Coal-fired unit ultra-low load stable operation of a coal pulverizing system and control method

Abstract

The present application belongs to the field of coal-fired power plant pulverized coal boiler equipment, and particularly relates to a pulverized coal system and control method for stable operation of a coal-fired unit under ultra-low load, comprising: a medium-speed coal mill, a burner, a boiler, a wind box, a fine powder separator, a first explosion door, a second explosion door, a moisture absorption pipe, a powder exhaust fan, a pulverized coal bin, a powder feeder, a pulverized coal mixer, a first valve, a second valve, a third valve and a fourth valve. Under the condition of ultra-low load of the unit, the coupling degree of the coal mill and the boiler is reduced, and compared with the medium-speed mill direct-fired pulverized coal system, the influence of the instability of the coal mill pulverizing on the stable combustion of the boiler under low load is avoided. The present application improves the air-pulverized coal distribution balance, improves the powder supply flexibility, and also improves the operation economy and safety of the pulverized coal system. The present application can effectively solve the problems of the direct-fired pulverized coal system under ultra-low load of the unit, and at the same time, does not affect the operation state of other load conditions, and the amount of transformation is small.

Description

Technical Field

[0001] This invention belongs to the field of pulverized coal boiler equipment for coal-fired power plants, and particularly relates to a pulverizing system and control method for stable operation of coal-fired units under ultra-low load. Background Technology

[0002] Currently, most coal-fired power units with a capacity of 300MW and above adopt direct-fired pulverizing systems. However, with the increasing demand for deep peak shaving in coal-fired power units, the shortcomings of direct-fired pulverizing systems under ultra-low load conditions are becoming increasingly prominent. On the one hand, under ultra-low load conditions, the adverse effects of air-coal concentration, air-coal balance, and coal quality disturbance on boiler combustion are non-linearly amplified. In direct-fired pulverizing systems, the air-coal distribution balance in the pulverizer outlet pipe is poor, and it is impossible to compensate and adjust the amount of pulverized coal in the primary air duct, which reduces the combustion stability of the unit at low load. On the other hand, for system safety considerations, the two bottom-level pulverizers still need to be kept running under ultra-low load conditions, while the total fuel demand is very low. This causes the pulverizers to deviate significantly from their rated output, resulting in high power consumption and poor economic efficiency. It also affects the safe operation and service life of the pulverizers. In addition, in order to ensure sufficient air ring velocity, the air-coal concentration is too low.

[0003] Based on the above analysis, the problems and shortcomings of the existing technology are as follows:

[0004] 1. High power consumption, poor economy, loud operating noise, and unsafety of coal mills: Under ultra-low load, in order to ensure system safety, it is necessary to keep the two bottom coal mills running, but the fuel demand is very small, which causes the coal mills to deviate significantly from the rated output, resulting in increased power consumption and decreased economy; at the same time, it affects the safe operation and service life of the coal mills.

[0005] 2. Low air-coal concentration: Under ultra-low load conditions, when two coal mills are operating, the air-coal ratio is reduced to ensure air velocity, resulting in a lower air-coal concentration.

[0006] 3. Poor air-coal distribution balance: Under ultra-low load, changes in air-coal concentration and coal quality will amplify the impact on combustion. The air-coal distribution balance of the outlet pipe of the direct-fired pulverizing system is poor and cannot be effectively compensated, affecting combustion stability.

[0007] 4. Reduced combustion stability at low loads: Changes in air-coal concentration and uniformity, as well as disturbances in coal quality, are amplified nonlinearly under ultra-low loads, reducing the combustion stability of the unit at low loads.

[0008] Therefore, the key technical problems that need to be solved in existing direct-fired pulverizing systems under ultra-low load conditions are improving economic efficiency (reducing power consumption), improving the balance of air-coal distribution and air-coal concentration, and improving the combustion stability of the unit at low loads. This also provides technical directions and design ideas for subsequent invention patents. Summary of the Invention

[0009] To address the problems existing in the prior art, this invention provides a pulverizing system and control method for stable operation of coal-fired power units under ultra-low loads. It modifies a medium-speed mill direct-fired pulverizing system by connecting a pulverized coal silo in series with the pulverized coal outlet pipe of a mill connected to the bottom burner, transforming it into an intermediate storage pulverizing system. The remaining mills retain their original system structure. Thus, under ultra-low loads, due to the presence of the silo, only one mill can operate, allowing its output to approach its economical output. The number of pulverized coal feeding pipelines is reduced, the required air volume is decreased, and the air-coal concentration is increased. Simultaneously, pulverized coal is supplied to the burner by the feeder; by adjusting the speed of different feeders, a balanced air-coal distribution can be achieved. This effectively improves the operational stability and economy of the unit under ultra-low loads, achieving stable combustion of the boiler under ultra-low loads.

