A system, process and control method for preparing dissolving pulp from waste fibers

Abstract

The present invention discloses a system and process for preparing dissolving pulp from waste fibers, and belongs to the technical field of recycling renewable resources in viscose fiber production. In order to recycle cellulose fibers from waste cellulose fiber textiles and other waste cellulose fiber products, produce dissolving pulp for viscose fibers, and finally realize the recycling of resources and reduce environmental pollution, a system for preparing dissolving pulp from waste fibers is proposed, which ensures that a continuous passage for preparing dissolving pulp from waste fibers is formed between a pulverizer, an air conveying device, a cyclone separator, a pretreatment device, a decolorization unit, a pulp washer, an impregnation barrel, a cooking machine, a bleaching tower, an acid treatment tank and a dissolving pulp storage tank, and cooperates with the preparation process and control method of the dissolving pulp to produce a finished pulp product with a quality very close to that of a pulp product produced from undyed fibers, and the spinning is not easy to clog the spinneret during viscose fiber production, and the decolorization clear liquid after separating the dye can be repeatedly reused, which greatly reduces the amount of sewage and reduces the pressure of sewage treatment.

Description

Technical Field

[0001] The invention relates to a dissolving pulp preparation system, process and control method, and in particular to a dissolving pulp preparation system, process and control method using waste fibers, belonging to the technical field of recycling of renewable resources in the production of cellulose regenerated fibers. Background Art

[0002] With the rapid growth of the world's population and the increasing demands of people for quality of life, the demand for textiles is increasing, but this in turn has shortened the use cycle of textiles, leading to the increasing scarcity of textile raw materials and a sharp increase in prices. At the same time, a large number of used waste textiles are landfilled or incinerated as garbage, causing waste of resources and environmental pollution.

[0003] In addition, there are also proposals to recycle and reuse waste textiles (waste yarns, waste fibers, etc.). For example, the prior art CN112608513A discloses a method and product for preparing cellulose dissolving pulp from waste polyester-cotton blended fabrics. However, the dyes fixed in the fibers are not separated, which is not conducive to the action of cellulase on cellulose during enzyme treatment. Moreover, it is difficult to remove the dyes during cooking, resulting in low whiteness of the produced dissolving pulp. Moreover, part of the dyes enter the cooking liquid, which is not conducive to the separation and purification of the monomers generated by the polyester fibers. Meanwhile, although the acid treatment to remove metal ions is placed before bleaching, the decomposition of hydrogen peroxide is slowed down during hydrogen peroxide bleaching, which is conducive to bleaching, but metal ion impurities are introduced when chemical materials are added. If there is no acid treatment again after bleaching, the metal ions in the dissolving pulp will be high. CN106182497A discloses a "process for preparing regenerated high-strength short fibers from waste fiber products", which is suitable for processing waste polyester fiber products with low cotton content: after the blended fibers are sorted by color and disinfected by sorting technology, the cotton fibers are melt-filtered and the polyester fibers are extruded and spun. CN105525463A discloses a "device for bleaching waste textiles with gaseous chlorine dioxide and a method for bleaching waste textiles with gaseous chlorine dioxide", which focuses on the generation method and bleaching process of gaseous chlorine dioxide, but chlorine dioxide is quite sensitive to heat, vibration, impact, friction, etc., and is very easy to decompose and explode, which has great safety hazards; CN107419579A discloses a "method for recycling waste cotton fabric biomass fibers to produce dissolving pulp", which realizes the recycling of waste cotton fabrics, but the method has poor applicability to dyeing raw materials, and it is difficult to produce high-quality dissolving pulp using dyeing raw materials.

[0004] It can be seen that the prior art still has the following technical problems:

[0005] First, since most waste textiles contain dyes, and the existing technology does not completely strip the dyes from colored waste textiles / yarns / fibers, that is, the dyes fixed on the fibers are not separated, making it difficult to bleach the fibers. In addition, a large amount of dyes still remain after bleaching (the dyes cannot be completely removed), and the whiteness is not high, which is not conducive to cellulose purification and the derivation of subsequent products;

[0006] Second, an enzyme treatment process is performed, but the enzyme used is cellulase or pectinase, which has an effect on cellulose or pectin, but has a very limited effect on dyes;

[0007] Third, the prepared dissolving pulp has a high impurity content, which makes subsequent viscose spinning difficult. Summary of the invention

[0008] In order to recycle cellulose fibers from waste cellulose fiber textiles and other waste cellulose fiber products, produce dissolving pulp for cellulose regenerated fibers (for dissolving pulp used to prepare viscose fibers, ash content ≤0.12%, iron content ≤14ppm; for dissolving pulp used to prepare lyocell fibers, ash content ≤0.7%, iron content ≤5ppm, total amount of heavy metal ions (including: copper, aluminum, nickel, manganese, cobalt, lead, etc.) ≤5ppm), and ultimately realize the recycling of resources and reduce environmental pollution, the present invention proposes a system, process and control method for preparing dissolving pulp from waste fibers.

[0009] In order to achieve the above technical objectives, the following technical solutions are proposed:

[0010] The first object of the technical scheme is to provide: a system for preparing dissolving pulp from waste fiber, comprising a crusher for crushing waste fiber products into flocculent waste fiber, a pneumatic conveying device for conveying waste fiber, a cyclone separator for separating waste fiber, a pretreatment device for pre-decolorizing separated waste fiber, a decolorization unit for stripping and decolorizing pre-decolorized fiber, a pulp washer for washing decolorized fiber, an impregnation machine for alkalizing washed fiber, a press for pressing alkali fiber pulp, a cooker for cooking pressed alkali fiber, a bleaching tower for bleaching cooked cellulose, and an acid treatment tank for acid-treating bleached fiber;

[0011] Crusher: The crusher outlet is connected to the air conveying device inlet, and the crusher is arranged in front of the air conveying device station;

[0012] Air conveying device: the discharge port of the air conveying device is connected with the feed port of the cyclone separator, and the air conveying device is arranged at the front side of the station of the cyclone separator;

[0013] Cyclone separator: the discharge port of the cyclone separator is connected with the feed port of the pretreatment device, and the cyclone separator is arranged at the front side of the station of the pretreatment device;

[0014] Pretreatment device: the discharge port of the pretreatment device is connected with the feed port of the decolorization unit, the pretreatment device is arranged at the front side of the station of the decolorization unit, and the pretreatment device is connected with the alkali solution delivery pipe I and the decolorization liquid delivery pipe I;

[0015] Decolorization unit: the discharging port of the decolorization unit is connected with the feeding port of the pulp washer, the decolorization unit is arranged in front of the station of the pulp washer, and the decolorization unit is connected with the alkali solution conveying pipe IV and the decolorization liquid conveying pipe II;

[0016] Pulp washer: the discharge port of the pulp washer is connected to the feed port of the impregnator, and the pulp washer is arranged in front of the station of the impregnator;

[0017] Impregnation machine: the impregnation machine outlet is connected with the press feed port, the impregnation machine is arranged in front of the press station, and the impregnation machine is connected with the alkali solution delivery pipe II;

[0018] Press: The discharge port of the press is connected to the feed port of the steamer, and the press is arranged in front of the station of the steamer;

[0019] Cooking machine: the discharge port of the cooking machine is connected with the feed port of the bleaching tower. The cooking machine is arranged in front of the station of the bleaching tower. The cooking machine is connected with the bleaching liquid conveying pipe III;

[0020] Bleaching tower: The discharge port of the bleaching tower is connected to an acid treatment tank, which is arranged at the rear side of the bleaching tower station, and the bleaching tower is connected to a bleaching agent delivery pipe;

[0021] Acid treatment tank: The discharge port of the acid treatment tank is connected to a dissolving pulp storage tank, and the acid treatment tank is connected to an acid liquid delivery pipe;

[0022] A continuous passage for preparing dissolving pulp from waste fiber products is formed between the pulverizer, the air conveying device, the cyclone separator, the pretreatment device, the decolorization unit, the pulp washer, the impregnation machine, the press, the cooking machine, the bleaching tower, the acid treatment tank and the dissolving pulp storage tank.

[0023] Preferably, a sorting device is provided at the front side of the station of the pulverizer, and a temporary storage bin is provided between the sorting device and the pulverizer, so that a continuous pre-processing passage for sorting, temporary storage and pulverizing of waste fiber products is formed between the sorting device, the temporary storage bin and the pulverizer. Among them, the sorting device classifies the recycled waste fiber products, that is, removes the waste fiber products that do not meet the requirements, which can ensure the controllability and stability of the subsequent process, and at the same time, also ensure the batch stability of the dissolving pulp product; the temporary storage bin is provided to temporarily store and transfer the sorted waste fiber products, and control them to be stably and smoothly transferred to the pulverizer, that is, to ensure the stability and controllability of the pulverizing process. In addition, the sorting device is also provided with a cotton content meter and a cotton fiber maturity meter to classify the waste fiber products entering the pulverizer.

[0024] Preferably, the pulverizer includes a coarse pulverizer and a fine pulverizer, the coarse pulverizer is arranged at the rear side of the station of the sorting device, and the fine pulverizer is arranged at the rear side of the station of the coarse pulverizer, and a pre-processing continuous passage for sorting, coarse pulverization and fine pulverization of waste fiber products is formed between the sorting device, the coarse pulverizer and the fine pulverizer. Among them, a conveyor / conveyor belt can be arranged between the sorting device, the coarse pulverizer and the fine pulverizer to ensure the continuous transportation of materials, thereby realizing the continuity and controllability of the process for preparing dissolving pulp from waste fibers.

[0025] Preferably, the cyclone separator is connected to a dust removal system to collect and process dust and the like formed by the cyclone separator, thereby improving the stability, environmental protection and safety of the working environment of the production line for preparing dissolving pulp from waste fibers.

[0026] Preferably, the pretreatment device is a refiner (such as a high-concentration refiner or a double-roll refiner), a screw feeder is provided on the front side of the refiner's station, a silo is provided on the front side of the screw feeder's station, the silo is provided on the rear side of the station at the cyclone separator's outlet, the silo is connected to the screw feeder through a weighing belt, and a continuous passage for waste fiber separation, collection, transportation, weighing and pre-decolorization is formed between the cyclone separator, the silo, the weighing belt, the screw feeder and the refiner.

