A low temperature, clean pulping process for wheat straw biomechanical pulp

Abstract

The application provides a low-temperature and clean pulping method of wheat straw biomechanical pulp, and relates to the field of low-temperature wheat straw biomechanical pulp. The low-temperature and clean pulping method of the wheat straw biomechanical pulp comprises the following steps: extrusion and wire twisting, first pre-steaming, first mechanical treatment, second pre-steaming, second mechanical treatment and post-treatment. The low-temperature and clean pulping method of the wheat straw biomechanical pulp can effectively reduce steam consumption, improve treatment efficiency, increase yield, improve pulping uniformity, avoid water treatment defects and loss of fine fibers in the pulping process, reduce treatment cost, and improve the cleanliness and environmental protection of pulping.

Description

Technical Field

[0001] This invention relates to the field of low-temperature wheat straw biomechanical pulp, and in particular to a low-temperature, clean pulping method for wheat straw biomechanical pulp. Background Technology

[0002] The cellulose content of wheat straw is similar to that of wood, comparable to the high value of broadleaf wood; its lignin content is lower than that of wood, approaching the low value of broadleaf wood. It is characterized by a high cellulose content, short and fine fibers, a loose and porous structure, and relatively large cell walls, which facilitates the penetration and reaction of pesticides into the fiber cells, resulting in relatively stable pulp. Simultaneously, the serrated arrangement of wheat straw epidermal cells increases the intercellular bonding strength, ensuring good tensile strength in the paper.

[0003] Traditional chemimechanical pulping methods for non-wood straw require extensive steam heating for fiber separation to achieve full lignin extraction. However, these methods are not only expensive and inefficient, resulting in low yields, but also suffer from poor pulp uniformity due to the uneven structure of wheat straw. Furthermore, the large-scale lignin extraction necessitates water treatment; the concentrated filtrate must be cooled before flocculation and sedimentation, and only after meeting effluent standards can it be discharged. This process involves high chemical consumption and low treatment efficiency.

[0004] Furthermore, wheat straw, due to its short fibers and numerous miscellaneous cells, produces a high content of fine fibers in its pulp. In traditional pulping processes, the filtrate contains a large amount of fine fibers, resulting in significant fiber loss. While centrifugation, multi-disc filtration, or biochemical treatment methods are employed, they still suffer from drawbacks such as high processing costs, significant fine fiber loss, loss of processing aids, and poor environmental friendliness.

[0005] Based on this, a low-temperature, clean pulping method for wheat straw biomechanical pulp is provided, which can effectively reduce steam consumption, improve processing efficiency, increase yield, and improve pulping uniformity, while avoiding water treatment defects and fine fiber loss during the pulping process, reducing processing costs, and improving the cleanliness and environmental friendliness of pulping. It has important technical significance and research value. Summary of the Invention

[0006] To address the technical problems existing in the prior art, this invention provides a low-temperature, clean pulping method for wheat straw biomechanical pulp, which can effectively reduce steam consumption, improve processing efficiency, increase yield, and improve pulping uniformity, while avoiding water treatment defects and fine fiber loss during the pulping process, reducing processing costs, and improving the cleanliness and environmental friendliness of pulping.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0008] A low-temperature, clean pulping method for wheat straw biomechanical pulp includes the following steps: extrusion and shredding, first pre-steaming, first mechanical treatment, second pre-steaming, second mechanical treatment, and post-treatment;

[0009] The extrusion and shredding method involves extruding and shredding wheat straw with a dryness of 45-50 wt% until the fineness of the material is 0.1-0.2 mm, and obtaining shredded material at a temperature of 80-85℃.

[0010] The first pre-steaming method is to adjust the pH of the spun yarn to 8-8.5, mix it evenly with the first additive, without the need for additional heat source heating, and pre-steam at 80-85℃ for 35-40 minutes to obtain the first pre-steamed material;

[0011] The first mechanical treatment method is to grind the first pre-steamed material to obtain a first-stage ground slurry at a temperature of 90-95℃;

[0012] The second pre-steaming method is to adjust the pH of the pulp after grinding to 9-9.5, mix it evenly with the second additive, without the need for additional heat source heating, and pre-steam at 90-93℃ for 20-25 minutes to obtain the second pre-steamed material;

[0013] The second mechanical treatment method is to grind the second pre-steamed material to obtain a two-stage grinding pulp at a temperature of 90-95℃.

[0014] The post-processing includes: extrusion, washing and concentration. The pulp after two-stage milling is extruded, washed and concentrated to obtain wheat straw biomechanical pulp.

[0015] Preferably, in the extrusion and twisting process, the extrusion and twisting temperature is controlled at 100-120℃;

[0016] During the extrusion and filtrate rolling process, water or concentrated filtrate generated during the post-extrusion process is added to adjust the dryness of the filtrate to 35-40 wt%.

[0017] Preferably, in the first pre-steaming, the amount of the first additive is controlled to be 500-550 ppm per ton of filament-forming material;

[0018] The first adjuvant consists of cellulase, pectinase, lipase, amylase, and xylanase, with a weight ratio of 30-35:10-12:8-10:5-6:35-40.

[0019] Preferably, in the first mechanical treatment, the pulp concentration is controlled at 20-25% and the pulp temperature is controlled at 120-130℃;

[0020] The pulp concentration of the first-stage milled pulp is 18-20%, and the pulp residue ratio is 20-25%.

