuel consumption during deep peak shaving and improves operating economy. Detailed Implementation

[0016] A variable-parameter nonlinear coal-fired power unit control method based on load command includes the following steps: Step 1: When the unit load drops below 30% of the rated load, implement combined control of plasma / micro-oil ignition and stable combustion with dynamic feedwater regulation: Step 2: Optimize the turbine regenerative system. Under low load conditions, shut down the emergency drain of the high-pressure heater and adopt the sliding pressure operation + steam injection valve regulation mode. Step 3: Under deep peak shaving conditions, adopt a high-output operation mode with fewer coal mills, operating only 2-3 coal mills in the bottom and middle layers, maintaining the output of a single coal mill at 60%-80% of its rated output, and controlling the fineness R90 of coal powder at 6%-8% by adjusting the speed of the dynamic separator, shortening the coal powder combustion time and improving the combustion efficiency under low load. Step 4: When the unit load is lower than 30%Pe, causing the economizer outlet flue gas temperature to be lower than the minimum continuous operating temperature of the SCR catalyst, start the combined flue gas bypass and feedwater bypass heating system. Step 5: Reconstruct the parameters of the coordinated control system and establish a variable parameter nonlinear PID control strategy based on load commands. In the 20%-40% load range, adjust the pressure pullback coefficient from 0.8 at high load to 0.3-0.5, reduce the main steam pressure control weight, prioritize the boiler combustion stability, introduce a furnace pressure fluctuation feedforward signal, and adjust the induced draft fan and forced draft fan dampers in advance when the load command changes to suppress furnace pressure fluctuations within ±100Pa.

[0017] The aforementioned variable-parameter nonlinear coal-fired power unit control method based on load commands includes the following steps in step one: (1) The plasma ignition device or micro-oil ignition device is put into the bottom burner (layer A) to maintain the furnace flame center temperature not lower than 1100℃. (2) Based on the characteristics of the once-through boiler or the steam drum boiler, dynamic bias control of feedwater is adopted: when the load is lower than 25%Pe, the feedwater temperature at the economizer inlet is increased to 260℃-280℃, and the superheat at the water-cooled wall outlet is controlled within a narrow range of 5℃-15℃ to prevent the water-cooled wall tube wall from overheating and the hydrodynamic instability.

[0018] The variable parameter nonlinear coal-fired power unit control method based on load command, wherein step two includes the following steps: (1) The unit adopts sliding pressure operation mode, and the main steam pressure decreases linearly with the load. At 20% load, the main steam pressure drops to 6-8 MPa; (2) Open the high-pressure cylinder steam injection valve to introduce a portion of new steam into the middle of the high-pressure cylinder, increase the flow rate of the last stage blades of the high-pressure cylinder, and prevent blade flutter and overheating due to air friction under low load.

[0019] The aforementioned variable-parameter nonlinear coal-fired power unit control method based on load commands includes the following steps in step four: (1) Open the economizer flue gas bypass damper to directly introduce some high-temperature flue gas to the SCR reactor inlet, so that the SCR inlet flue gas temperature is raised to 300℃-320℃; (2) Synchronously adjust the economizer feedwater bypass valve to reduce the heat absorption of the economizer and help increase the flue gas temperature.

Claims

1. A variable-parameter nonlinear coal-fired power unit control method based on load commands, characterized by: Includes the following steps: Step 1: When the unit load drops below 30% of the rated load, implement combined control of plasma / micro-oil ignition and stable combustion with dynamic feedwater regulation: Step 2: Optimize the turbine regenerative system. Under low load conditions, shut down the emergency drain of the high-pressure heater and adopt the sliding pressure operation + steam injection valve regulation mode. Step 3: Under deep peak shaving conditions, adopt a high-output operation mode with fewer coal mills, operating only 2-3 coal mills in the bottom and middle layers, maintaining the output of a single coal mill at 60%-80% of its rated output, and controlling the fineness R90 of coal powder at 6%-8% by adjusting the speed of the dynamic separator, shortening the coal powder combustion time and improving the combustion efficiency under low load. Step 4: When the unit load is lower than 30%Pe, causing the economizer outlet flue gas temperature to be lower than the minimum continuous operating temperature of the SCR catalyst, start the combined flue gas bypass and feedwater bypass heating system. Step 5: Reconstruct the parameters of the coordinated control system and establish a variable parameter nonlinear PID control strategy based on load commands. In the 20%-40% load range, adjust the pressure pullback coefficient from 0.8 at high load to 0.3-0.5, reduce the main steam pressure control weight, prioritize the boiler combustion stability, introduce a furnace pressure fluctuation feedforward signal, and adjust the induced draft fan and forced draft fan dampers in advance when the load command changes to suppress furnace pressure fluctuations within ±100Pa.

2. The variable parameter nonlinear coal-fired power unit control method based on load command according to claim 1, characterized in that: Step one includes the following steps: (1) The plasma ignition device or micro-oil ignition device is put into the bottom burner to maintain the furnace flame center temperature not lower than 1100℃; (2) Based on the characteristics of the once-through boiler or the steam drum boiler, dynamic bias control of feedwater is adopted: when the load is lower than 25%Pe, the feedwater temperature at the economizer inlet is increased to 260℃-280℃, and the superheat at the water-cooled wall outlet is controlled within a narrow range of 5℃-15℃ to prevent the water-cooled wall tube wall from overheating and the hydrodynamic instability.

3. The variable parameter nonlinear coal-fired power unit control method based on load command according to claim 1, characterized in that: Step two includes the following steps: (1) The unit adopts sliding pressure operation mode, and the main steam pressure decreases linearly with the load. At 20% load, the main steam pressure drops to 6-8 MPa; (2) Open the high-pressure cylinder steam injection valve to introduce a portion of new steam into the middle of the high-pressure cylinder, increase the flow rate of the last stage blades of the high-pressure cylinder, and prevent blade flutter and overheating due to air friction under low load.

4. The variable parameter nonlinear coal-fired power unit control method based on load command according to claim 1, characterized in that: Step four includes the following steps: (1) Open the economizer flue gas bypass damper to directly introduce some high-temperature flue gas to the SCR reactor inlet, so that the SCR inlet flue gas temperature is raised to 300℃-320℃; (2) Synchronously adjust the economizer feedwater bypass valve to reduce the heat absorption of the economizer and help increase the flue gas temperature.