Method for separating and purifying PVP (Polyvinyl Pyrrolidone) from silver-containing wastewater

Abstract

The invention relates to a method for separating and purifying PVP (Polyvinyl Pyrrolidone) from silver-containing wastewater. The method comprises the following steps: adjusting PH; performing membrane filtration; performing low-temperature concentration; biochemical oxidation; wherein low-temperature evaporation concentration equipment adopted for low-temperature concentration comprises a tank body separator, a steam compressor and a low-temperature evaporator, the tank body separator is connected with the low-temperature evaporator through a circulating pump and a circulating pipe, and steam is used for the low-temperature evaporator at the top of the tank body separator through the steam compressor; a plurality of film uniformizing pieces which are arranged downwards in a cambered surface shape are fixedly connected in the tank body separator at intervals up and down through a mounting shaft which is coaxially arranged, the liquid outlet end of the low-temperature evaporator communicates with the tank body separator through a plurality of liquid return branch pipes which are connected in parallel, and the liquid outlet ends of the liquid return branch pipes are arranged at the tops of the corresponding film uniformizing pieces in a one-to-one correspondence mode. Liquid is dispersed in a water film shape, the evaporation surface is increased, the evaporation efficiency is effectively improved, the evaporation treatment capacity is improved, and the overall treatment efficiency of silver-containing wastewater is improved.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, in particular to a method for separating and purifying PVP in silver-containing wastewater. Background Art

[0002] Ultrafine silver powder is mainly prepared by liquid phase chemical reduction. The reducing agent, dispersant, and silver salt required for the preparation of ultrafine silver powder by liquid phase reduction are all high-concentration chemical agents. The current ultrafine silver powder production plan is to use ascorbic acid (VC) as a reducing agent to reduce silver nitrate, and polyvinyl pyrrolidone (PVP) as a dispersant and protective agent to prepare ultrafine silver powder. The mother liquor remaining after the silver powder production has the characteristics of strong acidity, high salinity, high chemical oxygen demand, and high ammonia nitrogen. The treatment of this type of wastewater has always been an industry problem and will cause serious environmental pollution.

[0003] The existing PVP treatment process for separation and purification of silver-containing wastewater is to evaporate and concentrate the silver-containing wastewater after pretreatment with an alkali neutralization process and membrane filtration, and then carry out biochemical and oxidation. The condensed water enters the coagulation system and biochemical system for further treatment, and then is discharged into the park sewage station. However, the existing evaporation and concentration is to pass the waste liquid into the tank separator, use a circulating pump and a low-temperature evaporator to circulate the liquid in the tank separator, and then use the tank separator steam for the low-temperature evaporator through a steam compressor. However, because evaporation can only be carried out from the surface of the liquid in the tank separator, the evaporation efficiency is slow, and the evaporation amount is insufficient to supply the low-temperature evaporator, resulting in a slow processing speed and a long cycle.

[0004] Therefore, the purpose of the present invention is to design a method for separating and purifying PVP in silver-containing wastewater that can effectively increase the evaporation amount and evaporation rate of the tank separator, ensure that there is sufficient steam for the low-temperature evaporator, and thereby improve the efficiency of evaporation concentration and separation and purification of PVP. Summary of the invention

[0005] In view of the technical problems existing in the above-mentioned prior art, the present invention provides a method for separating and purifying PVP in silver-containing wastewater, which can effectively solve the technical problems existing in the above-mentioned prior art.

[0006] The technical solution of the present invention is:

[0007] A method for separating and purifying PVP in silver-containing wastewater comprises the following steps:

[0008] S1, pH adjustment: add alkali to the PVP-containing wastewater and mix well to adjust the pH to 3.5-5.0;

[0009] S2, membrane filtration: The PVP-containing wastewater after pH adjustment is concentrated by molecular sieve membrane filtration to produce membrane concentrated water and membrane produced water;

[0010] S3, low-temperature concentration: the membrane concentrated water is introduced into a low-temperature evaporation concentration device for low-temperature evaporation concentration to obtain evaporation concentrated water and evaporation condensate, the evaporation condensate is refluxed to the water inlet end of the molecular sieve membrane and mixed with the PVP-containing wastewater, and the evaporation concentrated water is discharged and collected for reprocessing;

