Process for separating salt from strong brine after ultrafiltration and reverse osmosis of coking wastewater

Abstract

The invention relates to the technical field of wastewater treatment, in particular to a process for separating salt from strong brine after ultrafiltration and reverse osmosis of coking wastewater, which comprises the following steps: separating a monovalent ion solution and a divalent ion solution from the strong brine after nanofiltration; removing COD from the divalent ion solution, and performing evaporative crystallization to obtain sodium sulfate crystals; carrying out high-pressure reverse osmosis treatment on the monovalent ion solution, and removing COD (Chemical Oxygen Demand) from the generated concentrated solution to obtain a sodium chloride concentrated solution; concentrating and decoloring the sodium chloride concentrated solution to obtain a decolored solution; introducing carbon dioxide and ammonia gas into the decoloring solution in a reaction device 1 to react, enabling the mother solution and redundant gas in the reaction device 1 to enter a reaction device 2 to react and precipitate, and performing vacuum filtration and drying on the separated precipitate to obtain a sodium bicarbonate product; the mother liquor in the reaction device 2 enters a reaction device 3, carbon dioxide and ammonia gas are introduced for reaction, the mother liquor in the reaction device 3 enters a cold separation device for cooling crystallization, separated crystals are filtered and dried, and an ammonium chloride product is obtained; and carrying out ammonia distillation treatment on the crystallized mother liquor in an ammonia distillation tower.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater treatment, and in particular relates to a process for separating salt from concentrated brine after ultrafiltration and reverse osmosis of coking wastewater. Background Art

[0002] Coking wastewater is complex and pollutes a wide range of areas. New coking plants are required to achieve zero discharge of coking wastewater. The current mainstream process is ultrafiltration + reverse osmosis to generate fresh water + brine. Disposal of brine is a key obstacle to achieving zero discharge of coking wastewater. Three common disposal methods are used: sintering mixing, ironmaking slag flushing, wet quenching, and salt separation. Whether used for sintering mixing, ironmaking slag flushing, or wet quenching, brine can cause equipment corrosion. Therefore, salt separation is a future development trend.

[0003] The mainstream salt separation process currently used in the industry is: nanofiltration + evaporation crystallization → sodium chloride + sodium sulfate. This process has the problems of low added value of sodium chloride and poor market sales. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a process for desalting concentrated brine after ultrafiltration and reverse osmosis of coking wastewater, so as to realize resource utilization and reduce the carbon emissions of coking enterprises.

[0005] To achieve the above objectives, the present invention adopts the following technical solutions:

[0006] A process for desalting concentrated brine after ultrafiltration and reverse osmosis of coking wastewater, the process specifically comprising:

[0007] After ultrafiltration and reverse osmosis of coking wastewater, the concentrated brine is separated into monovalent ion solution and divalent ion solution through nanofiltration. The divalent ion solution removes COD and then evaporates and crystallizes to obtain sodium sulfate crystals. The conductivity of the concentrated brine is ≥20000μS / cm.

[0008] The monovalent ion solution is treated by high-pressure reverse osmosis to produce a concentrated solution with a conductivity of ≥40,000 μS / cm; COD is removed to obtain a concentrated sodium chloride solution; the concentrated sodium chloride solution is concentrated and decolorized to obtain a decolorized solution;

[0009] The decolorized liquid is introduced into the reaction device 1, where carbon dioxide and ammonia are reacted. The mother liquid and excess gas in the reaction device 1 enter the reaction device 2 for reaction and precipitation. The precipitated precipitate is vacuum filtered and dried to obtain the sodium bicarbonate product.

[0010] The mother liquor in the reaction unit 2 enters the reaction unit 3, where carbon dioxide and ammonia are introduced for reaction. The mother liquor in the reaction unit 3 enters the cold precipitation unit for cooling and crystallization. The precipitated crystals are filtered and dried to obtain the ammonium chloride product. The mother liquor after crystallization enters the ammonia evaporation tower for ammonia evaporation.

[0011] The new water generated by the high-pressure reverse osmosis treatment of the monovalent ion solution is sent to the circulating water system for use.

[0012] The divalent ion solution is evaporated and crystallized using the MVR or MED process.

[0013] The source of the carbon dioxide is coke oven flue gas.

[0014] The pH range of the reaction device 1 is 6.0-8.0. The pH range of the reaction device 1 is 6.0-8.0.

[0015] The temperature of the reaction device 2 is controlled at 30-50°C.

[0016] The temperature of the cold separation device is controlled below 10°C.

[0017] The ammonia gas produced by the ammonia still is fed into the reaction device 1 and the reaction device 3, and the liquid containing sodium chloride and sodium carbonate produced is sent to the reaction device 1 for recycling.

