Pretreatment method for purifying and recycling NMMO (N-methylmorpholine-N-oxide) solvent for preparing cellulose fiber by solvent method

Abstract

The invention belongs to the technical field of NMMO (N-methylmorpholine-N-oxide) solvent purification and recovery, and discloses a pretreatment method for purification and recovery of an NMMO solvent in preparation of cellulose fibers by a solvent method. The pretreatment method comprises the following steps: injecting dilute solvent recovery liquid, dilute solvent wastewater and a flocculating agent into an efficient clarification device, so that the dilute solvent recovery liquid, the dilute solvent wastewater and the flocculating agent are fully mixed in the efficient clarification device, and a flocculation product is removed through secondary precipitation and filtration; discharging the clear liquid from which the flocculation product is removed to a multi-medium filter through a liquid outlet pipe of the efficient clarification device; the method comprises the following steps of: removing most solid suspended matters in clear liquid through a multi-medium filter, removing metal ions and residual solid impurities and colored groups through an anion-cation resin bed, and evaporating and concentrating through a solvent evaporation system or an MVR (mechanical vapor recompression), so that NMMO (N-methylmorpholine-N-oxide) concentration meeting the process requirement is used for a stock solution and a spinning workshop. The device is small in size and high in efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of NMMO solvent purification and recovery, and in particular relates to a pretreatment method for purifying and recovering NMMO solvent for preparing cellulose fibers by a solvent process. Background Art

[0002] In the process of preparing cellulose fiber by NMMO solvent method, in order to recycle more than 97.5% of NMMO solvent, it is necessary to recycle the foam wastewater with NMMO concentration below 5% produced from the stock solution workshop and the coagulation bath circulating water with a concentration of about 20% NMMO produced from the spinning workshop. These collected and recycled solvent aqueous solutions contain inorganic components such as dust or sand, and a large amount of undissolved organic solid suspended matter such as hemicellulose, cellulose degradation product polysaccharides and colored groups. These impurities need to be removed before entering the solvent purification and recovery filter device, otherwise it will greatly increase the cleaning frequency and regeneration cycle of the purification and recovery device, greatly increase the consumption of electricity, water and steam, and sewage treatment.

[0003] From the earliest installation of coarse filters at the solvent recovery outlets of the stock solution workshop and the spinning workshop, which could not meet the requirements of online continuous operation due to the small filtering area and frequent cleaning, to the later multiple filtration, and then to the NMMO solvent recovery process that is now widely used. Among them, the process flow of the solvent purification and recovery system in the prior art is as follows: the dilute solvent recovery liquid (also called spinning bath solution) containing 17% NMMO concentration produced by the whole plant is first injected into the primary sedimentation tank, and the dilute solvent wastewater and flocculant are used to remove part of the flocculation product, and then the vast majority of solid suspended turbidity is removed by a multi-media filter, the remaining solid impurities and colored groups are removed by an anion exchange bed, and the metal ions such as copper and iron are removed by a cation exchange bed (the combination of anion exchange bed and cation exchange bed is collectively referred to as yin and yang resin bed); and then the multi-effect evaporation system (also called solvent evaporation system) or MVR (steam mechanical recompression technology) is used for evaporation and concentration to reach the NMMO concentration required by the process (about 76-85%), and finally it is used for the stock solution and spinning workshop.

[0004] The current technology used for NMMO solvent recovery has the following problems:

[0005] (1) Primary sedimentation tank, with multiple sedimentation stages and a large floor space;

[0006] (2) Filtration in the primary sedimentation tank relies solely on the deadweight of solid particles, resulting in low sedimentation efficiency;

[0007] (3) The flocculation and sedimentation residue at the bottom of the sedimentation tank needs to be cleaned manually regularly, and continuous operation is not possible;

[0008] (4) The multi-media filter has a heavy operating load, a short filter operating cycle, and frequent regeneration and cleaning;

[0009] (5) The water production rate of the cation and anion resin beds is low, and the exchange rate in a single cycle is less than 25 times. Summary of the invention

[0010] The object of the present invention is to provide a pre-treatment method for purifying and recovering the solvent for preparing cellulose fiber NMMO by a solvent process, so as to solve at least one of the above-mentioned problems existing in the prior art.