[0010] This invention is implemented as follows: a pulverizing system for stable operation of a coal-fired unit under ultra-low load. The system employs a combination of a medium-speed coal mill and a fine powder separator, and utilizes a pulverized coal silo to achieve intermediate storage-type pulverized coal processing, ensuring a stable supply of pulverized coal even under ultra-low load conditions. The system connects the pulverized coal silo to multiple coal hoppers and pulverizers, allowing for more precise pulverized coal distribution. In terms of control strategy, the total fuel quantity integrates the coal quantity from multiple parts and adopts a waste gas pulverization method. Precise control of the pulverized coal delivery air volume is achieved by adjusting various valves, ensuring stable operation under ultra-low load conditions.

[0011] Furthermore, the pulverizing system for stable operation of coal-fired power units under ultra-low load includes: medium-speed coal mill, burner, boiler, air box, fine powder separator, first explosion-proof door, second explosion-proof door, moisture absorption pipe, exhaust fan, pulverized coal silo, pulverized coal feeder, pulverized coal mixer, first valve, second valve, third valve, and fourth valve;

[0012] The medium-speed coal mill is constructed as a single unit, integrating the coal mill, coal powder separator, and coal powder distributor. The outlet of the medium-speed coal mill is connected to the first air box via a first valve, and then converges with a moisture absorption pipe to connect to the fine powder separator. The fine powder separator has a first explosion-proof door at its upper end, and its lower end is connected to the coal powder silo. The coal powder silo has a moisture absorption pipe connected to the inlet pipe of the fine powder separator. The upper outlet of the fine powder separator is connected to a pulverized coal exhaust fan, which has two outlets: one goes to the coal mill inlet discharge pipe, serving as a recirculation pipe with a baffle plate acting as a hot air recirculation damper; the other is distributed by the second air box, then passes through the third valve and the coal powder mixer to connect to the burner. The lower end of the coal powder silo is connected to a pulverized coal feeder, which in turn connects to the coal powder mixer. Primary air is connected to the intermediate pipe between the third valve and the coal powder mixer via a fourth valve.

[0013] Furthermore, there is one fine powder separator and one pulverized coal silo. The outlet air-coal pipeline of a certain bottom coal mill (hereinafter referred to as Mill A) is connected to the fine powder separator, and the lower end of the fine powder separator is connected to the pulverized coal silo. The remaining 5 mills are direct-fired pulverizing systems, and the outlet air-coal pipelines of the mills are directly connected to the burners.

[0014] Furthermore, there are 6 coal hoppers at the bottom of the coal powder silo, each coal hopper is connected to a coal feeder, for a total of 6 coal feeders, which are connected to 6 coal powder mixers respectively.

[0015] Furthermore, the overall working process is as follows: the A-mill pulverizing system maintains intermediate storage mode throughout the full load process, that is, the pulverized coal ground by the pulverizer enters the pulverized coal silo, and is then fed to the boiler via the pulverizer; the other mills (B, C, D, E, and F mills) maintain direct-fired mode throughout the full load process, that is, the pulverized coal ground by the pulverizer directly enters the burner; under medium and high loads, the mill groups are switched on and off according to the original plan; under ultra-low loads (20% THA and below), only the bottom A mill is retained and operates in the form of an intermediate storage pulverizing system.

[0016] Furthermore, the overall control principle is as follows: the total fuel quantity consists of four parts: the amount of coal fed from the exhaust gas to the primary air pulverized coal pipe, the amount of coal fed by the pulverizer, the amount of coal fed by the B, C, D, E, and F pulverizers, and the amount of coal equivalent to fuel oil. The main fuel control commands are the coal feeding rates of the B, C, D, E, and F pulverizers and the coal feeding rate of the pulverizer; the pulverized coal level in the pulverized coal silo is controlled by interval control, which is controlled by the coal feeding rate of the A pulverizer; the pulverized coal delivery method is exhaust gas delivery, which is controlled by adjusting the opening of the second valve of the hot air recirculation valve to control the pulverized coal delivery volume of the primary air pulverized coal pipe, and the fourth valve is used for reverse air control.

