Acid bath impurity removal and purification method and system for flame-retardant fibers

Abstract

The invention belongs to the technical field of viscose acid bath production, and particularly relates to a flame-retardant fiber acid bath impurity removal and purification method and system. The spinning return acid bath is subjected to deep vacuum degassing, then nano sieve separation is performed, clean liquid is directly supplied to a flash evaporation system, concentrated liquid is subjected to flocculating agent and air flotation treatment and then evaporated and concentrated to the normal spinning acid bath concentration, tow filtration is performed finally, the acid bath with the high cleanliness index is obtained, and the purposes of resource recycling, energy conservation, emission reduction and pollution reduction can be achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of viscose acid bath production, and specifically relates to a method and system for removing impurities from a flame-retardant fiber acid bath. Background Art

[0002] With the intensified competition in the viscose industry, the scale of flame-retardant fiber production has expanded, and the application field has gradually broadened. How to increase the production capacity of flame-retardant fiber has become particularly important, especially to improve the quality of flame-retardant acid bath. At present, viscose enterprises have adopted the method of filament filtration and microporous combination filtration to purify the acid bath, but the flux decay rate of ordinary mechanical filtration is fast. In order to ensure the spinning amount, the flame-retardant acid bath cannot be completely filtered. Part of the acid bath enters the flash evaporation system directly without filtration, resulting in serious fouling and blockage of the flash evaporation system heater, difficulty in cleaning, decreased heat transfer capacity, and greatly increased steam consumption. Therefore, the filter flux is seriously attenuated, the heater is blocked and difficult to clean, and the energy consumption problem has become the biggest constraint for flame-retardant fiber to improve efficiency, reduce costs and sustainable development. The present invention fundamentally solves the problem that the traditional single filament filtration and microporous filtration flux decay in the production of flame-retardant fibers is serious, and the graphite tube of the acid bath evaporation system heater is blocked, the existing cleaning process cannot meet the process requirements, and continuous production cannot be achieved; the flame-retardant fiber cleaning cycle is extended to achieve full utilization of resources, and it has a promoting and guiding significance for the diversified development of functional varieties of the entire viscose fiber industry. Summary of the invention

[0003] In order to solve the deficiencies of the prior art, the present invention provides a method and system for removing impurities from a flame-retardant fiber acid bath. The present invention performs deep vacuum degassing on the spinning acid bath, then performs nano-sieve separation, directly supplies the clean liquid to the flash evaporation system, and the concentrated liquid is treated with a flocculant and air flotation, then evaporated and concentrated to a normal spinning acid bath concentration, and finally performs tow filtration to obtain an acid bath with a high cleanliness index, which can achieve the purpose of resource recycling, energy saving and emission reduction, and pollution reduction.

[0004] The technical solution provided by the present invention is as follows:

[0005] A flame retardant fiber acid bath impurity removal and purification method, comprising the following steps:

[0006] 1) The spinning acid bath is deeply degassed to remove the hydrogen sulfide, carbon disulfide and sulfide dissolved in the acid bath;

[0007] 2) filtering the degassed acid bath through a nano-sieve to obtain a clean solution and a concentrated solution;

[0008] 3) passing the clean liquid into a flash evaporation device;

[0009] The concentrated liquid is subjected to flocculation and flotation treatment to obtain a clear liquid and a scum respectively; the clear liquid is passed into a flash evaporation device; the scum is subjected to plate-and-frame filtration to obtain a filtrate and a filter residue; the filtrate is then passed into a flash evaporation device, and the filter residue is discharged to a sewage treatment plant for treatment;

[0010] 4) Concentrate the introduced acid bath to the spinning acid bath concentration by flash evaporation: sulfuric acid 118g / L-125g / L, zinc sulfate 25g / L-35g / L, sodium sulfate 350g / L-375g / L;

[0011] 5) The evaporated acid bath is subjected to tow filtering to obtain a spinning acid bath.

