A papermaking sludge treatment system and recycling method

Abstract

The application provides a papermaking sludge treatment system and recycling method, and belongs to the technical field of waste recycling. The recycling method comprises the following steps: mixing press sludge, primary sedimentation tank sludge and papermaking white water to obtain a first mixture with a sludge concentration of 3-10wt%; screening impurities after dispersing the first mixture to obtain a second mixture, adding a cationic charge neutralizer with a dry sludge mass of 0.5-3.0% to the second mixture, adding a high molecular bridging agent with a dry sludge mass of 0.5-3.0% to the second mixture, uniformly mixing to obtain modified sludge, mixing the modified sludge with papermaking pulp, and recycling to the papermaking process; wherein the press sludge is formed after the primary sedimentation tank sludge and / or deinking sludge is dewatered. In the recycling process, fine fibers contained in the sludge are fully recovered, and then a two-stage modification process is used to obtain modified sludge, so that the fine components are pre-agglomerated, and the binding force between the sludge particles and the paper pulp fibers is strengthened; the obtained paper can meet the requirements of core physical strength indicators.

Description

Technical Field

[0001] This invention belongs to the field of waste recycling technology, and relates to a papermaking sludge treatment system and recycling method. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] The papermaking process generates a large amount of papermaking sludge, which can be classified according to its source into primary sedimentation tank sludge, secondary biological sludge, tertiary chemical sludge, and deinking sludge. Various types of sludge are dewatered by plate and frame filter presses and other methods to form pressed sludge. Pressed sludge is usually disposed of as solid waste landfill or coal-fired in power plants, resulting in the waste of fiber resources in the sludge.

[0004] When sludge is reused in the papermaking process, the pressed sludge has a dense agglomerate structure, which cannot be fully dispersed by conventional stirring. This results in holes and pinholes in the paper produced during the papermaking process, and may even cause paper breakage on the paper machine, making it unable to meet product quality standards. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a papermaking sludge treatment system and reuse method that effectively disperses sludge clumps, removes impurities from the sludge, adds a sludge reuse agent, and mixes it with papermaking pulp. This achieves the invention's objective of ensuring that the core physical strength indicators of the finished paper are not reduced even with a sludge addition ratio of 3-7%.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: Firstly, a method for recycling papermaking sludge includes: Press sludge, primary sedimentation tank sludge, and papermaking white water are mixed to obtain a first mixture with a sludge concentration of 3-10 wt%. The first mixture is dispersed and impurities are removed by sieving to obtain a second mixture. 0.5-3.0% of a cationic charge neutralizer by weight of oven-dry sludge and 0.5-3.0% of a polymeric crosslinking agent by weight of oven-dry sludge are added to the second mixture. After mixing evenly, modified sludge is obtained. The modified sludge is mixed with papermaking pulp and reused in the papermaking process. The pressed sludge is formed by dewatering primary sedimentation tank sludge and / or deinking sludge.

[0007] Secondly, a papermaking sludge treatment system based on the above-mentioned papermaking sludge reuse method includes a sludge dispersion tank, a pressure screen, a mixing device, and a papermaking machine mixing tank connected in sequence. The sludge dispersion tank is connected to the papermaking white water conveying pipeline, and a high-shear fragmentation device is installed in the sludge dispersion tank to disperse and stir the press sludge. The pressure screen is used to remove impurities from the sludge. The mixing device is connected to a first dosing pump and a second dosing pump. The first dosing pump is used to add a cationic charge neutralizer, and the second dosing pump is used to add a polymeric crosslinking agent. The mixing tank of the paper machine is connected to the pre-paper tank of the paper machine.

