Energy-saving control method for hydrapulper process of paper mill

Abstract

The invention provides an energy-saving control method for a hydrapulper process of a paper mill. According to the process energy-saving control method for the hydrapulper of the paper mill, basic parameters are set in advance equal to the liquid level, the process stage, the concentration and the rotating speed, the first priority of control logic is overload protection, and when a motor has an overload risk, the speed of the motor is controlled to be reduced; the second priority of the control logic is liquid level safety limit, and when the liquid level is too low, the motor is controlled to decelerate or stop; the third priority of the control logic is process stage adjustment, the current process stage is judged, and the rotating speed range of the motor is limited based on the process stage; the fourth priority of the control logic is concentration dynamic optimization, and the rotating speed is adjusted based on the set concentration in different process stages. According to the energy-saving control method for the hydrapulper process of the paper mill, the problem that an existing pulper runs at a constant speed and cannot meet the production requirement is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of process control, in particular to a kind of paper mill hydro-pulper process energy-saving control method. BACKGROUND

[0002] Hydro-pulper is one of the core equipment in pulp and paper industry, especially in waste paper recycling (recycled paper production) process. Its main function is to use water shear to quickly disperse and disintegrate dry pulp board, waste paper, paperboard and other raw materials into single fibers in water, while separating most of the non-fiber impurities (such as plastic sheets, metals, sand, ropes, etc.), to prepare uniform pulp suspension for subsequent screening, purification, bleaching and other processes. The basic working process of hydro-pulper is that when the water in the pulper tank is injected to the set value, the pulp board, broke paper or waste paper is uniformly fed into the tank through the pulp board conveyor, and the rotor motor in the tank is started at the same time. The rotation of the rotor makes the pulp thrown from the center to the periphery, and a vortex is generated at its center, so that the pulp is subjected to strong water impact and shear, and intense mutual friction and soft rubbing are generated. At the same time, combined with the impact of the rotor itself, the pulp board and broke paper are disintegrated into single fibers in a wet state. The disintegrated pulp flows out through the screen, and the foreign matter and heavy residue are collected in the sediment tank and discharged regularly. When continuously running, the foreign matter and heavy residue enter the sediment well and are discharged after being treated by the impurity separator.

[0003] In the working process of traditional pulper, it is always maintained at constant speed. However, in actual production process, the pulp concentration in the pulper tank is different, and the requirement for motor speed is also different. Therefore, automatic control of motor speed for different stages of pulping process can not only effectively reduce the energy consumption of motor, but also reduce the wear of pulper. SUMMARY

[0004] To solve the problem that the existing pulper runs at constant speed and cannot meet the production requirements, the present application provides a paper mill hydro-pulper process energy-saving control method to solve the above problems.

[0005] A paper mill hydro-pulper process energy-saving control method, the basic parameters are set in advance, including liquid level, process stage, concentration and speed: The liquid level is set from low to high as H1 to H4 four preset values, the process stage is set in order as F1 to F4 four stages, and the switching time between F2-F4 three stages is set as T1-T3 respectively, the concentration is set as C1 to C4 four preset values, the speed is set from low to high as R1 to R5 five preset values, and the overload protection value of the motor is set. During operation, the current, power and torque of the motor are continuously recorded, the concentration and liquid level in the pulper are continuously recorded, and the running time of the pulper is continuously recorded. The first priority of the control logic is overload protection, the motor is controlled to slow down when there is an overload risk; the second priority of the control logic is liquid level safety limit, the motor is controlled to slow down or stop when the liquid level is too low; the third priority of the control logic is process stage adjustment, the current process stage is judged, and the motor speed range is limited based on the process stage; the fourth priority of the control logic is concentration dynamic optimization, the motor speed is adjusted based on the set concentration in different process stages.

[0006] In a preferred embodiment of the process energy saving control method for a paper mill hydro-pulper provided by the application, H1 is the minimum liquid level to avoid dry running or cavitation of the pulper, H4 is the maximum liquid level to avoid overflow of the pulper; C1 to C3 are the normal working concentration range, C2 includes C2-1 to C2-4, which are the target concentrations of F1 to F4 process stages respectively, C4 includes C4-1 to C4-4, which are the over-limit concentrations of F1 to F4 process stages respectively; R1 is the minimum speed to maintain the pulp suspension in the pulper, and R5 is the maximum speed of the pulper under mechanical and electrical limitations.

