Mixed coal pulverizing system of thermal power generating unit and deep peak regulation operation method of mixed coal pulverizing system

Abstract

The invention discloses a mixed coal pulverizing system of a thermal power generating unit and a deep peak regulation operation method of the mixed coal pulverizing system, and belongs to the technical field of coal pulverizing and combustion control of thermal power generating units. An air inlet of a direct blowing type coal pulverizing subsystem is connected with a hot air outlet of a boiler air preheater, and a coal pulverizing outlet of the direct blowing type coal pulverizing subsystem is connected to a boiler combustor; an air inlet of the warehouse type pulverizing subsystem is connected with an air system, and a pulverized coal outlet of the warehouse type pulverizing subsystem is connected to a boiler burner; a gas inlet of the exhaust gas closed type recirculation system is connected with an exhaust gas outlet of the storage bin type coal pulverizing subsystem, and a gas outlet of the exhaust gas closed type recirculation system is connected to a direct blowing coal mill inlet cold air duct of the direct blowing type coal pulverizing subsystem and a powder discharging fan inlet of the storage bin type coal pulverizing subsystem; the control subsystem is electrically connected with sensors and execution mechanisms in the direct blowing type coal pulverizing subsystem, the storage bin type coal pulverizing subsystem, the air system and the exhaust gas closed type recirculation system. The method is mainly used for solving the problems that a coal pulverizing system of a thermal power generating unit is unstable in output, unstable in combustion and low in 15%-100% load response speed under the 15%-30% THA ultra-low load working condition.

Description

Technical Field

[0001] This invention belongs to the field of pulverizing and combustion control technology for thermal power generating units, specifically relating to a hybrid pulverizing system for thermal power generating units and its deep peak-shaving operation method. Background Technology

[0002] With the continuous expansion of renewable energy grid connection, the grid's requirements for the peak-shaving capacity of thermal power units are increasing. Traditional pulverizing systems face numerous technical bottlenecks under low-load conditions:

[0003] 1. Direct-fired pulverizing system: When the load is below 50% BMCR, the output of the pulverizer decreases, the air-to-coal ratio increases, and the pulverized coal concentration decreases, leading to unstable combustion, reduced efficiency, and even the risk of fire extinguishing. In addition, the speed at which the direct-fired system responds to load changes is limited by the inertia of the pulverizer, making it unable to meet the requirements for rapid frequency regulation.

[0004] 2. Air temperature control problem: When the air preheater outlet air temperature drops at low load, the coal mill drying output is insufficient, the coal powder moisture content increases, and the combustion efficiency is affected.

[0005] 3. Environmental and safety challenges: Currently, exhaust gas is mostly discharged directly into the furnace or the atmosphere, causing excessive dust emissions or accumulation of combustibles inside the system, posing a risk of deflagration.

[0006] In summary, existing technologies cannot simultaneously solve the problems of combustion stability, load response speed, system safety, and operational economy under deep peak shaving conditions. Summary of the Invention

[0007] In order to solve the problems of unstable output, unstable combustion, and slow response speed of pulverizing system in thermal power units under ultra-low load conditions of 15%-30% THA, this invention provides a mixed pulverizing system for thermal power units and its deep peak-shaving operation method.

[0008] The technical solution adopted in this invention is:

[0009] The mixing and pulverizing system of thermal power units includes

[0010] The air inlet of the direct-fired pulverizing subsystem is connected to the hot air outlet of the boiler air preheater, and its pulverizing outlet is connected to the boiler burner.

[0011] The air inlet of the storage-type pulverizing subsystem is connected to the air system, and its pulverizing outlet is connected to the boiler burner.

[0012] The air inlet of the closed-loop recirculation system is connected to the exhaust outlet of the storage-type pulverizing subsystem, and its outlet is connected to the inlet cold air duct of the direct-fired coal mill of the direct-fired pulverizing subsystem and the exhaust fan inlet of the storage-type pulverizing subsystem.

[0013] The control subsystem is electrically connected to the sensors and actuators in the direct-blown pulverizing subsystem, the storage pulverizing subsystem, the air system, and the waste gas closed-loop recirculation system.

[0014] A method for deep peak-shaving operation of a pulverizing system in a thermal power unit, the method being used to handle the following operating conditions:

[0015] High-load operation: The operating mode is 3 direct-fired coal mills + 3 storage coal mills operating at full load. The air temperature control is: adjust the air temperature according to the coal quality changes and maintain the mill outlet temperature at 65-75℃.