[0021] Preferably, in the second pre-steaming process, the amount of the second auxiliary agent added is controlled to be 40-45 kg per ton of material;

[0022] The second auxiliary agent is composed of the following raw materials: hydrogen peroxide with a concentration of 33-35 wt%, sodium hydroxide solution with a concentration of 30-32 wt%, glycerin, sodium lignosulfonate, polyether-modified silicone defoamer, and diatomaceous earth; the weight ratio of hydrogen peroxide, sodium hydroxide solution, glycerin, sodium lignosulfonate, polyether-modified silicone defoamer, and diatomaceous earth is 10-11.5:39-41:5-5.5:9-11:3-3.2:32-35.

[0023] Preferably, in the second mechanical treatment, the pulp concentration is controlled at 13-15% and the pulp temperature is controlled at 120-130℃;

[0024] The slurry concentration after the second grinding stage is 12-13%, and the slurry residue rate is 4-6%.

[0025] Furthermore, the extrusion method involves extruding the pulp after the two-stage mill until the material dryness is ≥20wt%, thereby obtaining extruded material and concentrated filtrate.

[0026] The washing and concentration method is as follows: after the extruded material is de-emerged, it is pumped to a pressure screen by a slurry pump. After screening by the pressure screen, good pulp and screen residue are obtained. The good pulp is concentrated to a concentration of 8-10% by multiple pans to obtain wheat straw biomechanical pulp. The screen residue is recycled to the second pre-steamer and mixed with the pulp after the first grinding stage for heat preservation pre-steaming.

[0027] Preferably, in the washing and concentration process, the anti-potential concentration is controlled at 3-3.5%;

[0028] The concentration of the material entering the pressure screen is controlled at 1.2-1.5%, and the slag discharge rate of the pressure screen is 13-15%.

[0029] The diluted filtrate generated during the multi-plate concentration process is directly reused in the slurry pump and mixed with the extruded material after de-emergence for pressure screening.

[0030] Furthermore, the concentrated filtrate generated during the extrusion process is directly reused in the extrusion and twisting, first pre-evaporation, and second pre-evaporation processes.

[0031] The concentrated filtrate is reused for extrusion and shredding by mixing the concentrated filtrate with wheat straw and then extruding and shredding it.

[0032] The concentrated filtrate is reused in the first pre-distillation process by mixing the concentrated filtrate with the first auxiliary agent and the filtrate material and then pre-distilling it under heat.

[0033] The concentrated filtrate is reused in the second pre-distillation process, which involves mixing the concentrated filtrate with the second auxiliary agent and the pulp after the first grinding stage and then pre-distilling it under heat.

[0034] Preferably, in the first pre-distillation, the amount of concentrated filtrate added is 30-35% of the total weight of concentrated filtrate after deducting the weight of concentrated filtrate used for extrusion and shredding;

[0035] In the second pre-distillation, the amount of concentrated filtrate added is 65-70% of the weight of the remaining concentrated filtrate after deducting the weight of the concentrated filtrate used for extrusion and shredding from the total weight of the concentrated filtrate.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] (1) The low-temperature, clean pulping method for wheat straw biomechanical pulp of the present invention involves extruding and shredding wheat straw of a specific dryness to produce shredded material; using the shredded material in combination with a first auxiliary agent for a first pre-steaming, followed by a first mechanical treatment to produce a first-stage milled pulp; using the first-stage milled pulp in combination with a second auxiliary agent for a second pre-steaming, followed by a second mechanical treatment to produce a second-stage milled pulp; and the second-stage milled pulp undergoes post-treatment to obtain wheat straw biomechanical pulp. In the aforementioned preparation process, no additional heat source such as steam is required to provide heat, and there is no steam consumption. The heat energy converted from the mechanical energy of the pulp being processed in the extrusion and shredding, the first mechanical treatment, and the second mechanical treatment is sufficient to meet the heat requirements for pulp preparation (such as the first pre-steaming, the second pre-steaming, etc.). At the same time, it can effectively improve processing efficiency, increase yield, improve pulping uniformity, avoid water treatment defects and loss of fine fibers during the pulping process, reduce processing costs, and improve the cleanliness and environmental friendliness of pulping.

[0038] Compared to traditional pulping processes, which consume 0.8-1.2 tons of steam per ton of pulp, the low-temperature, clean pulping method for wheat straw biomechanical pulp in Examples 1-2 achieves zero steam consumption. It effectively recovers and utilizes the heat generated during the preparation process, and excess heat can further heat the system water (from ambient temperature to 60°C). Simultaneously, compared to traditional pulping processes, the pulp yield can be increased from 65% to over 82.7%, with a production capacity exceeding 300 tons per day. Furthermore, the pulp uniformity is excellent, with the content of fine fibers smaller than 200 mesh reduced from 45% to below 33.4%, and the pulp residue rate larger than 16 mesh reduced from 10% to below 3.6%.

[0039] (2) The low-temperature and clean pulping method of wheat straw biomechanical pulp of the present invention can be pulped in an environment of normal pressure and low temperature (80-95℃). The auxiliary components used in the pulping process can be recycled by the reuse of concentrated filtrate, which further saves the amount of auxiliary materials and reduces the pulping cost. At the same time, by recycling concentrated filtrate and dilute filtrate in stages during the pulping process, not only is there no waste liquid discharge in the pulping process, which is highly environmentally friendly and has no waste liquid treatment costs, thus greatly reducing the production cost, but it can also effectively reduce the loss of fine fibers during the pulping process and improve the pulping yield.

[0040] (3) The low-temperature and clean pulping method of wheat straw biomechanical pulp of the present invention produces wheat straw biomechanical pulp with an ISO brightness of 19-20, a freeness of 41-45°SR, a pH of 7.5-8, a water retention value of 180-190%, a breaking length of 4.5-5km, a ring crush index of 6.7-7.1N·m / g, and a folding endurance of 4 times.