[0011] In order to achieve the above object, the present invention adopts the following technical solutions:

[0012] A pretreatment method for purifying and recovering NMMO solvent for preparing cellulose fiber by solvent method, comprising a high-efficiency clarification device in which a liquid outlet pipe is connected to a multi-media filter, and the pretreatment method comprises the following steps:

[0013] The dilute solvent recovery liquid is mixed with the dilute solvent wastewater and the flocculant and injected into the high-efficiency clarification device, so that the dilute solvent recovery liquid, the dilute solvent wastewater and the flocculant are fully mixed in the high-efficiency clarification device, and the flocculation product is removed by secondary precipitation and filtration, and the clear liquid after the flocculation product is removed is discharged to the multi-media filter through the liquid outlet pipe of the high-efficiency clarification device;

[0014] The majority of suspended solids in the clear liquid are removed by a multi-media filter, and then the metal ions and the remaining solid impurities and colored groups are removed by a cation resin bed. The NMMO concentration that meets the process requirements is evaporated and concentrated by a solvent evaporation system or MVR to be used in the stock solution and spinning workshop.

[0015] A primary sedimentation zone is arranged in the middle of the high-efficiency clarification device, the lower end of which is connected to a primary sludge chamber, a mixer is arranged in the primary sedimentation zone, and the inlet of the mixer is connected to a water inlet pipe for injecting solution into the mixer; diffusers are arranged around the primary sedimentation zone, and a distributor for guiding the solution in the primary sedimentation zone into the diffuser is arranged on the upper part of the primary sedimentation zone; a secondary sedimentation zone connected to the diffuser is arranged around the lower part of the diffuser, and the lower end of the secondary sedimentation zone and the lower end of the diffuser are both connected to the secondary sludge chamber; a separation zone is arranged around the upper part of the diffuser, and the lower end of the separation zone is connected to the secondary sedimentation zone through an inclined tube packing chamber for filtering flocculation products; the liquid outlet pipe of the high-efficiency clarification device is connected to the separation zone.

[0016] As a preferred technical solution in the present invention, a mud discharge pipe is provided at the lower end of the high-efficiency clarification device, the primary mud chamber and the secondary mud chamber are connected to the mud discharge pipe through the slag discharge pipe, and an automatic discharge valve is provided on the slag discharge pipe.

[0017] As a preferred technical solution in the present invention, a diverter is provided in the primary sedimentation zone below the mixer outlet.

[0018] As a preferred technical solution in the present invention, a water distribution chamber is provided between the inclined tube packing chamber and the secondary sedimentation zone.

[0019] As a preferred technical solution in the present invention, a water outlet chamber connected to the separation zone is provided at the edge of the separation zone, and the liquid outlet pipe of the high-efficiency clarification device is connected to the water outlet chamber.

[0020] As a preferred technical solution in the present invention, a water collecting trough is provided on the inner wall of the separation zone, and the water outlet chamber is connected to the water collecting trough.

[0021] As a preferred technical solution in the present invention, an oblique tube filler is arranged in the oblique tube filler chamber, and the oblique tube filler is an ethylene-propylene copolymer honeycomb type oblique tube filler.

[0022] As a preferred technical solution of the present invention, the flocculant is a cationic flocculant, and the ratio of the flocculant to the dilute solvent recovery liquid is 0.5-2.5%.

[0023] Beneficial effects: Compared with the existing primary sedimentation tank, the high-efficiency clarification device of the present invention has a reasonable structural layout and, under the condition of processing the same amount of solvent, significantly reduces the occupied area, improves the space utilization rate, and reduces the proportion of solvent recovery liquid; improves the removal efficiency, and compared with the existing technology, improves the pretreatment impurity removal rate; the solid flocculant sedimentation residue is automatically cleaned, and long-term continuous operation is achieved; after the high-efficiency clarification device efficiently removes solid impurities, the turbidity value of the solution is significantly reduced; the service life of the multi-media filter is extended, and the service life of a single set of multi-stage filters is increased; the exchange rate of the anion and cation exchange resin is increased, the number of regeneration times is reduced, and the single set exchange cycle is increased, and the conductivity of the solvent after the exchange is significantly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the structure of the high-efficiency clarification device in the present invention.

