Desulfurization slurry pH whole-process control method based on Smith pre-estimation control

Abstract

The invention provides a desulfurization slurry pH whole-process control method based on Smith pre-estimation control, and relates to the technical field of pollutant purification, and the method comprises a Smith pre-estimation control main loop, a slurry supply flow control auxiliary loop, and a measurement pipeline flushing maintenance control. The problem that at present, most thermal power plants adopt slurry circulating pumps to control SO2 emission in a frequency conversion mode is solved, and the pH value is stabilized within a certain range by changing the fresh slurry amount. However, due to the fact that the desulfurization environment is poor and the pH value change has large inertia, the measurement duration is long, the accurate value of the pH value cannot be obtained, desulfurization operation of a unit is not facilitated, and pre-estimation control over the pH value of the slurry is very necessary.

Description

Technical Field

[0001] The present invention belongs to the technical field of pollutant purification, and more specifically, particularly relates to a whole-process control method of desulfurization slurry pH based on Smith predictive control. Background Art

[0002] At present, the SO2 emissions from coal-fired power plants have exceeded half of the total social SO2 emissions, and are showing an increasing trend year by year. my country has successively promulgated a series of policies and regulations, such as the "Emission Standards for Air Pollutants from Thermal Power Plants" and the "Action Plan for Energy Saving and Emission Reduction Upgrading and Renovation of Coal-fired Power (2014-2020)", which clearly point out that the SO2 emission concentration of thermal power plants must be controlled below 35mg / m. Limestone-gypsum wet flue gas desulfurization technology (WFGD) is one of the most effective SO2 control technologies for coal-fired units. The slurry pH value is a key parameter that determines the flue gas desulfurization efficiency. At present, most thermal power plants use slurry circulation pumps to control SO2 emissions by frequency conversion, and stabilize the pH value within a certain range by changing the amount of fresh slurry. However, due to the poor desulfurization environment, the pH value has a large inertia, resulting in a long measurement time, and the inability to obtain an accurate pH value, which is not conducive to the desulfurization operation of the unit, so it is very necessary to estimate and control the slurry pH value. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a whole-process control method of desulfurization slurry pH based on Smith predictive control to solve the problems raised by the background technology.

[0004] The whole process control method of desulfurization slurry pH based on Smith prediction control of the present invention is achieved by the following specific technical means:

[0005] A whole-process control method for desulfurization slurry pH based on Smith predictive control includes: a Smith predictive control main loop, a slurry flow control sub-loop, and a measuring pipeline flushing and holding control.

[0006] Furthermore, the Smith predictive main loop: Gc1(s) is the main controller, Gp1(s) ​​is the main loop control object, Gm(s) is the controlled object model, and according to the Smith predictive controller principle, Gm(s) can be divided into Gm0(s) which does not contain a time-delay link, and a pure time-delay link e-τs (generally with a lag of 5-6 minutes).

[0007]

[0008] Furthermore; the slurry flow sub-control: Gc2(s) is the sub-control controller, Gp2(s) is the inner loop control object, cascade control improves the response speed of the production process with large inertia and large time lag, and quickly suppresses the influence of disturbances. The output of the main PID based on Smith predictive control is used as the set value of the slurry flow control sub-loop PID. According to the correspondence between the slurry flow and the regulating valve opening, Gc2(s) adopts PI or PD method, and by adjusting P, I or D parameters, the slurry flow control inner loop is simplified to a proportional link (determined by the regulating valve amplification factor γm and the slope of the flow transmitter Yt) 1 / YmYt, which can not only quickly respond to the response of the unit to the slurry flow, but also quickly suppress the change of the slurry flow.

