CN109422396B

CN109422396B - Method for treating wastewater from catalyst production

Info

Publication number: CN109422396B
Application number: CN201710751665.XA
Authority: CN
Inventors: 殷喜平; 李叶; 刘志坚; 杨凌; 顾松园; 苑志伟; 张志民; 高晋爱; 安涛
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: 2023-02-24
Anticipated expiration: 2037-08-28
Also published as: CN109422396A

Abstract

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

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 to a catalyst containing 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 in wastewater by gas stripping deamination, a large amount of alkali is required to adjust the pH value, the alkali consumption is high, the alkali in the deaminated wastewater 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 is not greatly changed, the salt content in the wastewater is not reduced (20-30 g/L), the wastewater cannot be directly discharged, the desalting treatment is required to be further performed, the wastewater treatment operation cost is high, a large amount of alkali remains in the treated wastewater, the pH value is high, the 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.

To is coming toThe present invention has been made to achieve the above objects, and provides a method for treating wastewater from catalyst production, which contains NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ The method comprises the following steps of,

1) Introducing wastewater to be treated into an MVR evaporation device for evaporation to obtain concentrated solution containing ammonia vapor and sodium chloride crystals, wherein the wastewater to be treated contains the catalyst production wastewater;

2) Carrying out first solid-liquid separation on the concentrated solution containing the sodium chloride crystals, and cooling and crystallizing a liquid phase obtained by the first solid-liquid separation to obtain a crystallization solution containing sodium sulfate crystals;

3) Carrying out second solid-liquid separation on the crystallization liquid containing the sodium sulfate crystals;

wherein before the wastewater to be treated is evaporated, the pH value of the wastewater to be treated is adjusted to be more than 9; relative to 1mol of SO contained in the wastewater to be treated ₄ ^2- Cl contained in the wastewater to be treated ^- 9.5mol or more; the evaporation prevents the precipitation of sodium sulfate crystals, and the cooling prevents the precipitation of sodium chloride crystals.

By the technical scheme, the method aims at the content of NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ The wastewater is prepared by adjusting the pH value of the wastewater to be treated to a specific range in advance, evaporating to obtain sodium chloride crystals and ammonia water, further crystallizing and separating sodium chloride to obtain sodium chloride crystals, controlling the concentration of chloride ions in the first mother liquor entering the cooling crystallization, and separating by using the cooling crystallization to obtain sodium sulfate crystals. The method can respectively obtain high-purity sodium sulfate and sodium chloride, avoids the difficulty in the processes of mixed salt treatment and recycling, simultaneously completes the process of separating ammonia and salt, simultaneously heats 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 purpose of changing waste into valuable.

Furthermore, the sodium sulfate content in the mother liquor for preparing sodium sulfate is greatly reduced through cooling crystallization, the efficiency of preparing sodium chloride through evaporation can be improved, and simultaneously, before the liquid phase obtained by the first solid-liquid separation is cooled and crystallized, cl in the liquid phase is preferably adjusted by the catalyst production wastewater and sodium sulfate crystal eluent ^- The concentration of the sodium sulfate avoids the precipitation of sodium chloride in the cooling crystallization process, and improves the precipitation rate of the sodium sulfate in the cooling crystallization process.

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. Cooling crystallization device 32 and second heat exchange device

2. MVR evaporation plant 33, third heat transfer device

31. The first heat exchange device 35 and the fifth heat exchange device

36. Sixth heat exchanger 76, sixth circulating pump

51. Ammonia water storage tank 77 and seventh circulating pump

53. First mother liquor tank 78, eighth circulating pump

54. Second mother liquor tank 79 and ninth circulating pump

61. First pH value measuring device 80 and tenth circulating pump

62. Second pH value measuring device 81 and vacuum pump

63. Third pH value measuring device 82 and circulating water tank

71. First circulating pump 83 and tail gas absorption tower

72. Second circulating pump 91 and first solid-liquid separation device

73. Third circulating pump 92 and second solid-liquid separation device

74. Fourth circulating pump 101 and compressor

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 ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered 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,

wherein before the wastewater to be treated is evaporated, the pH value of the wastewater to be treated is adjusted to be more than 9; relative to 1mol of SO contained in the wastewater to be treated ₄ ^2- Cl contained in the wastewater to be treated ^- 9.5mol or more; the evaporation prevents the sodium sulfate from crystallizing out; the cooling crystallization prevents the sodium chloride from crystallizing out.

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 ⁺ Except that it contains NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ In addition, the catalyst production wastewater is not particularly limited.

In the present invention, the sequence of the first heat exchange, the adjustment of the pH value 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 separation of the catalyst production wastewater and the second solid-liquid, the preparation of the wastewater to be treated needs to be performed) 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, 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 evaporation to prevent the crystallization of sodium sulfate means that the concentration of sodium sulfate in the mixed system is controlled not to exceed the solubility under the evaporation conditions (including but not limited to temperature, pH, etc.), and sodium sulfate entrained by sodium chloride crystals or adsorbed on the surface is not excluded. When the content of sodium sulfate in the sodium chloride crystals obtained in general is 8 mass% or less (preferably 4 mass% or less) because of the difference in the water content of the crystals after the solid-liquid separation, it is considered that sodium sulfate is not crystallized and precipitated.

