Fiber Screening and Recycling Process for Recirculating Sizing Solution in Surface Sizing

Abstract

The present invention belongs to the technical field of papermaking, and particularly relates to a fiber screening and recycling process for the recycled sizing liquor in surface sizing. The process includes: feeding sizing stock from a sizing feed tank to a spraying chamber, controlling the sizing amount through a sizing upper roll, a sizing lower roll and a metering rod, and then transferring it to the paper. The excess sizing stock and fresh sizing stock are scraped off by the metering rod and flow into a reflux tank. After the recycled sizing liquor is pre-treated by pumping and centrifugal separation by a dreg remover, the heavy dregs are processed by a circular vibrating screen, and the recycled sizing liquor is recycled back to the reflux tank. The good pulp enters a square vibrating screen, is distributed to a stepped sieve plate through a porous sieve spraying chamber, and is respectively collected into a No. 1 or No. 2 collection tank. The sizing stock in the No. 1 collection tank is connected to a dreg remover. The dregs processed by the circular vibrating screen and the square vibrating screen are concentrated and screened, the impurities are sent to a pulper in a waste paper line for recycling, and the good pulp is incorporated into the core layer for papermaking. The fiber screening and recycling process for the recycled sizing liquor in surface sizing provided by the present invention has small material loss, high recycling rate, energy conservation and consumption reduction, and achieves zero emission of waste in papermaking.

Description

Technical Field

[0001] The present invention belongs to the technical field of papermaking, and particularly relates to a fiber screening and recycling process for the recycled sizing liquor in surface sizing. Background Art

[0002] In the field of pulp and paper making, the surface sizing process, as a key link to improve the quality and performance of paper, has been widely applied at home and abroad. Especially with the rapid development of film transfer sizing technology, not only the paper machine speed has been significantly increased, but also the sizing effect and surface properties of paper have been effectively improved. However, with the continuous progress of papermaking technology and the increasing production requirements, the surface sizing process also faces new challenges and problems.

[0003] First of all, although the increase in paper machine speed has brought a significant increase in production efficiency, it has also exacerbated the problem of stripping of fines on the paper surface. Due to the increase in paper machine speed, the stripping force on the fines on the paper surface also increases, and the viscosity and permeability of the sizing liquor itself further exacerbate the fiber stripping phenomenon. This not only affects the strength and uniformity of the paper, but also increases the fiber loss and sizing material waste in the production process.

[0004] Secondly, while pursuing high-efficiency production, large domestic papermaking enterprises have gradually equipped themselves with self-made mechanical pulp or chemical pulp lines. However, the wet pulp in the pipelines produced by these pulp lines often has not undergone sufficient heat dissipation treatment, resulting in a large amount of fiber fragments. After these fiber fragments enter the sizing system, they will seriously affect the stability of the sizing liquor and the sizing effect. In addition, some enterprises using waste paper pulping also face the problem of unstable waste paper quality. Excessive ash content in waste paper will carry a large amount of inorganic substances into the sizing system, further affecting the paper quality and production stability.

[0005] In view of the above problems, the prior art has proposed a surface sizing starch sizing liquor purification system and its application method. This system purifies the pulp by combining the use of equipment such as pressure screens, cleaners, and square vibrating screens. However, there are still some deficiencies in the actual application of this purification system. For example, the cleaner can only remove some heavy impurities by adjusting the pressure difference, and due to the adhesiveness of the sizing material, these heavy impurities often carry a large amount of fiber sizing material and are lost. In addition, the screen aperture of the square vibrating screen is relatively large (100 - 120 mesh), and the feeding trough is directly connected below the screen plate, which is prone to screen blockage and sizing material loss. At the same time, the removed impurities are directly discharged into the wastewater, which not only causes waste of resources, but also increases the difficulty and cost of water treatment. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the above-mentioned defects existing in the prior art, and provide a fiber screening and recycling process for the recycled sizing liquor in surface sizing, with small material loss, high recycling rate, energy saving and consumption reduction, and zero discharge of waste in papermaking.

