Coal-fired unit variable load control method and system for quickly adjusting the pulverized coal output of a coal mill

Abstract

The present application relates to the field of automatic control of thermal power generation, and in particular to a coal-fired unit variable load control method and system for quickly adjusting the pulverized coal output of a coal mill, which collects AGC load instructions and operation control mode signals, when the unit is in a coordinated control mode and the AGC load increase instruction is triggered, synchronously executes the reduction of the dynamic separator speed, the increase of the primary air volume feedforward, and the increase of the mill roller loading force; when the AGC load decrease instruction is triggered, synchronously executes the increase of the dynamic separator speed, the decrease of the primary air volume feedforward, and the decrease of the mill roller loading force; real-time collection of the actual value and the set value of the main steam pressure, calculation of the pressure deviation and the change rate, when the main steam pressure response meets the standard or the regulation duration reaches the preset upper limit, the three parameters are restored to the original values at a preset rate and then the method is exited. The present application quickly changes the pulverized coal output of the coal mill in the variable load starting stage through the coordinated short-time adjustment of the three control quantities, so that the main steam pressure response time is shortened by more than 30%.

Description

Technical Field

[0001] This invention relates to the field of automatic control for thermal power generation, specifically a method and system for variable load control of coal-fired power units that rapidly adjusts the pulverized coal output of coal mills. Background Technology

[0002] With the increasing penetration rate of new energy power generation (wind power, photovoltaic), coal-fired power generating units need to frequently participate in deep peak shaving of the power grid and have rapid automatic generation control (AGC) response capabilities. The key to improving the unit's load change rate lies in rapidly increasing the heat released by boiler combustion, thereby stabilizing the main steam pressure.

[0003] The large inertia and significant delay characteristics of the pulverizing system are the main factors limiting the rate of load change in coal-fired power units. In existing technologies, when the unit needs to rapidly increase the load, the control system immediately increases the coal feed rate and the primary air volume of the pulverizer. However, due to the inertia of the pulverized coal produced by the pulverizer and the strict screening of pulverized coal by the dynamic separator, there is a significant lag (typically 90-180 seconds) between the coal feed and its actual entry into the furnace for combustion. Traditional dynamic separator control strategies aim to maintain a constant pulverized coal fineness, and the rotational speed is usually set to a fixed value or adjusted positively with the coal feed rate (increasing the coal feed rate increases the rotational speed to prevent the pulverized coal from becoming too coarse). Although this strategy ensures combustion efficiency, in the initial stage of load change, the high-speed separator screens a large amount of freshly ground medium-sized pulverized coal back to the grinding disc for regrinding, resulting in a slow increase in the instantaneous pulverized coal concentration at the pulverizer outlet. The boiler heat release lags behind the load command, ultimately limiting the response speed of the main steam pressure. Excessive increases in the coal feed rate or primary air volume can easily lead to mill blockage or pipe wear.

[0004] Existing patents (such as CN117399152A) propose a directional approach of reducing separator speed during load increases and increasing separator speed during load decreases, but they do not provide specific calculation methods for adjustment amounts, safety constraints, or exit and recovery mechanisms based on main steam pressure response, making direct engineering implementation difficult. Furthermore, existing technologies lack a complete technical solution for the coordinated control of dynamic separator speed regulation with primary air volume feedforward and grinding roller loading force feedforward.

[0005] Therefore, how to fully utilize the adjustment capability of the pulverizing system to rapidly increase or decrease the effective pulverized coal output at the coal mill outlet without compromising subsequent combustion stability is a pressing technical problem in this field. This invention proposes a control method and system for improving the variable load rate of coal-fired power units by utilizing the adjustment capability of the pulverizing system, specifically for commonly used medium-speed mill systems. Summary of the Invention

[0006] The purpose of this invention is to provide a method and system for controlling the variable load of a coal-fired power unit by rapidly adjusting the pulverized coal output of the coal mill, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for rapidly adjusting the pulverized coal output of a coal-fired power unit under variable load control includes the following steps:

[0009] S1. Collects the load command changes and operation control mode signals of the unit's AGC. When the unit is in coordinated control mode and the AGC load increase command is triggered, it outputs a load increase adjustment signal; when the unit is in coordinated control mode and the AGC load decrease command is triggered, it outputs a load decrease adjustment signal.

[0010] S2. Based on the load increase or load decrease adjustment signal, simultaneously adjust the following three parameters of the coal mill for a short period of time:

[0011] (a) Dynamic separator speed: The speed is reduced when the load is increased and increased when the load is decreased. The adjustment amount is calculated based on the change in load command and is constrained by the upper and lower limits of the speed.

[0012] (b) Primary air volume: The feedforward increment is superimposed on the basic air volume. The feedforward increment is calculated based on the load command change and its rate of change, and is subject to air volume limit constraints.