[0025] In the figure: 1-water inlet pipe; 2-distributor; 3-water collecting trough; 4-water outlet chamber; 5-inclined tube filling chamber; 6-separation zone; 7-secondary sedimentation zone; 8-diffuser; 9-mixer; 10-water distribution chamber; 11-inclined tube filling; 12-primary sedimentation zone; 13-diverter; 14-secondary sludge chamber; 15-primary sludge chamber; 16-sludge discharge pipe. DETAILED DESCRIPTION

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the present invention will be briefly introduced below in combination with the drawings and the description of the embodiments or the prior art. Obviously, the following description of the structure of the drawings is only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention.

[0027] Example:

[0028] like Figure 1 As shown, this embodiment provides a pre-treatment method for purifying and recovering solvent for preparing cellulose fiber NMMO by solvent method, comprising a high-efficiency clarification device in which a liquid outlet pipe is connected to a multi-media filter, and the pre-treatment method comprises the following steps:

[0029] The dilute solvent recovery liquid is mixed with the dilute solvent wastewater and the flocculant and injected into the high-efficiency clarification device, so that the dilute solvent recovery liquid, the dilute solvent wastewater and the flocculant are fully mixed in the high-efficiency clarification device, and the flocculation product is removed by secondary precipitation and filtration, and the clear liquid after the flocculation product is removed is discharged to the multi-media filter through the liquid outlet pipe of the high-efficiency clarification device;

[0030] The majority of suspended solids in the clear liquid are removed by a multi-media filter, and then the metal ions and the remaining solid impurities and colored groups are removed by a cation resin bed. The NMMO concentration that meets the process requirements is evaporated and concentrated by a solvent evaporation system or MVR to be used in the stock solution and spinning workshop.

[0031] A primary sedimentation zone 12 is arranged in the middle of the high-efficiency clarification device, and a primary sludge chamber 15 is connected to the lower end of the primary sedimentation zone 12. The flocculation product produced in the primary sedimentation zone 12 is settled in the primary sludge chamber 15, so as to be discharged through the primary sludge chamber 15. The primary sedimentation zone 12 and the primary sludge chamber 15 are preferably formed in one piece and combined into a primary sedimentation unit, which is divided into two areas according to the main functions. A mixer 9 is arranged in the primary sedimentation zone 12, and the inlet of the mixer 9 is connected to an inlet pipe 1 for injecting a solution into the mixer 9. When the dilute solvent recovery liquid, the dilute solvent wastewater and the flocculant enter the inlet pipe 1, they will first enter the mixer 9 for mixing, and then enter the primary sedimentation zone 12, so as to achieve a better sedimentation effect in the primary sedimentation zone 12; diffusers 8 are arranged around the primary sedimentation zone 12, and a uniform distributor 2 is arranged on the upper part of the primary sedimentation zone 12 to guide the solution in the primary sedimentation zone 12 to the diffuser 8, so that the solution after settling in the primary sedimentation zone 12 enters uniformly. The diffuser 8 is provided with a secondary sedimentation zone 7 connected to the diffuser 8 around the lower part of the diffuser 8, and the lower end of the secondary sedimentation zone 7 and the lower end of the diffuser 8 are both connected with a secondary sludge chamber 14. The diffuser 8, the secondary sedimentation zone 7 and the connected secondary sludge chamber 14 are combined to form a secondary sedimentation unit, which is mainly used to collect flocculated sediments from the primary unit and realize the functions of diffusion and water distribution. The flocculated sediments after the secondary sedimentation fall into the secondary sludge chamber 14 and then are discharged through the secondary sludge chamber 14. After the solvent aqueous solution is flocculated and precipitated in the primary sedimentation zone 12, it still contains about 60% of solid flocculants. Then, the secondary unit composed of the diffuser 8 and the secondary sedimentation zone 7 can efficiently remove almost all of the solid flocculants. The separation zone 6 is provided around the upper part of the diffuser 8, and the lower end of the separation zone 6 is connected to the secondary sedimentation zone 7 through an inclined tube packing chamber 5 for filtering flocculated products. The liquid outlet pipe of the efficient clarification device is connected to the separation zone 6.