In the present invention, the MVR vaporizing device 2 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 conditions for the evaporation are not particularly limited, and may be appropriately selected as needed to achieve the purpose of precipitating crystals. In order to improve the efficiency of evaporation, the evaporation conditions include: the temperature is above 35 ℃ and the pressure is above-98 kPa; preferably, the conditions of evaporation include: the temperature is 45-175 ℃, and the pressure is-95 kPa-653 kPa; preferably, the conditions of evaporation include: the temperature is 60-160 ℃, and the pressure is-87 kPa-414 kPa; preferably, the conditions of the evaporation include: the temperature is 75-150 ℃, and the pressure is-73 kPa-292 kPa; preferably, the conditions of evaporation include: the temperature is 80-130 ℃, and the pressure is-66 kPa-117 kPa; preferably, the conditions of evaporation include: the temperature is 95-110 ℃, and the pressure is-37 kPa-12 kPa; preferably, the conditions of evaporation include: the temperature is 105-110 ℃, and the pressure is-23 kPa-12 kPa.

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 be treated and the amount of the wastewater 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 sodium chloride crystals are obtained during the evaporation, it is necessary to further satisfy the requirement that 1mol of SO is contained in the wastewater to be treated ₄ ^2- Cl contained in the wastewater to be treated ^- Is 9.5mol or more, preferably 10mol or more, more preferably 10 to 25mol. By reacting SO ₄ ^2- And Cl ^- The molar ratio of sodium sulfate to sodium chloride is controlled within the above range, and high-purity sodium chloride crystals can be obtained by evaporation, so that the separation of sodium sulfate and sodium chloride is realized.

Relative to 1mol of SO contained in the wastewater to be treated ₄ ^2- Cl contained in the wastewater to be treated ^- Specific examples of (3) may include, for example: 9.5mol, 10mol, 11mol, 12mol, 13mol, 14mol, 15mol, 16mol, 17mol, 18mol, 19mol, 20mol, 21mol, 22mol, 23mol, 24mol or 25mol, etc.

According to the present invention, the evaporation does not crystallize sodium sulfate in the wastewater to be treated (i.e., sodium sulfate does not become supersaturated), and preferably, the evaporation is performed so that the concentration of sodium sulfate in the concentrated solution is Y or less (preferably, 0.9Y to 0.99Y, and more preferably, 0.95Y to 0.98Y). Wherein Y is the concentration of sodium sulfate at which both sodium chloride and sodium sulfate in the concentrate are saturated under evaporative conditions. By controlling the degree of evaporation within the above range, as much sodium chloride as possible can be crystallized out under the condition that sodium sulfate is not precipitated out. By increasing the evaporation capacity as much as possible, the wastewater treatment efficiency can be improved, and the energy waste can be reduced.

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 crystallization of sodium sulfate in the concentrated solution. 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 2 and reduce the ammonia content in the liquid, it is preferable to return part of the liquid evaporated by the MVR evaporation device 2 (i.e. the liquid located inside the MVR evaporation device, hereinafter also referred to as circulating liquid) to the MVR evaporation device 2 for evaporation, and it is preferable to return the liquid to the MVR evaporation device 2 for evaporation after heating. The above-described process of returning the circulation liquid to the MVR evaporating device 2 may be returned to the first heat exchange process by, for example, the seventh circulation pump 77. The reflux ratio of the evaporation is as follows: the ratio of the amount of reflux to the total amount of liquid fed to the MVR evaporator 2 minus the amount of reflux. The reflux ratio may be set appropriately according to the evaporation amount to ensure that the MVR evaporation device 2 can evaporate the required amount of water and ammonia at a given evaporation temperature. The reflux ratio for the evaporation may be, for example, 10 to 200, preferably 50 to 170.

According to the present invention, preferably, the method further comprises compressing the ammonia-containing vapor before the first heat exchange. The compression of the ammonia-containing vapor may be performed by a compressor 101. The ammonia-containing steam is compressed, energy is input into the MVR evaporation system, the continuous process of waste water heating-evaporation-cooling is guaranteed, starting steam needs to be input when the MVR evaporation process is started, energy is supplied only through the compressor 101 after the continuous running state is achieved, and other energy does not need to be input. The compressor 101 may employ various compressors conventionally used in the art, such as a centrifugal fan, a turbine compressor, or a roots compressor. After compression by the compressor 101, the temperature of the ammonia-containing vapor is raised by 5 ℃ to 20 ℃.

According to the present invention, in order to make full use of the heat in the ammonia-containing vapor obtained by evaporation, it is preferable to subject the wastewater to be treated to a first heat exchange with the ammonia-containing vapor before feeding the wastewater to be treated to the MVR evaporation apparatus 2. In order to fully utilize the heat in the first mother liquor, it is more preferable to perform the first heat exchange between the wastewater to be treated and the first mother liquor before the wastewater to be treated is sent to the MVR evaporation device 2.