[0017] Another objective of this invention is to provide a control method for a pulverizing system used in the stable operation of a coal-fired unit under ultra-low load. The pulverized coal level control logic is as follows: three pulverized coal level measuring points obtain pulverized coal level feedback through a median selector. The difference between this feedback and the setpoint pulverized coal level is then processed by PID control, manual / automatic operation, and speed limiting to obtain the coal feeder command for feeder A. The total fuel quantity command divided by the number of automatic operations serves as the feedforward for the PID controller. The output command for feeder A is not greater than the maximum output of mill A.

[0018] Furthermore, the control logic for the coal feed rates of feeders B, C, D, E, and F, and the coal feed rates of pulverizers is as follows: The coal feed rate of feeder A, after lag, is added to the coal feed rate of hot air recirculation to obtain the coal output rate of mill A; the coal output rate of mill A is multiplied by the separation coefficient of the fine powder separator to obtain the amount of pulverized coal carried in the exhaust gas; the amount of pulverized coal carried in the exhaust gas is multiplied by the correction coefficient formed by the opening of the second and third valves to obtain the amount of pulverized coal from the exhaust gas to the primary air pulverized coal pipe; the difference between the amount of pulverized coal in the exhaust gas and the amount of pulverized coal from the exhaust gas to the primary air pulverized coal pipe is the amount of coal recirculated in the hot air. The sum of the coal feed rate of the pulverizers and the amount of coal from the exhaust gas to the primary air pulverized coal pipe is the amount of coal from the primary air pulverized coal pipe of mill A; the sum of the amount of coal from the primary air pulverized coal pipe of mill A, the coal feed rates of mills B, C, D, E, and F, and the coal equivalent of fuel oil is multiplied by the coal quality correction coefficient to obtain the actual total fuel quantity. The total fuel quantity command from the boiler main control system is compared with the actual fuel quantity as a setpoint. The deviation is processed by PID control and manual / automatic stations to form a fuel main control command for parallel control of the speeds of the B, C, D, E, and F coal feeders. The difference between this fuel main control command and the amount of coal transported from the exhaust gas to the primary air pulverized coal pipe is then used as the feeder speed command after speed limiting. Considering that the number of B, C, D, E, and F coal feeders and the pulverized coal feeders in automatic operation varies, resulting in different control gain in the control loop, the number of automatic coal feeders is used to obtain different proportional gain and integral time values ​​for the PID controllers through two different piecewise linear functions.

[0019] Furthermore, the primary air volume control in the primary air-coal pipe of mill A is achieved by adjusting the opening of the second valve. The control logic is as follows: the coal quantity in the primary air-coal pipe of mill A is converted into the set value of the primary air-coal pipe air volume demand by the function unit, and after being compared with the actual air volume of the main pipe, the second valve opening command is obtained after PID calculation, manual-automatic switch, and speed limiting.

[0020] Another object of the present invention is to provide a computer device, the computer device including a memory and a processor, the memory storing a computer program, which, when executed by the processor, causes the processor to perform the steps of the data synchronization optimization method between serially connected chips.

[0021] Another objective of this invention is to provide an information data processing terminal for implementing the data synchronization optimization system between the serially connected chips.

[0022] Based on the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solution to be protected by this invention are as follows:

[0023] First, under ultra-low load conditions, this invention reduces the coupling between the coal mill and the boiler, and compared with the medium-speed mill direct-fired pulverizing system, avoids the impact of the instability of coal mill pulverization on the stable combustion of the boiler under low load.

[0024] Secondly, this invention transforms the A-mill into a medium-storage pulverizing system, where the pulverizer supplies coal to the burner via a feeder, improving the balance of air-coal distribution and increasing supply flexibility. Only one pulverizer is retained in operation, bringing it close to its economical output, thus improving the economic efficiency and safety of the pulverizing system while also increasing the air-coal concentration. This invention effectively solves the problems of direct-fired pulverizing systems under ultra-low load conditions without affecting the operation of other load conditions, requiring minimal modification.