[0007] The fiber screening and recycling process for the recycled sizing liquor in the surface sizing described in the present invention includes the following steps:

[0008] (1) The sizing feed tank feeds the sizing spray chamber. The spray chamber sprays onto the surfaces of the sizing upper roll and the sizing lower roll. The metering bar controls the sizing amount on the surface through pressure, and then it is transferred to the paper. The sizing upper roll and the sizing lower roll circulate. The excess sizing material on the surface and the newly sprayed sizing material are scraped off by the metering bar again and flow into the return tank. The mass of the recycled sizing accounts for 90 - 95% of the feeding amount;

[0009] (2) The sizing liquor in the return tank is pumped to the deslagger through a pump for centrifugal separation for pretreatment of heavy impurities;

[0010] (3) The heavy slag at the bottom of the deslagger enters the circular vibrating screen to process the heavy slag, and the recycled sizing liquor is recycled to the return tank to form a short - cycle process;

[0011] (4) The good pulp coming from the deslagger is received by the square vibrating screen, enters the porous square - screen spray chamber for distribution, and enters the screen plate area. The four screen plates, namely 1# screen plate, 2# screen plate, 3# screen plate, and 4# screen plate, are tiled in a stepped manner with an angle of 1 - 3°. The 1# screen plate corresponds to the 1# screen - plate collecting chamber. The 1# screen - plate collecting chamber is connected to the 1# collecting tank. The sizing material in the 1# collecting tank is recycled back to the good - pulp outlet of the deslagger. The 2# screen plate, 3# screen plate, and 4# screen plate correspond to the 2# / 3# / 4# screen - plate collecting chambers. The 2# / 3# / 4# screen - plate collecting chambers are connected to the 2# collecting tank. The 2# collecting tank is connected to the feed tank for continued recycling;

[0012] (5) The slag after being processed by the circular vibrating screen and the square vibrating screen is connected to the recycled slag tank, and after concentration and screening, the screened impurities are transported to the pulper of the waste - paper line for recycling, and the screened good pulp is mixed into the core layer for papermaking.

[0013] The inlet pressure of the deslagger in step (2) is controlled at 250 - 300 kPa, and the pressure difference between the inlet and the outlet is controlled at 150 - 180 kPa.

[0014] The mesh number of the circular vibrating screen in step (3) is 200 meshes.

[0015] The concentration of the vibrating - screen slag after being processed by the circular vibrating screen in step (3) is ≥1.5%, and the ash content is ≥1%.

[0016] The hole diameter of the porous square - screen spray chamber in step (4) is 2 - 3 cm.

[0017] The mesh number of the 1# screen plate in step (4) is 60 - 80 meshes. The sizing material in the 1# collecting tank is recycled back to the good - pulp outlet of the deslagger, and the recycled flow rate is measured and controlled to be 15 - 20% of the flow rate into the square vibrating screen.

[0018] The mesh numbers of the 2# sieve plate, 3# sieve plate, and 4# sieve plate in step (4) are set to 120 mesh, 100 mesh, and 80 mesh in sequence.

[0019] The 2# collection tank in step (4) and the 1# collection tank are set to a one-way overflow structure.

[0020] In step (4), a movable spray water pipe is equipped on the square vibrating sieve. The water temperature of the spray water pipe is 60 - 70 °C, the moving speed is 0.01 - 0.1 m / s, and the spray pressure is 3 - 6 kPa.

[0021] In step (5), the concentration of the pulp after concentration is 2.5 - 3.5%.

[0022] In step (5), a first-stage three-stage pressure screen is used for screening.

[0023] Specifically, the fiber screening and recycling process of the recycled sizing liquid in surface sizing includes the following steps:

[0024] (1) The sizing feeding tank feeds materials to the sizing spray chamber. The spray chamber sprays on the surfaces of the sizing upper roll and the sizing lower roll. The metering rod controls the sizing amount on the surface through pressure, and then it is transferred to the paper. The sizing upper roll and the sizing lower roll cycle back. The excess sizing material on the surface and the newly sprayed sizing material are scraped off by the metering rod again and flow into the return tank. The quality of the returned sizing accounts for 90 - 95% of the feeding amount. When it is less than this ratio, missed coating will occur.

[0025] (2) The sizing liquid in the return tank is pumped to the deslagger through centrifugal separation for pretreatment of heavy impurities. The inlet pressure of the deslagger is controlled at 250 - 300 kPa, and the pressure difference between the inlet and the outlet is controlled at 150 - 180 kPa.