[0009]

[0010] When the model is set accurately Gm(s)=G2(s)Gp1(s), the above transfer function becomes:

[0011]

[0012] It can be obtained from equations (1-3) and (1-4) that, when the model is accurate, the characteristic equation of the closed-loop system no longer contains the time-delay link e-τs, so the parameters of Gc1(s) (PID) can be adjusted according to the time-delay-free part Gm0(s). During normal operation, the pH set value is generally maintained at around 5.2. The parameters of the Gc1(s) controller tend to be optimized for interference suppression, which makes the design of the Gc1(s) controller highly purposeful.

[0013] Further, the measuring pipeline flushing and maintenance design: the current installation and measurement method of the pH meter is to install a sampling tube on the pipeline after the gypsum slurry is discharged from the pump, and the slurry is allowed to flow through a large container through the sampling tube. The slurry in the container maintains continuous flow, and the pH meter probe is installed vertically or obliquely on the container to contact the measured liquid. The tested slurry enters the waste slurry pool or returns to the absorption tower. The measurement in the high-pressure fast fluid is changed to the measurement in the pressure-free slow fluid. This can greatly reduce the pressure and flow rate of the slurry, and almost no impact and friction will be generated on the pH electrode, greatly extending the service life of the electrode. It not only ensures the life of the technicians, but also greatly facilitates the inspection, maintenance and calibration of the maintenance personnel. Therefore, the sampling tube should be flushed regularly to avoid blockage. It can be determined according to the actual situation on site (generally flushed once an hour). The pH value measured during the flushing process is the pH value of the flushing water, which cannot be used as an adjustment parameter. In order to ensure the continuity of the slurry pH adjustment, the measurement pipeline flushing and holding logic is designed. When the flushing door is closed in place, the pH value and the output of the Smith predictive control PID are maintained at the current value, and the power is delayed for a period of time to ensure that the pH measurement is normal before resuming the slurry pH adjustment.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] 1. Benefits of Smith Estimated Main Circuit

[0016] According to the Smith predictive controller principle, the controlled object model Gm(s) is divided into a time-delay-free link Gm0(s) and a pure time-delay link e-τs. When the model is accurate, the characteristic equation of the closed-loop system does not contain a time-delay link, so the parameters of the main controller Gc1(s) (PID) can be adjusted according to the time-free part Gm0(s), thereby improving the accuracy and stability of control.

[0017] During normal operation, the pH set value is generally maintained at around 5.2, and the Gc1(s) controller parameters tend to suppress interference optimization, making the controller design highly purposeful and able to better cope with various interference factors, ensuring stable control of the pH value of the desulfurization slurry.

[0018] 2. Benefits of Slurry Flow Sub-regulation Control

[0019] The use of cascade control improves the response speed of production processes with large inertia and large time lag, and can quickly suppress the impact of disturbances.

[0020] Based on the output of the Smith predictive control main PID as the set value of the slurry flow control sub-loop PID, the sub-controller Gc2(s) adopts the PI or PD method, and by adjusting the P, I or D parameters, the inner loop of the slurry flow control is simplified to a proportional link, which can not only quickly respond to the unit's demand for slurry flow, but also quickly suppress the change of slurry flow, thereby ensuring the stable operation of the system.

[0021] 3. Benefits of measuring pipeline flushing and retention design

[0022] By adopting a specific pH meter installation and measurement method, the measurement in high-pressure fast fluid is changed to the measurement in pressure-free slow fluid, which greatly reduces the pressure and flow rate of the slurry, and almost does not cause impact and wear to the pH electrode, greatly extending the service life of the electrode, and also facilitating the inspection, maintenance and calibration of the inspection personnel.

[0023] The flushing and holding logic of the measurement pipeline is designed. When the flushing door is closed, the pH value and the output of the Smith predictive control PID are maintained at the current value, and the power is turned off for a period of time to ensure that the pH value measurement is normal. Then, the slurry pH value adjustment is resumed, which ensures the continuity of the slurry pH value adjustment and improves the reliability and stability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is the block diagram of the cascade PID based on Smith predictive control of the present invention.

[0025] Figure 2 Schematic diagram of compensating slurry pH by utilizing Smith predictive control.

