Coking wastewater treatment system

Abstract

The utility model relates to the technical field of water treatment, in particular to a coking wastewater treatment system which comprises an electrocatalytic oxidation unit, and a nanofiltration unit, a reverse osmosis unit, a fluorine and silicon removal unit and an evaporative crystallization unit which are connected in sequence, the electrocatalytic oxidation unit is connected with the nanofiltration unit and the evaporative crystallization unit so as to respectively receive nanofiltration concentrated water and evaporative crystallization mother liquor, and the electrocatalytic oxidation unit is used for carrying out electrocatalytic oxidation treatment on the nanofiltration concentrated water and the evaporative crystallization mother liquor; and an anode of the electrocatalytic oxidation unit adopts a boron-doped diamond electrode. By adopting the boron-doped diamond electrode as the anode of the electrocatalytic oxidation unit, electrocatalytic oxidation treatment can be directly carried out on the nanofiltration concentrated water and the evaporative crystallization mother liquor, enrichment of the nanofiltration concentrated liquor and the evaporative crystallization mother liquor is avoided, the purity of industrial salt is improved, meanwhile, the treatment cost of the mother liquor as hazardous waste is avoided, and the salt recovery cost is reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of water treatment, in particular to a coking wastewater treatment system. Background Art

[0002] Coking wastewater is generated during the production process of recovering by-products such as tar and benzene from the high-temperature pyrolysis of coal to obtain coke and gas. Its composition is complex, with problems such as high COD, high ammonia nitrogen, and high salt content, making it one of the most difficult-to-treat industrial wastewaters. Currently, the main treatment method is biochemical treatment + nanofiltration + reverse osmosis process, and a large amount of concentrated liquid will be generated during the membrane process.

[0003] The membrane concentrated liquid of coking wastewater contains a large amount of macromolecular organic matter, sulfate, chloride salt, etc. The existing process generally returns the concentrated liquid to the biochemical system for re-treatment, which not only increases the treatment load of the system and affects the treatment effect, but also difficult-to-degrade macromolecular organic matter, salts and other substances will continuously accumulate in the system, eventually causing a large number of microorganisms to die and the system to collapse; in addition, in the existing membrane concentrated liquid salt recovery process, mother liquor containing high-concentration organic pollutants will also be generated. If it is not effectively treated and continuously circulates and accumulates in the system, it will eventually affect the evaporation efficiency and salt quality. If it is directly treated as hazardous waste, the disposal cost is relatively high.

[0004] Therefore, removing organic pollutants from the membrane concentrated liquid of coking wastewater, improving the evaporation efficiency, and reducing the salt recovery cost are of great significance. Content of the Utility Model

[0005] The purpose of the utility model is to provide a coking wastewater treatment system to solve the treatment problem of the existing coking wastewater membrane concentrated liquid.

[0006] To achieve the above purpose, the utility model provides a coking wastewater treatment system, including an electrocatalytic oxidation unit and a nanofiltration unit, a reverse osmosis unit, a defluorination and desilication unit, and an evaporation crystallization unit connected in sequence, wherein:

[0007] The nanofiltration unit is used for primary filtration treatment of coking wastewater;

[0008] The reverse osmosis unit is used for secondary filtration treatment of the nanofiltration produced water;

[0009] The defluorination and desilication unit is used for defluorination and desilication treatment of the reverse osmosis concentrated water;

[0010] The evaporation crystallization unit is used for evaporation crystallization treatment of the reverse osmosis concentrated water after the defluorination and desilication treatment;

[0011] The electrocatalytic oxidation unit is connected to the nanofiltration unit and the evaporation crystallization unit to receive the nanofiltration concentrated water and the evaporation crystallization mother liquor respectively. The electrocatalytic oxidation unit is used to perform electrocatalytic oxidation treatment on the nanofiltration concentrated water and the evaporation crystallization mother liquor, and the anode of the electrocatalytic oxidation unit adopts a boron-doped diamond electrode.

[0012] Optionally, the coking wastewater treatment system further includes a pretreatment unit, which is used to remove fluorine, COD and hardness from the coking wastewater. The effluent of the pretreatment unit enters the nanofiltration unit.

[0013] Optionally, the nanofiltration unit filters the coking wastewater once under a pressure of 1-3 MPa.

[0014] Optionally, the reverse osmosis unit filters the coking wastewater twice under a pressure of 2-4 MPa.

