High wet strength waste paper continuous pulping process and horizontal tube continuous cooking reactor

Abstract

This application relates to a continuous pulping method for high wet strength waste paper and a horizontal tube continuous digester. The method involves continuously feeding shredded high wet strength waste paper into a horizontal tube continuous digester with an aspect ratio of 8:1, where it is mixed with water and PAE crosslinking breaking agent to form pulp. Steam is directly introduced into the reactor for heating, and a central rotating shaft with a shearing plate is driven to rotate at a low speed of 5-15 r / min, applying continuous and gentle mechanical agitation and shearing to the pulp. The pulp is then continuously processed and discharged. This application achieves an effective synergy between high temperature, chemical degradation, and mechanical shearing, breaking through the inefficiency bottleneck of traditional intermittent hydraulic pulping. It not only achieves continuous and efficient production but also effectively improves fiber dissociation rate and significantly reduces unit energy consumption and loss of pulp physical strength.

Description

Technical Field

[0001] This application relates to the field of waste paper treatment technology, and in particular to a continuous pulping method for high wet strength waste paper and a horizontal tube continuous cooking reactor. Background Technology

[0002] High-wet-strength waste paper refers to paper with added wet-strength agents such as polyamide epichlorohydrin resin (PAE) and melamine-formaldehyde resin (MF). It is widely used in banknotes, labels, packaging materials, and household paper. These wet-strength agents form a stable chemical cross-linking network between fibers, allowing the paper to maintain high physical strength even in humid environments. However, it is precisely this stable chemical structure that makes the recycling and reuse of high-wet-strength waste paper a major technical challenge in the industry.

[0003] Currently, the mainstream process for processing high-wet-strength waste paper is to use a hydrator for pulping. However, the mechanical shearing action of the hydrator alone is insufficient to effectively break down the paper, resulting in a large number of fibers not being fully dissociated, forming undispersed fiber bundles or small pieces of paper, which seriously affects the quality of recycled pulp. In order to improve the dissociation rate, factories have to take measures such as extending pulping time, increasing agitation intensity, or adding additional pretreatment processes. However, this not only effectively reduces production efficiency but also significantly increases unit energy consumption and may exacerbate mechanical damage to the fibers. Summary of the Invention

[0004] To address the aforementioned issues, this application provides a continuous pulping method for high wet strength waste paper with efficient processing and high-quality recycled pulp, as well as a horizontal tube continuous cooking reactor.

[0005] To achieve the above objectives, in a first aspect, embodiments of this application provide a continuous pulping method for high wet strength waste paper, comprising the following steps: The high-moisture-strength waste paper that has been shredded is continuously fed into the feed end of a horizontal tube continuous cooking reactor. Inside the reactor, the high wet strength waste paper is mixed with water and chemical agents to form a pulp. The pulp is then subjected to continuous cooking by heating and driving a rotating component inside the reactor to break down the chemical cross-linking structure of the wet strength agent in the high wet strength waste paper and dissociate the fibers. The slurry, after being cooked, is continuously discharged from the outlet of the reactor.

[0006] Preferably, the PAE crosslinking breaking agent includes sodium hydroxide, sodium silicate, and hydrogen peroxide; wherein, based on the weight of oven-dry waste paper, the amount of sodium hydroxide is 5%~8%, the amount of sodium silicate is 0.8%~1.5%, and the amount of hydrogen peroxide is 0.5%~1.2%.

[0007] Preferably, the liquid ratio of the slurry in the reactor is maintained at 1:6 to 1:8.

[0008] Preferably, the temperature of the cooking process is controlled within the range of 80℃ to 120℃.

[0009] Preferably, the temperature of the cooking process is controlled at 100°C.

[0010] Preferably, the rotational speed of the rotating component is controlled within the range of 5~15 r / min.

[0011] Preferably, the residence time of the slurry in the reactor is 30 to 50 minutes.

[0012] Preferably, the rotating component includes a central rotating shaft passing through the reactor and multiple sets of lifting plates arranged along the length direction on the central rotating shaft; the rotation of the lifting plates drives the slurry to turn over and generates kneading and shearing action on the slurry.

[0013] Preferably, the heating is achieved by directly introducing steam into the reactor.

[0014] Secondly, embodiments of this application provide a horizontal tube continuous digester for implementing the high wet strength waste paper continuous pulping method and horizontal tube continuous digester described in any embodiment of the first aspect, characterized in that it comprises: A cylindrical body with a length-to-diameter ratio of 8:1, with a feed end and a discharge end at each end; The central axis of rotation, which serves as the rotating component, penetrates the interior of the cylinder. Multiple sets of lifting plates are set on the central rotating shaft along the length of the central rotating shaft, and are used to lift, turn and throw the slurry at the bottom during rotation; The liquid injection port and steam inlet are located on the cylinder body and are used for injecting water, PAE crosslinking breaking agent, and directly introducing steam, respectively.

