A method for treating high-salt wastewater by controlling the mother liquor return amount to reduce the rate of impurity salt

Abstract

The application belongs to the field of chemical wastewater evaporation crystallization, and discloses a high-salt wastewater treatment method for controlling the return flow of mother liquor to reduce the rate of mixed salt. The method comprises the following steps: pumping the preheated high-salt wastewater into a falling film evaporator to obtain falling film evaporation concentrated mother liquor S1; mixing S1 with return flow mother liquor S4 to obtain a mixed liquid, precooling the mixed liquid, pumping the mixed liquid into a refrigeration crystallizer to obtain refrigeration crystal slurry, and pumping the refrigeration crystal slurry into a sodium sulfate decahydrate thickener to obtain first thick crystal slurry, and then performing solid-liquid separation treatment to obtain refrigeration crystallization post-mother liquor S2 and refrigeration crystallized sodium sulfate decahydrate; pumping the preheated S2 into a sodium chloride evaporation crystallizer to obtain evaporation crystal slurry, pumping the evaporation crystal slurry into a sodium chloride thickener to obtain second thick crystal slurry, and then performing solid-liquid separation treatment to obtain sodium chloride evaporation crystallization mother liquor S3 and sodium chloride wet material; and using part of S3 as the return flow mother liquor S4. The application controls the rate of mixed salt of the mother liquor drying unit by adjusting the return flow of the sodium chloride evaporation crystallization mother liquor S3.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of chemical wastewater evaporation crystallization, more specifically, relates to a high-salinity wastewater treatment method for reducing the rate of mixed salt by controlling the return amount of mother liquor. BACKGROUND

[0002] At present, the high-salinity wastewater in coal chemical industry, coking, petroleum and other industries mainly contains sodium sulfate and sodium chloride, accompanied by nitrate, COD and other impurities. After the separation and crystallization of sodium sulfate and sodium chloride, the amount of mixed salt (which belongs to hazardous waste) is still high, thereby increasing the operating cost of enterprises. Therefore, reducing the rate of mixed salt in high-salinity wastewater treatment has become one of the focuses of zero discharge.

[0003] The prior art CN115872567A discloses a salt separation zero discharge process and system with low mixed salt rate and high salt and nitrate quality. The mother liquor after the cold crystallization of sodium sulfate is subjected to mixed salt evaporation crystallization, and then the mixed salt enters the salt washing device for washing. This process flow is complex (mixed salt crystallization and mixed salt redissolution units are added), the control point of the salt washing device is difficult to control, and the condensate water washing increases the system processing capacity.

[0004] The prior art CN116835828A discloses a process and device for reducing the mixed salt rate of wastewater zero discharge, which comprises evaporation crystallization of sodium sulfate, cold crystallization of sodium sulfate decahydrate, resin softening tower, ozone catalytic oxidation tower, nanofiltration system, sodium chloride evaporation crystallization and mixed salt unit. This method inserts resin softening, oxidation tower and nanofiltration units in the evaporation crystallization system, which complicates the process flow and increases the operation difficulty of the evaporation crystallization system.

[0005] Therefore, there is an urgent need to propose a new high-salinity wastewater treatment method for reducing the rate of mixed salt by controlling the return amount of mother liquor. SUMMARY

[0006] The purpose of the present application is to overcome the shortcomings of the prior art and provide a high-salinity wastewater treatment method for reducing the rate of mixed salt by controlling the return amount of mother liquor. The method adjusts the return amount of sodium chloride evaporation crystallization mother liquor S3, thereby controlling the rate of mixed salt in the mother liquor drying unit.

[0007] In order to achieve the above purpose, the present application provides a high-salinity wastewater treatment method for reducing the rate of mixed salt by controlling the return amount of mother liquor, which comprises the following steps:

[0008] (1) pumping the high-salinity wastewater into a falling film evaporator after preheating to concentrate, to obtain falling film evaporation concentrated mother liquor S1;

[0009] (2) : mixing the falling film evaporation concentrated mother liquor S1 with the reflux mother liquor S4 to obtain a mixed liquor; precooling the mixed liquor and pumping it into a refrigeration crystallizer to obtain a refrigeration crystal slurry and pumping it into a sodium sulfate decahydrate thickener to obtain a first thick crystal slurry, and performing solid-liquid separation treatment to obtain a refrigeration crystallization post-mother liquor S2 and refrigeration crystallized sodium sulfate decahydrate;

[0010] (3) : preheating the refrigeration crystallization post-mother liquor S2 and pumping it into a sodium chloride evaporation crystallizer to obtain an evaporation crystal slurry and pumping it into a sodium chloride thickener to obtain a second thick crystal slurry, and performing solid-liquid separation treatment to obtain a sodium chloride evaporation crystallization mother liquor S3 and a sodium chloride wet material;

[0011] (4) : using part of the sodium chloride evaporation crystallization mother liquor S3 as the reflux mother liquor S4.