[0026] (3) The heavy slag at the bottom of the deslagger enters a 200-mesh circular vibrating sieve for treatment. The heavy impurities are removed. The recycled sizing liquid is pumped to the return tank through a pump to form a short-circuit flow and is processed in multiple stages to reduce the loss of sizing material. The vibrating sieve slag is recycled to the recycled slag tank, and the concentration of the vibrating sieve slag is ≥1.5%, and the ash content is ≥1%.

[0027] (4) The square vibrating screen receives the good pulp from the cleaner and enters the screen plate area through the pressure-stabilizing distribution of the multi-hole pipe with a length of 2 - 3 cm in the multi-hole square screen spraying cavity. The four screen plates, namely 1# screen plate, 2# screen plate, 3# screen plate, and 4# screen plate, are laid flat in a stepped manner with an angle of 1 - 3°. The 1# screen plate corresponds to the 1# screen plate collecting chamber, and the 1# screen plate collecting chamber is connected to the 1# collecting tank. The screen plate mesh number is 60 - 80 meshes to prevent the sizing material from clogging the screen mesh when coming out of the main pipe. The sizing material in the 1# collecting tank is recycled back to the good pulp outlet of the cleaner, and a flow meter is installed on the recycling pipeline to display the recycling flow rate, controlling the recycling flow rate to be 15 - 20% of the flow rate entering the square vibrating screen to avoid fluctuations in the feeding flow rate. The mesh numbers of the 2# screen plate, 3# screen plate, and 4# screen plate are set to 120 meshes, 100 meshes, and 80 meshes in sequence. The 2# screen plate, 3# screen plate, and 4# screen plate correspond to the 2# / 3# / 4# screen plate collecting chambers, and the 2# / 3# / 4# screen plate collecting chambers are connected to the 2# collecting tank. The 2# collecting tank is connected to the feeding tank for continuous reuse. A one-way overflow tank is set between the top of the 2# collecting tank and the 1# collecting tank, facilitating continuous processing when disassembling and replacing a certain screen plate. The square vibrating screen is equipped with a spray water pipe, which is movable. The temperature of the movable spray water is 60 - 70 °C, the moving speed is 0.01 - 0.1 m / s, and the spray pressure is 3 - 6 kPa.

[0028] (5) The residues processed by the circular vibrating screen and the square vibrating screen are connected to the recycling residue tank. After being concentrated to a concentration of 2.5 - 3.5% by the cylinder screen, they enter the first-stage three-stage pressure screen for screening. The screened impurities are transported to the pulper of the waste paper line for reuse, and the screened good pulp is mixed into the core layer for papermaking. Since there is enzyme-converted starch in the recycled materials in the residue tank, the strength of the broke pulp can be improved.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] After implementing the fiber screening and recycling process of the recycled sizing liquid in the surface sizing of the present invention, the papermaking sizing section no longer discharges waste sizing liquid. The monthly starch consumption for sizing is reduced by 6 - 10 tons, and the fiber unit consumption per ton of paper is reduced by 1 - 2 kg / t. The sieve residue content of the sizing liquid is reduced from 6500 ppm to 4368 - 4953 ppm, and the cleanliness of the sizing liquid is improved by 21.91% - 27.2%. The amount of defective products downgraded and reprocessed due to sizing streaks per month is reduced by 48 - 54 tons. The COD content of the wastewater received by the water plant from the paper machine is reduced from 7000 ppm to 5883 - 6627 ppm, the suspended solid content is reduced from 624 ppm to 408 - 603 ppm, and the TDS content is reduced from 2230 ppm to 1410 - 1896 ppm. Description of the Drawings

[0031] Figure 1 It is a schematic diagram of the fiber screening and recycling process of the recycled sizing liquid in the surface sizing of the present invention.

[0032] Figure 2 It is a schematic diagram of a square vibrating screen.

[0033] Figure 1 In the figure: 1. Sizing upper roll; 2. Sizing lower roll; 3. Feeding trough; 4. 2# collection trough; 5. 1# collection trough; 6. Square vibrating screen; 7. Return flow trough; 8. Deslagger; 9. Circular vibrating screen; 10. Recycling slag trough; 11. Cylinder screen; 12. Pressure screen; 13. Broke trough; 14. Paper.