[0018] Compared with the existing technology, the beneficial effects of the present invention are:

[0019] This invention can significantly reduce wastewater treatment costs and carbon emissions from coking plants. It efficiently utilizes concentrated brine, effectively recycling high-salt coking wastewater. The resulting sodium bicarbonate can be used as a raw material for dry flue gas desulfurization (SDS). The resulting ammonium chloride can be used as a raw material in agricultural fertilizers or compound fertilizers. This addresses the poor marketability of sodium chloride, a product currently produced by existing processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Flowchart of the present invention. DETAILED DESCRIPTION

[0021] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means more than two.

[0022] Unless otherwise specified or limited, the terms "mounted," "connected," and "connected" should be interpreted broadly. For example, they can refer to fixed, removable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediary; and internal communication between two components. Those skilled in the art will understand the specific meanings of these terms in the present invention based on specific circumstances.

[0023] like Figure 1 , a process for separating salt from concentrated brine after ultrafiltration and reverse osmosis of coking wastewater, the process specifically comprising:

[0024] After ultrafiltration and reverse osmosis of coking wastewater, the concentrated brine is separated into monovalent ion solution and divalent ion solution through nanofiltration; after COD is removed from the divalent ion solution, MVR or MED process is used for evaporation and crystallization to obtain sodium sulfate crystals;

[0025] The monovalent ion solution undergoes high-pressure reverse osmosis treatment to concentrate the solution, reducing subsequent process costs. The resulting fresh water is fed to the circulating water system, and the resulting concentrate is decolorized to produce a concentrated sodium chloride solution. This concentrated sodium chloride solution is then concentrated and decolorized to produce a decolorized solution. This decolorization process improves the purity of the final ammonium chloride product, resulting in a better product color.

[0026] The decolorized liquid is introduced into reactor 1, where coke oven flue gas is introduced as a source of carbon dioxide, and ammonia from the ammonia still is introduced to react. The pH of reactor 1 is in the range of 6.0-8.0. The reaction occurring in reactor 1 is: CO2 + NH3 + NaCl → NaHCO3 + NH4Cl.

[0027] The mother liquor (comprising NaHCO₃, NH₄Cl, a small amount of incompletely reacted NaCl, and Na₂CO₃ that has not fully reacted to form NaHCO₃) and excess gas from reaction unit 1 enters reaction unit 2 for reaction and precipitation. The reaction occurring within reaction unit 2 is: CO₂ + NaCO₃ → NaHCO₃. The temperature of reaction unit 2 is controlled at 30-50°C. The precipitate is vacuum filtered and dried to produce sodium bicarbonate, which can be used as a raw material for SDS flue gas dry desulfurization.

[0028] The mother liquor from reaction unit 2 (comprising NaHCO₃, a small amount of NaCl, NH₄HCO₃, and NH₄Cl) enters reaction unit 3, where carbon dioxide and ammonia are introduced for reaction. In reaction unit 3, the NaHCO₃, a small amount of NaCl, NH₄HCO₃, and NH₄Cl react under sufficient carbon dioxide and ammonia conditions to produce Na₂CO₃, a small amount of NaCl, (NH₄)₂CO₃, and NH₄Cl. The pH of reaction unit 3 is in the range of 6.0-8.0.

[0029] The mother liquor in the reaction device 3 (containing Na2CO3, a small amount of NaCl, (NH4)2CO3 and NH4Cl) enters the cold precipitation device for cooling and crystallization. The temperature of the cold precipitation device is controlled below 10°C. The precipitated crystals are filtered and dried to obtain ammonium chloride products; ammonium chloride can be used as a formula raw material in agricultural fertilizers or compound fertilizers.

[0030] The crystallized mother liquor (containing Na2CO3, a small amount of NaCl, (NH4)2CO3, and a small amount of NH4Cl) enters the ammonia evaporation tower for ammonia evaporation. The ammonia gas produced by the ammonia evaporation tower is fed into reactor 1 and reactor 3, and the resulting liquid containing sodium chloride and sodium carbonate is sent to reactor 1 for recycling.

[0031] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, and these simple modifications all fall within the scope of protection of the present invention. It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner unless there is any contradiction. In order to avoid unnecessary repetition, the present invention will no longer describe various possible combinations separately. In addition, the various different embodiments of the present invention can also be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

[0032] To make the objectives, technical solutions, and technical effects of the present invention more clear, the technical solutions in the embodiments of the present invention are now clearly and completely described. However, the embodiments described below are only some of the embodiments of the present invention, not all of them. In combination with the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0033] Example 1:

[0034] 1. After ultrafiltration and reverse osmosis of coking wastewater, the concentrated brine is separated into monovalent ion solution and divalent ion solution after nanofiltration.