[0041] (4) The low-temperature and clean pulping method of wheat straw biomechanical pulp of the present invention has a simple process flow, is easy to control in preparation process, has high environmental friendliness, and can be used for large-scale industrial production. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the process flow for a low-temperature, clean pulping method for wheat straw biomechanical pulp according to an embodiment of the present invention. Detailed Implementation

[0043] To provide a clearer understanding of the technical features, objectives, and effects of this invention, specific embodiments are now described. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0044] 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 exemplary embodiments of the present invention. As used herein, "first," "second," etc., are used to distinguish similar objects and are not used to describe a particular order or sequence. 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.

[0045] like Figure 1 As shown, this embodiment of the invention provides a low-temperature, clean pulping method for wheat straw biomechanical pulp, which includes the following steps: extrusion and shredding, first pre-steaming, first mechanical treatment, second pre-steaming, second mechanical treatment, and post-treatment.

[0046] The extrusion and shredding method involves continuously feeding wheat straw into a shredding machine, using production water or concentrated filtrate from the post-processing extrusion section (preferably concentrated filtrate), adjusting the dryness of the wheat straw to 45-50 wt%, controlling the extrusion and shredding temperature of the shredding machine to 100-120℃, and the extrusion and shredding power to 1000-1200 kW. The wheat straw is extruded and shredded by the shredding machine until it forms fine filaments with a fineness of 0.1-0.2 mm, and then discharged to obtain shredded material with a temperature of 80-85℃ and a dryness of 35-40 wt%. This material is then conveyed by a screw conveyor to the first pre-steaming chamber for the first pre-steaming.

[0047] During the extrusion and twisting process, add production water or concentrated filtrate from the post-processing extrusion section (concentrated filtrate is preferred) to adjust the dryness of the twisting material to 35-40 wt%.

[0048] The first pre-steaming method is as follows: the first pre-steaming chamber receives the filament material (temperature 80-85℃) conveyed by the screw conveyor, adjusts the pH to 8-8.5 with a sodium hydroxide solution with a mass concentration of 5-6wt%, and adds a first additive and concentrated filtrate (generated by the post-processing extrusion section) at the inlet of the first pre-steaming chamber. The amount of the first additive is controlled to be 500-550ppm per ton of filament material. After stirring and mixing evenly, the mixture is kept at 80-85℃ for 35-40 minutes to obtain the first pre-steamed material, which is then conveyed to a first-stage grinding mill via a chute for the first mechanical treatment.

[0049] In the first pre-steaming process, there is no need to use an additional heat source to heat the material. The heat generated by the shredding material during the aforementioned extrusion and shredding process, as well as the heat generated by the concentrated filtrate in the post-processing extrusion section, are used directly for pre-steaming.

[0050] In the first pre-distillation process, the amount of concentrated filtrate added is 30-35% of the weight of the remaining concentrated filtrate after deducting the weight of the concentrated filtrate used for extrusion and shredding from the total weight of the concentrated filtrate.

[0051] In this embodiment of the invention, the first adjuvant is a bio-compound enzyme specifically formulated according to the characteristics of wheat straw raw materials. It consists of cellulase, pectinase, lipase, amylase, and xylanase. All of the aforementioned enzymes are thermostable, capable of withstanding enzyme treatment environments of 90°C and pH < 10. The activity of cellulase is 3000-5000 U / g, pectinase is 3000-5000 U / g, lipase is 1000-3000 U / g, amylase is 2000-3000 U / g, and xylanase is 5000-6000 U / g. The weight ratio of cellulase, pectinase, lipase, amylase, and xylanase is 30-35:10-12:8-10:5-6:35-40.

[0052] The first mechanical processing method is as follows: a first-stage refiner receives the first pre-steamed material, controls the refinement concentration to be 20-25%, the refinement temperature to be 120-130℃, and the refinement energy consumption to be 200-220kWh / t, and performs high-consistency refinement treatment; after the high-consistency refinement treatment is completed, a first-stage refined pulp with a pulp concentration of 18-20%, a temperature of 90-95℃, and a pulp residue ratio of 20-25% is obtained, and is transported to the second pre-steaming chamber by a screw conveyor for the second pre-steaming.

[0053] During the first mechanical processing, cooling water is introduced to control the temperature of the high-consistency pulp and to adjust the pulp concentration of the pulp after a first stage of grinding.

[0054] The second pre-steaming method is as follows: the second pre-steaming chamber receives the first-stage milled pulp (temperature 90-95℃) conveyed by the screw conveyor. After adjusting the pH to 9-9.5 with a sodium hydroxide solution with a mass concentration of 3.5-4wt%, the second additive, concentrated filtrate (generated from the post-processing extrusion section), and pressure screen residue (if any) are added at the inlet of the second pre-steaming chamber. The amount of the second additive added is controlled to be 40-45kg per ton of material. After stirring and mixing evenly, the mixture is kept at 90-93℃ for 20-25 minutes to obtain the second pre-steamed material, which is then conveyed to the second-stage mill via a chute for the second mechanical treatment.

[0055] In the second pre-steaming process, there is no need to use an additional heat source to heat the material. The heat generated by the pulp after grinding in the first mechanical treatment process and the heat generated by the concentrated filtrate in the post-treatment extrusion section are used directly for pre-steaming.

[0056] In the second pre-distillation process, the amount of concentrated filtrate added is 65-70% of the weight of the remaining concentrated filtrate after deducting the weight of the concentrated filtrate used for extrusion and shredding from the total weight of the concentrated filtrate.