[0013] (c) Roller loading force: The feedforward increment is superimposed on the basic loading force. The feedforward increment is calculated based on the load command change and its rate of change, and is constrained by the upper and lower limits of the loading force.

[0014] S3. Real-time acquisition of the actual and set values ​​of the main steam pressure, and calculation of pressure deviation and pressure change rate;

[0015] S4. When the exit conditions are met, the dynamic separator speed, primary air volume and grinding roller loading force are restored to their original values ​​before adjustment at a preset rate. The exit conditions include the main steam pressure response meeting the standard or the adjustment duration reaching the preset upper limit.

[0016] S5. When all three parameters have returned to their original values, exit the current variable load control and wait for the next trigger.

[0017] As a further aspect of the present invention: the method for adjusting the speed of the dynamic separator in step S2 is as follows:

[0018] When the load increases, the target deceleration value ΔN j =k j ×ΔLoad, where ΔLoad is the load command change, k j The preset proportional coefficient determines the rotational speed after speed reduction: N0 - ΔN j Not lower than the minimum permissible speed N min N min≥0.4×N0, where N0 is the original rotational speed, and the deceleration duration is preset to 20-60 seconds;

[0019] When the load is reduced, the target acceleration value ΔN s =k s ×(ΔLoad / T), where T is the preset time constant, and k s The preset proportional coefficient determines the rotational speed after acceleration: N0 + ΔN s Not exceeding the maximum permissible speed N max N max ≤1.4×N0, and the acceleration duration is preset to 20-90 seconds.

[0020] As a further aspect of the present invention: the minimum permissible rotational speed N min The maximum permissible speed N is determined based on the volatile matter and grindability of the coal, ensuring that the particle size R90 of the pulverized coal at the separator outlet does not exceed 35% at this speed. max Determined based on the volatile matter and grindability of the coal.

[0021] As a further aspect of the present invention: the primary air volume feedforward increment ΔQ in step S2 air Calculate using the following formula:

[0022] ΔQ air =K A ×ΔLoad+K D ×d(ΔLoad) / dt;

[0023] Among them, K A K is the proportional gain coefficient. D Here, d(ΔLoad) / dt is the differential gain coefficient, and d(ΔLoad) / dt is the rate of change of the load command.

[0024] The final set value for the primary air volume is:

[0025] ;

[0026] in, The primary air volume is the baseline value generated from a preset function curve based on the current coal feed rate; the feedforward increment is limited by... ≤ΔQ air ≤ , It is 15% of the rated ventilation volume.

[0027] As a further aspect of the present invention: the feedforward increment ΔF of the grinding roller loading force in step S2 is calculated using the following formula:

[0028] ΔF=K F ×ΔLoad+K FD ×d(ΔLoad) / dt;

[0029] Among them, K F K is the proportional gain coefficient. FD The differential gain coefficient;

[0030] The final set value for the loading force of the grinding roller is:

[0031] F sp =F base (coal)+ΔF;

[0032] Among them, F base (coal) is the basic value of the loading force determined by the loading force-coal quantity function curve based on the current coal feed rate; the final set value of the grinding roller loading force is limited by F. min ≤F sp ≤F max F min F is set according to the need to prevent grinding disc vibration. max The pressure shall not exceed 90% of the rated working pressure of the hydraulic system.

[0033] As a further aspect of the present invention: the exit condition in step S4 is:

[0034] During load increase regulation, the recovery phase begins when any of the following conditions are met:

[0035] Condition A: The main steam pressure deviation e enters the preset dead zone and the pressure change rate dP st When / dt changes from a negative value to a positive value and remains so for more than 8 seconds, the preset dead zone is |e|≤0.3MPa;

[0036] Condition B: Adjust the duration to reach the preset maximum duration of 90 seconds;

[0037] During load reduction regulation, the recovery phase begins when any of the following conditions are met:

[0038] Condition A: The main steam pressure deviation e enters the preset dead zone and the pressure change rate dP st When / dt changes from a positive value to a negative value and remains so for more than 8 seconds, the preset dead zone is |e|≤0.3MPa;

[0039] Condition B: Adjust the duration to reach the preset maximum duration of 90 seconds.

[0040] As a further aspect of the present invention: the method for restoring the dynamic separator speed in step S4 is as follows: the speed is gradually restored from the current value to the original speed N0 at a ramp rate of 30-60 rpm / s; during the restoration process, if the main steam pressure exceeds the upper limit of the pressure setting value, the speed restoration is paused and the speed is restored at a preset rate, wherein the upper limit of the pressure setting value is P. sp +0.3MPa, where P spMain steam pressure setpoint.

[0041] As a further aspect of the present invention: the adjustment of the dynamic separator speed, the feedforward adjustment of the primary air volume and the feedforward adjustment of the grinding roller loading force in step S2 are executed synchronously, and all three are adjusted for a short time within a preset duration, and then synchronously restored after the exit condition is met.

