Automatic control strategy for fuel feeding and combustion of biomass circulating fluidized bed boiler

Abstract

The application discloses an automatic control strategy for fuel feeding and combustion of a biomass circulating fluidized bed boiler, and solves the problems of how to realize smooth control of oxygen content in a furnace and scientific and reasonable control of biomass fuel combustion; whether an internal disturbance factor or an external disturbance factor is distinguished; according to the distinguishing result, control frequencies of variable frequency speed regulation motors of secondary air fans and variable frequency speed regulation motors of biomass fuel screw feeders are simultaneously regulated to realize following of a variable load; the control frequency of the variable frequency speed regulation motor of the secondary air fan is mainly regulated, that is, when the load of the boiler changes, the secondary air volume is regulated first, and the fuel feeding of the boiler is adjusted following the secondary air volume to realize following change of the load; then, the oxygen content is identified to realize variable load control through air volume prediction, and the automatic biomass fuel feeding and combustion control of the circulating fluidized bed boiler is realized.

Description

Technical Field

[0001] This invention relates to a biomass circulating fluidized bed boiler, and more particularly to an automatic control strategy for fuel feeding and combustion in a biomass circulating fluidized bed boiler. Background Technology

[0002] Biomass circulating fluidized bed boilers burn a wide variety of biomass fuels with complex blends. The biomass fuel feeding system typically employs a screw feeder driven by a variable frequency drive (VFD) motor. Feeding is controlled on-site by adjusting the VFD motor's frequency. In power plants using biomass circulating fluidized bed boilers with back-pressure turbines, the quality and particle size of the biomass fuel vary considerably, and boiler load fluctuates frequently. Under the "heat-driven power generation" production model, power plants operate in a "furnace-following-turbine" manner, significantly increasing the difficulty of combustion control in biomass circulating fluidized bed boilers.

[0003] In power plants using biomass circulating fluidized bed boilers with back-pressure turbines, when the steam load of the circulating fluidized bed boiler fluctuates, unlike coal-fired boilers where changes in coal feed rate are used to address the load changes, the supply of biomass fuel and secondary air must be adjusted simultaneously. Furthermore, the steam load fluctuations in circulating fluidized bed boilers are caused by both internal and external disturbances. Identifying and distinguishing these disturbances, and dynamically adjusting the supply of secondary air and biomass fuel accordingly, becomes a problem that needs to be solved on-site. During the operation of the biomass circulating fluidized bed boiler, when the boiler furnace temperature is too high or too low, especially when there are large fluctuations in the continuity of biomass fuel supply or sudden changes in fuel type, how to automatically control the reasonable supply of biomass fuel in the furnace to ensure stable boiler operation becomes another challenge that needs to be addressed on-site. Summary of the Invention

[0004] This invention provides an automatic control strategy for fuel feeding and combustion in a biomass circulating fluidized bed boiler, solving the technical problem of how to achieve stable control of furnace oxygen and scientific and reasonable regulation of complete combustion of biomass fuel.

[0005] The present invention solves the above technical problems through the following technical solutions:

[0006] The overall concept of this invention is as follows: When the main steam flow rate of a biomass circulating fluidized bed boiler changes, it is first necessary to identify whether the change is caused by internal or external disturbances. Then, based on the identification results, the change in load is followed by simultaneously adjusting the control frequency of the variable frequency speed-regulating motor of the secondary air fan and the variable frequency speed-regulating motor of the biomass fuel screw feeder. The control frequency of the secondary air fan is the primary factor; that is, when the boiler load changes, the secondary air volume is adjusted first, and the boiler fuel feed is adjusted accordingly, thus achieving load-following control. Secondly, changes in feed volume are identified by oxygen content, and variable load control is achieved through air volume prediction. This invention can be summarized as "adjusting oxygen based on feed volume and determining load based on air volume," combined with trend prediction, dynamic proportional control, feedforward control, and dynamic interlocking to achieve scientific control of automatic feeding and combustion in a biomass fuel circulating fluidized bed boiler.

