Concentration method of sodium sulfate solution

Abstract

The invention belongs to the technical field of sodium sulfate-containing high-salinity wastewater treatment, and particularly relates to a concentration method of a sodium sulfate solution. The method is scientific and reasonable in design, sodium sulfate in the solution is crystallized and separated out through low-temperature crystallization, and then sodium sulfate decahydrate solid and low-temperature filtrate are produced through centrifugal separation. And meanwhile, by-produced heat in the low-temperature crystallization refrigeration process is used for heating low-temperature filtrate, after the heated filtrate is filtered by a membrane, produced purified water is discharged after reaching the standard, and produced strong brine is frozen, crystallized and concentrated again or enters a later stage for treatment. According to the invention, a freezing crystallization and film adding technology is utilized to partially or completely replace evaporative crystallization, so that the investment cost and the operation cost for treating the high-salinity wastewater containing sodium sulfate are greatly reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of sodium sulfate-containing high-salt wastewater treatment, and particularly relates to a method for concentrating a sodium sulfate solution. Background Art

[0002] The solution of high sodium sulfate wastewater is generally concentrated to 12%-18% by membrane, and then evaporated and crystallized by MVR or multi-effect evaporation system. However, whether it is MVR or multi-effect evaporation and crystallization, the investment cost and operation cost are very high, so many high-salinity wastewater projects cannot afford the high treatment costs and can only be shelved.

[0003] In view of this, the inventors hope to provide a method for concentrating a sodium sulfate solution, which can reduce the treatment cost of a solution containing high sodium sulfate content wastewater. Summary of the invention

[0004] The object of the present invention is to overcome the above-mentioned problems existing in the conventional technology and to provide a method for concentrating a sodium sulfate solution.

[0005] In order to achieve the above technical objectives and the above technical effects, the present invention is implemented through the following technical solutions:

[0006] The present invention provides a method for concentrating a sodium sulfate solution, comprising the following steps:

[0007] S1, cooling the high concentration sodium sulfate solution to allow sodium sulfate to crystallize;

[0008] S2, separating the crystal slurry after crystallization to produce sodium sulfate decahydrate solid and low-temperature filtrate;

[0009] S3, using the heat produced as a byproduct of the refrigeration process in step S1 to heat the low-temperature filtrate produced in step S2;

[0010] S4, filtering the high-temperature filtrate produced in step S3 through a high-pressure membrane to produce pure water and a high-concentration sodium sulfate solution.

[0011] Furthermore, in step S2, the produced sodium sulfate decahydrate solid can be evaporated and crystallized to remove crystal water, thereby producing anhydrous sodium sulfate and pure water.

[0012] Furthermore, in step S1, the heat produced as a by-product of the refrigeration process can be used to preheat the evaporation mother liquid after being heated by the heat pump unit.

[0013] Furthermore, in step S4, the purified water is treated until it meets the standards and then discharged.

[0014] Further, in step S4, the high concentration sodium sulfate solution is returned to step S1 for repeated crystallization.

[0015] Furthermore, in step S4, the high concentration sodium sulfate solution is directly evaporated and crystallized.

[0016] Furthermore, in step S4, the high concentration sodium sulfate solution is crystallized and concentrated twice or more times, and then evaporated and crystallized.

[0017] Furthermore, in step S4, the high concentration sodium sulfate solution is discharged to the back-end treatment.

[0018] The beneficial effects of the present invention are:

[0019] 1. The present invention uses low-temperature crystallization to crystallize sodium sulfate in the solution, and then centrifuges to produce sodium sulfate decahydrate solid and low-temperature filtrate. At the same time, the heat produced as a by-product of the low-temperature crystallization refrigeration process is used to heat the low-temperature filtrate. The heated filtrate is then filtered through a membrane to produce pure water that meets the discharge standards, and the concentrated brine is frozen, crystallized, and concentrated again or enters the back-end treatment.

[0020] 2. The present invention utilizes freezing crystallization and membrane technology to partially or completely replace evaporation crystallization, thereby significantly reducing the investment cost and operating cost of treating high-salt wastewater containing sodium sulfate.

[0021] 3. The method of the present invention is scientifically and reasonably designed. For example, a certain project processes 116 tons of wastewater per hour, with a sodium sulfate content of 14%, and requires the output of solid anhydrous sodium sulfate and pure water to meet the discharge standards. According to the traditional technology, MVR is used to evaporate 100 tons of water per hour, and 16 tons of anhydrous sodium sulfate are separated by centrifugation. The investment cost is about 45 million, the electricity consumption per hour is about 5000KW.H, and the steam is about 5 tons. The operating cost per hour is about 4800 yuan. However, using the technical solution of the present invention, the investment cost is about 36 million, the electricity consumption per hour is about 3200KW.H, no steam is consumed, the operating cost per hour is about 1950 yuan, the cost saving per hour is about 2850 yuan, the annual saving is 22.8 million yuan, and the investment saving is 9 million yuan.