[0057] In this embodiment of the invention, the second auxiliary agent is composed of the following raw materials: hydrogen peroxide with a concentration of 33-35 wt% (oxidizes lignin, reduces water retention value and lignin content in the filtrate), sodium hydroxide solution with a concentration of 30-32 wt% (softens raw materials and promotes lignin dissolution), glycerin (promotes pulp gloss), sodium lignosulfonate (promotes epidermal dissolution), polyether-modified silicone defoamer, and diatomaceous earth (adsorbs dissolved substances and improves pulp water permeability). The weight ratio of hydrogen peroxide, sodium hydroxide solution, glycerin, sodium lignosulfonate, polyether-modified silicone defoamer, and diatomaceous earth in the second auxiliary agent is 10-11.5:39-41:5-5.5:9-11:3-3.2:32-35.

[0058] The second mechanical processing method is as follows: a two-stage refiner receives the second pre-steamed material, controls the refinement concentration to be 13-15%, the refinement temperature to be 120-130℃, and the refinement energy consumption to be 400-450kWh / t, and performs refinement treatment (medium-consistency or high-consistency refinement); after the refinement treatment is completed, a two-stage refined pulp with a pulp concentration of 12-13%, a temperature of 90-95℃, and a pulp residue ratio of 4-6% is obtained, and is conveyed to the extruder by a screw conveyor for post-processing.

[0059] During the second mechanical processing, cooling water is introduced to control the temperature of the high-consistency pulp and to adjust the pulp concentration after the second grinding.

[0060] The post-processing includes: extrusion, washing and concentration.

[0061] The extrusion method is as follows: the extruder receives the second-stage milled slurry (temperature 90-95℃) conveyed by a screw conveyor, and extrudes the second-stage milled slurry until the material dryness is ≥20wt%, to obtain extruded material (dryness ≥20wt%) and concentrated filtrate (temperature about 90℃); the extruded material is conveyed to the anti-submersion slurry tank for further processing.

[0062] During the extrusion process, the concentrated filtrate contains 1-1.5 wt% fine fiber, 2.9-3.2 g / L lignin, 0.08-0.1 wt% residual additives, 10000-15000 mg / L dissolved matter, and 20000-30000 mg / L COD. The concentrated filtrate is directly reused in the extrusion and shredding, first pre-steaming, and second pre-steaming processes. Specifically, the concentrated filtrate is reused at the inlet of the shredding machine, mixed with wheat straw raw material, and then extruded and shredded; the concentrated filtrate is reused in the first pre-steaming chamber, mixed with the shredding material and the first additive for first pre-steaming; and the concentrated filtrate is reused in the second pre-steaming chamber, mixed with the pulp from the first grinding stage and the second additive for second pre-steaming.

[0063] The washing and concentration method is as follows: the extruded material is received in the anti-submersion slurry tank, and the anti-submersion concentration is controlled at 3-3.5%. After anti-submersion, the extruded material is pumped to the pressure screen by the slurry pump, and the inlet concentration is controlled at 1.2-1.5%, with a slag discharge rate of 13-15%. After screening by the pressure screen, good slurry and screen residue are obtained. The filter screen of the multi-disc thickener is controlled at 20 mesh, and the good slurry is concentrated to a concentration of 8-10% by the multi-disc thickener to obtain wheat straw biomechanical slurry, which is then transported to the slurry tower for storage. The screen residue is mixed with the subsequent first-stage milled slurry and then subjected to a second pre-distillation.

[0064] In this embodiment of the invention, the fine fiber content in the dilute filtrate generated during the concentration process of the multi-disc thickener is 0.03-0.05%, the dissolved matter content is 8000-10000 mg / L, the COD content is 8000-10000 mg / L, and the lignin content is 1-2%. The dilute filtrate is directly reused in the slurry pump and mixed with the extruded material after desulfurization for pressure screening.

[0065] The present invention will be further described below with reference to some specific embodiments.

[0066] Example 1

[0067] This embodiment provides a low-temperature, clean pulping method for wheat straw biomechanical pulp, the specific steps of which are as follows:

[0068] 1. Extrusion and thread rolling

[0069] Wheat straw is continuously fed into the shredder, using production water or concentrated filtrate from the post-processing extrusion section (concentrated filtrate is preferred). The dryness of the wheat straw is adjusted to 45wt%, the extrusion temperature of the shredder is controlled at 100℃, and the extrusion power is 1000kW. The wheat straw is extruded and shredded by the shredder until it becomes fine filaments with a fineness of 0.15mm. The material is then discharged, and the shredded material with a temperature of 80℃ and a dryness of 35wt% is obtained. It is then conveyed by a screw conveyor to the first pre-steaming chamber for the first pre-steaming.

[0070] During the extrusion and twisting process, add production water or concentrated filtrate from the post-processing extrusion section (concentrated filtrate is preferred) to adjust the dryness of the twisting material to 35wt%.

[0071] 2. First pre-steaming

[0072] The first pre-steaming chamber receives the filament material (temperature 80-85℃) conveyed by the screw conveyor. After adjusting the pH to 8 with a 5wt% sodium hydroxide solution, the first additive and concentrated filtrate (generated by the post-processing extrusion section) are added at the inlet of the first pre-steaming chamber. The addition amount of the first additive is controlled at 500ppm per ton of filament material. After stirring and mixing evenly, the mixture is kept at 80℃ for 40 minutes to obtain the first pre-steamed material, which is then conveyed to the first-stage grinding mill via a chute for the first mechanical treatment.

[0073] In the first pre-steaming process, there is no need to use an additional heat source to heat the material. The heat generated by the shredding material during the aforementioned extrusion and shredding process, as well as the heat generated by the concentrated filtrate in the post-processing extrusion section, are used directly for pre-steaming.

