High-frequency defibering-air flotation synergetic waste paper fine screening slag complete recycling system and method

Abstract

The invention discloses a high-frequency defibering-air flotation synergistic waste paper fine screening residue complete recycling system and method, and belongs to the technical field of waste paper pulping and solid waste recycling. According to the system, through a high-frequency defibering unit, an air flotation separation unit, a fiber recovery unit and a slag discharge energy regeneration unit which are sequentially connected in a closed loop mode, complete recycling of fine screening slag is achieved. The method comprises the following steps: carrying out high-frequency defibering on fine screening slag slurry at a specific low concentration (0.5%-1.1%); controlling the slag discharge rate of the air flotation separation unit to be 10-20%, and separating out clean slurry and high-calorific-value scum; concentrating and recycling the clean slurry; and the dehydrated scum is converted into biomass solid fuel with a calorific value of not less than 20MJ / kg or is pyrolyzed to produce gas. According to the invention, a complete industrial closed loop from'waste residue 'to'resource' is formed, efficient recovery (more than or equal to 80%) of fibers, deep removal (more than 90%) of large stickies and energy utilization of scum are synchronously realized, and the problem of treatment and disposal of terminal waste residue in the traditional process is solved.

Description

Technical Field

[0001] This invention relates to the field of waste paper pulping technology and solid waste resource utilization, specifically to a system and method for efficiently treating the tailings generated in the waste paper pulping fine screening process, and simultaneously realizing fiber recycling and energy utilization of the waste residue. Background Technology

[0002] Waste paper pulping is an important way to conserve resources and protect the environment. During the pulping and purification process, the fine screening step removes fine impurities from the pulp. However, the resulting fine screening residue still contains approximately 30%-50% high-quality long fibers. These fibers are difficult to reuse directly due to the large amount of adhesives, inks, and other impurities adhering to their surfaces. Currently, companies typically either simply reuse the fine screening residue or dispose of it as solid waste. The former leads to a vicious cycle of adhesives in the system, affecting paper quality and equipment operation; the latter results in wasted fiber resources and environmental pollution.

[0003] In existing technologies, thermal dispersion is an effective means of treating adhesives, but it requires raising the slurry concentration to a high level of 20%–35% and supplementing it with heating. This is severely incompatible with the inherent low concentration (usually <2%) and room temperature of fine screening residue. Applying this technology would involve extensive equipment and process modifications, resulting in high costs and significant challenges. Furthermore, while some technologies have revealed the principles of treating fine screening residue using "high-frequency descaling" or "air flotation separation," or even simply connecting the two in series, they suffer from fundamental flaws: these solutions only focus on the "separation" stage of impurities within the slurry, lacking an effective end-use solution for the high-calorific-value scum generated after separation. Typically, this scum, enriched with impurities, can only be disposed of as solid waste, increasing environmental risks and treatment costs, and wasting resources. This prevents the entire process from achieving true "resource utilization," severely restricting the economic feasibility and large-scale application of related technologies in industry. Therefore, there is an urgent need to develop a complete solution that can directly and efficiently treat fine screening residue under low-concentration, room-temperature conditions and enable the high-value utilization of the final waste residue. Summary of the Invention

[0004] The technical problem this invention aims to solve is to overcome the shortcomings of existing technologies and provide an integrated, industrially scalable high-frequency descaling-air flotation synergistic system and method for the complete resource recovery of waste paper fine screening residue. Through optimized unit coordination and process parameter control, this system not only efficiently recovers fibers and deeply removes impurities, but also converts high-calorific-value waste residue into energy products, achieving a closed loop from "waste treatment" to "resource and energy recovery."

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a high-frequency decomposition-air flotation synergistic system for the complete resource utilization of waste paper fine screening residue.

[0007] The system includes a high-frequency dewatering unit, an air flotation separation unit, a fiber recovery unit, and a slag discharge energy conversion unit, which are connected in sequence to form a closed loop for resource and energy recovery.