[0016] Medium load condition: The operating mode is 2 direct-fired coal mills + 2 storage coal mills, with 1 storage-type pulverizing subsystem in hot standby. The air temperature is controlled by adjusting the air temperature according to the coal quality changes, maintaining the mill outlet temperature at 65-75℃.

[0017] Deep peak shaving operation mode: The operation mode is 1 direct-fired coal mill + 1 storage coal mill, 1 storage-type pulverizing subsystem is on hot standby, the air temperature control is to raise the inlet air temperature of the storage-type pulverizing subsystem to the design reference temperature line through reheating, the exhaust gas treatment is to fully open the recirculation system with a circulation rate of 30-50% to maintain the air-powder balance of the system.

[0018] Hot standby mode: One storage-type pulverizing subsystem is kept in hot standby status, the storage pulverizer is kept at the minimum speed, and the pulverized coal silo is kept at 30%-70% material level, ready to respond to sudden load changes at any time.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] This invention is mainly used to solve the problems of unstable output and combustion of pulverizing system in thermal power units under ultra-low load conditions of 15%-30% THA, slow response speed of 15%-100% load, and to overcome the problem of reduced drying output caused by insufficient hot air temperature under low load conditions, eliminate the environmental and safety problems caused by direct exhaust gas emission, improve load response speed, and meet the requirements of rapid frequency regulation of the power grid.

[0021] The present invention has the following significant advantages

[0022] 1. Structural innovation, breakthrough in deep peak-shaving capability:

[0023] By structurally coupling the direct-fired pulverizing subsystem and the storage-type pulverizing subsystem in the air-coal process, and integrating the hot air reheating and exhaust gas closed-loop circulation units, the stability of air-coal concentration and air temperature under ultra-low load (15% THA) is ensured from a physical structure perspective, thus completely solving the problem of stable combustion under low load.

[0024] The minimum stable combustion load is reduced to 15% THA, which is more than 50% lower than that of traditional systems;

[0025] Even under 15% THA conditions, the combustion efficiency remains above 98.5%;

[0026] 2. Fast response and excellent frequency modulation performance:

[0027] Based on the "inventory" advantage of the coal powder silo in the storage-type pulverizing subsystem, the amount of coal powder fed into the furnace can be changed within seconds by adjusting the speed of the variable frequency feeder, achieving rapid load response (3%-5%BMCR / min) and meeting the stringent requirements of the power grid for primary frequency regulation.

[0028] The load change rate can reach 3%-5%BMCR / min, and the response speed is improved by 30%;

[0029] In the hot standby mode of the storage-type powder preparation subsystem, the response time for a sudden change in load (5%BMCR) is <30s;

[0030] 3. Safe and reliable, with significant environmental benefits:

[0031] The closed-loop exhaust gas design fundamentally eliminates the risk of combustible material leakage or accumulation; the pulverized coal silo is equipped with multiple monitoring and inerting systems, forming a complete safety fire barrier, completely eliminating the risk of spontaneous combustion and explosion, and the closed-loop exhaust gas avoids the accumulation of combustible material, thus improving the system's explosion-proof safety.

[0032] At the same time, the system effectively reduces NOx emissions under low-load conditions, with NOx emission concentrations decreasing by 15%-20% under low-load conditions;

[0033] 4. High compatibility and easy to modify and implement:

[0034] The core equipment in the device can be the same model as the existing direct-fired system, which greatly reduces the difficulty of technical transformation and the cost of spare parts. It is suitable for different coal qualities, especially high-moisture, low-calorific-value inferior coal, and has good engineering promotion value. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of the present invention;

[0036] Figure 2 This is a logic diagram of the operation mode switching under different loads of the present invention;

[0037] The components include: 1. Primary air fan; 2. Boiler air preheater; 3. Direct-fired coal mill; 4. Coal feeder; 5. Hot primary air main pipe; 6. Hot air reheating device; 7. Separator; 8. Pulverized coal silo; 9. Pulverized coal feeder; 10. Exhaust fan; 11. Injector; 12. Exhaust gas pipeline; 13. Recirculation main pipe; 14. Coal mill outlet pulverized coal conveying pipeline; 15. Inlet cold air duct; 16. Recirculation regulating valve; 17. Bypass valve; 18. Heating medium pipeline; 19. Nitrogen inerting interface; 20. Level gauge; 21. Sensor group; 22. Storage pulverizer; 23. Reheat hot air main pipe; 24. Cold primary air main pipe. Detailed Implementation

[0038] To better understand the purpose, structure, and function of this invention, the invention will be described in further detail below with reference to the accompanying drawings.

