A constant-volume and constant-quantity dissolving preparation system of aluminum sulfate for papermaking and a control method thereof

Abstract

This invention discloses a constant-volume, quantitative dissolution preparation system for aluminum sulfate used in papermaking and its control method, aiming to solve the problems of frequent clogging, large concentration fluctuations, and crude control in traditional dissolution processes. The system includes a solid quantitative feeding device, a dissolution tank, a quantitative water replenishment device, a homogenization and storage device, an intelligent detection system, and a central control unit. The control method adopts a sequential batch cycle: based on feedback signals from the weighing module, the central control unit sequentially completes precise quantitative water feeding and material addition. After forced dispersion and dissolution, concentration verification is performed, and additional material can be added to ensure that the concentration of each batch accurately meets the standard. After storage, based on feedback from the online pH meter in the paper machine's feeding trough, the feeding amount for the next batch is predictively adjusted using a PID algorithm, forming a dual closed-loop control across the system. This invention completely eliminates dissolution clogging, achieves unmanned operation, and precisely links solution preparation with the pH requirements of the paper machine's wet end, greatly improving sizing quality and chemical utilization efficiency.

Description

Technical Field

[0001] This invention relates to the field of papermaking wet-end chemical preparation technology, and more specifically, to an aluminum sulfate dissolution preparation system and its automatic control method for papermaking retention aid, filtration aid or sizing processes. Background Technology

[0002] In the papermaking process, aluminum sulfate is a key retention aid, filter aid, and sizing precipitant. The concentration and stability of its solution have a decisive impact on the wet end chemical balance of the paper machine and the quality of the finished paper.

[0003] Currently, paper mills generally use continuous dissolution methods such as Venturi suction or vertical spray gravity flow. This traditional process has the following three major drawbacks:

[0004] The dissolution process is prone to producing a "caking-void" phenomenon: when aluminum sulfate powder comes into contact with water, it readily hydrates rapidly on the surface to form a paste-like crust, preventing water from entering the interior and creating voids that are wet on the outside and dry on the inside. This phenomenon leads to frequent blockages in the dissolution riser, requiring a lot of manpower to stop and clear the blockages. Furthermore, the drastic concentration fluctuations that occur during the clearing process directly impact the downstream feeding system.

[0005] Large and delayed fluctuations in solution concentration: Traditional processes involve dissolving and conveying simultaneously, lacking sufficient homogenization and buffering time. The concentration of the prepared solution depends entirely on the instantaneous solid-liquid contact state, resulting in fluctuating concentrations in the storage tank, which are ultimately transmitted to the papermaking section, causing significant fluctuations in the sizing pH value of the top and bottom layers.

[0006] Reliance on manual experience and rough operation: The judgment of the amount of material to be fed, the amount of water to be added and the timing of unblocking depend entirely on the personal experience of the operators, making it impossible to achieve standardized quantitative control. This leads to serious waste of chemicals and increases the risk of personnel coming into contact with dust and corrosive materials.

[0007] Therefore, there is an urgent need for a new preparation system and method that can completely eliminate dissolution blockage, achieve dual stability of concentration and pH value, and be fully automated throughout the process. Summary of the Invention

[0008] The present invention aims to solve the problems in the prior art mentioned above, and provides a constant volume and quantitative dissolution preparation system for aluminum sulfate for papermaking and its control method. It creatively decomposes the continuous dynamic dissolution process into multiple controllable static batch cycles, realizing precise control of the entire chain of preparation and application.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows:

[0010] A system for the constant volume and quantitative dissolution preparation of aluminum sulfate for papermaking includes:

[0011] A quantitative feeding device is used to weigh and convey a preset weight of aluminum sulfate powder;

[0012] The dissolution reaction device is a corrosion-resistant dissolution tank with a stirring device. A weighing module is integrated on the dissolution tank to detect the total weight of the material in the tank in real time.

[0013] A quantitative water replenishment device, including a pipeline with a control valve and a flow meter, is used to add a preset weight of solvent into a dissolving tank;

[0014] The homogenization storage tank is connected to the dissolving tank via a transfer pump and pipeline;

[0015] The intelligent detection system includes a conductivity concentration meter installed in the dissolving tank and an online pH meter installed in the feeding trough of the paper machine;

[0016] The central control unit is electrically connected to the solid quantitative feeding device, the stirring device, the weighing module, the quantitative water replenishment device, the transfer pump, and the intelligent detection system, respectively.