[0011] S4, biochemical and Fenton oxidation: the membrane produced water passes through the biochemical system and Fenton oxidation system in turn and is discharged in compliance with the standards;

[0012] The low-temperature evaporation and concentration equipment used in step S3 includes a tank separator, a steam compressor and a low-temperature evaporator. The bottom of the tank separator is inclined and connected to the inclined end with a corresponding liquid outlet pipe. The side of the tank separator is connected to the raw liquid source through a corresponding liquid inlet pipe and a liquid inlet pump. A circulating pump arranged in parallel with the liquid inlet pump is installed on the liquid inlet pipe through a corresponding guide pipe. The circulating pump is used to circulate the liquid in the tank separator, and its liquid outlet is connected to the liquid inlet of the low-temperature evaporator; the top of the tank separator is connected to the steam inlet of the low-temperature evaporator through the steam compressor and the steam pipe, and the bottom of the low-temperature evaporator is provided with a condensed water discharge end; a plurality of uniform film parts arranged downward in an arc shape are fixedly connected in the tank separator through a coaxially arranged mounting shaft at intervals above and below; the liquid outlet of the low-temperature evaporator is connected to the tank separator through a plurality of parallel liquid return branch pipes, and the liquid outlets of each liquid return branch pipe are arranged one by one on the top of the corresponding uniform film part.

[0013] A corresponding bearing seat is fixedly installed on the outer side of the bottom of the tank separator, and the installation shaft is rotatably and fixedly installed in the tank separator through the bearing seat.

[0014] The mounting shaft is driven to rotate by a corresponding power mechanism, and the power mechanism comprises two impellers which are spaced apart and fixedly arranged in the liquid inlet pipe at the liquid inlet end, a corresponding driving shaft is connected and installed between the two impellers and the driving shaft is fixedly connected to the wheel axle of the impeller, the driving shaft extends into the tank separator and is connected to the mounting shaft through a meshing helical gear set; when the liquid inlet pump is running to feed, the flowing raw material liquid drives the impeller to rotate and drives the driving shaft to rotate, thereby driving the film uniforming member fixed on the mounting shaft to rotate.

[0015] The lower end portion of the mounting shaft extends toward the outside of the tank separator and penetrates into the guide tube disposed below the tank separator. The mounting shaft is driven to rotate by a corresponding power enhancement mechanism. The power enhancement mechanism includes a blade wheel fixedly mounted on the lower end portion of the mounting shaft. The blade wheel is provided with a plurality of blades having a bending direction that is the same as the liquid flow direction in the guide tube, and the edges of the blades are spaced apart from the inner side wall of the guide tube. A protective cover for covering the blade wheel is provided on the outer side of the guide tube.

[0016] The lower side of the installation shaft is located above the protective cover and is connected and installed with a corresponding bearing seat.

[0017] A liquid level sensor for detecting the height of the raw material liquid is installed below the lowest layer of the uniform membrane element in the tank separator. The liquid level sensor is electrically connected to the liquid inlet pump. When the liquid level sensor senses the liquid level, the liquid inlet pump stops running.

[0018] The liquid outlet pipe is equipped with a corresponding liquid outlet valve and a liquid outlet pump.

[0019] The liquid outlet end of the liquid return branch pipe is fixedly supported and provided with a corresponding joint assembly, and the joint assembly includes a three-way joint whose lateral end is connected and fixedly connected to the liquid return branch pipe, the installation shaft passes through the three-way joint and is connected to the longitudinal top end of the three-way joint through a corresponding sealing bearing, and the inner side wall of the longitudinal bottom end of the three-way joint is set at a distance from the installation shaft, and the distance is smaller than the aperture of the lateral end of the three-way joint.

[0020] A corresponding reinforcing fixing rod may also be fixedly connected between the outer side wall of the three-way joint of the joint assembly and the tank separator.