[0039] This invention applies to the hybrid pulverizing system of large coal-fired power units of 660MW and above and its operation method in deep peak shaving and rapid load response. Through the organic coupling of direct-fired and storage systems and the integrated innovation of hot air reheating technology and exhaust gas closed circulation system, the unit can achieve safe, stable and efficient operation within the 15%-100% load range.

[0040] like Figure 1 As shown, the present invention provides a mixing and pulverizing system for thermal power units, including...

[0041] The air inlet of the direct-fired pulverizing subsystem is connected to the hot air outlet of the boiler air preheater 2 through the hot primary air header 5, and its pulverizing outlet is connected to the boiler burner through a pipeline.

[0042] The air inlet of the storage-type pulverizing subsystem is connected to the air system through the reheat hot air header 23, and its pulverizing outlet is connected to the boiler burner.

[0043] The air inlet of the waste gas closed recirculation system is connected to the waste gas outlet of the storage-type pulverizing subsystem, and its outlet is connected to the inlet cold air duct 15 of the direct-fired coal mill 3 of the direct-fired pulverizing subsystem and the inlet of the exhaust fan 10 of the storage-type pulverizing subsystem.

[0044] The control subsystem is electrically connected to the sensors and actuators in the direct-blown pulverizing subsystem, the storage pulverizing subsystem, the air system, and the waste gas closed-loop recirculation system.

[0045] like Figure 1 As shown, the direct-fired pulverizing subsystem includes a direct-fired coal mill 3. The air inlet of the direct-fired coal mill 3 is connected to the hot air outlet of the boiler air preheater 2 through a hot primary air header 5. The air inlet of the boiler air preheater 2 is connected to the air outlet of the primary air fan 1. The number of primary air fans 1 is at least one, preferably two. The outlet of the direct-fired coal mill 3 is connected to the boiler burner through a pipeline.

[0046] The direct-fired coal mill 3 is fed by the coal feeder 4.

[0047] The primary air fan 1 is connected to the air inlet of the direct-fired coal mill 3 and the air inlet of the storage coal mill 22 through the cold primary air header 24 and the inlet cold air duct 15.

[0048] The cold primary air header 24 and the hot primary air header 5 are connected in parallel and simultaneously enter the air inlet of the direct-fired coal mill 3.

[0049] The primary cold air header 24 and the reheat hot air header 23 are connected in parallel and simultaneously enter the air inlet of the storage mill 22.

[0050] Direct-blown powder making subsystem

[0051] 1. Several medium-speed direct-fired coal mills (such as the ZGM type) can be used, each with an output of 40-60 t / h. The capacity of different units can be expanded.

[0052] 2. Integrate the existing coal mill's separator and sealing fan system to ensure the coal powder fineness meets the R90 requirement;

[0053] 3. Hot air is used as the desiccant, and the air temperature is controlled by the hot and cold air temperature regulating baffle at the outlet of the coal mill.

[0054] like Figure 1 As shown, the storage-type powder-making subsystem includes

[0055] The storage pulverizer 22 is a medium-speed pulverizer, the same model as the direct-fired pulverizer 3, and its air inlet is connected to the reheat hot air header 23 through a pipeline.

[0056] Separator 7 adopts a high-efficiency dynamic separator with a separation efficiency of over 90%. Its inlet is connected to the outlet of the storage pulverizer 22 through the pulverizer outlet conveying pipe 14.

[0057] The coal powder silo 8 has its inlet connected to the coal powder outlet of the separator 7 via a coal powder conveying pipeline; the coal powder silo 8 is made of steel (to meet the storage capacity of 0.5~3 hours) and is equipped with a safety monitoring system;

[0058] The pulverizer 9 is a variable frequency pulverizer, located at the bottom outlet of the pulverizer 8. The pulverizer 9 meteres and feeds pulverizers. Each pulverizer 8 is equipped with the same number of pulverizers 9 as the corresponding layer burners. The pulverizer quantity can be adjusted between 0 and 100%.

[0059] The exhaust fan 10 has its air outlet connected to the powder outlet of the powder feeder 9 via an injector 11. The discharge outlet of the injector 11 is connected to the boiler burner via a powder feeding pipe.

