CN109422395B

CN109422395B - Method for treating catalyst production wastewater

Info

Publication number: CN109422395B
Application number: CN201710751475.8A
Authority: CN
Inventors: 殷喜平; 李叶; 杨凌
Original assignee: China Petroleum and Chemical Corp; Sinopec Catalyst Co
Current assignee: China Petroleum and Chemical Corp; Sinopec Catalyst Co
Priority date: 2017-08-28
Filing date: 2017-08-28
Publication date: 2023-01-31
Anticipated expiration: 2037-08-28
Also published as: CN109422395A

Abstract

The invention relates to the field of sewage treatment, and discloses a method for treating catalyst production wastewater, wherein the catalyst production wastewater contains NH ₄ ⁺ 、SO ₄ ^2‑ 、Cl ^‑ And Na ⁺ The method comprises the following steps of 1) cooling and crystallizing wastewater to be treated to obtain a crystallization liquid containing sodium sulfate crystals, wherein the wastewater to be treated contains the catalyst production wastewater; 2) Carrying out first solid-liquid separation on the crystallization liquid containing the sodium sulfate crystals, and introducing a liquid phase obtained by the first solid-liquid separation into an MVR evaporation device for evaporation to obtain ammonia-containing steam and a concentrated solution containing sodium chloride crystals; 3) And carrying out second solid-liquid separation on the concentrated solution containing the sodium chloride crystals. The method can respectively obtain high-purity sodium sulfate and sodium chloride, and avoids the difficulty in the process of mixed salt treatment and recycling.

Description

Method for treating catalyst production wastewater

Technical Field

The invention relates to the field of sewage treatment, in particular to a method for treating catalyst production wastewater, and especially relates toContaining NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ The method for treating wastewater from catalyst production.

Background

In the production process of the oil refining catalyst, a large amount of inorganic acid alkali salts such as sodium hydroxide, hydrochloric acid, sulfuric acid, ammonium salts, sulfates, hydrochlorides and the like are needed, and a large amount of mixed sewage containing ammonium, sodium sulfate, sodium chloride and aluminosilicate is generated. For such sewage, the common practice in the prior art is that the pH value is adjusted to be within the range of 6 to 9, most of suspended matters are removed, then the biochemical method, the stripping method or the steam stripping method is adopted to remove ammonium ions, then the saline sewage is subjected to pH value adjustment, most of suspended matters are removed, the hardness, the silicon and part of organic matters are removed, then the saline sewage is subjected to ozone biological activated carbon adsorption oxidation or other advanced oxidation methods to remove most of organic matters, then the saline sewage enters an ion exchange device to further remove the hardness, and then the saline sewage enters a concentration device (such as reverse osmosis and/or electrodialysis) for concentration, and then the saline sewage is subjected to MVR evaporative crystallization or multiple-effect evaporative crystallization to obtain mixed miscellaneous salt of sodium sulfate and sodium chloride containing a small amount of ammonium salt; or is; firstly, adjusting the pH value to be within the range of 6.5-7.5, removing most suspended matters, then removing hardness, silicon and part of organic matters, removing most organic matters through ozone biological activated carbon adsorption oxidation or other advanced oxidation methods, then entering an ion exchange device for further removing hardness, entering a thickening device (such as reverse osmosis and/or electrodialysis) for concentration, and then adopting MVR (mechanical vapor recompression) evaporative crystallization or multi-effect evaporative crystallization to obtain the mixed salt of sodium sulfate and sodium chloride containing ammonium salt. However, these ammonium-containing mixed salts are currently difficult or expensive to treat, and the process of removing ammonium ions at the early stage adds additional cost to the treatment of wastewater.

In addition, the biochemical deamination can only treat wastewater with low ammonium content, and can not directly carry out biochemical treatment due to insufficient COD content in the catalyst sewage, and organic matters such as glucose or starch and the like are additionally added in the biochemical treatment process, so that the ammoniacal nitrogen can be treated by the biochemical method. The most important problems are that the total nitrogen of the wastewater after the biochemical deamination treatment is not up to the standard (the contents of nitrate ions and nitrite ions exceed the standard), advanced treatment is needed, in addition, the salt content in the wastewater is not reduced (20-30 g/L), the wastewater cannot be directly discharged, and further desalination treatment is needed.

In order to remove ammoniacal nitrogen from wastewater by gas stripping deamination, a large amount of alkali is needed to adjust the pH value, the alkali consumption is high, the alkali in the wastewater after deamination cannot be recovered, the pH value of the treated wastewater is high, the treatment cost is high, the COD content in the catalyst wastewater after gas stripping does not change greatly, the salt content in the wastewater is not reduced (20-30 g/L), the wastewater cannot be directly discharged, further desalting treatment is needed, the wastewater treatment operation cost is high, a large amount of alkali remains in the treated wastewater, the pH value is high, waste is large, and the treatment cost is up to 50 yuan/ton.

Disclosure of Invention

The invention aims to overcome the defect of NH content in the prior art ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ The wastewater treatment cost is high, and only mixed salt crystals can be obtained, and the NH-containing catalyst with low cost and environmental protection is provided ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ The method for treating wastewater can respectively recover ammonium, sodium sulfate and sodium chloride in the wastewater, and furthest recycle resources in the wastewater.

In order to achieve the above object, the present invention provides a method for treating catalyst production wastewater containing NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ The method comprises the following steps of,

1) Cooling and crystallizing the wastewater to be treated to obtain a crystallization liquid containing sodium sulfate crystals, wherein the wastewater to be treated contains the catalyst production wastewater;

2) Carrying out first solid-liquid separation on the crystallization liquid containing the sodium sulfate crystals, and introducing a liquid phase obtained by the first solid-liquid separation into an MVR evaporation device for evaporation to obtain ammonia-containing steam and a concentrated solution containing sodium chloride crystals;

3) Carrying out second solid-liquid separation on the concentrated solution containing the sodium chloride crystals;

wherein SO in the wastewater to be treated ₄ ^2- Has a concentration of 0.01mol/L or more, cl ^- The concentration of (A) is less than 5.2 mol/L; before the liquid phase obtained by the first solid-liquid separation is introduced into an MVR evaporation device, enabling the pH value of the liquid phase obtained by the first solid-liquid separation to be larger than 9; the evaporation did not crystallize out sodium sulfate.

By the technical scheme, the method aims at the content of NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ The sodium sulfate crystal is obtained by cooling, crystallizing and separating the catalyst production wastewater, then the pH value of a liquid phase obtained by solid-liquid separation is adjusted to a specific range, and then sodium chloride crystal and ammonia water are obtained by evaporation. The method can respectively obtain high-purity sodium sulfate and sodium chloride, avoids the difficulties in the processes of mixed salt treatment and recycling, simultaneously completes the process of separating ammonia and salt, simultaneously heats up the wastewater and cools the ammonia-containing steam by adopting a heat exchange mode without a condenser, reasonably utilizes the heat in the evaporation process, saves energy, reduces the wastewater treatment cost, recovers the ammonium in the wastewater in the form of ammonia water, recovers the sodium chloride and the sodium sulfate in the form of crystals respectively, does not generate waste residues and waste liquid in the whole process, and achieves the aim of changing waste into valuable.

Drawings

FIG. 1 is a schematic flow diagram of a method for treating wastewater from catalyst production according to an embodiment of the present invention.

Description of the reference numerals

1. MVR evaporation plant 54, second mother liquor jar

2. Cooling crystallization device 61 and first pH value measuring device

32. Second heat exchange device 62 and second pH value measuring device

33. Third heat exchange device 71 and first circulating pump

34. Fourth heat exchange device 72 and second circulating pump

36. Sixth heat exchange device 73 and third circulation pump

52. Ammonia storage tank 74 and fourth circulating pump

53. First mother liquor tank 76 and sixth circulating pump

77. Seventh circulating pump 83 and tail gas absorption tower

78. Eighth circulating pump 9, concentration device

79. Ninth circulating pump 91 and first solid-liquid separating apparatus

80. Tenth circulating pump 92, second solid-liquid separation device

81. Vacuum pump 102 and compressor

82. Circulating water pool

Detailed Description

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For numerical ranges, each range between its endpoints and individual point values, and each individual point value can be combined with each other to give one or more new numerical ranges, and such numerical ranges should be construed as specifically disclosed herein.

The present invention will be described below with reference to fig. 1, but the present invention is not limited to fig. 1.