[0027] Preferably, the decolorization unit includes a stirring tank, an upflow decolorization tower and a decolorization material receiving tank, wherein the stirring tank is arranged at the front side of the station of the upflow decolorization tower, and the stirring tank and the upflow decolorization tower are connected by a feed pipe; the decolorization material receiving tank is arranged at the rear side of the station of the upflow decolorization tower, and a continuous passage for stirring, stripping, decolorizing and temporarily storing waste fibers is formed between the stirring tank, the upflow decolorization tower and the decolorization material receiving tank. In the decolorization unit, a delivery pump is arranged on the pipeline according to actual needs to improve the continuity and controllability of the process for preparing dissolving pulp from waste fibers.

[0028] Preferably, there are at least two decolorization units to achieve continuous decolorization of waste fibers, so as to improve the decolorization effect and facilitate subsequent viscose spinning. According to actual needs, a pulp washer can be set at the rear side of the decolorization material receiving tank station in the corresponding decolorization unit to improve the decolorization quality and efficiency of the next decolorization unit. Furthermore, a screw squeezer is set between the decolorization material receiving tank and the pulp washer, that is, the pulp is dehydrated as necessary before pulping, which can reduce the amount of water for replacement washing during subsequent vacuum pulping, thereby reducing the amount of wastewater generated and energy consumption).

[0029] Preferably, a variable pitch screw conveyor is provided between the pulp washer and the impregnator to facilitate efficient and uniform delivery of the washed pulp to the impregnator. In the impregnation process, according to actual needs, an auxiliary impregnation barrel can also be provided at the rear side of the impregnator station to improve the impregnation effect of the fiber.

[0030] Preferably, the bleaching tower is connected to an alkali solution delivery pipe III, on which an alkali solution feed regulating valve and a flow sensor III are provided; and a pH detector II is provided on the bleaching tower.

[0031] Preferably, the acid treatment tank is connected to an acid liquid delivery pipe, on which an acid liquid feed regulating valve and a flow sensor IV are provided; and the acid treatment tank is provided with a pH detector III.

[0032] Preferably, the discharge port of the cooking machine is connected to a pulp discharge tank, and the pulp discharge tank is arranged at the rear side of the working station of the cooking machine;

[0033] The discharging port of the pulp discharge tank is connected with a pulp squeezer, which is arranged at the rear side of the station of the pulp discharge tank;

[0034] The pulping machine outlet is connected to a pulp storage tank, which is arranged at the rear side of the pulping machine station;

[0035] The outlet of the pulp storage tank is connected to a pulp refiner, which is arranged at the rear side of the station of the pulp storage tank;

[0036] The outlet of the pulping machine is connected to a pulp washer, which is arranged at the rear side of the station of the pulping machine;

[0037] The discharge port of the pulp washer is connected to the pulp pool, the discharge port of the pulp pool is connected to a desander, and the discharge port of the desander is connected to a thickener;

[0038] The discharge port of the concentrator is connected with the feed port of the bleaching tower;

[0039] A continuous passage for removing impurities from fibers is formed between the pulp discharge trough, pulp squeezer, pulp storage trough, pulp refiner, pulp washer, pulp pool, sand removal device and thickener.

[0040] Preferably, the system for preparing dissolving pulp from waste fibers is connected to a bleaching waste liquid treatment system, the bleaching waste liquid treatment system comprises a bleaching waste liquid receiving tank, a bleaching waste liquid treatment tank and a filtering device, the bleaching waste liquid receiving tank is connected to the pulp washer through a bleaching waste liquid recovery pipe, and a flow sensor I is provided on the bleaching waste liquid recovery pipe; the bleaching waste liquid receiving tank is connected to the bleaching waste liquid treatment tank, and a pH detector I is provided on the bleaching waste liquid treatment tank, the bleaching waste liquid treatment tank is connected to a hydrochloric acid delivery pipe and a bleaching waste liquid treatment agent delivery pipe, and a hydrochloric acid feed regulating valve is provided on the hydrochloric acid delivery pipe. A decolorization waste liquid treatment agent feed regulating valve and a flow sensor II are arranged on the decolorization waste liquid treatment agent delivery pipe; the decolorization waste liquid treatment tank is connected to the filtering device, the filtering device is connected to the pulp washer through a recycling pipe, or the filtering device is connected to the pre-decolorization liquid preparation tank of the pretreatment device through the recycling pipe, or the filtering device is connected to the decolorization liquid preparation tank of the decolorization unit through the recycling pipe, and a circulation passage for the recovery, treatment and reuse of the decolorization waste liquid is formed between the pulp washer, the decolorization waste liquid recovery pipe, the decolorization waste liquid receiving tank, the decolorization waste liquid treatment tank, the filtering device and the recycling pipe. Among them, the hydrochloric acid in the hydrochloric acid delivery pipe is used to first adjust the pH value of the decolorization waste liquid to 7-7.5. After the flocculent precipitate appears, the decolorization waste liquid treatment agent delivery pipe is used to add flocculant polyferric sulfate (0.04Kg / ton of decolorization waste liquid) and flocculant polyacrylamide (0.0026Kg / ton of decolorization waste liquid), separate the precipitate, and the clear liquid is returned to the pulp washing process or the pre-decolorization liquid / decolorization liquid preparation process.

[0041] Preferably, the system for preparing dissolving pulp from waste fibers is connected to a DCS system.

[0042] The second purpose of the technical solution is to provide: a process for preparing dissolving pulp from waste fibers, comprising:

[0043] 1) Removal of impurities: remove buttons, zippers and other metal debris from the recycled waste fiber products;

[0044] 2) Sorting: Use a cotton content meter to sort the waste fiber products after impurities are removed for the first time, that is, screen the waste fiber products with a cotton content of ≥95%; then, use a cotton fiber maturity meter to sort the waste fiber products with a cotton content of ≥95% for the second time, that is, temporarily store the waste fiber products with a maturity of ≥55% in temporary storage bin Ⅰ, and temporarily store the waste fiber products with a maturity of <55% in temporary storage bin Ⅱ;

[0045] 3) Crushing: crush the sorted waste fiber products into flocculent waste fibers, and control the waste fibers to be in the form of flakes or floccules with a length of less than 5 cm;

[0046] 4) Air conveying and separation: The crushed waste fibers are air conveyed to remove heavier non-fiber impurities (the power of the cyclone separator is set according to actual needs), and the waste fibers after impurities removal are obtained through separation;

[0047] 5) Pre-dispersion: Place the waste fibers after impurities removal in a pulping machine, add alkali solution and decolorizing solution I, wherein the alkali solution is sodium hydroxide with a concentration of 2.1-5.5 g / L, and the decolorizing solution I includes hydrosulfite with a concentration of 2.1-5-5 g / L and a surfactant with a concentration of 0.01-0.03 g / L, to disperse the sheet-like cloth pieces or flocculent fiber bundles into a high-concentration pulp porridge of single fibers;

[0048] 6) Decolorization and stripping: The obtained high-concentration pulp porridge is passed into the decolorization unit, alkali solution and decolorization solution II are added, the temperature in the decolorization unit is controlled at 70-95°C, and the color is stripped for 20-60 minutes to obtain the decolorized pulp porridge;

[0049] Among them, according to actual needs, preferably, three stripping treatments are included;

[0050] In the first stripping treatment, the alkali solution is sodium hydroxide with a concentration of 2.1 to 5.5 g / L, and the decolorizing solution II includes a hydrosulfite with a concentration of 2.1 to 5.5 g / L and a surfactant with a concentration of 0.01 to 0.03 g / L;

[0051] In the second and third stripping treatments, the alkali solution is sodium hydroxide with a concentration of 0.5 to 1.4 g / L, and the decolorizing solution II includes sodium hydrosulfite with a concentration of 0.5 to 1.4 g / L;

[0052] In this process, the decolorization is carried out in a closed decolorization unit to reduce contact with oxygen (reason: cotton fiber dyes include reactive dyes, direct dyes, ice dyes, mordant dyes, vat dyes, sulphur dyes, etc., and it is difficult to classify and process the recycled waste textiles one by one, so there must be multiple dyes at the same time. Among them, the vat dye is reduced to a soluble leuco sodium salt under alkaline conditions, and the dye can be restored to an insoluble state by oxidation by air and fixed on the fiber; and when the alkalinity is strong, the oxidized insoluble dye crystals are finer, which is not conducive to flocculation, but when the pH is adjusted to be close to neutral, the dye crystals can be quickly flocculated and separated);

[0053] 7) Washing: The stripped pulp is passed into the pulp washer in the press for washing. The washing water temperature is controlled to be ≥70°C, because high temperature water is conducive to the washing of dyes on the fiber; a vacuum pulp washer is preferred, and the pulp is dehydrated as necessary before vacuum washing (such as using a screw squeezer to dehydrate the pulp to a water content of ≤70%), which can reduce the amount of water used for replacement washing during subsequent vacuum washing, thereby reducing the amount of wastewater generated and energy consumption);

[0054] 8) Impregnation: the washed pulp is passed into an impregnation machine, alkali solution is added into the impregnation machine, the alkali solution concentration is controlled at 32-90 g / L, the impregnation temperature is 35-50°C, the impregnation time is 20-60 min, the pressed dryness after impregnation is controlled at 25-45%, the mass ratio of alkali fiber to alkali solution is controlled at 1:2.8-8, and the alkali content of alkali fiber is controlled at 15-50%;

[0055] 9) Pressing: The porridge after soaking is passed into the press to separate the solid and liquid, and the pressing dryness is controlled to be greater than 25%;

[0056] 10) Cooking: The pressed alkali fiber is passed into a cooker, and decolorizing solution III is added into the cooker to further remove the residual dye; the alkali used for cooking is controlled to be 13-18%, the liquid ratio is 1:2-4, the depolymerization temperature is 155-170°C, and the copper-ammonia viscosity of the fiber after cooking is controlled to be 13-22Mpa.s; wherein, the decolorizing solution III includes a hydrosulfite with a concentration of 4.0-7.5g / L and a surfactant with a concentration of 0.03-0.2g / L;

[0057] Alternatively, the pressed porridge is passed into a cooking machine, the concentration of the cooking alkali solution is controlled to be 30-70 g / L, and the liquid ratio is 1:6-9; oxygen is then introduced, the oxygen pressure is controlled to be 0.2-0.6 MPa, and the depolymerization temperature is 70-90°C. After cooking, the copper-ammonia viscosity of the fiber is controlled to be 13-22 MPa.s;

[0058] 11) Refining and sand removal: The cooked porridge is sequentially passed into the pulping machine, the refining machine and the sand removal device for refining and sand removal;

[0059] 12) Bleaching: The refined and desanded pulp is passed into a bleaching tower, and a bleaching agent (such as oxygen, sodium hypochlorite, hydrogen peroxide) is added to the bleaching tower for bleaching, and the whiteness is controlled to be greater than 80% (and the viscosity is controlled according to the purpose of the dissolving pulp, such as for the preparation of viscose long fiber, short fiber or lyocell fiber, etc.), to obtain the primary dissolving pulp;