According to a preferred embodiment of the present invention, the first heat exchange between the wastewater to be treated and the ammonia-containing steam is carried out by a first heat exchange device 31 and a second heat exchange device 32, respectively; the first heat exchange between the wastewater to be treated and the first mother liquor is carried out by a fifth heat exchange device 35. Specifically, the ammonia-containing steam passes through the second heat exchange device 32 and the first heat exchange device 31 in sequence, and the first mother liquor passes through the fifth heat exchange device 35; meanwhile, a part of the wastewater to be treated is subjected to heat exchange with the ammonia-containing steam condensate through the first heat exchange device 31, the rest part of the wastewater to be treated is subjected to heat exchange with the first mother liquor through the fifth heat exchange device 35, and then the two parts of wastewater to be treated are combined and then subjected to heat exchange with the ammonia-containing steam through the second heat exchange device 32, so that the wastewater to be treated is heated and evaporated conveniently, the ammonia-containing steam is condensed to obtain ammonia water, and the first mother liquor is cooled and crystallized conveniently. After heat exchange is carried out through the first heat exchange device 31, the temperature of the wastewater to be treated is raised to 44-174 ℃, preferably 94-109 ℃; after heat exchange is carried out by the fifth heat exchange device 35, the temperature of the wastewater to be treated is raised to 44-174 ℃, preferably 94-109 ℃; after the first heat exchange is performed by the second heat exchange device 32, the temperature of the wastewater to be treated is raised to 52-182 ℃, preferably 102-117 ℃.

The first heat exchange device 31, the second heat exchange device 32 and the fifth heat exchange device 35 are not particularly limited, and various heat exchangers conventionally used in the field can be used to achieve the purpose of exchanging heat between the ammonia-containing steam and the wastewater to be treated. 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. Preferably, a duplex stainless steel plate heat exchanger is used.

According to the invention, the pH of the waste water to be treated is preferably adjusted to a value greater than 9, preferably greater than 10.8, more preferably between 10.8 and 11.5, before it is passed into the MVR evaporator 2. The upper limit of the adjustment of the pH of the wastewater to be treated 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 wastewater to be treated to the above range, the ammonia can be ensured to be fully evaporated in the evaporation process, thereby improving the purity of the obtained sodium chloride.

Specific examples of adjusting the pH of the wastewater to be treated before introducing the wastewater to be treated into the MVR evaporation apparatus 2 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.

In the present invention, the method of adjusting the pH 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 may be used for the purpose of adjusting the pH. 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.

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 above-mentioned purpose of adjusting the pH value 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 evaporation process is performed in the MVR evaporation apparatus 2, and the first pH adjustment is performed by introducing and mixing the aqueous solution containing the basic substance into the pipe for feeding the catalyst production wastewater into the first heat exchange apparatus 31 before feeding the catalyst production wastewater into the first heat exchange apparatus 31 for the first heat exchange; the second pH adjustment is then carried out by introducing the aqueous solution containing the alkaline substance into the line which feeds the wastewater to be treated into the MVR evaporation plant 2 and mixing.

Through two pH value adjustments, the pH value of the wastewater to be treated is more than 9, preferably more than 10.8 before the wastewater is introduced into the MVR evaporation device 2. Preferably, the first pH adjustment is carried out to a pH greater than 7 (preferably 7-9), and the second pH adjustment is carried out to a pH greater than 9, preferably greater than 10.8.

In order to detect the pH values after the first pH adjustment and the second pH adjustment, it is preferable to provide a first pH measuring device 61 on the pipe for feeding the catalyst production wastewater into the first heat exchange device 31 to measure the pH value after the first pH adjustment, and provide a second pH measuring device 62 on the pipe for feeding the wastewater to be treated into the MVR evaporation device 2 to measure the pH value after the second pH adjustment.

According to the present invention, the first solid-liquid separation may be performed by a first solid-liquid separation device (e.g., a centrifuge, a belt filter, a plate filter, etc.) 91. After the first solid-liquid separation, the first mother liquor obtained by the first solid-liquid separation device 91 (i.e. the liquid phase obtained by the first solid-liquid separation) is sent to the cooling crystallization device 1 for cooling crystallization, and specifically, the first mother liquor can be sent to the cooling crystallization device 1 through the sixth circulation pump 76. 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, it is preferable that the sodium chloride crystals are first washed 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, preferably the sodium chloride crystals are washed with an aqueous solution of sodium chloride. 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 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 elutriation and rinsing are not particularly limited, and may be performed by a method generally used 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 elutriation and rinsing is not particularly limited, and may be 1 or more, and 2 to 4 times are preferable for obtaining sodium chloride crystals of higher purity. In the elutriation process, the washing liquid recovered by the first washing can be used in a countercurrent way when 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 solution. For the washing of the resulting liquid, it is preferably returned to the MVR evaporation device 2.

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 the liquid obtained in the subsequent washing of the sodium chloride crystals, 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 further eluted 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 saturated at the same time at a temperature corresponding to the sodium chloride crystals to be washed), and the eluted 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 is not excessively introduced, and the efficiency of wastewater treatment is improved.