[0021] Advantages of the present invention:

[0022] 1) The present invention adopts a process of pH adjustment, membrane filtration, low-temperature concentration and biochemical and Fenton oxidation to separate and purify PVP from silver-containing wastewater, and performs low-temperature concentration through a low-temperature evaporation and concentration device composed of a tank separator, a steam compressor and a low-temperature evaporator. The tank separator is connected to the low-temperature evaporator through a circulation pump and a circulation pipe, which are used to circulate the liquid in the tank separator and promote the efficiency of evaporation and concentration. The top of the tank separator uses steam for the low-temperature evaporator through the steam compressor to save energy. A plurality of film-leveling parts arranged downward in an arc shape are fixedly connected in the tank separator through a coaxially arranged mounting shaft at intervals above and below. The liquid outlet of the low-temperature evaporator is respectively connected to the tank separator through a plurality of parallel liquid return branch pipes, and the liquid outlets of each liquid return branch pipe are respectively arranged on the top of the corresponding film-leveling part in a one-to-one correspondence. By utilizing the coordinated arrangement of the liquid return pipe and the uniform membrane element, the circulating liquid forms a water film on the upper surface of each uniform membrane element. Compared with the original evaporation surface with only a single layer on the top of the liquid surface, not only the evaporation surface is significantly increased, but also the thickness of the thin water film is small, which effectively promotes the acceleration of evaporation efficiency and the increase of evaporation processing capacity, thereby promoting the concentration process of the low-temperature evaporator.

[0023] 2) The present invention utilizes a bearing seat and a power mechanism to cooperate to drive the rotating installation shaft. When the liquid inlet pump is running to feed, the flowing raw material liquid drives the wheel shaft of the impeller that is fixedly arranged at the liquid inlet end in the liquid inlet pipe to rotate, thereby driving the driving shaft installed on the wheel shaft to rotate; then the terminal end of the driving shaft is extended into the tank separator and connected to the installation shaft through a meshing helical gear set, thereby driving the installation shaft to drive the film-distributing member to rotate slowly. The rotating film-distributing member can disperse the liquid guided on its upper surface in a centrifugal shape, and further evenly disperse the liquid without increasing other energy consumption, so that the liquid film is thinner, and can cooperate with the film-distributing member arranged downward in an arc shape to promote the liquid to continue to be diverted and circulated downward, thereby further improving the evaporation efficiency, shortening the treatment time, and improving the overall treatment efficiency of silver-containing wastewater.

[0024] 3) The present invention further extends the installation shaft to the outside of the tank separator and penetrates into the guide tube arranged below the tank separator, and a blade wheel is fixedly installed at the lower end of the installation shaft. A plurality of blades with the same bending direction as the liquid flow direction in the guide tube are arranged at intervals on the blade wheel, and the edges of the blades are arranged at intervals from the inner wall of the guide tube. The impeller is driven to rotate when the liquid circulates, and then the installation shaft is further driven to rotate. The power mechanism is coordinated to drive the installation shaft to rotate without other energy consumption, thereby improving the practical effect of the present invention.

[0025] 4) The present invention further installs a corresponding liquid level sensor below the bottommost uniform film element in the tank separator, and the liquid level sensor is electrically connected to the liquid inlet pump. When the liquid level sensor senses the liquid level, the liquid inlet pump stops running to control the liquid level in the tank separator. The control of the liquid level can not only limit the liquid volume in the tank separator, effectively avoid increasing the rotation resistance of the installation shaft due to the increase in liquid volume, so as to promote the smooth rotation of the installation shaft, but also effectively avoid the liquid overflowing the uniform film element and making the uniform film element ineffective.

[0026] 5) The present invention adds a joint assembly between the liquid outlet of the return liquid branch pipe and the installation shaft, which is fixedly connected to the return liquid branch pipe through a three-way joint, and then the three-way joint and the installation shaft are connected through a sealing bearing. On the basis of ensuring the rotation of the installation shaft, the water outlet end of the return liquid branch pipe is set directly above the middle of the uniform membrane part by using the three-way joint, and the aperture is set to ensure that the water flow is guided downward along the circumference of the installation shaft to the uniform membrane part, thereby improving the comprehensiveness of liquid dispersion. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the structure of the low-temperature evaporation and concentration equipment in the present invention.

[0028] Figure 2 This is a top view of the installation shaft and impeller.