[0025] Third, existing direct-fired pulverizing systems exhibit significant defects under ultra-low load conditions due to their inherent structural characteristics. On one hand, in direct-fired pulverizing systems, the pulverized coal ground by the high-speed coal mill is separated by a separator and distributed by a distributor before entering six (or four) primary air-coal pipes. However, the uniformity of pulverized coal distribution by the distributor has a certain deviation, generally ±10%~20%. Coupled with pressure changes in each air-coal pipe during operation, the relative deviation of pulverized coal quantity can sometimes reach ±40%. When the coal-fired unit operates at ultra-low load, the impact of the pulverized coal quantity deviation of each burner on the boiler combustion stability is amplified. On the other hand, under ultra-low load conditions, the boiler requires very little fuel, but for the safety of unit operation, at least two coal mills must be kept running. This causes the output of the coal mills to deviate significantly from their economical output, resulting in uneconomical operation of the pulverizing system and even affecting the service life of the coal mills. At the same time, to maintain a certain air ring velocity, the air-coal concentration is too low. Both of these are inherent problems in the structure of the direct-fired pulverizing system itself, which cannot be solved by operational optimization. Moreover, under the background of deep peak shaving demand, they are becoming increasingly prominent under increasingly lower unit operating loads and are gradually attracting people's attention.

[0026] Therefore, this invention transforms one of the bottom coal mills into a medium-storage pulverizing method, while the other coal mills retain their original direct-fired pulverizing method. Under ultra-low load conditions, on the one hand, because the coal powder storage in the coal powder silo acts as a buffer and guarantee, only one coal mill can be kept in operation, improving the economy of the pulverizing system and the air-coal powder concentration; on the other hand, the uneven distribution of coal powder in the primary air-coal powder pipe at the coal mill outlet will not affect the boiler side. Multiple feeders directly supply coal powder to the burner, and there are coal powder quantity adjustment methods for each air-coal powder pipe, which can ensure the uniformity of coal powder quantity among them.

[0027] Fourth, the following are the significant technological advancements brought about by this invention:

[0028] 1. This invention describes the overall architecture of a pulverizing system for stable operation of a coal-fired power unit under ultra-low load. The technological advancement lies in constructing a composite system comprising a medium-speed coal mill, a fine powder separator, a pulverized coal silo, and a pulverizer, ensuring a stable supply of pulverized coal even under ultra-low load conditions to meet the boiler's combustion requirements.

[0029] 2. The key feature of this invention is the establishment of a direct connection between mill A and the fine powder separator, while the other five mills adopt a direct-fired pulverizing system. The technological advancement lies in simplifying the coal powder processing flow of mill A, while providing a highly efficient direct-fired pulverizing system for the other mills.

[0030] 3. This invention adds six coal hoppers and connects them to six coal feeders. The technological advancement lies in this configuration, which allows for more precise coal powder distribution and supply, improving the stability of the coal supply.

[0031] 4. This invention describes the operating process under different loads. When the unit operates under ultra-low load, the system operates by retaining the bottom A mill and using an intermediate storage-type pulverizing system. The technological advancement lies in providing a new operating mode for ultra-low load operation, ensuring stable operation under these conditions.

[0032] 5. This invention defines the overall control principles of the system. The technological advancement lies in clarifying the various components controlling the pulverized coal supply and how to precisely control the pulverized coal delivery air volume. By using exhaust gas for pulverized coal delivery and adjusting various valves, operational stability under ultra-low load conditions is further enhanced.

[0033] In summary, these technical solutions provide crucial technical support for the stable operation of coal-fired power units under ultra-low load conditions, and have brought about significant technological advancements in both system configuration and control strategies. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of the connection structure between the A mill, the pulverized coal bin, and the burner provided in an embodiment of the present invention;

[0036] Figure 2 This is the coal feed rate control logic diagram of feeder A provided in this embodiment of the invention;

[0037] Figure 3 This is a control logic diagram for the coal feeding rate of B\C\D\E\F coal feeders and the coal feeding rate of the pulverizer provided in the embodiments of the present invention;

[0038] Figure 4 This is a logic diagram for controlling the primary air volume of the primary air-powder pipe in mill A, provided in an embodiment of the present invention.

[0039] Figure 5These are temperature cloud maps provided in embodiments of the present invention; (a) shows no deviation; (b) shows a deviation of ±10%; (c) shows a deviation of ±20%.

[0040] Figure 6 These are velocity cloud maps provided in embodiments of the present invention; (a) shows no deviation; (b) shows ±10% deviation; (c) shows ±20% deviation.

[0041] In the diagram: 1. First valve; 2. Second valve; 3. Third valve; 4. Fourth valve; 5. First explosion-proof door; 6. Second explosion-proof door; 7. First air box; 8. Second air box. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0043] To address the problems existing in the prior art, the present invention provides a method, system, device, and terminal for optimizing data synchronization between serially connected chips. The present invention will be described in detail below with reference to the accompanying drawings.