[0032] It should be noted that, preferably, both the primary sludge chamber 15 and the secondary sludge chamber 14 are preferably quadrangular pyramid structures with openings gradually becoming smaller from top to bottom, so that the flocculation products settled inside each chamber can be smoothly discharged from the lower end.

[0033] Compared with the existing primary sedimentation tank, the high-efficiency clarification device of the present invention has a reasonable structural layout and, under the condition of processing the same amount of solvent, significantly reduces the occupied area, improves the space utilization rate, and reduces the proportion of solvent recovery liquid; improves the removal efficiency, and compared with the existing technology, improves the pretreatment impurity removal rate; the solid flocculant sedimentation residue is automatically cleaned, and long-term continuous operation is achieved; after the high-efficiency clarification device efficiently removes solid impurities, the turbidity value of the solution is significantly reduced; the service life of the multi-media filter is extended, and the service life of a single set of multi-stage filters is increased; the exchange rate of the anion and cation exchange resins is increased, the number of regeneration times is reduced, and the exchange cycle of a single set is increased, and the conductivity of the solvent after the exchange is significantly reduced.

[0034] As a preferred implementation scheme in this embodiment, it needs to be further explained that a mud discharge pipe 16 is provided at the lower end of the high-efficiency clarification device, and the primary mud chamber 15 and the secondary mud chamber 14 are connected to the mud discharge pipe 16 through a slag discharge pipe, and an automatic discharge valve is provided on the slag discharge pipe. The automatic discharge valve is operated intermittently, which can easily realize the automatic cleaning of the primary mud chamber 15 and the secondary mud chamber 14 and maintain long-term continuous operation. During continuous operation, the automatic discharge valve opens in sequence and discharges at a fixed time to keep the liquid level of the primary sedimentation unit and the secondary sedimentation unit as stable as possible.

[0035] As a preferred implementation scheme in this embodiment, it needs to be further explained that a diverter 13 is provided in the primary sedimentation area 12 below the outlet of the mixer 9 to prevent the solution from the mixer 9 from impacting the primary sludge chamber 15, thereby improving the sedimentation effect.

[0036] As a preferred implementation scheme in this embodiment, it needs to be further explained that a water distribution chamber 10 is provided between the inclined tube packing chamber 5 and the secondary sedimentation zone 7 .

[0037] As a preferred implementation scheme in this embodiment, it should be further explained that a water outlet chamber 4 connected to the separation zone 6 is provided at the edge of the separation zone 6, and the liquid outlet pipe of the high-efficiency clarification device is connected to the water outlet chamber 4 to achieve centralized discharge of the clear liquid. It should be noted that the discharged clear liquid can be first drained to a clear liquid storage tank for storage, and then pumped to the multi-media filter when needed.

[0038] As a preferred implementation scheme in this embodiment, it needs to be further explained that a water collecting trough 3 is provided on the inner wall of the separation zone 6, and the water outlet chamber 4 is connected to the water collecting trough 3, so that the water collecting trough 3 can be used to further collect the clear liquid on the surface of the separation zone 6.

[0039] As a preferred implementation scheme in this embodiment, it needs to be further explained that an oblique tube filler 11 is arranged in the oblique tube filler chamber 5, and the oblique tube filler 11 is a honeycomb oblique tube filler of ethylene-propylene copolymer material, which achieves a higher filtering effect.

[0040] As a preferred implementation scheme in this embodiment, it is necessary to further explain that the flocculant is a cationic flocculant, the ratio of the flocculant to the dilute solvent recovery liquid is 0.5-2.5% by mass, and the brand model is preferably FLOPAM FO 4650. The solid particles suspended in the solution are uniformly mixed under the action of the mixer through the agglomeration of the flocculants, and form particles of different particle sizes, and the larger particles quickly settle to the primary sludge chamber 15; after being removed by the primary sedimentation unit, the flocculated particles in the solution pass through the diffuser 8 and the water distribution chamber 10 and enter the inclined tube packing chamber 5. Preferably, an inclined tube with an inclination of 60 degrees is provided in the inclined tube packing chamber 5. According to the principle that different particle sizes bring different sedimentation times, almost all the smaller particles are settled in the inclined tube with an inclination of 60 degrees. This greatly reduces the operating burden of the subsequent multi-media filter and the anion-cation resin exchange bed.

