A method and device for purifying combined alkali mother II solution by PE membrane method

Abstract

The present invention relates to a method and device for purifying mother liquor by membrane method, wherein hot mother II liquor from combined alkali is sent to a sand filter device through a mother II liquid barrel under the action of a pump, and particulate matter and oily flocculants with a particle size of >1.0 mm are filtered out; the mother II liquor filtered by the sand filter device is sent to the bottom of a PE membrane filter device, and the filtrate after filtration by the PE membrane filter device is collected by a filtrate barrel, and then sent to an ammonia absorption process by a pump, and then sent to a carbonization alkali process to produce a soda ash product; the concentrated liquid at the bottom of the PE membrane filter device flows through a concentrated liquid storage barrel for collection; the crystal slurry in the concentrated liquid barrel is pumped to a filter press process, and the obtained solid waste is treated as general waste together with salt mud; or it is pumped to a salting out process to produce agricultural ammonium products. Compared with the method of purifying mother II liquor by ceramic membrane, the PE membrane filter device has a simple processing process, is easy to operate, has a low membrane production cost, and the turbidity of the treated mother II liquor can also meet production requirements.

Description

Technical Field

[0001] The present invention relates to a method and a device for purifying mother liquor by membrane method, and in particular to a method and a device for purifying mother II liquor of combined alkali by polyethylene (PE) membrane method. Background Art

[0002] In the process of producing soda ash by the combined alkali process, the content of calcium and magnesium ions in the mother II liquid needs to be strictly controlled. Their concentration will directly determine the turbidity of the solution and the whiteness of the product, thus affecting the quality of the product. The current purification process of the mother II liquid by the combined alkali process mainly adopts the first-level clarification process of the clarification tank to treat water-insoluble substances such as calcium and magnesium. However, this process is easily affected by production fluctuations. In addition, the effective clarification area of ​​the clarification tank is generally small, resulting in limited removal of calcium and magnesium ions in the mother II liquid after clarification. In addition, this process also has the disadvantages of large equipment size and high investment. Therefore, in order to improve the quality of soda ash products, it is urgent to optimize and improve the existing mother II liquid purification process.

[0003] Although there have been reports on relevant process optimization and improvement, there are still many drawbacks in these processes. For example, there is a process of treating mother II liquor using a ceramic membrane method (patents CN103523802B, CN104437097B, CN104445549B). Although this process can significantly reduce the turbidity of the mother liquor (<10NTU), it requires the use of two-stage ceramic microfiltration membranes to purify the mother II liquor, which makes the final purification process long, energy-intensive, and complex to operate. In addition, due to the limitations of existing membrane production technology, ceramic membranes account for about 2 / 3 of the operating costs, and the initial investment in device construction is very large. When Jiangxi Ganzhong Chlor-Alkali Company and Hebei Shenghua Chemical Co., Ltd. used the POLYMER / PV material membrane planted by Mingtai Company for purification tests, an admixture was added in advance to reduce the Ca in the mother liquor. 2+ The calcium precipitate is precipitated and then removed by membrane filtration. In the initial stage of filtration, 100% of solid particles can be intercepted and the turbidity of the filtrate is <10NTU. However, the ability of the planted membrane to filter the mother liquor is limited (<1.0m 3 / (m 2 h), the effective components in the mother liquor are lost more, and the impurity content of the inlet mother liquor has a greater impact on the filtration speed. In the paper "Purification of the mother liquor of soda ash to improve the quality of soda ash products", the LAROX purification filter was used to filter the mother II liquid by adsorptive filtration. Although the turbidity and water-insoluble content in the mother liquor can be reduced to below 10NTU or 10ppm, the filtration capacity of the filter can only be within 0.4-0.8m 3 / (m 2h) range, the mother liquor treatment capacity is far from meeting the needs of industrial production; Patent CN200820026794 provides a combined alkali mother liquor purification equipment system, which makes the turbidity range of the mother liquor less than 50NTU by adding and controlling the flow rate of flocculants. The mother liquor purification effect of this process is limited. In addition, the introduction of flocculants will make the surface of the filtered solids viscous, which will eventually increase the difficulty of filtering the crystal slurry at the bottom of the clarification tank and reduce the service life of the equipment.