[0012] According to the present application, preferably, the mass of the reflux mother liquor S4 accounts for 5-30% of the mass of the falling film evaporation concentrated mother liquor S1.

[0013] In the present application, in step (1), the high-salinity wastewater is first subjected to falling film evaporation concentration, so as to reduce the amount of the falling film evaporation concentrated mother liquor S1 entering the refrigeration crystallizer.

[0014] According to the present application, preferably, the operating temperature of the refrigeration crystallizer is -5℃ to 0℃.

[0015] According to the present application, preferably, the method further comprises mixing the refrigeration crystallized sodium sulfate decahydrate with condensate water to obtain a sodium sulfate dissolving solution; preheating the sodium sulfate dissolving solution and pumping it into a sodium sulfate evaporation crystallizer to obtain a sodium sulfate concentrated crystal slurry and pumping it into a sodium sulfate thickener to obtain a third thick crystal slurry, and performing solid-liquid separation treatment to obtain a sodium sulfate crystal wet material and a sodium sulfate mother liquor.

[0016] According to the present application, preferably, the mass ratio of the refrigeration crystallized sodium sulfate decahydrate to the condensate water is (0.8-1.2) :(0.8-1.2).

[0017] According to the present application, preferably, the sodium sulfate dissolving solution is preheated to 85-90℃ and then pumped into the sodium sulfate evaporation crystallizer.

[0018] According to the present application, preferably, the sodium sulfate mother liquor is refluxed to the sodium sulfate evaporation crystallizer.

[0019] In the present application, as a preferred solution, the solid-liquid separation treatment is realized by a centrifuge. The preheating is realized by a condensate water plate.

[0020] According to the present application, preferably, the sodium sulfate crystal wet material is sent into a fluidized bed for drying treatment to obtain a product sodium sulfate.

[0021] According to the application, preferably, the purity of the product sodium sulfate is greater than or equal to 98%.

[0022] According to the application, preferably, the mother liquor S2 after the frozen crystallization is preheated to 50-85 DEG C and then pumped into the sodium chloride evaporation crystallizer.

[0023] According to the application, preferably, the operating temperature of the sodium chloride evaporation crystallizer is 98-105 DEG C.

[0024] According to the application, preferably, the method further comprises sending the sodium chloride wet material into a fluidized bed for drying treatment to obtain the product sodium chloride.

[0025] According to the application, preferably, the method further comprises sending the remaining part of the sodium chloride evaporation crystallization mother liquor S3 into a mother liquor drying unit for treatment to obtain the mixed salt.

[0026] The beneficial effects of the technical scheme of the application are as follows:

[0027] The application controls the return amount of the sodium chloride evaporation crystallization mother liquor S3, adjusts the salt-nitrate ratio of the liquid into the frozen crystallizer (according to the common ion effect and the super-saturation degree generated by cooling, more sodium sulfate decahydrate solid is precipitated, and the sodium sulfate content in the mother liquor S2 after the frozen crystallization is reduced, see Figure 2 and Figure 3 ), and then controls the end composition of the mother liquor S2 after the frozen crystallization, successfully makes the concentration in the sodium chloride crystallization region and far away from the co-saturation point of sodium sulfate and sodium chloride (see Figure 4 and Figure 5 ) when the sodium chloride evaporation crystallizer is crystallized, so as to ensure the crystallization amount of the sodium chloride, and then reduce the mixed salt rate of the system.

[0028] The application does not need to increase the mixed salt evaporation crystallization unit, and the mother liquor S2 after the frozen crystallization is directly evaporated and crystallized to prepare sodium chloride.

[0029] After the sodium sulfate decahydrate of the frozen crystallization is hot melted, the sodium sulfate with a purity of greater than or equal to 98% is obtained through the evaporation crystallization, which meets the A-class first-class product requirements of the coal chemical industry by-product industrial sodium sulfate (T / CCT 001-2019).

[0030] Other features and advantages of the application will be described in detail in the following specific embodiment part. BRIEF DESCRIPTION OF DRAWINGS

[0031] The above and other objects, features and advantages of the application will become more apparent from the following detailed description of exemplary embodiments of the application taken in conjunction with the accompanying drawings, in which like reference characters generally refer to the same parts throughout the different views of the drawings.

