Inclined wire paper pulp flow uniformity control process based on ultrasonic shaking

Abstract

The invention relates to the technical field of papermaking, in particular to an inclined wire paper pulp flow uniformity control process based on ultrasonic shaking, which comprises the following steps: mixing primary pulp with recycled pulp, adding a zwitterionic dispersant, stirring, treating paper pulp with ultrasound and ozone, adding core-shell nanoparticles during treatment, regulating parameters through an intelligent shaking device according to pressure feedback, and controlling the flow uniformity of the inclined wire paper pulp. And finally, gradient dehydration forming is conducted on an inclined wire machine in combination with electric field auxiliary dispersion, three sections of vacuum areas are arranged, surface micro-nano treatment is conducted, and uniform flowing of paper pulp and high-quality forming of paper are achieved. Through cooperation of multiple technologies, the dispersity and flow uniformity of the paper pulp are remarkably improved, quantitative fluctuation of a paper banner is reduced, tensile strength is improved, meanwhile, the utilization rate of the recycled pulp is increased, drying time is shortened, and the method has the advantages of quality improvement, cost reduction and green production.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of papermaking, in particular to a slurry flow uniformity control process based on ultrasonic shaking. BACKGROUND

[0002] In modern papermaking industry, the inclined wire forming technology is widely used in the production of special paper and packaging paper due to its efficient dewatering and uniform papermaking characteristics. However, the flow uniformity of the slurry in the inclined wire headbox directly affects the paper basis weight distribution, fiber orientation and physical strength. The traditional process cannot effectively control the flocculation of the slurry in the dynamic flow process. The existing methods rely on mechanical stirring or adding conventional dispersants, which can temporarily disperse the fibers, but cannot break the hydrogen bonds between the fibers, resulting in local basis weight fluctuations, uneven thickness and other defects in the formed paper, which seriously affects the stability of the paper quality.

[0003] With the increase of the proportion of recycled fibers, the complexity of the slurry system increases, and the limitations of traditional control technology become more prominent. The ink particles, adhesives and fiber fragments remaining in the recycled pulp are easily entangled with the virgin fibers to form flocs, and the conventional dispersion means cannot achieve precise depolymerization of the small flocs. In addition, nano-scale additives such as silicon dioxide and calcium carbonate have poor dispersion stability in the slurry and are prone to agglomeration and sedimentation, which not only reduces the effectiveness of the additives, but also may block the filter screen of the papermaking equipment, affecting the production continuity.

[0004] Although ultrasonic technology and shaking devices have been applied to slurry treatment, existing researches are mostly limited to single technology level and lack of synergistic control mechanism. During ultrasonic treatment, too high power may cause fiber cutting, and too low power cannot achieve effective dispersion. The frequency and amplitude parameters of the shaking device are mostly set by experience and are difficult to adapt to the dynamic changes of different slurry characteristics. At the same time, the multi-phase interface interaction mechanism of fiber-additive-water phase in the slurry flow process has not been clarified, and how to build a self-adaptive slurry uniformization treatment system through the integration of multiple technologies and chemical control means is still a key problem restricting the upgrading of inclined wire papermaking technology. SUMMARY

[0005] (I) Technical problems solved

[0006] In view of the deficiencies of the prior art, the present application provides a slurry flow uniformity control process based on ultrasonic shaking for inclined wire.

[0007] (II) Technical solutions

[0008] A slurry flow uniformity control process based on ultrasonic shaking for inclined wire, comprising the following steps:

[0009] S1: mix virgin wood pulp with recycled pulp at a mass ratio of 7:3, add 0.05-0.15% of a zwitterionic dispersant with the chemical formula:

[0010]

[0011] wherein R is C 12 -C 18 alkyl, m = 2-4; stir uniformly, and the dispersant undergoes zwitterionic dissociation in the pulp system:

[0012]

[0013] The generated zwitterionic groups wrap the fiber surface through electrostatic interaction, forming a double-layer structure;

[0014] S2: send the pretreated pulp into an ultrasonic treatment device, set the ultrasonic frequency to 25-35 kHz, and the power density to 0.8-1.2 W / cm 2 , and pass in a volume fraction of 0.5-1.5% of ozone-oxygen mixed gas, with an ozone concentration of 10-20 mg / L;