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, so that sodium sulfate can be separated from wastewater favorably. The cooling crystallization merely precipitates sodium sulfate, and sodium chloride and the like entrained in or adsorbed on the surface of sodium sulfate crystals 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), and 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 needed, 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 preferably-10-0 ℃, and particularly preferably-4-2 ℃; the time (in terms of the residence time in the cooling crystallization apparatus 1) is 5min or more, preferably 60min to 180min, more preferably 90min to 150min, and still more preferably 120min to 130min. By controlling the cooling crystallization conditions within the above range, sodium sulfate can be sufficiently precipitated without precipitating sodium chloride.

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 temperature of the first mother liquor is lowered to precipitate sodium sulfate crystals. The cooling crystallization can be carried out by various cooling crystallization apparatuses 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 apparatus 1. The cooling part can lead the first mother liquor in the cooling crystallization device to be cooled to the condition required by cooling crystallization by introducing a cooling medium. The cooling crystallization device is preferably provided with a mixing part, such as a stirrer, and the first mother liquor is mixed to achieve the effect of uniform cooling, so that sodium sulfate in the first mother liquor can be fully precipitated, and the size of crystal grains can be 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 the circulating crystal slurry from colliding with the impeller at a high speed to generate a large amount of secondary crystal nuclei, and the circulating pump is preferably a centrifugal pump with low rotating speed, and more preferably a guide pump impeller with large flow and low rotating speed or an axial pump with large flow, low lift and low rotating speed.

In order to detect the pH value after the third pH adjustment, it is preferable to provide a third pH measuring device 63 on the line for feeding the first mother liquid to the third heat exchange device 33 to measure the pH value after the third pH adjustment.

According to the present invention, before the first mother liquor is subjected to cooling crystallization, it is preferable to adjust Cl in the first mother liquor ^- Wherein, X is the concentration of sodium chloride when sodium sulfate and sodium chloride in the crystallization liquid reach saturation under the condition of cooling crystallization. Preferably, the concentration of sodium chloride in the crystallization liquid is made to be 0.95X-0.999X. Thereby ensuring that sodium chloride is not separated out in the cooling and crystallizing process and simultaneously improving the separation rate of sodium sulfate. By adjusting Cl of the first mother liquor ^- The concentration of (4) is such that the concentration of sodium chloride in the crystallization liquid is X or less that sodium chloride does not precipitate (the sodium chloride content in the obtained crystal is 8 mass% or less, preferably 4 mass% or less, more preferably 3 mass% or less), the precipitation rate of sodium sulfate in the cooling crystallization process is increased, and the cooling crystallization efficiency is improved.

According to the invention, in order to ensure that the sodium sulfate crystals are obtained by cooling crystallization, SO is contained in the first mother liquor ₄ ^2- The concentration of (B) is preferably 0.01mol/L or more, more preferably 0.07mol/L or more, still more preferably 0.1mol/L or more, yet more preferably 0.2mol/L or more, and particularly preferably 0.3mol/L or more. According to the invention, in order to increase the purity of the sodium sulfate crystals obtained by cooling crystallization, the Cl in the first mother liquor ^- The concentration of (B) is preferably 5.2mol/L or less, more preferably 5mol/L or less, further preferably 4.5mol/L or less, and further preferably 4mol/L or less.

By adding SO in the first mother liquor ₄ ^2- 、Cl ^- The concentration is controlled in the range, so that the first evaporation can be fully performed, and simultaneously, sodium sulfate in the cooling crystal can be separated out without separating out sodium chloride, thereby achieving the aim of efficiently separating sodium sulfate. In the present invention, if SO is in said first mother liquor ₄ ^2- 、Cl ^- The concentration of (b) is not in the above range, and the concentration adjustment may be carried out before the cooling crystallization, and the concentration adjustment is preferably carried out by using the catalyst production wastewater, a washing solution after the elution of sodium sulfate crystals, sodium sulfate, etc., and is preferably carried outUsing the catalyst production wastewater, the catalyst production wastewater may be specifically mixed with the first mother liquor in the first mother liquor tank 53.

SO in the first mother liquor 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.

Additionally, cl is present in the first mother liquor ^- 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, and the like.

By crystallizing said cooled crystals at the above-mentioned temperature, cl ^- The concentration and the pH value are carried out, so that sodium sulfate can be fully precipitated in the cooling crystallization without precipitating sodium chloride, and the aim of separating and purifying the sodium sulfate is fulfilled.

In the present invention, in order to control the crystal grain size distribution in the cooling crystallization apparatus 1 and reduce the content of fine crystal grains, it is preferable that a part of the liquid crystallized by the cooling crystallization apparatus 1 (that is, the liquid located inside the cooling crystallization apparatus 1, hereinafter also referred to as a cooling circulation liquid) is mixed with the first mother liquid and then returned to the cooling crystallization apparatus 1 to be cooled and crystallized again. The above-mentioned process of returning the cooling circulation liquid to the cooling crystallization device 1 for crystallization may be, for example, by returning the cooling circulation liquid to the sixth heat exchanging device 36 by the second circulating pump 72, mixing with the first mother liquid, and then entering the cooling crystallization device 1 again for cooling crystallization. The circulation ratio of the cooling crystallization refers to: the ratio of the circulating amount to the total amount of the liquid fed into 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 1 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 crystal and the second mother liquor (i.e. the liquid phase obtained by the second solid-liquid separation) are obtained after the second solid-liquid separation is carried out on the crystallization liquid containing the sodium sulfate crystal. The method of the second solid-liquid separation is not particularly limited, and may be selected from one or more of centrifugation, filtration, and sedimentation, for example.