[0034] Figure 2 In the figure: 15. Good pulp inlet; 16. Porous square screen spray chamber; 17. 1# screen plate; 18. 2# screen plate; 19. 3# screen plate; 20. 4# screen plate; 21. Spray water pipe; 22. Spray water support; 23. 1# screen plate collection chamber; 24. 2# / 3# / 4# screen plate collection chamber. Specific implementation mode

[0035] The present invention will be further described below in conjunction with specific embodiments.

[0036] The % described in the present invention is the mass percentage.

[0037] In the surface sizing of the present invention, the fiber screening and recycling process of the recycled sizing solution is as Figure 1-2 shown, and the working steps are as follows:

[0038] (1) The sizing feeding trough 3 feeds the sizing spray chamber, and the spray chamber sprays on the surfaces of the sizing upper roll 1 and the sizing lower roll 2. The metering rod controls the sizing amount on the surface through pressure, and then it is transferred to the paper 14. The sizing upper roll 1 and the sizing lower roll 2 cycle back, and the excess sizing material on the surface and the newly sprayed sizing material are scraped off by the metering rod again and flow into the return flow trough 7. The mass of the returned sizing accounts for 90-95% of the feeding amount.

[0039] (2) The sizing solution in the return flow trough 7 is pumped to the deslagger 8 for centrifugal separation for pretreatment of heavy impurities. The inlet pressure of the deslagger 8 is controlled at 250-300 kPa, and the pressure difference between the inlet and outlet is controlled at 150-180 kPa.

[0040] (3) The heavy slag at the bottom of the deslagger 8 enters the 200-mesh circular vibrating screen 9 for treatment, and the heavy impurities are removed. The recycled sizing liquid is pumped to the return flow trough 7 through a pump to form a short-circuit flow process and multi-stage treatment to reduce the loss of sizing material. The slag from the circular vibrating screen 9 is recycled to the recycling slag trough 10, and the concentration of the vibrating screen slag is ≥1.5%, and the ash content is ≥1%.

[0041] (4) The square vibrating screen 6 receives the good pulp coming from the dreg remover 8, enters the porous square screen spraying cavity 16 from the good pulp inlet 15, and enters the screen plate area after being stably distributed through a porous pipe with a length of 2 - 3 cm. The four screen plates, namely the 1# screen plate 17, 2# screen plate 18, 3# screen plate 19, and 4# screen plate 20, are laid flat in a stepped manner with an angle of 1 - 3°. The 1# screen plate 17 corresponds to the 1# screen plate collecting chamber 23, and the 1# screen plate collecting chamber 23 is connected to the 1# collecting tank 5. The screen plate mesh number is 60 - 80 meshes to prevent the sizing material from clogging the screen mesh when coming out of the main pipe. The sizing material in the 1# collecting tank 5 is recycled back to the good pulp outlet of the dreg remover 8, and a flow meter is installed on the recycling pipeline to display the recycling flow rate, and the recycling flow rate is controlled to be 15 - 20% of the flow rate into the square vibrating screen 6 to avoid fluctuations in the feeding flow rate. The mesh numbers of the 2# screen plate 18, 3# screen plate 19, and 4# screen plate 20 are set to 120 meshes, 100 meshes, and 80 meshes in sequence. The 2# screen plate 18, 3# screen plate 19, and 4# screen plate 20 correspond to the 2# / 3# / 4# screen plate collecting chamber 24, and the 2# / 3# / 4# screen plate collecting chamber 24 is connected to the 2# collecting tank 4. The 2# collecting tank 4 is connected to the feeding tank 3, and the liquid material continues to be reused. The 2# collecting tank 4 and the 1# collecting tank 5 are provided with a one-way overflow structure, which is convenient for continuous processing when disassembling and replacing a certain screen plate. The square vibrating screen 6 is equipped with a spray water pipe 21, which is fixed on the spray water support 22 and is movable. The spray water temperature is 60 - 70°C, the moving speed is 0.01 - 0.1 m / s, and the spray pressure is 3 - 6 kPa.

[0042] (5) The dregs processed by the circular vibrating screen 9 and the square vibrating screen 6 are connected to the recycled dreg tank 10, concentrated to a concentration of 2.5 - 3.5% through the round mesh 11, and then enter the first-stage three-stage pressure screen 12 for screening. The screened impurities are transported to the pulper of the waste paper line for reuse, and the good pulp after screening enters the broke tank 13 and is formulated into the core layer for papermaking.