[0015] S3: deliver the ultrasonically treated pulp to the headbox of the inclined wire paper machine, start the intelligent shaking device, and monitor the dynamic pressure distribution of the pulp in the headbox in real time through the pressure sensor, adjust the shaking frequency and amplitude according to the pressure fluctuation feedback, and form a self-adaptive shaking field;

[0016] S4: add 0.02-0.08% of core-shell structure nanoparticles to the pulp during ultrasonic treatment and shaking, and the catechol groups on the surface of the nanoparticles form a hydrogen bond network with the hydroxyl groups on the fiber surface; the core of the core-shell structure nanoparticles is titanium dioxide with a particle size of 30-50 nm, and the shell is polydopamine with a thickness of 5-10 nm;

[0017] S5: the ultrasonically and shaken treated pulp is formed and dewatered on the inclined wire paper machine, the inclined wire angle is controlled at 18-22°, and a three-stage vacuum dewatering zone is set in the wire section with vacuum degrees of -20 kPa, -40 kPa, and -60 kPa in sequence, realizing gradient dewatering and forming of the pulp.

[0018] Preferably, 0.01-0.03% of an enzymatic enhancer is also added in S1, and reacted at 45-55°C for 20-30 minutes to selectively degrade the hemicellulose on the fiber surface and expose more hydroxyl groups; the enzymatic enhancer includes xylanase and cellulase with an enzyme activity ratio of 3:1.

[0019] Preferably, 0.005-0.015% of carbon quantum dots are added in the S2 ultrasonic synergistic treatment process, the carbon quantum dots generate fluorescence resonance energy transfer (FRET) effect under the action of ultrasonic, and the particle size of the carbon quantum dots is 2-5 nm.

[0020] Preferably, the control system of the intelligent shaking device in the S3 adopts a fuzzy PID algorithm, the shaking parameters are dynamically adjusted according to the amplitude, frequency and phase difference of pressure fluctuation, and the Reynolds number of the pulp flow is kept in a transition flow state of 2000-3000.

[0021] Preferably, the core-shell structure nanoparticles in the S4 are prepared by the following method: titanium dioxide nanoparticles are dispersed in a Tris buffer solution with a pH value of 8.5, dopamine hydrochloride with a concentration of 2-4 g / L is added, stirring reaction is carried out at 25-35 DEG C for 12-18 hours, and then centrifugal separation and drying are carried out.

[0022] Preferably, in the S4 nano-interface regulation process, a direct current electric field of 0.5-1.5 V is applied at the same time, so that the negatively charged fibers and nanoparticles are subjected to directional migration in the electric field.

[0023] Preferably, in the S5 gradient forming process, a micro-groove structure is arranged on the upper net part of the inclined net, the groove direction is at an angle of 45-60 DEG with the pulp flow direction, and the pulp is guided to form an ordered flow; the micro-groove structure has a groove width of 0.5-1 mm and a depth of 0.3-0.5 mm.

[0024] Preferably, after the S5 dewatering and forming, a steam penetration drying technology is adopted, the steam temperature is controlled to be 120-150 DEG C, the steam pressure is controlled to be 0.2-0.4 MPa, and the drying time is controlled to be 30-60 seconds.

[0025] Preferably, before the S1 pulp pretreatment, deep deinking treatment is carried out on the recycled pulp, a composite deinking agent composed of a non-ionic surfactant and a cationic polymer is adopted, and the deinking agent dosage is 0.3-0.8%.

[0026] Preferably, after the S5 gradient forming, online surface micro-nano structuring treatment is carried out on the paper, laser etching microstructures are formed on the surface of a calendering roller, and a regular array of micro-protrusions is formed on the surface of the paper.

[0027] (Three) beneficial technical effects

[0028] Compared with the prior art, the beneficial effects of the present application are:

[0029] 1. Zwitterionic dispersant forms a stable double electric layer on the fiber surface through unique zwitterionic dissociation characteristics, combines with ultrasonic cavitation effect and ozone oxidation, effectively cuts off hydrogen bonds between fibers and degrades lignin fragments, so that the dispersion degree of fibers is improved. The core-shell structure nanoparticles form a hydrogen bond network with the fiber surface, and further enhance the dispersion stability under the action of electric field, solving the problem of easy agglomeration of traditional additives.