[0015] The high wet strength waste paper continuous pulping method and horizontal tube continuous cooking reactor designed in this application effectively combine high temperature, chemical agents, and mechanical shear force to achieve continuous processing from feed to pulp output, overcoming the inefficiency of traditional intermittent production. Simultaneously, it can increase fiber dissociation rate from 70-85% to over 90% and reduce wet strength agent residue from 20-30% to below 15%. Furthermore, it can reduce the unit energy consumption of the hydrapulper to 200-300 kWh / t, and control the strength loss of the pulp after pulping to below 20%, thereby comprehensively improving processing efficiency and recycled pulp quality. Attached Figure Description

[0016] Figure 1This is a flowchart of the high wet strength waste paper continuous pulping method and the horizontal tube continuous cooking reactor provided in the embodiments of this application. Detailed Implementation

[0017] The preferred embodiments of this application are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit this application.

[0018] Example 1 This embodiment provides a continuous pulping method for high wet strength waste paper and a horizontal tube continuous digester. The specific process steps of this method are as follows: Step S1: Raw material preparation and feeding.

[0019] High-wet-strength waste packaging paperboard with added polyamide epichlorohydrin resin is used as the raw material. The high-wet-strength waste packaging paperboard is fed into a shredder for preliminary crushing to obtain paper sheets with a size of 5 cm by 5 cm. Subsequently, the crushed paper sheets are continuously and evenly fed into the feed end of a horizontal tube continuous digester at a rate of 10 tons per hour via a screw conveyor.

[0020] Step S2: Continuous steaming and cooking process.

[0021] The horizontal tube continuous cooking reactor includes a cylindrical body with a length-to-diameter ratio of 8:1. A central rotating shaft is installed through the inside of the cylinder. Multiple sets of lifting plates are provided on the central rotating shaft along its length. The cylinder also has a liquid injection port for liquid inlet and a steam inlet for aeration.

[0022] While the paper sheets enter the continuous digester in the horizontal tube, warm water and a chemical agent, namely PAE crosslinking remover, are injected in proportion, and the liquid-to-solid ratio of the pulp in the reactor is controlled to be maintained within the range of 1:6 to 1:8. To obtain a better material flow pattern, this embodiment preferably controls the liquid-to-solid ratio to be stable at 1:7. The PAE crosslinking remover includes sodium hydroxide (NaOH), sodium silicate (Na2SiO3), and hydrogen peroxide (H2O2). Based on the oven-dry weight of waste paper, the amount of sodium hydroxide is 7%, the amount of sodium silicate is 1%, and the amount of hydrogen peroxide is 0.8%.

[0023] Saturated steam is introduced into the horizontal tube continuous cooking reactor to control the reaction temperature at 80℃~120℃, for example, 100℃. Simultaneously, the central rotating shaft is driven to rotate at a speed of 5~15 r / min, for example, 10 revolutions per minute. During rotation, the lifting plates scoop up, turn over, and drop the slurry from the bottom, achieving uniform mixing of the slurry, the crosslinking breaking agent, and heat, and generating continuous and gentle mechanical kneading and shearing action on the slurry clumps.

[0024] By adjusting the feed speed of the screw conveyor and the valve opening at the discharge end of the horizontal tube continuous cooking reactor, the residence time of the pulp in the reactor is controlled to be 30-50 minutes. In this embodiment, the average residence time is preferably controlled to be 40 minutes, thereby ensuring that heat, chemical agents, and mechanical force can fully react synergistically. Under the synergistic effect of heat, chemical agents, and mechanical shear force, the chemical cross-linking structure of the polyamide epichlorohydrin resin, which acts as a wet strength agent in the high wet strength waste paper, is destroyed, and the fiber bundles are fully dissociated.

[0025] Step S3: Discharge and post-processing.

[0026] After the above reaction is completed, the pulp after cooking is continuously discharged from the outlet of the reactor. The continuously discharged good pulp is directly introduced into the subsequent screening and washing system for impurity removal, ultimately obtaining high-quality recycled pulp with high dissociation rate and low strength loss.

[0027] Comparative Example 1 The waste packaging paperboard raw material, which is the same as that in Example 1, is processed using a typical intermittent hydraulic pulping process in the existing technology.

[0028] The shredded paper was loaded into a 10-cubic-meter vertical hydraulic pulper, and water was added to adjust the pulp concentration to 12.5%. The same amount and proportion of the crosslinking breaking agent as in Example 1 were added. Steam was introduced to heat the pulp to 95 degrees Celsius, and then the pulp was broken down under high-intensity stirring for 90 minutes. After pulping, stirring was stopped, and the pulp was pumped into a pulp tank. This single batch processing includes the complete operation of loading, adding water and chemicals, heating, pulping, and discharging, with a total cycle time of approximately 120 minutes.