According to the present invention, the second solid-liquid separation may be performed by using a second solid-liquid separation device 92 (for example, a centrifuge, a belt filter, a plate filter, or the like). After the second solid-liquid separation, the second mother liquor obtained by the second solid-liquid separation device 92 is temporarily stored in the second mother liquor tank 54, and may be returned to the MVR evaporation device 2 by the ninth circulation pump 79 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 a second washing with water or a sodium sulfate solution, and may be dried when anhydrous sodium sulfate is required. The second washing method is preferably rinsing, and rinsing is preferably performed after solid-liquid separation.

The manner of the above-mentioned second solid-liquid separation and second 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 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 with higher purity. The second washing is preferably carried out using an aqueous sodium sulphate solution, the concentration of which is preferably such that the sodium chloride and the sodium sulphate reach simultaneously the concentration of sodium sulphate in a saturated aqueous solution at the temperature corresponding to the sodium sulphate crystals to be washed. As for the liquid resulting from the washing, it is preferable that the water or the washing solution of sodium sulfate aqueous solution is returned to the cooling crystallization device 1, for example, may be returned to the cooling crystallization device 1 by the tenth circulation pump 80.

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 1. By the above washing process, the purity of the obtained sodium sulfate crystals can be improved.

According to the present invention, in order to fully utilize the refrigeration capacity of the second mother liquor, it is preferable that the first mother liquor and the second mother liquor are subjected to the second heat exchange before the first mother liquor is cooled and crystallized.

According to a preferred embodiment of the present invention, the second heat exchange is performed by a third heat exchange device 33, and specifically, the first mother liquor and the second mother liquor are respectively passed through the third heat exchange device 33 and heat exchanged, so that the temperature of the first mother liquor is lowered to facilitate the cooling crystallization, and the temperature of the second mother liquor is raised to facilitate the evaporation. After heat exchange by the third heat exchange device 33, the temperature of the first mother liquor is-19.7-15.5 ℃, preferably-19-9 ℃, more preferably-4-6 ℃, 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 first mother liquor to a second heat exchange with a freezing liquid. According to a preferred embodiment of the present invention, the heat exchange between the first mother liquor and the refrigerating fluid is performed by the sixth heat exchange device 36, and specifically, the refrigerating fluid, the mixed liquid of the first mother liquor and the cooling circulation fluid are respectively passed through the sixth heat exchange device 36, and heat exchange is performed between the refrigerating fluid and the mixed liquid, so that the temperature of the mixed liquid of the first mother liquor and the cooling circulation fluid is further lowered to facilitate the cooling crystallization. The refrigerating fluid can adopt a refrigerating medium which is conventionally used for reducing the temperature in the field, as long as the temperature of the first mother liquor can meet the requirement of cooling crystallization.

The third heat exchanger 33 and the sixth heat exchanger 36 are not particularly limited, and various heat exchangers conventionally used in the art may be used to perform 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 third heat exchange device 33 and the sixth heat exchange device 36 are preferably heat exchangers made of plastic.

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 1, and the second heat exchange condenses the residual tail gas, i.e. the non-condensable gas discharged from the second heat exchange device 32. 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 preferably 50g/L or more, further preferably 60g/L or more, further 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 ⁺ The upper limit of (b) is 200g/L or less, preferably 150g/L or less, respectively; NH in catalyst production wastewater ₄ ⁺ Is 50g/L or less, preferably 30g/L or less.

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⁺ Inorganic salt ions such as rare earth element ions, 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 7, for example 6 to 7.

In addition, since the COD of the wastewater may block a membrane during concentration, affect the purity and color of salt during evaporative crystallization, and the like, the COD of the wastewater in the catalyst production is preferably as small as possible (preferably 20mg/L or less, and more preferably 10mg/L or less), and is preferably removed by oxidation during pretreatment, specifically, for example, by a biological method, an advanced oxidation method, and the like, and is preferably oxidized by an oxidizing agent such as a Fenton 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 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. Aiming at suspended matters, a solid-liquid separation method can be selected for removing impurities; for inorganic matters and organic matters, chemical precipitation, ion exchange and adsorption methods can be selected for removing impurities, such as weak acid cation exchange, activated carbon adsorption and the like; 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 wastewater of the present invention before the wastewater is treated by the treatment method of the present invention (preferably, after the above-mentioned impurity removal). 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, the efficiency of wastewater treatment can be improved, and energy waste caused by a large amount of evaporation is avoided.

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 as follows: 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; forward wash flow rate of 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 the concentration of the ED membrane are preferably: the current is 145-155A, and the voltage is 45-65V. As the ED membrane, for example, an ED membrane manufactured by easton corporation, japan can be used.