[0030] 2. The intelligent shaking device adjusts parameters in real time based on pressure fluctuations, so that the pulp keeps uniform flow in the transition flow state, and the basis weight fluctuation of the paper web is reduced to within 1.2%, which is lower than that of the traditional process. Gradient vacuum dewatering and micro-groove inclined screen design realize the ordered dewatering of pulp during the forming process, improve the fiber orientation degree, and improve the tensile strength and air permeability uniformity of the paper.

[0031] 3. Steam penetration drying and surface micro-nano structure treatment not only shorten the drying time, but also give the paper excellent surface performance. The application of enzymatic enhancer and composite deinking agent significantly improves the utilization rate of recycled pulp and reduces the consumption of virgin fibers. This process forms a full-process optimization scheme from pulp dispersion to paper forming through multi-technology collaborative innovation, effectively solves the technical bottlenecks of traditional processes, and has significant advantages in improving paper quality, reducing production cost and promoting green papermaking. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a process flow chart of the inclined screen pulp flow uniformity control process based on ultrasonic shaking proposed by the present application;

[0033] Figure 2 is a comparative diagram of the CV value of air permeability and the basis weight fluctuation of the examples and the comparative examples;

[0034] Figure 3 is a columnar comparison diagram of fiber dispersion degree and tensile strength of the examples and the comparative examples;

[0035] Figure 4 is a radar comparison diagram of performance data of the examples and the comparative examples after being made into a unified dimension. DETAILED DESCRIPTION

[0036] According to Figures 1 to 4 , the specific embodiments of the present application are as follows:

[0037] Example 1: conventional special pulp flow uniformity control

[0038] S1: pulp pretreatment

[0039] Take 350 kg of virgin wood pulp with a concentration of 4% and 150 kg of recycled pulp and put them into a 5 m3mixing tank. Weigh 0.25 kg of amphoteric dispersant, prepare a 5% aqueous solution, and then add it to the mixing tank. Set the stirring speed to 250 rpm and stir for 18 minutes. Monitor in real time using a Zeta potential instrument to ensure that the Zeta potential of the pulp stabilizes at -28 mV.

[0040] S2: Ultrasonic synergistic treatment

[0041] Pump the pretreated pulp into an ultrasonic treatment tank with a volume of 2 m3. Turn on the ozone generator and introduce ozone-oxygen mixed gas with an ozone concentration of 15 mg / L and a gas flow rate of 5 L / min. Set the ultrasonic frequency to 30 kHz and the power density to 1.0 W / cm 2 for 12 minutes. During this period, use a temperature sensor to control the pulp temperature at 42°C to prevent thermal damage to the fibers.

[0042] S3: Intelligent shaking regulation

[0043] After ultrasonic treatment, the pulp is transported to the headbox of the inclined wire paper machine with a volume of 1.5 m3. Start the intelligent shaking device. The device has a built-in pressure sensor that monitors pressure fluctuations in real time with an accuracy of ±0.1 kPa. Use a fuzzy PID algorithm to automatically adjust the shaking frequency to 10 Hz and the amplitude to 4 mm, maintaining the Reynolds number of the pulp at 2500.

[0044] S4: Nano-interface regulation

[0045] During ultrasonic treatment and shaking, prepare a 2% suspension of core-shell structured nanoparticles with a 40 nm titanium dioxide core and an 8 nm polydopamine shell. Add the suspension to the pulp at a rate of 5 L / min using a metering pump. At the same time, apply a direct current electric field of 1.0 V with an electrode spacing of 10 cm, and continue until the shaking is complete.