[0029] In the attached drawing: tank separator 1, steam compressor 2, low-temperature evaporator 3, liquid outlet pipe 4, liquid inlet pump 5, liquid inlet pipe 6, guide pipe 7, circulation pump 8, film uniforming member 9, liquid return branch pipe 10, bearing seat 11, mounting shaft 12, impeller 13, drive shaft 14, helical gear set 15, tee joint 16, blade wheel 17, protective cover 18, liquid level sensor 19, liquid outlet pump 20. DETAILED DESCRIPTION

[0030] In order to facilitate understanding by those skilled in the art, the structure of the present invention is further described in detail with reference to the embodiments in conjunction with the accompanying drawings:

[0031] Embodiment 1

[0032] refer to Figure 1 , a method for separating and purifying PVP from silver-containing wastewater, comprising the following steps:

[0033] S1, pH adjustment: add alkali to the PVP-containing wastewater and mix well to adjust the pH to 3.5-5.0;

[0034] S2, membrane filtration: The PVP-containing wastewater after pH adjustment is concentrated by molecular sieve membrane filtration to produce membrane concentrated water and membrane produced water;

[0035] S3, low-temperature concentration: the membrane concentrated water is introduced into a low-temperature evaporation concentration device for low-temperature evaporation concentration to obtain evaporation concentrated water and evaporation condensate, the evaporation condensate is refluxed to the water inlet end of the molecular sieve membrane and mixed with the PVP-containing wastewater, and the evaporation concentrated water is discharged and collected for reprocessing;

[0036] S4, biochemical and Fenton oxidation: the membrane produced water passes through the biochemical system and Fenton oxidation system in turn and is discharged in compliance with the standards;

[0037] The low-temperature evaporation and concentration equipment used in step S3 includes a tank separator 1, a steam compressor 2 and a low-temperature evaporator 3. The bottom of the tank separator 1 is inclined and connected to the inclined end with a corresponding liquid outlet pipe 4. The side of the tank separator 1 is connected to the raw liquid source through a corresponding liquid inlet pipe 6 and a liquid inlet pump 5. A circulating pump 8 is installed on the liquid inlet pipe 6 through a corresponding guide pipe 7 and is connected in parallel with the liquid inlet pump 5. The circulating pump 8 is used to circulate the liquid in the tank separator 1, and its liquid outlet is connected to the low-temperature evaporator 3. The top of the tank separator 1 is connected to the steam inlet end of the low-temperature evaporator 3 through the steam compressor 2 and the steam pipe, and the bottom of the low-temperature evaporator 3 is provided with a condensed water discharge end; a plurality of film-distributing members 9 arranged downward in an arc shape are fixedly connected at intervals in the tank separator 1 through a coaxially arranged mounting shaft 12; the liquid outlet end of the low-temperature evaporator 3 is connected to the tank separator 1 through a plurality of parallel liquid return branch pipes 10, and the liquid outlet ends of each liquid return branch pipe 10 are respectively arranged at the top of the corresponding film-distributing member 9.

[0038] The present invention adopts a process of pH adjustment, membrane filtration, low-temperature concentration and biochemical and Fenton oxidation to separate and purify PVP from silver-containing wastewater, and performs low-temperature concentration through a low-temperature evaporation and concentration device composed of a tank separator 1, a steam compressor 2 and a low-temperature evaporator 3. The tank separator 1 is connected to the low-temperature evaporator 3 through a circulation pump 8 and a circulation pipe, which is used to circulate the liquid in the tank separator 1 and promote the efficiency of evaporation and concentration. The top of the tank separator 1 uses steam for the low-temperature evaporator 3 through the steam compressor 2 to save energy. A plurality of film-leveling parts 9 arranged downward in an arc shape are fixedly connected in the tank separator 1 at intervals above and below through a coaxially arranged installation shaft 12. The liquid outlet of the low-temperature evaporator 3 is respectively connected to the tank separator 1 through a plurality of parallel liquid return branch pipes 10, and the liquid outlet ends of each liquid return branch pipe 10 are respectively arranged on the top of the corresponding film-leveling part 9 in a one-to-one correspondence. By utilizing the coordinated arrangement of the liquid return branch pipe 10 and the uniform membrane element, the circulating liquid forms a water film on the upper surface of each uniform membrane element. Compared with the original evaporation surface with only a single layer on the top of the liquid surface, not only the evaporation surface is significantly increased, but also the thickness of the thin water film is small, which effectively promotes the acceleration of evaporation efficiency and the increase of evaporation processing capacity, thereby promoting the concentration process of the low-temperature evaporator 3.