[0007] An automatic control strategy for fuel feeding and combustion in a biomass circulating fluidized bed boiler includes an operating circulating fluidized bed boiler, a secondary air fan, a screw feeder for conveying biomass fuel to the furnace, and a central control room. The screw feeder uses a variable frequency speed-regulating motor to control the feeding rate, and the secondary air fan uses a secondary air variable frequency speed-regulating motor to control the secondary air volume. A main steam flow measurement sensor and a main steam pressure measurement sensor are respectively installed at the main steam outlet of the biomass circulating fluidized bed boiler. A primary air measuring instrument and a secondary air measuring instrument are installed on the air path. A rate module is installed in the central control room. The strategy is characterized by the following steps:

[0008] The first step is to build a main steam pressure PID controller in the central control room, using the real-time main steam pressure value of the operating biomass circulating fluidized bed boiler as the input, the main steam pressure correction value as the output value, and the main steam pressure design value as the setpoint input value. The real-time main steam pressure value collected by the main steam pressure measurement sensor is input to the input terminal of the main steam pressure PID controller, so that the main steam pressure correction value can be obtained at the output terminal of the main steam pressure PID controller.

[0009] The second step is to build a secondary air PID controller by using the real-time measured value of the secondary air volume of the biomass circulating fluidized bed boiler as the input, the predicted value of the secondary air volume as the set-end input value, and the control frequency of the secondary air variable frequency speed control motor as the output value.

[0010] The third step is to collect the total air volume and the corresponding main steam flow rate of the boiler in real time during the continuous operation of the biomass circulating fluidized bed boiler in 20-minute intervals. The total air volume is divided by the corresponding main steam flow rate of the boiler, and iterative learning is continuously performed to finally obtain the learning value X of the total air volume divided by the corresponding main steam flow rate of the boiler.

[0011] Step 4: When the load of the biomass circulating fluidized bed boiler changes, first identify the cause of the load change, whether it is caused by internal or external disturbances; define an increase in main steam flow and a decrease in main steam pressure as an external disturbance; define an increase in main steam flow but an increase in main steam pressure or a constant increase in main steam pressure as an internal disturbance.

[0012] Step 5: Determine the target value of the main steam flow rate using the following method:

[0013] If the identified change in load of the biomass circulating fluidized bed boiler is caused by external disturbances, then the target value of the main steam flow rate is equal to the measured value of the main steam flow rate plus the output value of the main steam pressure PID controller in the first step.

[0014] If the identified load change in the biomass circulating fluidized bed boiler is caused by internal disturbance factors, then the target value of the main steam flow rate is the rated design value of the main steam flow rate of the biomass circulating fluidized bed boiler.

[0015] Step 6: Multiply the target value of the main steam flow obtained in Step 5 by the learning value X obtained in Step 3, and then subtract the primary air volume of the biomass circulating fluidized bed boiler to obtain the predicted secondary air volume.

[0016] Step 7: Input the predicted secondary air volume obtained in Step 6 into the setting terminal of the secondary air PID controller. The input terminal of the secondary air PID controller receives the real-time measurement value of the secondary air volume of the biomass circulating fluidized bed boiler. The output signal of the secondary air PID controller is used to regulate the secondary air variable frequency speed control motor to achieve the adjustment of the secondary air volume.

[0017] Step 8: Set up a feeding PID controller. Use the control frequency of the variable frequency speed control motor of the screw feeder as the output of the feeding PID controller, and use the oxygen content of the flue gas in the tail flue as the input of the feeding PID controller. Set the oxygen content of the flue gas in the tail flue to 5%-6% as the set value of the setting terminal SP of the feeding PID controller.

[0018] Step 9: Input the oxygen content of the flue gas measured by the oxygen content sensor in the tail flue into the rate module, and obtain the rate of change of the oxygen content of the flue gas per second at the output of the rate module.

[0019] Step 10: Using a specific moment as a baseline, collect and calculate the average rate of change (V) of the oxygen content in the flue gas per second over the 20 seconds preceding that baseline moment. O Simultaneously, the average value F of the control frequency F of the variable frequency speed control motor of the screw feeder within 20 seconds prior to the reference time was collected and calculated. 平均 The dynamic proportional coefficient P of the feed PID controller is calculated using the following formula: P = V O×F 平均 ×K; where K = 0.1 - 0.5;

[0020] Step 11: Embed the dynamic proportional coefficient P calculated in Step 10 into the feeding PID controller; input the real-time oxygen content of the flue gas measured by the oxygen content sensor in the tail flue into the input terminal of the feeding PID controller, and input the frequency signal of the output terminal of the feeding PID controller into the variable frequency speed control motor of the screw feeder. The feeding rate of the variable frequency speed control motor of the screw feeder is controlled by the feeding PID controller.