[0044] Taking a 660MW ultra-supercritical unit under a 20% THA stable operating condition as an example, the total fuel demand of the unit under this condition is 58t / h. The direct-fired pulverizing system uses an HP-1003 medium-speed pulverizer with a maximum output of 85.9t / h. However, for safety reasons, it is necessary to keep the two bottom mills running, resulting in an actual output of 29t / h for each mill. This deviates significantly from the economic operating condition of the pulverizer, increases its power consumption, and affects its safe operation. Furthermore, after the medium-speed pulverizer outlet is distributed by the pulverizer distributor, there is a large deviation in the amount of pulverized coal between different pulverized coal pipelines. There is no means to readjust the pulverized coal in each air-coal pipeline, which seriously affects the boiler combustion stability of the unit under 20% THA load and even lower loads. Therefore, in order to improve the stability and economy of the unit under ultra-low load operation, this invention combines the characteristics of direct-fired pulverizing system and intermediate storage pulverizing system, and transforms the bottom A mill into an intermediate storage pulverizing system, while the other coal mills (B, C, D, F, and E mills) retain the original system structure.

[0045] like Figure 1 As shown in the figure, the present invention provides a pulverizing system suitable for stable operation of coal-fired power units under ultra-low load, including a medium-speed coal mill, a burner, a boiler, a first air box 7, a second air box 8, a fine powder separator, a first explosion-proof door 5, a second explosion-proof door 6, a moisture absorption pipe, a pulverizing fan, a pulverized coal silo, a pulverized coal feeder, a pulverized coal mixer, a first valve 1, a second valve 2, a third valve 3, and a fourth valve 4.

[0046] The outlet of the medium-speed coal mill is connected to the first air box 7 via the first valve 1, and then to the fine powder separator via a moisture absorption pipe. The fine powder separator has a first explosion-proof door 5 at its upper end, and a coal powder silo at its lower end. The coal powder silo has a moisture absorption pipe connected to the inlet pipe of the fine powder separator 6. The outlet of the fine powder separator is connected to a pulverizer fan, which has two outlets: one goes to the coal mill inlet drop pipe, which is a recirculation pipe with a baffle plate on the pipe serving as a hot air recirculation damper; the other is distributed by the second air box 8, then passes through the third valve 3 and the coal powder mixer to the burner. The lower end of the coal powder silo is connected to a pulverizer feeder, which is connected to the coal powder mixer. Primary air is connected to the intermediate pipe between the third valve 3 and the coal powder mixer via valve 4.

[0047] The boiler furnace is a counter-flow combustion furnace, divided into a front wall and a rear wall. Each wall has 3 layers of burners and 2 layers of burnout air nozzles, with 6 burners per layer, for a total of 36 burners and 24 burnout air nozzles.

[0048] There are 6 coal mills, namely mill A, mill B, mill C, mill D, mill E and mill F. Among them, mill F is a spare coal mill. The pulverized coal outlet pipes of mills A, B and C are respectively connected to the lower, middle and upper layers of the front wall of the boiler furnace; the pulverized coal outlet pipes of mills D, E and F are respectively connected to the lower, middle and upper layers of the rear wall of the boiler furnace.

[0049] The system includes one fine powder separator and one pulverized coal silo. The outlet air-coal duct of a certain bottom-level coal mill (hereinafter referred to as Mill A) is connected to the fine powder separator, and the lower end of the fine powder separator is connected to the pulverized coal silo. The other five mills are direct-fired pulverizing systems, and the outlet air-coal ducts of the mills are directly connected to the burners.

[0050] The lower end of the pulverized coal silo has 6 coal hoppers, each connected to a pulverized coal feeder, for a total of 6 pulverized coal feeders, which are connected to 6 pulverized coal mixers respectively.

[0051] like Figure 1 As shown in the embodiment of the present invention, a pulverizing system suitable for stable operation of coal-fired power units under ultra-low load is provided. The overall working process is as follows: the A-mill pulverizing system maintains intermediate storage mode during the full load process, that is, the pulverized coal ground by the pulverizer enters the pulverized coal silo and is then fed to the boiler by the pulverizer via the pulverizer; the other mills (B, C, D, E, and F mills) maintain direct-fired mode during the full load process, that is, the pulverized coal ground by the pulverizer directly enters the burner; under medium and high loads, the mill groups are switched according to the original scheme; when under ultra-low load (20% THA and below), only the bottom A mill is retained and operates in the form of an intermediate storage pulverizing system.