The invention provides a method for treating wastewater generated in catalyst production, which contains NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ The method comprises the following steps of,

1) Cooling and crystallizing wastewater to be treated to obtain a crystallization liquid containing sodium sulfate crystals, wherein the wastewater to be treated contains the catalyst production wastewater;

wherein SO in the wastewater to be treated ₄ ^2- Has a concentration of 0.01mol/L or more, cl ^- The concentration of (A) is less than 5.2 mol/L; before the liquid phase obtained by the first solid-liquid separation is introduced into an MVR evaporation device, enabling the pH value of the liquid phase obtained by the first solid-liquid separation to be more than 9; the evaporation did not crystallize out sodium sulfate.

Preferably, the wastewater to be treated is the catalyst production wastewater; or the wastewater to be treated contains the catalyst production wastewater and a liquid phase obtained by the second solid-liquid separation.

More preferably, the wastewater to be treated is a mixed solution of the catalyst production wastewater and at least part of a liquid phase obtained by the second solid-liquid separation.

The method provided by the invention can be used for the treatment of the compounds containing NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ In addition to containing NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ In addition, the catalyst production wastewater is not particularly limited. SO contained in the wastewater to be treated from the viewpoint of improving the treatment efficiency of the wastewater ₄ ^2- Is 0.01mol/L or more, more preferably 0.07mol/L or more, further preferably 0.1mol/L or more, further preferably 0.2mol/L or more, particularly preferably 0.3mol/L or more, and may be, for example, 0.5 to 1mol/L, further preferably 0.6 to 0.7mol/L. And, cl in the wastewater to be treated ^- The concentration of (B) is 5.2mol/L or less, preferably 4.5mol/L or less, more preferably 3mol/L or less, preferably 0.01mol/L or more, more preferably 0.05mol/L or more, more preferably 0.1mol/L or more, further preferably 0.5mol/L or more, further preferably 1mol/L or more, further preferably 2mol/L or more, and may be, for example, 2 to 3mol/L. By adding SO in the wastewater to be treated ₄ ^2- 、Cl ^- The concentration of (3) is controlled in the above range, and sodium sulfate can be precipitated from the cooled crystals while sodium chloride and the like are hardly precipitated, thereby achieving the purpose of efficiently separating sodium sulfate.

SO in the wastewater to be treated ₄ ^2- Specific examples of the content include: 0.01mol/L, 0.03mol/L, 0.05mol/L, 0.08mol/L, 0.1mol/L, 0.2mol/L, 0.3mol/L, 0.4mol/L, 0.5mol/L, 0.6mol/L, 0.7mol/L, 0.8mol/L, 0.9mol/L, 1mol/L, 1.1mol/L, 1.2mol/L, 1.3mol/L, 1.4mol/L, or 1.5mol/L, and the like.

Cl in the wastewater to be treated ^- Specific examples of the content include: 0.01mol/L, 0.05mol/L, 0.1mol/L, 0.3mol/L, 0.6mol/L, 0.8mol/L, 1mol/L, 1.2mol/L, 1.4mol/L, 1.6mol/L, 1.8mol/L, 2.0mol/L, 2.2mol/L, 2.4mol/L, 2.6mol/L, 2.8mol/L, 3mol/L, 3.2mol/L, 3.4mol/L, 3.6mol/L, 3.8mol/L, 4mol/L, 4.5mol/L or 5mol/L, etc.

In the present invention, the order of the first heat exchange, the adjustment of the pH of the wastewater to be treated, and the preparation of the wastewater to be treated (in the case where the wastewater to be treated contains a liquid phase obtained by the solid-liquid separation of the catalyst production wastewater and the second solid-liquid separation, the preparation of the wastewater to be treated) is not particularly limited, and may be appropriately selected as needed and may be completed before the wastewater to be treated is cooled and crystallized.

In the present invention, the purpose of the cooling crystallization is to precipitate sodium sulfate, but sodium chloride, ammonium sulfate and the like are not precipitated, and sodium sulfate can be separated from wastewater favorably. The cooling crystallization merely precipitates sodium sulfate, and sodium chloride and the like carried by the sodium sulfate crystals or adsorbed on the surface are not excluded. In the present invention, the content of sodium sulfate in the obtained sodium sulfate crystals is preferably 92% by mass or more, more preferably 96% by mass or more, and further preferably 98% by mass or more), it is understood that the amount of the obtained sodium sulfate crystals is based on a dry basis. When the content of sodium sulfate in the obtained sodium sulfate crystal is within the above range, it is considered that only sodium sulfate is precipitated.

In the present invention, the conditions for the cooling crystallization are not particularly limited and may be appropriately selected as necessary, and the effect of crystallizing the sodium sulfate may be obtained. The cooling crystallization conditions may include: the temperature is-21.7-17.5 ℃, preferably-20-5 ℃, more preferably-10-5 ℃, further-10-0 ℃, and particularly preferably-4-0 ℃; the time (in terms of the residence time in the cooling crystallization apparatus 2) is 5min or more, preferably 60min to 180min, more preferably 90min to 150min, and still more preferably 120min to 150min. By controlling the cooling crystallization conditions within the above range, sodium sulfate can be sufficiently precipitated without precipitating other miscellaneous salts.

Specific examples of the temperature for cooling and crystallizing include: -21 ℃, -20 ℃, -19 ℃, -18 ℃, -17 ℃, -16 ℃, -15 ℃, -14 ℃, -13 ℃, -12 ℃, -11 ℃, -10 ℃, -9 ℃, -8 ℃, -7 ℃, -6 ℃, -5 ℃, -4 ℃, -3 ℃, -2 ℃, -1 ℃ or 0 ℃.

Specific examples of the time for cooling crystallization include: 5min, 6min, 7min, 8min, 10min, 15min, 20min, 25min, 30min, 35min, 40min, 45min, 50min, 52min, 54min, 56min, 58min, 60min, 65min, 70min, 75min, 80min, 85min, 90min, 95min, 100min, 105min, 110min, 115min, 120min, 130min, 140min, 150min, or 160min.

According to the present invention, the cooling crystallization is carried out in a continuous or batch manner, and the cooling crystallization is preferably carried out in a continuous cooling crystallization manner, as long as the purpose of precipitating sodium sulfate crystals by lowering the temperature of the wastewater to be treated is achieved. The cooling crystallization of sodium sulfate can be carried out by various cooling crystallization devices conventionally used in the art, for example, by using a continuous cooling crystallizer with an external cooling heat exchanger, or by using a crystallization tank having a cooling means, such as the cooling crystallization device 2. The cooling part can lead the wastewater to be treated in the cooling crystallization device to be cooled to the condition required by cooling crystallization by introducing a cooling medium. The cooling crystallization equipment is preferably provided with a blending part, such as a stirrer and the like, and the wastewater to be treated is blended to achieve the effect of uniform cooling, so that sodium sulfate in the wastewater can be fully separated out, and the grain size is increased. The cooling crystallization device is preferably provided with a circulating pump, so as to avoid generating a large amount of fine crystal nuclei and prevent crystal grains in circulating crystal slurry from colliding with an impeller at a high speed to generate a large amount of secondary crystal nuclei, and the circulating pump is preferably a low-rotation-speed centrifugal pump, more preferably a high-flow and low-rotation-speed guide pump impeller or a high-flow, low-lift and low-rotation-speed axial flow pump.

According to the invention, the pH value of the wastewater to be treated is preferably adjusted to be greater than 7 before the wastewater to be treated is subjected to cooling crystallization. Adjusting the pH value of the wastewater to be treated to ensure that NH is contained in the wastewater ₄ ⁺ Most of the ammonia exists in the form of ammonia molecules, so that the precipitation of ammonium sulfate and/or ammonium chloride is prevented in the cooling crystallization process, and the precipitation rate of sodium sulfate can be improved. Preferably, before the wastewater to be treated is cooled and crystallized, the pH of the wastewater to be treated is adjusted to 8 or more, so that precipitation of ammonium sulfate and/or ammonium chloride can be further suppressed. In the cooling crystallization step, the content of ammonium salt in the obtained crystal is preferably 1 mass% or less, more preferably 0.5 mass% or less.

In the present invention, the method of the pH adjustment is not particularly limited, and for example, the pH of the wastewater to be treated may be adjusted by adding an alkaline substance. The alkaline substance is not particularly limited, and the purpose of adjusting the pH value may be achieved. The alkaline substance is preferably NaOH in order not to introduce new impurities in the wastewater to be treated, increasing the purity of the crystals obtained. Further, the second mother liquor (i.e., the liquid phase obtained by the second solid-liquid separation) contains NaOH at a relatively high concentration, and it is also preferable to use the second mother liquor as the alkaline substance.

The manner of adding the basic substance may be any manner known in the art, but it is preferable to mix the basic substance with the wastewater to be treated in the form of an aqueous solution, and for example, an aqueous solution containing the basic substance may be introduced into a pipe through which the wastewater to be treated is introduced and mixed. The content of the alkaline substance in the aqueous solution is not particularly limited as long as the purpose of adjusting the pH can be achieved. However, in order to reduce the amount of water used and further reduce the cost, it is preferable to use a saturated aqueous solution of an alkaline substance or a second mother liquor. In order to monitor the pH value of the wastewater to be treated, the pH value of the wastewater to be treated may be measured after the above-mentioned pH value adjustment.