[0060] Among them, the oxygen-alkali bleaching process using oxygen: the oxygen dosage is 0.5-2% of the fiber weight, the pulp concentration is 4-12%, the alkali dosage is 1-4.5%, the oxygen pressure is 0.2-0.6MPa, the temperature is 70-100℃, and the bleaching time is 60-90min;

[0061] The sodium hypochlorite bleaching process is adopted: the temperature is controlled at 35-50℃, the bleaching pH is 8.5-9.5, the amount of sodium hypochlorite is 0.2-1.2% of the fiber weight, the pulp concentration is 4-12%, and the bleaching time is 60-90min;

[0062] The hydrogen peroxide bleaching process is adopted: the temperature is controlled at 45-65℃, the bleaching pH is 10.5-11.5, the amount of hydrogen peroxide is 0.5-5% of the fiber weight, the pulp concentration is 4-12%, and the bleaching time is 60-90 minutes;

[0063] 13) Acid treatment: adding acid, ash remover and iron remover to the primary dissolving pulp, wherein the acid includes hydrochloric acid, the ash remover includes sodium hexametaphosphate and organic phosphoric acid, and the iron remover includes oxalic acid and EDTA, and controlling the amount of hydrochloric acid to be 1.5-2% of the weight of the waste fiber, the amount of ash remover to be 0.3-0.6% of the weight of the waste fiber, and the amount of iron remover to be 0.2-0.4% of the weight of the waste fiber; at the same time, controlling the total amount of acid to be ≥1.5% (pH is 1.7-2), the temperature to be 30-50°C, and the acid treatment time to be 60-90 minutes, to obtain a dissolving pulp for producing cellulose regenerated fiber;

[0064] Among them, for dissolving pulp for producing viscose fiber, the ash content is controlled to be ≤0.12% and the iron content is ≤14ppm;

[0065] For dissolving pulp for producing lyocell fiber, the ash content is controlled to be ≤0.7%, the iron content is ≤5ppm, and the total amount of heavy metal ions (including: copper, aluminum, nickel, manganese, cobalt, lead, etc.) is ≤5ppm).

[0066] The third object of the technical solution is to provide: a control method for a system for preparing dissolving pulp from waste fibers, mainly including the control of a sorting process, a bleaching process, an acid treatment process and a bleaching waste liquid treatment process, specifically:

[0067] 1) Control of sorting process

[0068] The cotton content measuring device (RZ NIR5600 near-infrared spectrometer, Shenzhen Yingbo Testing Technology Co., Ltd., which can simultaneously detect multiple components qualitatively and quantitatively) installed on the sorting device collects cotton content signals, and uploads the cotton content signals to the DCS system. The DCS system compares the received cotton content signal (measured value) with the preset cotton content value (reference value: cotton content ≥95%): when the collected cotton content signal is equal to or greater than the preset cotton content value, the maturity signal is collected by the cotton fiber maturity measuring device (Y147-Ⅲ cotton fiber maturity meter, Shenzhen Yuanyuan Instrument Equipment Co., Ltd.) on the sorting device, and the maturity signal is uploaded to the DCS system. The DCS system controls the conveyor belt to send the waste fiber products with corresponding maturity signals into the corresponding temporary storage bins, such as: controlling the waste fiber products with maturity ≥55% to enter temporary storage bin Ⅰ, and controlling the waste fiber products with maturity <55% to enter temporary storage bin Ⅱ. Finally, according to actual needs, the two types of waste fiber products are subjected to subsequent processes in different proportions, and finally dissolving pulps of different specifications are obtained to prepare different fiber products.

[0069] When the collected cotton content signal is less than the preset cotton content value (reference value: cotton content ≥95%), the DCS system controls the conveyor belt to discharge the corresponding waste fiber products for other uses.

[0070] 2) Control of bleaching process

[0071] The flow sensor III on the alkali solution delivery pipe III and the pH detector II on the bleaching tower collect the flow signal and pH signal respectively, and upload the flow signal and pH signal to the DCS system. The DCS system compares the received pH signal (measured value) with the preset pH value: when the collected pH signal is equal to the set pH value, the DCS system sends a signal to the flow sensor III to maintain the collected flow rate;

[0072] When the collected pH signal is greater than the set pH value, the DCS system sends a signal to reduce the flow rate to the flow sensor III, and controls the adjustment of the alkali solution feed regulating valve. The adjusted pH signal is then returned to the DCS system for comparison again until the pH signal is equal to the set pH value.

[0073] When the collected pH signal is less than the set pH value, the DCS system sends a signal to increase the flow rate to the flow sensor III, and controls the adjustment of the alkali solution feed regulating valve. The adjusted pH signal is then returned to the DCS system for comparison again until the pH signal is equal to the set pH value.

[0074] The reference value of pH can be set according to actual needs. For example:

[0075] Using sodium hypochlorite bleaching method, the pre-set pH value is 8.5-9.5;

[0076] Using oxygen-alkali bleaching, the pre-set pH value is 10.5-11.5;

[0077] 3) Control of acid treatment process

[0078] The flow sensor IV on the acid delivery pipe and the pH detector III on the acid treatment tank collect the flow signal and pH signal respectively, and upload the flow signal and pH signal to the DCS system. The DCS system compares the received pH signal (measured value) with the preset pH value (reference value: pH value is 1.7-2): when the collected pH signal is equal to the set pH value, the DCS system sends a signal to the flow sensor IV to maintain the collected flow;

[0079] When the collected pH signal is greater than the set pH value, the DCS system sends a signal to increase the flow rate to the flow sensor IV, and controls the adjustment of the acid feed regulating valve. The adjusted pH signal is then returned to the DCS system for comparison again until the pH signal is equal to the set pH value.

[0080] When the collected pH signal is less than the set pH value, the DCS system sends a signal to reduce the flow rate to the flow sensor IV, and controls the adjustment of the acid feed regulating valve. The adjusted pH signal is then returned to the DCS system for comparison again until the pH signal is equal to the set pH value.

[0081] Among them, the reference value of pH can be specifically set according to actual needs.

[0082] 4) Control of decolorization waste liquid treatment process

[0083] A. pH control:

[0084] The flow sensor Ⅰ on the decolorization waste liquid recovery pipe and the pH detector Ⅰ on the decolorization waste liquid treatment tank collect the decolorization waste liquid flow signal and pH signal respectively, and upload the flow signal and pH signal to the DCS system. The DCS system compares the received pH signal (measured value) with the preset pH value (reference value: pH is 7-7.5): when the collected pH signal is equal to the set pH value, the DCS system sends a signal to the flow sensor Ⅰ to maintain the collected flow rate;

[0085] When the collected pH signal is greater than the set pH value, the DCS system sends a signal to increase the flow rate to the flow sensor I, and controls the hydrochloric acid feed regulating valve on the hydrochloric acid delivery pipe. The adjusted pH signal is then returned to the DCS system for comparison again until the pH signal is equal to the set pH value.

[0086] When the collected pH signal is less than the set pH value, the DCS system sends a signal to reduce the flow rate to the flow sensor I, and controls the hydrochloric acid feed regulating valve on the hydrochloric acid delivery pipe. The adjusted pH signal is then returned to the DCS system for comparison again until the pH signal is equal to the set pH value.

[0087] The pH reference value may be specifically set according to actual needs, such as different reference values ​​for different processes and different additives.

[0088] Control of decolorization waste liquid treatment agent:

[0089] The flow sensor I on the decolorization waste liquid recovery pipe and the flow sensor II on the decolorization waste liquid treatment agent delivery pipe are used to collect the decolorization waste liquid flow signal and the decolorization waste liquid treatment agent flow signal respectively, and then upload them to the DCS system respectively. The DCS system compares the received decolorization waste liquid treatment agent flow signal (measured value) with the preset decolorization waste liquid treatment agent flow value (reference value): when the collected decolorization waste liquid treatment agent flow signal is equal to the preset decolorization waste liquid treatment agent flow value, the DCS system sends a signal to the flow sensor II to maintain the collected flow;

[0090] When the collected flow signal of the decolorizing waste liquid treatment agent is greater than the preset flow value of the decolorizing waste liquid treatment agent, the DCS system sends a signal to reduce the flow to the flow sensor II, and controls and adjusts the decolorizing waste liquid treatment agent feed regulating valve on the decolorizing waste liquid treatment agent delivery pipe. The adjusted flow signal is then returned to the DCS system for comparison again until the collected flow signal of the decolorizing waste liquid treatment agent is equal to the preset flow value of the decolorizing waste liquid treatment agent.

[0091] When the collected flow signal of the decolorizing waste liquid treatment agent is less than the preset flow value of the decolorizing waste liquid treatment agent, the DCS system sends a signal to increase the flow to the flow sensor II, and controls and adjusts the decolorizing waste liquid treatment agent feed regulating valve on the decolorizing waste liquid treatment agent delivery pipe. The adjusted flow signal is then returned to the DCS system for comparison again until the collected flow signal of the decolorizing waste liquid treatment agent is equal to the preset flow value of the decolorizing waste liquid treatment agent.

[0092] The decolorization waste liquid treatment agent includes a flocculant and a coagulant aid; and the relationship between the decolorization waste liquid flow value and the treatment agent flow value can be specifically set according to actual needs.

[0093] In the present technical solution, the insurance powder (sodium dithionite) involved is a reducing stripping agent, and the surfactant (such as sodium dodecylbenzene sulfonate) is an impregnation aid, both of which can strip the dyes from the colored fibers and swell the fibers, thereby improving the efficiency and quality of subsequent processes.

[0094] The positional relationships involved in this technical solution, such as "front of the workstation", "rear of the workstation", "between", and "on", are defined according to the conditions under actual use. They are conventional terms in this technical field and are also conventional terms used by technical personnel in this field in actual use.