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 direct operation, and if the ion content of the catalyst production wastewater meets the conditions of the invention, the evaporation and then the cooling crystallization 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, cooling crystallization can be carried out firstly to obtain concentrated solution, solid-liquid separation is carried out to obtain sodium sulfate 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 evaporation is carried out to obtain sodium chloride 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 wastewater is obtained by sequentially removing impurities from wastewater generated in the production process of the molecular sieve by chemical precipitation, filtration, weak acid cation exchange method and ozone biological activated carbon adsorption oxidation method, and sequentially concentrating the wastewater by ED membrane concentration and reverse osmosis method.

Example 1

As shown in FIG. 1, the catalyst production wastewater (containing 120g/L NaCl and Na) ₂ SO ₄ 48g/L、NH ₄ Cl23g/L、(NH ₄ ) ₂ SO ₄ 9.35g/L, pH 6.8) at a feed rate of 8.40m ³ A rate of/h was fed to a pipeline of the treatment system, and a sodium hydroxide aqueous solution having a concentration of 45.16 mass% was introduced into the pipeline to perform a first pH adjustment, and the adjusted pH was monitored by a first pH measuring device 61 (pH meter) (measurement value 9.1); then 3.40m by the first circulation pump 71 ³ The catalyst production wastewater is sent into a first mother liquor in a first mother liquor tank 53 to be mixed, the other part of the catalyst production wastewater is sent into a first heat exchange device 31 to exchange heat with the first ammonia-containing steam condensate, the rest part of the catalyst production wastewater is mixed with a second mother liquor returned by a ninth circulating pump 79 and then sent into a fifth heat exchange device 35 to exchange heat with the first mother liquor, then the wastewater after heat exchange of the first heat exchange device 31 and the fifth heat exchange device 35 is combined to obtain wastewater to be treated, the temperature is measured to be 80 ℃, wherein Cl ^- Has a concentration of 4.284mol/L, SO ₄ ^2- Has a concentration of 0.1945mol/L, cl ^- /SO ₄ ^2- Is 22.025; introducing a 45.16 mass% aqueous sodium hydroxide solution into a pipe for feeding the wastewater to be treated into the second heat exchange device 32 to perform a second pH adjustment, and monitoring the adjusted pH by a second pH measuring device 62 (pH meter) (measurement value 11); then, the wastewater to be treated is sent into a second heat exchange device 32 to exchange heat with ammonia-containing steam and is heated to 107 ℃; finally, the mixture is introduced into an MVR evaporation device 2 (a falling film and forced circulation two-stage MVR evaporation crystallizer) for evaporation to obtain concentrated solution containing ammonia vapor and sodium chloride crystals, wherein the evaporation temperature is 100 ℃, the pressure is-22.83 kPa, and the evaporation capacity is 7.71m ³ H is used as the reference value. After being compressed by the compressor 101 (the temperature is raised by 17 ℃), the ammonia-containing steam exchanges heat with wastewater to be treated and wastewater produced by the catalyst in the second heat exchange device 32 and the first heat exchange device 31 in sequence to obtain ammonia water, and the ammonia water is stored in the ammonia water storage tank 51. In addition, in order to increase the solid content in the MVR evaporation apparatus 2, a part of the liquid evaporated in the MVR evaporation apparatus 2 is sent to the MVR evaporation apparatus 2 again as a circulation liquid by the seventh circulation pump 77 to be evaporatedAnd (reflux ratio: 154). The degree of evaporation was monitored by a densitometer provided on the MVR evaporation apparatus 2, and the concentration of sodium sulfate in the evaporation concentrate was controlled to 0.9625Y (51.3 g/L).

Sending the concentrated solution containing sodium chloride crystals into a first solid-liquid separation device 91 (centrifugal machine) for solid-liquid separation and leaching to obtain 9.81m per hour ³ Contains NaCl 308.6g/L and Na ₂ SO ₄ 51.3g/L、NaOH2.2g/L、NH ₃ 0.17g/L of the first mother liquor was temporarily stored in the first mother liquor tank 53. After the obtained sodium chloride solid (wherein the content of sodium sulfate is less than 3.2 mass%) is washed by using 308.6g/L sodium chloride solution which is equal to the dry mass of sodium chloride, part of sodium chloride crystal filter cake is used for preparing 308.6g/L sodium chloride solution, 1419.17kg sodium chloride crystal filter cake with the water content of 14 mass% is obtained every hour, the sodium chloride crystal filter cake is dried in a drier, 1220.49kg sodium chloride (the purity is 99.5 mass%) is obtained every hour, and the second washing liquid obtained by washing is circulated to the position before the second pH value adjustment through an eighth circulating pump 78.