[0007] In a preferred embodiment of the process energy saving control method for a paper mill hydro-pulper provided by the application, the overload protection comprises: Based on the records of the current motor current, power and torque, overload protection judgment is made, and the motor is controlled to slow down when the record value approaches or exceeds the overload protection value; The liquid level safety limit comprises: Based on the records of the current liquid level in the pulper, safety limit judgment is made, and the motor is controlled to slow down below R1 or stop when the record value is below H1; when the record value is in the low liquid level region H1-H2, the maximum motor speed is limited to R2; when the record value is in the normal liquid level region H2-H3 and the high liquid level region H3-H4, the maximum motor speed is limited to R5; The process stage adjustment comprises: Based on multiple record values, the current process stage is comprehensively judged, the motor speed is limited to R3-R5 when the current process stage is judged to be F1, the motor speed is limited to R3-R4 when the current process stage is judged to be F2, the motor speed is limited to R1-R2 when the current process stage is judged to be F3, and the motor speed is limited to R2-R3 when the current process stage is judged to be F4; The concentration dynamic optimization comprises: Based on C2-1 to C2-4 under the current process stage, dynamic optimization judgment is made with the current concentration, the motor speed is increased when the record value of the current concentration is greater than the target concentration, and the motor speed is decreased when the record value of the current concentration is less than the target concentration.

[0008] In a preferred embodiment of the process energy saving control method of the hydraulic pulper in a paper mill provided by the application, in the process stage adjustment process, the current process stage is comprehensively judged based on the record of the pulper running time, the record value and variation trend of the concentration in the pulper, and the record value and variation trend of the current, power or torque of the motor.

[0009] When the pulper running time is less than T1, it is judged as F1 or F2, when the running time is between T1 and T2, it is judged as F3, and when the running time is between T2 and T3, it is judged as F4. When the slurry concentration in the pulper is between C2 and C3 and fluctuates violently, it is judged as F1, when the concentration is between C1 and C3 and the fluctuation tends to be stable towards C2, it is judged as F2, and when the concentration is close to C2 and remains basically stable, it is judged as F3 or F4. When the current, power or torque of the motor is large, it is judged as F1, gradually decreases, is judged as F2, remains basically stable, is judged as F3, and further decreases, is judged as F4.

[0010] The first priority of the judgment logic is the motor state judgment, the second priority of the judgment logic is the concentration state judgment, and the third priority of the judgment logic is the running time judgment.

[0011] In a preferred embodiment of the process energy saving control method of the hydraulic pulper in a paper mill provided by the application, in the concentration dynamic optimization process, the concentration is adjusted in advance, the speed is increased in advance when the concentration rapidly rises, and the speed is decreased in advance when the concentration rapidly falls. In the concentration dynamic optimization process, when the concentration needs to be increased, the motor speed is decreased while measures such as reducing water addition or increasing feeding are taken to cooperate with the increase of the concentration.

[0012] In a preferred embodiment of the process energy saving control method of the hydraulic pulper in a paper mill provided by the application, in the concentration dynamic optimization process, when the record value of the current concentration reaches C4-1 to C4-4 under the current process stage, a special process is triggered, the control logic of the process stage adjustment and the control logic of the concentration dynamic optimization are ignored, the motor is controlled to enter R3-R5, and when the concentration reaches C2-1 to C2-4 under the current process stage and is stably maintained for a certain period of time, the control logic of the process stage adjustment and the control logic of the concentration dynamic optimization are restored.

[0013] In the special process, the motor speed is first controlled to enter R4-R5, when the concentration starts to stably decrease, the motor speed is changed to R3-R4, when the concentration reaches C2-1 to C2-4 under the current process stage, the control logic of the concentration dynamic optimization is restored, and when the concentration is stably maintained for a certain period of time, the control logic of the process stage adjustment is restored.

[0014] Compared with the prior art, the paper mill hydraulic pulper process energy-saving control method has the following beneficial effects: 1、The scheme provided by the present application combines the concentration, liquid level in the pulper, and the working time and motor state of the pulper, and automatically controls the motor speed for different stages of the pulper working process, which can not only improve the pulping efficiency, reduce the energy consumption of the motor, and ensure the pulp quality, but also reduce the wear of the pulper.