[0017] The central control unit is configured to control the operation of the solid quantitative feeding device, the quantitative water replenishment device, and the transfer pump based on the feedback signals from the conductivity concentration meter and the online pH meter. Through sequential batch quantitative dissolution and dual closed-loop feedback control, it realizes the fixed-volume quantitative preparation of aluminum sulfate solution and the precise control of the pH value of the feeding tank.

[0018] Furthermore, the quantitative feeding device is a loss-in-weight feeder or a precision screw feeder, installed at the outlet of the aluminum sulfate raw material silo, forming a quantitative feeding system with dual weight verification together with the weighing module.

[0019] Furthermore, the dissolving tank has a volume of 4-8m³. 3 The vertical cylindrical corrosion-resistant tank includes a stirring device comprising a stirring motor located at the upper part of the tank, a stirring rod connected to the output shaft of the stirring motor, and a downward-pressing upper blade and a dispersing disc lower blade located at the lower part of the stirring rod.

[0020] Furthermore, the weighing module is integrated and installed at the bottom of the dissolving tank or on the support leg.

[0021] A method for controlling the quantitative and constant-volume dissolution preparation of aluminum sulfate for papermaking using the above system, wherein the central control unit executes the following cyclic steps:

[0022] S1, Constant volume water inlet: Control the quantitative water replenishment device to inject water into the dissolving tank. When the weight signal fed back by the weighing module reaches the first preset weight, the water inlet stops.

[0023] S2. Quantitative feeding: Start the stirring device, then start the quantitative feeding device to add aluminum sulfate powder. When the total weight increase fed by the weighing module reaches the second preset weight, stop feeding.

[0024] S3. Forced dispersion and dissolution: The stirring device runs at a preset speed for a preset time to force the aluminum sulfate powder to disperse throughout the liquid phase system;

[0025] S4. Static homogenization and concentration verification: After stirring, the solution concentration is detected by a conductivity meter. If the concentration is lower than the lower threshold, steps S2 and S3 are repeated to add more material until the concentration reaches the standard. If the concentration reaches the standard, proceed to step S5.

[0026] S5. Transfer and store for later use: Start the transfer pump to transfer all the solution in the dissolving tank to the homogenization storage tank for use by the paper machine. After the transfer is completed, return to step S1 to start the next batch preparation.

[0027] Furthermore, it also includes a dual closed-loop feedback control step S6:

[0028] During the operation of the paper machine, the central control unit acquires the pH value collected by the online pH meter in the feeding tank in real time. When the measured pH value deviates from the preset process window, the second preset weight in step S2 of the next preparation batch is automatically and predictively adjusted through the PID control algorithm, that is, the amount of aluminum sulfate fed is adjusted, so as to accurately correct the pH value of the feeding tank by changing the concentration of the preparation solution, thus forming a closed-loop control across the system.

[0029] Furthermore, the feeding tank includes a surface feeding tank and a bottom feeding tank, and the online pH meter is respectively installed in the surface feeding tank and the bottom feeding tank. The central control unit performs the fine adjustment based on the comprehensive feedback or independent feedback of the two pH values.

[0030] Furthermore, in step S4, the concentration meeting the standard means that the deviation between the solution concentration corresponding to the measured conductivity and the target concentration is within ±0.1%.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] 1. This invention completely avoids the risk of caking and blockage caused by continuous dissolution of risers by using a batch-type "one-pot method" static dissolution. The entire feeding, dissolution and transfer process is fully automated, freeing manpower from heavy and dangerous unblocking operations and solving unnecessary labor costs.

[0033] 2. Because the concentration of each batch is precisely determined and verified, and is directly controlled by the backend pH value requirements, this invention completely eliminates the traditional practice of adding excessive amounts to ensure production. According to experimental verification, this invention reduces the consumption of aluminum sulfate from 3.6 kg / t paper to 2.0 kg / t paper, a reduction of 44.4%, saving more than 660,000 yuan in chemical value annually.

[0034] 3. This invention ensures high uniformity of chemical concentration from the source, and achieves large closed-loop control across multiple processes by directly setting the control target as the pH value of the paper machine feed. This narrows the pH fluctuation range of the top / bottom sizing to within ±0.1, greatly improving the stability of sizing effect and paper quality.

