Effectively removing impurities such as stickies, waxes, and plastics from waste paper pulp is one of the key issues in the production technology of waste paper pulp.
At present, the methods of treating light impurities mainly include thermal dispersion and cold treatment. Compared with the two, the thermal dispersion method can not effectively remove light impurities, but it is dispersed into tiny particles left in the slurry, with the recycling of waste paper eventually become a scourge. The disadvantage of the cold treatment method is that the yield is low because the screening purification is multi-stage and multi-stage.
The loss of fiber is more; however, the cold treatment method does not require steam heating, and the power consumption is low; the process flow is less expensive and the investment can be removed from the slurry without leaving behind.
In order to improve the appearance and intrinsic quality of the product, after many inspections and comprehensive comparisons, the factory decided to use the cold process process in the waste paper pulping section, and the main equipment used light residue remover.
1 How light residue cleaner works
The lightweight slag remover adopts the principle of vortex centrifugal cleaning, that is, the use of plastic impurities, waxes and hot melt adhesives has lower density than fiber and water, and the fibers and impurities are separated by centrifugal force. Lightweight cleaners are roughly classified into three types: forward cleaners, reverse cleaners, and scroll cleaners. Taking a scroll-type cleaner as an example, the slurry enters the slurry inlet of the upper part of the deslagizer along a tangential direction at a high flow rate, and a conical flow guiding fluid is provided at the top of the deslagizer to stabilize the slurry in the de-drossing apparatus. The vortex flows. The fibers in the pulp flow are thrown toward the drum wall under the action of centrifugal force, and are driven downward by the feed pressure to make a downward spiral movement. After passing through the cylinder section and the cone section, the slurry flows out from the good slurry port at the bottom of the cone cylinder; Lightweight impurities with a medium density less than that of water and fibers, and the low pressure zone where the air gathers toward the center of the vortex during the vortex flow of the slurry, are drawn by a tailings diversion tube that extends toward the center of the vortex.
2 Application of Lightweight Cleaner
2.1 Equipment Selection and Configuration
(1)Selection of slurry pump: Because the pulp concentration of the light residue remover is less than 1%, centrifugal pump or water pump can be used; In addition, due to the requirement of light pulp cleaner pressure at 0 Between .2 and 0.35 MPa, the head of the slurry pump should be considered according to the layout of the pipeline. The head of the pump should be greater than or equal to the head of the pipeline loss plus 0.2-0.35 MPa.
(2) The slurry supply tank in front of the pump should be equipped with a white or clear water pipe to dilute the slurry.
(3) According to the type of slurry and the position of the slag remover in the system, select the appropriate slag removal rate. If a two-stage slag remover is used, the solids slag removal rate in the first stage is 6%-10%. The second stage of solids slagging rate is 8%-12%.
2.2 Factors influencing the efficiency of slag removal
How to achieve the best combination of the throughput of slurry and the tailings discharge rate is the key to the full play of the role of lightweight cleaners. In the use, attention should be paid to the following five aspects:
(1) Feeding concentration of the slag cleaner The maximum operating concentration of the light slag remover is about 1%. When the feed concentration exceeds 1%, the slag removal efficiency will be significantly reduced, especially for the removal of lighter particles with smaller particles. . Practice shows that the pulp concentration of a slag remover is controlled at 0.7%-0.8%, and the feed concentration of the secondary slag remover is controlled at
0.5%-0.6% works best.
(2) For the same pulping pressure and pulping pressure of the deslagger, the higher pulping density requires a larger pressure difference between the inlet and outlet; on the other hand, if the pressure difference between the inlet and outlet pulps is the same, A lower feed density results in a slightly larger throughput. Through the determination of a single slag cleaner, the slag removal pressure of 0.2 MPa is ensured at 0.07-O. The increase of the pressure difference between the inlet and outlet of slurry in the range of 12 MPa can increase the removal rate of impurities. In addition, since the design pressure of the slag remover is 0.4 MPa, the feed pressure during use must not exceed 0.35 MPa.
C3) The slag removal rate The relationship between removal efficiency and slag removal rate is determined by measuring single slag cleaner: When the volume slag removal rate is greater than 10%, the removal efficiency is improved slowly; when the slag removal rate exceeds 15% , Further increasing the slag removal rate has little effect on the improvement of the slag removal efficiency. In the case of a certain difference between the inlet and outlet pressures, an excessively high volume slag discharge rate requires a high feed and discharge pressure, which increases the power consumption and increases the slag removal amount of the second stage deslagger. Therefore, the appropriate slag removal rate should be selected according to the type of slurry, and the power consumption should be minimized under the premise of achieving the desired effect.