[0015] 2、The scheme provided by the present application is optimized based on the original pulping processing scheme, and can fully adapt to different system conditions of various paper mills, and is convenient to access control. DETAILED DESCRIPTION

[0016] The technical solutions in the embodiments of the present application will be described clearly and completely below, and the described embodiments are only a part of the embodiments of the present application, not all the embodiments.

[0017] The motor speed comprehensive control of the hydraulic pulper is a core optimization process, which aims to improve the pulping efficiency, reduce the energy consumption, ensure the pulp quality, and protect the equipment. Combining the concentration, time and liquid level to control the speed is the key to realize intelligent and efficient operation. The influence of each parameter on the demand of motor speed is as follows: Concentration: In the case of high concentration, higher torque is needed to overcome the increased viscosity of the pulp and the friction between fibers. Within the power allowable range, the speed is increased to maintain sufficient shear force to effectively disperse the fibers. However, blindly increasing the speed may cause the motor to overload.

[0018] In the case of low concentration, the pulp has good fluidity and requires less torque. At this time, maintaining or appropriately reducing the speed can ensure the dispersion effect to achieve the purpose of energy saving.

[0019] Time: In the initial stage of the pulper working process, the concentration is high or changes sharply after feeding, and the speed needs to be adjusted according to the concentration strategy. As the dispersion proceeds, the fibers are gradually dispersed, the concentration decreases, and the required dispersion force decreases, so the speed can be gradually lowered to achieve the purpose of energy saving.

[0020] In the middle stage of the working process, the main goal is to maintain the suspension and uniform mixing of the pulp, rather than strong dispersion. At this time, maintaining a low speed can meet the requirements and significantly save energy.

[0021] In the later stage of the working process, in order to ensure that the pulp can be smoothly pumped out, a certain speed needs to be maintained to prevent sedimentation, and the speed strategy needs to be coordinated with the liquid level drop and the demand of the discharge pump.

[0022] Liquid level: In high liquid level condition, the pulp volume is large, the rotor immersion depth is deep, and the hydraulic circulation path is long. The speed needs to be appropriately increased to ensure that the pulp in the tank, especially the bottom and edge, is fully circulated and disintegrated, and to prevent sedimentation and dead zones. However, the concentration factor needs to be considered.

[0023] In low liquid level condition, the rotor may be partially exposed or shallowly immersed, and the range of hydraulic action is reduced. The speed usually needs to be significantly reduced to maintain only basic suspension.

[0024] The working process of a paper mill hydraulic pulper includes three processing stages: water adding stage, pulping stage, and pulp pumping stage. The water adding stage includes water adding, material feeding, and preliminary pulping of the fed material. The pulping stage includes formal pulping of the fed material and circulation and homogenization of the pulp. The pulp pumping stage is to cooperate with the pumping pump to ensure smooth pumping of the pulp.

[0025] Specific to the motor speed control process stage. At the beginning of the water adding stage, the concentration is low, and the speed requirement is not high. As the pulp board feeding increases, the speed requirement gradually increases. As a process stage, it is recorded as the initial pulping stage F1. In the pulping stage, the motor speed is high to achieve the desired crushing effect. After a period of time, the speed is appropriately reduced to obtain more uniform pulp. The former is regarded as a process stage and recorded as the fine pulping stage F2, and the latter is regarded as another process stage and recorded as the circulation stage F3. In the pulp pumping stage, the former needs to maintain a high speed to ensure sufficient tumbling of the pulp and avoid uneven mixing of dilution water, forming a concentration gradient. In the later stage, as the liquid level in the tank decreases, the speed gradually decreases. As a process stage, it is recorded as the discharge stage F4.

[0026] Based on the statistics of the time spent in each process stage F1-F4, the average value is taken, and the time for switching between the three stages F2-F4 is set as T1-T3, respectively.

[0027] The liquid level is set to four preset values H1-H4 from low to high. H1 is the minimum liquid level to avoid dry running or cavitation of the pulper, and H4 is the maximum liquid level to avoid overflow of the pulper. H1-H2 is the low liquid level region, H2-H3 is the normal liquid level region, and H3-H4 is the high liquid level region.