[0041] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A pre-treatment method for purifying and recovering NMMO solvent for preparing cellulose fiber by solvent method, characterized in that: The invention comprises a high-efficiency clarification device in which a liquid outlet pipe is connected to a multi-media filter, and the pre-treatment method comprises the following steps: The dilute solvent recovery liquid is mixed with the dilute solvent wastewater and the flocculant and injected into the high-efficiency clarification device, so that the dilute solvent recovery liquid, the dilute solvent wastewater and the flocculant are fully mixed in the high-efficiency clarification device, and the flocculation product is removed by secondary precipitation and filtration, and the clear liquid after the flocculation product is removed is discharged to the multi-media filter through the liquid outlet pipe of the high-efficiency clarification device; The majority of suspended solids in the clear liquid are removed by a multi-media filter, and then the metal ions and the remaining solid impurities and colored groups are removed by a cation resin bed. The NMMO concentration that meets the process requirements is evaporated and concentrated by a solvent evaporation system or MVR to be used in the stock solution and spinning workshop. A primary sedimentation zone (12) is arranged in the middle of the high-efficiency clarification device, the lower end of the primary sedimentation zone (12) is connected to a primary sludge chamber (15), a mixer (9) is arranged in the primary sedimentation zone (12), and an inlet of the mixer (9) is connected to an inlet pipe (1) for injecting a solution into the mixer (9); a diffuser (8) is arranged around the primary sedimentation zone (12), and a liquid inlet (8) is arranged on the upper part of the primary sedimentation zone (12) to guide the solution in the primary sedimentation zone (12) into the diffuser (8). The diffuser (2) is provided with a secondary sedimentation zone (7) connected to the diffuser (8) around the lower part of the diffuser (8), and the lower end of the secondary sedimentation zone (7) and the lower end of the diffuser (8) are both connected to a secondary sludge chamber (14); the upper part of the diffuser (8) is provided with a separation zone (6) around the upper part of the diffuser (8), and the lower end of the separation zone (6) is connected to the secondary sedimentation zone (7) through an inclined tube packing chamber (5) for filtering flocculation products; the liquid outlet pipe of the high-efficiency clarification device is connected to the separation zone (6).

2. The pre-treatment method according to claim 1, characterized in that: A mud discharge pipe (16) is provided at the lower end of the high-efficiency clarification device, and the primary mud chamber (15) and the secondary mud chamber (14) are both connected to the mud discharge pipe (16) through the mud discharge pipe, and an automatic discharge valve is provided on the mud discharge pipe.

3. The pre-treatment method according to claim 1, characterized in that: A flow divider (13) is provided in the primary sedimentation zone (12) below the outlet of the mixer (9).

4. The pre-treatment method according to claim 1, characterized in that: A water distribution chamber (10) is provided between the inclined tube packing chamber (5) and the secondary sedimentation zone (7).

5. The pre-treatment method according to claim 1, characterized in that: A water outlet chamber (4) connected to the separation zone (6) is provided at the edge of the separation zone (6), and a liquid outlet pipe of the high-efficiency clarification device is connected to the water outlet chamber (4).

6. The pre-treatment method according to claim 5, characterized in that: A water collecting trough (3) is provided on the inner wall of the separation zone (6), and the water outlet chamber (4) is connected to the water collecting trough (3).

7. The pre-treatment method according to claim 1, characterized in that: The inclined tube packing chamber (5) is provided with an inclined tube packing (11), and the inclined tube packing (11) is a honeycomb type inclined tube packing made of ethylene-propylene copolymer material.

8. The pre-treatment method according to claim 1, characterized in that: The flocculant is a cationic flocculant, and the ratio of the flocculant to the dilute solvent recovery liquid is 0.5-2.5%.

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