(4) The temperature of the slurry with a higher slurry temperature is conducive to the separation of fibers and impurities, thereby improving the slag removal efficiency. However, when the temperature of the treated slurry is high, care should be taken to install expansion joints on the incoming and outgoing pipelines.
(5) The process layout method is the problem of classification and segmentation. The multi-segment arrangement is to reduce the loss of slurry and reduce the amount of good fibers discharged in the slurry; multi-stage arrangement is to further improve the quality of the slurry. From the perspective of production practice, the use of multi-stage treatment can improve the quality of the slurry, but the power consumption is exponentially increased. With multi-stage treatment, the fiber loss can be appropriately reduced, but the power consumption of one section is increased every time a section is added. Therefore, from the comprehensive consideration of quality requirements and economical and reasonable factors, a two-stage setting is generally used. In special cases, for example when dealing with waxy substances and waste paper pulps with high hot melt adhesives, two-stage, two-stage settings may be considered in order to achieve a higher pulp cleanliness.
2.3 Use of slag remover and common faults
Any operation failure and abnormal operation may lead to a significant drop in the efficiency of slag removal. Therefore, equipment failures and abnormal operation should be avoided in a timely manner. In the actual operation, pay attention to the following items:
(1) Fully open the valve of the slurry pipe of the equipment, close the valve of the slurry pipe, then start the slurry pump with water, then slowly open the slurry valve, and do not start the slurry pump with the slurry valve fully opened, so as to avoid The momentary strong impact damages the dross cleaner.
(2) Gradually open the feed-in valve, adjust the opening of the discharge valve, and adjust the number of use of the slag-removal device so that the feed pressure and discharge pressure meet the requirements, and obtain the required throughput of the slurry. If the pressure difference is found to be too large, check the following: (1) whether the slag remover is clogged; (c) whether the opening of the inlet and outlet priming pipes is proper;
3 whether the number of open slag scrapers is sufficient. If the pressure difference is found to be too small, check the following: 1) whether the head and flow rate of the slurry pump is insufficient; (2) if the number of the slag skimmers to be opened is too large; and (3) whether the valve opening of the smelting mains is not suitable.
(3) During use, it is necessary to always pay attention to whether the tailings discharge of the deslagging device is normal (spray and slag are discharged into a mist or umbrella shape) and whether there is a blockage phenomenon. If there is no tailings discharged, check to see if the tailings drainage tube is clogged. If it is found that the individual slag remover is clogged, there is no need to stop or close the slag remover. Simply rotate the stern drainage pipe.
90' Pull down about 60mm (to avoid completely pulling out the drainage tube), the blockage can be washed out, immediately after the drainage tube is inserted back and locked; 2 into the slurry valve is open or blocked. If it is found that the amount of tailings discharge is too large, it is necessary to check: 1 whether the conical port under the deslagging device is blocked; 2 whether the good slurry port is blocked; 3 whether the pressure of the good slurry outlet is too large; and 4 if the pressure difference between the inlet and outlet is too small. If you find that the tailings discharge is too small, you should check: 1 whether the opening of the inlet valve is sufficient or blocked; 2 whether the outlet pressure of the slurry is too small; 3 whether the head of the slurry pump is too small; 4 the opening of the inlet and outlet manifolds is it suitable.
(4) After the system is shut down, the system shall be operated with water for 5 minutes in a timely manner to prevent the slurry from becoming dry and causing plugging of the slag remover.
2.4 Overhaul of the residue remover
Lightweight cleaners without any moving parts, and the parts are used anti-corrosion and wear-resistant materials, so the general situation does not require daily shutdown maintenance, a comprehensive inspection every 3 months can be. The main contents of the inspection are as follows:
(1) Whether the deslagging device is deformed.
(2) The wear of the ceramic ring at the taper under the slag remover shall be replaced if it has been severely worn and has caused a drop in slag removal efficiency.
(3) Whether each seal ring is in good condition.
(4) The accuracy of the pressure gauge indication.
3 Conclusion
Lightweight slag remover is very effective for removing large size plastic films, waxes, stickies and other impurities, especially the removal rate of foam can reach 98%. However, it is difficult to remove light impurities with a size of less than 1.5 mm and cannot meet the requirements of high-grade paper and paperboard, but it still needs to cooperate with fine-slit screening or thermal dispersion systems for processing. In addition, the tailings of lightweight cleaners contain a large amount of plastics, waxes, and stickies that are very small in density. If discharged directly to a wastewater treatment plant, the conventional sedimentation method cannot be effectively treated. It needs to be combined with air floatation to be effective. This causes some difficulties in the recovery of waste water, and it can only be used to incinerate the tailings.
In short, since the use of lightweight slag remover in the pulping process, the appearance quality of the finished product of the factory has been greatly improved, the product grade has been improved, and failures such as broken ends, pasting nets, and sticky cylinders have been reduced.