[0029] The performance of the recycled pulp obtained in Example 1 and Comparative Example 1 was tested, and the energy consumption of the two processes was statistically compared. The results are shown in Table 1.

[0030] Table 1: Comparison of the effects of Example 1 and Comparative Example 1 As shown in Table 1, the experimental data comparison reveals that, compared to the intermittent processing of Comparative Example 1, the method employed in Example 1, under continuous production conditions, achieves a fiber dissociation rate of 92.5% and a wet strength agent residue of 13.1%, indicating an effective improvement in the dissociation degree and purity of the regenerated pulp. Furthermore, the unit energy consumption of this example is reduced to 265 kWh per ton, effectively saving production costs. Because the horizontal tube continuous cooking reactor uses low-speed lifting plates to provide mechanical force, it avoids the high-intensity mechanical damage of traditional hydraulic pulpers, resulting in a physical strength loss rate of only 17.5% after pulping, thus better preserving the initial physical strength of the fibers.

[0031] The high wet strength waste paper continuous pulping method and horizontal tube continuous cooking reactor designed in this application effectively combine high temperature, chemical agents, and mechanical shear force to achieve continuous processing from feed to pulp output, overcoming the inefficiency of traditional intermittent production. Simultaneously, it can increase fiber dissociation rate from 70-85% to over 90% and reduce wet strength agent residue from 20-30% to below 15%. Furthermore, it can reduce the unit energy consumption of the hydrapulper to 200-300 kWh / t, and control the strength loss of the pulp after pulping to below 20%, thereby comprehensively improving processing efficiency and recycled pulp quality.

[0032] In the description of this application, it should be noted that the terms "vertical", "up", "down", "horizontal", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0033] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0034] Finally, it should be noted that the above descriptions are merely preferred embodiments of this application and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A continuous pulping process of high wet strength waste paper, characterized by, Includes the following steps: The high-moisture-strength waste paper that has been shredded is continuously fed into the feed end of a horizontal tube continuous cooking reactor. Inside the reactor, the high wet strength waste paper is mixed with water and PAE crosslinking breaking agent to form a pulp. The pulp is then subjected to continuous cooking by heating and driving the rotating components inside the reactor to apply mechanical shear force, thereby breaking down the chemical crosslinking structure of the wet strength agent in the high wet strength waste paper and dissociating the fibers. The slurry, after being cooked, is continuously discharged from the outlet of the reactor.

2. The continuous high wet strength recycled paper pulping process of claim 1 wherein, The PAE crosslinking breaking agent includes sodium hydroxide, sodium silicate, and hydrogen peroxide; wherein, based on the weight of oven-dry waste paper, the amount of sodium hydroxide is 5%~8%, the amount of sodium silicate is 0.8%~1.5%, and the amount of hydrogen peroxide is 0.5%~1.2%.

3. The continuous pulping method for high wet strength waste paper according to claim 1 or 2, characterized in that, The liquid ratio of the slurry in the reactor is controlled to be maintained at 1:6 to 1:

8.

4. The continuous pulping method for high wet strength waste paper according to claim 1, characterized in that, The temperature of the cooking process is controlled within the range of 80℃ to 120℃.

5. The continuous pulping method for high wet strength waste paper according to claim 4, characterized in that, The temperature of the cooking process is controlled at 100°C.

6. The continuous pulping method for high wet strength waste paper according to claim 1, characterized in that, The rotational speed of the rotating component is controlled within the range of 5~15 r / min.

7. The continuous pulping method for high wet strength waste paper according to claim 1, characterized in that, The residence time of the slurry in the reactor is 30 to 50 minutes.

8. The continuous pulping method for high wet strength waste paper according to claim 1, characterized in that, The rotating component includes a central rotating shaft passing through the reactor and multiple sets of lifting plates arranged along the length of the central rotating shaft; the rotation of the lifting plates drives the slurry to turn over and produces kneading and shearing effects on the slurry.

9. The continuous pulping method for high wet strength waste paper according to claim 1, characterized in that, The heating is achieved by directly introducing steam into the reactor.

10. A horizontal tube continuous digester for implementing the high wet strength waste paper continuous pulping method according to any one of claims 1 to 9, characterized in that, include: A cylindrical body with a length-to-diameter ratio of 8:1, with a feed end and a discharge end at each end; The central axis of rotation, which serves as the rotating component, penetrates the interior of the cylinder. Multiple sets of lifting plates are set on the central rotating shaft along the length of the central rotating shaft, and are used to lift, turn and throw the slurry at the bottom during rotation; The liquid injection port and steam inlet are located on the cylinder body and are used for injecting water, PAE crosslinking breaking agent, and directly introducing steam, respectively.

Images