[0028] The speed is set to five preset values R1 to R5 from low to high, and an overload protection value of the motor is also set. R1 is the minimum speed to maintain the suspension of the pulp in the pulper, and R5 is the maximum speed of the pulper under mechanical and electrical limitations. R2-R4 are set based on the actual process.

[0029] The concentration is set to four preset values C1 to C4. C1 to C3 are the normal working concentration range of the pulper. C2 includes C2-1 to C2-4, which are the target concentrations of F1-F4 process stages respectively, and C4 includes C4-1 to C4-4, which are the over-standard concentrations of F1-F4 process stages respectively.

[0030] On this basis, while the pulper is normally processing pulp, the motor speed is dynamically controlled. The first priority of the control logic is overload protection: Based on the records of the current motor current, power and torque, overload protection judgment is made. When the record value approaches or exceeds the overload protection value, the motor is controlled to slow down to prevent the motor and transmission mechanism from being damaged by overload. Overload protection is a common solution and will not be described here.

[0031] The second priority of the control logic is liquid level safety limit: Based on the records of the current liquid level in the pulper, safety limit judgment is made.

[0032] When the record value is below H1, the motor is controlled to slow down below R1 or stop. At this time, if the speed is too high, strong eddy current and air suction will be generated, resulting in decreased efficiency, oxidation, foam, increased mechanical impact and wear on the rotor and the slot body, and energy waste on ineffective hydraulic disturbance. Reducing the speed can protect the equipment and reduce energy consumption. Based on the same reason, when the record value is in the low liquid level area H1-H2, the maximum motor speed is limited to R2.

[0033] When the record value is in the normal liquid level area H2-H3 and the high liquid level area H3-H4, the pulper can normally carry out disintegration processing. The maximum motor speed is limited to R5.

[0034] The third priority of the control logic is process stage adjustment: In turn, based on the records of the pulper running time, based on the records and trends of the concentration in the pulper, and based on the records and trends of the motor current, power or torque, the current process stage is judged, and the motor speed range is limited based on the process stage.

[0035] Specifically, based on the records of the pulper running time: The pulper running time is less than T1, which is judged as F1 or F2. According to the actual processing situation, the time fluctuation of the pulping stage is large, and F1 and F2 cannot be accurately defined. The running time is between T1 and T2, which is judged as F3. The running time is between T2 and T3, which is judged as F4. According to the actual processing situation, the time fluctuation of the circulating and pumping stages is small, and F3 and F4 can be roughly defined.

[0036] Based on the records and trends of the concentration in the pulper: At the beginning of feeding, the concentration is large and unstable. Therefore, the concentration of the slurry in the pulper is between C2 and C3, and the fluctuation is large, which can be judged as F1. As the disintegration proceeds, the concentration gradually decreases and tends to be stable. Therefore, the concentration is between C1 and C3, and the fluctuation tends to be stable in the direction of C2, which can be judged as F2. After the disintegration is completed, the concentration is basically stable. Therefore, the concentration is close to C2, and the concentration remains basically stable near C2, which can be judged as F3 or F4.

[0037] Based on the recorded values and variation trends of the current, power or torque of the motor: At the beginning of feeding, the concentration is large, so the current, power or torque of the motor is also large, which can be judged as F1. As the disintegration proceeds, the concentration gradually decreases, so the current, power or torque of the motor also gradually decreases, which can be judged as F2. After the disintegration is completed, the concentration is basically stable, so the current, power or torque of the motor is also basically stable, which can be judged as F3. As the discharge proceeds, the current, power or torque of the motor will further decrease, which can be judged as F4.

[0038] The first priority of the judgment logic is the motor state judgment, the second priority of the judgment logic is the concentration state judgment, and the third priority of the judgment logic is the running time judgment. Directly judging according to the motor state is easy to misjudge due to lack of reference, and judging in turn according to time, concentration and motor state, and finally judging according to the motor state, can accurately define the process stage.

[0039] Limit the motor speed range based on the process stage, specifically: when the current process stage is judged as F1, limit the motor speed to R3-R5. When the current process stage is judged as F2, limit the motor speed to R3-R4. When the current process stage is judged as F3, limit the motor speed to R1-R2. When the current process stage is judged as F4, limit the motor speed to R2-R3.