[0008] The beneficial effects of this invention are as follows: This invention uses raw materials free of chemical sludge, fully recovers the fine fibers contained in the sludge, and achieves full dispersion of the clump-like sludge through high-shear fragmentation. Then, a two-stage modification process is employed to obtain modified sludge. Specifically, a high charge-density cationic polymer is used to disrupt the colloidal stability of the sludge through charge neutralization, reducing the negative charge on the particle surface and achieving pre-coagulation of fine components; high molecular weight cationic polyacrylamide, through polymer bridging and entrapment, forms dense, shear-resistant sludge flocs, strengthening the bonding force between sludge particles and pulp fibers; the resulting paper meets the core physical strength requirements. Attached Figure Description

[0009] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0010] Figure 1 This is a schematic diagram of the papermaking sludge treatment system in Example 1.

[0011] Figure 2 This is a schematic diagram showing the connection relationship between the mixing device, the first dosing pump, and the second dosing pump in Example 1.

[0012] Figure 3 This is a schematic diagram of the static mixer in Example 1.

[0013] The components include: 1. Sludge dispersion tank; 2. Sludge buffer tank; 3. Pressure screen; 4. Sludge feeding tank; 5. Mixing device; 51. First dosing pump; 52. Second dosing pump; 6. Paper machine mixing tank; 7. Paper machine pre-forming tank; 8. Sludge lifting pump. Detailed Implementation

[0014] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0015] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0016] Terminology Explanation: Primary sedimentation tank sludge: In the process of papermaking wastewater treatment, the sludge obtained by gravity sedimentation in the primary sedimentation tank mainly contains fine fibers, fillers and suspended impurities.

[0017] Sludge concentration: This is the percentage of dry sludge in the mixture by mass, and can be measured using a microwave concentration meter.

[0018] One or more embodiments of the present invention provide a method for recycling papermaking sludge, comprising the following steps: Press sludge, primary sedimentation tank sludge, and papermaking white water are mixed to obtain a first mixture with a sludge concentration of 3-10 wt%. The first mixture is dispersed and impurities are removed by sieving to obtain a second mixture. 0.5-3.0% of a cationic charge neutralizer by weight of oven-dry sludge and 0.5-3.0% of a polymeric crosslinking agent by weight of oven-dry sludge are added to the second mixture. After mixing evenly, modified sludge is obtained. The modified sludge is mixed with papermaking pulp and reused in the papermaking process. Among them, the pressed sludge is formed by dewatering the sludge from the primary sedimentation tank and / or the deinking sludge; for paper mills with a deinking process, the deinking sludge can be used as raw material for pressed sludge together with the primary sedimentation tank pressed sludge after pressing and dewatering; for paper mills without a deinking process, the pressed sludge is obtained only by dewatering the primary sedimentation tank sludge; for larger paper mills, the production line using sludge and the pollution control workshop may be far apart, and the liquid primary sedimentation tank sludge cannot be directly transported. It can be squeezed and dewatered into pressed sludge and then transferred to the production line using sludge.

[0019] Because biochemical and chemical sludge have problems such as high ash content, difficulty in dewatering, and low reuse value, the pressing sludge used in the above process does not contain biochemical or chemical sludge. Its core components are fine fibers, inorganic fillers, and papermaking additive residues, with a fiber content of 35-50%. Compared with other types of sludge, it has fiber reuse value and does not affect the performance of paper products. High-shear fragmentation is used to fully dissociate the sludge fibers, preventing problems such as paper holes and paper breaks caused by clumps of fibers. After further screening to remove impurities, two modifiers are added to achieve pre-coagulation of fine components and enhance the binding ability of sludge particles and paper fibers. After being reused in the paper production process, paper products that meet quality requirements can be obtained.

[0020] Optionally, the dispersion method includes high-shear fragmentation or hydraulic pulping to achieve sludge dispersion.

[0021] The process of screening out impurities is used to remove plastic fragments, coarse fiber bundles, and large particulate impurities, preventing them from abrading the paper machine wire, clogging pipes, and headbox after reuse.