[0035] 2. The divalent ion solution is treated with a high-efficiency COD removal device to remove COD, and then the MVR process is used for evaporation and crystallization to obtain sodium sulfate crystals.

[0036] 3. The monovalent ion solution is treated by high-pressure reverse osmosis, and the new water produced is sent to the circulating water system for use. The concentrated liquid is sent to the high-efficiency COD removal device to remove COD and obtain a concentrated sodium chloride solution.

[0037] 4. The concentrated sodium chloride solution is sent to the decolorization kettle for concentration and decolorization to obtain a decolorized liquid.

[0038] 5. The decolorized liquid is fed to reactor 1, where coke oven flue gas is introduced as a source of carbon dioxide. Ammonia produced in the ammonia still in the by-product recovery workshop is also introduced. The following reaction occurs within reactor 1: CO2 + NH3 + NaCl → NaHCO3 + NH4Cl. The pH of reactor 1 is 6.8.

[0039] The liquid mother liquor 1 in the device (composition includes NaHCO3, NH4Cl, a small amount of NaCl that is not completely reacted, and Na2CO3 that is not completely reacted to generate NaHCO3;) and excess CO2 and a small amount of NH3 enter the reaction device 2.

[0040] 6. Control the temperature of Reactor 2 at 35°C to allow NaHCO3 to precipitate. Vacuum filtration and drying yield the sodium bicarbonate product. The primary reaction occurring within Reactor 2 is: CO2 + NaCO3 → NaHCO3. Residual gas from Reactor 2 is collected and disposed of without pollution.

[0041] 7. Mother liquor II from Reactor 2 (comprising NaHCO₃, a small amount of NaCl, NH₄HCO₃, and NH₄Cl) enters Reactor 3. Coke oven flue gas is introduced into Reactor 3 as a source of carbon dioxide. Ammonia produced in the ammonia still in the by-product recovery workshop is also introduced into Reactor 3. In the presence of sufficient carbon dioxide and ammonia, NaHCO₃, a small amount of NaCl, NH₄HCO₃, and NH₄Cl react to produce Na₂CO₃, a small amount of NaCl, (NH₄)₂CO₃, and NH₄Cl. The pH of Reactor 3 is 7.2.

[0042] 8. Mother Liquor 3 from Reactor 3 (comprising Na2CO3, a small amount of NaCl, (NH4)2CO3, and NH4Cl) enters the cold precipitation unit, where the temperature is controlled at 8°C for crystallization. NH4Cl crystals are then filtered and dried to yield the NH4Cl product. The liquid remaining after crystallization in the cold precipitation unit becomes Mother Liquor 4 (comprising Na2CO3, a small amount of NaCl, (NH4)2CO3, and a small amount of NH4Cl).

[0043] 9. The mother liquor 4 enters the ammonia still. Ammonia gas is generated at the top of the ammonia still and is fed into the reaction unit 1 and the reaction unit 3. The bottom liquid, mainly composed of NaCl and Na2CO3, is sent to the reaction unit 1 for recycling.

[0044] Example 2:

[0045] 1. After ultrafiltration and reverse osmosis of coking wastewater, the concentrated brine is separated into monovalent ion solution and divalent ion solution after nanofiltration.

[0046] 2. The divalent ion solution is subjected to a high-efficiency COD removal device to remove COD, and then the MED process is used for evaporation and crystallization to obtain sodium sulfate crystals.

[0047] 3. The monovalent ion solution is treated by high-pressure reverse osmosis, and the new water produced is sent to the circulating water system for use. The concentrated liquid is sent to the high-efficiency COD removal device to remove COD and obtain a concentrated sodium chloride solution.

[0048] 4. The concentrated sodium chloride solution is sent to the decolorization kettle for concentration and decolorization to obtain a decolorized liquid.

[0049] 5. The decolorized liquid is fed to Reactor 1, where coke oven flue gas is introduced as a source of carbon dioxide. Ammonia produced in the ammonia still in the by-product recovery workshop is also introduced. Within Reactor 1, the following reaction occurs: CO2 + NH3 + NaCl → NaHCO3 + NH4Cl. The pH of Reactor 1 is 7.1. The mother liquor (consisting of NaHCO3, NH4Cl, a small amount of incompletely reacted NaCl, and Na2CO3 that has not fully reacted to form NaHCO3) enters Reactor 2, along with excess CO2 and a small amount of NH3.