[0060] Each coal pulverizer 8 is equipped with the same number of exhaust fans as the corresponding layer burners, with the air volume adjustable between 40% and 110%.

[0061] The number of storage mill 22, separator 7, pulverized coal bin 8, feeder 9, exhaust fan 10, and ejector 11 can be multiple, and the number of each component is the same, with each component connected in a one-to-one correspondence.

[0062] The storage-type milling subsystem has several independent storage systems, which are organically coupled with the direct-blowing milling subsystem.

[0063] The storage mill 22 is fed by the coal feeder 4.

[0064] like Figure 1 As shown, the air system includes a hot air reheating device 6. The air inlet side of the hot air reheating device 6 is connected to the hot primary air main pipe 5 through a branch air duct, and its air outlet side is connected to the reheat hot air main pipe 23.

[0065] The hot air reheating device 6 is connected to the heating medium pipeline 18.

[0066] like Figure 1 As shown, the branch duct consists of two parallel branch pipes, one of which is equipped with a bypass valve 17 for controlling the on / off state, and the other is equipped with a hot air reheating device 6.

[0067] like Figure 1 As shown, the pulverized coal silo 8 is equipped with a level gauge 20 and a sensor group 21 for monitoring its internal state, and is also equipped with a nitrogen inerting interface 19; the bottom cone of the pulverized coal silo 8 is equipped with a fluidizing air interface.

[0068] Sensor group 21 includes a temperature sensor, a CO concentration sensor, and a pressure sensor.

[0069] The hot air reheating device 6 in the air system adopts a tubular heat exchanger or a plate heat exchanger and is arranged after the hot primary air header 5 to raise the inlet air temperature of the storage coal mill 22 to above the design requirement temperature under each load section, so as to ensure the drying output at low load.

[0070] 1. The direct-blowing powder making subsystem adopts a hot primary air main pipe + branch pipe structure to ensure uniform air volume distribution;

[0071] 2. The storage-type powder making subsystem adopts a reheated hot air main pipe + branch pipe structure and is equipped with intelligent dampers to achieve precise air volume control;

[0072] 3. All air ducts have an insulation thickness of ≥150mm to reduce heat loss.

[0073] like Figure 1 As shown, the waste gas closed-loop recirculation system includes

[0074] The exhaust gas pipeline 12 has its inlet connected to the exhaust gas outlet of the separator 7 and its outlet connected to the dust removal fan 10.

[0075] The recirculation main pipe 13 has its inlet connected to the outlet of the exhaust gas pipe 12 via the recirculation regulating valve 16; its outlet is divided into two paths, one of which is connected to the inlet cold air duct 15 of the direct-fired coal mill 3, and the other is connected to the inlet of the exhaust fan 10.

[0076] like Figure 1 As shown, the exhaust gas pipeline 12 is also provided with a branch line leading to the boiler burner; the recirculation main pipe 13 is provided with an explosion-proof pressure relief device and a wind speed monitoring device.

[0077] The waste gas closed-loop recirculation system is equipped with a recirculation main pipe 13 and branch pipes, which are made of wear-resistant steel. The wind speed is controlled at 18-30m / s. It is equipped with a pneumatic regulating damper, wind speed monitoring device, and explosion-proof pressure relief device. It can achieve 0-100% ratio recirculation adjustment to avoid waste gas discharge and maintain the system air-powder balance.

[0078] like Figure 1 As shown, the control subsystem is a distributed control system (DCS), which is configured as follows:

[0079] Receives monitoring signals from level gauge 20, sensor group 21, wind speed monitoring device, etc.

[0080] Based on the received signals and external load commands, control signals are output to the actuators to adjust the operating status of each damper, valve, coal feeder 4, variable frequency powder feeder 9 and exhaust fan 10, thereby achieving automatic switching of operating modes.

[0081] The pulverized coal silo is equipped with multiple monitoring systems: online monitoring of temperature, CO concentration, and material level, with data connected to the DCS.

[0082] Nitrogen gas flow inerting system: Nitrogen gas inerting interface 19 is provided;

[0083] Intelligent control system: Based on DCS multivariable predictive control, it realizes automatic switching and optimization of operating modes.

[0084] The core of this hybrid pulverizing system lies in the organic coupling of the direct-blown pulverizing subsystem, the storage-type pulverizing subsystem, the air system, and the exhaust gas closed-loop recirculation system through specific pipelines, air ducts, monitoring points, and control valves, forming a flexible, efficient, and coordinated whole.