[0042] The present invention also proposes a variable load control system for coal-fired power units that rapidly adjusts the pulverized coal output of a coal mill to implement the method described in any of the preceding claims, comprising:

[0043] Data acquisition module: used to collect unit load commands, main steam pressure, coal mill feed rate, primary air volume and current speed of dynamic separator in real time;

[0044] Variable load triggering judgment module: used to output load increase adjustment signal or load decrease adjustment signal according to the operation control mode signal, AGC load increase command and AGC load decrease command;

[0045] Dynamic separator speed control module: Receives the trigger signal, calculates the target speed value and upper and lower speed limits according to preset logic, and generates a speed adjustment command;

[0046] Primary air volume control module: used to calculate the primary air volume feedforward increment based on the load command change and its rate of change, add it to the basic air volume setpoint, and generate a primary air volume adjustment command;

[0047] The grinding roller loading force control module is used to calculate the feedforward increment of the grinding roller loading force based on the change in load command and its rate of change, and then add it to the basic loading force set value to generate a loading force adjustment command.

[0048] Pressure response monitoring module: used to calculate the main steam pressure deviation and rate of change in real time;

[0049] Parameter recovery control module: used to generate recovery commands for rotation speed, air volume and loading force at a set rate when the exit conditions are met;

[0050] Execution interface module: Used to convert various regulation commands into 4-20mA or communication signals, and output them to the frequency converter driver or regulating valve of the corresponding actuator.

[0051] As a further aspect of the present invention: the dynamic separator speed control module, the primary air volume control module, and the grinding roller loading force control module are controlled by the same trigger signal and synchronously output adjustment commands; the parameter recovery control module synchronously outputs recovery commands for the three parameters when the exit conditions are met.

[0052] Compared with the prior art, the beneficial effects of the present invention are:

[0053] 1. Significantly improve the main steam pressure response speed: In the initial stage of load change (within 0-60 seconds), by actively reducing the speed of the dynamic separator, the screening of coal powder fineness is relaxed, the instantaneous coal powder concentration at the coal mill outlet is increased, the boiler combustion heat is released in advance, and the main steam pressure response time is shortened by about 30%, which provides pressure release space for subsequent load increase; during the load reduction process, the amount of coal powder entering the boiler is rapidly reduced to achieve the goal of rapid load reduction.

[0054] 2. Balancing combustion stability and fuel economy: By setting a minimum engine speed limit (N... min The system features a short time window to prevent combustion delays, a sharp increase in fly ash carbon content, or furnace negative pressure fluctuations caused by excessively coarse pulverized coal (particle size greater than 300μm). The entire adjustment process is a "short-term, limited-amplitude" active disturbance, and the speed automatically recovers after the load change ends, without affecting the fineness of the pulverized coal and combustion efficiency under steady-state conditions.

[0055] 3. No new hardware required, easy to implement in engineering: This method is based entirely on the logic configuration in the existing distributed control system (DCS). Only the algorithm for setting the speed of the dynamic separator needs to be modified. No additional sensors or actuators are required. It has low investment cost and strong scalability.

[0056] 4. Improve AGC performance indicators: By compensating for the "under-response" period of coal mill inertia, the actual load of the unit can better track AGC commands, improve the regulation rate and regulation accuracy, and bring direct economic benefits to the power plant. Attached Figure Description

[0057] Figure 1 This is a schematic diagram of the control system module structure of the present invention.

[0058] Figure 2 This is an overall flowchart of the method for rapidly adjusting the pulverized coal output of a coal-fired power unit under variable load control according to the present invention.

[0059] Figure 3 This is a block diagram of the dynamic separator speed adjustment trigger judgment logic of the present invention.

[0060] Figure 4 This is a flowchart of the dynamic speed adjustment mechanism of the dynamic separator of the present invention.

[0061] Figure 5 This is a block diagram of the parameter recovery and exit logic calculation for this invention.

[0062] Figure 6 The figure shows the field test results of shortening the main steam pressure response time after adopting the control method of the present invention. Detailed Implementation

[0063] The technical solution of the present invention will be further described in detail below with reference to specific embodiments.

[0064] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0065] Example 1

[0066] This embodiment uses a coal-fired power generation unit (such as a 600MW subcritical unit) as an example to illustrate the application of the control method of the present invention under rapid load increase conditions.

[0067] 1. Initial operating conditions

[0068] The unit is operating under coordinated control mode, with a current load of 500MW and a main steam pressure setpoint P. sp The actual main steam pressure is 16.0 MPa, P. st The pressure is 16.0 MPa. Multiple coal mills (e.g., four) are operating. The initial speed of the dynamic separator, N0, is 300 rpm (corresponding to a frequency converter frequency of 14 Hz). The current coal feed rate is 180 t / h. The basic value of the primary air volume is... For a capacity of 120 t / h, the basic value of the grinding roller loading force F base (coal) is 120kN.