[0074] In the first pre-distillation process, the amount of concentrated filtrate added is 30% of the weight of the remaining concentrated filtrate after deducting the weight of the concentrated filtrate used for extrusion and shredding from the total weight of the concentrated filtrate.

[0075] The first adjuvant consists of cellulase, pectinase, lipase, amylase, and xylanase. All of these enzymes are thermostable, capable of withstanding enzyme treatment environments of 90℃ and pH < 10. The activity of cellulase is 5000 U / g, pectinase is 4000 U / g, lipase is 2000 U / g, amylase is 3000 U / g, and xylanase is 6000 U / g. The weight ratio of cellulase, pectinase, lipase, amylase, and xylanase is 30:10:8:5:35.

[0076] 3. First mechanical processing

[0077] The first-stage refiner receives the first pre-steamed material, controls the refinement concentration at 20%, the refinement temperature at 120℃, and the refinement energy consumption at 200kWh / t, and performs high-consistency refinement treatment. After the high-consistency refinement treatment is completed, a first-stage refined pulp with a pulp concentration of 18%, a temperature of 90℃, and a pulp residue ratio of 20% is obtained, and is then conveyed by a screw conveyor to the second pre-steaming chamber for the second pre-steaming.

[0078] During the first mechanical processing, cooling water is introduced to control the temperature of the high-consistency pulp and to adjust the pulp concentration of the pulp after a first grinding stage.

[0079] In this step, the pulp residue ratio refers to the percentage of the residue remaining on the screen after the first-stage milled pulp has passed through a Somerville 0.15mm sieve and been screened at 750 r / min for 30 minutes, which accounts for the total weight of the first-stage milled pulp.

[0080] 4. Second pre-steaming

[0081] The second pre-steaming chamber receives a first-stage milled pulp (at 90°C) conveyed by a screw conveyor. After adjusting the pH to 9 with a 4wt% sodium hydroxide solution, a second additive and concentrated filtrate (generated from the post-processing extrusion section) are added at the inlet of the second pre-steaming chamber. The amount of the second additive is controlled at 40kg per ton of material. After stirring and mixing evenly, the mixture is kept at 90°C for 25 minutes to obtain the second pre-steamed material, which is then conveyed to the second-stage mill via a chute for the second mechanical processing.

[0082] In the second pre-steaming process, there is no need to use an additional heat source to heat the material. The heat generated by the pulp after grinding in the first mechanical treatment process and the heat generated by the concentrated filtrate in the post-treatment extrusion section are used directly for pre-steaming.

[0083] In the second pre-distillation process, the amount of concentrated filtrate added is 70% of the weight of the remaining concentrated filtrate after deducting the weight of the concentrated filtrate used for extrusion and shredding from the total weight of the concentrated filtrate.

[0084] The second auxiliary agent is composed of the following raw materials: 35wt% hydrogen peroxide, 32wt% sodium hydroxide solution, glycerin, sodium lignosulfonate, polyether-modified silicone defoamer, and diatomaceous earth. The weight ratio of hydrogen peroxide, sodium hydroxide solution, glycerin, sodium lignosulfonate, polyether-modified silicone defoamer, and diatomaceous earth in the second auxiliary agent is 10:39:5:9:3:32.

[0085] 5. Second mechanical processing

[0086] The second-stage refiner receives the second pre-steamed material, controls the refinement concentration at 13%, the refinement temperature at 120℃, and the refinement energy consumption at 400kWh / t, and performs refinement treatment. After refinement treatment, a second-stage refined pulp with a pulp concentration of 12%, a temperature of 90℃, and a pulp residue rate of 4% is obtained, and is conveyed to the extruder by a screw conveyor for post-processing.

[0087] During the second mechanical processing, cooling water is introduced to control the temperature of the high-consistency pulp and to adjust the pulp concentration after the second grinding.

[0088] In this step, the pulp residue ratio refers to the percentage of the residue remaining after the second-stage mill pulp is screened through a Somerville 0.15mm sieve at 750 r / min for 30 minutes, relative to the total weight of the first-stage mill pulp.

[0089] 6. Post-processing

[0090] ① Extrusion

[0091] The extruder receives the second-stage milled slurry (temperature 90℃) from the screw conveyor and extrudes the slurry until the material dryness is ≥20wt%, obtaining extruded material (dryness 20.2wt%) and concentrated filtrate (temperature 90℃); the extruded material is conveyed to the anti-submersion slurry tank for further processing.

[0092] The concentrated filtrate contains 1.4 wt% fine fiber, 3.1 g / L lignin, 0.09 wt% residual additives, 12000 mg / L dissolved matter, and 26000 mg / L COD. The concentrated filtrate is directly reused in the extrusion and shredding, first pre-steaming, and second pre-steaming processes. Specifically, the concentrated filtrate is reused at the inlet of the shredding machine, mixed with wheat straw raw material, and then extruded and shredded; the concentrated filtrate is reused in the first pre-steaming chamber, mixed with the shredding material and the first additive for the first pre-steaming; and the concentrated filtrate is reused in the second pre-steaming chamber, mixed with the pulp from the first grinding stage and the second additive for the second pre-steaming.

[0093] ② Washing and Concentration

[0094] The anti-submersion slurry tank receives the extruded material and controls the anti-submersion concentration to 3.5%. After anti-submersion, the extruded material is pumped to the pressure screen by the slurry pump, and the inlet concentration is controlled to 1.5% with a slag discharge rate of 15%. After screening by the pressure screen, good slurry and screen residue are obtained. The filter screen of the multi-disc thickener is controlled to be 20 mesh. The good slurry is concentrated to a concentration of 10% by the multi-disc thickener to obtain wheat straw biomechanical slurry, which is then transported to the slurry tower for storage. The screen residue is mixed with the subsequent first-stage milled slurry and then undergoes a second pre-distillation.