[0085] 1. The connections between the subsystems are as follows:

[0086] Direct-fired pulverizing subsystem: Hot primary air → Coal mill → Pulverized coal pipeline → Burner

[0087] Storage-type pulverizing subsystem: Reheat air → Coal mill → Fine powder separator → (Pulverized coal → Pulverized coal silo → Pulverizer → Exhaust fan → Burner; Exhaust gas → Recirculation system or burner)

[0088] Closed-loop exhaust gas recirculation system: Exhaust fan outlet → Recirculation duct → Coal mill inlet cold air duct

[0089] 2. Connection between the air source and the primary air system:

[0090] The hot air outlet of air preheater 2 is divided into two paths:

[0091] One path delivers the hot primary air to the direct-blown pulverizing subsystem via the hot primary air header 5. This header features a double-layer insulation design to reduce heat loss.

[0092] Another path leads to the hot air reheating device 6 (such as a tubular steam heat exchanger) via a branch duct. The hot air is reheated to further increase its temperature. The heated hot air is then transported to the storage-type pulverizing subsystem via the reheated hot air header 23.

[0093] 3. Internal connections of the direct-blown powder making subsystem:

[0094] The primary hot air main pipe 5 is connected to the inlet hot air duct of each direct-fired coal mill 3 through various branch pipes (equipped with intelligent regulating dampers).

[0095] The outlet of each direct-fired coal mill 3 is directly connected to the corresponding burner via a pulverized coal pipeline. The pulverized coal pipeline is equipped with measuring points for wind speed, concentration, and temperature, and the data is uploaded to the DCS in real time.

[0096] 4. Internal connections of the storage-type powder making subsystem:

[0097] The reheat hot air main pipe 23 is connected to the inlet of each storage coal mill 22 in the storage system via branch pipes equipped with pneumatic regulating dampers and air volume measuring devices.

[0098] The outlet of each storage mill 22 is connected to the separator 7.

[0099] The outlet of separator 7 is divided into two paths:

[0100] Coal powder side: Qualified coal powder is transported by pneumatic means through the coal powder conveying pipeline to the top of the steel coal powder silo 8, and the coal powder silo 8 is equipped with a separator 7.

[0101] Exhaust gas side: Gas with a low powder concentration (i.e. exhaust gas) is discharged from the upper outlet of separator 7 and enters exhaust gas pipeline 12.

[0102] A dedicated fluidizing air is introduced into the bottom cone of the pulverized coal silo 8 to prevent pulverized coal from caking. The bottom outlet of the pulverized coal silo 8 is connected to the inlet of the pulverizer 9 via a flange.

[0103] The outlet of the pulverizer 9 is connected to the ejector 11 via a pulverizer discharge pipe. In the ejector 11, pulverized coal is mixed with the conveying air from the exhaust fan 10 to form a uniform gas-powder two-phase flow.

[0104] Recirculation air source: from exhaust gas recirculation main pipe 13.

[0105] The pulverized coal airflow from the outlet of the pulverized coal exhaust fan 10 is transported to the boiler burner through the pulverized coal delivery pipeline.

[0106] 5. Connection of exhaust gas treatment system:

[0107] The exhaust gas generated by separator 7 in all storage-type powder-making subsystems is collected into the exhaust gas pipeline. The exhaust gas pipeline is split into two paths at the rear end, and the flow direction is controlled by a pneumatic three-way valve or a parallel regulating damper:

[0108] One route: directly to the boiler burner.

[0109] Second route: Leads to exhaust gas recirculation main pipe 13.

[0110] The exhaust gas recirculation header 13 draws some or all of the exhaust gas back to the inlet cold air duct of the direct-fired coal mill: where it mixes with the cold primary air while maintaining the required airflow at the inlet of the direct-fired coal mill 3.

[0111] Dust removal fan 10 inlet: As part of the conveying air, it realizes closed circulation.

[0112] The recirculation pipeline is equipped with explosion-proof doors (rupture disc type), wind speed measuring devices, CO concentration monitoring, and pneumatic regulating dampers to ensure system safety.

[0113] 6. Monitoring and control system connection:

[0114] Connect to all intelligent devices on site via the DCS control system:

[0115] It receives sensor signals from all air ducts, pipelines, coal mills, and coal powder silos, including temperature, pressure, flow rate, concentration, material level, and CO content.