[0015] Optionally, the fluorine and silicon removal unit includes a reaction tank, a coagulation tank, a flocculation tank and a sedimentation tank connected in sequence. The reaction tank is used to add a fluorine removal agent and a sodium hydroxide solution. The coagulation tank is used to add a coagulant. The flocculation tank is used to add a flocculant. The sedimentation tank is used to achieve solid-liquid separation.

[0016] Optionally, in the reverse osmosis concentrated water after fluorine and silicon removal, the concentration of fluoride does not exceed 30 mg / L, and the concentration of silicon dioxide does not exceed 40 mg / L.

[0017] Optionally, the evaporation efficiency of the evaporation crystallization unit is not less than 85%, and the purity of the crystalline salt is not less than 97.5%.

[0018] Optionally, the plate spacing between the anode and the cathode of the electrocatalytic oxidation unit is 2-5 mm.

[0019] Optionally, the high current density of the electrocatalytic oxidation unit is 500-1000 A / m 2 。

[0020] In the coking wastewater treatment system provided by the present utility model, it has at least one of the following beneficial effects:

[0021] 1) By using a BDD electrode as the anode of the electrocatalytic oxidation unit, the organic pollutants in the membrane concentrate can be treated directly, efficiently and thoroughly, avoiding the enrichment of the concentrate;

[0022] 2) The evaporation crystallization mother liquor can be directly treated, avoiding the enrichment of the mother liquor, improving the purity of the industrial salt, and at the same time eliminating the disposal cost of the mother liquor as hazardous waste, reducing the salt recovery cost;

[0023] 3) The process is simple, easy to control, and convenient for engineering application. Brief Description of the Drawings

[0024] Those of ordinary skill in the art should understand that the provided drawings are used to better understand the present utility model and do not constitute any limitation to the scope of the present utility model. Among them:

[0025] Figure 1 is a structural block diagram of a coking wastewater treatment system provided by an embodiment of the present utility model;

[0026] Figure 2 is a flowchart of a coking wastewater treatment method provided by an embodiment of the present utility model.

[0027] Among them:

[0028] 1 - Pretreatment unit; 2 - Nanofiltration unit; 3 - Reverse osmosis unit; 4 - Defluorination and desilication unit; 5 - Evaporation and crystallization unit; 6 - Electro-catalytic oxidation unit. Detailed Description of the Embodiments

[0029] To make the objectives, advantages and features of the present utility model clearer, the following further describes the present utility model in detail with reference to the drawings and specific embodiments. It should be noted that the drawings are in a very simplified form and use non-precise scales, only for conveniently and clearly assisting in explaining the objectives of the embodiments of the present utility model. To make the objectives, features and advantages of the present utility model more obvious and understandable, please refer to the drawings. It should be noted that the structures, scales, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those skilled in this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present utility model. Any modification of the structure, change of the proportional relationship or adjustment of the size, under the condition of being the same or similar to the effects that the present utility model can produce and the objectives that can be achieved, should still fall within the scope covered by the technical content disclosed by the present utility model.

[0030] As used in the present utility model, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. As used in the present utility model, the term "or" is generally used in the sense of including "and / or" unless the context clearly dictates otherwise. As used in the present utility model, the term "several" is generally used in the sense of including "at least one" unless the context clearly dictates otherwise. As used in the present utility model, the term "at least two" is generally used in the sense of including "two or more" unless the context clearly dictates otherwise. In addition, the terms "first", "second", "third" are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first", "second", "third" may explicitly or implicitly include one or at least two of such features.

[0031] In the description of the present utility model, unless otherwise clearly specified and defined, the terms "mounted", "connected", "connected to", "fixed" shall be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the connection inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present utility model can be understood according to specific circumstances.

[0032] Please refer to Figure 1 , this embodiment provides a coking wastewater treatment system, including an electrocatalytic oxidation unit 6 and a nanofiltration unit 2, a reverse osmosis unit 3, a defluorination and desilication unit 4, and an evaporation and crystallization unit 5 connected in sequence, wherein:

[0033] The nanofiltration unit 2 is used for performing a primary filtration treatment on the coking wastewater;

[0034] The reverse osmosis unit 3 is used for performing a secondary filtration treatment on the nanofiltration product water;

[0035] The defluorination and desilication unit 4 is used for performing defluorination and desilication treatments on the reverse osmosis concentrate;

[0036] The evaporation and crystallization unit 5 is used for performing an evaporation and crystallization treatment on the reverse osmosis concentrate after the defluorination and desilication treatments;

[0037] The electrocatalytic oxidation unit 6 is connected to the nanofiltration unit 2 and the evaporation and crystallization unit 5 to receive the nanofiltration concentrate and the evaporation and crystallization mother liquor respectively. The electrocatalytic oxidation unit 6 is used for performing an electrocatalytic oxidation treatment on the nanofiltration concentrate and the evaporation and crystallization mother liquor, and the anode of the electrocatalytic oxidation unit 6 adopts a boron-doped diamond electrode.