[0040] The fourth priority of the control logic is the dynamic optimization of concentration: Based on C2-1 to C2-4 under the current process stage, dynamic optimization judgment is made with the current concentration. When the current concentration is greater than the target concentration, the motor speed is increased, and when the current concentration is less than the target concentration, the motor speed is decreased. Anticipatory adjustment is made, the speed is increased in advance when the concentration rises rapidly, and the speed is decreased in advance when the concentration decreases rapidly. During the dynamic optimization of concentration, one control of water addition or feeding is allowed, so as to quickly reduce or increase the concentration, and cooperate with the water-based pulping provided by the motor, to adjust the concentration to the target concentration in the current process stage.

[0041] In the concentration dynamic optimization process, when the record value of the current concentration reaches C4-1 to C4-4 under the current process stage, a special process is triggered. The control logic of the process stage adjustment and the control logic of the concentration dynamic optimization are ignored, and the motor is directly controlled to enter R4-R5. When the concentration begins to steadily decrease, the motor speed is reduced to R3-R4. When the concentration reaches C2-1 to C2-4 under the current process stage, the control logic of the concentration dynamic optimization is restored. When the concentration is stably maintained for a certain period of time, the control logic of the process stage adjustment is restored.

[0042] Based on the above control logic, the general flow of a once pulping operation is as follows First, water and materials are added to the pulper. As the liquid level rises, the motor is started after reaching H1, and the maximum motor speed is limited to R2. The priority of the liquid level safety limit is high, so the control logic of the process stage adjustment and the concentration dynamic optimization cannot increase the speed.

[0043] When the liquid level continues to rise above H2, the maximum motor speed is R5. At this time, based on the logic of the process stage adjustment, it is judged that the current is F1, and the motor speed is limited to R3-R5. Based on the logic of the concentration dynamic optimization, the motor is kept at a high speed to quickly reduce the concentration. At the same time, due to the limitation of the overload protection, the motor is finally maintained at a speed of about R4.

[0044] As the pulping proceeds, the concentration gradually decreases. Based on the logic of the concentration dynamic optimization, the speed is also gradually reduced. As the concentration continues to decrease and tends to be stable. Based on the logic of the process stage adjustment, it is judged that the current is F2, and the motor speed is limited to R3-R4. Based on the logic of the concentration dynamic optimization, the speed change is controlled to make the concentration close to the target concentration.

[0045] When the concentration is basically stable, based on the logic of the process stage adjustment, it is judged that the current is F3, and the motor speed is limited to R1-R2, only maintaining basic suspension. After entering the pumping stage, based on the logic of the process stage adjustment, it is judged that the current is F4, and the speed is appropriately increased to R2-R3 to ensure that the pulp is sufficiently tumbled to prevent sedimentation. At the same time, as the liquid level decreases, the liquid level safety limit limits the maximum motor speed to R2 until the pulping process of the current batch is completed.

[0046] The above only describes the embodiments of the present application, and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation using the content of the present application specification, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A paper mill hydraulic pulper process energy-saving control method, characterized in that: Pre-set basic parameters, including liquid level, process stage, concentration, and speed: The liquid level is set to four preset values ​​from low to high: H1 to H4. The process stages are set to four stages from F1 to F4 in order. The switching time between the three stages F2-F4 is set to T1-T3 respectively. The concentration is set to four preset values ​​from C1 to C4. The speed is set to five preset values ​​from low to high: R1 to R5. The overload protection value of the motor is set. During operation, the current, power and torque of the motor are continuously recorded, as are the concentration and liquid level in the pulper, and the operation time of the pulper; The first priority of the control logic is overload protection, which controls the motor to slow down when there is a risk of overload; the second priority of the control logic is liquid level safety limit, which controls the motor to slow down or stop when the liquid level is too low; the third priority of the control logic is process stage adjustment, which determines the current process stage and limits the motor speed range based on the process stage; the fourth priority of the control logic is concentration dynamic optimization, which adjusts the speed based on the set concentration in different process stages.

2. The paper mill hydraulic pulper process energy-saving control method according to claim 1, characterized in that: H1 is the minimum liquid level to avoid dry running or cavitation of the pulper, and H4 is the maximum liquid level to avoid overflow of the pulper; C1 to C3 are the normal working concentration ranges, C2 includes C2-1 to C2-4, which are the target concentrations of the F1-F4 process stages respectively, and C4 includes C4-1 to C4-4, which are the excess concentrations of the F1-F4 process stages respectively; R1 is the minimum speed to maintain the suspension of the pulp in the pulper, and R5 is the maximum speed of the pulper under mechanical and electrical limitations.