According to a preferred embodiment of the present invention, the cooling crystallization is performed in the cooling crystallization device 2, and the pH adjustment is performed by introducing and mixing the aqueous solution containing the alkaline substance in the pipe that feeds the wastewater to be treated to the first cooling crystallization device 2 before feeding the wastewater to be treated to the cooling crystallization device 2. And the adjusted pH is measured by the first pH measuring device 61 after the adjustment.

By carrying out the cooling crystallization at the above temperature and pH, sodium sulfate can be sufficiently precipitated in the cooling crystallization without precipitating sodium chloride, ammonium sulfate and/or ammonium chloride, thereby achieving the purpose of separating and purifying sodium sulfate.

In the present invention, in order to control the crystal size distribution in the cooling crystallization device 2 and reduce the content of fine crystal grains, it is preferable that a part of the liquid crystallized by the cooling crystallization device 2 (i.e., the liquid located inside the cooling crystallization device 2, hereinafter also referred to as cooling circulation liquid) is mixed with the wastewater to be treated and then returned to the cooling crystallization device 2 for cooling crystallization again. The process of returning the cooling circulation liquid to the cooling crystallization device 2 for crystallization can be, for example, by returning the cooling circulation liquid to the sixth heat exchange device 36 through the second circulation pump 72, mixing the cooling circulation liquid with the wastewater to be treated, then entering the sixth heat exchange device 36 for heat exchange, and then entering the cooling crystallization device 2 again for cooling crystallization. The return amount of the cooling crystallization circulating liquid can be defined by a circulation ratio of cooling crystallization, wherein the circulation ratio of cooling crystallization is as follows: the ratio of the circulating amount to the total amount of the liquid fed to the cooling crystallization device minus the circulating amount. The circulation ratio may be appropriately set according to the supersaturation degree of sodium sulfate in the cooling crystallization apparatus 2 to ensure the particle size of sodium sulfate crystals. In order to control the particle size distribution of crystals obtained by cooling crystallization and to reduce the content of fine crystal grains, it is preferable to control the supersaturation degree to less than 1.5g/L, more preferably to less than 1g/L.

In the invention, the sodium sulfate crystals and the first mother liquor (i.e. the liquid phase obtained by the first solid-liquid separation) are obtained after the first solid-liquid separation is carried out on the crystallization liquid containing the sodium sulfate crystals. The method of the first solid-liquid separation is not particularly limited, and may be selected from, for example, one or more of centrifugation, filtration, and sedimentation.

According to the present invention, the first solid-liquid separation may be performed by using a first solid-liquid separation device (for example, a centrifuge, a filter, or the like) 91. After the first solid-liquid separation, the first mother liquor obtained by the first solid-liquid separation device 91 is temporarily stored in the first mother liquor tank 53, and may be sent to the MVR evaporation apparatus 1 by the sixth ring pump 76 to be evaporated. In addition, it is difficult to avoid that impurities such as chlorine ions, free ammonia, and hydroxide ions are adsorbed on the obtained sodium sulfate crystals, and in order to remove the adsorbed impurities, reduce the odor of solid salts, reduce corrosiveness, and improve the purity of the crystals, the sodium sulfate crystals are preferably subjected to first washing with water or a sodium sulfate solution, and may be dried when anhydrous sodium sulfate is required to be obtained.

The manner of the first solid-liquid separation and the first washing is not particularly limited, and may be carried out, for example, by using a solid-liquid separation apparatus which is conventional in the art, or may be carried out on a staged solid-liquid separation apparatus such as a belt filter. The washing is not particularly limited and may be carried out by a method conventional in the art. The first wash comprises panning and/or rinsing. The first washing method is preferably rinsing, and more preferably rinsing is performed after solid-liquid separation. The number of washing is not particularly limited, and may be 1 or more, and is preferably 2 to 4 times in order to obtain sodium sulfate crystals of higher purity. The first washing is preferably carried out using an aqueous sodium sulfate solution (the concentration of which is preferably such that the sodium chloride and the sodium sulfate reach the concentration of sodium sulfate in the saturated aqueous solution at the same time at the temperature corresponding to the sodium sulfate crystals to be washed). The liquid generated by washing is preferably returned to the cooling crystallization device 2, and for example, the liquid can be returned to the sixth heat exchange device 36 through the eighth circulating pump 78, mixed with the wastewater to be treated, then enters the sixth heat exchange device 36 for heat exchange, and then enters the cooling crystallization device 2 again for cooling crystallization.

According to a preferred embodiment of the present invention, after cooling and crystallizing the obtained crystal liquid containing sodium sulfate, solid-liquid separation is performed by a solid-liquid separation apparatus, and the crystal obtained by the solid-liquid separation is rinsed again with an aqueous sodium sulfate solution (the concentration of the aqueous sodium sulfate solution is the concentration of sodium sulfate in an aqueous solution in which sodium chloride and sodium sulfate are simultaneously saturated at a temperature corresponding to the sodium sulfate crystal to be washed), and the rinsed liquid is returned to the cooling and crystallizing apparatus 2. By the above washing process, the purity of the obtained sodium sulfate crystals can be improved.

In the present invention, in order to reduce the cost of wastewater treatment, after the first solid-liquid separation is completed, the first mother liquor is preferably subjected to a concentration treatment before being introduced into the MVR evaporation apparatus 1. The degree of the concentration is not particularly limited as long as the concentration treatment does not precipitate crystals in the liquid phase obtained by the first solid-liquid separation. The concentration treatment may be carried out by a concentration method conventional in the art, for example, a reverse osmosis method, an electrodialysis method, or the like. Among them, from the viewpoint of cost reduction and improvement in efficiency of subsequent evaporation, the concentration treatment is preferably carried out by an electrodialysis method, for example, by the concentration device 9 (electrodialysis device). The concentrated solution obtained by the electrodialysis method is evaporated in the next step, and the diluted solution is preferably returned to the concentration step before the treatment of the catalyst production wastewater, and is treated by the method of the invention after being further concentrated. The liquid volume in the evaporation process can be reduced through the concentration, and the evaporation efficiency is improved, so that the wastewater treatment efficiency is improved, and the cost is reduced.

According to the invention, in order to fully utilize the cold energy of the first mother liquor, the first mother liquor and the wastewater to be treated are preferably subjected to first heat exchange before the wastewater to be treated is subjected to cooling crystallization.

According to a preferred embodiment of the present invention, the first heat exchange is performed by the second heat exchange device 32, and specifically, the first mother liquor and the wastewater to be treated are respectively passed through the second heat exchange device 32 to exchange heat, so that the temperature of the wastewater to be treated is lowered to facilitate the cooling crystallization, and the temperature of the first mother liquor is raised to facilitate the evaporation. After the first heat exchange is carried out by the second heat exchange device 32, the temperature of the wastewater to be treated is-20.7-16.5 ℃, preferably-5-10 ℃, and is close to the temperature of cooling crystallization.

According to the present invention, in order to facilitate the cooling crystallization, it is preferable to further subject the wastewater to be treated to the first heat exchange with the refrigerant liquid. According to a preferred embodiment of the present invention, the first heat exchange between the wastewater to be treated and the refrigerating fluid is performed by the sixth heat exchange device 36, and specifically, the refrigerating fluid and the wastewater to be treated are respectively passed through the sixth heat exchange device 36 to exchange heat therebetween, so that the temperature of the wastewater to be treated is lowered to facilitate the cooling crystallization. The refrigerating fluid can be the refrigerating fluid which is used for reducing the temperature conventionally in the field, as long as the temperature of the wastewater to be treated can meet the requirement of cooling crystallization.

The second heat exchange device 32 and the sixth heat exchange device 36 are not particularly limited, and various heat exchangers conventionally used in the art may be used to achieve the purpose of heat exchange. Specifically, a jacketed heat exchanger, a plate heat exchanger, a shell-and-tube heat exchanger, or the like may be mentioned, with the plate heat exchanger being preferred. The material of the heat exchanger can be specifically selected according to the needs, for example, in order to resist the corrosion of chloride ions, the heat exchanger of duplex stainless steel, titanium and titanium alloy, hastelloy can be selected as the material, and the heat exchanger containing plastic material can be selected when the temperature is lower. The second heat exchange device 32 is preferably a heat exchanger made of plastic.