[0069] 2. AGC load increase command triggered

[0070] At t=0, the power grid AGC issues a load increase command with a target load of 550MW, ΔLoad=50MW, and a required load increase rate of 10MW / min. The system collects the load command change and operation control mode signals from the unit's AGC. The unit's operation control mode display shows the unit is operating in coordinated control mode, and the unit's load increase judgment signal changes from 0 to 1, while the unit's load decrease judgment signal displays 0 (e.g., ...). Figure 3 If the trigger judgment logic shown is executed, then a "reduce separator speed" signal is output, triggering the control logic of this invention. The overall flow of the control method of this invention is as follows: Figure 2 As shown.

[0071] 3. Synchronous adjustment of three parameters

[0072] (1) Dynamic separator speed regulation

[0073] Upon receiving the instruction to "reduce separator speed", a speed reduction command is immediately sent to the frequency converter controller of the coal mill dynamic separator.

[0074] Take k j=8 (example value, adjusted through field testing), ΔN j =k j ×ΔLoad = 8 × 50 = 400 rpm. N0 = 300 rpm, after speed reduction the speed is 300 - 400 = -100 rpm, which is lower than the lower limit constraint. Set the minimum allowable speed N. min N min The amount of nitrogen (N) is determined based on the volatile matter and grindability of the coal, generally ensuring... min ≥0.4×N0, and ensure that the particle size R90 of the pulverized coal at the separator outlet (the residual percentage passing through a 90μm sieve) does not exceed 25%-35% at this rotational speed, to avoid increased unburned carbon loss and the risk of slagging in the furnace. In this embodiment, N min ≥0.4×300=120rpm, therefore the target speed is set to N. min =120rpm (corresponding to a frequency converter frequency of approximately 5.6Hz), that is, a decrease from 14Hz to approximately 5.6Hz. The deceleration duration is preset to 30 seconds.

[0075] After deceleration, the rotational speed is N0-ΔN j =120rpm, not lower than the minimum permissible speed N min (120 rpm), meeting the lower speed limit constraint. The adjustment process for the dynamic separator speed is as follows: Figure 4 As shown.

[0076] (2) Primary air volume feedforward regulation

[0077] During load increase, the increased coal feed rate requires a corresponding increase in primary air volume to promptly transport pulverized coal from the mill to the furnace. In traditional control methods, the primary air volume is generated as a setpoint from the coal feed rate via a function curve f(coal), resulting in a response lag. This invention superimposes a feedforward control variable, the calculation formula of which is as follows:

[0078] ΔQ air =K A ×ΔLoad+K D ×d(ΔLoad) / dt;

[0079] Among them, K A K is the proportional gain coefficient. D Here, K is the differential gain coefficient, d(ΔLoad) / dt is the load command change rate, and K is taken as... A =0.05 (example value), K D =0.02 (example value), load change rate d(ΔLoad) / dt=10 / 60≈0.167MW / s.

[0080] ΔQ air=0.05×50+0.02×0.167=2.5+0.0033≈2.50t / h.

[0081] Primary air volume final set value =120+2.50=122.50t / h.

[0082] To prevent excessively abrupt adjustments to the primary air volume from causing coal blockage or pipe wear, a limiting constraint is applied to the feedforward quantity: ≤ΔQ air ≤ ,in The ventilation capacity is set according to the coal mill's ventilation capacity, with a typical value of 15% of the rated ventilation volume. In this embodiment... =120×15%=18t / h, 2.50t / h is within the limit.

[0083] (3) Feedforward adjustment of grinding roller loading force

[0084] The grinding roller loading force directly determines the grinding output of the coal mill. During load increase, if the loading force is insufficient when the coal quantity suddenly increases, the coal powder on the grinding disc will not be ground sufficiently, resulting in a decrease in powder output efficiency and limiting the instantaneous output capacity of the pulverizing system. This invention increases the grinding roller loading force instantaneously during load increase through a feedforward method, thereby enhancing the instantaneous pulverizing capacity. This ensures that the coal mill has sufficient grinding pressure in the initial stage of increased coal quantity, and works in conjunction with the dynamic separator speed regulation to accelerate the powder output rate. The feedforward calculation formula for the grinding roller loading force is as follows:

[0085] ΔF=K F ×ΔLoad+K FD ×d(ΔLoad) / dt;

[0086] Among them, K F K is the proportional gain coefficient. FD Let K be the differential gain coefficient; F =2.0kN / MW (example value), K FD =0.5 (example value).

[0087] ΔF=2.0×50+0.5×0.167=100+0.0835≈100.08kN.

[0088] The final set value for the loading force of the grinding roller is:

[0089] F sp =F base (coal)+ΔF;

[0090] Among them, F base (coal) is the basic value of the loading force determined by the loading force-coal quantity function curve based on the current coal feed rate; the final set value of the grinding roller loading force is limited by F. min≤F sp ≤F max , where F min F is set according to the need to prevent grinding disc vibration. max The pressure shall not exceed 90% of the rated working pressure of the hydraulic system.