[0022] Optionally, the cationic charge neutralizer includes one or more of polydiallyldimethylammonium chloride (PolyDADMAC), polyamine, polyethyleneimine, and dimethylamine-epoxychloropropane copolymer; used to disrupt the colloidal stability of sludge through charge neutralization, reduce the negative charge on the particle surface, and achieve pre-coagulation of fine particles. The fine particles refer to particles with a particle size of less than 76 μm in sludge, including fine fibers, inorganic fillers (calcium carbonate, talc, kaolin, titanium dioxide, etc.), colloidal papermaking additive residues (sizing agents, reinforcing agents, defoamers, etc.), and soluble organic matter, etc., which are suspended solids that can pass through a 200-mesh sieve; the pre-coagulation refers to the aggregation of fine particles into primary flocs with a particle size of 100~500 μm. The effects of pre-coagulation include: reducing the specific surface area of ​​fine molecules, reducing their ineffective adsorption in the system, and improving the utilization rate of chemicals; increasing the retention rate of fine molecules in the paper sheet and reducing the white water circulation load; providing adsorption nodes for subsequent polymeric crosslinking agents, making the crosslinked flocs more compact and shear-resistant; and preventing fine molecules from being lost with white water during papermaking, thereby improving the fiber resource recovery rate.

[0023] Optionally, the polymeric crosslinking agent includes one or more of cationic polyacrylamide, amphoteric polyacrylamide, and modified starch; through polymeric crosslinking and entrapment, a dense, shear-resistant sludge floc is formed, strengthening the binding force between sludge particles and pulp fibers; wherein the sludge particles are a composite aggregate composed of fine fibers, inorganic fillers, colloidal papermaking additive residues, and microbial metabolites, wherein the content of fine fibers is 35-50 wt%, the content of inorganic fillers is 30-45 wt%, the content of colloidal papermaking additive residues is 5-15 wt%, and the zeta potential of the sludge particle surface is -30 to -15 mV, which is the main reason why it is difficult to directly bind with negatively charged pulp fibers. However, the technical obstacle of difficult binding can be overcome by using a cationic charge neutralizing agent for pre-modification treatment.

[0024] Optionally, the cationic polyacrylamide is a high molecular weight cationic polyacrylamide with a molecular weight range of 8 million to 18 million and an ionicity of 20% to 40%. When the molecular weight is less than 8 million, the polymer molecular chain length is insufficient, the polymer bridging ability is weak, the formed flocs are loose and have poor shear resistance, resulting in insufficient bonding force between sludge particles and pulp fibers. Under the shear force of the paper machine wire section, they are easily redispersed, and the retention rate decreases. When the molecular weight is greater than 18 million, the polymer is difficult to dissolve, and it is easy to form undissolved gel particles that are unevenly distributed in the sludge. Local excess leads to problems such as excessively large flocs and decreased paper uniformity. Moreover, the solution viscosity is too high, which affects pumping metering. When the ionicity is less than 20%, the cationic charge is insufficient, and the neutralization of the negative charge on the surface of the sludge particles is not sufficient. The adsorption of the bridging agent is low, and the flocculation effect is poor. When the ionicity is greater than 40%, the molecular chain is excessively extended, the molecular conformation is too rigid, the bridging flexibility decreases, and the excessive charge may cause the surface charge of the sludge particles to reverse (from negative to positive), leading to redispersibility problems and a decrease in floc stability.

[0025] Optionally, a cationic charge neutralizer is first added to the second mixture, followed by static mixing and then the addition of a polymeric bridging agent. After uniform mixing, modified sludge is obtained. During the process, the charge neutralizer has a low viscosity. After the solution is diluted with water, it is rapidly dispersed into the sludge system through shearing action, thus completing charge neutralization. The high molecular weight cationic polyacrylamide has a high viscosity and needs to be premixed and dispersed with water. The premixing and dispersion mainly relies on the shearing and diversion action generated inside the static mixer (or reducer) on the addition equipment to achieve premixing with water. No additional mixing device is required. The spiral blades inside the static mixer repeatedly divide and change the flow direction of the fluid, and dozens of diversion-convergence cycles can be completed within a unit length, resulting in high mixing efficiency. After the diluted high molecular weight PAM solution comes into contact with the sludge, it is rapidly dispersed into the sludge system through shearing action, thus completing bridging adsorption.