[0021] When the difference between the real-time main steam pressure value measured by the main steam pressure sensor and the design value of the main steam pressure is greater than 0.2 MPa, and the rate of increase of the real-time main steam pressure value per second is greater than 0.002 MPa, the rate of increase of the real-time main steam pressure value per second is multiplied by the corresponding real-time main steam flow rate, the product is multiplied by -1, and the final product is added to the output of the secondary air PID controller as the first feedforward quantity. Together, they serve as the control frequency of the secondary air variable frequency speed control motor to regulate the secondary air volume.

[0022] Using the main steam pressure value as the abscissa (in megapascals) and the negative frequency value as the ordinate (in hertz), the following coordinate points are marked on this coordinate system: (12.5 1), (13.3 2), (13.4 3), and (13.5 4). Connect these four points with straight lines to form a broken line curve function of main steam pressure versus secondary air control frequency. Use this broken line curve function of secondary air control frequency as the second feedforward quantity, add it to the output of the secondary air PID controller, and use it together as the control frequency of the secondary air variable frequency speed control motor to regulate the secondary air volume.

[0023] When the rate of change of oxygen content in the flue gas in the tail flue is V O When the deviation is higher than +0.06% or lower than -0.06%, the proportional coefficient P of the feed PID controller is calculated using the following formula: P = 1.2 × V O ×F 平均 ×K; where K = 0.1-0.5.

[0024] When the bed temperature measured by the bed temperature sensor is higher than 850℃, or when the bed temperature rises by more than 8℃ within 30 seconds, the output value of the feeding PID controller is increased by a lockout function, ensuring that the output value of the feeding PID controller is not greater than the output value when the lockout function is activated. When the bed temperature measured by the bed temperature sensor is lower than 750℃, or when the bed temperature drops by more than 6℃ within 30 seconds, the output value of the feeding PID controller is decreased by a lockout function, ensuring that the output value of the feeding PID controller is not less than the output value when the lockout function is activated.

[0025] When the difference between the oxygen content of the flue gas measured by the oxygen content sensor in the tail flue and the set value of the setting terminal SP of the feed PID controller is greater than 1%, and the increase in the oxygen content of the flue gas per second is greater than 0.04%, the main steam flow measured by the main steam flow sensor at this time is multiplied by the increase in the oxygen content of the flue gas per second at this time, and then multiplied by -0.15. The resulting product is used as the first feedforward quantity and superimposed on the output terminal of the feed PID controller. The frequency obtained after superposition is used to control the variable frequency motor of the screw feeder.

[0026] When the oxygen content of the flue gas measured by the oxygen content measuring sensor in the tail flue is less than 3%, and the oxygen content of the flue gas is still decreasing per second, the main steam flow measured by the main steam flow measuring sensor at this time is multiplied by the decrease in oxygen content of the flue gas per second at this time, and then multiplied by 0.3. The resulting product is used as the second feedforward quantity and superimposed on the output of the feed PID controller. The frequency obtained after superposition is used to control the variable frequency motor of the screw feeder.

[0027] Using the percentage of oxygen content in the flue gas measured by the oxygen content sensor in the tail flue as the abscissa and the negative frequency value (in Hertz) as the ordinate, the following coordinate points are marked on this coordinate: (3% 0.5), (2% 1), (1% 1.5), and (0.5% 3). Connect these four points with straight lines to form a broken line curve function of flue gas oxygen content versus the variable frequency motor control frequency of the screw feeder. Use this broken line curve function of the variable frequency motor control frequency as the third feedforward quantity, superimpose it on the output of the feeder PID controller, and use the frequency obtained after superposition to regulate the variable frequency motor of the screw feeder.

