Variable gain control method in pH transition region

Abstract

The invention relates to a variable gain control method in a pH transition region, which is characterized in that aiming at the characteristic that the pH is abruptly changed in a neutralization process, a variable gain controller is used for automatically calculating and controlling the adding flow of a neutralization reagent, and when a pH measured value is in a sensitive region or the transition region, the adding flow of the neutralization reagent is controlled. Gains required when the pH measurement value is in different regions can be automatically calculated by using a variable gain controller, and stable control is realized; when the pH value transition zone parameter is unknown, the automatic test module and the slope test module can be used to automatically calculate the pH value transition zone parameter, and the pH value transition zone parameter is input to the variable gain controller.

Description

Technical Field

[0001] The invention relates to the technical field of solution pH value control, and in particular to a variable gain control method in a pH transition zone. Background Art

[0002] The neutralization process is a common process in the chemical industry. It usually refers to the chemical reaction in which acid and alkali react to produce salt and water. The use of pH control in the neutralization process is a common control demand scenario in the chemical industry. If the neutralization effect is not good, it may cause adverse consequences such as equipment corrosion and inability to treat wastewater and waste liquid.

[0003] The characteristic of the acid-base neutralization process is that the pH value changes dramatically with the increase of the amount of acid or alkali added in the sensitive range, while the pH value changes slowly with the increase of the amount of acid / alkali added outside the sensitive range. Based on this characteristic, the use of ordinary controllers to control the pH value of the neutralization process may not meet the control requirements. When the pH value cannot be automatically and stably controlled, it not only increases labor costs, but may even cause upstream production equipment to reduce production or stop due to insufficient processing capacity of the material handling system.

[0004] CN103695570A discloses a control method for a cane juice sulfur fumigation neutralization reaction control system, which uses the cane juice sulfur fumigation neutralization reaction control system to control the cane juice sulfur fumigation neutralization reaction process, including process control of the pre-ashing process, the primary heating process, the sulfur fumigation neutralization process, and the secondary heating process; the process control of the sulfur fumigation neutralization process includes four sub-processes: pH value analysis, ultrasonic enhancement, neutralization liquid stirring, and flow rate adjustment. The invention uses feedback regulation to adjust the neutralization reaction process in real time, and can accurately control the sucrose flow rate, sucrose solution pH value, primary heating and secondary heating temperature of the sulfur fumigation neutralization reaction device.

[0005] CN110745932A discloses a three-level wastewater pH control method and system based on DCS, comprising the following steps: (1) using a tool to collect process wastewater flow, pH value, and pH value of wastewater in a fine adjustment tank and a protection tank, and communicating them into the DCS; (2) obtaining the amount of acid / alkali entering the primary rough adjustment tank through a preset soft instrument, multiplying it by a neutralization proportional factor as the set value of the neutralizer, and performing preliminary neutralization in the primary rough adjustment tank; (3) continuing to add a neutralizer for adjustment according to the deviation between the pH value of the wastewater in the fine adjustment tank and the set value, and assigning different PID parameters to the controller according to the different intervals of the pH value of the wastewater in the titration curve; (4) continuing to add a neutralizer for adjustment according to the deviation between the pH value of the wastewater in the protection tank and the set value when the deviation exceeds the set interval.

[0006] The above neutralization reaction process control or pH value control method can realize real-time control of the solution pH value, but when the set value of the neutralization process pH value control is located in the sensitive area or the process fluctuation causes the pH value measurement value to fluctuate between the sensitive area and the non-sensitive area, the ordinary control algorithm may cause the pH value measurement value to fluctuate greatly, making it difficult to meet the control requirements, or there are problems of complex process operation and high cost.

[0007] Therefore, in view of the shortcomings of the existing technology, it is urgently necessary to provide a method that can automatically calculate the gain required when the pH value is in different regions, achieve smooth control and simple process. Summary of the invention

[0008] The object of the present invention is to provide a variable gain control method in a pH transition zone, which can realize pH control when the pH setting value of the neutralization process is located in the sensitive zone and transition zone of the titration curve.