[0035] 4. The system architecture and control logic of this invention are also applicable to the preparation of all papermaking chemicals that require on-site dissolution and have high requirements for concentration and addition accuracy, such as caustic soda, magnesium sulfate, and calcium carbonate, providing a standardized and reproducible modular solution for wet-end chemical preparation. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the overall structure of the system of the present invention;

[0037] Figure 2 This is a schematic flowchart of the method of the present invention;

[0038] In the diagram: 1. Aluminum sulfate raw material silo; 2. Dissolving tank; 3. Homogenization storage tank; 4. Feeding tank; 5. Control valve; 6. Flow meter; 7. Feeder; 8. Weighing module; 9. Stirring rod; 10. Stirring motor; 11. Upper impeller; 12. Lower impeller; 13. Conductivity concentration meter; 14. Transfer pump; 15. Surface feeding tank; 16. Bottom feeding tank; 17. Online pH meter. Detailed Implementation

[0039] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0040] Taking the PM6 paper machine with an annual output of 435,000 tons of paper as an example, it originally adopted the vertical pipe dissolution method, which was prone to clogging, had a high labor intensity, and consumed as much as 3.6 kg / t of paper of aluminum sulfate.

[0041] like Figure 1 As shown, the core of this renovation is: a volume increased from the original 1.5m³. 3 Upgraded to 5m 3 The dissolving tank 3 is equipped with a corrosion-resistant double-layer paddle agitator, and a high-precision weighing module 8 is integrated on the support legs. A loss-in-weight feeder 7 is installed at the outlet of the aluminum sulfate raw material silo 1. Water replenishment is completed through a pipeline with a control valve 5 and a flow meter 6. The dissolved solution is transferred to a 10m³... 3 The homogenization storage tank 3 is used for the process. The key control point is that online pH meters 17 are installed in both the surface layer feeding tank 15 and the bottom layer feeding tank 16, and all signals are fed into the newly added central control unit.

[0042] like Figure 2 As shown, the control method operates as follows:

[0043] The central control unit is programmed to prepare 3500 kg per batch with a target concentration of 10%. The operating procedure is as follows:

[0044] S1, Constant volume water intake: Open control valve 5 to add water. After the weighing module 8 reports that 3150kg of water has been added, close the valve.

[0045] S2. Quantitative feeding: Start the mixing motor at 10 to 150 rpm, and then start the loss-in-weight feeder 7. When the weighing module 8 detects that the total weight has increased by 350 kg (i.e., 350 kg of aluminum sulfate has been accurately added), turn off the feeder 7.

[0046] S3. Forced dispersion and dissolution: The stirring device runs for 10 minutes to force the aluminum sulfate powder to disperse throughout the liquid phase system;

[0047] S4. Static homogenization and concentration verification: After stirring for 10 minutes, turn off the motor and let it stand. Use conductivity meter 13 to detect the concentration. If it shows 10.0%±0.1%, it is qualified. If the concentration is too low due to batch differences of raw materials, the program will automatically restart the feeder 7 to add a small amount of aluminum sulfate until it fully meets the standard.

[0048] S5. Transfer and Circulation: Start the transfer pump 14 to transfer the qualified solution from the entire tank into the homogenization storage tank 3 for later use. After emptying, the system will automatically start the next cycle.

[0049] S6. Cross-system pH closed-loop control: During operation, staff noticed that the online pH meter 17 in the bottom feeding tank 16 showed a continuous drop in pH value from a stable 4.5 to 4.4. After calculation, the PID controller in the central control unit automatically adjusted the target value of the next batch of aluminum sulfate feed from 350kg to 352kg. By slightly increasing the concentration, the pH value of the feeding tank was precisely brought back to the set point of 4.5.

[0050] Test results:

[0051] After nearly nine months of continuous and stable operation, the system completely eliminated the clogging problem and achieved unattended operation. The aluminum sulfate consumption per unit of volume from January to March 2024 was successfully reduced from 3.6 kg / t to 2.0 kg / t in the same period of 2025, saving 696.506 tons of aluminum sulfate per year and 661,680.7 yuan per year, a reduction of 44.4%. Moreover, the pH fluctuation of the top / bottom layers remained stable within an extremely narrow range of ±0.1, significantly improving the sizing quality of the finished paper.