[0095] The beneficial technical effects brought about by adopting this technical solution are:

[0096] 1. The present invention uses waste fibers (colored fibers) to be decolorized, washed, stripped of dyes and cooked one or more times continuously, and a stripping agent is added during cooking to strengthen the stripping of dyes, and oxidative stripping is performed during bleaching. Finally, the quality of the finished pulp product is very close to that of the undyed fiber, and the spinneret is not easily blocked during the spinning of viscose fibers;

[0097] The present invention uses a decolorizing liquid containing dyes to separate and treat the dyes before oxidation. The dyes can be incinerated as solid waste or landfilled after solidification (for example, dyes such as indigo can be recovered and reused for re-dyeing), which has little environmental pollution. At the same time, the clear decolorizing liquid after the dyes are separated can be reused repeatedly, which greatly reduces the amount of sewage and reduces the pressure of sewage treatment;

[0098] Second, by using the preparation system of the present invention, every 1kg of waste fiber products recycled can reduce the emission of 3.6kg of CO2 and save 6000L of water; therefore, the recycling of waste fiber products not only effectively reduces the emission of CO2, but also saves water resources;

[0099] Third, in the purification of cellulose fibers of the present invention, the dye is stripped and recycled for reuse, which is also beneficial to the purification of polyester fibers in the raw waste fiber products when they are decomposed into monomers and recycled for high value. BRIEF DESCRIPTION OF THE DRAWINGS

[0100] Figure 1 is a process flow chart of the present invention;

[0101] Figure 2 It is a schematic diagram of the working principle of the present invention (I);

[0102] Figure 3 This is a schematic diagram of the working principle of the present invention (II);

[0103] Figure 4 This is a structural diagram of the present invention (I);

[0104] Figure 5 This is the structural diagram of the present invention (II);

[0105] Figure 6 It is a schematic diagram of the working principle of the sorting device involved in the present invention;

[0106] Figure 7 The present invention relates to a logic control diagram of a sorting process;

[0107] Figure 8 This is a schematic diagram of the decolorization unit structure in the present invention;

[0108] Fig. 9 It is the layout diagram of the equipment involved in the refining and sand removal process of the present invention;

[0109] Fig.10It is a schematic diagram of the working principle of the bleaching tower involved in the present invention;

[0110] Fig.11 The present invention relates to a logic control diagram of a bleaching process;

[0111] Fig.12 It is a schematic diagram of the working principle of the acid treatment tank in the present invention;

[0112] Fig.13 It is a logic control diagram of the acid treatment process in the present invention;

[0113] Fig.14 It is a schematic diagram of the working principle of the decolorization waste liquid treatment system of the present invention;

[0114] In the figure, 1, sorting device, 2, temporary storage bin, 3, crusher, 301, coarse crusher, 302, fine crusher, 4, air delivery device, 5, cyclone separator, 6, pretreatment device, 7, decolorization unit, 701, stirring tank, 702, upflow decolorization tower, 703, decolorization material receiving tank, 8, pulp washer, 9, impregnation machine, 10, press, 11, cooking machine, 12, bleaching tower, 13, dissolving pulp storage tank, 14, alkali solution delivery pipe I, 15, decolorization liquid delivery pipe I, 16, alkali solution delivery pipe IV, 17, decolorization Color liquid conveying pipe II, 18, alkali liquid conveying pipe II, 19, decolorizing liquid conveying pipe III, 20, bleaching agent conveying pipe, 21, dust removal system, 22, screw feeder, 23, silo, 24, weighing belt, 25, feeding pipe, 26, screw squeezer, 27, variable pitch screw conveyor, 28, auxiliary immersion barrel, 29, DCS system, 30, acid treatment tank, 31, decolorizing waste liquid treatment system, 310, decolorizing waste liquid receiving tank, 311, decolorizing waste liquid treatment tank, 312, filtering device, 313, decolorizing waste liquid recovery pipe;

[0115] 32. Cotton content measuring device, 33. Cotton fiber maturity measuring device;

[0116] 34. Alkali solution delivery pipe III, 35. Flow sensor III, 36. pH detector II, 37. Alkali solution feed regulating valve;

[0117] 38. Flow sensor IV, 39. pH detector III, 40. Acid feed regulating valve;

[0118] 41. Flow sensor Ⅰ, 42. pH detector Ⅰ, 43. Hydrochloric acid feed regulating valve;

[0119] 44. Decolorization waste liquid treatment agent delivery pipe, 45. Flow sensor II, 46. Decolorization waste liquid treatment agent feed regulating valve, 47. Acid delivery pipe, 48. Hydrochloric acid delivery pipe;

[0120] 49. Pulper, 50. Pulp storage tank, 51. Pulp refiner, 52. Pulp washer, 53. Pulp pool, 54. Sand removal device, 55. Thickener, 56. Pulp discharge tank. DETAILED DESCRIPTION

[0121] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0122] Example 1

[0123] This embodiment provides: a system for preparing dissolving pulp from waste fibers, such as Figure 1 , Figure 4 As shown, it includes a crusher 3 for crushing waste fiber products into flocculent waste fibers, a wind conveying device 4 for conveying waste fibers, a cyclone separator 5 for separating waste fibers, a pretreatment device 6 for pre-decolorizing separated waste fibers, a decolorization unit 7 for stripping and decolorizing pre-decolorized fibers, a pulp washer 8 for washing decolorized fibers, an impregnation machine 9 for alkalizing washed fibers, a press 10 for pressing alkali fiber porridge, a cooker 11 for cooking pressed alkali fibers, a bleaching tower 12 for bleaching cooked cellulose, and an acid treatment tank 30 for acid-treating bleached fibers;

[0124] Crusher 3: The discharge port of crusher 3 is connected with the feed port of air conveying device 4, and crusher 3 is arranged in front of the station of air conveying device 4;

[0125] Air conveying device 4: the discharge port of the air conveying device 4 is connected with the feed port of the cyclone separator 5, and the air conveying device 4 is arranged at the front side of the station of the cyclone separator 5;

[0126] Cyclone separator 5: the discharge port of the cyclone separator 5 is connected with the feed port of the pretreatment device 6, and the cyclone separator 5 is arranged at the front side of the station of the pretreatment device 6;

[0127] Pretreatment device 6: the discharge port of the pretreatment device 6 is connected to the feed port of the decolorization unit 7, the pretreatment device 6 is arranged at the front side of the station of the decolorization unit 7, and the pretreatment device 6 is connected to the alkali solution delivery pipe Ⅰ14 and the decolorization liquid delivery pipe Ⅰ15;

[0128] Decolorization unit 7: the discharge port of the decolorization unit 7 is connected with the feed port of the pulp washer 8. The decolorization unit 7 is arranged at the front side of the station of the pulp washer 8. The decolorization unit 7 is connected with an alkali solution delivery pipe IV16 and a decolorization liquid delivery pipe II17;

[0129] Pulp washer 8: the discharge port of the pulp washer 8 is connected with the feed port of the impregnator 9, and the pulp washer 8 is arranged at the front side of the station of the impregnator 9;

[0130] Impregnator 9: The discharge port of impregnator 9 is connected to the feed port of press 10. Impregnator 9 is arranged in front of the station of press 10. Impregnator 9 is connected to alkali solution delivery pipe II 18;

[0131] Press 10: The discharge port of the press 10 is connected to the feed port of the steamer 11, and the press 10 is arranged at the front side of the station of the steamer 11;

[0132] Cooking machine 11: the discharge port of the cooking machine 11 is connected to the feed port of the bleaching tower 12, the cooking machine 11 is arranged at the front side of the station of the bleaching tower 12, and the cooking machine 11 is connected to the decolorizing liquid conveying pipe III19;

[0133] Bleaching tower 12: The discharge port of the bleaching tower 12 is connected to an acid treatment tank 30, which is arranged at the rear side of the station of the bleaching tower 12, and the bleaching tower 12 is connected to a bleaching agent delivery pipe 20;

[0134] Acid treatment tank 30: the discharging port of the acid treatment tank 30 is connected to the dissolving pulp storage tank 13, and the acid treatment tank 30 is connected to the acid liquid conveying pipe 47;

[0135] A continuous passage for preparing dissolving pulp from waste fiber products is formed among the pulverizer 3, the air conveying device 4, the cyclone separator 5, the pretreatment device 6, the decolorizing unit 7, the pulp washer 8, the impregnator 9, the press 10, the steam cooker 11, the bleaching tower 12, the acid treatment tank 30 and the dissolving pulp storage tank 13.

[0136] The system for preparing dissolving pulp from waste fibers is connected to the DCS system 29 and has a high degree of automation, high reliability, strong anti-interference ability, etc.

[0137] Example 2

[0138] On the basis of Example 1, this example defines the equipment and arrangement involved in the pre-treatment (sorting) of waste fiber products as follows to further illustrate the technical solution.

[0139] A sorting device 1 is provided at the front side of the station of the pulverizer 3, and a temporary storage bin 2 is provided between the sorting device 1 and the pulverizer 3. A continuous pre-processing passage for sorting, temporary storage and pulverizing of waste fiber products is formed between the sorting device 1, the temporary storage bin 2 and the pulverizer 3. Among them, the sorting device 1 classifies the recycled waste fiber products, that is, removes the waste fiber products that do not meet the requirements, which can ensure the controllability and stability of the subsequent process, and at the same time, also ensure the batch stability of the dissolving pulp product; the setting of the temporary storage bin 2 temporarily stores and transfers the sorted waste fiber products, and controls them to be stably and smoothly transferred to the pulverizer 3, that is, to ensure the stability and controllability of the pulverization process. In addition, a cotton content meter 32 and a cotton fiber maturity meter 33 are also provided on the sorting device 1 to classify the waste fiber products entering the pulverizer 3.

[0140] Example 3

[0141] On the basis of Examples 1-2, this Example defines the equipment and arrangement involved in the pre-treatment (crushing) of waste fiber products as follows to further illustrate the technical solution.

[0142] The pulverizer 3 includes a coarse pulverizer 301 and a fine pulverizer 302. The coarse pulverizer 301 is arranged at the rear side of the station of the sorting device 1, and the fine pulverizer 302 is arranged at the rear side of the station of the coarse pulverizer 301. A continuous pre-treatment passage for sorting, coarse pulverization and fine pulverization of waste fiber products is formed between the sorting device 1, the coarse pulverizer 301 and the fine pulverizer 302. Among them, a conveyor / conveyor belt can be arranged between the sorting device 1, the coarse pulverizer 301 and the fine pulverizer 302 to ensure the continuous transportation of materials, thereby realizing the continuity and controllability of the process for preparing dissolving pulp from waste fibers.

[0143] In addition, the cyclone separator 5 is connected to a dust removal system 21, which collects and processes the dust and the like formed by the cyclone separator 5, thereby improving the stability, environmental protection and safety of the working environment of the production line for preparing dissolving pulp from waste fibers.

[0144] Example 4

[0145] On the basis of Examples 1-3, this example further limits the pre-processing device 6 to further illustrate the technical solution.