[0026] Optionally, the mass ratio of the modified sludge to the paper pulp is (1~8):(92~99), specifically including: modified sludge, virgin paper pulp and waste pulp with an oven-dry mass ratio of (3~7):(88~97):(0~5).

[0027] Optionally, the sludge concentration in the first mixture is 4 to 6 wt%.

[0028] Optionally, the paper pulp includes one or more of virgin paper pulp and waste pulp; the treated sludge can be used to produce various types of packaging paper such as high-strength corrugated base paper, kraft linerboard, and yarn tube paper. The process parameters can be flexibly adjusted and are easy to promote and apply in the industry.

[0029] One or more embodiments of the present invention provide a papermaking sludge treatment system based on the above-mentioned papermaking sludge reuse method, comprising a sludge dispersion tank, a pressure screen, a mixing device and a papermaking machine mixing tank connected in sequence; The sludge dispersion tank is connected to the papermaking white water conveying pipeline, and a high-shear fragmentation device is installed in the sludge dispersion tank to disperse and stir the press sludge. The pressure screen is used to remove impurities from the sludge. The mixing device is connected to a first dosing pump and a second dosing pump. The first dosing pump is used to add a cationic charge neutralizer, and the second dosing pump is used to add a polymeric crosslinking agent. The mixing tank of the paper machine is connected to the pre-paper tank of the paper machine.

[0030] Optionally, a sludge buffer tank is provided between the sludge dispersion tank and the pressure screen; the sludge buffer tank is used to store a certain amount of sludge to ensure continuous sludge treatment; then, it is sent to the pressure screen for screening and purification by a booster pump.

[0031] Optionally, a sludge feeding tank is provided between the pressure screen and the mixing device; the sludge feeding tank is used to store the good slurry after the pressure screen, buffer the flow fluctuations before and after the process, and ensure a continuous supply of sludge; it also keeps the sludge suspended evenly through the stirring (or aeration) device in the tank, avoids concentration stratification, and provides a stable basis for subsequent precise dosing; it also provides stable suction conditions for the variable frequency metering pump, so that the amount of sludge added can be precisely adjusted through flow control.

[0032] Optionally, the sludge dispersion tank is equipped with a high-shear fragmentation device or a hydraulic pulper.

[0033] Optionally, the pressure screen is one or more of an upflow pressure screen, a perforated screen, and a jumping screen; the screen gap specification is 0.10mm~0.30mm, used to remove plastic fragments, coarse fiber bundles, and large particle impurities; the screen residue after screening contains a large number of coarse fiber bundles, sand, plastic pieces, and other impurities, and is transported to the pulping workshop pulper for reuse; the good pulp enters the sludge feeding tank for later use.

[0034] Optionally, the papermaking sludge treatment system of the papermaking sludge reuse method includes a sludge dispersion tank, a sludge buffer tank, a pressure screen, a sludge feeding tank, a mixing device, and a papermaking machine mixing tank connected in sequence.

[0035] Optionally, the mixing device can be a static mixer or a reducer, both of which can be used to achieve uniform mixing of sludge and recycling agent.

[0036] Optionally, the first dosing pump is connected to the inlet of the mixing device, and the second dosing pump is connected to the outlet of the mixing device; or, both the first and second dosing pumps are connected to the inlet of the mixing device. The first dosing method is suitable for equipment with short pipeline mixing lengths. Through a static mixer, sequential dosing is achieved, with the charge neutralizing agent pre-coagulating at the front of the mixer and the bridging agent bridging at the rear, resulting in good modification and dense flocs. The second dosing method is suitable for equipment with low flow rates and small pipe diameters. The two agents are added at a certain distance, relying on turbulence inside the equipment pipeline for mixing. The equipment is simple, but the modification effect is slightly inferior to the first method. The two methods can be flexibly selected according to equipment conditions and the required modification effect.

[0037] The present invention will be further described below with reference to specific embodiments.