[0032] Figure 1A process flow diagram of a high-salinity wastewater treatment method for controlling the mother liquor reflux amount to reduce the impure salt rate according to the embodiment 1 of the present application is shown.

[0033] Figure 2 A partial enlarged view of the sodium sulfate-sodium chloride-water solid-liquid phase equilibrium diagram at 100°C sodium chloride crystallization under different reflux mother liquor S4 reflux amounts according to the embodiment 1 of the present application is shown.

[0034] Figure 3 A partial enlarged view of the sodium sulfate-sodium chloride-water solid-liquid phase equilibrium diagram at 100°C sodium chloride crystallization under different reflux mother liquor S4 reflux amounts according to the embodiment 1 of the present application is shown.

[0035] Figure 4 A process flow diagram of a high-salinity wastewater treatment method for controlling the mother liquor reflux amount to reduce the impure salt rate according to the embodiment 1 of the present application is shown.

[0036] Figure 5 A partial enlarged view of the sodium sulfate-sodium chloride-water solid-liquid phase equilibrium diagram at 100°C sodium chloride crystallization under different reflux mother liquor S4 reflux amounts according to the embodiment 1 of the present application is shown. DETAILED DESCRIPTION

[0037] The preferred embodiments of the present application will be described in more detail below. Although the preferred embodiments of the present application are described below, it is understood that the present application can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that the present application will be thorough and complete, and will fully convey the scope of the present application to those skilled in the art.

[0038] Embodiment 1

[0039] The present embodiment provides a high-salinity wastewater treatment method for controlling the mother liquor reflux amount to reduce the impure salt rate, in which the TDS of the high-salinity wastewater is 94017.8 mg / L (including 2190.3 mg / L of impurities such as COD), sodium chloride accounts for 3.46%, and sodium sulfate accounts for 7.29%;

[0040] As shown in Figure 1 the method includes the following steps:

[0041] (1) The high-salinity wastewater is preheated and then pumped into a falling film evaporator to be concentrated by 2 times to obtain a falling film evaporation concentrated mother liquor S1;

[0042] (2): mixing the falling film evaporation concentrated mother liquor S1 with the reflux mother liquor S4 (the mass of the reflux mother liquor S4 accounts for 10% of the mass of the falling film evaporation concentrated mother liquor S1), to obtain a mixed solution; pre-cooling the mixed solution to 40-50℃, then pumping into a refrigeration crystallizer, cooling to 0℃, to obtain a refrigeration crystal slurry and pumping into a sodium sulfate decahydrate thickener, after the mass fraction of the refrigeration crystal slurry is increased to 30%-50%, to obtain a first thick crystal slurry, and centrifugal solid-liquid separation treatment is performed, to obtain a refrigeration crystallization post-mother liquor S2 (containing 12.15% of sodium chloride and 1.35% of sodium sulfate, see Figure 2 、 Figure 3 ) and refrigeration crystallized sodium sulfate decahydrate;

[0043] (3): pre-heating the refrigeration crystallization post-mother liquor S2 to 55-65℃ by a condensate water plate, then pumping into a sodium chloride evaporation crystallizer, and warming to 100℃, at this time, the concentration of sodium chloride has gradually deviated from the sodium sulfate and sodium chloride co-saturation point (see Figure 4 、 Figure 5 in detail), to obtain an evaporation crystal slurry and pumping into a sodium chloride thickener, after the mass fraction of the evaporation crystal slurry is increased to 30%-50%, to obtain a second thick crystal slurry, and centrifugal solid-liquid separation treatment is performed, to obtain a sodium chloride evaporation crystallization mother liquor S3 and a sodium chloride wet material; the sodium chloride wet material is sent into a fluidized bed for drying treatment, to obtain a product sodium chloride;

[0044] (4): using part of the sodium chloride evaporation crystallization mother liquor S3 as the reflux mother liquor S4; the remaining part of the sodium chloride evaporation crystallization mother liquor S3 is sent into a mother liquor drying unit for treatment, to obtain a miscellaneous salt (miscellaneous salt rate is 23.71%).

[0045] (5): hot-melting mixing the refrigeration crystallized sodium sulfate decahydrate with an equal mass of condensate water, to obtain a sodium sulfate dissolution liquid; pre-heating the sodium sulfate dissolution liquid to 85-90℃, then pumping into a sodium sulfate evaporation crystallizer, to obtain a sodium sulfate concentrated crystal slurry and pumping into a sodium sulfate thickener, after the mass fraction of the sodium sulfate concentrated crystal slurry is increased to 30%-50%, to obtain a third thick crystal slurry, and centrifugal solid-liquid separation treatment is performed, to obtain a sodium sulfate crystal wet material and a sodium sulfate mother liquor. The sodium sulfate mother liquor is refluxed to the sodium sulfate evaporation crystallizer; the sodium sulfate crystal wet material is sent into a fluidized bed for drying treatment, to obtain a product sodium sulfate (purity reaches 98.3%).