[0046] S5: Gradient forming

[0047] Form the pulp on the paper machine with an inclined wire angle of 20°. The wire section is set with three sections of vacuum dewatering: Zone 1 has a vacuum degree of -20 kPa and a dewatering time of 15 seconds; Zone 2 has a vacuum degree of -40 kPa and a dewatering time of 20 seconds; and Zone 3 has a vacuum degree of -60 kPa and a dewatering time of 25 seconds. After forming, the paper is dried by steam penetration at 130°C, 0.3 MPa, and 45 seconds. Then, the surface is micro-nano structured by a calendering roller, with 0.8 mm wide and 0.4 mm deep micro-grooves engraved at an angle of 50°.

[0048] Example 2: High recycled pulp ratio packaging pulp treatment

[0049] S1: Pulp pretreatment

[0050] Mix 280 kg of 3% concentration of virgin wood pulp with 320 kg of recycled pulp, add 0.4 kg of zwitterionic dispersant. At the same time, add 2.4 kg of composite deinking agent (mass ratio of non-ionic surfactant to cationic polymer 2:1), set the stirring speed to 280 rpm, and stir for 20 minutes to complete the deinking and dispersion.

[0051] S2: Ultrasonic synergistic treatment

[0052] Pump the pretreated pulp into the ultrasonic treatment tank, turn on the ozone generator, and pass in the ozone-oxygen mixed gas with an ozone concentration of 20 mg / L and a gas flow rate of 5 L / min. Set the ultrasonic frequency to 30 kHz and the power density to 1.2 W / cm 2 , treat for 15 minutes to strengthen fiber dispersion and impurity degradation. During the treatment process, the pulp temperature is controlled by a temperature sensor to prevent fiber heat damage.

[0053] S3: Intelligent shaking regulation

[0054] The pulp after ultrasonic treatment is transported to the headbox of the inclined wire paper machine, and the intelligent shaking device is started. The built-in pressure sensor in the device monitors the pressure fluctuation in real time, and uses the fuzzy PID algorithm to automatically adjust the shaking frequency to 12 Hz and the amplitude to 5 mm, ensuring uniform flow of the pulp.

[0055] S4: Nano-interface regulation

[0056] During the ultrasonic treatment and shaking process, 3.2 kg of core-shell structured nanoparticles are prepared into a 2% suspension, which is added to the pulp at a speed of 5 L / min through a metering pump. At the same time, a direct current electric field of 1.5 V is applied with an electrode spacing of 10 cm, which lasts until the shaking ends, enhancing the bonding force between the fibers and the additives.

[0057] S5: Gradient forming

[0058] The pulp is formed on the inclined wire paper machine, and the wire section is set with three sections of vacuum dewatering zone: Zone 1 vacuum degree -25 kPa, dewatering time 15 seconds; Zone 2 vacuum degree -45 kPa, dewatering time 20 seconds; Zone 3 vacuum degree -65 kPa, dewatering time 25 seconds. After forming, the paper is dried by steam penetration (150°C, 0.3 MPa, 45 seconds), and then the surface is treated by a calendering roller.

[0059] Example 3: Fine regulation of ultra-thin pulp

[0060] S1: Pulp pretreatment

[0061] Take the concentration of 5% of the original wood pulp 420 kg and low density recycled pulp 80 kg, into the stirring tank. Take the amphoteric ion dispersant 0.15 kg, prepare 5% aqueous solution and add to the stirring tank to avoid excessive dispersion leading to fiber strength decline. Set the stirring speed, stir for a certain time, monitor in real time by Zeta potential instrument to ensure the stability of the paper pulp Zeta potential.

[0062] S2: ultrasonic synergistic treatment

[0063] Pump the pretreated pulp into the ultrasonic treatment tank, start the ozone generator, and pass in the ozone-oxygen mixed gas. Set the ultrasonic frequency to 25 kHz and the power density to 0.8 W / cm2, and treat for 10 minutes to reduce the risk of fiber cutting. During the treatment, the temperature of the pulp is controlled in the appropriate range by the temperature sensor to prevent thermal damage to the fiber.

[0064] S3: intelligent shaking regulation

[0065] The pulp after ultrasonic treatment is transported to the inclined wire paper machine flow box, and the intelligent shaking device is started. The built-in pressure sensor in the device monitors the pressure fluctuation in real time, and the fuzzy PID algorithm is used to automatically adjust the shaking frequency to 8 Hz and the amplitude to 3 mm, which cooperates with the micro-groove inclined wire (groove width 0.5 mm, depth 0.3 mm) to guide the pulp to form a stable thin layer flow.