[0028] This invention first identifies whether changes in the boiler's main steam flow are caused by internal or external disturbances. Based on the identification results, a target value for the boiler's main steam flow is determined accordingly. Simultaneously, an iterative learning method is used to couple the total air volume with the main steam flow to obtain a learned value reflecting changes in the main steam flow. Finally, the target main steam flow value is multiplied by the learned value, and the primary air volume is subtracted to obtain a predicted value for the secondary air volume. This predicted value is then input into the setting terminal of the secondary air PID controller, thereby achieving the control of secondary air that involves factors causing changes in the boiler's main steam flow, creatively demonstrating this approach. This invention proposes a strategy to address load fluctuations in biomass circulating fluidized bed boilers, primarily by adjusting the secondary air volume. Based on the principle of "constant oxygen content," the invention regulates the biomass fuel feed rate, pioneering a method for biomass-fueled circulating fluidized bed boilers to ensure relatively stable oxygen content in the flue gas by real-time adjustment of the biomass fuel feed rate. This guarantees stable environmental emission and thermal efficiency indicators for the boiler. Furthermore, it develops strategies to address significant changes in boiler bed temperature and substantial increases or decreases in furnace oxygen content, comprehensively controlling the delivery of biomass fuel. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the main steam pressure PID controller of the present invention;

[0030] Figure 2 This is a schematic diagram of the secondary air PID controller of the present invention;

[0031] Figure 3 This is a schematic diagram of the PID controller for controlling the frequency of the variable frequency speed control motor of the screw feeder according to the present invention. Detailed Implementation

[0032] The present invention will now be described in detail with reference to the accompanying drawings:

[0033] An automatic control strategy for fuel feeding and combustion in a biomass circulating fluidized bed boiler includes an operating circulating fluidized bed boiler, a secondary air fan, a screw feeder for conveying biomass fuel to the furnace, and a central control room. The screw feeder uses a variable frequency speed-regulating motor to control the feeding rate, and the secondary air fan uses a secondary air variable frequency speed-regulating motor to control the secondary air volume. A main steam flow measurement sensor and a main steam pressure measurement sensor are respectively installed at the main steam outlet of the biomass circulating fluidized bed boiler. A primary air measuring instrument and a secondary air measuring instrument are installed on the air path. A rate module is installed in the central control room. The strategy is characterized by the following steps:

[0034] The first step is to build a main steam pressure PID controller using the real-time main steam pressure value of the operating biomass circulating fluidized bed boiler as the input, the main steam pressure correction value as the output value, and the main steam pressure design value as the set-end input value. The real-time main steam pressure value collected by the main steam pressure measurement sensor is input to the input end of the main steam pressure PID controller, so that the main steam pressure correction value can be obtained at the output end of the main steam pressure PID controller.

[0035] The second step is to build a secondary air PID controller by using the real-time measured value of the secondary air volume of the biomass circulating fluidized bed boiler as the input, the predicted value of the secondary air volume as the set-end input value, and the control frequency of the secondary air variable frequency speed control motor as the output value.

[0036] The third step is to collect the total air volume and the corresponding main steam flow rate of the boiler in real time during the continuous operation of the biomass circulating fluidized bed boiler in 20-minute intervals. The total air volume is divided by the corresponding main steam flow rate of the boiler, and iterative learning is continuously performed to finally obtain the learning value X of the total air volume divided by the corresponding main steam flow rate of the boiler.

[0037] Step 4: When the load of the biomass circulating fluidized bed boiler changes, first identify whether the load change is caused by internal or external disturbances. An increase in main steam flow and a decrease in main steam pressure are defined as external disturbances, while an increase in main steam flow but an increase or no change in main steam pressure are defined as internal disturbances. Alternatively, all changes in main steam pressure caused by factors other than external disturbances during boiler operation can be defined as internal disturbances.

[0038] Step 5: Determine the target value of the main steam flow rate using the following method:

[0039] If the identified load change in the biomass circulating fluidized bed boiler is caused by external disturbances, then the target value of the main steam flow rate is equal to the measured value of the main steam flow rate plus the output value of the main steam pressure PID controller in the first step (the main steam pressure correction value).

[0040] If the identified load change in the biomass circulating fluidized bed boiler is caused by internal disturbance factors, then the target value of the main steam flow rate is the rated design value of the main steam flow rate of the biomass circulating fluidized bed boiler.