3.40m as above ³ The catalyst production wastewater/h was mixed with the first mother liquor in the first mother liquor tank 53 (concentration of NaCl therein was measured to be 260g/L, na was measured) ₂ SO ₄ The concentration of the sodium sulfate is 38.2 g/L), the first mother liquor is subjected to heat exchange with a mixed solution of catalyst production wastewater and second mother liquor through a fifth heat exchange device 35 through a sixth circulating pump 76, then is subjected to heat exchange with the second mother liquor through a third heat exchange device 33 to reduce the temperature to 0 ℃, then is mixed with sodium sulfate crystal eluent and cooling circulating liquid, is further subjected to heat exchange with refrigerating liquid through a sixth heat exchange device 36, and is sent into a cooling crystallization device 1 (continuous freezing crystallization tank) to be cooled and crystallized, so that a crystallization liquid containing sodium sulfate crystals is obtained. Wherein the cooling crystallization temperature is-4 deg.C, the time is 125min, and the circulation amount of the cooling crystallization is controlled to be 300m ³ And h, controlling the supersaturation degree of sodium sulfate in the cooling crystallization process to be not more than 1.0g/L.

Sending the crystal liquid containing sodium sulfate crystals obtained by the cooling crystallization device 1 into a second solid-liquid separation device 92 (centrifugal machine) for solid-liquid separation and leaching, and obtaining 11.60m per hour ³ Contains 296g/L NaCl and Na ₂ SO ₄ 14.5g/L、NH ₃ 2.93g/L of the first mother liquor was temporarily stored in the second mother liquor tank 54, and after the obtained sodium sulfate crystals (in which the sodium chloride content was 3.1% by mass or less) were washed with 14.5g/L of a sodium sulfate solution equivalent to the dry mass of sodium sulfate, 1946.10kg of a sodium sulfate decahydrate crystal cake having a purity of 99.0% by mass and a water content of 75% by mass per hour was obtained.

In this example, 7.71m of ammonia water having a concentration of 1.0 mass% was obtained per hour in the ammonia water tank 51 ³ 。

In addition, the tail gas discharged from the cooling crystallization device 1 and the second heat exchange device 32 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 a 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 68g/L, na ₂ SO ₄ 100g/L、NH ₄ Cl 24g/L、(NH ₄ ) ₂ SO ₄ 35.9g/L of catalyst production wastewater with pH of 6.7 is treated, and the feeding amount is 13.3m ³ H; will be 5.0m ³ Cl in wastewater to be treated obtained by mixing/h catalyst production wastewater with second mother liquor returned by the ninth circulating pump 79 ^- And SO ₄ ^2- Is 18.948; mixing the rest of the catalyst production wastewater with the first mother liquor in the first mother liquor tank 53, wherein the concentration of NaCl in the obtained mixed liquor is 247.0g/L, and Na ₂ SO ₄ The concentration of (B) was 43.6g/L.

The evaporation temperature is 75 ℃, the pressure is-72.75 kPa, and the evaporation capacity is 8.90m ³ H; the cooling crystallization temperature is-2 deg.C, and the time is 120min.

The first solid-liquid separating device 91 is arranged every hour1462.30kg of sodium chloride crystal cake with a water content of 15 mass% was obtained, and 1242.96kg of sodium chloride (purity of 99.5 mass%) was finally obtained per hour; obtained 25.58m per hour ³ The concentration of NaCl is 305.1g/L and Na ₂ SO ₄ 57.5g/L、NaOH 0.80g/L、NH ₃ 0.35g/L of the first mother liquor.

The second solid-liquid separation device 92 obtained 7269.86kg (purity: 99.1% by mass) of a sodium sulfate decahydrate crystal cake containing 74.5% by mass of water per hour; obtain 28.02m per hour ³ The concentration is NaCl298.9g/L and Na ₂ SO ₄ 15.7g/L、NH ₃ 5.11g/L of second mother liquor.

The ammonia water of 8.90m was obtained at a concentration of 2.3 mass% per hour in the ammonia water tank 51 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 NaCl-containing 99g/L and Na ₂ SO ₄ 101g/L、NH ₄ Cl 26g/L、(NH ₄ ) ₂ SO ₄ 27g/L of catalyst production wastewater with pH of 6.9 is treated, and the feeding amount is 12.15m ³ H; will be 5.0m ³ Cl in wastewater to be treated obtained by mixing/h catalyst production wastewater with second mother liquor returned by the ninth circulating pump 79 ^- And SO ₄ ^2- Is 16.938; mixing the rest of the catalyst production wastewater with the first mother liquor in the first mother liquor tank 53 to obtain a mixed solution containing 238.5g/L of NaCl and Na ₂ SO ₄ The concentration of (B) was 47.1g/L.

The evaporation temperature is 50 ℃, the pressure is-92.67 kPa, and the evaporation capacity is 8.76m ³ H; the cooling crystallization temperature is-4 deg.C, and the time is 120min.

The first solid-liquid separation device 91 obtained 1788.93kg of a sodium chloride crystal cake having a water content of 14 mass% per hour, and finally 1538.48kg of sodium chloride (purity of 99.5 mass%) per hour; the first solid-liquid separation device 91 gave 17.77 m/hr ³ The concentration of NaCl is 294.6g/L and Na ₂ SO ₄ 65.7g/L、NaOH 0.22g/L、NH ₃ 0.23g/L of the first mother liquor.