[0091] The actual set value of the grinding roller loading force is F sp =F base (coal)+ΔF=120+100.08=220.08kN.

[0092] In this embodiment, F max =250kN (90% of rated working pressure), 220.08kN is within the limit.

[0093] The aforementioned dynamic separator speed regulation, primary air volume feedforward regulation, and grinding roller loading force feedforward regulation are executed synchronously when the trigger signal arrives, and all three are adjusted for a short period of time within a preset duration.

[0094] 4. Main steam pressure response monitoring

[0095] Real-time acquisition of actual main steam pressure P st With pressure setpoint P sp The deviation e=P sp -P st And calculate the pressure change rate dP st / dt.

[0096] After the adjustment begins, the main steam pressure is monitored in real time. At t=30 seconds, the main steam pressure drops from 16.0 MPa to approximately 15.6 MPa (pressure drop during the initial load increase), and the pressure change rate dP st / dt is negative. At t=45 seconds, the boiler combustion heat begins to be released, and the pressure rises back to approximately 15.8 MPa, dP st / dt changes from negative to positive.

[0097] 5. Parameter recovery

[0098] When in the "reducing separator speed" state, the speed recovery phase will begin if any of the following conditions are met:

[0099] Condition A: The actual main steam pressure deviation e enters the preset dead zone (e, e|≤0.3MPa) and the actual pressure change rate dP st / dt changes from a negative value to a positive value and remains positive for more than 8 seconds;

[0100] Condition B: The duration of the deceleration command has reached the preset maximum duration t. max (For example, 90 seconds).

[0101] In this embodiment, when t=45 seconds, |e|=|16.0-15.8|=0.2MPa≤0.3MPa, and dP st If / dt changes from negative to positive for more than 8 seconds, and recovery condition A is met (e.g., ... Figure 5 (The recovery and exit logic shown) enters the parameter recovery phase.

[0102] The recovery method is as follows:

[0103] Dynamic separator speed: at a preset ramp rate R up (For example, 30-60 rpm / s) reduce the dynamic separator speed from the current value N. current Gradually increase the rotational speed back to the original speed N0 to avoid sudden increases in speed that could cause abrupt changes in the fineness of the pulverized coal and disrupt combustion. In this embodiment, the speed is increased from 120 rpm to 300 rpm at a rate of 45 rpm / s, with a recovery time of approximately 4 seconds.

[0104] Primary air volume: Cancel feedforward increment ΔQ air Return to the set rate =120t / h.

[0105] Roller loading force: Remove the feedforward increment ΔF and return to F at the set rate. base (coal) = 120kN.

[0106] Overshoot prevention: During the speed recovery process, if the main steam pressure exceeds the upper limit of the pressure setpoint (P... sp If the pressure exceeds +0.3 MPa, the speed increase will be paused or slightly reduced. In this embodiment, during the recovery process, the main steam pressure continued to rise to 16.0 MPa and entered a steady state without overshoot.

[0107] 6. Steady-state maintenance

[0108] When the dynamic separator speed returns to N0=300rpm and the primary air volume returns to =120t / h, grinding roller loading force restored to F base When (coal)=120kN, exit this fast load change control logic and wait for the next trigger.

[0109] 7. Control Effect

[0110] To verify the practical effect of the control method of this invention in rapid load change of coal-fired power units, a field application test under rapid load increase conditions was conducted on a large coal-fired power generating unit. By rapidly adjusting key parameters such as the separator motor frequency (reducing the frequency from 14Hz to 10Hz) and increasing the primary air volume, the field test verified that after adopting the control method of this invention, the response time of the main steam header pressure was shortened by about 30% (from 140s to about 100s). Figure 6(As shown). During the test, combustion stability indicators such as fly ash carbon content and furnace negative pressure were all within safe ranges, and no abnormal fluctuations were observed.

[0111] Example 2

[0112] This embodiment illustrates the application of the same unit under rapid load reduction conditions.

[0113] 1. Initial operating conditions

[0114] The unit is operating under coordinated control mode, with a current load of 550MW and a main steam pressure setpoint P. sp The actual main steam pressure is 16.0 MPa. st The pressure is 16.0 MPa. Multiple coal mills (e.g., four) are operating, the initial speed of the dynamic separator is N0 = 300 rpm, and the current coal feed rate is 200 t / h.

[0115] 2. AGC load reduction command triggered

[0116] At t=0, the power grid AGC issues a load reduction command with a target load of 500MW and ΔLoad=-50MW. The changes in the unit's AGC load command and the operating control mode signals are collected. The unit's operating control mode indicates that the unit is operating in coordinated control mode. Furthermore, the unit's load increase judgment signal displays 0, and the unit's load reduction judgment signal changes from 0 to 1. In this case, a "increase separator speed" signal is output, triggering the control logic of this invention.