[0046] Example 2

[0047] The embodiment provides a high-salt wastewater treatment method for controlling the reflux amount of a mother liquor to reduce the miscellaneous salt rate, and the difference between the embodiment and the example 1 is that:

[0048] The mass of the reflux mother liquor S4 accounts for 15% of the mass of the falling film evaporation concentrated mother liquor S1;

[0049] The mother liquor S2 after freeze crystallization contains 13.05% of sodium chloride and 1.29% of sodium sulfate;

[0050] The impurity salt rate is 17.23%;

[0051] The purity of the product sodium sulfate reaches 98.3%.

[0052] Example 3

[0053] The difference between this example and Example 1 is that:

[0054] The mass of the reflux mother liquor S4 accounts for 20% of the mass of the falling film evaporation concentrated mother liquor S1;

[0055] The mother liquor S2 after freeze crystallization contains 13.85% of sodium chloride and 1.25% of sodium sulfate;

[0056] The mother liquor S2 after freeze crystallization is preheated to 80-85°C by a condensate water plate and then pumped into a sodium chloride evaporation crystallizer;

[0057] The impurity salt rate is 11.19%;

[0058] The purity of the product sodium sulfate reaches 98.2%.

[0059] Example 4

[0060] The difference between this example and Example 1 is that:

[0061] The mass of the reflux mother liquor S4 accounts for 25% of the mass of the falling film evaporation concentrated mother liquor S1;

[0062] The mother liquor S2 after freeze crystallization contains 14.57% of sodium chloride and 1.22% of sodium sulfate;

[0063] The mother liquor S2 after freeze crystallization is preheated to 80-85°C by a condensate water plate and then pumped into a sodium chloride evaporation crystallizer;

[0064] The impurity salt rate is 5.31%;

[0065] The purity of the product sodium sulfate reaches 98.2%.

[0066] Comparative Example 1

[0067] The high-salt wastewater treatment method provided in this comparative example is used to treat high-salt wastewater, and the TDS of the high-salt wastewater is 94017.8 mg / L (of which the impurities such as COD are 2190.3 mg / L), the sodium chloride accounts for 3.46%, and the sodium sulfate accounts for 7.29%;

[0068] The method comprises the following steps:

[0069] (1): The high-salt wastewater is preheated and pumped into a falling film evaporator to be concentrated twice to obtain falling film evaporation concentrated mother liquor S1;

[0070] (2): The falling film evaporation concentrated mother liquor S1 is pre-cooled to 40-50 ° C and then pumped into a freezing crystallizer, cooled to 0 ° C to obtain a frozen slurry and pumped into a sodium sulfate decahydrate thickener. After the mass fraction of the frozen slurry is concentrated to 30%-50%, a first thick slurry is obtained, and the mother liquor S2 after freezing crystallization (containing 9.98% sodium chloride and 1.59% sodium sulfate, see Figure 2 、 Figure 3 ) and frozen crystallized sodium sulfate decahydrate;

[0071] (3): The mother liquor S2 after freezing and crystallization is preheated to 55-65℃ through the condensation water plate and then pumped into the sodium chloride evaporation crystallizer and heated to 100℃. At this time, the concentration of sodium chloride during crystallization is close to the saturation point of sodium sulfate and sodium chloride (see Figure 4 、 Figure 5 ), obtaining an evaporated slurry and pumping it into a sodium chloride thickener, where the mass fraction of the evaporated slurry is concentrated to 30%-50%, thereby obtaining a second thickened slurry, which is then subjected to solid-liquid separation in a centrifuge to obtain a sodium chloride evaporation crystallization mother liquor S3 and a sodium chloride wet material; the sodium chloride wet material is fed into a fluidized bed for drying to obtain a sodium chloride product;

[0072] (4): The sodium chloride evaporation crystallization mother liquor S3 is sent to the mother liquor drying unit for treatment to obtain impure salt (impurity salt rate is 70.82%).