[0116] Output control commands to various actuators such as regulating dampers, baffles, coal feeder speed 4, pulverizer speed 9, exhaust fan speed 10, recirculation regulating valve 16, and nitrogen injection valve.

[0117] The control system automatically coordinates the start-up, shutdown, output distribution, and air volume ratio of the direct-blowing system and the storage system according to preset logic (such as load-air-coal ratio curve, air temperature setpoint, and safety interlock conditions).

[0118] A method for deep peak-shaving operation of a pulverizing system in a thermal power unit, the method being used to handle the following operating conditions:

[0119] High-load operation (75%-100% BMCR): The operating mode is 3 direct-fired coal mills and 3 storage coal mills operating at full load. The air temperature control is as follows: adjust the air temperature according to the coal quality changes and maintain the mill outlet temperature at 65-75℃ (adjusted according to coal quality conditions).

[0120] Medium load condition (30%-75% THA): The operating mode is 2 direct-fired coal mills and 2 storage coal mills in operation, with 1 storage-type pulverizing subsystem in hot standby. The air temperature is controlled by adjusting the air temperature according to the coal quality changes to maintain the mill outlet temperature at 65-75℃.

[0121] Deep peak shaving operation (15%-30% THA): The operating mode is 1 direct-fired coal mill and 3+1 storage coal mills in operation, with 1 storage-type pulverizing subsystem in hot standby. The air temperature is controlled by raising the inlet air temperature of the storage-type pulverizing subsystem to the design reference temperature line through reheating. The exhaust gas treatment is achieved by fully opening the recirculation system with a circulation rate of 30-50% to maintain the air-powder balance of the system.

[0122] Hot standby mode: A storage-type pulverizing subsystem is kept in hot standby status, the storage pulverizer 22 is kept at the minimum speed, and the pulverized coal silo 8 is kept at 30%-70% material level, ready to respond to sudden load changes at any time.

[0123] The following uses a 660MW supercritical coal-fired power unit as an example to illustrate the specific implementation of the present invention:

[0124] 1.1 System Design

[0125] Coal mills: 6 medium-speed coal mills, including 3 direct-fired coal mills and 3+3 storage silo coal mills.

[0126] Pulverized coal silos 8: 3 steel silos, 80m³

[0127] 9:12 variable frequency powder feeders, 4 per compartment

[0128] Hot air reheating unit 6: Tubular or plate heat exchanger, designed output 1300kW

[0129] 2.2 Control System Implementation

[0130] 2.2.1 Control Strategy

[0131] A multivariable predictive control algorithm is adopted, based on the following input variables:

[0132] External signals: load commands, power grid frequency regulation signals

[0133] Internal signals: Boiler main control output, air-to-coal ratio, oxygen content, air temperature

[0134] Equipment status: coal mill output, pulverized coal silo level, pulverized coal feeder speed

[0135] 2.2.2 Mode Switching Logic

[0136] High load (75-100% BMCR): Mainly operated by 3 direct blowing systems + 3 storage silo feeding systems.

[0137] Medium load (30-75% BMCR): Direct blowing and storage systems operate in combination. During periods of rapid load increase and decrease, powder feeding is the main method of adjustment. When the load falls into the predetermined target stage, the direct blowing system is cross-regulated to maintain the stability of the predetermined load.

[0138] Deep peak shaving (15-30% THA): 1 direct-fired mill + 1 storage system. The storage system controls the pulverized coal concentration to remain above the conveying red line, and the storage system is in hot standby mode. Under ultra-low load conditions, the operation mode is optimized to "1 direct-fired mill + 1 storage mill". The inlet air temperature of a single storage mill is significantly increased by a centralized heat source, and the excess exhaust gas generated is returned to the mill inlet in a closed loop to achieve self-balancing within the system.

[0139] Emergency frequency adjustment mode: Prioritizes adjusting the speed of the powder feeder in the storage system.

[0140] 2.2.3 Safety Interlock Protection

[0141] Coal mill outlet temperature > 75℃: Automatically open cold air damper

[0142] Powder hopper temperature > 65℃ or CO > 100ppm: Automatic nitrogen inerting will be initiated.