[0039] A liquid level sensor 19 for detecting the height of the raw material liquid is installed below the lowest layer of the uniform membrane element 9 in the tank separator 1. The liquid level sensor 19 is electrically connected to the liquid inlet pump 5. When the liquid level sensor 19 senses the liquid level, the liquid inlet pump 5 stops running.

[0040] The present invention further installs a corresponding liquid level sensor 19 below the lowest uniform film member 9 in the tank separator 1. The liquid level sensor 19 is electrically connected to the liquid inlet pump 5. When the liquid level sensor 19 senses the liquid level, the liquid inlet pump 5 stops running to control the liquid level in the tank separator 1. The control of the liquid level can not only limit the liquid volume in the tank separator 1, effectively avoid increasing the rotation resistance of the mounting shaft 12 due to the increase in liquid volume, so as to promote the smooth rotation of the mounting shaft 12, but also effectively avoid the liquid overflowing the uniform film member 9 and making the uniform film member 9 lose its effectiveness.

[0041] The liquid outlet pipe 4 is provided with a corresponding liquid outlet valve and a liquid outlet pump 20 .

[0042] Embodiment 2

[0043] refer to Figure 1-2 The difference between this embodiment and the first embodiment is that a corresponding bearing seat 11 is fixedly installed on the outer side of the bottom of the tank separator 1, and the mounting shaft 12 is rotatably fixedly installed in the tank separator 1 through the bearing seat 11.

[0044] The installation shaft 12 is driven to rotate by a corresponding power mechanism, and the power mechanism includes two impellers 13 that are spaced apart and fixedly arranged in the liquid inlet pipe 6 at the liquid inlet end, and a corresponding drive shaft 14 is connected and installed between the two impellers 13, and the drive shaft 14 is fixedly connected to the wheel axle of the impeller 13, and the drive shaft 14 extends into the tank separator 1 and is connected to the installation shaft 12 through a meshing helical gear set 15; when the liquid inlet pump 5 is running to feed, the flowing raw material liquid drives the impeller 13 to rotate and drives the drive shaft 14 to rotate, thereby driving the film uniforming member 9 fixed to the installation shaft 12 to rotate.

[0045] The present invention utilizes the bearing seat 11 and the power mechanism to cooperate and drive the installation shaft 12 to rotate. When the liquid feed pump 5 is running to feed, the flowing raw material liquid drives the wheel shaft of the impeller 13 which is fixedly arranged at the liquid feed end in the liquid feed pipe 6 to rotate, thereby driving the driving shaft 14 installed on the wheel shaft to rotate; then the terminal end of the driving shaft 14 is extended into the tank separator 1 and connected to the installation shaft 12 through the meshing helical gear set 15, thereby driving the installation shaft 12 to drive the film-distributing member 9 to rotate slowly. The rotating film-distributing member 9 can disperse the liquid guided on its upper surface in a centrifugal shape, and further evenly disperse the liquid without increasing other energy consumption, so that the liquid film is thinner, and can cooperate with the film-distributing member 9 arranged downward in an arc shape to promote the liquid to continue to be diverted and circulated downward, thereby further improving the evaporation efficiency, shortening the treatment time, and improving the overall treatment efficiency of the silver-containing wastewater.

[0046] The lower end of the mounting shaft 12 extends toward the outside of the tank separator 1 and penetrates into the guide tube 7 disposed below the tank separator 1. The mounting shaft 12 is driven to rotate by a corresponding power enhancement mechanism. The power enhancement mechanism includes a blade wheel 17 fixedly mounted on the lower end portion of the mounting shaft 12. The blade wheel 17 is provided with a plurality of blades having a bending direction that is the same as the liquid flow direction in the guide tube 7 at intervals, and the edges of the blades are spaced apart from the inner side wall of the guide tube 7. The outer side of the guide tube 7 is connected to a protective cover 18 for covering the blade wheel 17.