In the present invention, the purpose of the evaporation is to precipitate sodium chloride and to evaporate ammonia without precipitating sodium sulfate, so that sodium chloride can be separated from the wastewater to be treated well. The evaporation merely precipitates sodium chloride and does not exclude sodium sulfate entrained by sodium chloride crystals or adsorbed on the surface. In the present invention, when the content of sodium sulfate in the obtained sodium chloride crystal is 8% by mass or less (preferably 4% by mass or less, more preferably 2% by mass or less), it is considered that only sodium chloride is precipitated, and sodium sulfate is not precipitated.

In the present invention, the MVR vaporizing device 1 is not particularly limited, and may be various MVR vaporizing devices conventionally used in the art. For example, it may be one or more selected from the group consisting of an MVR falling film evaporator, an MVR forced circulation evaporator, an MVR-FC continuous crystallization evaporator, and an MVR-OSLO continuous crystallization evaporator. Among them, preferred are an MVR forced circulation evaporator and an MVR-FC continuous crystallization evaporator, and more preferred is a falling film + forced circulation two-stage MVR evaporative crystallizer.

In the present invention, the evaporation conditions for the evaporation are not particularly limited, and may be appropriately selected as needed to achieve the purpose of precipitating crystals. The conditions of the evaporation may include: the temperature is above 17.5 ℃, and the pressure is above-101 kPa; preferably, the conditions of evaporation include: the temperature is 35-110 ℃, and the pressure is-98 kPa-12 kPa; preferably, the conditions of the evaporation include: the temperature is 45-110 ℃, and the pressure is-95 kPa-12 kPa; preferably, the conditions of evaporation include: the temperature is 50-100 ℃, and the pressure is-93 kPa to-22 kPa.

In the present invention, it is understood that the ammonia-containing steam is what is known in the art as secondary steam. The pressures are all pressures in gauge pressure.

In the present invention, the operation pressure of evaporation is preferably the saturated vapor pressure of the evaporated feed liquid. Further, the evaporation amount of the evaporation may be appropriately selected depending on the capacity of the apparatus to treat and the amount of the waste water to be treated, and may be, for example, 0.1m ³ More than h (e.g. 0.1 m) ³ /h～500m ³ /h)。

In order to ensure that the evaporation process can give sodium chloride crystals of high purity, it is preferable to use SO contained in the liquid phase obtained by the first solid-liquid separation for 1mol ₄ ^2- Cl contained in the liquid phase obtained by the first solid-liquid separation ^- Is 9.5mol or more, preferably 10mol or more, preferably 20mol or more, more preferably 44mol or more, more preferably 50mol or more, more preferably 74mol or more, preferably 460mol or less, more preferably 233mol or less, further preferably 75mol or less, and may be, for example, 9.5mol, 10.5mol, 11mol, 11.5mol, 12mol, 12.5mol, 13mol, 13.5mol, 14mol, 14.5mol, 15mol, 15.5mol, 16mol, 16.5mol, 17mol, 17.5mol, 18mol, 18.5mol, 19mol, 19.5mol, 20mol, 21mol, 22mol, 23mol, 25mol, 27mol, 29mol, 31mol, 35mol, 40mol, 45mol, 50mol or the like. By reacting SO ₄ ^2- And Cl ^- The molar ratio of (A) is controlled to be aboveWithin the range, pure sodium chloride crystals can be obtained through evaporation, so that the separation of sodium sulfate and sodium chloride is realized, and the energy consumption in the cooling crystallization process is reduced.

According to the present invention, the higher the evaporation proceeds, the better, from the viewpoint of improving the efficiency of wastewater treatment; however, if the evaporation exceeds a certain level, sodium sulfate is crystallized and a concentrated solution containing only sodium chloride crystals cannot be obtained. Therefore, the evaporation is performed to such an extent that sodium sulfate does not crystallize out, that is, the evaporation is performed so that the concentration of sodium sulfate in the concentrated solution becomes Y or less (where Y is the concentration of sodium sulfate at which both sodium sulfate and sodium chloride in the concentrated solution are saturated under the evaporation conditions). Preferably, the evaporation is such that the concentration of sodium sulphate in the concentrate is from 0.9Y to 0.99Y, more preferably from 0.95Y to 0.98Y. By controlling the degree of evaporation within the above range, it is possible to ensure that as much sodium chloride is precipitated as possible during the evaporation process, and the evaporation can be carried out at a higher efficiency, thereby obtaining a concentrated solution containing only sodium chloride crystals.

In the present invention, the degree of progress of the evaporation is monitored by monitoring the concentration of the liquid obtained by the evaporation, and specifically, the concentration of the liquid obtained by the evaporation is controlled within the above range so that the evaporation does not cause the precipitation of sodium sulfate crystals in the first mother liquor. The concentration of the liquid obtained by evaporation is monitored by measuring the density, which can be measured, in particular, by using a densitometer.

In the present invention, in order to increase the solid content in the MVR evaporation device 1 and reduce the ammonia content in the liquid, it is preferable to return part of the liquid evaporated by the MVR evaporation device 1 (i.e. the liquid located inside the MVR evaporation device, hereinafter also referred to as circulating liquid) to the MVR evaporation device 1 for evaporation, and it is preferable to return the liquid to the MVR evaporation device 1 after heating for evaporation. The above-described process of returning the circulation liquid to the MVR evaporating device 1 may be returned to the second heat exchange process by, for example, the seventh circulation pump 77. The reflux ratio of the evaporation refers to: the ratio of the amount of reflux to the total amount of liquid fed to the MVR evaporator minus the amount of reflux. The reflux ratio can be set appropriately according to the evaporation amount to ensure that the MVR evaporation device can evaporate the required amount of water and ammonia at a given evaporation temperature. The reflux ratio of the evaporation may be, for example, 10 to 200, preferably 15 to 100.

According to the present invention, preferably, the method further comprises compressing the ammonia-containing vapor before the second heat exchange. The compression of the ammonia-containing vapor may be performed by a compressor 102. The ammonia-containing steam is compressed, energy is input into the MVR evaporation system, the continuous process of waste water heating, evaporation and cooling is guaranteed, starting steam needs to be input when the MVR evaporation process is started, energy is supplied only through the compressor 102 after a continuous running state is achieved, and other energy does not need to be input. The compressor 102 may be any compressor conventionally used in the art, such as a centrifugal fan, a turbine compressor, a roots compressor, or the like. After compression by the compressor 102, the temperature of the ammonia-containing vapor is raised by 5 ℃ to 20 ℃.

In order to fully utilize the heat of the evaporated ammonia-containing vapor according to the present invention, it is preferable to subject the first mother liquor to a second heat exchange with the ammonia-containing vapor before the first mother liquor is sent to the MVR evaporation apparatus 1.

According to a preferred embodiment of the present invention, the second heat exchange of the first mother liquor with the ammonia-containing vapor is performed by a third heat exchange means 33 and a fourth heat exchange means 34, respectively. Specifically, the first mother liquor sequentially passes through the third heat exchange device 33 and the fourth heat exchange device 34, and ammonia-containing steam sequentially passes through the fourth heat exchange device 34 and the third heat exchange device 33, so that the first mother liquor is heated to be evaporated conveniently, and the ammonia-containing steam is condensed to obtain ammonia water. After heat exchange is carried out by the third heat exchange device 33, the temperature of the first mother liquor is raised to be more than 16.5 ℃, preferably 34-109 ℃, and more preferably 44-109 ℃; after heat exchange by the fourth heat exchange device 34, the temperature of the first mother liquor is raised to above 17 ℃, preferably 40 ℃ to 117 ℃, and preferably 50 ℃ to 117 ℃.

The third heat exchange device 33 and the fourth heat exchange device 34 are not particularly limited, and various heat exchangers conventionally used in the art can be used to exchange heat between the ammonia-containing steam and the first mother liquor. Specifically, it may be a jacketed heat exchanger, a plate heat exchanger, a shell-and-tube heat exchanger, or the like, with the plate heat exchanger being preferred. The material of the heat exchanger can be specifically selected according to the needs, for example, in order to resist the corrosion of chloride ions, the heat exchanger of duplex stainless steel, titanium and titanium alloy, hastelloy can be selected as the material, and the heat exchanger containing plastic material can be selected when the temperature is lower. Preferably, a duplex stainless steel plate heat exchanger is used.

According to the present invention, it is preferred to adjust the pH of the first mother liquor to a value greater than 9, preferably greater than 10.8, more preferably between 10.8 and 11.5, before passing the first mother liquor to the MVR evaporation unit 1. The upper limit of the adjustment of the pH of the first mother liquor (that is, the liquid phase obtained by the first solid-liquid separation) is not limited, and may be, for example, 14 or less, preferably 13.5 or less, and more preferably 13 or less. By adjusting the pH value of the first mother liquor to the above range, ammonia can be ensured to be fully evaporated in the evaporation process, thereby improving the purity of the obtained sodium chloride. The pH adjustment of the first mother liquor may be performed in the manner of pH adjustment of the wastewater to be treated as described above, except that the pH adjustment range is different.