[0009] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0010] The present invention provides a variable gain control method in a pH transition region, the variable gain control method comprising the following steps:

[0011] During the neutralization process, the pH value is measured to control the feed flow rate of the neutralizing agent, wherein a variable gain controller is used to automatically calculate and control the feed flow rate of the neutralizing agent, specifically including:

[0012] The variable gain controller divides the neutralization process into a transition zone and a non-transition zone by setting the pH mutation point parameter and the pH transition zone parameter, and obtains the gain values ​​of different zones at the same time;

[0013] The pH transition zone parameters are obtained by manual input setting or automatic test calculation. The automatic test calculation is performed using an automatic test module and a slope test module, and the obtained results are automatically input into the variable gain controller by the automatic test module.

[0014] The variable gain control method in the pH transition zone provided by the present invention aims at the characteristic of sudden change of pH in the neutralization process, and uses a variable gain controller to automatically calculate and control the addition flow rate of the neutralizing reagent. When the pH measurement value is in the sensitive zone or the transition zone, the ordinary control algorithm may cause the pH measurement value to fluctuate greatly, which is difficult to meet the control requirements. However, the use of the variable gain controller can automatically calculate the gain required when the pH measurement value is in different areas, thereby achieving smooth control. When the parameters of the pH transition zone are unknown, the automatic test module and the slope test module can be used to automatically calculate the parameters of the pH transition zone, and the pH transition zone parameters can be input into the variable gain controller.

[0015] In the present invention, the pH value mutation point parameters include a first mutation point and a second mutation point. The first mutation point is the pH value corresponding to the point where the change trend of the pH value with the addition amount of the neutralizing reagent changes (from stable to steep) during the neutralization process, denoted as Break1; the second mutation point is the pH value corresponding to the point where the change trend of the pH value with the addition amount of the neutralizing reagent changes (from steep to stable) during the neutralization process, denoted as Break2.

[0016] Preferably, the non-transition region includes a sensitive region and a non-sensitive region.

[0017] Within the sensitive region (Break1 < pH < Break2, where Break1 and Break2 are both pH mutation points), the pH value changes drastically with the increase in the addition amount of the neutralizing reagent, while outside the non-sensitive region (pH ≤ Break1 or pH ≥ Break2), the pH value changes slowly with the increase in the addition amount of the neutralizing reagent.

[0018] Preferably, the gain value of the non-transition region is given by the user according to the response characteristics of the control loop.

[0019] Preferably, the gain value of the transition region is automatically calculated by a variable gain controller.

[0020] In the present invention, the pH transition zone parameters include a first transition zone and a second transition zone. The first transition zone is a transition zone in which the pH value changes from a steady state to a steep state as the amount of neutralizing agent added changes during the neutralization process. The starting point of the first transition zone is represented by Transition 1-; the end point is represented by Transition 1+; the second transition zone is a transition zone in which the pH value changes from a steep state to a steady state as the amount of neutralizing agent added changes during the neutralization process. The starting point of the second transition zone is represented by Transition 2-; the end point is represented by Transition 2+. According to the different pH change trends during the neutralization process, it is divided into 5 intervals, and each interval is controlled by a different gain, as follows: non-sensitive area, corresponding to the pH value interval (0, Transition 1-), corresponding to the gain K=K1; the first transition zone, corresponding to the pH value interval (Transition 1-, Transition 1+), the corresponding gain is automatically calculated by the variable gain controller; sensitive area, corresponding to the pH value interval (Transition 1+, Transition 2-), corresponding to the gain K=K2; the second transition zone, corresponding to the pH value interval (Transition 2-, Transition 2+), the corresponding gain is automatically calculated by the variable gain controller; non-sensitive area, corresponding to the pH value interval (Transition 2+, 14), corresponding to the gain K=K3; wherein, K1, K2, and K3 are given by the user according to the response characteristics of the control loop, and the proportional gain of the variable gain controller in the interval between the first transition zone and the second transition zone changes with the change of the measured value to meet the requirements of the transition zone for the performance of the variable gain controller.

[0021] Preferably, the step of automatically calculating the transition zone gain value by the variable gain controller specifically comprises:

[0022] (1) Provide n sets of coordinates (pH) to the variable gain controller n , K n ) is used to define the change curve of the variable gain controller, n represents an integer ≥ 2, the n sets of coordinates at least include two sets of coordinates of the starting point and the ending point of the transition zone, and the n sets of coordinates satisfy:

[0023] pH n-1 <pH n

[0024] K n-1 <K n ;

[0025] Where: pH n is the horizontal coordinate of the nth group of coordinates, indicating the pH value; K n is the ordinate of the nth group of coordinates, indicating the gain value corresponding to the pH value;

[0026] (2) Calculate the transition zone gain value based on the provided n sets of coordinates. The calculation formula is as follows:

[0027]

[0028] Where: pH(x) represents the n-1 ,pH n ] is the pH value of any point in the interval; K(x) represents the gain value corresponding to pH(x);

[0029] (3) The calculation formula of the output value OUT of the variable gain controller is as follows:

[0030]

[0031] Where: OUT(t) represents the output value of the variable gain controller at time t; K() represents the gain value at time t; Δ(t) represents the difference between the measured value and the set value at time t; T I Indicates the integration time in seconds.