[0117] 3. Three parameters are adjusted synchronously in opposite directions.

[0118] (1) Dynamic separator speed regulation

[0119] Upon receiving the instruction to "increase the separator speed", the variable frequency controller of the coal mill dynamic separator is immediately sent an acceleration command.

[0120] Take k s =8 (example value), T=60s, ΔN s =k s ×(ΔLoad / T)=8×50 / 60≈6.67rpm. N0=300rpm, the speed after acceleration is 300+6.67=306.67rpm. Set the maximum allowable speed N. max N max The amount of nitrogen (N) is determined based on the volatile matter and grindability of the coal, generally ensuring... max ≤1.4×N0. In this embodiment, N max =1.4×300=420rpm, 306.67rpm is within the limit, safe. The acceleration duration is preset to 40 seconds.

[0121] (2) Primary air volume feedforward regulation

[0122] ΔLoad=-50MW

[0123] ΔQ air =K A ×ΔLoad+K D ×d(ΔLoad) / dt=0.05×(-50)+0.02×(-0.167)≈-2.50t / h, the primary air volume decreases.

[0124] Primary air volume final set value .

[0125] Limiting check: ≤ΔQ air ≤ -18t / h ≤ -2.50t / h ≤ 18t / h, not exceeding the limit.

[0126] (3) Feedforward adjustment of grinding roller loading force

[0127] ΔF=K F ×ΔLoad+K FD ×d(ΔLoad) / dt=2.0×(-50)+0.5×(-0.167)≈-100.08kN, the loading force decreases.

[0128] Actual grinding roller loading force setting value F sp =F base (coal)+ΔF.

[0129] Amplitude limit check: F min ≤F sp ≤F max The limit has not been exceeded.

[0130] The aforementioned dynamic separator speed regulation, primary air volume feedforward regulation, and grinding roller loading force feedforward regulation are executed synchronously when the trigger signal arrives, and all three are adjusted for a short period of time within a preset duration.

[0131] 4. Main steam pressure response and recovery

[0132] Real-time acquisition of actual main steam pressure P st With pressure setpoint P sp The deviation e=P sp -P st And calculate the pressure change rate dP st / dt.

[0133] After regulation begins, the main steam pressure rises from 16.0 MPa (pressure rise during the initial load reduction phase), reaching 16.2 MPa at t=40 seconds before starting to decline. st / dt changes from positive to negative.

[0134] When in the "increase separator speed" state, the speed recovery phase will begin if any of the following conditions are met:

[0135] Condition A: The actual main steam pressure deviation e enters the preset dead zone (e, e|≤0.3MPa) and the actual pressure change rate dP st / dt changes from a positive value to a negative value and remains so for more than 8 seconds;

[0136] Condition B: The duration of the acceleration command has reached the preset maximum duration t. max (For example, 90 seconds).

[0137] In this embodiment, recovery condition A is met, and the parameter recovery phase begins.

[0138] The recovery method is as follows: the dynamic separator speed gradually recovers from the current value to the original speed N0 at a preset ramp rate R_up; the primary air volume feedforward increment ΔQ is canceled. air Return to the set rate The feedforward increment ΔF of the grinding roller loading force is removed, and the force returns to F at a set rate. base (coal).

[0139] 5. Control effect

[0140] The main steam pressure quickly tracked the set value and entered a steady state without excessive overshoot, and the load change rate met the AGC assessment requirements.

[0141] Example 3

[0142] This embodiment illustrates the specific deployment architecture of the control system of the present invention.

[0143] The control method of this invention is based on the existing distributed control system (DCS) of the unit, requiring no additional hardware. For example... Figure 1 As shown, a control system for implementing the above method includes:

[0144] Data acquisition module: used to collect unit load commands, main steam pressure, coal mill feed rate, primary air volume and current speed of dynamic separator in real time;

[0145] Variable load triggering judgment module: used to output load increase adjustment signal or load decrease adjustment signal based on the operation control mode signal, AGC load increase command and AGC load decrease command;

[0146] Dynamic separator speed control module: Receives the trigger signal, calculates the target speed value and upper and lower speed limits according to preset logic, and generates a speed adjustment command;

[0147] Primary air volume control module: used to calculate the primary air volume feedforward increment based on the load command change and its rate of change, add it to the basic air volume setpoint, and generate a primary air volume adjustment command;

[0148] The grinding roller loading force control module is used to calculate the feedforward increment of the grinding roller loading force based on the change in load command and its rate of change, and then add it to the basic loading force set value to generate a loading force adjustment command.

[0149] Pressure response monitoring module: used to calculate the main steam pressure deviation and rate of change in real time;

[0150] Parameter recovery control module: used to generate recovery commands for rotation speed, air volume and loading force at a set rate when the exit conditions are met;

[0151] Execution interface module: used to convert various adjustment commands into 4-20mA or communication signals and output them to the frequency converter driver or control valve of the corresponding actuator.