[0146] The pretreatment device 6 is a refiner (such as a high-concentration refiner or a double-roll refiner), a screw feeder 22 is arranged at the front side of the refiner station, a silo 23 is arranged at the front side of the screw feeder 22 station, the silo 23 is arranged at the rear side of the station at the discharge port of the cyclone separator 5, the silo 23 is connected to the screw feeder 22 through a weighing belt 24, and a continuous passage for waste fiber separation, collection, transportation, weighing and pre-decolorization is formed between the cyclone separator 5, the silo 23, the weighing belt 24, the screw feeder 22 and the refiner.

[0147] Example 5

[0148] On the basis of Examples 1-4, this example further defines the decolorization unit 7 to further illustrate the technical solution.

[0149] like Figure 8 As shown, the decolorization unit 7 includes a stirring tank 701, an upflow decolorization tower 702 and a decolorization material receiving tank 703. The stirring tank 701 is arranged at the front side of the station of the upflow decolorization tower 702, and the stirring tank 701 and the upflow decolorization tower 702 are connected by a feed pipe 25; the decolorization material receiving tank 703 is arranged at the rear side of the station of the upflow decolorization tower 702, and a continuous passage for stirring, stripping, decolorizing and temporarily storing waste fibers is formed between the stirring tank 701, the upflow decolorization tower 702 and the decolorization material receiving tank 703. In the decolorization unit 7, according to actual needs, a delivery pump is arranged on the pipeline to improve the continuity and controllability of the process of preparing dissolving pulp from waste fibers.

[0150] Among them, there are at least two decolorization units 7 to achieve continuous decolorization of waste fibers to improve the decolorization effect and facilitate subsequent viscose spinning. According to actual needs, a pulp washer 8 can be set at the rear side of the decolorization material receiving tank 703 station in the corresponding decolorization unit 7 to improve the decolorization quality and efficiency of the next decolorization unit 7. Furthermore, a screw squeezer 26 is set between the decolorization material receiving tank 703 and the pulp washer 8, that is, the pulp is dehydrated as necessary before pulp washing, which can reduce the amount of water replaced and washed during subsequent vacuum pulp washing, thereby reducing the amount of wastewater generated and energy consumption.

[0151] Example 6

[0152] On the basis of embodiments 1-5, this embodiment is provided with a variable pitch screw conveyor 27 between the pulp washer 8 and the impregnator 9, so as to efficiently and evenly convey the washed pulp to the impregnator 9. Also, in the impregnation process, according to actual needs, an auxiliary impregnation barrel 28 may be provided at the rear side of the station of the impregnator 9 to improve the impregnation effect of the fiber.

[0153] Example 7

[0154] On the basis of Examples 1-6, in order to further control the ash content in the dissolving pulp, this Example makes the following restrictions: Fig. 9 As shown, the discharge port of the cooking machine 11 is connected to a pulp discharge tank 56, and the pulp discharge tank 56 is arranged at the rear side of the station of the cooking machine 11;

[0155] The discharge port of the slurry discharge tank 56 is connected to a slurry squeezer 49, which is arranged at the rear side of the station of the slurry discharge tank 56;

[0156] The discharge port of the pulp squeezer 49 is connected to a pulp storage tank 50, which is arranged at the rear side of the station of the pulp squeezer 49;

[0157] The outlet of the pulp storage tank 50 is connected to a pulp refiner 51, which is arranged at the rear side of the station of the pulp storage tank 50;

[0158] The outlet of the pulping machine 51 is connected to a pulp washer 8, which is arranged at the rear side of the station of the pulping machine 51;

[0159] The discharge port of the pulp washer 8 is connected to the pulp pool 53, the discharge port of the pulp pool 53 is connected to the sand removal device 54, the discharge port of the sand removal device 54 is connected to the thickener 55; the discharge port of the thickener 55 is connected to the feed port of the bleaching tower 12;

[0160] A continuous passage for removing impurities from fibers is formed between the pulp discharge trough 56, the pulp squeezer 49, the pulp storage trough 50, the pulp refiner 51, the pulp washer 8, the pulp tank 53, the sand removal device 54 and the concentrator 55.

[0161] Example 8

[0162] On the basis of Examples 1-7, this example further defines the bleaching tower 12 to further illustrate the technical solution.

[0163] The bleaching tower 12 is connected to an alkali solution delivery pipe III 34 , on which an alkali solution feed regulating valve 37 and a flow sensor III 35 are provided; the bleaching tower 12 is provided with a pH detector II 36 .

[0164] In addition, an acid liquid feed regulating valve 40 and a flow sensor IV38 are provided on the acid liquid delivery pipe 47; and a pH detector III39 is provided on the acid treatment tank 3030.

[0165] Example 9

[0166] Based on Examples 1-8, this example further defines:

[0167] like Figure 5 , Fig.14As shown, the system for preparing dissolving pulp from waste fibers is connected to a bleaching waste liquid treatment system 31, which includes a bleaching waste liquid receiving tank 310, a bleaching waste liquid treatment tank 311 and a filtering device 312. The bleaching waste liquid receiving tank 310 is connected to the pulp washer 8 through a bleaching waste liquid recovery pipe 313, and a flow sensor Ⅰ41 is provided on the bleaching waste liquid recovery pipe 313; the bleaching waste liquid receiving tank 310 is connected to the bleaching waste liquid treatment tank 311, and a pH detector Ⅰ42 is provided on the bleaching waste liquid treatment tank 311. The bleaching waste liquid treatment tank 311 is connected to a hydrochloric acid delivery pipe 48 and a bleaching waste liquid treatment agent delivery pipe 44, and a hydrochloric acid feed regulator is provided on the hydrochloric acid delivery pipe 48. The throttle valve 43 and the bleaching waste liquid treatment agent delivery pipe 44 are provided with a bleaching waste liquid treatment agent feed regulating valve 46 and a flow sensor II 45; the bleaching waste liquid treatment tank 311 is connected to the filtering device 312, and the filtering device 312 is connected to the pulp washer 8 through a recycling pipe, or the filtering device 312 is connected to the pre-bleaching liquid preparation tank of the pretreatment device 6 through a recycling pipe, or the filtering device 312 is connected to the bleaching liquid preparation tank of the bleaching unit 7 through a recycling pipe, and a circulation passage for the recovery, treatment and reuse of the bleaching waste liquid is formed between the pulp washer 8, the bleaching waste liquid recovery pipe 313, the bleaching waste liquid receiving tank 310, the bleaching waste liquid treatment tank 311, the filtering device 312 and the recycling pipe.

[0168] Among them, the hydrochloric acid in the hydrochloric acid delivery pipe 48 is used to first adjust the pH value of the decolorization waste liquid to 7-7.5. After the flocculent precipitate appears, the decolorization waste liquid treatment agent delivery pipe 44 is used to add flocculant polyferric sulfate (0.04Kg / ton of decolorization waste liquid) and flocculant polyacrylamide (0.0026Kg / ton of decolorization waste liquid), separate the precipitate, and the clear liquid is returned to the pulp washing process or the pre-decolorization liquid / decolorization liquid preparation process.

[0169] Example 10

[0170] This embodiment provides: a process for preparing dissolving pulp from waste fibers, such as Figure 2-3 As shown, including:

[0171] 1) Removal of impurities: remove buttons, zippers and other metal debris from the recycled waste fiber products;

[0172] 2) Sorting: Use a cotton content meter to sort the waste fiber products after impurities are removed for the first time, that is, screen the waste fiber products with a cotton content of ≥95%; then, use a cotton fiber maturity meter to sort the waste fiber products with a cotton content of ≥95% for the second time, that is, temporarily store the waste fiber products with a maturity of ≥55% in temporary storage bin Ⅰ, and temporarily store the waste fiber products with a maturity of <55% in temporary storage bin Ⅱ;

[0173] 3) Crushing: crush the sorted waste fiber products into flocculent waste fibers, and control the waste fibers to be in the form of flakes or floccules with a length of less than 5 cm;

[0174] 4) Air conveying and separation: The crushed waste fibers are air conveyed to remove heavier non-fiber impurities (the power of the cyclone separator is set according to actual needs), and the waste fibers after impurities removal are obtained through separation;

[0175] 5) Pre-dispersion: Place the waste fibers after impurities removal in a pulping machine, add alkali solution and decolorizing solution I, wherein the alkali solution is sodium hydroxide with a concentration of 2.1-5.5 g / L, and the decolorizing solution I includes hydrosulfite with a concentration of 2.1-5-5 g / L and a surfactant with a concentration of 0.01-0.03 g / L, to disperse the sheet-like cloth pieces or flocculent fiber bundles into a high-concentration pulp porridge of single fibers;

[0176] 6) Decolorization and stripping: The obtained high-concentration pulp porridge is passed into the decolorization unit, and alkali solution and decolorization solution II (decolorization solution II includes a stripping agent with a concentration of 2.1-5.5 g / L and an impregnation auxiliary agent with a concentration of 0.01-0.03 g / L) are added. The temperature in the decolorization unit is controlled at 70-95°C, and the color is stripped for 20-60 minutes to obtain pulp porridge;

[0177] Among them, the stripping agent is a reducing stripping agent (such as: insurance powder-sodium dithionite), and the impregnation auxiliary agent can be a surfactant. This process can not only strip the dyes of colored fibers, but also swell the fibers, thereby improving the efficiency and quality of subsequent processes. In this process, it is carried out in a closed decolorization unit to reduce contact with oxygen (reason: cotton fiber dyes include reactive dyes, direct dyes, ice dyes, mordant dyes, reducing dyes, sulphur dyes, etc., and it is difficult to classify and process the recycled waste textiles one by one, so there must be multiple dyes at the same time. Among them, reducing dyes are reduced to soluble leuco sodium salts under alkaline conditions, and can be restored to insoluble dyes fixed on the fibers by oxidation by air; and when the alkalinity is strong, the oxidized insoluble dye crystals are finer, which is not conducive to flocculation, but when the pH is adjusted to be close to neutral, the dye crystals can be quickly flocculated and separated);

[0178] In addition, the number of stripping times can be limited according to actual needs, and the concentrations of the alkali solution and decolorizing solution II will be adjusted accordingly;

[0179] 7) Washing: The stripped pulp is passed into the pulp washer in the press for washing. The washing water temperature is controlled to be ≥70°C, because high temperature water is conducive to the washing of dyes on the fiber; a vacuum pulp washer is preferred, and the pulp is dehydrated as necessary before vacuum washing (such as using a screw squeezer to dehydrate the pulp to a water content of ≤70%), which can reduce the amount of water used for replacement washing during subsequent vacuum washing, thereby reducing the amount of wastewater generated and energy consumption);