[0022] Of course, any product implementing the present invention does not necessarily need to achieve all of the above advantages at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0024] Figure 1 It is a schematic diagram of the process of sodium sulfate solution concentration method;

[0025] Figure 2It is a schematic diagram of the process of solid evaporation and crystallization of sodium sulfate decahydrate;

[0026] Figure 3 A schematic diagram of a process for preheating the evaporation mother liquid by utilizing the by-product heat in step S1;

[0027] Figure 4 This is a schematic diagram of the process of evaporating and crystallizing the concentrated sodium sulfate solution produced in step S4;

[0028] Figure 5 This is a schematic diagram of the specific application in Example 3. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] The present invention provides a method for concentrating a sodium sulfate solution, comprising the following steps:

[0031] S1, cooling the high concentration sodium sulfate solution to allow sodium sulfate to crystallize;

[0032] S2, separating the crystal slurry after crystallization to produce sodium sulfate decahydrate solid and low-temperature filtrate;

[0033] S3, using the heat produced as a byproduct of the refrigeration process in step S1 to heat the low-temperature filtrate produced in step S2;

[0034] S4, filtering the high-temperature filtrate produced in step S3 through a high-pressure membrane to produce pure water and a high-concentration sodium sulfate solution.

[0035] The relevant specific embodiments of the present invention are as follows:

[0036] Example 1

[0037] like Figure 1 As shown, this embodiment provides a method for concentrating a sodium sulfate solution, comprising the following steps:

[0038] S1, cooling the high concentration sodium sulfate solution to allow sodium sulfate to crystallize;

[0039] S2, separating the crystal slurry after crystallization to produce sodium sulfate decahydrate solid and low-temperature filtrate;

[0040] S3, using the heat produced as a byproduct of the refrigeration process in step S1 to heat the low-temperature filtrate produced in step S2;

[0041] S4, the high temperature filtrate produced in step S3 is filtered through a high pressure membrane to produce pure water and a high concentration sodium sulfate solution. The pure water is treated to meet the standards and then discharged.

[0042] In this embodiment, the high concentration sodium sulfate solution is returned to step S1 for repeated crystallization.

[0043] like Figure 2 As shown, the sodium sulfate decahydrate solid produced in step S2 can be evaporated and crystallized to remove crystal water, thereby producing anhydrous sodium sulfate and pure water.

[0044] like Figure 3 As shown, the heat produced as a by-product of the refrigeration process in step S1 can be used to preheat the evaporation mother liquid after being heated by the heat pump unit.

[0045] Example 2

[0046] This embodiment provides a method for concentrating a sodium sulfate solution, comprising the following steps:

[0047] S1, cooling the high concentration sodium sulfate solution to allow sodium sulfate to crystallize;

[0048] S2, separating the crystal slurry after crystallization to produce sodium sulfate decahydrate solid and low-temperature filtrate;

[0049] S3, using the heat produced as a byproduct of the refrigeration process in step S1 to heat the low-temperature filtrate produced in step S2;

[0050] S4, the high temperature filtrate produced in step S3 is filtered through a high pressure membrane to produce pure water and a high concentration sodium sulfate solution. The pure water is treated to meet the standards and then discharged.

[0051] In this embodiment, the high concentration sodium sulfate solution is directly evaporated and crystallized.

[0052] like Figure 2 As shown, the sodium sulfate decahydrate solid produced in step S2 can be evaporated and crystallized to remove crystal water, thereby producing anhydrous sodium sulfate and pure water.

[0053] like Figure 3 As shown, the heat produced as a by-product of the refrigeration process in step S1 can be used to preheat the evaporation mother liquid after being heated by the heat pump unit.

[0054] Example 3

[0055] This embodiment provides a method for concentrating a sodium sulfate solution, comprising the following steps:

[0056] S1, cooling the high concentration sodium sulfate solution to allow sodium sulfate to crystallize;

[0057] S2, separating the crystal slurry after crystallization to produce sodium sulfate decahydrate solid and low-temperature filtrate;

[0058] S3, using the heat produced as a byproduct of the refrigeration process in step S1 to heat the low-temperature filtrate produced in step S2;

[0059] S4, the high temperature filtrate produced in step S3 is filtered through a high pressure membrane to produce pure water and a high concentration sodium sulfate solution. The pure water is treated to meet the standards and then discharged.