[0032] In step (1), two sets of coordinates of the starting point and the ending point of the transition zone, i.e., for the first transition zone, the coordinates when pH=Transition 1- and pH=Transition 1+ are provided, and for the second transition zone, the coordinates when pH=Transition 2- and pH=Transition 2+ are provided.

[0033] Preferably, the step of automatically testing and calculating the pH transition zone parameters includes: during the test, the ramp test module increases or decreases the flow rate of the neutralizing reagent according to the set climbing rate, and continuously monitors the process gain value. The pH values ​​corresponding to the process gain values ​​reaching 30% and 50% are respectively the starting point and the ending point of the transition zone. At the same time, the automatic test module automatically inputs the results into the variable gain controller.

[0034] Preferably, the step of automatically testing and calculating the pH transition zone parameters specifically includes:

[0035] (a) The Ramp+ function block in the ramp test module sets the ramp rate and inputs it into the set value of the flow controller, so that the flow of the flow controller gradually increases according to the set ramp rate. At this time, if the neutralizing agent is an alkali solution, the measured pH value gradually increases; if the neutralizing agent is an acid solution, the measured pH value gradually decreases;

[0036] (b) If the measured value rises to the set value +2 (the test target range is 0 to 7), or the measured value decreases to the set value -2 (the test target range is 7 to 14), the test ends; the Ramp-function block sets the ramp rate and inputs it into the set value of the flow controller, so that the flow of the flow controller gradually decreases according to the set ramp rate until the measured pH value returns to the value before the test, and the test ends;

[0037] (c) Detection process gain change, calculated as follows:

[0038]

[0039] Among them: a t pV is the process gain at time t during the automatic test calculation process of the automatic test module; t is the pH value measured at time t; F t is the flow rate of the flow controller at time t;

[0040] If the pH increases during the test:

[0041]

[0042] Where: k at+ It represents the rate of change of process gain at time t during the test process of increasing pH;

[0043] If the pH decreases during the test:

[0044]

[0045] Where: k at- It represents the rate of change of process gain at time t during the test process of pH decrease;

[0046] (d) The range of the first transition zone obtained by the test is (Transition 1-, Transition 1+), and the range of the second transition zone is (Transition 2-, Transition 2+).

[0047] Preferably, the neutralizing agent comprises an acid solution or an alkali solution.

[0048] Preferably, the neutralization process is carried out in a neutralization device, one end of the neutralization device is connected to a process material feed pipeline, and the other end is connected to a pumping device, and the process material feed pipeline is externally connected to a neutralization reagent feed pipeline.

[0049] Preferably, a flow controller is provided on the process material feed pipeline, and the flow controller is used to control the feed flow rate of the process material.

[0050] Preferably, the discharge pipeline of the pumping device is provided with a branch, and the branch is connected to the neutralization device.

[0051] Preferably, a feed main pH online detector is provided on the common pipeline of the neutralizing reagent feed pipeline and the process material feed pipeline, and a circulation line pH online detector is provided on the branch line of the pumping device. The circulation line pH online detector is cascaded with the feed main pH online detector and the feed flow of the neutralizing reagent is controlled through a variable gain controller.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] The variable gain control method in the pH transition zone provided by the present invention aims at the characteristic of sudden change of pH in the neutralization process, and uses a variable gain controller to automatically calculate and control the addition flow rate of the neutralizing reagent. When the pH measurement value is in the sensitive zone or the transition zone, the ordinary control algorithm may cause the pH measurement value to fluctuate greatly, which is difficult to meet the control requirements. However, the use of the variable gain controller can automatically calculate the gain required when the pH measurement value is in different areas, thereby achieving smooth control. When the parameters of the pH transition zone are unknown, the automatic test module and the slope test module can be used to automatically calculate the parameters of the pH transition zone, and the pH transition zone parameters can be input into the variable gain controller. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a control schematic diagram of the variable gain control method in the pH transition zone provided by the present invention;