[0143] 2.3 Running effect

[0144] After simulating this invention on a 660MW unit, the following operational results were obtained:

[0145] 2.3.1. Peak Shaving Depth:

[0146] The minimum stable load reaches 99MW 15% THA, and under this load:

[0147] Combustion efficiency: 98.8%

[0148] NOx emissions <250mg / Nm³

[0149] 2.3.2. Load Response:

[0150] The maximum load change rate can reach 5% BMCR / min 33MW / min

[0151] 2.3.3. Economic Indicators:

[0152] The power consumption of the wind turbine decreased by 0.15%.

[0153] The annual increase in peak shaving revenue is approximately 12 million yuan.

[0154] This invention solves the current technical problem through an innovative technical solution:

[0155] 1. Load response and air-coal decoupling technology: When the power grid requires an increase in load, the DCS prioritizes and quickly increases the speed of the feeder 9 of the storage-type pulverizing subsystem, instantly injecting the qualified pulverized coal pre-stored in the pulverized coal bin 8 into the furnace, achieving a second-level response.

[0156] Meanwhile, the DCS calculates the required total coal quantity based on the new load command and instructs the direct-fired pulverizer 3 and the storage pulverizer 22 to slowly increase the coal feed rate. Since the pulverizing process (pulverizer operation) and the combustion process (pulverizer feeding) are physically decoupled through the pulverized coal silo 8, the pulverizer can always operate near its economic output range without being disturbed by short-term load fluctuations, thus ensuring pulverizing efficiency and system stability.

[0157] 2. Wind temperature protection technology

[0158] At low load (<50% THA), the outlet air temperature of boiler air preheater 2 will drop, especially at ultra-low load stages, where it may not meet the drying output requirements of the coal mill.

[0159] At this time, the hot air reheating device 6 is put into operation. The DCS adjusts the opening of the regulating valve to control the steam flow into the heat exchanger, further heating the hot air leading to the storage pulverizer 22. This ensures that even at extremely low unit loads, the pulverizer inlet air temperature is always higher than the required drying reference temperature for the coal, guaranteeing the dryness of the pulverized coal and thus maintaining combustion stability and efficiency.

[0160] 3. Waste gas recirculation technology:

[0161] Under ultra-low load conditions (15%-30% THA), the amount of pulverized coal produced by the storage-type pulverizing subsystem is small, and the corresponding amount of exhaust gas directly introduced into the furnace may cause unstable combustion or flameout.

[0162] At this point, the DCS switches the three-way valve, closing the exhaust gas passage to the furnace and fully opening the recirculation passage. The exhaust gas is then completely returned to the pulverizer inlet or the exhaust fan 10 inlet.

[0163] The objectives were achieved as follows: (1) Maintaining the air volume balance within the system and avoiding blockage of the powder conveying pipe due to low air volume; (2) Reducing dust emissions to the external environment.

[0164] 4. Intelligent control technology:

[0165] The DCS's built-in multivariate predictive control algorithm takes load commands as the primary input and simultaneously analyzes multiple variables such as real-time coal quality data (e.g., received base moisture and volatile matter), air temperature parameters, and equipment status (coal mill current and pulverized coal silo level).

[0166] Employing a multivariate predictive control algorithm, the system automatically selects the optimal operating mode for the current load (such as "3+3", "2+2", or "1+1+hot standby") and calculates the optimal setpoints for each damper opening, fan speed, and coal (pulverized) feed. The entire switching and adjustment process is smooth and automatic, requiring no manual intervention, thus achieving safe, stable, and efficient autonomous operation of the system across a wide load range.

[0167] Meanwhile, the control system monitors key parameters in real time, such as the coal mill outlet temperature, powder bin level, and CO concentration, and implements automatic interlock protection.

[0168] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A pulverizing system for thermal power units, characterized in that: include The air inlet of the direct-fired pulverizing subsystem is connected to the hot air outlet of the boiler air preheater (2), and its pulverizing outlet is connected to the boiler burner. The air inlet of the storage-type pulverizing subsystem is connected to the air system, and its pulverizing outlet is connected to the boiler burner. The air inlet of the closed-loop recirculation system is connected to the exhaust outlet of the storage-type pulverizing subsystem, and its outlet is connected to the inlet cold air duct (15) of the direct-fired coal mill (3) of the direct-fired pulverizing subsystem and the inlet of the exhaust fan (10) of the storage-type pulverizing subsystem. The control subsystem is electrically connected to the sensors and actuators in the direct-blown pulverizing subsystem, the storage pulverizing subsystem, the air system, and the waste gas closed-loop recirculation system.