[0066] S4: nano-interface regulation

[0067] During the ultrasonic treatment and shaking process, 0.075 kg of carbon quantum dots is prepared into a suspension and added to the pulp through a metering pump. The dispersion state of the fiber is monitored in real time to ensure the uniformity of the paper.

[0068] S5: gradient forming

[0069] The pulp is formed on the inclined wire paper machine, and the wire section is set with three sections of vacuum dewatering area: the first section has a vacuum degree of -18 kPa and a dewatering time of 15 seconds; the second section has a vacuum degree of -38 kPa and a dewatering time of 20 seconds; the third section has a vacuum degree of -58 kPa and a dewatering time of 25 seconds. After forming, the paper is dried by steam penetration, and then subjected to subsequent treatment to prevent deformation of the ultra-thin paper.

[0070] Comparative example: traditional pulp treatment process

[0071] Pulp mixing: mix the original pulp and recycled pulp at a ratio of 7:3, add only 0.03% of the conventional anionic dispersant, and stir at a speed of 180 rpm for 10 minutes.

[0072] Mechanical stirring dispersion: secondary dispersion is carried out by a common stirrer without ultrasonic treatment.

[0073] Fixed parameter shaking: the shaking device operates at a fixed frequency of 6 Hz and an amplitude of 2 mm without pressure feedback adjustment.

[0074] Common forming: 15° angle of wire, single vacuum dewatering zone (vacuum degree -30 kPa), no surface micro-nano treatment.

[0075] The production stability of the examples and the comparative examples was compared, as shown in the following table:

[0076] Table 1

[0077] Group Example 1 Example 2 Example 3 Comparative Example Air permeability CV value (%) 3.2 3.5 3.0 7.5 Production paper breakage times (times / shift) 1 2 1 8 Drying time (seconds) 45 40 30 60

[0078] The CV value of the air permeability of the example group was reduced by 53%-60%, the paper breaking frequency was reduced by 75%-88%, and the drying time was shortened by 33%-50%, indicating that the process significantly improved the production stability and efficiency.

[0079] The cross direction basis weight fluctuation of the examples and the comparative examples was compared, as shown in the following table:

[0080] Table 2

[0081] Group Example 1 Example 2 Example 3 Comparative Example Cross direction basis weight fluctuation (%) 1.1 1.3 1.0 2.8 Fiber dispersion (%) 92 89 90 75 Tensile strength (N / m) 450 420 380 300

[0082] The cross direction basis weight fluctuation of the example group was significantly lower than that of the comparative examples, with a minimum of 1.0%; the fiber dispersion was improved by 15%-27%, and the tensile strength was improved by 27%-50%, reflecting the improvement effect of the process on the uniformity and strength of the paper.

[0083] Although embodiments of the present application have been shown and described, it is to be understood that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for controlling the uniformity of flow of inclined wire pulp based on ultrasonic shaking, characterized in that, Includes the following steps: S1: Mix virgin wood pulp and recycled pulp at a mass ratio of 7:3, and add 0.05-0.15% of an amphoteric dispersant, wherein the general chemical formula of the amphoteric dispersant is: Where R is C 12 -C 18 Alkyl group, m = 2-4; after thorough stirring, the dispersant undergoes an amphoteric dissociation reaction in the pulp system: The generated zwitterionic groups coat the fiber surface through electrostatic interaction, forming an electric double layer structure. S2: The pretreated pulp is fed into an ultrasonic treatment device, with the ultrasonic frequency set to 25-35kHz and the power density to 0.8-1.2W / cm³. 2 An ozone-oxygen mixture with a volume fraction of 0.5-1.5% is introduced, and the ozone concentration is 10-20 mg / L. S3: The ultrasonically treated pulp is transported to the headbox of the inclined wire paper machine, and the intelligent shaking device is activated. The dynamic pressure distribution of the pulp in the headbox is monitored in real time through pressure sensors. The shaking frequency and amplitude are adjusted according to the pressure fluctuation feedback to form an adaptive oscillation field. S4: During ultrasonic treatment and shaking, 0.02-0.08% of core-shell structured nanoparticles are added to the pulp. The catechol groups on the surface of the nanoparticles form a hydrogen bond network with the hydroxyl groups on the fiber surface. The core of the core-shell structured nanoparticles is titanium dioxide with a particle size of 30-50 nm, and the outer shell is polydopamine with a thickness of 5-10 nm. S5: The pulp treated by ultrasonic vibration is formed and dewatered on an inclined wire paper machine. The angle of the inclined wire is controlled at 18-22°, and a three-stage vacuum dewatering zone is set in the wire section. The vacuum degree is -20kPa, -40kPa and -60kPa respectively, so as to realize the gradient dewatering and forming of the pulp.