[0095] The dilute filtrate produced during the concentration process of the multi-disc thickener contains 0.04% fine fiber, 9000 mg / L dissolved matter, 9200 mg / L COD, and 1.6% lignin. The dilute filtrate is directly reused in the slurry pump and mixed with the extruded material after desulfurization for pressure screening.

[0096] The wheat straw biomechanical pulp prepared in this embodiment has an ISO brightness of 19, a freeness of 41°SR, a water retention value of 180%, a pH of 7.7, a breaking length of 4.5 km, a ring crush index of 6.7 N·m / g, and a folding endurance of 4 times. The wheat straw biomechanical pulp exhibits good pulp uniformity, with 33.4% of the pulp containing fine fibers smaller than 200 mesh and 3.6% of the pulp containing pulp residue larger than 16 mesh. The yield of the wheat straw biomechanical pulp in this embodiment is 82.7%, and the production capacity is 300 t / d.

[0097] Example 2

[0098] This embodiment provides a low-temperature, clean pulping method for wheat straw biomechanical pulp, the specific steps of which are as follows:

[0099] 1. Extrusion and thread rolling

[0100] Wheat straw is continuously fed into the shredder. Using production water or concentrated filtrate from the post-processing extrusion section (concentrated filtrate is preferred), the dryness of the wheat straw is adjusted to 45wt%. The extrusion and shredding temperature of the shredder is controlled at 110℃, and the extrusion and shredding power is 1000kW. The wheat straw is extruded and shredded by the shredder until it becomes fine filaments with a fineness of 0.1mm. The material is then discharged, and the shredded material with a temperature of 82℃ and a dryness of 35wt% is obtained. It is then conveyed by a screw conveyor to the first pre-steaming chamber for the first pre-steaming.

[0101] During the extrusion and twisting process, add production water or concentrated filtrate from the post-processing extrusion section (concentrated filtrate is preferred) to adjust the dryness of the twisting material to 35wt%.

[0102] 2. First pre-steaming

[0103] The first pre-steaming chamber receives the filament material (temperature 82℃) conveyed by the screw conveyor. After adjusting the pH to 8 with a 5wt% sodium hydroxide solution, the first additive and concentrated filtrate (generated by the post-processing extrusion section) are added at the inlet of the first pre-steaming chamber. The addition amount of the first additive is controlled at 520ppm per ton of filament material. After stirring and mixing evenly, the mixture is kept at 82℃ for 35 minutes to obtain the first pre-steamed material, which is then conveyed to the first-stage grinding mill via a chute for the first mechanical treatment.

[0104] In the first pre-steaming process, there is no need to use an additional heat source to heat the material. The heat generated by the shredding material during the aforementioned extrusion and shredding process, as well as the heat generated by the concentrated filtrate in the post-processing extrusion section, are used directly for pre-steaming.

[0105] In the first pre-distillation process, the amount of concentrated filtrate added is 30% of the weight of the remaining concentrated filtrate after deducting the weight of the concentrated filtrate used for extrusion and shredding from the total weight of the concentrated filtrate.

[0106] The first adjuvant consists of cellulase, pectinase, lipase, amylase, and xylanase. All of these enzymes are thermostable, capable of withstanding enzyme treatment environments of 90℃ and pH < 10. The activity of cellulase is 5000 U / g, pectinase is 4000 U / g, lipase is 2000 U / g, amylase is 3000 U / g, and xylanase is 6000 U / g. The weight ratio of cellulase, pectinase, lipase, amylase, and xylanase is 32:11:9:5.5:37.

[0107] 3. First mechanical processing

[0108] The first-stage refiner receives the first pre-steamed material, controls the refinement concentration at 20%, the refinement temperature at 120℃, and the refinement energy consumption at 200kWh / t, and performs high-consistency refinement treatment. After the high-consistency refinement treatment is completed, a first-stage refined pulp with a pulp concentration of 18.5%, a temperature of 92℃, and a pulp residue ratio of 20% is obtained, and is then transported to the second pre-steaming chamber by a screw conveyor for the second pre-steaming.

[0109] During the first mechanical processing, cooling water is introduced to control the temperature of the high-consistency pulp and to adjust the pulp concentration of the pulp after a first grinding stage.

[0110] In this step, the pulp residue ratio refers to the percentage of the residue remaining on the screen after the first-stage milled pulp has passed through a Somerville 0.15mm sieve and been screened at 750 r / min for 30 minutes, which accounts for the total weight of the first-stage milled pulp.

[0111] 4. Second pre-steaming

[0112] The second pre-steaming chamber receives a first-stage milled pulp (at 92°C) conveyed by a screw conveyor. After adjusting the pH to 9 with a 4wt% sodium hydroxide solution, a second additive and concentrated filtrate (generated from the post-processing extrusion section) are added at the inlet of the second pre-steaming chamber. The amount of the second additive is controlled at 42kg per ton of material. After stirring and mixing evenly, the mixture is kept at 91°C for 20 minutes to obtain the second pre-steamed material, which is then conveyed to the second-stage mill via a chute for the second mechanical processing.

[0113] In the second pre-steaming process, there is no need to use an additional heat source to heat the material. The heat generated by the pulp after grinding in the first mechanical treatment process and the heat generated by the concentrated filtrate in the post-treatment extrusion section are used directly for pre-steaming.

[0114] In the second pre-distillation process, the amount of concentrated filtrate added is 70% of the weight of the remaining concentrated filtrate after deducting the weight of the concentrated filtrate used for extrusion and shredding from the total weight of the concentrated filtrate.