[0038] Example 1 A papermaking sludge treatment system, such as Figure 1 As shown, it includes a sludge dispersion tank 1, a sludge buffer tank 2, a pressure screen 3, a sludge feeding tank 4, a mixing device 5, and a paper machine mixing tank 6 connected in sequence, and is connected to the paper machine pre-forming tank 7 through the paper machine mixing tank 6; The sludge dispersion tank 1 is connected to the papermaking white water conveying pipeline. The sludge dispersion tank 1 is equipped with a high-shear fragmentation device to disperse and stir the pressed sludge. When mixing with white water, an intermittent process is adopted: first, half a tank of papermaking white water is added to the sludge dispersion tank 1, and then the solid pressed sludge is fed into the sludge dispersion tank 1 after being weighed by a loader, and / or the liquid primary sedimentation tank sludge is pumped into the sludge dispersion tank 1, and then white water is added to the required level to control a relatively stable concentration.

[0039] Pressure screen 3 is an upflow pressure screen with a screen gap specification of 0.20mm, used to remove plastic fragments, coarse fiber bundles and large particle impurities; the screen residue after screening contains a large number of coarse fiber bundles, sand, plastic pieces and other impurities, which are transported to the pulping workshop pulper for reuse; the good pulp enters the sludge feeding tank 4 for standby.

[0040] like Figure 2 As shown, the mixing device 5 is connected to the first dosing pump 51 and the second dosing pump 52 respectively. The first dosing pump 51 is used to add high charge density cationic polymer, and the second dosing pump 52 is used to add high molecular weight cationic polyacrylamide.

[0041] The mixing device 5 is as follows Figure 3 The static mixer shown includes a cylindrical shell with multiple spiral blades inside. After the fluid enters, it is repeatedly divided and its flow direction is changed by the internal components, which can complete the mixing without relying on external power. The first dosing pump 51 is connected to the inlet of the static mixer, and the second dosing pump 52 is connected to the outlet of the static mixer.

[0042] The first dosing pump 51 and the second dosing pump 52 are respectively connected to the mixing device 5 via clean water pipelines, which are used to deliver the high charge density cationic polymer and the high molecular weight cationic polyacrylamide at set concentrations.

[0043] The outlets of sludge dispersion tank 1, sludge buffer tank 2, and sludge feeding tank 4 are respectively connected to sludge lifting pump 8 to provide power for sludge transportation.

[0044] A variable frequency metering pump is installed upstream of the paper machine mixing tank 6, which can accurately feed modified sludge into the paper machine mixing tank 6.

[0045] The sludge conveying pipe between the sludge feeding tank 4 and the mixing device 5 is connected to the papermaking white water conveying pipe, forming a white water dilution pipe. The papermaking white water is used to dilute the sludge (concentration 5~8wt%) output from the sludge feeding tank to a suitable concentration for chemical dosing (3~5wt%), ensuring sufficient contact between the chemicals and the sludge. White water replaces clean water to achieve internal circulation of the water system, reducing clean water consumption. The concentration of sludge entering the mixing device is controlled by adjusting the white water flow rate. Above the sludge lift pump 8 downstream of the sludge feeding tank 4 in the diagram, a sludge concentration adjustment system (indicated by the dashed line) is installed. A white water inlet point is set before the sludge conveying pipe enters the mixing device. Based on the sludge concentration value detected by the concentration meter after the sludge lift pump 8, the opening of the pneumatic regulating valve in the white water pipeline is adjusted to control the concentration of sludge entering the mixing device.

[0046] The papermaking sludge reuse method based on the papermaking sludge treatment system of this embodiment includes the following process.

[0047] Sludge from primary sedimentation tank sludge and deinking sludge dewatering was selected as the sludge raw material. The pressed sludge and primary sedimentation tank sludge are transported into sludge dispersion tank 1 and mixed with papermaking white water to obtain a first mixture with a sludge concentration of 5 wt%. After being treated by a high-shear fragmentation device in the sludge dispersion tank, the first mixture is pumped to sludge buffer tank 2.