[0052] This invention provides a control method for a pulverizing system suitable for stable operation under ultra-low load in a coal-fired unit. The general control principle is as follows: the total fuel quantity consists of four parts: the amount of coal fed from the exhaust gas to the primary air pulverized coal pipe, the amount of coal fed by the pulverizer, the amount of coal fed by the B, C, D, E, and F mills, and the amount of coal equivalent to fuel oil. The main fuel control commands are the amount of coal fed by the B, C, D, E, and F mills and the amount of coal fed by the pulverizer; the pulverized coal level in the pulverized coal silo is controlled by interval control, which is controlled by the amount of coal fed by the A mill; the pulverized coal delivery method is exhaust gas delivery, which is controlled by adjusting the opening of the second valve 2 to control the amount of pulverized coal delivered by the primary air pulverized coal pipe, and valve 4 is used for reverse air control.

[0053] like Figure 2 As shown in the embodiment of the present invention, a control method for a pulverizing system suitable for stable operation under ultra-low load in a coal-fired unit is provided. The pulverized coal silo level control logic is as follows: the pulverized coal silo level feedback is obtained from three pulverized coal silo level measuring points through a median selector, and the difference between the feedback and the setpoint is processed by PID calculation, manual / automatic station, and speed limit to obtain the coal feed command for feeder A. The total fuel quantity command divided by the number of automatic feeders serves as the feedforward for the PID controller. The output command of feeder A is not greater than the maximum output of mill A.

[0054] like Figure 3 As shown, the control method for a pulverizing system suitable for stable operation under ultra-low load in a coal-fired unit, as described in this invention, uses the following control logic for the coal feed rates of feeders B, C, D, E, and F: The coal feed rate of feeder A is delayed and then added to the hot air recirculation coal rate to obtain the coal output rate of mill A; the coal output rate of mill A is multiplied by the separation coefficient of the fine powder separator to obtain the amount of pulverized coal carried in the exhaust gas; the amount of pulverized coal carried in the exhaust gas is multiplied by the correction coefficient formed by the opening of the second valve 2 and the third valve 3 to obtain the amount of pulverized coal from the exhaust gas to the primary air pulverized coal pipe; the difference between the amount of pulverized coal in the exhaust gas and the amount of pulverized coal from the exhaust gas to the primary air pulverized coal pipe is the amount of coal recirculated in the hot air. The sum of the coal feeder rate and the amount of coal from the exhaust gas to the primary air pulverized coal pipe is the amount of coal from the primary air pulverized coal pipe of mill A; the sum of the amount of coal from the primary air pulverized coal pipe of mill A, the coal feed rates of mills B, C, D, E, and F, and the coal equivalent of fuel oil is multiplied by the coal quality correction coefficient to obtain the actual total fuel quantity. The total fuel quantity command from the boiler main control system is compared with the actual fuel quantity as a setpoint. The deviation is processed by PID control and manual / automatic stations to form a fuel main control command for parallel control of the speeds of the B, C, D, E, and F coal feeders. The difference between this fuel main control command and the amount of coal transported from the exhaust gas to the primary air pulverized coal pipe is then used as the feeder speed command after speed limiting. Considering that the number of B, C, D, E, and F coal feeders and the pulverized coal feeders in automatic operation varies, resulting in different control gain in the control loop, the number of automatic coal feeders is used to obtain different proportional gain and integral time values ​​for the PID controllers through two different piecewise linear functions.

[0055] like Figure 4As shown in the figure, the present invention provides a control method for a pulverizing system suitable for stable operation of a coal-fired unit under ultra-low load. The primary air volume control in the primary air-coal pipe of mill A is achieved by adjusting the second valve 2. The control logic is as follows: the coal quantity in the primary air-coal pipe of mill A is converted into the primary air-coal pipe air volume demand set value by the function, compared with the actual air volume of the main pipe, and then processed by PID calculation, manual / automatic switch, and speed limit to obtain the opening command of the second valve 2.

[0056] An application embodiment of the present invention provides a computer device, which includes a memory and a processor. The memory stores a computer program, and when the computer program is executed by the processor, the processor performs the steps of a control method for a pulverizing system that operates stably under ultra-low load in a coal-fired unit.

[0057] An application embodiment of the present invention provides an information data processing terminal, which is used to realize the stable operation of the pulverizing system of a coal-fired unit under ultra-low load.