[0026] In the figure, the corresponding relationship between the component names and the figure numbers is as follows:

[0027] R(s): set value;

[0028] D(s): interference;

[0029] Y(s): output value;

[0030] Gc1(s): master control PID;

[0031] Go2(s): Sub-control PID;

[0032] Gp2(s): secondary control object;

[0033] Gp(s): master control object;

[0034] Gm(s):Smith model. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with specific embodiments, and the advantages and features of the present invention will become clearer as the description proceeds. However, these embodiments are exemplary only and do not constitute any limitation to the scope of the present invention. It should be understood by those skilled in the art that the details and forms of the technical solution of the present invention may be modified or replaced without departing from the spirit and scope of the present invention, but these modifications and replacements all fall within the scope of protection of the present invention.

[0036] Example:

[0037] As attached Figure 1 As shown:

[0038] The present invention provides a whole-process control method for pH of desulfurization slurry based on Smith predictive control, comprising: a Smith predictive control main loop, a slurry flow control sub-loop, and a measuring pipeline flushing and holding control.

[0039] Among them, the Smith predictive main loop: Gc1(s) is the main controller, Gp1(s) ​​is the main loop control object, Gm(s) is the controlled object model, and according to the Smith predictive controller principle, Gm(s) can be divided into Gm0(s) without a time-delay link, and a pure time-delay link e-τs (generally with a lag of 5-6 minutes).

[0040]

[0041] Among them, the slurry flow sub-control: Gc2(s) is the sub-control controller, Gp2(s) is the inner loop control object, cascade control improves the response speed of the production process with large inertia and large time lag, and quickly suppresses the influence of disturbances. The output of the main PID based on Smith predictive control is used as the set value of the slurry flow control sub-loop PID. According to the corresponding relationship between the slurry flow and the regulating valve opening, Gc2(s) adopts PI or PD method, and by adjusting the P, I or D parameters, the slurry flow control inner loop is simplified to a proportional link (determined by the regulating valve amplification factor γm and the slope of the flow transmitter Yt) 1 / YmYt, which can not only quickly respond to the response of the unit to the slurry flow, but also quickly suppress the change of the slurry flow.

[0042]

[0043] When the model is set accurately Gm(s)=G2(s)Gp1(s), the above transfer function becomes:

[0044]

[0045] It can be obtained from equations (1-3) and (1-4) that, when the model is accurate, the characteristic equation of the closed-loop system no longer contains the time-delay link e-τs, so the parameters of Gc1(s) (PID) can be adjusted according to the time-delay-free part Gm0(s). During normal operation, the pH set value is generally maintained at around 5.2. The parameters of the Gc1(s) controller tend to be optimized for interference suppression, which makes the design of the Gc1(s) controller highly purposeful.

[0046] Among them, the measuring pipeline flushing and holding design: the current installation and measurement method of the pH meter is to install a sampling tube on the pipeline after the gypsum slurry is discharged from the pump, and the slurry is allowed to flow through a large container through the sampling tube. The slurry in the container maintains continuous flow, and the pH meter probe is installed vertically or obliquely on the container to contact the liquid to be measured. The tested slurry enters the waste slurry pool or returns to the absorption tower, and the measurement in the high-pressure fast fluid is changed to the measurement in the pressure-free slow fluid. This can greatly reduce the pressure and flow rate of the slurry, and almost no impact and friction will be generated on the pH electrode, which greatly extends the service life of the electrode and greatly facilitates the inspection, maintenance and calibration of maintenance personnel. Therefore, the sampling tube must be flushed regularly to avoid blockage. It can be determined according to the actual situation on site (generally flushed once an hour). During the flushing process, the pH value measured is the pH value of the flushing water, which cannot be used as an adjustment parameter. In order to ensure the continuity of the slurry pH value adjustment, the measuring pipeline flushing and holding logic is designed. When the flushing door is closed, the pH value and the output of the Smith estimated control PID are maintained at the current value, and the power is delayed for a period of time to ensure that the pH value measurement is normal and then the slurry pH value adjustment is restored.