[0152] The specific deployment method is as follows:

[0153] The data acquisition module utilizes the existing analog input channels of the DCS to acquire signals from the main steam pressure transmitter, coal feeder weighing signal, primary air volume measurement device, and separator frequency converter feedback speed. Each control module (trigger judgment, speed calculation, air volume calculation, loading force calculation, pressure monitoring, and recovery control) is configured as a function block in the DCS control logic page, with a sampling period of 100ms-200ms.

[0154] The dynamic separator speed control module, primary air volume control module, and grinding roller loading force control module are controlled by the same trigger signal and output adjustment commands synchronously; the parameter recovery control module outputs recovery commands for the three parameters synchronously when the exit conditions are met.

[0155] In the execution interface module, speed regulation commands are sent to the separator frequency converter via the DCS's analog output channel (4-20mA); primary air volume regulation commands are sent to the primary air damper actuator via the DCS's analog output channel; and loading force regulation commands are sent to the hydraulic system's proportional control valve via the DCS's analog output channel. Signal transmission between modules is achieved through the DCS's internal database variables, eliminating the need for external communication interfaces.

[0156] The specific settings for the above parameters need to be determined through on-site load step tests based on the actual operating conditions of the unit. The values ​​may vary depending on the type of coal and the model of the coal mill, but they are all within the typical range given in this invention.

[0157] This method and system for rapidly adjusting the pulverized coal output of coal-fired power units can be directly implemented through logic configuration in existing coal-fired power unit DCS without the need for additional hardware. It is applicable to various direct-fired pulverizing systems with medium-speed coal mills and dynamic separators. Field tests have verified that this method can significantly shorten the main steam pressure response time during unit load changes, improve AGC performance indicators, and has broad industrial application prospects and significant economic benefits.

[0158] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these should also be considered within the scope of protection of the present invention. These will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A method for variable load control of coal-fired power units that rapidly adjusts the pulverized coal output of a coal mill, characterized in that, Includes the following steps: S1. Collects the load command changes and operation control mode signals of the unit's AGC. When the unit is in coordinated control mode and the AGC load increase command is triggered, it outputs a load increase adjustment signal; when the unit is in coordinated control mode and the AGC load decrease command is triggered, it outputs a load decrease adjustment signal. S2. Based on the load increase or load decrease adjustment signal, simultaneously adjust the following three parameters of the coal mill for a short period of time: (a) Dynamic separator speed: The speed is reduced when the load is increased and increased when the load is decreased. The adjustment amount is calculated based on the change in load command and is constrained by the upper and lower limits of the speed. (b) Primary air volume: The feedforward increment is superimposed on the basic air volume. The feedforward increment is calculated based on the load command change and its rate of change, and is subject to air volume limit constraints. (c) Roller loading force: The feedforward increment is superimposed on the basic loading force. The feedforward increment is calculated based on the load command change and its rate of change, and is constrained by the upper and lower limits of the loading force. S3. Real-time acquisition of the actual and set values ​​of the main steam pressure, and calculation of pressure deviation and pressure change rate; S4. When the exit conditions are met, the dynamic separator speed, primary air volume and grinding roller loading force are restored to their original values ​​before adjustment at a preset rate. The exit conditions include the main steam pressure response meeting the standard or the adjustment duration reaching the preset upper limit. S5. When all three parameters have returned to their original values, exit the current variable load control and wait for the next trigger.

2. The method for rapid adjustment of pulverized coal output in a coal-fired power unit according to claim 1, characterized in that, The method for adjusting the speed of the dynamic separator in step S2 is as follows: When the load increases, the target deceleration value ΔN j =k j ×ΔLoad, where ΔLoad is the load command change, k j The preset proportional coefficient determines the rotational speed after speed reduction: N0 - ΔN j Not lower than the minimum permissible speed N min N min ≥0.4×N0, where N0 is the original rotational speed, and the deceleration duration is preset to 20-60 seconds; When the load is reduced, the target acceleration value ΔN s =k s ×(ΔLoad / T), where T is the preset time constant, and k s The preset proportional coefficient determines the rotational speed after acceleration: N0 + ΔN s Not exceeding the maximum permissible speed N max N max ≤1.4×N0, and the acceleration duration is preset to 20-90 seconds.

3. The method for rapid adjustment of pulverized coal output in a coal-fired power unit according to claim 2, characterized in that, The minimum permissible speed N min The maximum permissible speed N is determined based on the volatile matter and grindability of the coal, ensuring that the particle size R90 of the pulverized coal at the separator outlet does not exceed 35% at this speed. max Determined based on the volatile matter and grindability of the coal.