[0004] Therefore, it is urgent to invent a low-cost, high-efficiency treatment technology for removing water-insoluble substances such as calcium and magnesium in mother II liquid and thereby reducing the turbidity of mother II liquid. Summary of the invention

[0005] The purpose of the present invention is to reduce the cost of mother II liquid treatment, improve the mother II liquid treatment capacity, simplify the operation process, and provide a method and device for purifying mother II liquid of combined alkali by PE membrane method, so that the turbidity in the mother II liquid after treatment is lower than 10NTU, meeting the needs of producing high-quality soda ash products by combined alkali method.

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

[0007] A device for purifying mother II liquid of combined alkali by PE membrane method, characterized in that it comprises a hot mother II liquid barrel 1, a slurry pump 2, a sand filter device 3, a PE membrane filter device 4, a filtrate barrel 5, a centrifugal pump 6, an ammonia absorption process 7, a carbonization alkali process 8, a concentrated liquid barrel 9, a concentrated liquid pump 10, a filter press process 11, a salting out process 12, a compressed air tank 13 and related pipelines; the hot mother II liquid from the combined alkali enters the hot mother II liquid barrel 1, the outlet of the hot mother II liquid barrel 1 is connected to the top inlet of the sand filter device 3 through the slurry pump 2, the bottom outlet of the sand filter device is connected to the bottom inlet of the PE membrane filter device 4 through a pipeline, and the side outlet of the sand filter device is connected to the side inlet of the concentrated liquid barrel 9 through a pipeline; An inlet connected to the outlet pipeline of the compressed air tank 13 is provided at the bottom of the PE membrane filter device 4, the side outlet of the PE membrane filter device 4 is connected to the filtrate barrel 5 through a pipeline, and the bottom outlet of the PE membrane filter device is connected to the side inlet of the concentrate barrel 9 through a pipeline; the outlet of the filtrate barrel 5 is connected to the centrifugal pump 6, the ammonia absorption process 7, and the carbonization alkali making process 8 in sequence through a pipeline; a branch is separated from the outlet pipeline of the centrifugal pump 6 and connected to the bottom inlet of the sand filter device 3; the outlet of the concentrate barrel 9 is connected to the concentrate pump 10 through a pipeline, and the outlet pipeline of the concentrate pump 10 is divided into two branches, one branch is connected to the filter press process 11 through a pipeline, and the other branch is connected to the salting-out process 12 through a pipeline.

[0008] The present invention provides a method for purifying combined alkali mother II solution by PE membrane method, comprising the following steps:

[0009] (1) The hot mother II liquid from the combined alkali is sent to the sand filter device through the mother II liquid barrel under the action of a pump to filter and remove particles with a particle size greater than 1.0 mm and oily flocculants;

[0010] (2) The mother II liquid filtered by the sand filter is sent to the bottom of the PE membrane filter. The filtrate after filtering by the PE membrane filter is collected in a filtrate bucket and then sent to the ammonia absorption process by a pump, and then sent to the carbonization alkali production process to produce soda ash products;

[0011] (3) The concentrate at the bottom of the PE membrane filtration device flows through a concentrate storage tank for collection;

[0012] (4) The slurry in the concentrate tank is pumped to the filter press process, and the solid waste obtained is treated as general waste together with the salt mud; or it is pumped to the salting out process to produce agricultural ammonium products.

[0013] The hot mother II solution in step (1) is characterized by: Ca 2+ The concentration is 70-100ppm, Mg 2+ The concentration is 30-50ppm, the temperature is 27℃-30℃, and the turbidity is 80-130NTU.

[0014] The operating pressure of the PE membrane filtration device in step (2) is 0.2 MPa, and the pore size of the PE membrane assembly is 5-10 um.

[0015] The pressure of the air in the compressed air tank in the step (3) is 0.6 MPa.

[0016] Preferably, the sand filter device is backwashed with the filtrate after membrane filtration every 12 hours to remove the retained matter on the sand filter layer, and the backwash liquid is sent to the concentrate tank.