[0047] The present invention further extends the installation shaft 12 to the outside of the tank separator 1 and penetrates into the guide tube 7 provided below the tank separator 1, and a blade wheel 17 is fixedly installed at the lower end of the installation shaft 12. A plurality of blades having the same bending direction as the liquid flow direction in the guide tube 7 are arranged at intervals on the blade wheel 17, and the edges of the blades are arranged at intervals from the inner wall of the guide tube 7. The impeller 13 is driven to rotate when the liquid circulates, and the installation shaft 12 is further driven to rotate. The installation shaft 12 is driven to rotate in coordination with the power mechanism without other energy consumption, thereby improving the practical effect of the present invention.

[0048] The lower side of the installation shaft 12 is located above the protective cover 18 and is connected and installed with a corresponding bearing seat 11, so as to further enhance the installation stability of the installation shaft 12.

[0049] The liquid outlet end of the liquid return branch pipe 10 is fixedly supported with a corresponding joint assembly, and the joint assembly includes a three-way joint 16 whose transverse end is connected and fixedly connected to the liquid return branch pipe 10, and the installation shaft 12 passes through the three-way joint 16 and is connected to the longitudinal top end of the three-way joint 16 through a corresponding sealing bearing, and the inner side wall of the longitudinal bottom end of the three-way joint 16 is spaced apart from the installation shaft 12, and the spacing is smaller than the aperture of the transverse end of the three-way joint 16.

[0050] The present invention adds a joint assembly between the liquid outlet of the liquid return branch pipe 10 and the installation shaft 12, which is fixedly connected to the liquid return branch pipe 10 through a three-way joint, and then the three-way joint and the installation shaft 12 are connected through a sealed bearing. On the basis of ensuring the rotation of the installation shaft 12, the water outlet end of the liquid return branch pipe 10 is set directly above the middle of the membrane uniformity member 9 by using the three-way joint, and the aperture is set to ensure that the water flow is guided downward along the circumference of the installation shaft 12 to the membrane uniformity member 9, thereby improving the comprehensiveness of liquid dispersion.

[0051] A corresponding reinforcing fixing rod may also be fixedly connected between the outer side wall of the three-way joint 16 of the joint assembly and the tank separator 1 to improve the installation stability of the joint assembly.

[0052] It should be pointed out that the implementation principle and technical effects of this embodiment are the same as those of Embodiment 1. For the sake of brief description, for matters not mentioned in this embodiment, reference may be made to the corresponding contents in Embodiment 1.

[0053] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for separating and purifying PVP from silver-containing wastewater, characterized in that: The steps include: S1, pH adjustment: add alkali to the PVP-containing wastewater and mix well to adjust the pH to 3.5-5.0; S2, membrane filtration: The PVP-containing wastewater after pH adjustment is concentrated by molecular sieve membrane filtration to produce membrane concentrated water and membrane produced water; S3, low-temperature concentration: the membrane concentrated water is introduced into a low-temperature evaporation concentration device for low-temperature evaporation concentration to obtain evaporation concentrated water and evaporation condensate, the evaporation condensate is refluxed to the water inlet end of the molecular sieve membrane and mixed with the PVP-containing wastewater, and the evaporation concentrated water is discharged and collected for reprocessing; S4, biochemical and Fenton oxidation: the membrane produced water passes through the biochemical system and Fenton oxidation system in turn and is discharged in compliance with the standards; The low-temperature evaporation and concentration equipment used in step S3 comprises a tank separator (1), a steam compressor (2) and a low-temperature evaporator (3); the bottom of the tank separator (1) is inclined and connected to the inclined end with a corresponding liquid outlet pipe (4); the side of the tank separator (1) is connected to the raw liquid source through a corresponding liquid inlet pipe (6) and a liquid inlet pump (5); a circulating pump (8) is installed on the liquid inlet pipe (6) through a corresponding flow guide pipe (7) and is connected in parallel with the liquid inlet pump (5); the circulating pump (8) is used to circulate the liquid in the tank separator (1), and its liquid outlet is connected to the low-temperature evaporator (3); The liquid inlet end of the evaporator (3); the top of the tank separator (1) is connected to the steam inlet end of the low-temperature evaporator (3) through the steam compressor (2) and the steam pipe, and the bottom of the low-temperature evaporator (3) is provided with a condensed water discharge end; a plurality of film-distributing members (9) arranged downward in an arc shape are fixedly connected in the tank separator (1) via a coaxially arranged mounting shaft (12) at intervals above and below; the liquid outlet end of the low-temperature evaporator (3) is connected to the tank separator (1) through a plurality of parallel liquid return branch pipes (10), and the liquid outlet ends of the respective liquid return branch pipes (10) are respectively arranged at the top of the corresponding film-distributing member (9).