[0060] In this embodiment, Figure 4 As shown, the high concentration sodium sulfate solution is crystallized and concentrated twice or more times, and then evaporated and crystallized.

[0061] like Figure 2 As shown, the sodium sulfate decahydrate solid produced in step S2 can be evaporated and crystallized to remove crystal water, thereby producing anhydrous sodium sulfate and pure water.

[0062] like Figure 3 As shown, the heat produced as a by-product of the refrigeration process in step S1 can be used to preheat the evaporation mother liquid after being heated by the heat pump unit.

[0063] A specific application of this embodiment is: Figure 5 As shown, taking the treatment of 116 tons of high-salt water per hour as an example, of which the salt content is 16 tons, the traditional technology needs to evaporate 100 tons of water. With the current most energy-saving MVR technology, the cost of evaporating 1 ton of water is about 45 yuan, and the cost of evaporating 100 tons of water is about 4500 yuan. However, using this technology, only 25 tons of water need to be evaporated, and the evaporation cost is only 1125 yuan. In addition, the cost of freezing crystallization and high-pressure membrane filtration is about 1200 yuan, and the total cost is about 2325 yuan, which is only 2325 / 4500=52% of the traditional technology, saving 48%.

[0064] Example 4

[0065] This embodiment provides a method for concentrating a sodium sulfate solution, comprising the following steps:

[0066] S1, cooling the high concentration sodium sulfate solution to allow sodium sulfate to crystallize;

[0067] S2, separating the crystal slurry after crystallization to produce sodium sulfate decahydrate solid and low-temperature filtrate;

[0068] S3, using the heat produced as a byproduct of the refrigeration process in step S1 to heat the low-temperature filtrate produced in step S2;

[0069] S4, the high temperature filtrate produced in step S3 is filtered through a high pressure membrane to produce pure water and a high concentration sodium sulfate solution. The pure water is treated to meet the standards and then discharged.

[0070] In this embodiment, the high concentration sodium sulfate solution is discharged into the back-end treatment.

[0071] like Figure 2 As shown, the sodium sulfate decahydrate solid produced in step S2 can be evaporated and crystallized to remove crystal water, thereby producing anhydrous sodium sulfate and pure water.

[0072] like Figure 3 As shown, the heat produced as a by-product of the refrigeration process in step S1 can be used to preheat the evaporation mother liquid after being heated by the heat pump unit.

[0073] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for concentrating a sodium sulfate solution, characterized in that: The steps include: S1, cooling the high concentration sodium sulfate solution to allow sodium sulfate to crystallize; S2, separating the crystal slurry after crystallization to produce sodium sulfate decahydrate solid and low-temperature filtrate; S3, using the heat produced as a byproduct of the refrigeration process in step S1 to heat the low-temperature filtrate produced in step S2; S4, filtering the high-temperature filtrate produced in step S3 through a high-pressure membrane to produce pure water and a high-concentration sodium sulfate solution.

2. The method for concentrating a sodium sulfate solution according to claim 1, characterized in that: In step S2, the produced sodium sulfate decahydrate solid can be evaporated and crystallized to remove crystal water, thereby producing anhydrous sodium sulfate and pure water.

3. The sodium sulfate decahydrate evaporative crystallization according to claim 1, characterized in that In step S1, the heat produced as a by-product of the refrigeration process can be used to preheat the evaporation mother liquid after being heated by the heat pump unit.

4. The method for concentrating sodium sulfate solution according to claim 1, characterized in that: In step S4, the purified water is treated until it meets the standards and then discharged.

5. The method for concentrating a sodium sulfate solution according to any one of claims 1 to 4, characterized in that: In step S4, the high concentration sodium sulfate solution is returned to step S1 for repeated crystallization.

6. The method for concentrating a sodium sulfate solution according to any one of claims 1 to 4, characterized in that: In step S4, the high concentration sodium sulfate solution is directly evaporated and crystallized.

7. The method for concentrating a sodium sulfate solution according to any one of claims 1 to 4, characterized in that: In step S4, the high concentration sodium sulfate solution is crystallized and concentrated twice or more times, and then evaporated and crystallized.

8. The method for concentrating a sodium sulfate solution according to any one of claims 1 to 4, characterized in that: In step S4, the high concentration sodium sulfate solution is discharged to the back-end treatment.

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