[0058] The following is a further description based on the experimental process and data of this invention:

[0059] The pulverized coal distribution uniformity of the pulverized coal distributor used in the medium-speed mill direct-fired pulverizing system has a certain deviation accuracy, generally ±10%~20%. In addition, due to pressure changes in each air-coal pipe during actual operation, the relative deviation of pulverized coal quantity can sometimes even reach ±40%. To compare and explore the impact of different pulverized coal quantity deviations on boiler combustion stability under ultra-low load conditions, a geometric model of the opposed combustion furnace of a 660MW supercritical unit was established using modeling software such as Gambit. The combustion process of each burner was then simulated in thermal numerical mode on FLUENT software under different air-coal pipe pulverized coal quantity deviation conditions (no deviation, ±10% deviation, ±20% deviation) with only the bottom burner of the front wall retained under 20% ultra-low load conditions. The velocity field and temperature field on a specific cross section (z = 12.8635 m cross section) near the bottom burner were obtained.

[0060] Figure 5 and Figure 6Temperature and velocity cloud maps of different pulverized coal amounts at specific cross-sections near the bottom burner are shown. It is evident that with no deviation and only the bottom burner operating, combustion is stable, the air-coal flow rate is uniform, and the peak outlet temperature of each burner is close to 2000℃. However, as the air-coal deviation increases, problems arise such as large differences in peak outlet temperatures of each burner, inconsistent flame lengths, and uneven air-coal velocities. Even with a deviation of ±20%, some burners experience flameout. Numerical simulation results show that under ultra-low load conditions, the air-coal balance in each air-coal pipe is a crucial factor affecting stable combustion in the boiler at low loads. The pulverizing system and control method proposed in this invention can effectively regulate the air-coal balance in the air-coal pipes. Maintaining only one mill operation also increases the air-coal concentration, achieving stable unit operation under ultra-low loads.

[0061] The following are two specific implementation examples and their solutions:

[0062] Example 1: Pulverizing System for Small Coal-fired Units

[0063] 1. System Configuration:

[0064] The main structure consists of one medium-speed coal mill, one fine powder separator, one coal powder silo, and one coal feeder.

[0065] The air-coal duct at the outlet of mill A is directly connected to the fine powder separator, and the lower end of the fine powder separator is connected to the coal powder silo, forming a simplified process.

[0066] 2. Implementation plan:

[0067] During ultra-low load operation, only mill A is used to operate the intermediate storage pulverizing system to ensure a stable supply of pulverized coal.

[0068] The control strategy is based on the general control principle, using exhaust gas to deliver powder and adjusting the second valve of hot air recirculation to control the powder delivery volume of the primary air powder pipe.

[0069] Example 2: Pulverizing System for Large Coal-fired Units

[0070] 1. System Configuration:

[0071] Six medium-speed coal mills are used, one of which is an A-mill, and the other five are direct-fired pulverizing systems.

[0072] Six coal hoppers are installed and connected to six coal feeders to ensure efficient and rapid coal powder supply.

[0073] 2. Implementation plan:

[0074] During medium-to-high load operation, the original mill group switching scheme is maintained, while during ultra-low load operation, only the bottom A mill is retained and operated using the intermediate storage-type pulverizing system.

[0075] The control strategy is also based on the general control principle. The coal powder supply of mill A is controlled by the coal powder level in the powder silo, while the other five mills directly send the ground coal powder into the burner.

[0076] These two embodiments have been appropriately adapted for coal-fired units of different sizes to ensure stability and efficiency under various operating conditions.