At present, the methods of treating light impurities mainly include thermal dispersion and cold treatment. Compared with the two, the thermal dispersion method can not effectively remove light impurities, but it is dispersed into tiny particles left in the slurry, with the recycling of waste paper eventually become a scourge. The disadvantage of the cold treatment method is that the yield is low because the screening purification is multi-stage and multi-stage.
The loss of fiber is more; however, the cold treatment method does not require steam heating, and the power consumption is low; the process flow is less expensive and the investment can be removed from the slurry without leaving behind.
In order to improve the appearance and intrinsic quality of the product, after many inspections and comprehensive comparisons, the factory decided to use the cold process process in the waste paper pulping section, and the main equipment used light residue remover.
1 How light residue cleaner works
The lightweight slag remover adopts the principle of vortex centrifugal cleaning, that is, the use of plastic impurities, waxes and hot melt adhesives has lower density than fiber and water, and the fibers and impurities are separated by centrifugal force. Lightweight cleaners are roughly classified into three types: forward cleaners, reverse cleaners, and scroll cleaners. Taking a scroll-type cleaner as an example, the slurry enters the slurry inlet of the upper part of the deslagizer along a tangential direction at a high flow rate, and a conical flow guiding fluid is provided at the top of the deslagizer to stabilize the slurry in the de-drossing apparatus. The vortex flows. The fibers in the pulp flow are thrown toward the drum wall under the action of centrifugal force, and are driven downward by the feed pressure to make a downward spiral movement. After passing through the cylinder section and the cone section, the slurry flows out from the good slurry port at the bottom of the cone cylinder; Lightweight impurities with a medium density less than that of water and fibers, and the low pressure zone where the air gathers toward the center of the vortex during the vortex flow of the slurry, are drawn by a tailings diversion tube that extends toward the center of the vortex.
2 Application of Lightweight Cleaner
2.1 Equipment Selection and Configuration
(1)Selection of slurry pump: Because the pulp concentration of the light residue remover is less than 1%, centrifugal pump or water pump can be used; In addition, due to the requirement of light pulp cleaner pressure at 0 Between .2 and 0.35 MPa, the head of the slurry pump should be considered according to the layout of the pipeline. The head of the pump should be greater than or equal to the head of the pipeline loss plus 0.2-0.35 MPa.
(2) The slurry supply tank in front of the pump should be equipped with a white or clear water pipe to dilute the slurry.
(3) According to the type of slurry and the position of the slag remover in the system, select the appropriate slag removal rate. If a two-stage slag remover is used, the solids slag removal rate in the first stage is 6%-10%. The second stage of solids slagging rate is 8%-12%.
2.2 Factors influencing the efficiency of slag removal
How to achieve the best combination of the throughput of slurry and the tailings discharge rate is the key to the full play of the role of lightweight cleaners. In the use, attention should be paid to the following five aspects:
(1) Feeding concentration of the slag cleaner The maximum operating concentration of the light slag remover is about 1%. When the feed concentration exceeds 1%, the slag removal efficiency will be significantly reduced, especially for the removal of lighter particles with smaller particles. . Practice shows that the pulp concentration of a slag remover is controlled at 0.7%-0.8%, and the feed concentration of the secondary slag remover is controlled at
0.5%-0.6% works best.
(2) For the same pulping pressure and pulping pressure of the deslagger, the higher pulping density requires a larger pressure difference between the inlet and outlet; on the other hand, if the pressure difference between the inlet and outlet pulps is the same, A lower feed density results in a slightly larger throughput. Through the determination of a single slag cleaner, the slag removal pressure of 0.2 MPa is ensured at 0.07-O. The increase of the pressure difference between the inlet and outlet of slurry in the range of 12 MPa can increase the removal rate of impurities. In addition, since the design pressure of the slag remover is 0.4 MPa, the feed pressure during use must not exceed 0.35 MPa.
C3) The slag removal rate The relationship between removal efficiency and slag removal rate is determined by measuring single slag cleaner: When the volume slag removal rate is greater than 10%, the removal efficiency is improved slowly; when the slag removal rate exceeds 15% , Further increasing the slag removal rate has little effect on the improvement of the slag removal efficiency. In the case of a certain difference between the inlet and outlet pressures, an excessively high volume slag discharge rate requires a high feed and discharge pressure, which increases the power consumption and increases the slag removal amount of the second stage deslagger. Therefore, the appropriate slag removal rate should be selected according to the type of slurry, and the power consumption should be minimized under the premise of achieving the desired effect.
(4) The temperature of the slurry with a higher slurry temperature is conducive to the separation of fibers and impurities, thereby improving the slag removal efficiency. However, when the temperature of the treated slurry is high, care should be taken to install expansion joints on the incoming and outgoing pipelines.