[0048] The sludge buffer tank 2 stores a set amount of sludge to ensure continuous sludge treatment. The sludge is then pumped to the pressure screen 3 for screening and purification. The good slurry after screening is the second mixture, which is then pumped to the sludge feeding tank 4 for later use.

[0049] The second mixture in the sludge feeding tank 4 is pumped to the static mixer. Before entering the static mixer, it is mixed with 1.8% high charge density cationic polymer (based on the dry sludge mass) delivered by the first dosing pump 51. Charge neutralization and pre-coagulation modification are completed in the static mixer. Then, at the outlet of the static mixer, it is mixed with 1.8% high molecular weight cationic polyacrylamide (based on the dry sludge mass) delivered by the second dosing pump 52 to complete polymer crosslinking modification and obtain modified sludge. The modified sludge is then precisely added to the paper machine mixing tank 6 via a frequency conversion metering pump.

[0050] In the mixing tank 6 of the paper machine, modified sludge, virgin pulp and waste pulp are mixed evenly in a ratio of 5:90:5 (octane dry weight ratio) to form a homogeneous slurry. The homogeneous slurry is pumped into the paper machine flow system through the pre-paper tank 7 to complete papermaking and prepare high-strength corrugated base paper (compliant with GB / T 13023) product; where the ratio is the ratio of oven dry weight.

[0051] Comparative Example 1 This comparative example serves as the blank group corresponding to Example 1. The main raw material used in its preparation is domestic OCC waste paper. The preparation method includes conventional OCC pulping processes such as waste paper shredding, screening, sand removal, and thickening. The difference from Example 1 is: The raw materials used are only OCC waste paper raw materials, without using press sludge or primary sedimentation tank sludge, and without adding two modifiers: high charge density cationic polymer and high molecular weight cationic polyacrylamide; Accordingly, the preparation method does not involve the steps of adding sludge and the two reagents mentioned above.

[0052] Detection Example 1 The product performance of Example 1 and Comparative Example 1 was tested, including physical strength indicators such as paper ring crush index and breaking length, as well as retention rate and wire dewatering performance. The test results are shown in Table 1.

[0053] The ring crush index of the finished paper is tested according to GB / T 2679.8 "Determination of Ring Crush Strength of Corrugated Base Paper", and the ring crush index = ring crush strength / basis weight; the breaking length is tested according to GB / T 12914-2018 "Determination of Tensile Strength of Paper and Paperboard - Constant Speed ​​Tensile Test (20 mm / min)"; the retention rate is calculated based on the online pulp concentration and white water concentration, and the retention rate = (online pulp concentration - white water concentration) / online pulp concentration × 100%; the dewatering performance of the wire section is characterized by the freeness or freeness of the pulp; the steam consumption per ton of finished paper refers to the amount of steam consumed (t / t paper).

[0054] Table 1

[0055] By comparing the performance differences between Example 1 and Comparative Example 1, it can be demonstrated that the two-stage modification process improves the sludge reuse effect, and the addition of modified sludge does not affect the paper production indicators.

[0056] Example 2 A papermaking sludge treatment system differs from Example 1 as follows.

[0057] A hydraulic pulper is installed in sludge dispersion tank 1 to disperse the sludge.

[0058] A settling device is added between the sludge feeding tank 4 and the mixing device 5 to further purify the sludge and remove fine silt from it.

[0059] An online concentration meter is installed at the outlet of the variable frequency metering pump, which is connected to the pump via a controller. The following closed-loop control logic enables precise control of the amount of oven-dry sludge added: the online concentration meter detects the sludge concentration at the pump outlet in real time and feeds the concentration signal back to the controller (PLC or DCS); the controller adjusts the frequency of the metering pump based on the deviation between the concentration signal and the set amount of oven-dry sludge added—when the detected concentration × flow rate (amount of oven-dry sludge) is higher than the set value, the pump frequency is reduced, decreasing the sludge volumetric flow rate; when the detected concentration × flow rate is lower than the set value, the pump frequency is increased, increasing the sludge volumetric flow rate; this closed-loop control ensures precise control of the amount of oven-dry sludge added, guaranteeing the stability of the modified sludge and paper pulp ratio.