[0012] In the above technical solution:

[0013] In the production of flame-retardant fibers, the acid is recycled during spinning to perform deep degassing to remove hydrogen sulfide, carbon disulfide and a small amount of sulfide in the acid bath;

[0014] The acid bath is then separated through a nano-sieve to obtain clean liquid and concentrated liquid, and the clean liquid directly enters the flash evaporation system;

[0015] The concentrated liquid is added with a flocculant to agglomerate the flame retardant in the flame retardant acid bath, and the scum and the acid bath are separated by air flotation. The macromolecular organic matter and flame retardants such as silicon dioxide, silicic acid, and orthosilicic acid are separated through the scum.

[0016] The floating scum is filtered by plate and frame filter to form filter residue and acid bath filtrate. The filtrate is returned to the flash evaporation system. The acid bath clear liquid after flotation enters the flash evaporation system and then evaporates and concentrates to remove the water brought in during the spinning process.

[0017] The concentrate is finally filtered through tow to remove possible evaporation precipitates, impurities, acid sludge, dirt and colloid, etc., to obtain a highly clean acid bath, which can be directly used as a working acid bath.

[0018] The above technical solution solves the problems of serious attenuation of single-tow filtration and microporous filtration flux in flame-retardant fiber production, and blockage of graphite tube in heater of acid bath evaporation system, thereby overcoming the problems that the existing cleaning process cannot meet the process requirements and cannot be produced continuously. It can extend the cleaning cycle of flame-retardant fibers and realize full utilization of resources.

[0019] Preferably, in step 1), the absolute pressure is controlled at 80mba-100mba.

[0020] The flow rate of the spinning acid return of a flame retardant fiber production line is 350m 3 / h-370m 3 / h. Based on the above technical solution, the spinning acid can be deeply degassed, and the absolute pressure is controlled at 80mba-100mba. The degassing vacuum degree of conventional viscose fiber production is controlled below 140mba. Deep vacuum degassing and higher vacuum degree further reduce the solubility of hydrogen sulfide, carbon disulfide and sulfide dissolved in the spinning acid, improve the removal efficiency of sulfur-containing gas and sulfide, improve the transparency of the acid bath, the turbidity detection is below 50NTU, and save energy.

[0021] Preferably, in step 2), the pore size of the nanosieve is 50 nm-150 nm.

[0022] In the above technical scheme, after degassing, the acid bath enters the nanosieve (50nm-150nm) for separation, the clean liquid directly enters the flash evaporation system, the concentrated liquid is flocculated and flotation treated, and the particle size distribution of the flame retardant fiber is tested before the aperture of the nanosieve is selected. The large particle components in the flame retardant fiber acid bath are silicon dioxide, orthosilicic acid and silicic acid. The solid particles are larger than 170nm through the particle size test, so a nanosieve below 150nm is selected.

[0023] The nano-sieve with a diameter of less than 150 nm was used to filter the acid bath, and the particle size distribution of the flame-retardant fiber acid bath with a diameter of 170 nm was tested by a particle size analyzer, which was 0%. This indicates that the nano-sieve intercepted 100% of the large particles in the flame-retardant acid bath, and the turbidity of the acid bath was further tested to be below 1 NTU.

[0024] The turbidity of the acid bath treated with nano-sieve is below 1 NTU, and it can be used as flash acid supply, directly supplying two sets of flash acid without filtering through a microporous filter.

[0025] Specifically, flocculation and flotation treatment are performed, and flocculants are added into the flotation tank for flocculation; a micro-bubble generating device is provided in the flotation tank to generate uniform bubbles from the bottom for flotation.

[0026] Preferably, in step 2), a flocculant is added to the concentrated solution, and the amount of the flocculant added is 0.2 to 0.5 of the mass of the concentrated solution.

[0027] More preferably, the flocculant is added in two steps. In the first step, air is continuously blown into the acid bath concentrate, and 1 / 2-3 / 4 of the amount of flocculant is first added; in the second step, 1 / 2-1 / 4 of the amount of flocculant is added.

[0028] Based on the above technical solution, a two-step method is adopted. The first step is to agglomerate large particles first, and the second step is to agglomerate small particles fully. The overall amount of flocculant added in the two-step method is 30%-50% less than that in the one-step method.