[0115] The second auxiliary agent is composed of the following raw materials: 35wt% hydrogen peroxide, 32wt% sodium hydroxide solution, glycerin, sodium lignosulfonate, polyether-modified silicone defoamer, and diatomaceous earth. The weight ratio of hydrogen peroxide, sodium hydroxide solution, glycerin, sodium lignosulfonate, polyether-modified silicone defoamer, and diatomaceous earth in the second auxiliary agent is 10.8:40:5.3:10:3.1:33.

[0116] 5. Second mechanical processing

[0117] The second-stage refiner receives the second pre-steamed material, controls the refinement concentration at 13%, the refinement temperature at 120℃, and the refinement energy consumption at 400kWh / t, and performs refinement treatment. After the refinement treatment, a second-stage refined pulp with a pulp concentration of 12%, a temperature of 92℃, and a pulp residue rate of 4% is obtained, and is then conveyed to the extruder by a screw conveyor for post-processing.

[0118] During the second mechanical processing, cooling water is introduced to control the temperature of the high-consistency pulp and to adjust the pulp concentration after the second grinding.

[0119] In this step, the pulp residue ratio refers to the percentage of the residue remaining after the second-stage mill pulp is screened through a Somerville 0.15mm sieve at 750 r / min for 30 minutes, relative to the total weight of the first-stage mill pulp.

[0120] 6. Post-processing

[0121] ① Extrusion

[0122] The extruder receives the second-stage milled slurry (temperature 92℃) from the screw conveyor and extrudes the slurry until the material dryness is ≥20wt%, obtaining extruded material (dryness 20.1wt%) and concentrated filtrate (temperature 91℃); the extruded material is conveyed to the anti-submersion slurry tank for further processing.

[0123] The concentrated filtrate contains 1.3 wt% fine fiber, 3.0 g / L lignin, 0.1 wt% residual additives, 13000 mg / L dissolved matter, and 26500 mg / L COD. The concentrated filtrate is directly reused in the extrusion and shredding, first pre-steaming, and second pre-steaming processes. Specifically, the concentrated filtrate is reused at the inlet of the shredding machine, mixed with wheat straw raw material, and then extruded and shredded; the concentrated filtrate is reused in the first pre-steaming chamber, mixed with the shredding material and the first additive for first pre-steaming; and the concentrated filtrate is reused in the second pre-steaming chamber, mixed with the pulp from the first grinding stage and the second additive for second pre-steaming.

[0124] ② Washing and Concentration

[0125] The anti-submersion slurry tank receives the extruded material and controls the anti-submersion concentration to 3.5%. After anti-submersion, the extruded material is pumped to the pressure screen by the slurry pump, and the inlet concentration is controlled to 1.5% with a slag discharge rate of 15%. After screening by the pressure screen, good slurry and screen residue are obtained. The filter screen of the multi-disc thickener is controlled to be 20 mesh. The good slurry is concentrated to a concentration of 10% by the multi-disc thickener to obtain wheat straw biomechanical slurry, which is then transported to the slurry tower for storage. The screen residue is mixed with the subsequent first-stage milled slurry and then undergoes a second pre-distillation.

[0126] The dilute filtrate produced during the concentration process of the multi-disc thickener contains 0.03% fine fiber, 9200 mg / L dissolved matter, 9300 mg / L COD, and 1.3% lignin. The dilute filtrate is directly reused in the slurry pump and mixed with the extruded material after desulfurization for pressure screening.

[0127] The wheat straw biomechanical pulp prepared in this embodiment has an ISO brightness of 20, a freeness of 45°SR, a pH of 7.5, a water retention value of 190%, a breaking length of 5 km, a ring crush index of 7.1 N·m / g, and a folding endurance of 4 times. The wheat straw biomechanical pulp exhibits good pulp uniformity, with 30.9% of the pulp containing fine fibers smaller than 200 mesh and 3.3% of the pulp containing pulp residue larger than 16 mesh. The yield of the wheat straw biomechanical pulp in this embodiment is 85.0%, and the production capacity is 320 t / d.

[0128] As can be seen, the low-temperature, clean pulping method for wheat straw biomechanical pulp in Examples 1-2 involves extruding and shredding wheat straw to a specific dryness level to produce shredded material; then, after a first pre-steaming process using the shredded material and a first auxiliary agent, a first mechanical treatment is performed to produce a first-stage milled pulp; finally, after a second pre-steaming process using the first-stage milled pulp and a second auxiliary agent, a second mechanical treatment is performed to produce a second-stage milled pulp; and finally, the second-stage milled pulp undergoes post-treatment to obtain wheat straw biomechanical pulp. In the aforementioned preparation process, no additional heat source such as steam is required, and there is no steam consumption. The heat energy converted from the mechanical energy of the pulp during extrusion and shredding, the first mechanical treatment, and the second mechanical treatment is sufficient to meet the heat requirements for pulp preparation (such as the first and second pre-steaming). Simultaneously, it effectively improves processing efficiency, yield, and pulp uniformity while avoiding water treatment defects and fine fiber loss during the pulping process, reducing processing costs, and improving the cleanliness and environmental friendliness of the pulping process.

[0129] Compared to traditional pulping processes, which consume 0.8-1.2 tons of steam per ton of pulp, the low-temperature, clean pulping method for wheat straw biomechanical pulp in Examples 1-2 achieves zero steam consumption. It effectively recovers and utilizes the heat generated during the preparation process, and excess heat can further heat the system water (from room temperature to 60°C). Simultaneously, compared to traditional pulping processes, the pulp yield can be increased from 65% to over 82.7%, with better pulp uniformity. The content of fine fibers smaller than 200 mesh in the pulp can be reduced from 45% to below 35%, and the pulp residue rate larger than 16 mesh can be reduced from 10% to below 4%.