[0038] It should be noted that the BDD electrocatalytic oxidation method is an advanced water treatment technology. It uses "boron-doped diamond (BDD) electrode material" to degrade organic pollutants in water, and has the advantages of high efficiency, environmental protection, and no need to add chemical reagents. During the electrolysis process, the BDD electrode can directly or indirectly oxidize the organic matter in water into non-toxic and harmless inorganic substances (such as carbon dioxide and water). This technology is particularly suitable for treating high-risk organic wastewater, such as the membrane concentrate composed of nanofiltration concentrate and the evaporation crystallization mother liquor. Based on this, by using the BDD electrode as the anode of the electrocatalytic oxidation unit 6, the present utility model can directly perform electrocatalytic oxidation treatment on the nanofiltration concentrate and the evaporation crystallization mother liquor, avoid the enrichment of the nanofiltration concentrate and the evaporation crystallization mother liquor, improve the purity of industrial salt, and at the same time eliminate the disposal cost of the mother liquor as hazardous waste, reducing the salt recovery cost.

[0039] Preferably, the coking wastewater treatment system further includes a pretreatment unit 1, and the pretreatment unit 1 is used for defluorination, COD removal, and hardness removal of the coking wastewater, and the effluent of the pretreatment unit 1 enters the nanofiltration unit 2. In this embodiment, the coking wastewater first enters the pretreatment unit 1, and the pretreatment unit 1 is mainly used for pretreatment such as defluorination, COD removal, and hardness removal of the influent of the nanofiltration unit 2 to prevent excessive fluoride, COD, calcium ions, and magnesium ions in the coking wastewater from affecting the normal operation of the nanofiltration membrane and the reverse osmosis membrane.

[0040] The effluent of the pretreatment unit 1 enters the nanofiltration unit 2, and the nanofiltration unit 2 is used for primary filtration treatment of the coking wastewater to separate divalent ions and monovalent ions in the coking wastewater, that is, salt separation treatment.

[0041] Preferably, the nanofiltration unit 2 performs primary filtration on the coking wastewater at a pressure of 1-3 MPa.

[0042] The water produced by the nanofiltration unit 2 enters the reverse osmosis unit 3, and the reverse osmosis unit 3 is used for secondary filtration treatment of the nanofiltration produced water, which is equivalent to concentrating the nanofiltration produced water. The reverse osmosis produced water can meet the discharge standards or be reused, and the reverse osmosis concentrate enters the defluorination and desilication unit 4.

[0043] Preferably, the reverse osmosis unit 3 performs secondary filtration on the coking wastewater at a pressure of 2-4 MPa.

[0044] In this embodiment, the defluorination and desilication unit 4 includes a reaction tank, a coagulation tank, a flocculation tank and a sedimentation tank connected in sequence. The reaction tank is used to add a defluorinating agent and a sodium hydroxide solution. The coagulation tank is used to add a coagulant. The flocculation tank is used to add a flocculant. The sedimentation tank is used to achieve solid-liquid separation. Before the reverse osmosis concentrated water is subjected to evaporation crystallization, defluorination and desilication treatment are required to prevent blockage or corrosion of the evaporation crystallization unit 5. The utility model removes fluoride and silicon dioxide in the wastewater by the method of chemical reagent + precipitation + filtration. When the fluoride and silicon dioxide are lower than the set concentration, they can enter the evaporation crystallization unit 5.

[0045] In this embodiment, the sodium hydroxide solution is mainly used to adjust the PH value. Generally, the defluorinating agent is acidic, and the defluorinating agent has better defluorination effect under neutral conditions. Therefore, the sodium hydroxide solution is added to adjust the PH to neutral to ensure the defluorination effect.

[0046] In this embodiment, the coagulant includes but is not limited to polyaluminum chloride (PAC), the flocculant includes but is not limited to polyacrylamide (PAM), and the sedimentation tank is used to separate the supernatant and the precipitate. The supernatant enters the evaporation crystallization unit 5 for evaporation crystallization treatment.