[0047] in, Figure 2By using Smith predictive control to compensate for the hysteresis of the slurry pH value and cascade PID, and a dedicated pH meter to measure the pipeline flushing and holding logic, the slurry pH value can be automatically controlled throughout the entire process, reducing the operating workload of operators.

[0048] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for controlling the pH of a desulfurized slurry in the whole process based on Smith predictive control, characterized in that: include: Smith estimates the control of the main circuit, the slurry flow control sub-circuit, and the measurement pipeline flushing to maintain control.

2. A method for controlling the pH of a desulfurized slurry in the whole process based on Smith predictive control according to claim 1, characterized in that: The Smith predictive main loop: Gc1(s) is the main controller, Gp1(s) ​​is the main loop control object, Gm(s) is the controlled object model. According to the Smith predictive controller principle, Gm(s) can be divided into Gm0(s) without a time-delay link, and a pure time-delay link e-τs (generally with a lag of 5-6 minutes).

3. The whole process control method of desulfurization slurry pH based on Smith predictive control according to claim 1, characterized in that: The slurry flow sub-control: Gc2(s) is the sub-control controller, Gp2(s) is the inner loop control object, and the cascade control improves the response speed of the production process with large inertia and large time lag, and quickly suppresses the influence of disturbances. The output of the main PID based on Smith predictive control is used as the set value of the slurry flow control sub-loop PID. According to the corresponding relationship between the slurry flow and the regulating valve opening, Gc2(s) adopts PI or PD method, and by adjusting the P, I or D parameters, the slurry flow control inner loop is simplified to a proportional link (determined by the regulating valve amplification factor γm and the slope of the flow transmitter Yt) 1 / YmYt, which can not only quickly respond to the response of the unit to the slurry flow, but also quickly suppress the change of the slurry flow. When the model is set accurately Gm(s)=G2(s)Gp1(s), the above transfer function becomes: It can be obtained from equations (1-3) and (1-4) that, when the model is accurate, the characteristic equation of the closed-loop system no longer contains the time-delay link e-τs, so the parameters of Gc1(s) (PID) can be adjusted according to the time-delay-free part Gm0(s). During normal operation, the pH set value is generally maintained at around 5.

2. The parameters of the Gc1(s) controller tend to be optimized for interference suppression, which makes the design of the Gc1(s) controller highly purposeful.

4. The whole process control method of desulfurization slurry pH based on Smith predictive control according to claim 1, characterized in that: The measuring pipeline flushing and holding design: the current installation and measurement method of the pH meter is to install a sampling tube on the pipeline after the gypsum slurry is discharged from the pump, and the slurry is allowed to flow through a large container through the sampling tube. The slurry in the container maintains continuous flow, and the pH meter probe is installed vertically or obliquely on the container to contact the liquid to be measured. The tested slurry enters the waste slurry pool or returns to the absorption tower, and the measurement in the high-pressure fast fluid is changed to the measurement in the pressure-free slow fluid. This can greatly reduce the pressure and flow rate of the slurry, and almost no impact and friction will be generated on the pH electrode, which greatly extends the service life of the electrode and greatly facilitates the inspection, maintenance and calibration of maintenance personnel. Therefore, the sampling tube must be flushed regularly to avoid blockage. It can be determined according to the actual situation on site (generally flushed once an hour). During the flushing process, the pH value measured is the pH value of the flushing water, which cannot be used as an adjustment parameter. In order to ensure the continuity of the slurry pH value adjustment, the measuring pipeline flushing and holding logic is designed. When the flushing door is closed, the pH value and the output of the Smith predictive control PID are maintained at the current value, and the power is delayed for a period of time to ensure that the pH value measurement is normal before resuming the slurry pH value adjustment.

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