[0017] The bottom of the PE membrane filtration device 4 is provided with an inlet connected to the compressed air tank 13. Preferably, the air in the compressed air tank is used to aerate and backwash the PE membrane every 2 hours to remove the retained matter attached to the membrane assembly and reduce the pressure difference between the inside and outside of the membrane assembly.

[0018] The concentrated liquid pump 10 pipeline is connected to the filter pressing process mainly to utilize the solids obtained in the filter pressing process and the salt mud to be treated as general waste; the concentrated liquid pump 10 pipeline is connected to the salting out process mainly to utilize the salting out process to obtain the agricultural ammonium product.

[0019] The sand particle size in the sand filter device in step (2) is 1.0 mm; the characteristics of the filtrate at the top after filtering through the PE membrane device are: temperature of 27°C-30°C, turbidity of 4-10 NTU, Ca 2+ The concentration is 20-30ppm, Mg 2+ The concentration is 10-18ppm; the preferred processing capacity of the PE membrane filtration device is 1.0-2.0m3 / (m 2 h).

[0020] In the step (3), the solid volume content in the concentrated liquid is above 40%, and the air pressure in the compressed air tank is 0.6 MPa.

[0021] The sand filter device of the present invention is mainly used to remove particles with larger particle sizes and oily flocculants, so as to avoid the difficulty of backwashing due to the presence of a small amount of oil on the surface of the PE membrane component in the later stage.

[0022] We proposed to send the concentrated liquid to the filtration process in order to solve the problem of the whereabouts of the concentrated liquid when the ammonium amine production line is shut down due to production fluctuations; sending it to the salting out process is mainly to improve the utilization rate of raw materials.

[0023] The method of the present invention has the following advantages:

[0024] (1) Compared with the ceramic membrane purification method of mother II liquid, the PE membrane method has a simple treatment process, easy operation, low membrane production cost, and the turbidity of the treated mother II liquid can also meet production needs.

[0025] (2) No additives or flocculants are required during the purification of the mother II liquid, which reduces the operating intensity. The filtrate is used as the backwash liquid of the sand filter device to avoid the problem of mother liquid expansion.

[0026] (3) The solids in the concentrate are effectively treated without causing secondary pollution.

[0027] (4) Compared with the processing capacity of mother II liquid by LAROX purification filter and planting membrane process, the processing capacity of PE membrane filtration device is significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The present invention is a schematic diagram of a PE membrane method for purifying alkali mother II liquid.

[0029] Among them: 1-hot mother II liquid barrel, 2-slurry pump, 3-sand filter device, 4-PE membrane filtration device, 5-filtrate barrel, 6-centrifugal pump, 7-ammonia absorption process, 8-carbonization alkali making process, 9-concentrated liquid barrel, 10-concentrated liquid pump, 11-filter pressure process, 12-salting out process, 13-compressed air tank.

[0030] Figure 2 The invention discloses a PE membrane method for purifying mother II liquid before and after treatment by a device for purifying mother II liquid of combined alkali. DETAILED DESCRIPTION

[0031] The present invention is described in detail below with reference to specific embodiments.

[0032] The device for purifying the mother II liquid of the combined alkali by the PE membrane method of the present invention comprises a hot mother II liquid barrel 1, a slurry pump 2, a sand filter device 3, a PE membrane filter device 4, a filtrate barrel 5, a centrifugal pump 6, an ammonia absorption process 7, a carbonization alkali process 8, a concentrated liquid barrel 9, a concentrated liquid pump 10, a filter press process 11, a salting-out process 12, a compressed air tank 13 and related pipelines; the hot mother II liquid from the combined alkali enters the hot mother II liquid barrel 1, the outlet of the hot mother II liquid barrel 1 is connected to the top inlet of the sand filter device 3 through the slurry pump 2, the bottom outlet of the sand filter device is connected to the bottom inlet of the PE membrane filter device 4 through a pipeline, and the side outlet of the sand filter device is connected to the side inlet of the concentrated liquid barrel 9 through a pipeline; An inlet connected to the outlet pipeline of the compressed air tank 13 is provided at the bottom of the E membrane filter device 4, the side outlet of the PE membrane filter device 4 is connected to the filtrate barrel 5 through a pipeline, and the bottom outlet of the PE membrane filter device is connected to the side inlet of the concentrate barrel 9 through a pipeline; the outlet of the filtrate barrel 5 is connected to the centrifugal pump 6, the ammonia absorption process 7, and the carbonization alkali making process 8 in sequence through a pipeline; a branch is separated from the outlet pipeline of the centrifugal pump 6 and connected to the bottom inlet of the sand filter device 3; the outlet of the concentrate barrel 9 is connected to the concentrate pump 10 through a pipeline, and the outlet pipeline of the concentrate pump 10 is divided into two branches, one of which is connected to the filter press process 11 through a pipeline, and the other is connected to the salting-out process 12 through a pipeline.