[0041] Step 6: Multiply the target value of the main steam flow obtained in Step 5 by the learning value X obtained in Step 3, and then subtract the primary air volume of the biomass circulating fluidized bed boiler to obtain the predicted secondary air volume.

[0042] Step 7: Input the predicted secondary air volume obtained in Step 6 into the setting terminal of the secondary air PID controller. The input terminal of the secondary air PID controller receives the real-time measurement value of the secondary air volume of the biomass circulating fluidized bed boiler. The output signal of the secondary air PID controller is used to regulate the secondary air variable frequency speed control motor to achieve the adjustment of the secondary air volume. The above method of secondary air volume regulation is targeted at whether the boiler load changes due to external or internal disturbances, and follows the principle of "load determined by air volume". For fluctuations in boiler load, the main approach is to regulate the secondary air volume. By accurately predicting the secondary air volume and first inputting the predicted value into the setting terminal of the secondary air PID controller, and then adjusting the PID controller, stable operation is achieved when the boiler load changes.

[0043] Step 8: Set up a feeding PID controller. Use the control frequency of the variable frequency speed control motor of the screw feeder as the output of the feeding PID controller, and use the oxygen content of the flue gas in the tail flue as the input of the feeding PID controller. Set the oxygen content of the flue gas in the tail flue to 5%-6% as the set value of the setting terminal SP of the feeding PID controller.

[0044] Step 9: Input the oxygen content of the flue gas measured by the oxygen content sensor in the tail flue into the rate module, and obtain the rate of change of the oxygen content of the flue gas per second at the output of the rate module.

[0045] Step 10: Using a specific moment as a baseline, collect and calculate the average rate of change (V) of the oxygen content in the flue gas per second over the 20 seconds preceding that baseline moment. O Simultaneously, the average value F of the control frequency F of the variable frequency speed control motor of the screw feeder within 20 seconds prior to the reference time was collected and calculated. 平均 The dynamic proportional coefficient P of the feed PID controller is calculated using the following formula: P = V O ×F 平均 ×K; where K=0.1-0.5; that is, the dynamic proportional coefficient P at each moment reflects the average factor of the rate of change of flue gas oxygen content in the previous 20 seconds and the average factor of the control frequency of the variable frequency speed control motor, so that the proportional coefficient of the feed PID controller always follows the trend of oxygen content change in the boiler furnace, and achieves close tracking of the combustion status in the boiler.

[0046] Step 11: Embed the dynamic proportional coefficient P calculated in Step 10 into the feeding PID controller; input the real-time oxygen content of the flue gas measured by the oxygen content sensor in the tail flue into the input terminal of the feeding PID controller, and input the frequency signal of the output terminal of the feeding PID controller into the variable frequency speed control motor of the screw feeder. The feeding rate of the variable frequency speed control motor of the screw feeder is controlled by the feeding PID controller; thus, the dynamic proportional coefficient P and the feeding PID controller follow the changes in oxygen content to jointly control the boiler feed and achieve stable oxygen content in the boiler combustion.

[0047] When the difference between the real-time main steam pressure value measured by the main steam pressure sensor and the design value of the main steam pressure is greater than 0.2 MPa, and the rate of increase of the real-time main steam pressure value per second is greater than 0.002 MPa, the rate of increase of the real-time main steam pressure value per second is multiplied by the corresponding real-time main steam flow rate, and the product is multiplied by -1. The final product is then used as the first feedforward quantity and added to the output of the secondary air PID controller. Together, they serve as the control frequency of the secondary air variable frequency speed control motor to regulate the secondary air volume. When the boiler main steam pressure rises sharply, the aforementioned secondary air PID control method is no longer sufficient. By using the above method, the control frequency of the variable frequency motor of the secondary air fan is directly reduced, and the secondary air volume is significantly reduced. By controlling combustion, the main steam pressure is stabilized.