3. The paper mill hydraulic pulper process energy-saving control method according to claim 1 or 2, characterized in that: The overload protection: Based on the current records of the motor's current, power, and torque, overload protection is determined. When the recorded values ​​approach or exceed the overload protection value, the motor is controlled to slow down. Said liquid level safety limits: Based on the record of the current liquid level in the pulper, a safety limit judgment is made. When the recorded value is lower than H1, the motor speed is controlled to be reduced to below R1 or shut down. When the recorded value is in the low liquid level range H1-H2, the maximum motor speed is limited to R2. When the recorded value is in the normal liquid level range H2-H3 and the high liquid level range H3-H4, the maximum motor speed is limited to R5. The process stage adjustment: Based on multiple recorded values, the current process stage is comprehensively judged. When the current process stage is judged to be F1, the motor speed is limited to R3-R5. When the current process stage is judged to be F2, the motor speed is limited to R3-R4. When the current process stage is judged to be F3, the motor speed is limited to R1-R2. When the current process stage is judged to be F4, the motor speed is limited to R2-R3. The concentration is dynamically optimized: Based on C2-1 to C2-4 in the current process stage, dynamic optimization judgment is performed with the current concentration. When the recorded value of the current concentration is greater than the target concentration, the motor speed is increased. When the recorded value of the current concentration is less than the target concentration, the motor speed is reduced.

4. The paper mill hydraulic pulper process energy-saving control method according to claim 3, characterized in that: During the process stage adjustment, the current process stage is comprehensively judged based on the record of the pulper running time, the recorded value and change trend of the concentration in the pulper, and the recorded value and change trend of the motor current, power or torque.

5. The paper mill hydraulic pulper process energy-saving control method according to claim 4, characterized in that: If the pulper running time is less than T1, it is judged as F1 or F2; if the running time is between T1 and T2, it is judged as F3; if the running time is between T2 and T3, it is judged as F4; If the pulp concentration in the pulper is between C2 and C3 and fluctuates violently, it is judged as F1; if the concentration is between C1 and C3 and fluctuates toward C2 and tends to be stable, it is judged as F2; ​​if the concentration is close to C2 and remains basically stable, it is judged as F3 or F4; The motor's current, power or torque is large, which is judged as F1. It gradually decreases and is judged as F2. It is basically stable and is judged as F3. It further decreases and is judged as F4.

6. The paper mill hydraulic pulper process energy-saving control method according to claim 5, characterized in that: The first priority of the judgment logic is the motor state judgment, the second priority of the judgment logic is the concentration state judgment, and the third priority of the judgment logic is the running time judgment.

7. The paper mill hydraulic pulper process energy-saving control method according to claim 3, characterized in that: During the dynamic optimization of concentration, the concentration is adjusted in advance, the speed is increased in advance when the concentration rises rapidly, and the speed is reduced in advance when the concentration drops rapidly.

8. The paper mill hydraulic pulper process energy-saving control method according to claim 3, characterized in that: During the dynamic optimization of concentration, when the concentration needs to be increased, the motor speed is reduced while taking measures such as reducing water addition or increasing feed to increase the concentration.

9. The paper mill hydraulic pulper process energy-saving control method according to claim 7 or 8, characterized in that: During the dynamic optimization of concentration, when the recorded value of the current concentration reaches C4-1 to C4-4 under the current process stage, special processing is triggered, the control logic of the process stage adjustment and the control logic of the dynamic optimization of concentration are ignored, and the motor is controlled to enter R3-R5. When the concentration reaches C2-1 to C2-4 under the current process stage and remains stable for a certain period of time, the control logic of the process stage adjustment and the control logic of the dynamic optimization of concentration are restored.

10. The paper mill hydraulic pulper process energy-saving control method according to claim 9, characterized in that: During the special treatment process, the motor speed is first controlled to enter R4-R5. When the concentration begins to steadily decrease, the motor speed is changed to R3-R4. When the concentration reaches C2-1 to C2-4 under the current process stage, the control logic of dynamic concentration optimization is restored. When the concentration is stable for a certain period of time, the control logic of process stage adjustment is restored.