[0008] The high-frequency debonding unit is used to mechanically debond the fine screening residue pulp generated during waste paper pulping at a pulp concentration of 0.5% to 1.1%, in order to peel off and disperse adhesives, inks, and other hydrophobic impurities adhering to the fiber surface. Preferably, the high-frequency debonding unit is a high-frequency debonding machine, whose grinding tooth gap is optimized to 1.0±0.3mm to avoid fiber damage while effectively peeling off adhesives. Furthermore, the specific edge load (SEL) of the high-frequency debonding machine is controlled within the range of 60 to 150 J / m.

[0009] The air flotation separation unit, with its feed end connected to the discharge end of the high-frequency disintegration unit, is used to perform air flotation separation on the disintegrated slurry, controlling the overall slag discharge rate of the system between 10% and 20%, thereby separating clean slurry from slag enriched with impurities. Preferably, a flotation device with a bubble diameter of 0.5–2.0 mm is used. Further, a chemical agent composed of one or more of the following chemicals—polydimethylsiloxane, sulfobetaine, and ethylene oxide-propylene oxide block copolymer—is added to the air flotation separation unit to enhance the hydrophobicity and flocculation effect of impurity particles and improve separation efficiency; preferably, the ethylene oxide-propylene oxide block copolymer contains ethylene oxide segments accounting for 45%–60% of the total mass.

[0010] The fiber recycling unit has its feed end connected to the clean pulp outlet of the air flotation separation unit. It is used to concentrate the clean pulp to a concentration of 5% to 12% and reuse it in the main pulping process, such as by conveying it to the good pulp tank, high-consistency pulp storage tower or directly for papermaking pulping, thereby realizing efficient closed-loop recycling of fiber resources.

[0011] The slag discharge energy conversion unit has its feed end connected to the slag discharge port of the air flotation separation unit, and is used to perform energy conversion treatment on the slag. Preferably, the slag, after dewatering, has a dryness greater than 35% and a calorific value of 20-28 MJ / kg. Further, the slag discharge energy conversion unit may include a biomass molding device for pressing the dewatered slag into solid fuel with a calorific value of not less than 20 MJ / kg; or it may include a pyrolysis gasification device for pyrolyzing the dewatered slag at a temperature of 500℃-600℃ to produce syngas and bio-oil.

[0012] Secondly, the present invention also provides a method for the complete resource utilization of waste paper fine screening residue using the system described above.

[0013] The method includes the following steps:

[0014] S1. Delamination treatment: The slurry discharged from the waste paper pulping and fine screening process is adjusted to a concentration of 0.5% to 1.1% and then sent to the high-frequency delamination unit for mechanical delamination treatment;

[0015] S2. Air flotation separation: The slurry after decomposition is sent into the air flotation separation unit, and chemical agents composed of one or more chemicals from polydimethylsiloxane, sulfobetaine, and ethylene oxide-propylene oxide block copolymer are added to improve the separation efficiency, control the overall slag discharge rate to 10% to 20%, and separate clean slurry and slag.

[0016] S3. Fiber recovery: The clean pulp is concentrated to a concentration of 5% to 12% and then transported to a good pulp storage tower or a high-consistency pulp storage tower or used directly for papermaking pulp preparation.

[0017] S4. Energy Conversion: After the scum is dehydrated to a dryness of more than 35%, it is sent to the scum discharge energy conversion unit to produce biomass solid fuel with a calorific value of not less than 20 MJ / kg, or it is pyrolyzed and gasified at 500℃~600℃ to produce syngas and bio-oil.

[0018] Preferably, the method achieves a removal rate of more than 90% for large adhesives in the fine screening residue, while recovering no less than 80% of usable fibers.

[0019] The beneficial effects of this invention are as follows:

[0020] 1. Synergistic effect and significant results: The synergistic process of "mechanical peeling followed by interface separation" overcomes the limitations of single technologies. This technology has excellent effects on the fine screening of various waste papers, such as mixed office waste paper (MOW), old newsprint (ONP), and old corrugated cardboard (OCC), with a fiber recovery rate of no less than 80%, a removal rate of large adhesives exceeding 90%, and can further reduce pulp dust and residual ink concentration.