The second solid-liquid separation device 92 obtains 6113.15kg (purity: 98.9 mass%) of a sodium sulfate decahydrate crystal cake containing 74 mass% of water per hour; yield 20.05m per hour ³ The concentration of NaCl 296.3g/L and Na ₂ SO ₄ 14.6g/L、NH ₃ 5.6g/L of the second mother liquor.

Ammonia water of 8.76m was obtained at a concentration of 1.9 mass% per hour in the ammonia water tank 51 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 various technical features being combined 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 wastewater generated in catalyst production, wherein the wastewater contains NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ Characterized in that the method comprises the following steps,

1) Introducing the wastewater to be treated into an MVR evaporation device for evaporation to obtain ammonia-containing steam and concentrated solution containing sodium chloride crystals;

wherein the wastewater to be treated contains the catalyst production wastewater and a liquid phase obtained by the second solid-liquid separation;

before the wastewater to be treated is evaporated, adjusting the pH value of the wastewater to be treated to be more than 9;

relative to 1mol of SO contained in the wastewater to be treated ₄ ^2- Cl contained in the wastewater to be treated ^- 9.5mol or more;

the evaporation prevents the sodium sulfate from crystallizing out, and the cooling crystallization prevents the sodium chloride from crystallizing out;

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 1mol of SO contained in the wastewater to be treated is added ₄ ^2- Cl contained in the wastewater to be treated ^- Is 10mol or more.

3. The method according to claim 2, wherein the pH of the wastewater to be treated is adjusted to 10.8 or more before the wastewater to be treated is subjected to evaporation.

4. The method according to claim 1, wherein SO is contained in the liquid phase obtained by the first solid-liquid separation before the liquid phase obtained by the first solid-liquid separation is subjected to cooling crystallization ₄ ^2- Has a concentration of 0.01mol/L or more and Cl ^- The concentration of (B) is 5.2mol/L or less.

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

6. The process of claim 1, wherein the evaporation is carried out such that the concentration of sodium sulfate in the concentrate is Y or less, where Y is the concentration of sodium sulfate at which both sodium sulfate and sodium chloride in the concentrate are saturated under the conditions of evaporation.

7. The process of claim 6, wherein the evaporation provides a sodium sulfate concentration in the concentrate of 0.9Y to 0.99Y.

8. The method of any one of claims 1-7, wherein the conditions of evaporation comprise: the temperature is above 35 ℃ and the pressure is above-98 kPa.

9. The method of claim 8, wherein the conditions of evaporation comprise: the temperature is 45-175 ℃, and the pressure is-95 kPa-653 kPa.

10. The method of claim 9, wherein the conditions of evaporation comprise: the temperature is 60-160 ℃, and the pressure is-87 kPa-414 kPa.

11. The method of claim 10, wherein the conditions of evaporation comprise: the temperature is 75-150 ℃, and the pressure is-73 kPa-292 kPa.

12. The method of claim 11, wherein the conditions of evaporation comprise: the temperature is 80-130 ℃, and the pressure is-66 kPa-117 kPa.

13. The method of claim 12, wherein the conditions of evaporation comprise: the temperature is 95-110 ℃, and the pressure is-37 kPa-12 kPa.

14. The method according to any one of claims 1 to 7, wherein the temperature of the cooling crystallization is from-21.7 ℃ to 17.5 ℃.

15. The method according to claim 14, wherein the temperature of the cooling crystallization is from-20 ℃ to 5 ℃.

16. The method according to claim 15, wherein the temperature of the cooling crystallization is from-10 ℃ to 5 ℃.

17. The method according to claim 16, wherein the temperature of the cooling crystallization is from-10 ℃ to 0 ℃.

18. The method according to claim 14, wherein the cooling crystallization time is 5min or more.

19. The method of claim 18, wherein the cooling crystallization time is 60min to 180min.

20. The method of claim 19, wherein the cooling crystallization time is 90min to 150min.

21. The method according to any one of claims 1 to 7, wherein the wastewater to be treated is subjected to a first heat exchange with the ammonia-containing steam and ammonia water is obtained before the wastewater to be treated is subjected to evaporation.

22. The process according to any one of claims 1 to 7, wherein the liquid phase obtained by the first solid-liquid separation is subjected to a second heat exchange with the liquid phase obtained by the second solid-liquid separation before the liquid phase obtained by the first solid-liquid separation is subjected to cooling crystallization.

23. The method according to any one of claims 1 to 7, further comprising subjecting the concentrated solution containing sodium chloride crystals to a first solid-liquid separation to obtain sodium chloride crystals.

24. The method of claim 23, further comprising washing the resulting sodium chloride crystals.

25. The method according to any one of claims 1 to 7, further comprising subjecting the sodium sulfate crystal-containing crystal liquid to a second solid-liquid separation to obtain sodium sulfate crystals.

26. The method of claim 25, further comprising washing the resulting sodium sulfate crystals.

27. The process of any one of claims 1 to 7, wherein the catalyst production wastewater is wastewater from a molecular sieve, alumina or refinery catalyst production process.

28. The method of claim 27, further comprising removing impurities and concentrating the catalyst process wastewater.