[0033] The main function of the inlet pipelines at the bottom 3 of the sand filter device is to backwash the sand filter device with the filtrate after membrane filtration every 12 hours to remove the retained materials on the sand filter layer;

[0034] The bottom of the PE membrane filtration device 4 is provided with an inlet connected to the compressed air tank 13, which is used to aerate and backwash the membrane assembly with high-pressure air every 2 hours to remove the retained matter attached to the membrane assembly and reduce the pressure difference between the inside and outside of the membrane assembly;

[0035] The concentrate pump 10 pipeline is connected to the filter pressing process mainly to utilize the solids obtained in the filter pressing process and the salt mud to be treated as general waste.

[0036] The concentrate pump 10 pipeline is connected to the salting-out process mainly to sell the agricultural ammonium obtained in the salting-out process as a product.

[0037] As shown in the accompanying drawings, a method and device for purifying combined alkali mother II liquid by a PE membrane method of the present invention comprises the following steps:

[0038] (1) The hot mother II liquid from the combined alkali is sent to the sand filter device through the mother II liquid barrel under the action of the pump, and the particles with larger particle size (>1.0mm) and oily flocculants are removed by preliminary filtration;

[0039] The hot mother II liquid is characterized by: Ca 2+ The concentration is 70-100ppm, Mg 2+The concentration is 30-50ppm, the temperature is 27℃-30℃, and the turbidity is 80-130NTU;

[0040] (2) The mother II liquid filtered by the sand filter is sent to the bottom of the PE membrane filter. The filtrate after filtering by the PE membrane filter is collected in the filtrate bucket and then sent to the ammonia absorption process by a pump, and then sent to the carbonization alkali production process to produce soda ash products; in addition, 1% of the total filtrate is taken from the bottom of the sand filter every 12 hours to flow into the device for backwashing, and the backwashing liquid is sent to the concentrate bucket;

[0041] The sand particle size in the sand filter device is 1.0 mm;

[0042] The characteristics of the filtrate at the top after filtration by the PE membrane device are: temperature of 27°C-30°C, turbidity of 4-10NTU, Ca 2+ The concentration is 20-30ppm, Mg 2+ Concentration is 10-18ppm;

[0043] The operating pressure of the PE membrane filtration device is 0.2MPa, and the processing capacity is 1.0-2.0m 3 / (m 2 h), the pore size of the PE membrane component is 5-10um;

[0044] (3) The concentrated liquid at the bottom of the PE membrane filtration device flows through the concentrated liquid storage tank for collection, and the PE membrane is aerated and backwashed every 2 hours using air from a compressed air tank;

[0045] The solid volume content in the concentrated liquid is above 40%, and the air pressure in the compressed air tank is 0.6 MPa.

[0046] (4) The slurry in the concentrate tank is pumped to the filter press process, and the solid waste obtained is treated as general waste together with the salt mud; or it is pumped to the salting out process to produce agricultural ammonium products.