[0021] 2. Complete resource utilization pathway: It innovatively integrates the slag energy conversion unit, which directly converts traditional terminal waste into standardized biomass solid fuel or pyrolyzes it into bio-oil / syngas, achieving zero emissions of solid waste and energy recovery, and greatly improving the economic and environmental benefits of the project.

[0022] 3. Improve pulp properties: This technology can not only recover fibers, but also improve the physical strength of the recovered pulp by removing impurities and improving fiber morphology.

[0023] 4. Stable process and easy to implement: The system operates at low concentration and ambient temperature, the equipment occupies a small area, and there is no need to carry out large-scale high temperature and high concentration transformation of the existing production line. By optimizing core parameters such as specific boundary load (SEL) and slag discharge rate, stable and controllable treatment of different raw materials can be achieved. Attached Figure Description

[0024] Figure 1 This is a process flow diagram of the system of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1: Production of biomass pellet fuel from MOW fine screen residue

[0027] Step S1: De-icing treatment

[0028] Raw material: MOW fine screening residue discharged from the fine screening section of a waste paper pulping line of a paper mill, with an initial concentration of about 1.0%.

[0029] Equipment and parameters: The high-frequency scavenging unit of this invention is used. The high-frequency scavenging machine of this unit adopts a conical plate grinding disc. As a preferred but non-limiting example, the grinding disc has an outer diameter of 260 mm and an inner diameter of 130 mm; the fixed disc has 3 layers of grinding teeth, and the moving disc has 2 layers of grinding teeth, which are interlocked; the grinding teeth are regularly arranged cuboid protrusions, the distance between two adjacent grinding teeth in the circumferential direction varies from 10 to 30 mm, the length and width are 10 mm each, and the height is 20 mm; the gap between the grinding teeth of the moving disc and the fixed disc is set to 1.0 mm.

[0030] Operation: Adjust the concentration of the finely screened slurry to 0.8% and pump it into the dewatering machine. Control the rotor speed at 7500 rpm. At this time, the operating status of the equipment can be characterized by the specific boundary load (SEL).

[0031] The formula for calculating SEL is:

[0032]

[0033] In the formula: P A —Average total energy, W;

[0034] P NL —Average no-load capacity, W;

[0035] L—Total boundary length, m / s (related to the number of grinding teeth, their arrangement, and rotational speed).

[0036] Under this specific structure and rotational speed, the measured SEL value is approximately 90 J / m, falling within the optimal process window of 60–150 J / m. This shear force is sufficient to peel off the adhesive while preventing the fibers from being cut.

[0037] Step S2: Air flotation separation

[0038] Equipment: After slurry is loosened, it flows by gravity into a rectangular deinking flotation cell (air flotation separation unit).

[0039] Reagents and Operation: A composite reagent is continuously added to the feed pipe. This reagent is prepared by a 5:1 mass ratio of ethylene oxide to propylene oxide block copolymer, with 55% of the total mass being polydimethylsiloxane and ethylene oxide segments. The total addition amount is 0.6% of the dry sludge weight. By adjusting the dissolved air tank pressure (0.4-0.5 MPa) and the scraper speed, the overall sludge discharge rate of the flotation cell is precisely controlled at 20%. The floating sludge is scraped into the collection tank, while the clean sludge at the bottom is discharged from the overflow weir.

[0040] Step S3: Fiber recycling

[0041] The clean pulp (concentration of about 1%) discharged from the air flotation unit is pumped into a multi-disc thickener (fiber recovery unit). After thickening, the pulp concentration reaches 8%, and it is directly transported to the pulping tank in the papermaking workshop by a medium-consistency pulp pump to be mixed with the main pulp for production.

[0042] Step S4: Energy Conversion (Formed Fuel Pathway)

[0043] The scum scraped off from the air flotation unit (with a moisture content of approximately 95%) is first dewatered by a screw press to obtain a filter cake with a dryness of approximately 40%. Sampling and testing revealed its lower heating value to be 21.5 MJ / kg.