[0043] Example 1

[0044] The fiber screening and recycling process of the recycled sizing liquid in the surface sizing includes the following steps:

[0045] (1) The feeding tank 3 for sizing supplies materials to the sizing spraying cavity, and the spraying cavity sprays on the surfaces of the sizing upper roll 1 and the sizing lower roll 2. The metering rod controls the sizing amount on the surface through pressure, and then it is transferred to the paper 14. The sizing upper roll 1 and the sizing lower roll 2 cycle back, and the excess sizing material on the surface and the newly sprayed sizing material are scraped off again by the metering rod and flow into the recycling tank 7. The mass of the recycled material accounts for 90% of the feeding amount.

[0046] (2) The sizing liquid in the recycling tank 7 is pumped to the dreg remover 8 for centrifugal separation and heavy impurity pretreatment. The inlet pressure of the dreg remover 8 is controlled at 250 kPa, and the pressure difference between the inlet and outlet is controlled at 150 kPa.

[0047] (3) The heavy slag at the bottom of the cleaner 8 enters the 200-mesh circular vibrating screen 9 for treatment. The heavy impurities are removed, and the recycled glue liquid is pumped to the reflux tank 7 through a pump, forming a short-circuit process with multi-stage treatment to reduce the loss of sizing material. The slag from the circular vibrating screen 9 is recycled to the recycled slag tank 10. The concentration of the vibrating screen slag is 1.5%, and the ash content is 1.2%.

[0048] (4) The square vibrating screen 6 receives the good pulp coming from the cleaner 8 and enters the porous square screen spray chamber 16 from the good pulp inlet 15. After being evenly distributed through a porous pipe with a length of 2 - 3 cm for pressure stabilization, it enters the screen plate area. The four screen plates, namely the 1# screen plate 17, 2# screen plate 18, 3# screen plate 19, and 4# screen plate 20, are tiled in a stepped manner with an angle of 1°. The 1# screen plate 17 corresponds to the 1# screen plate collecting chamber 23, and the 1# screen plate collecting chamber 23 is connected to the 1# collecting tank 5. The screen plate mesh number is 60 meshes to prevent the sizing material from clogging the screen mesh when coming out of the main pipe. The sizing material in the 1# collecting tank 5 is recycled back to the good pulp outlet of the cleaner 8, and a flow meter is installed on the recycling pipeline to display the recycling flow rate, controlling the recycling flow rate to be 15% of the flow rate entering the square vibrating screen 6 to avoid fluctuations in the feeding flow rate. The mesh numbers of the 2# screen plate 18, 3# screen plate 19, and 4# screen plate 20 are set to 120 meshes, 100 meshes, and 80 meshes in sequence. The 2# screen plate 18, 3# screen plate 19, and 4# screen plate 20 correspond to the 2# / 3# / 4# screen plate collecting chamber 24, and the 2# / 3# / 4# screen plate collecting chamber 24 is connected to the 2# collecting tank 4. The 2# collecting tank 4 is connected to the feeding tank 3, and the liquid is recycled for further use. The 2# collecting tank 4 and the 1# collecting tank 5 are provided with a one-way overflow structure, which is convenient for continuous treatment when disassembling and replacing a certain screen plate for cleaning. The square vibrating screen 6 is equipped with a spray water pipe 21, which is fixed on the spray water support 22 and is movable. The temperature of the spray water is 60 °C, the moving speed is 0.01 m / s, and the spray pressure is 3 kPa.

[0049] (5) The slag after being treated by the circular vibrating screen 9 and the square vibrating screen 6 is connected to the recycled slag tank 10. After being concentrated to a concentration of 2.5% by the cylinder screen 11, it enters the first-stage three-stage pressure screen 12 for screening. The screened impurities are transported to the pulper of the waste paper line for recycling, and the good pulp after screening enters the broke tank 13 and is used for core layer papermaking.

[0050] After implementing the above fiber screening and recycling process for the reflux sizing liquid in surface sizing, the papermaking sizing section no longer discharges waste sizing liquid. The monthly starch consumption for sizing is reduced by 6 tons, and the fiber consumption per ton of paper is reduced by 1 kg / t. The residue content of the sizing liquid is 4953 ppm, and the cleanliness of the sizing liquid is improved by 22.45%. The amount of defective products downgraded and reprocessed due to sizing streaks per month is reduced by 54 tons. The COD of the wastewater received by the water plant from the paper machine is 5883 ppm, the solid suspended matter content is 408 ppm, and the TDS content is 1410 ppm.