2. The pulverizing system for thermal power units according to claim 1, characterized in that: The direct-fired pulverizing subsystem includes a direct-fired coal mill (3). The air inlet of the direct-fired coal mill (3) is connected to the hot air outlet of the boiler air preheater (2) through a hot primary air header (5). The outlet of the direct-fired coal mill (3) is connected to the boiler burner through a pipeline.

3. The pulverizing system for thermal power units according to claim 1, characterized in that: The storage-type powder-making subsystem includes The coal storage mill (22) has its air inlet connected to the reheat hot air main pipe (23) via a pipeline; The separator (7) is connected to the outlet of the storage pulverizer (22) via the pulverizer outlet conveying pipe (14); The coal powder silo (8) has its inlet connected to the coal powder outlet of the separator (7) via a coal powder conveying pipe. The pulverizer (9) is located at the bottom outlet of the pulverized coal silo (8); The exhaust fan (10) has its air outlet connected to the powder outlet of the powder feeder (9) via an injector (11), and the discharge port of the injector (11) is connected to the boiler burner via a powder feeding pipe.

4. The pulverizing system for thermal power units according to claim 3, characterized in that: The air system includes a hot air reheating device (6), the air inlet side of which is connected to the hot primary air main pipe (5) through a branch air duct, and its air outlet side is connected to the reheat hot air main pipe (23).

5. The pulverizing system for thermal power units according to claim 4, characterized in that: The branch duct consists of two parallel branch pipes, one of which is equipped with a bypass valve (17) for controlling the on / off state, and the other is equipped with a hot air reheating device (6).

6. The pulverizing system for thermal power units according to claim 4, characterized in that: The pulverized coal silo (8) is equipped with a level gauge (20) and a sensor group (21) for monitoring its internal state, and is also equipped with a nitrogen inerting interface (19); the bottom cone of the pulverized coal silo (8) is equipped with a fluidizing air interface.

7. The pulverizing system for thermal power units according to claim 1, characterized in that: The waste gas closed recirculation system includes The exhaust gas pipeline (12) has its inlet connected to the exhaust gas outlet of the separator (7) and its outlet connected to the dust removal fan (10); The recirculation main pipe (13) has its inlet connected to the outlet of the exhaust gas pipe (12); its outlet is divided into two paths, one of which is connected to the inlet cold air duct (15) of the direct-fired coal mill (3), and the other is connected to the inlet of the pulverizing fan (10).

8. The pulverizing system for thermal power units according to claim 7, characterized in that: The exhaust gas pipeline (12) is also provided with a branch line leading to the boiler burner; the recirculation main pipe (13) is provided with an explosion-proof pressure relief device and a wind speed monitoring device.

9. The pulverizing system for thermal power units according to claim 1, characterized in that: The control subsystem is a distributed control system (DCS), which is configured as follows: Receive monitoring signals from the level gauge (20), sensor group (21), and wind speed monitoring device; Based on the received signals and external load commands, the control signals are output to the actuators to adjust the operating status of each damper, valve, coal feeder (4), variable frequency powder feeder (9) and exhaust fan (10), thereby realizing automatic switching of operating modes.

10. A method for deep peak shaving operation of a pulverizing system for a thermal power unit according to any one of claims 1 to 9, characterized in that: The method is used to handle the following working conditions: High load condition: The operating mode is 3 direct-fired coal mills (3) + 3 storage coal mills (22) operating at full load. The air temperature control is: adjust the air temperature according to the coal quality change and maintain the mill outlet temperature at 65-75℃. Medium load condition: The operating mode is 2 direct-fired coal mills (3) + 2 storage coal mills (22) in operation, 1 storage type pulverizing subsystem is in hot standby, and the air temperature is controlled by adjusting the air temperature according to the coal quality change to maintain the mill outlet temperature at 65-75℃. Deep peak shaving operation: The operating mode is 1 direct-fired coal mill (3) + 1 storage coal mill (22) in operation, 1 storage pulverizing subsystem is in hot standby, the air temperature control is to raise the inlet air temperature of the storage pulverizing subsystem to the design reference temperature line through reheating, the exhaust gas treatment is to fully open the recirculation system with a circulation rate of 30-50% to maintain the air-powder balance of the system; Hot standby mode: A storage-type pulverizing subsystem is kept in hot standby mode, the storage pulverizer (22) is kept at the lowest speed, and the pulverized coal bin (8) is kept at 30%-70% material level, ready to respond to sudden load changes at any time.

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