[0130] Unless otherwise stated, all percentages used in this invention are mass percentages.

[0131] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention 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 the present invention should be included within the protection scope of the present invention.

Claims

1. A low-temperature, clean pulping method for wheat straw biomechanical pulp, characterized in that, The process includes the following steps: extrusion and spun yarn, first pre-steaming, first mechanical treatment, second pre-steaming, second mechanical treatment, and post-treatment; The extrusion and shredding method involves extruding and shredding wheat straw with a dryness of 45-50 wt% until the fineness of the material is 0.1-0.2 mm, and obtaining shredded material at a temperature of 80-85℃. During the extrusion and twisting process, the extrusion and twisting temperature is controlled at 100-120℃; During the extrusion and filtrate rolling process, the concentrated filtrate generated during the post-extrusion process is added to adjust the dryness of the filtrate to 35-40 wt%. The first pre-steaming method is to adjust the pH of the spun yarn to 8-8.5, mix it evenly with the first additive, without the need for additional heat source heating, and pre-steam at 80-85℃ for 35-40 minutes to obtain the first pre-steamed material; In the first pre-steaming process, the amount of the first additive is controlled to be 500-550 ppm per ton of filament-rolling material; The first adjuvant consists of cellulase, pectinase, lipase, amylase, and xylanase, with a weight ratio of 30-35:10-12:8-10:5-6:35-40. All cellulase, pectinase, lipase, amylase, and xylanase are thermostable enzymes, tolerant of enzyme treatment environments of 90℃ and pH < 10. The enzyme activities of cellulase, pectinase, lipase, amylase, and xylanase are 3000-5000 U / g, lipase, amylase, and xylanase are 1000-3000 U / g, amylase, and xylanase are 5000-6000 U / g. The first mechanical treatment method is to grind the first pre-steamed material, control the grinding concentration to be 20-25%, the grinding temperature to be 120-130℃, and obtain a first-stage grinding pulp at a temperature of 90-95℃. The pulp concentration of the first-stage milled pulp is 18-20%, and the pulp residue ratio is 20-25%. The second pre-steaming method is to adjust the pH of the pulp after grinding to 9-9.5, mix it evenly with the second additive, without the need for additional heat source heating, and pre-steam at 90-93℃ for 20-25 minutes to obtain the second pre-steamed material; In the second pre-steaming process, the amount of the second auxiliary agent added is controlled to be 40-45 kg per ton of material; The second auxiliary agent is composed of the following raw materials: hydrogen peroxide with a concentration of 33-35 wt%, sodium hydroxide solution with a concentration of 30-32 wt%, glycerin, sodium lignosulfonate, polyether-modified silicone defoamer, and diatomaceous earth; the weight ratio of hydrogen peroxide, sodium hydroxide solution, glycerin, sodium lignosulfonate, polyether-modified silicone defoamer, and diatomaceous earth is 10-11.5:39-41:5-5.5:9-11:3-3.2:32-35. The second mechanical treatment method is to grind the second pre-steamed material, control the grinding concentration to be 13-15%, the grinding temperature to be 120-130℃, and obtain a two-stage grinding pulp at a temperature of 90-95℃. The slurry concentration after the second grinding stage is 12-13%, and the slurry residue rate is 4-6%. The post-processing includes: extrusion, washing and concentration. The pulp after two-stage milling is extruded, washed and concentrated to obtain wheat straw biomechanical pulp. The extrusion method is to extrude the pulp after the two-stage mill until the material dryness is ≥20wt%, and obtain extruded material and concentrated filtrate. The concentrated filtrate generated during the extrusion process is directly reused in the extrusion and twisting, first pre-evaporation, and second pre-evaporation processes. The concentrated filtrate is reused for extrusion and shredding by mixing the concentrated filtrate with wheat straw and then extruding and shredding it. The concentrated filtrate is reused in the first pre-distillation process by mixing the concentrated filtrate with the first auxiliary agent and the filtrate material and then pre-distilling it under heat. The concentrated filtrate is reused in the second pre-distillation process, which involves mixing the concentrated filtrate with the second auxiliary agent and the pulp after the first grinding stage and then pre-distilling it under heat.

2. The low-temperature, clean pulping method for wheat straw biomechanical pulp according to claim 1, characterized in that, The washing and concentration method is as follows: after the extruded material is de-emerged, it is pumped to a pressure screen by a slurry pump. After screening by the pressure screen, good pulp and screen residue are obtained. The good pulp is concentrated to a concentration of 8-10% by multiple pans to obtain wheat straw biomechanical pulp. The screen residue is recycled to the second pre-steamer and mixed with the pulp after the first grinding stage for heat preservation pre-steaming.

3. The low-temperature, clean pulping method for wheat straw biomechanical pulp according to claim 2, characterized in that, In the washing and concentration process, the anti-potential concentration is controlled at 3-3.5%; The concentration of the material entering the pressure screen is controlled at 1.2-1.5%, and the slag discharge rate of the pressure screen is 13-15%. The diluted filtrate generated during the multi-plate concentration process is directly reused in the slurry pump and mixed with the extruded material after de-emergence for pressure screening.

4. The low-temperature, clean pulping method for wheat straw biomechanical pulp according to claim 1, characterized in that, In the first pre-distillation, the amount of concentrated filtrate added is 30-35% of the total weight of concentrated filtrate after deducting the weight of concentrated filtrate used for extrusion and shredding; In the second pre-distillation, the amount of concentrated filtrate added is 65-70% of the weight of the remaining concentrated filtrate after deducting the weight of the concentrated filtrate used for extrusion and shredding from the total weight of the concentrated filtrate.

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