Claims

1. A system for the constant-volume, quantitative dissolution and preparation of aluminum sulfate for papermaking, characterized in that, include: A quantitative feeding device is used to weigh and convey a preset weight of aluminum sulfate powder; The dissolution reaction device is a corrosion-resistant dissolution tank (2) with a stirring device. A weighing module is integrated on the dissolution tank (2) to detect the total weight of the material in the tank in real time. A quantitative water replenishment device includes a pipeline with a control valve (5) and a flow meter (6) for adding a preset weight of solvent into the dissolving tank (2); The homogenization storage tank (3) is connected to the dissolving tank (2) via a transfer pump (14) and pipeline; The intelligent detection system includes a conductivity concentration meter (13) installed in the dissolving tank (2) and an online pH meter (17) installed in the paper machine feeding tank. The central control unit is electrically connected to the solid quantitative feeding device, the stirring device, the weighing module, the quantitative water replenishment device, the transfer pump, and the intelligent detection system, respectively. The central control unit is configured to control the operation of the solid quantitative feeding device, the quantitative water replenishment device and the transfer pump (14) based on the feedback signals of the conductivity concentration meter (13) and the online pH meter (17). Through sequential batch quantitative dissolution and dual closed-loop feedback control, the fixed volume quantitative preparation of aluminum sulfate solution and the precise control of the pH value of the feeding tank are realized.

2. The system according to claim 1, characterized in that, The quantitative feeding device is a loss-in-weight feeder (7) or a precision screw feeder, installed at the outlet of the aluminum sulfate raw material silo (1), and together with the weighing module, forms a quantitative feeding system with dual weight verification.

3. The system according to claim 1, characterized in that, The dissolving tank (2) has a volume of 4-8m³. 3 The vertical cylindrical corrosion-resistant tank includes a stirring motor (10) located at the top of the tank, a stirring rod (9) connected to the output shaft of the stirring motor (10), and a downward-pressing upper blade (11) located at the top of the stirring rod (9) and a dispersion disc type lower blade (12) located at the bottom.

4. The system according to claim 1, characterized in that, The weighing module (8) is integrated and installed at the bottom of the dissolving tank (2) or on the support leg.

5. A method for controlling the quantitative and constant-volume dissolution preparation of aluminum sulfate for papermaking using the system described in any one of claims 1 to 4, characterized in that, The central control unit performs the following cyclical steps: S1, constant volume water intake: control the quantitative water supply device to inject water into the dissolving tank (2), and stop water intake when the weight signal fed back by the weighing module reaches the first preset weight; S2. Quantitative feeding: Start the stirring device, then start the quantitative feeding device to add aluminum sulfate powder. When the total weight increase fed by the weighing module reaches the second preset weight, stop feeding. S3. Forced dispersion and dissolution: The stirring device runs at a preset speed for a preset time to force the aluminum sulfate powder to disperse throughout the liquid phase system; S4. Static homogenization and concentration verification: After stirring, the concentration of the solution is detected by a conductivity meter (13). If the concentration is lower than the lower limit threshold, steps S2 and S3 are repeated to supplement the feed until the concentration reaches the standard. If the concentration reaches the standard, proceed to step S5. S5, Transfer for later use: Start the transfer pump (14) to transfer all the solution in the dissolving tank (2) to the homogenization storage tank (3) for use by the paper machine. After the transfer is completed, return to step S1 to enter the next batch preparation.

6. The control method according to claim 5, characterized in that, It also includes the dual closed-loop feedback control step S6: During the operation of the paper machine, the central control unit obtains the pH value collected by the online pH meter (17) in the feeding tank (4) in real time. When the measured pH value deviates from the preset process window, the second preset weight of step S2 in the next batch of preparation is automatically and predictively adjusted by the PID control algorithm, that is, the amount of aluminum sulfate fed is adjusted, so as to accurately correct the pH value of the feeding tank (4) by changing the concentration of the preparation solution, thus forming a closed-loop control across the system.

7. The control method according to claim 5, characterized in that, The feeding tank (4) includes a surface feeding tank (15) and a bottom feeding tank (16). The online pH meter (17) is respectively installed in the surface feeding tank (15) and the bottom feeding tank (16). The central control unit performs the fine adjustment based on the comprehensive feedback or independent feedback of the two pH values.

8. The control method according to claim 5, characterized in that, In step S4, the concentration meeting the standard means that the deviation between the solution concentration corresponding to the measured conductivity and the target concentration is within ±0.1%.

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