[0047] Example 1

[0048] (1) The hot mother II liquid from the combined alkali is sent to a sand filter device with a sand particle size of 1.0 mm through a mother II liquid barrel under the action of a pump, and a preliminary filtration is performed to remove particles with larger particle sizes and oily flocculants;

[0049] (2) The mother II liquid filtered by the sand filter device is sent to the bottom of the PE membrane filter device with a pore size of 5um. After the PE membrane is filtered, the filtrate at the top is collected in the filtrate bucket and then sent to the ammonia absorption process by a pump, and then sent to the carbonization alkali production process to produce soda ash products. Every 12 hours, 1% of the total filtrate is taken from the bottom of the sand filter device to flow into the device for backwashing, and the backwashing liquid is sent to the concentrate bucket;

[0050] (3) The concentrated liquid at the bottom of the PE membrane filtration device flows through the concentrated liquid storage tank for collection, and the PE membrane is aerated and backwashed every 2 hours using air from a compressed air tank;

[0051] (4) The slurry in the concentrate barrel is pumped to the salting-out process to produce agricultural ammonium products.

[0052] After testing: the temperature of the hot mother II liquid before treatment was 28℃, the turbidity was 80NTU, and the Ca 2+ The concentration is 70ppm, Mg 2+ The concentration is 30ppm; the filtrate temperature after passing through the PE membrane filter is 28℃, the turbidity is 4NTU, and the Ca 2+ The concentration is 20ppm, Mg 2+ The concentration is 10ppm and the processing capacity of the PE membrane filter is 1.2m 3 / (m 2 h), the solid volume percentage of the concentrate is 50%.

[0053] Example 2

[0054] (1) The hot mother II liquid from the combined alkali is sent to a sand filter device with a sand particle size of 1.0 mm through a mother II liquid barrel under the action of a pump, and a preliminary filtration is performed to remove particles with larger particle sizes and oily flocculants;

[0055] (2) The mother II liquid filtered by the sand filter device is sent to the bottom of the PE membrane filter device with a pore size of 5um. After the PE membrane is filtered, the filtrate at the top is collected in the filtrate bucket and most of the filtrate is pumped to the ammonia absorption process, and then sent to the carbonization alkali production process to produce soda ash products. Every 12 hours, 1% of the total filtrate is taken from the bottom of the sand filter device to flow into the device for backwashing, and the backwashing liquid is sent to the concentrate bucket;

[0056] (3) The concentrated liquid at the bottom of the PE membrane filtration device flows through the concentrated liquid storage tank for collection, and the PE membrane is aerated and backwashed every 2 hours using air from a compressed air tank;

[0057] (4) The slurry in the concentrate tank is pumped to the filter press process, and the resulting solid waste is treated as general waste together with the salt mud.

[0058] After testing: the temperature of the hot mother II liquid before treatment was 28℃, the turbidity was 130NTU, and the Ca 2+ The concentration is 100ppm, Mg 2+ The concentration is 50ppm; the filtrate temperature after passing through the PE membrane filter is 28℃, the turbidity is 5NTU, and the Ca 2+ The concentration is 25ppm, Mg 2+ The concentration is 13ppm and the processing capacity of the PE membrane filter is 1.0m 3 / (m2 h), the solid volume percentage of the concentrate is 52%.

[0059] Example 3

[0060] (1) The hot mother II liquid from the combined alkali is sent to a sand filter device with a sand particle size of 1.0 mm through a mother II liquid barrel under the action of a pump, and a preliminary filtration is performed to remove particles with larger particle sizes and oily flocculants;

[0061] (2) The mother II liquid filtered by the sand filter device is sent to the bottom of the PE membrane filter device with a pore size of 10um. After the PE membrane is filtered, the filtrate at the top is collected in the filtrate bucket and most of the filtrate is pumped to the ammonia absorption process, and then sent to the carbonization alkali production process to produce soda ash products. Every 12 hours, 1% of the total filtrate is taken from the bottom of the sand filter device to flow into the device for backwashing, and the backwashing liquid is sent to the concentrate bucket;

[0062] (3) The concentrate at the bottom of the PE membrane filtration device flows through the concentrate storage tank for collection, and the PE membrane is aerated and backwashed with factory air every 2 hours;

[0063] (4) The slurry in the concentrate barrel is pumped all the way to the filter press process, and the solid waste obtained is treated as general waste together with the salt mud; it is also pumped all the way to the salting out process to produce agricultural ammonium products.