[0073] (5): The frozen crystallized sodium sulfate decahydrate is hot-melted and mixed with an equal mass of condensed water to obtain a sodium sulfate solution; the sodium sulfate solution is preheated to 80-90°C and then pumped into a sodium sulfate evaporation crystallizer to obtain a sodium sulfate concentrated slurry, which is then pumped into a sodium sulfate thickener. After the mass fraction of the sodium sulfate concentrated slurry is concentrated to 30%-50%, a third thick slurry is obtained, which is subjected to solid-liquid separation treatment in a centrifuge to obtain a sodium sulfate crystal wet material and a sodium sulfate mother liquor. The sodium sulfate mother liquor is refluxed to the sodium sulfate evaporation crystallizer; the sodium sulfate crystal wet material is sent to a fluidized bed for drying to obtain a sodium sulfate product (with a purity of 98.5%).

[0074] While various embodiments of the present invention have been described above, the above description is intended to be illustrative, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for treating high-salt wastewater by controlling the mother liquor reflux rate and reducing the impurity salt rate, characterized in that: The method comprises the following steps: (1): The high-salt wastewater is preheated and pumped into the falling film evaporator for concentration to obtain the falling film evaporation concentrated mother liquor S1; (2): The falling film evaporation concentrated mother liquor S1 is mixed with the reflux mother liquor S4 to obtain a mixed liquor; the mixed liquor is pre-cooled and pumped into a freezing crystallizer to obtain a frozen slurry, which is then pumped into a sodium sulfate decahydrate thickener to obtain a first thick slurry, and subjected to solid-liquid separation treatment to obtain a frozen crystallized mother liquor S2 and frozen crystallized sodium sulfate decahydrate; (3): The mother liquor S2 after frozen crystallization is preheated and pumped into the sodium chloride evaporation crystallizer to obtain evaporation slurry, which is then pumped into the sodium chloride thickener to obtain a second thick slurry. After solid-liquid separation, the sodium chloride evaporation crystallization mother liquor S3 and sodium chloride wet material are obtained; (4): using part of the sodium chloride evaporation crystallization mother liquor S3 as the reflux mother liquor S4; The mass of the reflux mother liquor S4 accounts for 5-30% of the mass of the falling film evaporation concentrated mother liquor S1.

2. The method for treating high-salt wastewater by controlling the mother liquor reflux rate and reducing the impurity salt rate according to claim 1, wherein: The operating temperature of the freezing crystallizer is -5°C to 0°C.

3. The method for treating high-salt wastewater by controlling the mother liquor reflux rate and reducing the impurity salt rate according to claim 1, wherein: The method further comprises hot-melting and mixing the frozen crystallized sodium sulfate decahydrate with condensed water to obtain a sodium sulfate solution; preheating the sodium sulfate solution and pumping it into a sodium sulfate evaporation crystallizer to obtain a sodium sulfate concentrated slurry; and pumping the solution into a sodium sulfate thickener to obtain a third thick slurry; and performing solid-liquid separation to obtain a sodium sulfate crystal wet material and a sodium sulfate mother liquor.

4. The method for treating high-salt wastewater by controlling the mother liquor reflux rate and reducing the impurity salt rate according to claim 3, wherein: The mass ratio of the frozen crystallized sodium sulfate decahydrate to the condensed water is (0.8-1.2): (0.8-1.2); The sodium sulfate solution is preheated to 85-90° C. and then pumped into a sodium sulfate evaporation crystallizer.

5. The method for treating high-salt wastewater by controlling the mother liquor reflux rate and reducing the impurity salt rate according to claim 3, wherein: reflux the sodium sulfate mother liquor to the sodium sulfate evaporation crystallizer; The sodium sulfate crystal wet material is sent to a fluidized bed for drying to obtain product sodium sulfate.

6. The method for treating high-salt wastewater by controlling the mother liquor reflux rate and reducing the impurity salt rate according to claim 5, wherein: The purity of the product sodium sulfate is ≥98%.

7. The method for treating high-salt wastewater by controlling the mother liquor reflux rate and reducing the impurity salt rate according to claim 1, wherein: The mother liquor S2 after freezing and crystallization is preheated to 50-85°C and then pumped into the sodium chloride evaporation crystallizer; The operating temperature of the sodium chloride evaporation crystallizer is 98-105°C.

8. The method for treating high-salt wastewater by controlling the mother liquor reflux rate and reducing the impurity salt rate according to claim 1, wherein: The method further comprises feeding the sodium chloride wet material into a fluidized bed for drying to obtain product sodium chloride.

9. The method for treating high-salt wastewater by controlling the mother liquor reflux rate and reducing the impurity salt rate according to claim 1, wherein: The method further comprises sending the remaining portion of the sodium chloride evaporation crystallization mother liquor S3 into a mother liquor drying unit for treatment to obtain impurity salts.

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