[0077] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A pulverizing system for stable operation of a coal-fired power unit under ultra-low load, characterized in that, The system employs a combination of a medium-speed coal mill and a fine powder separator, and utilizes a coal powder silo to achieve intermediate storage-type coal powder processing, ensuring a stable supply of coal powder even under ultra-low load conditions. The system connects the coal powder silo to multiple coal hoppers and feeders, allowing for more precise coal powder distribution. In terms of control strategy, the total fuel quantity integrates the coal quantity from multiple parts and adopts a waste gas delivery method. The precise control of the delivery air volume is achieved by adjusting various valves, ensuring stable operation under ultra-low load conditions. The pulverizing system for stable operation at ultra-low load in coal-fired power units includes: The outlet of the medium-speed coal mill is connected to the first air box via the first valve, and then to the fine powder separator via the moisture absorption pipe. The fine powder separator is equipped with a first explosion-proof door at the top and a coal powder silo at the bottom. The coal powder silo has a moisture absorption pipe connected to the inlet pipe of the fine powder separator. The outlet of the fine powder separator is connected to the exhaust fan. The fan outlet is divided into two paths: one path goes to the coal mill inlet exhaust pipe, which is a recirculation pipe, and the baffle on the pipe is a hot air recirculation damper; the other path is distributed by the second air box, then passes through the third valve and the coal powder mixer to the burner. The coal powder silo is connected to the feeder at the bottom, and the feeder is connected to the coal powder mixer. The primary air is connected to the intermediate pipe between the third valve and the coal powder mixer via the fourth valve. There is one fine powder separator and one pulverized coal silo. The air-coal duct at the outlet of mill A is connected to the fine powder separator, and the lower end of the fine powder separator is connected to the pulverized coal silo. The other 5 mills are direct-fired pulverizing systems, and the air-coal duct at the outlet of the mill is directly connected to the burner. There are 6 coal hoppers at the lower end of the pulverized coal silo, and each coal hopper is connected to one pulverizer, for a total of 6 pulverizers, which are connected to 6 pulverized coal mixers respectively. The overall working process is as follows: The A pulverizer system maintains an intermediate storage mode during full load, meaning that the pulverized coal from the pulverizer enters the pulverized coal silo and is then fed to the boiler via the pulverizer; the other mills maintain a direct-fired mode during full load, meaning that the pulverized coal from the pulverizer directly enters the burner; under medium and high loads, the mill groups are switched on and off according to the original plan; under ultra-low loads, only the bottom A mill is retained and operates in the form of an intermediate storage pulverizer system. The general control principle is as follows: the total fuel quantity consists of four parts: the amount of coal fed from the exhaust gas to the primary air pulverized coal pipe, the amount of coal fed by the pulverizer, the amount of coal fed by the B, C, D, E, and F pulverizers, and the amount of coal equivalent to fuel oil; the main fuel control commands are the amount of coal fed by the B, C, D, E, and F pulverizers and the amount of coal fed by the pulverizer; the pulverized coal level in the pulverized coal bin is controlled by interval control, which is controlled by the amount of coal fed by the A pulverizer; the pulverized coal delivery method is exhaust gas delivery, which is controlled by adjusting the opening of the second valve of the hot air recirculation to control the amount of pulverized coal delivered by the primary air pulverized coal pipe, and the fourth valve is used for reverse air control.

2. A control method for a pulverizing system used in a coal-fired power unit operating stably under ultra-low load as described in claim 1, characterized in that, By employing multi-parameter integrated control and optimization, high-precision and high-stability control of the pulverizing system under ultra-low load conditions of coal-fired power units is achieved.

3. The control method for a pulverizing system operating stably under ultra-low load in a coal-fired unit as described in claim 2, characterized in that, The actual coal powder level in the coal powder silo is fed back by using the median value of three-point coal powder level measurement, and then PID control is performed with the set value to achieve stable coal powder supply control. The optimal coal feed rate for each coal mill and feeder is calculated based on the coal outlet rate of mill A, the separation coefficient of the fine powder separator, the correction coefficient of the second valve opening, and the correction coefficient of the third valve opening. The total fuel quantity command of the boiler main control is compared with the actual fuel quantity, and the speed control command of the BF coal feeder and pulverizer is obtained through PID control. Based on the different number of BF coal feeders and pulverizers that are automatically put into operation, two piecewise linear functions are used to obtain different PID parameters to improve the control performance of the control loop. The amount of coal discharged from mill A is compensated for with lag and then added to the amount of coal recirculated by hot air, taking into account the impact of the amount of coal recirculated by hot air.

4. The control method for a pulverizing system operating stably under ultra-low load in a coal-fired unit as described in claim 2, characterized in that, The control logic for the coal feed rate of feeders B, C, D, E, and F, and the coal feed rate of pulverizers is as follows: This integrated approach combines several key parameters, including the coal output of mill A, the separation coefficient of the fine powder separator, and the valve opening correction coefficient. This integrated method enables the pulverizing system to achieve precise control of each mill and feeder even under ultra-low load conditions, ensuring a stable supply of coal.

5. The control method for a pulverizing system operating stably under ultra-low load in a coal-fired unit as described in claim 4, characterized in that, Also includes: Two piecewise linear functions are used to adapt to different operating conditions by adjusting the proportional gain and integral time of the PID controller.

6. The control method for a pulverizing system operating stably under ultra-low load in a coal-fired unit as described in claim 2, characterized in that, The primary air volume control in the primary air-coal pipe of mill A is achieved by adjusting the opening of the second valve. The control logic is as follows: the coal quantity in the primary air-coal pipe of mill A is converted into the set value of the primary air-coal pipe air volume demand by the function unit. After being compared with the actual air volume of the main pipe, the second valve opening command is obtained after PID calculation, manual-automatic switch, and speed limiting.

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