Specific examples of adjusting the pH of the first mother liquor before passing the first mother liquor into the MVR evaporator 1 include: 9. 9.5, 9.6, 9.7, 9.8, 9.9, 10, 10.1, 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9, 11, 11.1, 11.2, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9, 12, 12.2, 12.4, 12.6, 12.8, 13, 13.5, or 14, etc.

According to a preferred embodiment of the present invention, an aqueous solution of a basic substance is introduced into the line feeding the first mother liquor into the MVR evaporator 1 and mixed with the first mother liquor before the first mother liquor is fed into the MVR evaporator 1 for pH adjustment. And the pH of the adjusted first mother liquor may be monitored by the second pH measuring device 62.

According to the present invention, the second solid-liquid separation may be performed by a second solid-liquid separation device (e.g., a centrifuge, a belt filter, a plate filter, etc.) 92. After the second solid-liquid separation, the second mother liquor obtained by the second solid-liquid separation device 92 (i.e. the liquid phase obtained by the second solid-liquid separation) is returned to the cooling crystallization device 2 for cooling crystallization again, and specifically, the second mother liquor can be returned to the previous pH adjustment by the ninth circulation pump 79. In addition, it is difficult to avoid that the obtained sodium chloride crystals adsorb certain impurities such as sulfate ions, free ammonia, hydroxide ions, etc., and in order to remove the adsorbed impurities, reduce the odor of solid salts, reduce corrosiveness, and improve the purity of the crystals, the sodium chloride crystals are preferably subjected to secondary washing with water, the catalyst production wastewater, or a sodium chloride solution and dried. In order to avoid dissolution of the sodium chloride crystals during washing, the sodium chloride crystals are preferably washed with an aqueous sodium chloride solution. More preferably, the concentration of the sodium chloride aqueous solution is preferably the concentration of sodium chloride in the aqueous solution at which sodium chloride and sodium sulfate reach saturation simultaneously at the temperature corresponding to the sodium chloride crystals to be washed.

The form of the second solid-liquid separation and the second washing is not particularly limited, and may be carried out, for example, by using a combination of an elutriation apparatus and a solid-liquid separation apparatus which are conventional in the art, or may be carried out on a staged solid-liquid separation apparatus such as a belt filter. The second washing mode comprises elutriation and/or rinsing. The above-mentioned elutriation and rinsing are not particularly limited and may be carried out by a method conventional in the art. The number of elutriation and rinsing is not particularly limited, and may be 1 or more, and is preferably 2 to 4 times in order to obtain sodium chloride crystals of higher purity. In the elutriation process, the catalyst production wastewater is generally not recycled when being used as an elutriation liquid, and the washing liquid recovered by the second washing can be recycled in a counter-current manner when being used as the elutriation liquid. Before the elutriation, it is preferable to perform preliminary solid-liquid separation by sedimentation to obtain a slurry containing sodium chloride crystals (the liquid content may be 35% by mass or less). In the elutriation process, 1 to 20 parts by weight of a liquid is used for elutriation with respect to 1 part by weight of a slurry containing sodium chloride crystals. The rinsing is preferably carried out using an aqueous sodium chloride solution, the concentration of which is preferably the concentration of sodium chloride in an aqueous solution in which sodium chloride and sodium sulfate are simultaneously saturated at the temperature corresponding to the sodium chloride crystals to be rinsed. In order to further enhance the elutriation effect and obtain sodium chloride crystals with higher purity, it is preferable to perform elutriation using the eluted eluent. For the liquid generated by washing, it is preferable that the elutriation liquid of the catalyst production wastewater is returned to the MVR evaporation device 1 before the pH adjustment before cooling and crystallization, and the other washing liquid is returned.

According to a preferred embodiment of the present invention, the concentrated solution containing sodium chloride crystals obtained by evaporation is subjected to preliminary solid-liquid separation by settling, then elutriated in another elutriation tank using a liquid obtained when sodium chloride crystals are subsequently washed, the elutriated concentrated solution containing sodium chloride crystals is sent to a solid-liquid separation apparatus for solid-liquid separation, the crystals obtained by solid-liquid separation are washed with an aqueous sodium chloride solution (the concentration of the aqueous sodium chloride solution is the concentration of sodium chloride in an aqueous solution in which sodium chloride and sodium sulfate are simultaneously saturated at a temperature corresponding to the sodium chloride crystals to be washed), and the washed liquid is returned to the elutriation as an elutriation liquid. Through the washing process combining elutriation and leaching, the purity of the obtained sodium chloride crystal is improved, washing liquid cannot be introduced too much, and the efficiency of wastewater treatment is improved.

According to a preferred embodiment of the invention, the tail gas generated by cooling crystallization is discharged after ammonia removal; and discharging the tail gas which is remained by the condensation of the second heat exchange after ammonia removal. The tail gas generated by the cooling crystallization is the tail gas discharged from the cooling crystallization device 2, and the second heat exchange condenses the remaining tail gas, i.e. the non-condensable gas discharged from the fourth heat exchange device 34. The ammonia in the tail gas is removed, so that the pollutant content in the discharged tail gas can be further reduced, and the tail gas can be directly discharged.

As the method of removing ammonia, absorption may be performed by the off-gas absorption tower 83. The off-gas absorption column 83 is not particularly limited, and may be any of various absorption columns conventionally used in the art, such as a plate-type absorption column, a packed absorption column, a falling film absorption column, or an empty column. Circulating water is arranged in the tail gas absorption tower 83, the circulating water circulates in the tail gas absorption tower 83 under the action of the fourth circulating pump 74, water can be supplemented into the tail gas absorption tower 83 from the circulating water tank 82 through the third circulating pump 73, fresh water can be supplemented into the circulating water tank 82, and meanwhile the temperature of working water of the vacuum pump 81 and the ammonia content can be reduced. The flow of the off-gas and the circulating water in the off-gas absorption tower 83 may be in a counter-current or co-current flow, preferably in a counter-current flow. The circulating water can be supplemented by additional fresh water. In order to ensure the sufficient absorption of the tail gas, dilute sulfuric acid may be further added to the tail gas absorption tower 83 to absorb a small amount of ammonia and the like in the tail gas. The circulating water can be used as ammonia water or ammonium sulfate solution for production or direct sale after absorbing tail gas. The off gas may be introduced into the off gas absorption tower 83 by a vacuum pump 81.

In the present invention, the catalyst production wastewater is not particularly limited as long as it contains NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ The wastewater is obtained. In addition, the method is particularly suitable for treating high-salt ammonium-containing wastewater. The wastewater from the catalyst production of the present invention may be specifically wastewater from the production of a molecular sieve, alumina or an oil refining catalyst, or wastewater from the production of a molecular sieve, alumina or an oil refining catalyst after the following impurity removal and concentration. It is preferable that the wastewater from the production of molecular sieves, alumina or refinery catalysts is subjected to the following impurity removal and concentration.

As NH in the catalyst production wastewater ₄ ⁺ May be 8mg/L or more, preferably 300mg/L or more.

As Na in the wastewater from the catalyst production ⁺ May be 510mg/L or more, preferably 1g/L or more, more preferably 2g/L or more, further preferably 4g/L or more, further preferably 8g/L or more, further preferably 16g/L or more, further preferably 32g/L or more, further preferably 40g/L or more, further preferably 50g/L or more, further preferably 60g/L or more.

As SO in wastewater from the production of said catalyst ₄ ^2- May be 1g/L or more, preferably 2g/L or more, more preferably 4g/L or more, further preferably 8g/L or more, further preferably 16g/L or more, further preferably 32g/L or more, further preferably 40g/L or more, further preferablyMore preferably 50g/L or more, still more preferably 60g/L or more, and still more preferably 70g/L or more.

As Cl in the catalyst production wastewater ^- May be 970mg/L or more, more preferably 2g/L or more, further preferably 4g/L or more, further preferably 8g/L or more, further preferably 16g/L or more, further preferably 32g/L or more, further preferably 40g/L or more, further preferably 50g/L or more, further preferably 60g/L or more.

NH contained in the catalyst production wastewater ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ The upper limit of (3) is not particularly limited. SO in the wastewater from catalyst production from the viewpoint of easy wastewater treatment ₄ ^2- 、Cl ^- And Na ⁺ Respectively 200g/L or less, preferably 150g/L or less, preferably 100g/L or less; NH in catalyst production wastewater ₄ ⁺ Is 50g/L or less, preferably 30g/L or less, and preferably 20g/L or less.