2. The process for controlling the uniformity of inclined wire pulp flow based on ultrasonic shaking according to claim 1, characterized in that, It also includes adding 0.01-0.03% of an enzymatic enhancer to S1, reacting at 45-55°C for 20-30 minutes to selectively degrade hemicellulose on the fiber surface and expose more hydroxyl groups; the enzymatic enhancer includes xylanase and cellulase, with an enzyme activity ratio of 3:

1.

3. The process for controlling the uniformity of inclined wire pulp flow based on ultrasonic shaking according to claim 1, characterized in that, It also includes adding 0.005-0.015% carbon quantum dots during the S2 ultrasonic synergistic treatment process. The carbon quantum dots generate fluorescence resonance energy transfer (FRET) effect under ultrasonic action, and the particle size of the carbon quantum dots is 2-5 nm.

4. The process for controlling the uniformity of inclined wire pulp flow based on ultrasonic shaking according to claim 1, characterized in that, The control system of the intelligent shaking device in S3 adopts a fuzzy PID algorithm to dynamically adjust the shaking parameters according to the amplitude, frequency and phase difference of the pressure fluctuation, so that the Reynolds number of the pulp flow is maintained in the transition flow state of 2000-3000.

5. The process for controlling the uniformity of inclined wire pulp flow based on ultrasonic shaking according to claim 1, characterized in that, The core-shell structured nanoparticles in S4 are prepared by the following method: titanium dioxide nanoparticles are dispersed in Tris buffer solution at pH 8.5, dopamine hydrochloride at a concentration of 2-4 g / L is added, the mixture is stirred at 25-35℃ for 12-18 hours, and then dried after centrifugation.

6. The process for controlling the uniformity of inclined wire pulp flow based on ultrasonic shaking according to claim 1, characterized in that, During the S4 nano-interface modulation process, a DC electric field of 0.5-1.5V is applied simultaneously to cause the negatively charged fibers and nanoparticles to migrate directionally in the electric field.

7. The process for controlling the uniformity of inclined wire pulp flow based on ultrasonic shaking according to claim 1, characterized in that, During the S5 gradient forming process, a microgroove structure is set on the upper part of the inclined wire mesh, with the groove direction forming an angle of 45-60° with the pulp flow direction to guide the pulp to form an orderly flow. The microgroove structure has a groove width of 0.5-1mm and a depth of 0.3-0.5mm.

8. The process for controlling the uniformity of inclined wire pulp flow based on ultrasonic shaking according to claim 1, characterized in that, After S5 dehydration molding, steam penetration drying technology is used to control the steam temperature at 120-150℃, the steam pressure at 0.2-0.4MPa, and the drying time at 30-60 seconds.

9. The process for controlling the uniformity of inclined wire pulp flow based on ultrasonic shaking according to claim 1, characterized in that, Before the S1 pulp pretreatment, the recycled pulp is subjected to deep deinking treatment using a composite deinking agent composed of a nonionic surfactant and a cationic polymer, with a dosage of 0.3-0.8%; the nonionic surfactant is Tween-60 and the cationic polymer is cationic polyacrylamide.

10. The process for controlling the uniformity of inclined wire pulp flow based on ultrasonic shaking according to claim 1, characterized in that, After S5 gradient forming, the paper undergoes online surface micro-nano structuring treatment. By laser etching microstructures on the surface of the calendering roller, a regularly arranged array of micro-protrusions is formed on the paper surface.

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