[0029] Specifically, in step 3), the flocculant in the acid bath concentrate is added, and after the acid bath flotation, a scraper is used to remove the scum, and the lower layer of the acid bath clear liquid is directly transported to the acid bath evaporation system through a pump.

[0030] Based on the above technical solution, the turbidity of the lower acid bath is below 3NTU after flocculation and flotation, and it directly enters the flash evaporation system without filtration, simplifying the filtration process.

[0031] Specifically, the acid bath flotation scum in step 3) is filtered by a plate and frame filter, the filtrate is recycled to the acid bath system, and the filter residue is discharged to a sewage treatment plant for treatment. The scum is a mixture of flocculant and flame retardant with low viscosity and can be treated by high-pressure plate and frame filtration.

[0032] Specifically, the plate and frame filtrate can be evaporated and concentrated to the normal spinning acid bath concentration by flash evaporation, sulfuric acid 118g / L-125g / L, zinc sulfate 25g / L-35g / L, sodium sulfate 350g / L-375g / L.

[0033] Furthermore, the clean liquid obtained after the nano-sieve filtration is used as the backwash liquid for the tow filtration.

[0034] Furthermore, the backwash liquid after backwashing is subjected to plate and frame filtration, and the obtained filtrate is reused in the flash evaporation system.

[0035] Based on the above technical solution, in step 5), the acid bath is filtered by tow after evaporation, and the clean acid bath obtained after filtration is used as the acid for flame retardant fiber production. The flash evaporated acid is fully filtered by tow filtration to further improve the turbidity of the acid bath, ensure the quality of the acid bath for spinning, and realize the recycling of the acid bath;

[0036] The periodic backwashing of the tow filter adopts the acid bath of the lower clear liquid after air flotation, and the filtrate can be recycled into the system;

[0037] The filter residue from the periodic backwashing of the tow filter can be filtered by a plate and frame filter, and the plate and frame filtration steps in step 3) are repeated. The filtrate is returned to the acid bath system, and the filter residue is discharged to the sewage treatment plant for treatment;

[0038] The plate and frame filter uses nano-sieve clean liquid for flushing, which enables acid bath recycling, reduces production water consumption, and prolongs the service life of the tow.

[0039] In the above technical solution:

[0040] Flame retardant fiber production spinning acid return flow rate is 350m 3 / h-370m 3 / h, and the net liquid is 160m 3 / h-170m 3 / h;

[0041] After filtering through the nano sieve, the concentrate flow rate is 190m 3 / h-200m 3 / h, for flocculation and flotation treatment;

[0042] After filtering through the nano sieve, the net liquid flow rate is 160m 3 / h-170m 3 / h direct supply flash evaporation;

[0043] The concentrated liquid is added with a flocculant, and the amount of the flocculant added is 0.2 to 0.5 thousandths of the mass of the concentrated liquid, which is 0.38 tons to 1 ton;

[0044] The flocculant is added in two steps. In the first step, air is continuously blown into the acid bath concentrate, and 1 / 2-3 / 4 of the amount of flocculant is first added, which is 0.19 tons to 0.75 tons. In the second step, 0.19 tons to 0.25 tons of flocculant is added.

[0045] After acid bath flotation, the scraper is used to remove the scum flow rate of 20m 3 / h-30m 3 / h, the lower acid bath clear liquid is 170m 3 / h, directly transported to the acid bath evaporation system through a pump;

[0046] 20m 3 / h-30m 3 / h Acid bath gas flotation slag is filtered by plate and frame filter, 15m 3 / h-22.5m 3 / h filtrate is recycled to the acid bath system, and the filter residue is discharged to the sewage plant for treatment;

[0047] 15m 3 / h-22.5m 3 / h The plate and frame filtrate is mixed with the nano-sieve clean liquid and evaporated to concentrate to the normal spinning acid bath concentration, sulfuric acid 118g / L-125g / L, zinc sulfate 25g / L-35g / L, sodium sulfate 350g / L-375g / L;

[0048] After evaporation 320m 3 / h-330m 3 / h acid bath adopts tow filtration, and the turbidity of the acid bath is 10NTU-30NTU.