[0044] The dewatered scum is fed into a ring-type biomass pellet mill. Under high pressure and high temperature (mold temperature approximately 90℃), it is extruded into regular cylindrical pellets with a diameter of 8mm and a length of 10-30mm. The calorific value of the pellet fuel is not less than 20MJ / kg, making it suitable as a high-quality industrial boiler fuel.

[0045] Effect detection and data:

[0046] Fiber recovery rate: Through mass balance calculation, the system achieves an 80% recovery rate of usable fibers in the fine screening residue.

[0047] Adhesive removal rate: Image analyzer was used to detect the slurry before and after treatment. The large adhesive content decreased from the initial 18770 mm. 2 / kg, reduced to 1304mm 2 / kg, removal rate 93%.

[0048] Physical properties of the pulp: The recycled pulp is formed into a weight of 75 g / m³. 2 The tensile index of the hand-coated sheet increased from the initial 32.1 Nm / g to 37.9 N·m / g, an increase of 18%, and the bursting index increased from the initial 1.93 kPa·m. 2 / g, increased to 2.51kPa·m 2 / g, an increase of 30%.

[0049] Resource utilization rate: The system ultimately discharges no solid waste. All the fiber and organic matter in the fine screening residue are converted into products, achieving a complete resource utilization rate of 100%.

[0050] Example 2: Processing and pyrolysis gasification of old newsprint (ONP) fine screening residue

[0051] This embodiment demonstrates another pathway for energy conversion.

[0052] Steps S1-S3:

[0053] The basic operation is the same as in Example 1. For the ONP fine screening residue, the disintegration concentration is adjusted to 1.0%, the air flotation slag discharge rate is controlled at 18%, and the air flotation chemical is prepared by mixing sulfobetaine and an ethylene oxide-propylene oxide block copolymer with ethylene oxide segments accounting for 60% of the total mass at a mass ratio of 2:3, with a total addition amount of 0.8% of the dry residue. The resulting fiber recovery rate can reach 82%, the adhesive removal rate is 91%, and the tensile index and burst index of the paper increase by 70% and 85%, respectively.

[0054] Step S4: Energy conversion (pyrolysis gasification pathway)

[0055] The dehydrated scum (38% dryness, 22 MJ / kg calorific value) is fed into a continuous fluidized bed pyrolysis reactor (slag discharge energy conversion unit).

[0056] To optimize the pyrolysis process, thermogravimetric-differential thermogravimetric (TG-DTG) analysis was first performed on the scum, and the apparent activation energy E of the main pyrolysis stage (approximately 300-500℃) was calculated using the Coats-Redfern integral method. Based on the calculated E value (e.g., 65 kJ / mol), the temperature of the pyrolysis section of the reactor was set to 550℃.

[0057] The scum undergoes rapid pyrolysis in an anaerobic environment. The gaseous products, after cyclone separation and dust removal, enter a condensation system. The condensable components condense into a dark brown, free-flowing bio-oil, with a yield of approximately 25% of the dry-basis scum. The non-condensable gases (mainly CO, H2, and CH4) are collected as syngas, with a calorific value of approximately 12-15 MJ / Nm³. 3 It can be used for boiler heating or power generation. Only a small amount of solid residue is discharged.

[0058] Further explanation of process control:

[0059] 1. The core role of specific boundary load (SEL): SEL serves as a bridge connecting equipment structure (grinding teeth) and process effect (stripping). The range of 60–150 J / m described in the claims is an optimized range determined through extensive experimentation, ensuring good stripping effects on various types of waste paper pulp screening residue and its adhesives. Technicians can fine-tune the rotation speed within this range to achieve the optimal SEL value based on the actual pulp characteristics.

[0060] 2. The Art of Balancing System Slag Discharge Rate: A slag discharge rate of 10%–20% is the key operating window obtained through system experiments in this invention. If the slag discharge rate is too low (<10%), impurities will not be completely removed; if it is too high (>20%), fiber loss will increase dramatically. Operating within this range achieves the optimal balance between impurity removal and fiber retention.