[0051] Example 2

[0052] The fiber screening and recycling process for the recycled sizing liquid in surface sizing includes the following steps:

[0053] (1) The sizing feed tank 3 feeds the sizing spray chamber, and the spray chamber sprays onto the surfaces of the sizing upper roll 1 and the sizing lower roll 2. The metering rod controls the sizing amount on the surface through pressure, and then it is transferred onto the paper 14. The sizing upper roll 1 and the sizing lower roll 2 cycle back, and the excess sizing material on the surface and the newly sprayed sizing material are scraped off again by the metering rod and flow into the return tank 7. The mass of the recycled sizing accounts for 92% of the feeding amount.

[0054] (2) The sizing liquid in the return tank 7 is pumped to the deslagger 8 for centrifugal separation for heavy impurity pretreatment. The inlet pressure of the deslagger 8 is controlled at 280 kPa, and the pressure difference between the inlet and outlet is controlled at 165 kPa.

[0055] (3) The heavy slag at the bottom of the deslagger 8 enters the 200-mesh circular vibrating screen 9 for treatment, and the heavy impurities are removed. The recycled sizing liquid is pumped to the return tank 7 through a pump to form a short-circuit flow and is processed in multiple stages to reduce the loss of sizing material. The slag from the circular vibrating screen 9 is recycled to the recycled slag tank 10. The concentration of the vibrating screen slag is 1.7%, and the ash content is 1.5%.

[0056] (4) The square vibrating screen 6 receives the good pulp coming from the deslagger 8, enters the porous square screen spray chamber 16 from the good pulp inlet 15, and enters the screen plate area through a 2 - 3 cm porous pipe for pressure stabilization and distribution. The four screen plates, namely the 1# screen plate 17, the 2# screen plate 18, the 3# screen plate 19, and the 4# screen plate 20, are tiled in a stepped manner with an angle of 2°. The 1# screen plate 17 corresponds to the 1# screen plate collecting chamber 23, and the 1# screen plate collecting chamber 23 is connected to the 1# collecting tank 5. The mesh number of the screen plate is 70 meshes to prevent the sizing material coming out of the main pipe from clogging the screen mesh. The sizing material in the 1# collecting tank 5 is recycled back to the good pulp outlet of the deslagger 8, and a flow meter is installed on the recycled pipeline to display the recycled flow rate. The recycled flow rate is controlled at 15% of the flow rate entering the square vibrating screen 6 to avoid fluctuations in the feeding flow rate. The mesh numbers of the 2# screen plate 18, the 3# screen plate 19, and the 4# screen plate 20 are set to 120 meshes, 100 meshes, and 80 meshes in sequence. The 2# screen plate 18, the 3# screen plate 19, and the 4# screen plate 20 correspond to the 2# / 3# / 4# screen plate collecting chambers 24, and the 2# / 3# / 4# screen plate collecting chambers 24 are connected to the 2# collecting tank 4. The 2# collecting tank 4 is connected to the feed tank 3, and the liquid is reused. The 2# collecting tank 4 and the 1# collecting tank 5 are provided with a one-way overflow structure, which is convenient for continuous processing when disassembling and replacing a certain screen plate. The square vibrating screen 6 is equipped with a spray water pipe 21, which is fixed on the spray water support 22 and is movable. The temperature of the spray water is 65 °C, the moving speed is 0.05 m / s, and the spray pressure is 5 kPa.

[0057] (5) The slag processed by the circular vibrating screen 9 and the square vibrating screen 6 is fed into the recycled slag tank 10. After being concentrated to a concentration of 3.0% by the round mesh 11, it enters the first-stage three-section pressure screen 12 for screening. The screened impurities are transported to the pulper of the waste paper line for reuse, and the good pulp after screening enters the broke tank 13 and is incorporated into the core layer for papermaking.

[0058] After implementing the above fiber screening and recycling process for the recycled sizing liquor in surface sizing, the papermaking sizing section no longer discharges waste sizing liquor. The monthly starch consumption for sizing is reduced by 8 tons, and the fiber consumption per ton of paper is reduced by 1.4 kg / t. The residue content in the sizing liquor is 4683 ppm, and the cleanliness of the sizing liquor is improved by 21.95%. The amount of defective products downgraded and reprocessed due to sizing streaks per month is reduced by 48 tons. The COD of the wastewater received by the water plant from the paper machine is 6416 ppm, the solid suspended matter content is 468 ppm, and the TDS content is 1710 ppm.