[0049] The invention also provides a flame retardant fiber acid bath impurity removal and purification system, comprising:

[0050] Deep degassing device;

[0051] A nanosieve connected to the deep degassing device, having a concentrated liquid outlet and a clean liquid outlet;

[0052] A flocculation and flotation device connected to the nano-sieve, which has a drug addition port, a scum outlet and a clear liquid outlet;

[0053] A plate-and-frame filter connected to the flocculation and flotation device, having a filtrate outlet;

[0054] a flash evaporation device, which is connected to the clean liquid outlet, the clear liquid outlet and the filtrate outlet respectively;

[0055] and a tow filter connected to the flash evaporation device.

[0056] Furthermore, the tow filter has a backwash liquid inlet and a backwash liquid outlet, and the clean liquid outlet of the nanosieve, the backwash liquid inlet, the backwash liquid outlet and the plate-and-frame filter are sequentially connected.

[0057] Specifically, the deep degassing device is connected to the spinning acid return pipe.

[0058] Specifically, the tow filter is connected to the acid bath outlet pipe.

[0059] Beneficial effects of the present invention:

[0060] The present invention solves the problems of serious attenuation of single-tow filtration and microporous filtration flux in flame-retardant fiber production, blockage of graphite tube of heater in acid bath evaporation system, etc., thereby overcoming the problems that the existing cleaning process cannot meet the process requirements and cannot be produced continuously, and can extend the cleaning cycle of flame-retardant fibers and realize full utilization of resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 It is a structural schematic diagram of the flame retardant fiber acid bath impurity removal and purification system provided by the present invention.

[0062] Figure 2 The present invention provides a flow chart of a flame retardant fiber acid bath impurity removal and purification system.

[0063] Attached Figure 1 The structures represented by the labels are listed below:

[0064] 1. Deep degassing device, 2. Nano sieve, 3. Flocculation flotation device, 4. Plate and frame filter, 5. Flash evaporation device, 6. Tow filter. DETAILED DESCRIPTION

[0065] The principles and features of the present invention are described below. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0066] Unless otherwise specified, the test methods used in the embodiments of the present invention are conventional methods; the materials and reagents used are reagents and materials that can be obtained from commercial channels unless otherwise specified.

[0067] The flocculant is a prior art, can be purchased, and is a modified PMA flocculant.

[0068] Nanosieve is an existing technology and can be purchased. It is a high-acid and high-salt resistant nanomolecular sieve with a pore size of 50-150nm.

[0069] Example 1

[0070] A method for removing impurities from a flame retardant fiber acid bath: the spinning acid bath is subjected to deep vacuum degassing, followed by nano-sieve separation, the clean liquid is directly supplied to a flash evaporation system, the concentrated liquid is subjected to flocculant flotation treatment, and then evaporated and concentrated to a normal spinning acid bath concentration, and finally the tow is filtered to achieve a highly clean acid bath, comprising the following steps:

[0071] 1) The spinning flow rate of a flame retardant fiber production line is 350m 3 / h, for deep degassing, the absolute pressure is controlled at 80mba.

[0072] 2) The spinning flow rate of flame retardant fiber production is 350m 3 / h, and obtain 160m3 of clean liquid 3 / h direct supply flash evaporation, concentrated liquid flow rate 190m 3 / h for flocculation and flotation treatment.

[0073] 3) 190m 3 / hThe flocculant is added to the concentrated liquid, and the amount of flocculant added is 0.02% of the concentrated liquid flow rate, which is 0.38 tons.

[0074] 4) The flocculant is added in two steps. In the first step, air is continuously blown into the acid bath concentrate, and 1 / 2 of the amount of flocculant added, which is 0.19 tons, is first added. In the second step, 0.19 tons of flocculant is added.

[0075] 5) 190m 3 / h The flocculant in the acid bath concentrate is added. After the acid bath flotation, the scraper is used to remove the scum. The flow rate is 20m 3 / h, the lower acid bath clear liquid is 170m 3 / h is directly delivered to the acid bath evaporation system through a pump.