[0055] Among them: 1, neutralization device; 2, process material feed pipeline; 3, pumping device; 4, branch; 5, neutralization reagent feed pipeline; 6, flow controller; 7, feed main pipe pH online detector; 8, circulation pipeline pH online detector. DETAILED DESCRIPTION

[0056] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0057] Example 1

[0058] This embodiment provides a variable gain control method in a pH transition region, the variable gain control method comprising the following steps:

[0059] During the neutralization process, the pH value is measured to control the feed flow rate of the neutralizing agent. In this embodiment, the neutralizing agent is alkali solution. The control schematic diagram is as follows: Figure 1As shown, the neutralization process is carried out in a neutralization device 1, one end of the neutralization device 1 is connected to a process material feed pipeline 2, and the other end is connected to a pumping device 3, the discharge pipeline of the pumping device 3 is provided with a branch 4, and the branch 4 is connected to the neutralization device 1; the process material feed pipeline 2 is externally connected to a neutralization reagent feed pipeline 5;

[0060] The process material feed pipeline 2 is provided with a flow controller 6, and the flow controller 6 is used to control the feed flow rate of the process material; a feed main pipe pH online detector 7 is provided on the common pipeline of the neutralization reagent feed pipeline 5 and the process material feed pipeline 2, and a circulation line pH online detector 8 is provided on the branch 4 of the pumping device 3. The circulation line pH online detector 8 is cascaded with the feed main pipe pH online detector 7 and controls the feed flow rate of the alkali solution through the variable gain control logic of the variable gain controller.

[0061] The specific steps of automatically calculating and controlling the feed flow rate of alkali solution using a variable gain controller include:

[0062] The required control value is pH = 4. When the system fluctuates, the fluctuation range of the pH value is 2-7. According to the titration curve of the neutralization process, the pH mutation point parameters of the variable gain controller are set: Break 1 = 3.5, Break 2 = 6.4. The pH transition zone parameters are automatically tested and calculated using the automatic test module and the ramp test module. The specific steps include:

[0063] The Ramp+ function block in the ramp test module sets the ramp rate to 0.1 kg / s until the pH value increases to 6. The test ends. The Ramp- function block sets the flow rate of the flow controller to decrease the ramp rate to 0.1 kg / s until the pH value decreases to the set value pH=4. The test ends. The automatic test module calculates the change in process gain during the test and finally calculates the end point of the transition zone Transition 1+=3.9.

[0064] The Ramp- function block sets the flow controller's flow rate reduction ramp rate to 0.1 kg / s until the pH value drops to 2, and the test ends. The Ramp+ function block sets the flow controller's flow rate increase ramp rate to 0.1 kg / s until the pH value returns to the set value of pH=4, and the test ends. The automatic test module calculates the change in process gain during the test and finally calculates the starting point of the transition zone Transition 1-=3.2;

[0065] The neutralization process is divided into a transition zone, a sensitive zone, and a non-sensitive zone, and gain values ​​of different zones are obtained at the same time. The gain values ​​of the sensitive zone and the non-sensitive zone are given by the user according to the response characteristics of the control loop, and the gain value of the transition zone is automatically calculated by a variable gain controller. The variable gain controller sets the control gain according to the input Break 1, Break 2, Transition 1-, and Transition 1+, and automatically calculates the variable gain in the transition zone. The gain actually calculated by the variable gain controller in this embodiment is shown in Table 1.

[0066] Table 1

[0067] Corresponding pH value Gain (2，3.2) K＝0.15 (3.2，3.9) K(x)=-0.17·PH(x)+0.66 (3.9，7) K＝0.03

[0068] Comparative Example 1

[0069] This comparative example provides a method for controlling pH value, which is carried out by adopting the DCS-based tertiary wastewater pH control method disclosed in CN110745932A.

[0070] The control method can control the pH value of the solution in real time. However, when the set value of the pH value control of the neutralization process is located in a sensitive area or the process fluctuation causes the pH value measurement value to fluctuate between the sensitive area and the non-sensitive area, it may cause the pH value measurement value to fluctuate greatly, making it difficult to meet the control requirements.