[0180] 8) Impregnation: the washed pulp is passed into an impregnation machine, alkali solution is added into the impregnation machine, the alkali solution concentration is controlled at 32-90 g / L, the impregnation temperature is 35-50°C, the impregnation time is 20-60 min, the pressed dryness after impregnation is controlled at 25-45%, the mass ratio of alkali fiber to alkali solution is controlled at 1:2.8-8, and the alkali content of alkali fiber is controlled at 15-50%;

[0181] 9) Pressing: The porridge after soaking is passed into the press to separate the solid and liquid, and the pressing dryness is controlled to be greater than 25%;

[0182] 10) Cooking: The pressed alkali fiber is passed into a cooker, and decolorizing solution III is added into the cooker to further remove the residual dye; the alkali used for cooking is controlled to be 13-18%, the liquid ratio is 1:2-4, the depolymerization temperature is 155-170°C, and the copper-ammonia viscosity of the fiber after cooking is controlled to be 13-22Mpa.s; wherein, the decolorizing solution III includes a hydrosulfite with a concentration of 4.0-7.5g / L and a surfactant with a concentration of 0.03-0.2g / L;

[0183] Alternatively, the pressed porridge is passed into a cooking machine, the concentration of the cooking alkali solution is controlled to be 30-70 g / L, and the liquid ratio is 1:6-9; oxygen is then introduced, the oxygen pressure is controlled to be 0.2-0.6 MPa, and the depolymerization temperature is 70-90°C. After cooking, the copper-ammonia viscosity of the fiber is controlled to be 13-22 MPa.s;

[0184] 11) Refining and sand removal: The cooked porridge is sequentially passed into the pulping machine, the refining machine and the sand removal device for refining and sand removal;

[0185] 12) Bleaching: The refined pulp and the pulp porridge after sand removal are passed into the bleaching tower, and a bleaching agent (such as oxygen, sodium hypochlorite, hydrogen peroxide) is added into the bleaching tower for bleaching, and the whiteness is controlled to be greater than 80% (and the viscosity is controlled according to the purpose of the dissolving pulp, such as for the preparation of viscose long fiber, short fiber or lyocell fiber, etc.), to obtain the primary dissolving pulp;

[0186] Among them, the oxygen-alkali bleaching process using oxygen: the oxygen dosage is 0.5-2% of the fiber weight, the pulp concentration is 4-12%, the alkali dosage is 1-4.5%, the oxygen pressure is 0.2-0.6MPa, the temperature is 70-100℃, and the bleaching time is 60-90min;

[0187] The sodium hypochlorite bleaching process is adopted: the temperature is controlled at 35-50℃, the bleaching pH is 8.5-9.5, the amount of sodium hypochlorite is 0.2-1.2% of the fiber weight, the pulp concentration is 4-12%, and the bleaching time is 60-90min;

[0188] The hydrogen peroxide bleaching process is adopted: the temperature is controlled at 45-65℃, the bleaching pH is 10.5-11.5, the amount of hydrogen peroxide is 0.5-5% of the fiber weight, the pulp concentration is 4-12%, and the bleaching time is 60-90 minutes;

[0189] 13) Acid treatment: adding acid, ash remover and iron remover to the primary dissolving pulp, wherein the acid includes hydrochloric acid, the ash remover includes sodium hexametaphosphate and organic phosphoric acid, and the iron remover includes oxalic acid and EDTA, and controlling the amount of hydrochloric acid to be 1.5-2% of the weight of the waste fiber, the amount of ash remover to be 0.3-0.6% of the weight of the waste fiber, and the amount of iron remover to be 0.2-0.4% of the weight of the waste fiber; at the same time, controlling the total amount of acid to be ≥1.5% (pH is 1.7-2), the temperature to be 30-50°C, and the acid treatment time to be 60-90 minutes, to obtain a dissolving pulp for producing cellulose regenerated fiber;

[0190] Among them, for dissolving pulp for producing viscose fiber, the ash content is controlled to be ≤0.12% and the iron content is ≤14ppm;

[0191] For dissolving pulp for producing lyocell fiber, the ash content is controlled to be ≤0.7%, the iron content is ≤5ppm; the total amount of heavy metal ions is ≤5ppm.

[0192] Among them, the requirements and control conditions involved are further limited according to actual needs, equipment size, etc.

[0193] Example 10

[0194] This embodiment provides: a control method for preparing dissolving pulp from waste fibers, which mainly includes the control of sorting process, the control of bleaching process and the control of acid treatment process, specifically:

[0195] 1) Control of sorting process

[0196] like Figure 6-7As shown, a cotton content measuring device (RZ NIR5600 near-infrared spectrometer, Shenzhen Yingbo Testing Technology Co., Ltd., which can simultaneously detect multiple components qualitatively and quantitatively) is used to collect cotton content signals, and the cotton content signals are uploaded to the DCS. The DCS compares the received cotton content signal (measured value) with the preset cotton content value (reference value: cotton content ≥95%): when the collected cotton content signal is equal to or greater than the preset cotton content value, the maturity signal is collected by the cotton fiber maturity measuring device (Y147-Ⅲ cotton fiber maturity meter, Shenzhen Yuanyuan Instrument Equipment Co., Ltd.) on the sorting device, and the maturity signal is uploaded to the DCS. The DCS controls the conveyor belt to send the waste fiber products corresponding to the maturity signal into the corresponding temporary storage bin, such as: controlling the waste fiber products with a maturity of ≥55% to enter the temporary storage bin Ⅰ, and controlling the waste fiber products with a maturity of <55% to enter the temporary storage bin Ⅱ. Finally, according to actual needs, the two types of waste fiber products are subjected to subsequent processes in different proportions, and finally dissolving pulps of different specifications are obtained to prepare different fiber products.

[0197] When the collected cotton content signal is less than the preset cotton content value (reference value: cotton content ≥95%), the DCS controls the conveyor belt to discharge the corresponding waste fiber products for other uses.

[0198] )Control of bleaching process

[0199] like Figure 10-11 As shown, the flow sensor III on the alkali solution delivery pipe III and the pH detector II on the bleaching tower respectively collect the flow signal and the pH signal, and upload the flow signal and the pH signal to the DCS. The DCS compares the received pH signal (measured value) with the preset pH value: when the collected pH signal is equal to the set pH value, the DCS sends a signal to the flow sensor III to maintain the collected flow;

[0200] When the collected pH signal is greater than the set pH value, the DCS sends a signal to reduce the flow rate to the flow sensor III, and controls the adjustment of the alkali solution feed regulating valve. The adjusted pH signal is then returned to the DCS for comparison again until the pH signal is equal to the set pH value.

[0201] When the collected pH signal is less than the set pH value, DCS sends a signal to increase the flow rate to flow sensor III, and controls the adjustment of the alkali solution feed regulating valve. The adjusted pH signal is then returned to DCS for comparison again until the pH signal is equal to the set pH value.

[0202] The reference value of pH can be set according to actual needs. For example:

[0203] Using sodium hypochlorite bleaching method, the pre-set pH value is 8.5-9.5;

[0204] Using oxygen-alkali bleaching, the pre-set pH value is 10.5-11.5;

[0205] 4) Control of acid treatment process

[0206] like Figure 12-13 As shown, the flow sensor IV on the acid delivery pipe and the pH detector III on the acid treatment tank collect the flow signal and pH signal respectively, and upload the flow signal and pH signal to the DCS. The DCS compares the received pH signal (measured value) with the preset pH value (reference value: pH value is 1.7-2): when the collected pH signal is equal to the set pH value, the DCS sends a signal to the flow sensor III to maintain the collected flow;

[0207] When the collected pH signal is greater than the set pH value, the DCS sends a signal to increase the flow rate to the flow sensor IV, and controls the adjustment of the acid feed regulating valve. The adjusted pH signal is then returned to the DCS for comparison again until the pH signal is equal to the set pH value.

[0208] When the collected pH signal is less than the set pH value, the DCS sends a signal to reduce the flow rate to the flow sensor IV, and controls and adjusts the acid feed regulating valve. The adjusted pH signal is then returned to the DCS for comparison again until the pH signal is equal to the set pH value.

[0209] Among them, the reference value of pH can be specifically set according to actual needs.

[0210] Embodiment 11

[0211] Based on Example 9, this example provides: a process for preparing dissolving pulp from waste fibers, specifically comprising:

[0212] Take 1 kg of cotton-like denim fibers after impurity removal, sorting, crushing, air conveying and separation, add 3 L of decolorizing liquid (alkali concentration 6 g / L, hydrosulfite concentration 6 g / L, surfactant 0.7 g / L), mix well, and grind the cotton-like fibers into pulp porridge of single fibers in a pulping machine;

[0213] Add 16L of 80℃ decolorizing solution (alkali concentration 6g / L, sodium hypochlorite concentration 6g / L, surfactant 0.7g / L) to the above pulp porridge for the first decolorization, keep warm for 1h, and dehydrate (control the moisture content to 50%); then add 16L of 80℃ decolorizing solution (alkali concentration 2g / L, sodium hypochlorite concentration 2g / L, surfactant 0.2g / L) to the dehydrated pulp porridge for the second decolorization, keep warm for 1h, and dehydrate (control the moisture content to 50%); then add 16L of 80℃ decolorizing solution (alkali concentration 2g / L, sodium hypochlorite concentration 2g / L, surfactant 0.2g / L) to the dehydrated pulp porridge for the third decolorization, keep warm for 1h and dehydrate; then, wash 3 times with 70℃ hot water; use 4L of water for each washing, dehydrate after each washing, and obtain recovered fiber;

[0214] The washed recycled fiber is impregnated and squeezed (using conventional technology), then added to a 15L electric rotary cooking pot, and cooked with alkali solution (control liquid ratio of 1:3, alkali amount of 18%), 20g of sodium hydrosulfite, and 2g of surfactant sodium dodecylbenzene sulfonate. During cooking, keep the temperature at 135℃ for 60min and at 165℃ for 120min.

[0215] The pulp after cooking was washed and bleached. The pulp concentration was 12%, the pH value was 10.5, the amount of hydrogen peroxide was 4% of the denim fiber, the temperature was 55°C, and the bleaching time was 120 minutes. Then, HCL was added to adjust the pH to 2, 0.5g of sodium hexametaphosphate and 0.3g of oxalic acid were added, and the treatment time was 60 minutes. Then, it was washed and tested. The results are shown in Table 1.