[0060] The mixing device 5 is a reducer, the diameter of which changes according to the sludge flow direction, including three sections: thin pipe - thick pipe - thin pipe; the first dosing pump 51 and the second dosing pump 52 are both connected to the inlet of the reducer, which can achieve uniform mixing of sludge and two agents.

[0061] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for recycling papermaking sludge, characterized in that, The process includes the following steps: mixing press sludge, primary sedimentation tank sludge, and papermaking white water to obtain a first mixture with a sludge concentration of 3-10 wt%; dispersing the first mixture and sieving out impurities to obtain a second mixture; adding 0.5-3.0% of a cationic charge neutralizer by weight of oven-dry sludge to the second mixture; adding 0.5-3.0% of a polymeric crosslinking agent by weight of oven-dry sludge to the second mixture; mixing thoroughly to obtain modified sludge; and mixing the modified sludge with papermaking pulp for reuse in the papermaking process. The pressed sludge is formed by dewatering primary sedimentation tank sludge and / or deinking sludge.

2. The method for recycling papermaking sludge as described in claim 1, characterized in that, The cationic charge neutralizer includes one or more of high charge density cationic polymers and polyethyleneimine; the polymeric crosslinking agent includes one or more of cationic polyacrylamide, amphoteric polyacrylamide, and modified starch.

3. The method for recycling papermaking sludge as described in claim 2, characterized in that, The cationic polyacrylamide is a high molecular weight cationic polyacrylamide with a molecular weight range of 8 million to 18 million and an ionicity of 20 to 40%.

4. The method for recycling papermaking sludge as described in claim 1, characterized in that, First, a cationic charge neutralizer is added to the second mixture. After static mixing, a polymeric crosslinking agent is added. After mixing evenly, modified sludge is obtained.

5. The method for recycling papermaking sludge as described in claim 1, characterized in that, The mass ratio of the modified sludge to the paper pulp is (1~8):(92~99); specifically, it includes: modified sludge, virgin paper pulp and waste pulp with an oven-dry mass ratio of (3~7):(88~97):(0~5); Alternatively, the sludge concentration in the first mixture is 4-6 wt%.

6. The method for recycling papermaking sludge as described in claim 1, characterized in that, The papermaking pulp includes one or more of virgin papermaking pulp and waste pulp.

7. A papermaking sludge treatment system based on the papermaking sludge reuse method as described in any one of claims 1-6, characterized in that, It includes a sludge dispersion tank, a pressure screen, a mixing device, and a paper machine mixing tank connected in sequence; The sludge dispersion tank is connected to the papermaking white water conveying pipeline, and a high-shear fragmentation device is installed in the sludge dispersion tank to disperse and stir the press sludge. The pressure screen is used to remove impurities from the sludge. The mixing device is connected to a first dosing pump and a second dosing pump. The first dosing pump is used to add a high charge density cationic polymer, and the second dosing pump is used to add a high molecular weight cationic polyacrylamide. The mixing tank of the paper machine is connected to the pre-paper tank of the paper machine.

8. The papermaking sludge treatment system as described in claim 7, characterized in that, A sludge buffer tank is provided between the sludge dispersion tank and the pressure screen; a sludge feeding tank is provided between the pressure screen and the mixing device.

9. The papermaking sludge treatment system as described in claim 7, characterized in that, The pressure screen is one or more of the following: upflow pressure screen, perforated screen, and skip screen; the screen gap specification is 0.10mm~0.30mm; Alternatively, the sludge dispersion tank may be equipped with a high-shear fragmentation device or a hydraulic pulper; Alternatively, the mixing device may be a static mixer or a reducer.

10. The papermaking sludge treatment system as described in claim 8, characterized in that, The first dosing pump is connected to the inlet of the mixing device, and the second dosing pump is connected to the outlet of the mixing device; or, both the first dosing pump and the second dosing pump are connected to the inlet of the mixing device.

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