[0071] In summary, the variable gain control method in the pH transition zone provided by the present invention uses a variable gain controller to automatically calculate and control the addition flow rate of the neutralizing reagent in view of the sudden change of pH during the neutralization process. When the pH measurement value is in the sensitive zone or the transition zone, the ordinary control algorithm may cause the pH measurement value to fluctuate greatly, which is difficult to meet the control requirements. The use of a variable gain controller can automatically calculate the gain required when the pH measurement value is in different areas, thereby achieving smooth control. When the pH transition zone parameters are unknown, the automatic test module and the slope test module can be used to automatically calculate the pH transition zone parameters, and the pH transition zone parameters can be input into the variable gain controller.

[0072] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A variable gain control method in a pH transition region, characterized in that: The variable gain control method comprises the following steps: During the neutralization process, the pH value is measured to control the feed flow rate of the neutralizing agent, wherein a variable gain controller is used to automatically calculate and control the feed flow rate of the neutralizing agent, specifically including: The variable gain controller divides the neutralization process into a transition zone and a non-transition zone by setting the pH mutation point parameter and the pH transition zone parameter, and obtains the gain values ​​of different zones at the same time; The pH transition zone parameters are obtained by manual input setting or automatic test calculation. The automatic test calculation is performed using an automatic test module and a slope test module, and the obtained results are automatically input into the variable gain controller by the automatic test module.

2. The variable gain control method according to claim 1, characterized in that: The non-transition area includes a sensitive area and a non-sensitive area.

3. The variable gain control method according to claim 1 or 2, characterized in that: The gain value in the non-transition zone is set by the user according to the response characteristics of the control loop.

4. The variable gain control method according to any one of claims 1 to 3, characterized in that: The gain value of the transition zone is automatically calculated by a variable gain controller.

5. The variable gain control method according to any one of claims 1 to 4, characterized in that: The step of automatically calculating the transition zone gain value by the variable gain controller specifically includes: (1) Provide n sets of coordinates (pH) to the variable gain controller n , K n ) is used to define the change curve of the variable gain controller, n represents an integer ≥ 2, the n sets of coordinates at least include two sets of coordinates of the starting point and the ending point of the transition zone, and the n sets of coordinates satisfy: pH n-1 pH n K n-1 <K n ; Where: pH n is the horizontal coordinate of the nth group of coordinates, indicating the pH value; K n is the ordinate of the nth group of coordinates, Indicates the gain value corresponding to the pH value; (2) Calculate the transition zone gain value based on the provided n sets of coordinates. The calculation formula is as follows: Where: pH(x) represents the n-1 , pH n ] is the pH value of any point in the interval; K(x) represents the gain value corresponding to pH(x); (3) The calculation formula of the output value OUT of the variable gain controller is as follows: Where: OUT(t) represents the output value of the variable gain controller at time t; K(t) represents the gain value at time t; Δ(t) represents the difference between the measured value and the set value at time t; T I Indicates the integration time in seconds.

6. The variable gain control method according to any one of claims 1 to 5, characterized in that: The steps of automatically testing and calculating the parameters of the pH transition zone include: during the test, the ramp test module increases or decreases the flow of the neutralizing reagent according to the set ramp rate, and continuously monitors the process gain value. The pH values ​​corresponding to the process gain values ​​reaching 30% and 50% are respectively the starting point and the ending point of the transition zone. At the same time, the automatic test module automatically inputs the results into the variable gain controller.

7. The variable gain control method according to any one of claims 1 to 6, characterized in that: The neutralizing agent includes acid or alkali; Preferably, the neutralization process is carried out in a neutralization device, one end of the neutralization device is connected to a process material feed pipeline, and the other end is connected to a pumping device, and the process material feed pipeline is externally connected to a neutralization reagent feed pipeline.

8. The variable gain control method according to claim 7, characterized in that: A flow controller is provided on the process material feed pipeline, and the flow controller is used to control the feed flow of the process material.

9. The variable gain control method according to claim 7 or 8, characterized in that: The discharge pipeline of the pumping device is provided with a branch, and the branch is connected to the neutralization device.

10. The variable gain control method according to any one of claims 7 to 9, characterized in that: A feed main pipe pH online detector is arranged on the common pipeline of the neutralizing reagent feed pipeline and the process material feed pipeline, and a circulation pipeline pH online detector is arranged on the branch line of the pumping device. The circulation pipeline pH online detector is cascaded with the feed main pipe pH online detector and controls the feed flow of the neutralizing reagent through a variable gain controller.

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