[0048] Using the main steam pressure value as the abscissa (in megapascals) and the negative frequency value as the ordinate (in hertz), the following coordinate points are marked on this coordinate system: (12.5 1), (13.3 2), (13.4 3), and (13.5 4). Connecting these four points with straight lines forms a piecewise linear curve function of the main steam pressure versus the secondary air control frequency. This piecewise linear curve function of the secondary air control frequency is used as the second feedforward and added to the output of the secondary air PID controller, serving as the control frequency of the secondary air variable frequency speed control motor to regulate the secondary air volume. This measure, through the piecewise linear curve input method, achieves a scientific response to the large fluctuations in secondary air volume caused by boiler load.

[0049] When the rate of change of oxygen content in the flue gas in the tail flue is V O When the deviation is higher than +0.06% or lower than -0.06%, the proportional gain of the feed PID controller is calculated using the following formula: P = 1.2 × V O ×F 平均 ×K; where K = 0.1-0.5.

[0050] When the bed temperature measured by the bed temperature sensor is higher than 850℃, or when the bed temperature rises by more than 8℃ within 30 seconds, the output value of the feeding PID controller is increased by a lockout function, ensuring that the output value of the feeding PID controller is not greater than the output value when the lockout function is activated. When the bed temperature measured by the bed temperature sensor is lower than 750℃, or when the bed temperature drops by more than 6℃ within 30 seconds, the output value of the feeding PID controller is decreased by a lockout function, ensuring that the output value of the feeding PID controller is not less than the output value when the lockout function is activated. The lockout function of the PID controller is used to suppress overshoot of biomass fuel.

[0051] When the difference between the oxygen content measured by the oxygen content sensor in the tail flue and the set value of the feed PID controller's setpoint SP is greater than 1%, and the increase in oxygen content per second is greater than 0.04%, the product of the main steam flow rate measured by the main steam flow rate sensor at this time multiplied by the increase in oxygen content per second at this time, and then multiplied by -0.15, is used as the first feedforward quantity and superimposed on the output of the feed PID controller. The frequency obtained after superposition is used to control the variable frequency motor of the screw feeder. When the oxygen content increases drastically, the normal adjustment of the feed PID controller can no longer achieve the target. At this time, the frequency of the variable frequency motor is directly intervened by the feedforward quantity to stabilize the oxygen content in the furnace.

[0052] When the oxygen content of the flue gas measured by the oxygen content measuring sensor in the tail flue is less than 3%, and the oxygen content of the flue gas is still decreasing per second, the main steam flow measured by the main steam flow measuring sensor at this time is multiplied by the decrease in oxygen content of the flue gas per second at this time, and then multiplied by 0.3. The resulting product is used as the second feedforward quantity and superimposed on the output of the feed PID controller. The frequency obtained after superposition is used to control the variable frequency motor of the screw feeder.

[0053] Using the percentage of oxygen content in the flue gas measured by the oxygen content sensor in the tail flue as the abscissa and the negative frequency value (in Hertz) as the ordinate, the following coordinate points are marked on this coordinate: (3% 0.5), (2% 1), (1% 1.5), and (0.5% 3). Connecting these four points with straight lines forms a piecewise linear curve function of flue gas oxygen content versus the control frequency of the variable frequency motor of the screw feeder. This piecewise linear curve function of the variable frequency motor control frequency is used as the third feedforward quantity and superimposed on the output of the feeding PID controller. The frequency obtained after superposition is used to regulate the variable frequency motor of the screw feeder. By using the piecewise linear function as a feedforward quantity to directly intervene in the frequency of the variable frequency motor, the extreme drop in oxygen content is smoothly suppressed.