[0059] Example 3

[0060] The fiber screening and recycling process for the recycled sizing liquor in surface sizing described above includes the following steps:

[0061] (1) The sizing feed tank 3 supplies materials to the sizing spray chamber. The spray chamber sprays onto the surfaces of the sizing upper roll 1 and the sizing lower roll 2. The metering rod controls the sizing amount on the surface through pressure, and then it is transferred to the paper 14. The sizing upper roll 1 and the sizing lower roll 2 cycle back, and the excess sizing material on the surface and the newly sprayed sizing material are scraped off by the metering rod again and flow into the return tank 7. The mass of the returned sizing accounts for 95% of the feeding amount.

[0062] (2) The sizing liquor in the return tank 7 is pumped to the deslagger 8 for centrifugal separation and heavy impurity pretreatment. The inlet pressure of the deslagger 8 is controlled at 300 kPa, and the pressure difference between the inlet and outlet is controlled at 180 kPa.

[0063] (3) The heavy slag at the bottom of the deslagger 8 enters the 200-mesh circular vibrating screen 9 for treatment. The heavy impurities are removed, and the recycled sizing liquid is pumped to the return tank 7 through a pump to form a short-circuit flow process. Through multi-stage treatment, the loss of sizing material is reduced. The slag from the circular vibrating screen 9 is recycled to the recycled slag tank 10. The concentration of the vibrating screen slag is 1.8%, and the ash content is 1.8%.

[0064] (4)The square vibrating screen 6 receives the good pulp coming from the dreg remover 8, enters the porous square screen spraying cavity 16 from the good pulp inlet 15, and enters the screen plate area after being stabilized and distributed through a porous pipe with a length of 2 - 3 cm. The four screen plates, namely the 1# screen plate 17, 2# screen plate 18, 3# screen plate 19, and 4# screen plate 20, are laid flat in a stepped manner with an angle of 3°. The 1# screen plate 17 corresponds to the 1# screen plate collecting chamber 23, and the 1# screen plate collecting chamber 23 is connected to the 1# collecting tank 5. The mesh number of the screen plate is 80 meshes to prevent the sizing material from clogging the screen mesh when coming out of the main pipe. The sizing material in the 1# collecting tank 5 is recycled back to the good pulp outlet of the dreg remover 8, and a flow meter is installed on the recycling pipeline to display the recycling flow rate, and the recycling flow rate is controlled to be 20% of the flow rate entering the square vibrating screen 6 to avoid fluctuations in the feeding flow rate. The mesh numbers of the 2# screen plate 18, 3# screen plate 19, and 4# screen plate 20 are set to 120 meshes, 100 meshes, and 80 meshes in sequence. The 2# screen plate 18, 3# screen plate 19, and 4# screen plate 20 correspond to the 2# / 3# / 4# screen plate collecting chamber 24, and the 2# / 3# / 4# screen plate collecting chamber 24 is connected to the 2# collecting tank 4. The 2# collecting tank 4 is connected to the feeding tank 3, and the liquid is recycled. The 2# collecting tank 4 and the 1# collecting tank 5 are provided with a one-way overflow structure, which is convenient for continuous processing when disassembling and replacing a certain screen plate. The square vibrating screen 6 is equipped with a spray water pipe 21, which is fixed on the spray water support 22 and is movable. The temperature of the spray water is 70 °C, the moving speed is 0.1 m / s, and the spray pressure is 6 kPa.

[0065] (5)The dregs processed by the circular vibrating screen 9 and the square vibrating screen 6 are connected to the recycled dreg tank 10, concentrated to a concentration of 3.5% through the round screen 11, and then enter the first-stage three-stage pressure screen 12 for screening. The screened impurities are transported to the pulper of the waste paper line for recycling, and the good pulp after screening enters the broke tank 13 and is used for core layer papermaking.