[0047] In this embodiment, in the reverse osmosis concentrated water after defluorination and desilication treatment, the concentration of fluoride does not exceed 30 mg / L, and the concentration of silicon dioxide does not exceed 40 mg / L.

[0048] Preferably, the evaporation crystallization unit 5 is an MVR evaporator. The evaporation efficiency of the MVR evaporator is not less than 85%, and the purity of the crystalline salt is not less than 97.5%. The evaporation efficiency can be controlled by adjusting the evaporation rate and the flow rate of the concentrated liquid to improve the purity of the crystalline salt. At the same time, the concentration of the evaporation mother liquor is increased, and the high-concentration mother liquor generated enters the electro-catalytic oxidation unit 6 for treatment.

[0049] In this embodiment, the electro-catalytic oxidation unit 6 is used to perform electro-catalytic oxidation treatment on the nanofiltration concentrated water and the evaporation crystallization mother liquor. Under a high current density and a certain plate spacing, a large number of hydroxyl radicals are generated by the BDD electrode, which can efficiently degrade or even completely mineralize organic substances. At the same time, it also has a strong oxidation effect on ammonia nitrogen, and the treated wastewater can reach the discharge standard.

[0050] Preferably, the plate spacing between the anode and the cathode of the electro-catalytic oxidation unit 6 is 2-5 mm.

[0051] Preferably, the high current density of the electro-catalytic oxidation unit 6 is 500-1000 A / m 2 。

[0052] Based on the same technical concept, such as Figure 2As shown in the figure, an embodiment of the present invention also provides a method for treating coking wastewater, comprising the following steps:

[0053] Perform nanofiltration treatment on coking wastewater;

[0054] Perform reverse osmosis treatment on the nanofiltration produced water;

[0055] Perform defluorination and desilication treatment on the reverse osmosis concentrated water;

[0056] Perform evaporation crystallization treatment on the reverse osmosis concentrated water after the defluorination and desilication treatment;

[0057] Perform electrocatalytic oxidation treatment on the nanofiltration concentrated water and the evaporation crystallization mother liquor, and use a boron-doped diamond electrode as the anode for the electrocatalytic oxidation.

[0058] The technical concept of the present invention is further elaborated through two specific embodiments below.

[0059] Embodiment 1

[0060] The nanofiltration concentrated water enters the membrane concentrated liquid collection barrel, and the produced water enters the reverse osmosis unit 3; adjust the reverse osmosis pressure to 3 MPa, the produced water is recycled, and the concentrated water is collected and defluorinated and desilicated by adding defluorinating agents, PAC, PAM, etc. until the fluoride concentration in the concentrated water is 30 mg / L and the silica concentration is 40 mg / L, and then precipitation and filtration are carried out; the filtered wastewater enters the MVR evaporator for treatment, adjust the evaporation rate and the flow rate of the concentrated waste liquid to control the evaporation efficiency to 85%, the purity of the produced crystalline industrial salt is 97.5%, and the produced mother liquor enters the membrane concentrated liquid collection barrel; the membrane concentrated liquid (the water quality index is shown in Table 1) composed of the nanofiltration concentrated water and the MVR mother liquor enters the electrocatalytic oxidation unit 6, the anode uses a BDD electrode, the cathode uses a titanium electrode, the distance between the anode and cathode plates is 3 mm, and the current density is set to 550 A / m 2 , after reacting for 1 h, the COD of the membrane concentrated liquid drops below 80 mg / L, and the ammonia nitrogen drops below 10 mg / L, meeting the discharge standard of the "Emission Standard of Pollutants for Coking Chemical Industry" (GB16171-2012).

[0061]

[0062] Table 1

[0063] Embodiment 2

[0064] The nanofiltration concentrate enters the membrane concentrate collection tank, and the produced water enters the reverse osmosis unit 3; the reverse osmosis pressure is adjusted to 4 MPa, the produced water is recycled, and the concentrate is collected and defluorinated and desilicated by adding defluorinating agents, PAC, PAM, etc. until the fluoride concentration in the concentrate is 25 mg / L and the silica concentration is 30 mg / L, and then precipitation and filtration are carried out; the filtered wastewater enters the MVR evaporator for treatment, and the evaporation rate and the flow rate of the concentrated waste liquid are adjusted to control the evaporation efficiency at 88%, the purity of the produced crystalline industrial salt is 98.5%, and the produced mother liquor enters the membrane concentrate collection tank; the membrane concentrate (the water quality indexes are shown in Table 2) composed of the nanofiltration concentrate and the MVR mother liquor enters the electrocatalytic oxidation unit 6, the anode uses a BDD electrode, the cathode uses a titanium electrode, the distance between the anode and cathode plates is 3 mm, and the current density is set at 700 A / m 2 , after reacting for 2 h, the COD of the membrane concentrate drops below 80 mg / L, and the ammonia nitrogen drops below 10 mg / L, meeting the discharge standard of the "Pollutant Discharge Standard for Coking Chemical Industry" (GB16171-2012).