[0076] 6) 20m 3 / h Acid bath gas flotation slag is filtered by plate and frame filter, 15m 3 / hThe filtrate is recycled to the acid bath system and the filter residue is discharged to the sewage plant for treatment.

[0077] 7) 15m 3 / hThe plate and frame filtrate is mixed with the nanosieve clean liquid and evaporated to concentrate to the normal spinning acid bath concentration, sulfuric acid 118g / l, zinc sulfate 25g / l, sodium sulfate 350g / l, and the acid bath turbidity is 10NTU.

[0078] 8) 320m after evaporation 3 / h acid bath is filtered by tow, and the clean acid bath obtained after filtration is used as acid for flame retardant fiber production. The tow filter is periodically backwashed by flotation and the lower clear liquid of the acid bath is used. The filtrate is recycled into the system, and the filter residue is treated with a plate and frame filter, and step 6 is repeated).

[0079] Example 2

[0080] A method for removing impurities from a flame retardant fiber acid bath: the spinning acid bath is subjected to deep vacuum degassing, followed by nano-sieve separation, the clean liquid is directly supplied to a flash evaporation system, the concentrated liquid is subjected to flocculant flotation treatment, and then evaporated and concentrated to a normal spinning acid bath concentration, and finally the tow is filtered to achieve a highly clean acid bath, comprising the following steps:

[0081] 1) Single-line 30,000-ton capacity flame-retardant fiber production spinning acid return flow rate is 370m 3 / h, for deep degassing, the absolute pressure is controlled at 100mba.

[0082] 2) Flame retardant fiber production spinning acid return flow rate is 370m 3 / h, and obtain 170m3 of clean liquid 3 / h direct supply flash evaporation, concentrated liquid flow rate 200m 3 / h for flocculation and flotation treatment.

[0083] 3) 200m 3 / hThe flocculant is added to the concentrated liquid, and the amount of flocculant added is 0.5% of the concentrated liquid flow rate, which is 1 ton.

[0084] 4) The flocculant is added in two steps. In the first step, air is continuously blown into the acid bath concentrate, and 3 / 4 of the amount of flocculant added, which is 0.75 tons, is first added; in the second step, 1 / 4 of the amount of flocculant added, which is 0.25 tons, is added.

[0085] 5) 200m 3 / h The flocculant in the acid bath concentrate is added. After the acid bath flotation, the scraper is used to remove the scum. The flow rate is 30m 3 / h, the lower acid bath clear liquid is 170m 3 / h is directly delivered to the acid bath evaporation system through a pump.

[0086] 6) 30m 3 / h Acid bath flotation slag is filtered by plate and frame filter, 22.5m 3 / hThe filtrate is recycled to the acid bath system and the filter residue is discharged to the sewage plant for treatment.

[0087] 7)22.5m 3 / hThe plate and frame filtrate is mixed with the nano-sieve clean liquid and evaporated to concentrate to the normal spinning acid bath concentration, sulfuric acid 125g / l, zinc sulfate 35g / l, sodium sulfate 375g / l.

[0088] 8) 330m after evaporation3 / h acid bath is filtered by tow, and the turbidity of the acid bath is 30NTU. After filtration, the clean acid bath is used as acid for flame retardant fiber production. The tow filter is backwashed periodically by the clear liquid of the acid bath after flotation, and the filtrate is recycled to the system. The filter residue is then treated by a plate and frame filter, and step 6 is repeated).

[0089] Example 3

[0090] A method for removing impurities from a flame retardant fiber acid bath: the spinning acid bath is subjected to deep vacuum degassing, followed by nano-sieve separation, the clean liquid is directly supplied to a flash evaporation system, the concentrated liquid is subjected to flocculant flotation treatment, and then evaporated and concentrated to a normal spinning acid bath concentration, and finally the tow is filtered to achieve a highly clean acid bath, comprising the following steps:

[0091] 1) The spinning and acid return flow rate of a flame retardant fiber production line is 360m 3 / h, for deep degassing, the absolute pressure is controlled at 90mba.