[0066] After implementing the above fiber screening and recycling process for the recycled sizing liquid in surface sizing, the papermaking sizing section no longer discharges waste sizing liquid. The monthly starch consumption for sizing is reduced by 10 tons, and the fiber consumption per ton of paper is reduced by 2 kg / t. The residue content in the sizing liquid is 4368 ppm, and the cleanliness of the sizing liquid is improved to 27.2%. The amount of defective products downgraded and reprocessed due to sizing streaks per month is reduced by 52 tons. The COD of the wastewater received by the water plant from the paper machine is 6627 ppm, the suspended solid content is 603 ppm, and the TDS content is 1896 ppm.

Claims

1. A fiber screening and recycling process for the reflux sizing liquid in surface sizing, characterized in that: It includes the following steps: (1) The sizing feeding tank feeds the sizing spray chamber. The spray chamber sprays onto the surfaces of the sizing upper roller and the sizing lower roller. The metering rod controls the sizing amount on the surface through pressure, and then it is transferred to the paper. The sizing upper roller and the sizing lower roller circulate. The excess sizing material on the surface and the newly sprayed sizing material are scraped off by the metering rod again and flow into the reflux tank. The quality of the reflux accounts for 90 - 95% of the feeding amount; (2) The sizing liquid in the reflux tank is pumped to the deslagger through a pump for centrifugal separation for pretreatment of heavy impurities; (3) The heavy slag at the bottom of the deslagger enters the circular vibrating screen to process the heavy slag. The recycled sizing liquid is reused to the reflux tank to form a short circulation process; The concentration of the vibrating screen slag after being processed by the circular vibrating screen in step (3) is ≥1.5%, and the ash content is ≥1%; (4) The square vibrating screen receives the good pulp coming from the deslagger, enters the porous square screen spray chamber for distribution, and enters the screen plate area. The four screen plates, namely 1# screen plate, 2# screen plate, 3# screen plate, and 4# screen plate, are tiled in a stepped manner with an angle of 1 - 3°. The 1# screen plate corresponds to the 1# screen plate collecting chamber. The 1# screen plate collecting chamber is connected to the 1# collecting tank. The sizing material in the 1# collecting tank is recycled to the good pulp outlet of the deslagger. The 2# screen plate, 3# screen plate, and 4# screen plate correspond to the 2# / 3# / 4# screen plate collecting chambers. The 2# / 3# / 4# screen plate collecting chambers are connected to the 2# collecting tank. The 2# collecting tank is connected to the feeding tank for continuous reuse; The mesh number of the 1# screen plate is 60 - 80 meshes. The sizing material in the 1# collecting tank is recycled to the good pulp outlet of the deslagger. The reflux flow rate is measured, and the reflux flow rate is controlled to be 15 - 20% of the flow rate entering the square vibrating screen; The mesh numbers of the 2# screen plate, 3# screen plate, and 4# screen plate are set to 120 meshes, 100 meshes, and 80 meshes in sequence; The 2# collecting tank and the 1# collecting tank in step (4) are set to a one-way overflow structure; A movable spray water pipe is equipped on the square vibrating screen. The water temperature of the spray water pipe is 60 - 70°C, the moving speed is 0.01 - 0.1 m / s, and the spray pressure is 3 - 6 kPa; (5) The slag processed by the circular vibrating screen and the square vibrating screen is connected to the recycled slag tank, concentrated and screened. The screened impurities are transported to the pulper of the waste paper line for reuse, and the screened good pulp is blended into the core layer for papermaking.

2. The fiber screening and recycling process for the recycled sizing liquid in surface sizing according to claim 1, wherein: The inlet pressure of the deslagger in step (2) is controlled at 250 - 300 kPa, and the pressure difference between the inlet and outlet is controlled at 150 - 180 kPa.

3. The fiber screening and recycling process for the recycled sizing liquid in surface sizing according to claim 1, characterized in that: The mesh number of the circular vibrating screen in step (3) is 200 meshes.

4. The fiber screening and recycling process for the recycled sizing liquid in surface sizing according to claim 1, wherein: The hole diameter of the porous square screen spray chamber in step (4) is 2 - 3 cm.

5. The fiber screening and recycling process for the recycled sizing liquor in surface sizing according to claim 1, characterized in that: The concentration of the pulp after concentration in step (5) is 2.5 - 3.5%.

6. The fiber screening and recycling process for the recycled sizing liquor in surface sizing according to claim 1, characterized in that: The screening in step (5) uses a first-stage three-stage pressure screen.

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