2. A method for separating and purifying PVP in silver-containing wastewater according to claim 1, characterized in that: A corresponding bearing seat (11) is fixedly mounted on the outer side of the bottom of the tank separator (1), and the mounting shaft (12) is rotatably fixedly mounted in the tank separator (1) via the bearing seat (11).

3. A method for separating and purifying PVP in silver-containing wastewater according to claim 2, characterized in that: The installation shaft (12) is driven to rotate by a corresponding power mechanism, and the power mechanism comprises two impellers (13) which are spaced apart and fixedly arranged in the liquid inlet pipe (6) at the liquid inlet end. A corresponding drive shaft (14) is connected and installed between the two impellers (13), and the drive shaft (14) is fixedly connected to the wheel axle of the impeller (13). The drive shaft (14) extends into the tank separator (1) and is connected to the installation shaft (12) through a meshing helical gear set (15). When the liquid inlet pump (5) is running to feed, the flowing raw material liquid drives the impeller (13) to rotate and drives the drive shaft (14) to rotate, thereby driving the uniform film member (9) fixedly connected to the installation shaft (12) to rotate.

4. A method for separating and purifying PVP in silver-containing wastewater according to claim 2, characterized in that: The lower end of the mounting shaft (12) extends toward the outside of the tank separator (1) and penetrates into the guide tube (7) arranged below the tank separator (1). The mounting shaft (12) is driven to rotate by a corresponding power enhancement mechanism. The power enhancement mechanism comprises a blade wheel (17) fixedly mounted on the lower end of the mounting shaft (12). The blade wheel (17) is provided with a plurality of blades with a bending direction that is the same as the direction of liquid flow in the guide tube (7) at intervals, and the edges of the blades are spaced apart from the inner side wall of the guide tube (7). The outer side of the guide tube (7) is connected to a protective cover (18) for covering the blade wheel (17).

5. A method for separating and purifying PVP in silver-containing wastewater according to claim 4, characterized in that: The lower side of the installation shaft (12) is located above the protective cover (18) and is also connected and installed with a corresponding bearing seat (11).

6. A method for separating and purifying PVP in silver-containing wastewater according to claim 1, characterized in that: A liquid level sensor (19) for detecting the height of the raw material liquid is installed below the lowest layer of the uniform membrane element (9) in the tank separator (1). The liquid level sensor (19) is electrically connected to the liquid inlet pump (5). When the liquid level sensor (19) senses the liquid level, the liquid inlet pump (5) stops running.

7. A method for separating and purifying PVP in silver-containing wastewater according to claim 1, characterized in that: The liquid outlet pipe (4) is provided with a corresponding liquid outlet valve and a liquid outlet pump (20).

8. A method for separating and purifying PVP in silver-containing wastewater according to claim 1, characterized in that: The liquid outlet end of the liquid return branch pipe (10) is fixedly supported and provided with a corresponding joint assembly, the joint assembly comprising a three-way joint (16) whose transverse end is connected and fixedly connected to the liquid return branch pipe (10), the installation shaft (12) passes through the three-way joint (16) and is connected to the longitudinal top end of the three-way joint (16) through a corresponding sealing bearing, the inner side wall of the longitudinal bottom end of the three-way joint (16) is spaced apart from the installation shaft (12), and the spacing is smaller than the aperture of the transverse end of the three-way joint (16).

9. A method for separating and purifying PVP in silver-containing wastewater according to claim 8, characterized in that: A corresponding reinforcing fixing rod may also be fixedly connected between the outer side wall of the three-way joint (16) of the joint assembly and the tank separator (1).

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