[0092] 2) Flame retardant fiber production spinning acid return flow rate is 360m 3 / h, and obtain 165m3 of clean liquid 3 / h direct supply flash evaporation, concentrated liquid flow rate 195m 3 / h for flocculation and flotation treatment.

[0093] 3)195m 3 / hThe flocculant is added to the concentrated liquid, and the amount of flocculant added is 0.3 / 1000 of the concentrated liquid flow rate, which is 0.68 tons.

[0094] 4) The flocculant is added in two steps. In the first step, air is continuously blown into the acid bath concentrate, and 5 / 8 of the amount of flocculant is first added, which is 0.425 tons. In the second step, 3 / 8 of the amount of flocculant is added, which is 0.255 tons.

[0095] 5)195m 3 / h The flocculant in the acid bath concentrate is added. After the acid bath flotation, the scraper is used to remove the scum. The flow rate is 25m 3 / h, the lower acid bath clear liquid is 170m 3 / h is directly delivered to the acid bath evaporation system through a pump.

[0096] 6) 25m 3 / h Acid bath gas flotation slag is filtered by plate and frame filter, 18.75m 3 / hThe filtrate is recycled to the acid bath system and the filter residue is discharged to the sewage plant for treatment.

[0097] 7)18.75m 3 / hThe plate and frame filtrate is mixed with the nanosieve clean liquid and evaporated to concentrate to the normal spinning acid bath concentration, sulfuric acid 122g / l, zinc sulfate 30g / l, sodium sulfate 368g / l.

[0098] 8) After evaporation, the 325m / h acid bath is filtered by tow, and the turbidity of the acid bath is 20NTU. After filtration, the clean acid bath is used as acid for flame retardant fiber production. The tow filter is backwashed periodically by the acid bath lower clear liquid after flotation, and the filtrate is recycled. The filter residue is treated by a plate and frame filter, and step 6 is repeated.

[0099] Comparative Example 1

[0100] Referring to Example 1, the difference is that without deep degassing, the spinning acid return is directly filtered by nanosieve, and the operation cycle of the nanosieve is shortened from 16-18 hours to 10-12 hours, indicating that the soluble impurities in the acid bath clog the sieve holes of the nanosieve, the flux attenuation is serious, the frequency of alkali washing is increased, the caustic soda consumption is increased, and the service life of the nanosieve is seriously affected.

[0101] Comparative Example 2

[0102] Referring to Example 1, the difference is that flash evaporation is directly carried out after deep degassing. During the evaporation process of the flame retardant acid bath, the secondary gas carries impurities such as silicon dioxide, silicic acid and orthosilicic acid to block the shell of the graphite tube preheater, causing the heat transfer coefficient of the graphite tube preheater to decrease, increasing steam consumption, and scaling will also occur if the graphite tube heater runs for a long time, causing the acid bath circulation volume to decay and reducing the evaporation volume. The existing normal flash alkali washing through periodic parking cannot completely clean the silicon scale, causing the scaling to gradually increase, affecting the continuous production and operation of the flame retardant fiber.

[0103] Comparative Example 3

[0104] Refer to Example 1, the difference is that the flocculant is added once. When a qualified acid bath is obtained, the amount of flocculant used is 1.3-1.4 times the amount added twice, and the amount of flocculant added is calculated to achieve the same turbidity of 10-15 NTU through the acid bath.

[0105] Example 4

[0106] like Figure 1 , 2 As shown, the flame retardant fiber acid bath impurity removal and purification system includes: a deep degassing device 1; a nano sieve 2 connected to the deep degassing device 1, which has a concentrated liquid outlet and a clean liquid outlet; a flocculation flotation device 3 connected to the nano sieve 2, which has a dosing port, a scum outlet and a clear liquid outlet; a plate-frame filter 4 connected to the flocculation flotation device 3, which has a filtrate outlet; a flash evaporation device 5, which is respectively connected to the clean liquid outlet, the clear liquid outlet and the filtrate outlet; and a tow filter 6 connected to the flash evaporation device 5. The tow filter 6 has a backwash liquid inlet and a backwash liquid outlet, and the clean liquid outlet, the backwash liquid inlet, the backwash liquid outlet of the nano sieve 2 and the plate-frame filter 4 are connected in sequence. The deep degassing device 1 is connected to the spinning acid return pipe. The tow filter 6 is connected to the acid bath outlet pipe.