[0064] After testing: the temperature of the hot mother II liquid before treatment was 30℃, the turbidity was 130NTU, and the Ca 2+ The concentration is 100ppm, Mg 2+ The concentration is 50ppm; the filtrate temperature after passing through the PE membrane filter is 30℃, the turbidity is 10NTU, and the Ca 2+ The concentration is 30ppm, Mg 2 + The concentration is 18ppm and the processing capacity of the PE membrane filter is 2.0m 3 / (m 2 h), the solid volume percentage of the concentrate is 41%.

[0065] Example 4

[0066] (1) The hot mother II liquid from the combined alkali is sent to a sand filter device with a sand particle size of 1.0 mm through a mother II liquid barrel under the action of a pump, and a preliminary filtration is performed to remove particles with larger particle sizes and oily flocculants;

[0067] (2) The mother II liquid filtered by the sand filter device is sent to the bottom of the PE membrane filter device with a pore size of 10um. After the PE membrane is filtered, the filtrate at the top is collected in the filtrate bucket and most of the filtrate is pumped to the ammonia absorption process, and then sent to the carbonization alkali production process to produce soda ash products. Every 12 hours, 1% of the total filtrate is taken from the bottom of the sand filter device to flow into the device for backwashing, and the backwashing liquid is sent to the concentrate bucket;

[0068] (3) The concentrate at the bottom of the PE membrane filtration device flows through the concentrate storage tank for collection, and the PE membrane is aerated and backwashed with factory air every 2 hours;

[0069] (4) The slurry in the concentrate barrel is pumped all the way to the filter press process, and the solid waste obtained is treated as general waste together with the salt mud; it is also pumped all the way to the salting out process to produce agricultural ammonium products.

[0070] After testing: the temperature of the hot mother II liquid before treatment was 27℃, the turbidity was 120NTU, and the Ca 2+ The concentration is 90ppm, Mg 2+ The concentration is 40ppm; the filtrate temperature after passing through the PE membrane filter is 27℃, the turbidity is 8NTU, and the Ca 2+ The concentration is 26ppm, Mg 2+ The concentration is 15ppm and the processing capacity of the PE membrane filter is 1.9m 3 / (m 2 h), the solid volume percentage of the concentrate is 43%.

[0071] Example 5

[0072] (1) The hot mother II liquid from the combined alkali is sent to a sand filter device with a sand particle size of 1.0 mm through a mother II liquid barrel under the action of a pump, and a preliminary filtration is performed to remove particles with larger particle sizes and oily flocculants;

[0073] (2) The mother II liquid filtered by the sand filter device is sent to the bottom of the PE membrane filter device with a pore size of 8um. After the PE membrane is filtered, the filtrate at the top is collected in the filtrate bucket and most of the filtrate is pumped to the ammonia absorption process, and then sent to the carbonization alkali production process to produce soda ash products. Every 12 hours, 1% of the total filtrate is taken from the bottom of the sand filter device to flow into the device for backwashing, and the backwashing liquid is sent to the concentrate bucket;

[0074] (3) The concentrate at the bottom of the PE membrane filtration device flows through the concentrate storage tank for collection, and the PE membrane is aerated and backwashed with factory air every 2 hours;

[0075] (4) The slurry in the concentrate barrel is pumped all the way to the filter press process, and the solid waste obtained is treated as general waste together with the salt mud; it is also pumped all the way to the salting out process to produce agricultural ammonium products.

[0076] After testing: the temperature of the hot mother II liquid before treatment was 27℃, the turbidity was 120NTU, and the Ca 2+ The concentration is 90ppm, Mg 2+ The concentration is 40ppm; the filtrate temperature after passing through the PE membrane filter is 27℃, the turbidity is 6NTU, and the Ca 2+ The concentration is 23ppm, Mg 2+ The concentration is 14ppm and the processing capacity of the PE membrane filter is 1.7m 3 / (m 2 h), the solid volume percentage of the concentrate is 45%.