(5) The process layout method is the problem of classification and segmentation. The multi-segment arrangement is to reduce the loss of slurry and reduce the amount of good fibers discharged in the slurry; multi-stage arrangement is to further improve the quality of the slurry. From the perspective of production practice, the use of multi-stage treatment can improve the quality of the slurry, but the power consumption is exponentially increased. With multi-stage treatment, the fiber loss can be appropriately reduced, but the power consumption of one section is increased every time a section is added. Therefore, from the comprehensive consideration of quality requirements and economical and reasonable factors, a two-stage setting is generally used. In special cases, for example when dealing with waxy substances and waste paper pulps with high hot melt adhesives, two-stage, two-stage settings may be considered in order to achieve a higher pulp cleanliness.
2.3 Use of slag remover and common faults
Any operation failure and abnormal operation may lead to a significant drop in the efficiency of slag removal. Therefore, equipment failures and abnormal operation should be avoided in a timely manner. In the actual operation, pay attention to the following items:
(1) Fully open the valve of the slurry pipe of the equipment, close the valve of the slurry pipe, then start the slurry pump with water, then slowly open the slurry valve, and do not start the slurry pump with the slurry valve fully opened, so as to avoid The momentary strong impact damages the dross cleaner.
(2) Gradually open the feed-in valve, adjust the opening of the discharge valve, and adjust the number of use of the slag-removal device so that the feed pressure and discharge pressure meet the requirements, and obtain the required throughput of the slurry. If the pressure difference is found to be too large, check the following: (1) whether the slag remover is clogged; (c) whether the opening of the inlet and outlet priming pipes is proper;
3 whether the number of open slag scrapers is sufficient. If the pressure difference is found to be too small, check the following: 1) whether the head and flow rate of the slurry pump is insufficient; (2) if the number of the slag skimmers to be opened is too large; and (3) whether the valve opening of the smelting mains is not suitable.
(3) During use, it is necessary to always pay attention to whether the tailings discharge of the deslagging device is normal (spray and slag are discharged into a mist or umbrella shape) and whether there is a blockage phenomenon. If there is no tailings discharged, check to see if the tailings drainage tube is clogged. If it is found that the individual slag remover is clogged, there is no need to stop or close the slag remover. Simply rotate the stern drainage pipe.
90' Pull down about 60mm (to avoid completely pulling out the drainage tube), the blockage can be washed out, immediately after the drainage tube is inserted back and locked; 2 into the slurry valve is open or blocked. If it is found that the amount of tailings discharge is too large, it is necessary to check: 1 whether the conical port under the deslagging device is blocked; 2 whether the good slurry port is blocked; 3 whether the pressure of the good slurry outlet is too large; and 4 if the pressure difference between the inlet and outlet is too small. If you find that the tailings discharge is too small, you should check: 1 whether the opening of the inlet valve is sufficient or blocked; 2 whether the outlet pressure of the slurry is too small; 3 whether the head of the slurry pump is too small; 4 the opening of the inlet and outlet manifolds is it suitable.
(4) After the system is shut down, the system shall be operated with water for 5 minutes in a timely manner to prevent the slurry from becoming dry and causing plugging of the slag remover.
2.4 Overhaul of the residue remover
Lightweight cleaners without any moving parts, and the parts are used anti-corrosion and wear-resistant materials, so the general situation does not require daily shutdown maintenance, a comprehensive inspection every 3 months can be. The main contents of the inspection are as follows:
(1) Whether the deslagging device is deformed.
(2) The wear of the ceramic ring at the taper under the slag remover shall be replaced if it has been severely worn and has caused a drop in slag removal efficiency.
(3) Whether each seal ring is in good condition.
(4) The accuracy of the pressure gauge indication.
3 Conclusion
Lightweight slag remover is very effective for removing large size plastic films, waxes, stickies and other impurities, especially the removal rate of foam can reach 98%. However, it is difficult to remove light impurities with a size of less than 1.5 mm and cannot meet the requirements of high-grade paper and paperboard, but it still needs to cooperate with fine-slit screening or thermal dispersion systems for processing. In addition, the tailings of lightweight cleaners contain a large amount of plastics, waxes, and stickies that are very small in density. If discharged directly to a wastewater treatment plant, the conventional sedimentation method cannot be effectively treated. It needs to be combined with air floatation to be effective. This causes some difficulties in the recovery of waste water, and it can only be used to incinerate the tailings.
In short, since the use of lightweight slag remover in the pulping process, the appearance quality of the finished product of the factory has been greatly improved, the product grade has been improved, and failures such as broken ends, pasting nets, and sticky cylinders have been reduced.
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