[0065]

[0066] Table 2

[0067] It can be seen that the degradation effects and the purity of the recovered salt in the above two embodiments show that the process method of the present invention has good effects on the degradation of organic matter and ammonia nitrogen in the coking wastewater membrane concentrate and the improvement of the purity of the recovered salt.

[0068] In summary, the embodiment of the present invention provides a coking wastewater treatment system. By using a BDD electrode as the anode of the electrocatalytic oxidation unit 6, it can directly perform electrocatalytic oxidation treatment on the nanofiltration concentrate and the evaporation crystallization mother liquor, avoid the enrichment of the nanofiltration concentrate and the evaporation crystallization mother liquor, improve the purity of the industrial salt, and at the same time eliminate the disposal cost of the mother liquor as hazardous waste and reduce the salt recovery cost.

[0069] In addition, it should also be recognized that although the present invention has been disclosed above with preferred embodiments, the above embodiments are not intended to limit the present invention. For any person skilled in the art, without departing from the scope of the technical solution of the present invention, many possible changes and modifications can be made to the technical solution of the present invention by using the technical content disclosed above, or modified into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still belong to the scope of protection of the technical solution of the present invention.

Claims

1. A coking wastewater treatment system, characterized in that, It includes an electrocatalytic oxidation unit, a nanofiltration unit, a reverse osmosis unit, a defluorination and desilication unit, and an evaporation and crystallization unit connected in sequence, where: The nanofiltration unit is used for primary filtration treatment of coking wastewater; The reverse osmosis unit is used for secondary filtration treatment of the nanofiltration product water; The defluorination and desilication unit is used for defluorination and desilication treatment of the reverse osmosis concentrate; The evaporation and crystallization unit is used for evaporation and crystallization treatment of the reverse osmosis concentrate after defluorination and desilication treatment; The electrocatalytic oxidation unit is connected to the nanofiltration unit and the evaporation and crystallization unit to receive the nanofiltration concentrate and the evaporation and crystallization mother liquor respectively. The electrocatalytic oxidation unit is used for electrocatalytic oxidation treatment of the nanofiltration concentrate and the evaporation and crystallization mother liquor, and the anode of the electrocatalytic oxidation unit adopts a boron-doped diamond electrode.

2. The coking wastewater treatment system according to claim 1, wherein The coking wastewater treatment system further includes a pretreatment unit, which is used for defluorination, COD removal, and hardness removal of the coking wastewater, and the effluent of the pretreatment unit enters the nanofiltration unit.

3. The coking wastewater treatment system according to claim 1, wherein The nanofiltration unit performs primary filtration on the coking wastewater under a pressure of 1 - 3 MPa.

4. The coking wastewater treatment system according to claim 1, wherein The reverse osmosis unit performs secondary filtration on the coking wastewater under a pressure of 2 - 4 MPa.

5. The coking wastewater treatment system according to claim 1, wherein The defluorination and desilication unit includes a reaction tank, a coagulation tank, a flocculation tank, and a sedimentation tank connected in sequence. The reaction tank is used for adding a defluorinating agent and a sodium hydroxide solution, the coagulation tank is used for adding a coagulant, the flocculation tank is used for adding a flocculant, and the sedimentation tank is used for realizing solid-liquid separation.

6. The coking wastewater treatment system according to claim 1, wherein In the reverse osmosis concentrate after defluorination and desilication treatment, the concentration of fluoride does not exceed 30 mg / L, and the concentration of silicon dioxide does not exceed 40 mg / L.

7. The coking wastewater treatment system according to claim 1, characterized in that, The evaporation efficiency of the evaporation and crystallization unit is not less than 85%, and the purity of the crystal salt is not less than 97.5%.

8. The coking wastewater treatment system according to claim 1, characterized in that, The plate spacing between the anode and the cathode of the electrocatalytic oxidation unit is 2 - 5 mm.

9. The coking wastewater treatment system according to claim 1, characterized in that The high current density of the electrocatalytic oxidation unit is 500 - 1000 A / m 2 .

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