[0077] The technical solutions disclosed and proposed by the present invention can be realized by those skilled in the art by referring to the contents of this article and appropriately changing the conditions, routes and other links. Although the methods and preparation techniques of the present invention have been described through preferred embodiments, relevant technicians can obviously modify or re-combine the methods and technical routes described herein without departing from the content, spirit and scope of the present invention to realize the final preparation technology. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all considered to be included in the spirit, scope and content of the present invention.

Claims

1. A device for purifying alkali mother II liquid by PE membrane method, characterized in that The invention comprises a hot mother II liquid barrel (1), a slurry pump (2), a sand filter device (3), a PE membrane filter device (4), a filtrate barrel (5), a centrifugal pump (6), an ammonia absorption process (7), a carbonization alkali process (8), a concentrate barrel (9), a concentrate pump (10), a filter press process (11), a salting-out process (12), a compressed air tank (13) and related pipelines; the hot mother II liquid from the combined alkali enters the hot mother II liquid barrel (1), the outlet of the hot mother II liquid barrel (1) is connected to the top inlet of the sand filter device (3) through the slurry pump (2), the bottom outlet of the sand filter device is connected to the bottom inlet of the PE membrane filter device (4) through a pipeline, and the side outlet of the sand filter device is connected to the side inlet of the concentrate barrel (9) through a pipeline; the bottom of the PE membrane filter device (4) is provided with a connection The inlet of the outlet pipeline of the compressed air tank (13) and the side outlet of the PE membrane filter device (4) are connected to the filtrate barrel (5) through a pipeline, and the bottom outlet of the PE membrane filter device is connected to the side inlet of the concentrate barrel (9) through a pipeline; the outlet of the filtrate barrel (5) is connected to the centrifugal pump (6), the ammonia absorption process (7), and the carbonization alkali production process (8) in sequence through a pipeline; a branch of the outlet pipeline of the centrifugal pump (6) is connected to the bottom inlet of the sand filter device (3); the outlet of the concentrate barrel (9) is connected to the concentrate pump (10) through a pipeline, and the outlet pipeline of the concentrate pump (10) is divided into two branches, one of which is connected to the filter press process (11) through a pipeline, and the other is connected to the salting process (12) through a pipeline; the operating pressure of the PE membrane filter device is 0.2 MPa, and the pore size of the PE membrane assembly is 5-10µm.

2. A method for purifying alkali mother II liquid by PE membrane method using the device of claim 1, characterized in that The following steps are involved: (1) The hot mother II liquid from the combined alkali is sent to the sand filter device through the mother II liquid barrel under the action of a pump to filter and remove particles with a particle size greater than 1.0 mm and oily flocculants; (2) The mother II liquid filtered by the sand filter is sent to the bottom of the PE membrane filter. The filtrate after filtering by the PE membrane filter is collected in a filtrate bucket and then sent to the ammonia absorption process by a pump, and then sent to the carbonization alkali production process to produce soda ash products; (3) The concentrate at the bottom of the PE membrane filtration device flows through a concentrate storage tank for collection; (4) The slurry in the concentrate tank is pumped to the filter press process, and the solid waste obtained is treated as general waste together with the salt mud; or it is pumped to the salting out process to produce agricultural ammonium products.

3. The method according to claim 2, characterized in that The hot mother II solution in step (1) is characterized by: Ca 2+ The concentration is 70-100 ppm, Mg 2+ The concentration is 30-50 ppm and the temperature is 27 o C-30 o C, turbidity is 80-130 NTU.

4. The method according to claim 2, characterized in that The pressure of the air in the compressed air tank is 0.6 Mpa.

5. The method according to claim 2, characterized in that The filtrate after membrane filtration is used to backwash the sand filter device every 12 hours to remove the retained materials on the sand filter layer, and the backwash liquid is sent to the concentrate tank.

6. The method according to claim 2, characterized in that The bottom of the PE membrane filtration device (4) is provided with an inlet connected to a compressed air tank (13), and the air in the compressed air tank is used to aerate and backwash the PE membrane every 2 hours to remove retained matter attached to the membrane assembly and reduce the pressure difference between the inside and outside of the membrane assembly.

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