From the viewpoint of reducing energy consumption in the treatment process, SO contained in the catalyst production wastewater ₄ ^2- The higher the content, the better, the content is preferably 0.01mol/L or more, more preferably 0.1mol/L or more, still more preferably 0.2mol/L or more, and still more preferably 0.5mol/L or more, and for example, may be 0.2 to 1.5mol/L. From the viewpoint of improving the purity of the sodium sulfate product, cl contained in the wastewater from the catalyst production is ^- Is 5.2mol/L or less, preferably 4.7mol/L or less, more preferably 3.5mol/L or less, and may be, for example, 0.5 to 3.5mol/L. By adding SO contained in the wastewater ₄ ^2- And Cl ^- The concentration of the sodium sulfate is limited in the range, pure sodium sulfate can be obtained by crystallization in the cooling crystallization process, energy is saved, and the treatment process is more economical.

In the present invention, the inorganic salt ions contained in the catalyst production wastewater are other than NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ In addition, it may contain Mg ²⁺ 、Ca ²⁺ 、K ⁺ 、Fe ³⁺ And rare earth element ion and the like，Mg ²⁺ 、Ca ²⁺ 、K ⁺ 、Fe ³⁺ The content of each inorganic salt ion such as a rare earth element ion is preferably 100mg/L or less, more preferably 50mg/L or less, still more preferably 10mg/L or less, and particularly preferably no other inorganic salt ion is contained. By controlling the other inorganic salt ions within the above range, the purity of the sodium sulfate crystals and sodium chloride crystals finally obtained can be further improved. In order to reduce the content of other inorganic salt ions in the catalyst production wastewater, the following impurity removal is preferably performed.

The TDS of the catalyst production wastewater may be 1.6g/L or more, preferably 4g/L or more, more preferably 8g/L or more, further preferably 16g/L or more, further preferably 32g/L or more, further preferably 40g/L or more, further preferably 50g/L or more, further preferably 60g/L or more, further preferably 100g/L or more, further preferably 150g/L or more, further preferably 200g/L or more.

In the present invention, the pH of the catalyst production wastewater is preferably 4 to 8, for example 6.2 to 6.6.

In addition, since the COD of the wastewater may block a membrane during concentration, affect the purity and color of a salt during evaporative crystallization, etc., the COD of the wastewater from the catalyst production is preferably as small as possible (preferably 20mg/L or less, more preferably 10mg/L or less), and is preferably removed by oxidation during pretreatment, specifically, by biological method, advanced oxidation method, etc., and is preferably oxidized by an oxidizing agent such as Fenton's reagent when the COD content is very high.

In the invention, in order to reduce the concentration of impurity ions in the wastewater, ensure the continuous and stable operation of the treatment process and reduce the equipment operation and maintenance cost, the catalyst production wastewater is preferably subjected to impurity removal before being treated by the treatment method. Preferably, the impurity removal is selected from one or more of solid-liquid separation, chemical precipitation, adsorption, ion exchange and oxidation.

As the solid-liquid separation, filtration, centrifugation, sedimentation, or the like may be mentioned; as the chemical precipitation, pH adjustment, carbonate precipitation, magnesium salt precipitation, and the like may be mentioned; the adsorption can be physical adsorption and/or chemical adsorption, and the specific adsorbent can be selected from activated carbon, silica gel, alumina, molecular sieve, natural clay and the like; as the ion exchange, either one of a strongly acidic cation resin and a weakly acidic cation resin can be used; as the oxidation, various oxidizing agents conventionally used in the art, such as ozone, hydrogen peroxide, and potassium permanganate, can be used, and in order to avoid introduction of new impurities, ozone, hydrogen peroxide, and the like are preferably used.

The specific impurity removal mode can be specifically selected according to the types of impurities contained in the catalyst production wastewater. For suspended matters, a solid-liquid separation method can be selected for removing impurities; for inorganic and organic substances, chemical precipitation, ion exchange, and adsorption can be selected to remove impurities, such as weak acid cation exchange, and activated carbon adsorption; for organic matters, impurities can be removed by adopting an adsorption and/or oxidation mode, wherein an ozone biological activated carbon adsorption oxidation method is preferred. According to a preferred embodiment of the invention, the catalyst production wastewater is subjected to impurity removal by sequentially carrying out filtration, a weak acid cation exchange method and an ozone biological activated carbon adsorption oxidation method. Through the impurity removal process, most suspended matters, hardness, silicon and organic matters can be removed, the scaling risk of the device is reduced, and the continuous and stable operation of the wastewater treatment process is ensured.

In the present invention, the wastewater having a low salt content may be concentrated to have a salt content within a range required for the catalyst production wastewater of the present invention before the treatment by the treatment method of the present invention (preferably, after the above-mentioned removal of impurities). Preferably, the concentration is selected from ED membrane concentration and/or reverse osmosis; more preferably, the concentration is performed by ED membrane concentration and reverse osmosis, and the order of performing the ED membrane concentration and the reverse osmosis is not particularly limited. The ED membrane concentration and reverse osmosis treatment apparatus and conditions may be performed in a manner conventional in the art, and may be specifically selected according to the condition of wastewater to be treated. Specifically, as the concentration of the ED membrane, a one-way electrodialysis system or a reversed electrodialysis system can be selected for carrying out; as the reverse osmosis, a roll membrane, a plate membrane, a disc-tube membrane, a vibrating membrane or a combination thereof can be selected for use. Through the concentration can improve the efficiency of waste water treatment, avoid the energy waste that a large amount of evaporations caused.

In a preferred embodiment of the invention, the catalyst production wastewater is wastewater generated by chemical precipitation, filtration, weak acid cation exchange and ozone biological activated carbon adsorption oxidation of wastewater generated in the molecular sieve production process, and is concentrated by an ED membrane and a reverse osmosis method.

The conditions for the above chemical precipitation are preferably: sodium carbonate is used as a treating agent, 1.2 to 1.4mol of sodium carbonate is added relative to 1mol of calcium ions in the wastewater, the pH value of the wastewater is adjusted to be more than 7, the reaction temperature is 20 to 35 ℃, and the reaction time is 0.5 to 4 hours.

The conditions for the filtration are preferably: the filtering unit adopts a double-layer filtering material multi-medium filter consisting of anthracite and quartz sand, the grain diameter of the anthracite is 0.7-1.7mm, the grain diameter of the quartz sand is 0.5-1.3mm, and the filtering speed is 10-30m/h. After the filter material is used, the regeneration method of 'gas back flushing-gas and water back flushing-water back flushing' is adopted to regenerate the filter material, and the regeneration period is 10-15h.

The conditions for the weak acid cation exchange method are preferably: the pH value range is 6.5-7.5; the temperature is less than or equal to 40 ℃, the height of the resin layer is 1.5-3.0m, the HCl concentration of the regeneration liquid is as follows: 4.5-5 mass%; the dosage of the regenerant (calculated by 100%) is 50-60kg/m ³ Wet resin; the flow rate of the regeneration liquid HCl is 4.5-5.5m/h, and the regeneration contact time is 35-45min; the forward washing flow rate is 18-22m/h, and the forward washing time is 2-30min; the running flow rate is 15-30m/h; as the acidic cation exchange resin, for example, there can be used a Gallery Senno chemical Co., ltd, SNT brand D113 acidic cation exchange resin.

The conditions of the above-mentioned ozone biological activated carbon adsorption oxidation method are preferably: the retention time of the ozone is 50-70min, and the empty bed filtration rate is 0.5-0.7m/h.

The conditions for concentrating the ED membrane are preferably: the current is 145-155A, and the voltage is 45-65V. The ED membrane may be, for example, an ED membrane manufactured by astone corporation of japan.

The conditions for the reverse osmosis are preferably: the operation pressure is 5.4-5.6MPa, the water inlet temperature is 25-35 ℃, and the pH value is 6.5-7.5. The reverse osmosis membrane is, for example, a seawater desalination membrane TM810C manufactured by Dongli corporation of Lanxingdong.

According to the invention, when the wastewater treatment is started, the catalyst production wastewater can be used for directly starting operation, and if the ion content of the catalyst production wastewater meets the conditions of the invention, the cooling crystallization can be carried out firstly and then the evaporation can be carried out according to the conditions of the invention; if the ion content of the catalyst production wastewater does not meet the conditions of the invention, evaporation can be carried out firstly to obtain concentrated solution, and solid-liquid separation is carried out to obtain sodium chloride crystals and second mother liquor, then the second mother liquor is mixed with the catalyst production wastewater to adjust the ion content of the wastewater to be treated to be in the range required by the invention, and then evaporation is carried out to obtain sodium sulfate crystals. Of course, the ion content of the wastewater to be treated can be adjusted by using sodium sulfate or sodium chloride in the initial stage as long as the wastewater to be treated satisfies the SO content in the wastewater to be treated in the present invention ₄ ^2- 、Cl ^- The requirements are met.