[0216]

[0217] Example 12

[0218] Based on Example 9, this example provides: a process for preparing dissolving pulp from waste fibers, specifically comprising:

[0219] Take 1 kg of cotton-like denim fibers after impurity removal, sorting, crushing, air conveying and separation, add 3 L of decolorizing liquid (alkali concentration 6 g / L, hydrosulfite concentration 6 g / L, surfactant 0.7 g / L), mix well, and grind the cotton-like fibers into pulp porridge of single fibers in a pulping machine;

[0220] Add 16L of 80℃ decolorizing solution (alkali concentration 6g / L, sodium hypochlorite concentration 6g / L, surfactant 0.7g / L) to the above pulp porridge for the first decolorization, keep warm for 1h, and dehydrate (control the moisture content to 60%); then add 16L of 80℃ decolorizing solution (alkali concentration 2g / L, sodium hypochlorite concentration 2g / L, surfactant 0.2g / L) to the dehydrated pulp porridge for the second decolorization, keep warm for 1h, and dehydrate (control the moisture content to 60%); then add 16L of 80℃ decolorizing solution (alkali concentration 2g / L, sodium hypochlorite concentration 2g / L, surfactant 0.2g / L) to the dehydrated pulp porridge for the third decolorization, keep warm for 1h and dehydrate; then, wash 4 times with 70℃ hot water; use 5L of water for each washing, dehydrate after each washing, and obtain recovered fiber;

[0221] The washed recycled fibers are impregnated and squeezed (using conventional technology), then added to a 15L electric rotary cooking pot, and alkaline solution (the liquid ratio is controlled to be 1:7.3, and the alkali concentration is 50g / L) and 1g EDTA are added, and oxygen (the oxygen pressure is controlled to be 0.4MPa) is introduced for cooking. During cooking, the temperature is kept at 80℃ for 90min;

[0222] After the pulp is washed after cooking, it is bleached. During bleaching, the pulp concentration is 12%, the pH value is 10.5, the amount of hydrogen peroxide is 4% of the denim fiber, the temperature is 55℃, and the bleaching time is 120min. Then it is treated with acid. For the first acid treatment, HCL is added to adjust the pH ≤ 2, 0.4g of sodium hexametaphosphate and 0.2g of oxalic acid are added, and the treatment is 60min before washing with deionized water; for the second acid treatment, HCL is added to adjust the pH value to 3, 1g of EDTA is added, and the treatment is 60min. Then, it is washed and tested. The results are shown in Table 2.

[0223]

Claims

1. A process for preparing dissolving pulp from waste fibers, characterized in that: The steps include: 1) Removal of impurities: remove buttons, zippers and other metal debris from the recycled waste fiber products; 2) Sorting: using a cotton content measuring device to sort the waste fiber products after impurities are removed for the first time, obtaining waste fiber products with a cotton content equal to or greater than a preset value of cotton content, and also obtaining waste fiber products with a cotton content less than a preset value of cotton content, and discharging the waste fiber products with a cotton content less than the preset value of cotton content; Then, a cotton fiber maturity measuring device is used to sort the waste fiber products with a cotton content equal to or greater than a preset value for cotton content for a second time, and the waste fiber products with corresponding maturity are sent to the corresponding temporary storage bin for temporary storage; 3) Crushing: crush the sorted waste fiber products into flocculent waste fibers, and control the waste fibers to be in the form of flakes or floccules less than 5 cm in length; 4) Air conveying and separation: The crushed waste fibers are air conveyed, and then separated by cyclones to obtain the impurity-free waste fibers; 5) Pre-dispersion: Place the waste fibers after impurities removal in a pulping machine, add alkali solution and decolorizing liquid I, and disperse the flakes or flocculent fiber bundles into a high-concentration pulp porridge of single fibers; 6) Decolorization and stripping: The obtained high-concentration pulp porridge is passed into the decolorization unit, alkali solution and decolorization solution II are added, the temperature in the decolorization unit is controlled at 70-95°C, and the color is stripped for 20-60 minutes to obtain the decolorized pulp porridge; 7) Washing: Put the stripped pulp into the pulp washer, control the washing water temperature to ≥70℃, and wash; 8) Impregnation: The washed pulp is passed into an impregnation machine, and alkali solution is added to the impregnation machine to control the pressing dryness after impregnation to be 25-45%, and the alkali content of the alkali fiber to be 15-50%; 9) Pressing: The porridge after soaking is passed into the press to separate the solid and liquid, and the pressing dryness is controlled to be greater than 25%; 10) Cooking: Put the pressed alkali fiber into the cooking machine, add decolorizing liquid III, cook, and control the copper-ammonia viscosity of the fiber after cooking to 13-22 mPa.s; 11) Refining and sand removal: The cooked porridge is sequentially passed into the pulping machine, the refining machine and the sand removal device for refining and sand removal; 12) Bleaching: The refined and degritted pulp is passed into a bleaching tower, and a bleaching agent is added to the bleaching tower for bleaching. The whiteness is controlled to be greater than 80% to obtain the primary dissolving pulp; 13) Acid treatment: Add acid, ash remover and iron remover to the primary dissolving pulp, control the total amount of acid to ≥1.5%, pH value to 1.7-2, temperature to 30-50°C, acid treatment time to 60-90 min, and obtain dissolving pulp for producing cellulose regenerated fiber.

2. The process for preparing dissolving pulp from waste fibers according to claim 1, characterized in that: In step 2), the first sorting: the waste fiber products with cotton content ≥ 95% are screened out; Second sorting: Among the waste fiber products with cotton content ≥95%, those with maturity ≥55% are screened out.

3. The process for preparing dissolving pulp from waste fibers according to claim 1, characterized in that: In step 5), the alkali solution is sodium hydroxide with a concentration of 2.1 to 5.5 g / L, and the decolorizing solution I includes sodium hydrosulfite with a concentration of 2.1 to 5.5 g / L and a surfactant with a concentration of 0.01 to 0.03 g / L.

4. The process for preparing dissolving pulp from waste fibers according to claim 1, characterized in that: In step 6), three stripping treatments are included; In the first stripping treatment, the alkali solution is sodium hydroxide with a concentration of 2.1 to 5.5 g / L, and the decolorizing solution II includes sodium hydrosulfite with a concentration of 2.1 to 5.5 g / L and a surfactant with a concentration of 0.01 to 0.03 g / L; In the second and third stripping treatments, the alkali solution is sodium hydroxide with a concentration of 0.5 to 1.4 g / L, and the decolorizing solution II includes hydrosulfite with a concentration of 0.5 to 1.4 g / L.

5. The process for preparing dissolving pulp from waste fibers according to claim 1, characterized in that: In step 7), before the washing process, the decolorized porridge is dehydrated to a water content of ≤70% using a screw squeezer.

6. The process for preparing dissolving pulp from waste fibers according to claim 1, characterized in that: In step 8), the concentration of the alkali solution is 32 to 90 g / L, the immersion temperature is 35 to 50° C., and the immersion time is 20 to 60 min.

7. The process for preparing dissolving pulp from waste fibers according to claim 1, characterized in that: In step 10), the decolorizing solution III includes a sodium hypochlorite with a concentration of 4.0 to 7.5 g / L and a surfactant with a concentration of 0.03 to 0.2 g / L, and the cooking temperature is controlled to be 155 to 170°C; Alternatively, after the squeezed porridge is passed into a cooking machine, oxygen is introduced into the cooking machine, the oxygen pressure is controlled to be 0.2-0.6 MPa, and the cooking temperature is controlled to be 70-90°C.

8. The process for preparing dissolving pulp from waste fibers according to claim 1, characterized in that: In step 12), The oxygen-alkali bleaching method is adopted: the oxygen dosage is 0.5-2% of the weight of the waste fiber, the pulp concentration is 4-12%, the alkali dosage is 1-4.5% of the weight of the waste fiber, the oxygen pressure is 0.2-0.6MPa, the temperature is 70-100℃, and the bleaching time is 60-90min; Alternatively, a sodium hypochlorite bleaching method is used: the temperature is controlled at 35-50°C, the pH is 8.5-10, the amount of sodium hypochlorite is 0.2-1.2% of the weight of the waste fiber, the pulp concentration is 4-12%, and the bleaching time is 60-90 minutes; Alternatively, a hydrogen peroxide bleaching method is used: the temperature is controlled at 45-65°C, the pH is 10-12.5, the amount of hydrogen peroxide is 0.5-5% of the weight of the waste fiber, the pulp concentration is 4-12%, and the bleaching time is 60-90 minutes.

9. The process for preparing dissolving pulp from waste fibers according to claim 1, characterized in that: In step 13), the acid includes hydrochloric acid, the ash remover includes sodium hexametaphosphate and organic phosphoric acid, and the iron remover includes oxalic acid and EDTA. The amount of hydrochloric acid is controlled to be 1.5-2% of the weight of the waste fiber, the amount of the ash remover is controlled to be 0.3-0.6% of the weight of the waste fiber, and the amount of the iron remover is controlled to be 0.2-0.4% of the weight of the waste fiber.

10. The process for preparing dissolving pulp from waste fibers according to claim 1, characterized in that: For dissolving pulp used to prepare viscose fiber, the ash content is ≤0.12% and the iron content is ≤14ppm; For dissolving pulp used to prepare lyocell fiber, the ash content is ≤0.7%, the iron content is ≤5ppm; the total amount of heavy metal ions is ≤5ppm.