[0050] 6. Control the temperature of reaction unit 2 at 45°C to allow NaHCO3 to precipitate. Vacuum filter and dry to obtain sodium bicarbonate. The main reaction in reaction unit 2 is: CO2 + NaCO3 → NaHCO3.

[0051] 7. Mother liquor II from Reactor 2 (comprising NaHCO₃, a small amount of NaCl, NH₄HCO₃, and NH₄Cl) enters Reactor 3. Coke oven flue gas is introduced into Reactor 3 as a source of carbon dioxide. Ammonia produced in the ammonia still in the by-product recovery workshop is also introduced into Reactor 3. In the presence of sufficient carbon dioxide and ammonia, NaHCO₃, a small amount of NaCl, NH₄HCO₃, and NH₄Cl react to produce Na₂CO₃, a small amount of NaCl, (NH₄)₂CO₃, and NH₄Cl. The pH of Reactor 3 is in the range of 7.5.

[0052] 8. Mother Liquor 3 from Reactor 3 (comprising Na2CO3, a small amount of NaCl, (NH4)2CO3, and NH4Cl) enters the cold precipitation unit, where the temperature is controlled at 9°C for crystallization. NH4Cl crystals are then filtered and dried to yield the NH4Cl product. The liquid remaining after crystallization in the cold precipitation unit becomes Mother Liquor 4 (comprising Na2CO3, a small amount of NaCl, (NH4)2CO3, and a small amount of NH4Cl).

[0053] 9. The mother liquor 4 enters the ammonia still. Ammonia gas is generated at the top of the ammonia still and is fed into the reaction unit 1 and the reaction unit 3. The bottom liquid, mainly composed of NaCl and Na2CO3, is sent to the reaction unit 1 for recycling.

[0054] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and basic spirit of the invention, and the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A process for desalting concentrated brine after ultrafiltration and reverse osmosis of coking wastewater, characterized in that: The process is specifically as follows: After ultrafiltration and reverse osmosis of coking wastewater, the concentrated brine is separated into monovalent ion solution and divalent ion solution through nanofiltration; The divalent ion solution removes COD and evaporates and crystallizes to obtain sodium sulfate crystals; The monovalent ion solution is subjected to high-pressure reverse osmosis treatment, and the resulting concentrated solution is decolorized to obtain a sodium chloride concentrated solution after COD removal. The sodium chloride concentrated solution is then concentrated and decolorized to obtain a decolorized solution. The decolorizing liquid is introduced into the reaction device 1, where excess carbon dioxide and ammonia are reacted. The mother liquid and excess gas in the reaction device 1 enter the reaction device 2 for reaction and precipitation. The precipitated precipitate is vacuum filtered and dried to obtain the sodium bicarbonate product. The mother liquor in the reaction unit 2 enters the reaction unit 3, where carbon dioxide and ammonia are introduced for reaction. The mother liquor in the reaction unit 3 enters the cold precipitation unit for cooling and crystallization. The precipitated crystals are filtered and dried to obtain the ammonium chloride product. The mother liquor after crystallization enters the ammonia evaporation tower for ammonia evaporation.

2. The process for desalting concentrated brine after ultrafiltration and reverse osmosis of coking wastewater according to claim 1, characterized in that: The new water generated by the high-pressure reverse osmosis treatment of the monovalent ion solution is sent to the circulating water system for use.

3. The process for desalting concentrated brine after ultrafiltration and reverse osmosis of coking wastewater according to claim 1, characterized in that: The divalent ion solution is evaporated and crystallized using the MVR or MED process.

4. The process for desalting concentrated brine after ultrafiltration and reverse osmosis of coking wastewater according to claim 1, characterized in that: The source of the carbon dioxide is coke oven flue gas.

5. The process for desalting concentrated brine after ultrafiltration and reverse osmosis of coking wastewater according to claim 1, characterized in that: The pH range of the reaction device 1 is 6.0-8.

0. The pH range of the reaction device 1 is 6.0-8.

0.

6. The process for desalting concentrated brine after ultrafiltration and reverse osmosis of coking wastewater according to claim 1, characterized in that: The temperature of the reaction device 2 is controlled at 30-50°C.

7. The process for desalting concentrated brine after ultrafiltration and reverse osmosis of coking wastewater according to claim 1, characterized in that: The temperature of the cold separation device is controlled below 10°C.

8. The process for desalting concentrated brine after ultrafiltration and reverse osmosis of coking wastewater according to claim 1, characterized in that: The ammonia gas produced by the ammonia still is fed into the reaction device 1 and the reaction device 3, and the liquid containing sodium chloride and sodium carbonate produced is sent to the reaction device 1 for recycling.

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