The present invention will be described in detail below by way of examples.

In the following examples, the catalyst production wastewater is wastewater from a molecular sieve production process, which is subjected to chemical precipitation, filtration, weak acid cation exchange and ozone biological activated carbon adsorption oxidation in sequence to remove impurities, and is subjected to ED membrane concentration and reverse osmosis concentration in sequence.

Example 1

As shown in FIG. 1, the catalyst production wastewater (containing NaCl 38g/L and Na) ₂ SO ₄ 100g/L、NH ₄ Cl10g/L、(NH ₄ ) ₂ SO ₄ 26.75g/L, pH 6.2) at a feed rate of 10m ³ The flow rate of the mother liquor is/h fed into a pipeline of the treatment system, and then the mother liquor is mixed with the second mother liquor returned by the ninth circulating pump 79 to obtain wastewater to be treated (Cl is measured therein) ^- Has a concentration of 2.42mol/L, SO ₄ ^2- 0.689 mol/L), introducing a 45.16 mass% aqueous sodium hydroxide solution into the pipe to adjust the pH value for the first time, monitoring the adjusted pH value by a first pH value measuring device 61 (pH meter) (measurement value is 8), and then sending the wastewater to be treated by a first circulating pump 71And (3) entering a second heat exchange device 32 (a heat exchanger made of plastic materials) to perform first heat exchange with the first mother liquor to reduce the temperature of the wastewater to be treated to 3 ℃, then mixing the wastewater with the circulating liquid of the cooling crystallization device 2 (a freezing crystallization tank) conveyed by a second circulating pump 72, performing heat exchange with the freezing liquid through a sixth heat exchange device 36 to further reduce the temperature, and then sending the mixture into the cooling crystallization device 2 to perform cooling crystallization to obtain a crystallization liquid containing sodium sulfate crystals. Wherein the cooling crystallization temperature is-4 deg.C, the time is 120min, and the circulation amount of the cooling crystallization is controlled to 1137m ³ And h, controlling the supersaturation degree of sodium sulfate in the cooling crystallization process to be not more than 1g/L.

The above-mentioned crystal liquid containing sodium sulfate crystals was fed to a first solid-liquid separation apparatus 91 (centrifuge) to conduct solid-liquid separation, thereby obtaining 13.69 m/hr ³ Contains NaCl 200.8g/L and Na ₂ SO ₄ 27.5g/L、NH ₃ 5.4g/L of the first mother liquor was temporarily stored in the first mother liquor tank 53, and 3389.91kg of a sodium sulfate decahydrate crystal cake having a purity of 98.4 mass% and a water content of 75 mass% was obtained per hour.

The first mother liquor is sent to the second heat exchange device 32 for heat exchange through a sixth circulating pump 76, and then sent to the concentration device 9 (electrodialysis device) for electrodialysis concentration, wherein the flow rate of the concentrated solution is 10.87m ³ H, containing 202.3g/L NaCl and Na ₂ SO ₄ 27.7g/L、NH ₃ 7.7g/L, and carrying out the next evaporation on the concentrated solution, wherein the flow rate of the concentrated dilute solution is 2.82m ³ H, containing NaCl 97.5g/L and Na ₂ SO ₄ 13.3g/L、NH ₃ 3.5g/L, and returning the concentrated dilute solution to be used as the wastewater of catalyst production for treatment.

The evaporation process is carried out in an MVR evaporation plant 1 (falling film + forced circulation two-stage MVR evaporative crystallizer). Sending the concentrated solution into a third heat exchange device 33 (a duplex stainless steel plate type heat exchanger) to exchange heat with the ammonia-containing steam condensate, then sending the concentrated solution into a fourth heat exchange device 34 (a duplex stainless steel plate type heat exchanger) to exchange heat with the compressed ammonia-containing steam, then introducing a sodium hydroxide aqueous solution with the concentration of 45.16 mass percent into a pipeline sent into the MVR evaporation device 1 again to adjust the pH value, and monitoring the adjusted pH value through a second pH value measuring device 62 (a pH meter) (measuring value is measured)10.8) were evaporated in an MVR evaporator 1 to give a concentrated solution containing sodium chloride crystals and ammonia-containing vapor. The evaporation temperature is 100 ℃, the pressure is-22.83 kPa, and the evaporation capacity is 5.12m ³ H is the ratio of the total weight of the catalyst to the total weight of the catalyst. After being compressed by the compressor 102 (the temperature is increased by 16 ℃), the ammonia-containing steam exchanges heat with the first mother liquor in the fourth heat exchange device 34 and the third heat exchange device 33 in sequence to obtain ammonia water, and the ammonia water is stored in the ammonia water storage tank 52. In addition, in order to increase the solid content in the MVR evaporation apparatus 1, part of the liquid evaporated in the MVR evaporation apparatus 1 was sent again to the MVR evaporation apparatus 1 as a circulating liquid by the seventh circulating pump 77 to be evaporated (reflux ratio 46.3). The degree of evaporation was monitored by a densitometer provided in the MVR evaporation apparatus 1, and the concentration of sodium sulfate in the concentrated solution was controlled to 0.9626Y (51.5 g/L).

The concentrated solution containing sodium chloride crystals obtained by evaporation is sent to a second solid-liquid separation device 92 (centrifugal machine) for second solid-liquid separation, and 5.85m is obtained per hour ³ Contains 309.1g/L NaCl and Na ₂ SO ₄ 51.5g/L、NaOH 1.4g/L、NH ₃ 0.27g/L of the second mother liquor is temporarily stored in the second mother liquor tank 54, and can be conveyed to the catalyst production wastewater introduction pipe through the ninth circulating pump 79 to be mixed with the catalyst production wastewater, so as to obtain wastewater to be treated. The obtained sodium chloride solid (498.83 kg of sodium chloride crystal cake with a water content of 14 mass% per hour, wherein the sodium sulfate content is 2.0 mass% or less) was washed with 309g/L of a sodium chloride solution equivalent to the dry mass of sodium chloride, and dried in a dryer to obtain 428.99kg of sodium chloride (purity of 99.5 mass%) per hour, and the second washing liquid obtained by washing was circulated to the MVR evaporation apparatus 1 by the tenth circulation pump 80.

In this example, 5.12m of ammonia water having a concentration of 1.7% by mass per hour was obtained in the ammonia water tank 52 ³ 。

In addition, the tail gas discharged from the cooling crystallization device 2 and the fourth heat exchange device 34 is introduced into a tail gas absorption tower 83 through a vacuum pump 81 for absorption, circulating water is introduced into the tail gas absorption tower 83, the circulating water circulates in the tail gas absorption tower 83 under the action of the fourth circulating pump 74, water is supplemented into the tail gas absorption tower 83 from a circulating water tank 82 through a third circulating pump 73, and fresh water is supplemented into the circulating water tank 82, so that the temperature and the ammonia content of the water for operating the vacuum pump 81 are reduced. Dilute sulfuric acid is further introduced into the tail gas absorption tower 83 to absorb ammonia and the like in the tail gas. The starting phase of MVR evaporation was initiated by steam at a temperature of 143.3 ℃.

Example 2

The treatment of the catalyst production wastewater was carried out in the same manner as in example 1, except that: for NaCl-containing 46g/L, na ₂ SO ₄ 96g/L、NH ₄ Cl 12g/L、(NH ₄ ) ₂ SO ₄ 25.5g/L of catalyst production wastewater with pH of 6.6 is treated to obtain Cl in the wastewater to be treated ^- Has a concentration of 2.43mol/L, SO ₄ ^2- The concentration of (b) is 0.687mol/L. The temperature of the wastewater to be treated after heat exchange by the second heat exchange device 32 is 5 ℃.

Cooling and crystallizing at-2 deg.C for 125min; the evaporation temperature is 75 ℃, the pressure is-72.74 kPa, and the evaporation capacity is 5.32m ³ /h。

The first solid-liquid separation device 91 yielded 3446.63kg (purity: 98.6 mass%) of a sodium sulfate decahydrate crystal cake containing 76 mass% of water per hour; yield 13.17m per hour ³ The concentration of NaCl is 202.8g/L and Na ₂ SO ₄ 29.8g/L、NH ₃ 7.8g/L of the first mother liquor.