11. A system for preparing dissolving pulp from waste fibers, characterized in that: The process for preparing dissolving pulp from waste fibers as claimed in any one of claims 1 to 10 adopts the system, the system comprising a crusher (3) for crushing waste fiber products into flocculent waste fibers, a pneumatic conveying device (4) for conveying waste fibers, a cyclone separator (5) for separating waste fibers, a pretreatment device (6) for pre-decolorizing separated waste fibers, a decolorization unit (7) for stripping and decolorizing pre-decolorized fibers, a pulp washer (8) for washing decolorized fibers, an impregnation machine (9) for alkalizing washed fibers, a press (10) for pressing alkali fiber pulp, a cooker (11) for cooking pressed alkali fibers, a bleaching tower (12) for bleaching cooked cellulose, and an acid treatment tank (30) for acid-treating the bleached fibers; The pulverizer (3) is arranged at the front side of the working station of the air conveying device (4), and the discharge port of the pulverizer (3) is connected to the feed port of the air conveying device (4); The cyclone separator (5) is arranged at the rear side of the working station of the air conveying device (4), and the discharge port of the air conveying device (4) is connected to the feed port of the cyclone separator (5); The pretreatment device (6) is arranged at the rear side of the station of the cyclone separator (5), and the discharge port of the cyclone separator (5) is connected to the feed port of the pretreatment device (6); The decolorization unit (7) is arranged at the rear side of the workstation of the pretreatment device (6); the discharge port of the pretreatment device (6) is connected to the feed port of the decolorization unit (7); the pretreatment device (6) is connected to an alkali solution delivery pipe I (14) and a decolorization solution delivery pipe I (15); The pulp washer (8) is arranged at the rear side of the station of the decolorization unit (7); the discharge port of the decolorization unit (7) is connected to the feed port of the pulp washer (8); the decolorization unit (7) is connected to an alkali solution delivery pipe IV (16) and a decolorization liquid delivery pipe II (17); The impregnator (9) is arranged at the rear side of the workstation of the pulp washer (8), and the discharge port of the pulp washer (8) is connected to the feed port of the impregnator (9); The press (10) is arranged at the rear side of the workstation of the impregnator (9), the discharge port of the impregnator (9) is connected to the feed port of the press (10), and the impregnator (9) is connected to an alkali solution delivery pipe II (18); The cooking machine (11) is arranged at the rear side of the working station of the pressing machine (10); the discharge port of the pressing machine (10) is connected to the feed port of the cooking machine (11); and the cooking machine (11) is connected to a decolorizing liquid delivery pipe III (19); The bleaching tower (12) is arranged at the rear side of the workstation of the steamer (11); the discharge port of the steamer (11) is connected to the feed port of the bleaching tower (12); and the bleaching tower (12) is connected to a bleaching agent delivery pipe (20); The acid treatment tank (30) is arranged at the rear side of the workstation of the bleaching tower (12); the discharge port of the bleaching tower (12) is connected to the feed port of the acid treatment tank (30); the acid treatment tank (30) is connected to an acid liquid delivery pipe (47); and the discharge port of the acid treatment tank (30) is connected to a dissolving pulp storage tank (13); A continuous passage for preparing dissolving pulp from waste fiber products is formed between the pulverizer (3), the air conveying device (4), the cyclone separator (5), the pretreatment device (6), the decolorizing unit (7), the pulp washer (8), the impregnator (9), the press (10), the steamer (11), the bleaching tower (12), the acid treatment tank (30) and the dissolving pulp storage tank (13).

12. The system for preparing dissolving pulp from waste fibers according to claim 11, characterized in that: A sorting device (1) is arranged at the front side of the workstation of the pulverizer (3); a temporary storage bin (2) is arranged between the sorting device (1) and the pulverizer (3); a pre-processing continuous passage for sorting, temporarily storing and pulverizing waste fiber products is formed between the sorting device (1), the temporary storage bin (2) and the pulverizer (3); and a cotton content meter (32) and a cotton fiber maturity meter (33) are arranged on the sorting device (1).

13. The system for preparing dissolving pulp from waste fibers according to claim 12, characterized in that: The pulverizer (3) comprises a coarse pulverizer (301) and a fine pulverizer (302); the coarse pulverizer (301) is arranged at the rear side of the workstation of the sorting device (1); the fine pulverizer (302) is arranged at the rear side of the workstation of the coarse pulverizer (301); and a pre-processing continuous passage for sorting, coarse pulverization and fine pulverization of waste fiber products is formed between the sorting device (1), the coarse pulverizer (301) and the fine pulverizer (302).

14. The system for preparing dissolving pulp from waste fibers according to claim 11, characterized in that: The cyclone separator (5) is connected to a dust removal system (21).

15. The system for preparing dissolving pulp from waste fibers according to claim 11, characterized in that: The pretreatment device (6) is a pulping machine, a screw feeder (22) is arranged at the front side of the station of the pulping machine, a silo (23) is arranged at the front side of the station of the screw feeder (22), the silo (23) is arranged at the rear side of the station of the discharge port of the cyclone separator (5), the silo (23) is connected to the screw feeder (22) via a weighing belt (24), and a continuous passage for waste fiber separation, collection, transportation, weighing and pre-decolorization is formed between the cyclone separator (5), the silo (23), the weighing belt (24), the screw feeder (22) and the pulping machine.

16. The system for preparing dissolving pulp from waste fibers according to claim 11, characterized in that: The decolorization unit (7) comprises a stirring tank (701), an upflow decolorization tower (702) and a decolorization material receiving tank (703); the stirring tank (701) is arranged at the front side of the workstation of the upflow decolorization tower (702); the stirring tank (701) and the upflow decolorization tower (702) are connected via a feed pipe (25); the decolorization material receiving tank (703) is arranged at the rear side of the workstation of the upflow decolorization tower (702); a continuous passage for stirring, stripping, decolorizing and temporarily storing waste fibers is formed between the stirring tank (701), the upflow decolorization tower (702) and the decolorization material receiving tank (703).

17. The system for preparing dissolving pulp from waste fibers according to claim 16, characterized in that: There are at least two decolorizing units (7).

18. The system for preparing dissolving pulp from waste fibers according to claim 17, characterized in that: A screw squeezer (26) is provided between the decolorized material receiving tank (703) and the pulp washer (8).

19. The system for preparing dissolving pulp from waste fibers according to claim 11, characterized in that: A variable pitch screw conveyor (27) is provided between the pulp washer (8) and the impregnator (9), and an auxiliary impregnation barrel (28) is provided at the rear side of the station of the impregnator (9).

20. The system for preparing dissolving pulp from waste fibers according to claim 11, characterized in that: The discharge port of the cooking machine (11) is connected to a pulp discharge trough (56), and the pulp discharge trough (56) is arranged at the rear side of the working station of the cooking machine (11); The discharge port of the pulp discharge trough (56) is connected to a pulp squeezer (49), and the pulp squeezer (49) is arranged at the rear side of the station of the pulp discharge trough (56); The discharge port of the pulping machine (49) is connected to a pulp storage tank (50), and the pulp storage tank (50) is arranged at the rear side of the station of the pulping machine (49); The outlet of the pulp storage tank (50) is connected to a pulp refiner (51), and the pulp refiner (51) is arranged at the rear side of the workstation of the pulp storage tank (50); The outlet of the pulping machine (51) is connected to a pulp washer (8), and the pulp washer (8) is arranged at the rear side of the working station of the pulping machine (51); The discharge port of the pulp washer (8) is connected to the pulp pool (53), the discharge port of the pulp pool (53) is connected to a sand removal device (54), and the discharge port of the sand removal device (54) is connected to a thickener (55); The discharge port of the concentrator (55) is connected to the feed port of the bleaching tower (12); A continuous passage for removing impurities from fibers is formed between the pulp discharge trough (56), the pulp squeezer (49), the pulp storage trough (50), the pulp refiner (51), the pulp washer (8), the pulp tank (53), the sand removal device (54) and the thickener (55).

21. The system for preparing dissolving pulp from waste fibers according to claim 11, characterized in that: The system for preparing dissolving pulp from waste fibers is connected to a bleaching waste liquid treatment system (31), and the system for preparing dissolving pulp from waste fibers is also connected to a DCS system (29).

22. A control method for preparing dissolving pulp from waste fibers, characterized in that: The process for preparing dissolving pulp from waste fibers according to any one of claims 1 to 10 adopts the control method, and the control method includes the control of the sorting process: The cotton content signal is collected by the cotton content measuring device arranged on the sorting device, and the cotton content signal is uploaded to the DCS system, and the DCS system compares the received cotton content signal with the preset cotton content value: when the collected cotton content signal is equal to or greater than the preset cotton content value, the maturity signal is collected by the cotton fiber maturity measuring device on the sorting device, and the maturity signal is uploaded to the DCS system, and the DCS system controls the conveyor belt to send the waste fiber products corresponding to the maturity signal into the corresponding temporary storage bin; When the collected cotton content signal is less than the preset cotton content value, the DCS system controls the conveyor belt to discharge the corresponding waste fiber products for other processing.

23. The control method for preparing dissolving pulp from waste fibers according to claim 22, characterized in that: The preset cotton content value is 95%.

24. The control method for preparing dissolving pulp from waste fibers according to claim 22, characterized in that: The DCS system controls the conveyor belt to deliver the waste fiber products corresponding to the maturity signal into the corresponding temporary storage bin, including: Waste fiber products with a maturity of ≥55% are controlled to enter a temporary storage warehouse, and waste fiber products with a maturity of <55% are controlled to enter another temporary storage. Then, according to actual needs, the two types of waste fiber products are subjected to subsequent processes in different proportions, and finally dissolving pulp of different specifications is obtained to prepare different fiber products.

25. The control method for preparing dissolving pulp from waste fibers according to claim 22, characterized in that: The control method also includes the control of the bleaching process: The flow sensor III on the alkali solution delivery pipe III and the pH detector II on the bleaching tower collect the flow signal and pH signal respectively, and upload the flow signal and pH signal to the DCS system. The DCS system compares the received pH signal with the preset pH value: when the collected pH signal is equal to the set pH value, the DCS system sends a signal to the flow sensor III to maintain the collected flow rate; When the collected pH signal is greater than the set pH value, the DCS system sends a signal to reduce the flow rate to the flow sensor III, and controls the adjustment of the alkali solution feed regulating valve, and returns the adjusted pH signal to the DCS system for comparison again until the pH signal is equal to the set pH value; When the collected pH signal is less than the set pH value, the DCS system sends a signal to increase the flow rate to the flow sensor III, and controls the adjustment of the alkali solution feed regulating valve, and returns the adjusted pH signal to the DCS system for comparison again until the pH signal is equal to the set pH value.

26. The control method for preparing dissolving pulp from waste fibers according to claim 25, characterized in that: Using sodium hypochlorite bleaching method, the pre-set pH value is 8.5-9.5; The oxygen-alkali bleaching method is adopted, and the pre-set pH value is 10.5-11.

5.

27. The control method for preparing dissolving pulp from waste fibers according to claim 22, characterized in that: The control method also includes the control of the acid treatment process: The flow sensor IV on the acid delivery pipe and the pH detector III on the acid treatment tank collect the flow signal and pH signal respectively, and upload the flow signal and pH signal to the DCS system. The DCS system compares the received pH signal with the preset pH value: when the collected pH signal is equal to the set pH value, the DCS system sends a signal to the flow sensor IV to maintain the collected flow rate; When the collected pH signal is greater than the set pH value, the DCS system sends a signal to increase the flow rate to the flow sensor IV, and controls the adjustment of the acid feed regulating valve. The adjusted pH signal is then returned to the DCS system for comparison again until the pH signal is equal to the set pH value. When the collected pH signal is less than the set pH value, the DCS system sends a signal to reduce the flow rate to the flow sensor IV, and controls the acid feed regulating valve to adjust the pH signal. The adjusted pH signal is then returned to the DCS system for comparison again until the pH signal is equal to the set pH value.

28. The control method for preparing dissolving pulp from waste fibers according to claim 27, characterized in that: The pre-set pH value is 1.7-2.

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