[0061] 3. Selectivity of energy conversion path: The two paths of "solid fuel" and "pyrolysis gasification" are not mutually exclusive. The plant can flexibly choose or combine them according to the characteristics of slag, local energy prices and environmental protection policies, which reflects the adaptability and economy of this system solution.

[0062] Parts of this invention not described in detail are to be understood and practiced according to ordinary technical knowledge in the art. Although the invention has been shown through preferred embodiments, those skilled in the art should understand that various modifications and substitutions can be made to the system configuration and process parameters without departing from the principles and spirit of the invention, and all such modifications and substitutions should fall within the protection scope defined by the claims of this invention.

Claims

1. A high-frequency decomposition-air flotation synergistic system for the complete resource utilization of waste paper fine screening residue, characterized in that, It includes a high-frequency dewatering unit, an air flotation separation unit, a fiber recovery unit, and a slag energy conversion unit that are connected in sequence to form a closed loop of resource and energy recovery; The high-frequency decomposition unit is used to mechanically decompose the fine screening residue slurry at a slurry concentration of 0.5% to 1.1%. The air flotation separation unit is connected to the high-frequency descaling unit and is used to perform air flotation separation on the descaled slurry and control its slag discharge rate at 10% to 20% in order to separate clean slurry from slag rich in impurities. The fiber recovery unit is connected to the clean pulp outlet of the air flotation separation unit and is used to concentrate and store the clean pulp or to directly use it for papermaking pulp preparation. The slag discharge energy conversion unit is connected to the slag discharge port of the air flotation separation unit and is used to convert the slag into solid fuel or pyrolysis gas with a calorific value of not less than 20 MJ / kg.

2. The system according to claim 1, characterized in that, The slag energy conversion unit includes a biomass molding device for pressing slag with a dryness of more than 35% after dewatering into solid fuel.

3. The system according to claim 1, characterized in that, The slag discharge energy conversion unit includes a pyrolysis gasification device, which is used to pyrolyze the dehydrated slag at a temperature of 500℃~600℃ to produce bio-oil and syngas.

4. A method for the complete resource utilization of waste paper fine screening residue using the system described in claim 1, characterized in that, Includes the following steps: S1. Decontamination treatment: The concentration of the waste paper pulping residue slurry is adjusted to 0.5% to 1.1% and then sent to the high-frequency decontamination unit for decontamination treatment; S2, Air flotation separation: The slurry after decomposition is sent to the air flotation separation unit, and the overall slag discharge rate is controlled at 10% to 20% to separate clean slurry and slag. S3. Fiber recovery: The clean pulp is concentrated to a concentration of 5% to 12%, and placed in a good pulp storage tower or a high-consistency pulp storage tower or used directly for papermaking pulp preparation; S4. Energy Conversion: After dewatering the scum, it is transported to the scum discharge energy conversion unit to produce biomass solid fuel with a calorific value of not less than 20MJ / kg, or to produce syngas and bio-oil through pyrolysis and gasification.

5. The method according to claim 4, characterized in that, In step S1, the operating ratio of the high-frequency evacuation unit to the specific edge load (SEL) is controlled within the range of 60 to 150 J / m.

6. The method according to claim 4, characterized in that, In step S2, a chemical agent consisting of one or more chemicals selected from polydimethylsiloxane, sulfobetaine, and ethylene oxide-propylene oxide block copolymer is added to the air flotation separation unit; wherein the ethylene oxide-propylene oxide block copolymer contains ethylene oxide segments accounting for 45% to 60% of the total mass.

7. The method according to claim 4, characterized in that, In step S4, the scum, after dewatering, has a dryness greater than 35% and a calorific value of 20-28 MJ / kg.

8. The method according to claim 4, characterized in that, The method achieves a removal rate of over 90% for large adhesives in the fine screening residue, while recovering no less than 80% of the fibers.

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