In the electrodialysis concentration, the flow rate of concentrated solution is 10.65m ³ H, containing 200.5g/L NaCl and Na ₂ SO ₄ 29.5g/L、NH ₃ 8.3g/L, the flow rate of the concentrated dilute solution is 2.51m ³ H, containing 106.3g/L NaCl and Na ₂ SO ₄ 15.6g/L、NH ₃ 4.0g/L。

615.44kg of sodium chloride crystallized filter cake with the water content of 15 mass% is obtained by the second solid-liquid separation device 92 every hour, and finally 523.12kg of sodium chloride (the purity is 99.5 mass%) is obtained every hour; the second solid-liquid separation device 92 gave a volume of 5.45m per hour ³ The concentration of NaCl is 305.3g/L and Na ₂ SO ₄ 57.6g/L、NaOH 0.50g/L、NH ₃ 0.3g/L of the second mother liquor.

5.32m of ammonia water having a concentration of 1.6 mass% was obtained per hour in the ammonia water tank 52 ³ The ammonia water can be reused in the production process of the molecular sieve.

Example 3

The treatment of the catalyst production wastewater was carried out in the same manner as in example 1, except that: for the solution containing 33g/L NaCl and Na ₂ SO ₄ 90g/L、NH ₄ Cl 10g/L、(NH ₄ ) ₂ SO ₄ 27.7g/L of catalyst production wastewater with pH of 6.3 is treated to obtain Cl in the wastewater to be treated ^- Has a concentration of 2.177mol/L, SO ₄ ^2- The concentration of (b) was 0.693mol/L. The temperature of the wastewater to be treated after heat exchange by the second heat exchange device 32 is 3 ℃.

Cooling and crystallizing at-4 deg.C for 120min; the evaporation temperature is 50 deg.C, the pressure is-92.67 kPa, and the evaporation capacity is 4.61m ³ /h。

The first solid-liquid separation device 91 yielded 3197.06kg (purity: 98.9 mass%) of a sodium sulfate decahydrate crystal cake containing 74.5 mass% of water per hour; yield 13.38m per hour ³ The concentration of NaCl 178.6g/L and Na ₂ SO ₄ 32.5g/L、NH ₃ 7.6g/L of the first mother liquor.

In the electrodialysis concentration, the flow rate of concentrated solution is 9.83m ³ H, containing 194.6g/L NaCl and Na ₂ SO ₄ 35.4g/L、NH ₃ 5.5g/L, the flow rate of the concentrated dilute solution is 3.56m ³ H, containing 67.2g/L NaCl and Na ₂ SO ₄ 12.2g/L、NH ₃ 2.8g/L。

The second solid-liquid separation device 92 obtained 456.92kg of sodium chloride crystallized cake with a water content of 15 mass% per hour, and finally 388.38kg of sodium chloride (purity of 99.5 mass%) per hour; the second solid-liquid separation device 92 gave a volume of 5.30 m/hr ³ The concentration of NaCl is 294.7g/L and Na ₂ SO ₄ 65.7g/L、NaOH 0.14g/L、NH ₃ 0.3g/L of the second mother liquor.

4.61m of ammonia water having a concentration of 1.9% by mass was obtained per hour in the ammonia water tank 52 ³ The ammonia water can be reused in the production process of the molecular sieve.

The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.

Claims

1. Method for treating catalyst production wastewater containing NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ Characterized in that the method comprises the following steps,

1) Cooling and crystallizing the wastewater to be treated to obtain a crystallization liquid containing sodium sulfate crystals;

wherein SO in the wastewater to be treated ₄ ^2- Has a concentration of 0.01mol/L or more and Cl ^- The concentration of (A) is less than 5.2 mol/L;

before the liquid phase obtained by the first solid-liquid separation is introduced into an MVR evaporation device, enabling the pH value of the liquid phase obtained by the first solid-liquid separation to be larger than 9;

the evaporation ensures that sodium sulfate does not crystallize and separate out;

the wastewater to be treated contains the catalyst production wastewater and a liquid phase obtained by the second solid-liquid separation; NH in the catalyst production wastewater ₄ ⁺ Is more than 8mg/L, SO ₄ ^2- Is more than 1g/L, cl ^- Over 970mg/L of Na ⁺ Is more than 510 mg/L.

2. The method according to claim 1, wherein SO contained in the wastewater to be treated ₄ ^2- The concentration of (b) is 0.1mol/L or more.

3. The method according to claim 2, wherein SO contained in the wastewater to be treated ₄ ^2- The concentration of (b) is 0.2mol/L or more.

4. The method according to claim 1, wherein Cl contained in the wastewater to be treated ^- The concentration of (B) is 4.5mol/L or less.

5. The method according to claim 1, wherein the pH of the wastewater to be treated is adjusted to be greater than 7 before the wastewater to be treated is subjected to cooling crystallization.

6. The method according to claim 1, wherein the SO contained in the liquid phase obtained by the first solid-liquid separation is 1mol relative to the SO contained in the liquid phase ₄ ^2- Cl contained in the liquid phase obtained by the first solid-liquid separation ^- 9.5mol or more.

7. The method according to claim 1, wherein the SO contained in the liquid phase obtained by the first solid-liquid separation is 1mol relative to the SO contained in the liquid phase ₄ ^2- Cl contained in the liquid phase obtained by the first solid-liquid separation ^- Is 10mol or more.

8. The method according to claim 1, wherein the pH of the wastewater to be treated is adjusted to 8 or more before the wastewater to be treated is subjected to cooling crystallization.

9. The process of claim 1, wherein the pH of the liquid phase from the first solid-liquid separation is adjusted to a value greater than 10 prior to passing the liquid phase from the first solid-liquid separation to the MVR evaporator.

10. The method of claim 1, wherein the adjusting the pH is performed with NaOH.

11. The method of claim 1, wherein the evaporating is performed such that the concentration of sodium sulfate in the concentrated solution is Y or less, wherein Y is the concentration of sodium sulfate at which both sodium sulfate and sodium chloride in the concentrated solution are saturated under the conditions of the evaporating.

12. The process of claim 11, wherein the evaporation provides a sodium sulfate concentration in the concentrate of 0.9Y to 0.99Y.

13. The process of claim 1 wherein the liquid phase from the first solid-liquid separation is subjected to a concentration treatment prior to passing it to the MVR evaporator.

14. The method according to claim 13, wherein the concentration treatment does not crystallize the liquid phase obtained by the first solid-liquid separation.

15. The method according to claim 13, wherein the concentration treatment is performed by a reverse osmosis method or an electrodialysis method.

16. The method of claim 13, wherein the concentration treatment is performed by an electrodialysis method.

17. The method according to any one of claims 1 to 16, wherein the temperature of the cooling crystallization is from-21.7 ℃ to 17.5 ℃.

18. The method according to claim 17, wherein the temperature of the cooling crystallization is from-20 ℃ to 5 ℃.

19. The method according to claim 18, wherein the temperature of the cooling crystallization is from-10 ℃ to 5 ℃.

20. The method of claim 19, wherein the temperature of the cooling crystallization is from-10 ℃ to 0 ℃.

21. The method according to claim 17, wherein the cooling crystallization time is 5min or more.

22. The method of claim 21, wherein the cooling crystallization time is 60min to 180min.

23. The method of claim 22, wherein the cooling crystallization time is 90min to 150min.

24. The method of any one of claims 1-16, wherein the conditions of evaporation comprise: the temperature is above 17.5 ℃ and the pressure is above-101 kPa.

25. The method of claim 24, wherein the conditions of evaporation comprise: the temperature is 35-110 ℃, and the pressure is-98 kPa-12 kPa.

26. The method of claim 25, wherein the conditions of evaporation comprise: the temperature is 45-110 ℃, and the pressure is-95 kPa-12 kPa.

27. The method of claim 26, wherein the conditions of evaporation comprise: the temperature is 50-100 ℃, and the pressure is-93 kPa to-22 kPa.

28. The method according to claim 1, wherein the wastewater to be treated is subjected to a first heat exchange with a liquid phase obtained by the first solid-liquid separation before the wastewater to be treated is subjected to cooling crystallization.

29. The method according to claim 1, wherein the ammonia-containing vapor is subjected to a second heat exchange with the liquid phase obtained by the first solid-liquid separation to obtain ammonia water before the liquid phase obtained by the first solid-liquid separation is passed to an MVR evaporation apparatus.

30. The method according to any one of claims 1 to 16, further comprising subjecting the sodium sulfate crystal-containing crystalline liquid to a first solid-liquid separation to obtain sodium sulfate crystals.

31. The method of claim 30, further comprising washing the resulting sodium sulfate crystals.

32. The method according to any one of claims 1 to 16, further comprising subjecting the concentrated solution containing sodium chloride crystals to a second solid-liquid separation to obtain sodium chloride crystals.

33. The method of claim 32, further comprising washing the resulting sodium chloride crystals.

34. The process of any of claims 1-16, wherein the catalyst production wastewater is wastewater from a molecular sieve, alumina, or refinery catalyst production process.

35. The method of claim 34, further comprising removing impurities and concentrating the catalyst production wastewater.