Claims

1. An automatic control strategy for fuel feeding and combustion in a biomass circulating fluidized bed boiler, comprising an operating circulating fluidized bed boiler, a secondary air fan, a screw feeder for conveying biomass fuel to the furnace, and a central control room; wherein the screw feeder uses a variable frequency speed-regulating motor to control the feeding rate, and the secondary air fan uses a secondary air variable frequency speed-regulating motor to control the secondary air volume; a main steam flow measurement sensor and a main steam pressure measurement sensor are respectively installed at the main steam outlet of the biomass circulating fluidized bed boiler, a primary air measuring instrument and a secondary air measuring instrument are installed on the air path, and a rate module is installed in the central control room; characterized in that... The following steps: The first step is to build a main steam pressure PID controller that uses the real-time main steam pressure value of the operating biomass circulating fluidized bed boiler as input, the main steam pressure correction value as output, and the main steam pressure design value as the setpoint input. The real-time main steam pressure value collected by the main steam pressure measurement sensor is input to the input terminal of the main steam pressure PID controller, so that the main steam pressure correction value can be obtained at the output terminal of the main steam pressure PID controller. The second step is to build a secondary air PID controller that uses the real-time measured value of the secondary air volume of the biomass circulating fluidized bed boiler as the input, the predicted value of the secondary air volume as the set-end input value, and the control frequency of the secondary air variable frequency speed control motor as the output value. The third step is to collect the total air volume and the corresponding main steam flow rate of the boiler in real time during the continuous operation of the biomass circulating fluidized bed boiler in 20-minute intervals. The total air volume is divided by the corresponding main steam flow rate of the boiler, and iterative learning is continuously performed to finally obtain the learning value X of the total air volume divided by the corresponding main steam flow rate of the boiler. Step 4: When the load of the biomass circulating fluidized bed boiler changes, first identify whether the load change is caused by internal or external disturbances. An increase in main steam flow and a decrease in main steam pressure are defined as external disturbances; an increase in main steam flow but an increase in main steam pressure or a change that remains unchanged are defined as internal disturbances. Step 5: Determine the target value for the main steam flow rate: If the identified change in load of the biomass circulating fluidized bed boiler is caused by external disturbances, then the target value of the main steam flow rate is equal to the measured value of the main steam flow rate plus the output value of the main steam pressure PID controller in the first step. If the identified load change in the biomass circulating fluidized bed boiler is caused by internal disturbance factors, then the target value of the main steam flow rate is the rated design value of the main steam flow rate of the biomass circulating fluidized bed boiler. Step 6: Multiply the target value of the main steam flow obtained in Step 5 by the learning value X obtained in Step 3, and then subtract the primary air volume of the biomass circulating fluidized bed boiler to obtain the predicted secondary air volume. Step 7: Input the predicted secondary air volume obtained in Step 6 into the setting terminal of the secondary air PID controller. The input terminal of the secondary air PID controller receives the real-time measurement value of the secondary air volume of the biomass circulating fluidized bed boiler. The output signal of the secondary air PID controller is used to regulate the secondary air variable frequency speed control motor to achieve the adjustment of the secondary air volume.

2. The automatic control strategy for fuel feeding and combustion of a biomass circulating fluidized bed boiler according to claim 1, characterized by the following steps: Step 8: Set up a feeding PID controller. Use the control frequency of the variable frequency speed control motor of the screw feeder as the output of the feeding PID controller, and use the oxygen content of the flue gas in the tail flue as the input of the feeding PID controller. Set the oxygen content of the flue gas in the tail flue to 5%-6% as the set value of the setting terminal SP of the feeding PID controller. Step 9: Input the oxygen content of the flue gas measured by the oxygen content sensor in the tail flue into the rate module, and obtain the rate of change of the oxygen content of the flue gas per second at the output of the rate module. Step 10: Using a specific moment as a baseline, collect and calculate the average rate of change (V) of the oxygen content in the flue gas per second over the 20 seconds preceding that baseline moment. O Simultaneously, the average value F of the control frequency F of the variable frequency speed control motor of the screw feeder within 20 seconds prior to the reference time was collected and calculated. 平均 The dynamic proportional coefficient P of the feed PID controller is calculated using the following formula: P = V O ×F 平均 ×K; where K = 0.1 - 0.5; Step 11: Embed the dynamic proportional coefficient P calculated in Step 10 into the feeding PID controller; input the real-time oxygen content of the flue gas measured by the oxygen content sensor in the tail flue into the input terminal of the feeding PID controller, and input the frequency signal of the output terminal of the feeding PID controller into the variable frequency speed control motor of the screw feeder. The feeding rate of the variable frequency speed control motor of the screw feeder is controlled by the feeding PID controller.