4. The method for rapid adjustment of pulverized coal output in a coal-fired power unit according to claim 1, characterized in that, The primary air volume feedforward increment ΔQ mentioned in step S2 air Calculate using the following formula: ΔQ air =K A ×ΔLoad+K D ×d(ΔLoad) / dt, Among them, K A K is the proportional gain coefficient. D Here, d(ΔLoad) / dt is the differential gain coefficient, and d(ΔLoad) / dt is the rate of change of the load command. The final set value for the primary air volume is: ， in, The primary air volume is the baseline value generated from a preset function curve based on the current coal feed rate; the feedforward increment is limited by... ≤ΔQ air ≤Δ , It is 15% of the rated ventilation volume.

5. The method for rapidly adjusting the pulverized coal output of a coal-fired power unit according to claim 1, characterized in that, The feedforward increment ΔF of the grinding roller loading force in step S2 is calculated using the following formula: ΔF=K F ×ΔLoad+K FD ×d(ΔLoad) / dt, Among them, K F K is the proportional gain coefficient. FD The differential gain coefficient; The final set value for the loading force of the grinding roller is: F sp =F base (coal)+ΔF, Among them, F base (coal) is the basic value of the loading force determined by the loading force-coal quantity function curve based on the current coal feed rate; the final set value of the grinding roller loading force is limited by F. min ≤F sp ≤F max F min F is set according to the need to prevent grinding disc vibration. max The pressure shall not exceed 90% of the rated working pressure of the hydraulic system.

6. The method for rapidly adjusting the pulverized coal output of a coal-fired power unit according to claim 1, characterized in that, The exit condition described in step S4 is: During load increase regulation, the recovery phase begins when any of the following conditions are met: Condition A: The main steam pressure deviation e enters the preset dead zone and the pressure change rate dP st When / dt changes from a negative value to a positive value and remains so for more than 8 seconds, the preset dead zone is |e|≤0.3MPa; Condition B: Adjust the duration to reach the preset maximum duration of 90 seconds; During load reduction regulation, the recovery phase begins when any of the following conditions are met: Condition A: The main steam pressure deviation e enters the preset dead zone and the pressure change rate dP st When / dt changes from a positive value to a negative value and remains so for more than 8 seconds, the preset dead zone is |e|≤0.3MPa; Condition B: Adjust the duration to reach the preset maximum duration of 90 seconds.

7. The method for rapidly adjusting the pulverized coal output of a coal-fired power unit according to claim 1, characterized in that, The method for restoring the dynamic separator speed in step S4 is as follows: the speed is gradually restored from the current value to the original speed N0 at a ramp rate of 30-60 rpm / s; during the restoration process, if the main steam pressure exceeds the upper limit of the pressure setting value, the speed restoration is paused and the speed is restored at a preset rate, where the upper limit of the pressure setting value is P. sp +0.3MPa, where P sp Main steam pressure setpoint.

8. The method for rapidly adjusting the pulverized coal output of a coal-fired power unit according to claim 1, characterized in that, In step S2, the adjustment of the dynamic separator speed, the feedforward adjustment of the primary air volume, and the feedforward adjustment of the grinding roller loading force are performed synchronously, and all three are adjusted for a short time within a preset duration, and then synchronously restored after the exit condition is met.

9. A variable load control system for a coal-fired power unit that implements the method described in any one of claims 1-8 for rapidly adjusting the pulverized coal output of a coal mill, characterized in that, include: Data acquisition module: used to collect unit load commands, main steam pressure, coal mill feed rate, primary air volume and current speed of dynamic separator in real time; Variable load triggering judgment module: used to output load increase adjustment signal or load decrease adjustment signal according to the operation control mode signal, AGC load increase command and AGC load decrease command; Dynamic separator speed control module: Receives the trigger signal, calculates the target speed value and upper and lower speed limits according to preset logic, and generates a speed adjustment command; Primary air volume control module: used to calculate the primary air volume feedforward increment based on the load command change and its rate of change, add it to the basic air volume setpoint, and generate a primary air volume adjustment command; The grinding roller loading force control module is used to calculate the feedforward increment of the grinding roller loading force based on the change in load command and its rate of change, and then add it to the basic loading force set value to generate a loading force adjustment command. Pressure response monitoring module: used to calculate the main steam pressure deviation and rate of change in real time; Parameter recovery control module: used to generate recovery commands for rotation speed, air volume and loading force at a set rate when the exit conditions are met; Execution interface module: used to convert various adjustment commands into 4-20mA or communication signals and output them to the frequency converter driver or regulating valve of the corresponding actuator.

10. The variable load control system for coal-fired power units that rapidly adjusts the pulverized coal output of a coal mill according to claim 9, characterized in that, The dynamic separator speed control module, primary air volume control module, and grinding roller loading force control module are controlled by the same trigger signal and output adjustment commands synchronously; the parameter recovery control module outputs recovery commands for the three parameters synchronously when the exit conditions are met.

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