[0107] The flame retardant fiber acid bath impurity removal and purification method provided by the present invention can be carried out on the above system.

[0108] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for removing impurities and purifying flame retardant fibers by acid bath, characterized in that: The following steps are involved: 1) The spinning acid bath is deeply degassed to remove the hydrogen sulfide, carbon disulfide and sulfide dissolved in the acid bath; 2) filtering the degassed acid bath through a nano-sieve to obtain a clean solution and a concentrated solution; 3) passing the clean liquid into a flash evaporation device; The concentrated liquid is subjected to flocculation and flotation treatment to obtain a clear liquid and a scum respectively; the clear liquid is passed into a flash evaporation device; The scum is subjected to plate and frame filtration to obtain a filtrate and a filter residue; the filtrate is then passed into a flash evaporation device; 4) Concentrate the introduced acid bath to the spinning acid bath concentration by flash evaporation: sulfuric acid 118g / L-125g / L, zinc sulfate 25g / L-35g / L, sodium sulfate 350g / L-375g / L; 5) The evaporated acid bath is subjected to tow filtering to obtain a spinning acid bath.

2. The method for removing impurities and purifying the flame retardant fiber by acid bath according to claim 1, characterized in that: In step 1), the absolute pressure is controlled at 80mba-100mba.

3. The method for removing impurities and purifying flame retardant fibers by acid bath according to claim 1, characterized in that: In step 2), the pore size of the nanosieve is 50nm-150nm.

4. The method for removing impurities and purifying the flame retardant fiber by acid bath according to claim 1, characterized in that: In step 2), a flocculant is added to the concentrated solution, and the amount of the flocculant added is 0.2 to 0.5 of the mass of the concentrated solution.

5. The method for removing impurities and purifying the flame retardant fiber by acid bath according to claim 4, characterized in that: The flocculant is added in two steps. In the first step, air is continuously blown into the acid bath concentrate, and 1 / 2-3 / 4 of the amount of flocculant is first added; in the second step, 1 / 2-1 / 4 of the amount of flocculant is added.

6. The method for removing impurities and purifying flame-retardant fibers by acid bath according to any one of claims 1 to 5, characterized in that: The clean liquid obtained after the nano-sieve filtration is used as the backwash liquid for the tow filtration.

7. The method for removing impurities and purifying flame retardant fibers by acid bath according to claim 6, characterized in that: The backwash liquid after backwashing is filtered through plate and frame, and the obtained filtrate is returned to the flash evaporation system.

8. A flame retardant fiber acid bath impurity removal and purification system, characterized in that: include: Deep degassing device (1); A nanosieve (2) connected to the deep degassing device (1), having a concentrated liquid outlet and a clean liquid outlet; A flocculation and flotation device (3) connected to the nano-sieve (2), which has a drug addition port, a scum outlet and a clear liquid outlet; A plate-and-frame filter (4) connected to the flocculation and flotation device (3), having a filtrate outlet; a flash evaporation device (5), which is connected to the clean liquid outlet, the clear liquid outlet and the filtrate outlet respectively; and a tow filter (6) connected to the flash evaporation device (5).

9. The flame retardant fiber acid bath impurity removal and purification system according to claim 8, characterized in that: The tow filter (6) has a backwash liquid inlet and a backwash liquid outlet, and the clean liquid outlet of the nanosieve (2), the backwash liquid inlet, the backwash liquid outlet and the plate-and-frame filter (4) are sequentially connected.

10. The flame retardant fiber acid bath impurity removal and purification system according to claim 8, characterized in that: The deep degassing device (1) is connected to the spinning acid return pipe; The tow filter (6) is connected to the acid bath outlet pipe.

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