3. The automatic control strategy for fuel feeding and combustion of a biomass circulating fluidized bed boiler according to claim 1, characterized in that, When the difference between the real-time main steam pressure value measured by the main steam pressure sensor and the design value of the main steam pressure is greater than 0.2 MPa, and the rate of increase of the real-time main steam pressure value per second is greater than 0.002 MPa, the rate of increase of the real-time main steam pressure value per second is multiplied by the corresponding real-time main steam flow rate, and the product is multiplied by -1. The final product is then added to the output of the secondary air PID controller as the first feedforward quantity, which together serve as the control frequency of the secondary air variable frequency speed control motor to regulate the secondary air volume.

4. The automatic control strategy for fuel feeding and combustion of a biomass circulating fluidized bed boiler according to claim 1, characterized in that, Using the main steam pressure value as the abscissa (megapascals) and the negative frequency value as the ordinate (hertz), the following coordinate points are marked on this coordinate system: (12.5 1), (13.3 2), (13.4 3), and (13.5 4). Connect these four points with straight lines to form a broken line curve function of the main steam pressure and the secondary air control frequency. Use this broken line curve function of the secondary air control frequency as the second feedforward quantity, add it to the output of the secondary air PID controller, and use it together as the control frequency of the secondary air variable frequency speed control motor to regulate the secondary air volume.

5. The automatic control strategy for fuel feeding and combustion of a biomass circulating fluidized bed boiler according to claim 2, characterized in that, When the rate of change of oxygen content in the flue gas in the tail flue is V O When the value is above +0.06% or below -0.06%, the proportional gain P of the feed PID controller is 1.2 × V. O ×F 平均 ×K; where K = 0.1-0.

5.

6. The automatic control strategy for fuel feeding and combustion of a biomass circulating fluidized bed boiler according to claim 2 or 5, characterized in that, When the bed temperature measured by the bed temperature sensor is higher than 850℃, or when the bed temperature rises by more than 8℃ within 30 seconds, the output value of the feeding PID controller is increased by the interlock function to ensure that the output value of the feeding PID controller is not greater than the output value when the interlock function is activated. When the bed temperature measured by the bed temperature sensor is lower than 750℃, or when the bed temperature drops by more than 6℃ within 30 seconds, the output value reduction interlock function of the feeding PID controller is activated to ensure that the output value of the feeding PID controller is not less than the output value when the interlock function is activated.

7. The automatic control strategy for fuel feeding and combustion of a biomass circulating fluidized bed boiler according to claim 2, characterized in that, When the difference between the oxygen content of the flue gas measured by the oxygen content sensor in the tail flue and the set value of the setting terminal SP of the feed PID controller is greater than 1%, and the increase in the oxygen content of the flue gas per second is greater than 0.04%, the main steam flow measured by the main steam flow sensor at this time is multiplied by the increase in the oxygen content of the flue gas per second at this time, and then multiplied by -0.

15. The resulting product is used as the first feedforward quantity and superimposed on the output terminal of the feed PID controller. The frequency obtained after superposition is used to control the variable frequency motor of the screw feeder.

8. The automatic control strategy for fuel feeding and combustion of a biomass circulating fluidized bed boiler according to claim 2, characterized in that, When the oxygen content of the flue gas measured by the oxygen content measuring sensor in the tail flue is less than 3%, and the oxygen content of the flue gas is still decreasing per second, the main steam flow measured by the main steam flow measuring sensor at this time is multiplied by the decrease in oxygen content of the flue gas per second at this time, and then multiplied by 0.

3. The resulting product is used as the second feedforward quantity and superimposed on the output of the feed PID controller. The frequency obtained after superposition is used to control the variable frequency motor of the screw feeder.

9. The automatic control strategy for fuel feeding and combustion of a biomass circulating fluidized bed boiler according to claim 2, characterized in that, Using the percentage of oxygen content in the flue gas measured by the oxygen content sensor in the tail flue as the abscissa and the negative frequency value as the ordinate, in Hertz, the following coordinate points are marked on this coordinate: (3% 0.5), (2% 1), (1% 1.5), (0.5% 3). Connect these four points with straight lines to form a broken line curve function of flue gas oxygen content and variable frequency motor control frequency of the screw feeder. Use the broken line curve function of variable frequency motor control frequency as the third feedforward quantity, superimpose it on the output of the feeder PID controller, and use the frequency obtained after superposition to regulate the variable frequency motor of the screw feeder.

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