CN109422399B

CN109422399B - Method for treating waste water containing ammonium salt

Info

Publication number: CN109422399B
Application number: CN201710751942.7A
Authority: CN
Inventors: 殷喜平; 李叶; 顾松园; 陈玉华; 刘志坚; 安涛; 伊红亮
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: 2023-02-17
Anticipated expiration: 2037-08-28
Also published as: CN109422399A

Abstract

The invention relates to the field of sewage treatment, and discloses a method for treating ammonium salt-containing wastewater, wherein the ammonium salt-containing wastewater contains NH ₄ ⁺ 、SO ₄ ^2‑ 、Cl ^‑ And Na ⁺ The method comprises the following steps of 1) evaporating wastewater to be treated to obtain ammonia-containing steam and concentrated solution containing sodium chloride crystals, wherein the wastewater to be treated contains the ammonium salt-containing 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 ammonium salt-containing wastewater

Technical Field

The invention relates to the field of sewage treatment, in particular to a method for treating ammonium salt-containing wastewater, and especially relates to a method for treating NH-containing wastewater ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ The method for treating waste water containing ammonium salt.

Background

In the production process of the oil refining catalyst, a large amount of inorganic acid-base 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 6-9, most of suspended matters are removed, then the biochemical method, the blow-off method or the steam stripping method is adopted to remove ammonium ions, then the salt-containing sewage is subjected to pH value adjustment, most of suspended matters are removed, hardness, silicon and part of organic matters are removed, most of organic matters are removed through ozone biological activated carbon adsorption oxidation or other advanced oxidation methods, then the salt-containing sewage enters an ion exchange device for further hardness removal, enters an enrichment device (such as reverse osmosis or electrodialysis) for concentration, and then MVR evaporative crystallization or multiple-effect evaporative crystallization is adopted 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 to treat or expensive to treat, and the process of removing ammonium ions at the early stage additionally increases the cost of wastewater treatment.

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 ammonium salt-containing wastewater containing NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ The method comprises the following steps of,

1) Evaporating the wastewater to be treated to obtain ammonia-containing steam and a concentrated solution containing sodium chloride crystals, wherein the wastewater to be treated contains the ammonium salt-containing 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 ^- 7.15mol or more; the cooling crystallization prevents the sodium chloride from crystallizing out.

By the technical scheme, the method aims at the content of NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ The pH value of the wastewater to be treated is adjusted to a specific range in advance, sodium chloride crystals and ammonia water are obtained through evaporation, the chloride ion concentration of the first mother liquor entering the cooling crystallization is controlled, and then the sodium sulfate crystals are obtained through cooling crystallization and separation. 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 method improves the concentration multiple and the evaporation efficiency of evaporation by matching evaporation and cooling treatment, reduces the amount of circulating liquid in a treatment system, and can achieve the effect of energy conservation; by cooling the junctionThe crystal greatly reduces the sodium sulfate content in the mother liquor for preparing sodium sulfate, can improve the efficiency of preparing sodium chloride by evaporation, and simultaneously, before the liquid phase obtained by the first solid-liquid separation is cooled and crystallized, the Cl in the waste water containing ammonium salt and the sodium sulfate crystal leacheate are preferably adjusted by the ammonium salt and the sodium sulfate crystal leacheate ^- 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 ammonium salt-containing wastewater according to an embodiment of the present invention;

FIG. 2 is a schematic flow diagram of a method for treating ammonium salt-containing wastewater according to another embodiment of the present invention.

Description of the reference numerals

1. Cooling crystallization device 72 and second circulation pump

2. MVR evaporation plant 73, third circulating pump

22. Low-temperature treatment tank 74 and fourth circulation pump

31. First heat exchange device 76 and sixth circulating pump

32. Second heat exchanger 77, seventh circulating pump

33. Third heat exchange device 78, eighth circulating pump

35. Fifth heat exchange device 79 and ninth circulating pump

36. Sixth heat exchange device 80, tenth circulating pump

51. Ammonia water storage tank 81 and vacuum pump

53. First mother liquor tank 82 and circulating water tank

54. Second mother liquor tank 83 and tail gas absorption tower

61. First pH value measuring device 91 and first solid-liquid separation device

62. Second pH value measuring device 92 and second solid-liquid separation device

63. Third pH value measuring device 101 and compressor

71. First circulating pump

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 to 2, but the present invention is not limited to fig. 1 to 2.

The invention provides a method for treating ammonium salt-containing wastewater, which contains NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ The method comprises the following steps of,

Preferably, the wastewater to be treated is the wastewater containing ammonium salt; or the wastewater to be treated contains the ammonium salt-containing 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 ammonium salt-containing 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 ammonia-containing gas containing NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ Except that it contains NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ In addition, the ammonium salt-containing wastewater is not particularly limited.

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 solid-liquid separation of the ammonium salt-containing 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, for example, 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 is performed to separate ammonia and salts in the wastewater by precipitating sodium chloride or precipitating sodium chloride together with sodium sulfate and evaporating ammonia. According to the present invention, by controlling the conditions of evaporation, sodium chloride is precipitated first and further sodium sulfate is precipitated as the solvent is decreased, thereby obtaining a concentrated solution containing sodium chloride crystals (containing only sodium chloride crystals or sodium chloride crystals and sodium sulfate crystals).

In the present invention, the evaporation may be performed using an evaporation apparatus conventional in the art, such as an MVR evaporation apparatus, a single-effect evaporation apparatus, a flash evaporation apparatus, or a multi-effect evaporation apparatus. As the MVR evaporation means, for example, 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 may be mentioned. 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 evaporation crystallizer. The evaporator as the single-effect evaporator or the multiple-effect evaporator may be, for example, one or more selected from falling-film evaporators, rising-film evaporators, wiped-plate evaporators, central-circulation-tube-type multiple-effect evaporators, basket-suspended evaporators, external-heat evaporators, forced-circulation evaporators and lien evaporators. Among them, a forced circulation evaporator and an external heating evaporator are preferable. The multiple-effect evaporation apparatus may further include other evaporation auxiliary components, such as a demister for further separating liquid foam, a condenser for condensing all secondary steam, and a vacuum apparatus for pressure reduction, as necessary. The number of evaporators included in the multi-effect evaporation apparatus is not particularly limited, and may be 2 or more, and more preferably 3 to 5. According to a preferred embodiment of the present invention, the evaporation is performed by means of an MVR evaporation device 2.

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 increase the efficiency of the 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 the 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.

When the multi-effect evaporation device is used for evaporation, and concurrent flow or countercurrent flow feeding is adopted, the evaporation condition refers to the evaporation condition of the last evaporator of the multi-effect evaporation device; when advection feeding is employed, the conditions of evaporation include the evaporation conditions of each effect evaporator of the multi-effect evaporation apparatus. Moreover, in order to fully utilize the heat in the evaporation process, the difference between the evaporation temperatures of the two adjacent evaporator effects is preferably 5-30 ℃; more preferably, the evaporating temperatures of two adjacent effect evaporators differ by 10 ℃ to 20 ℃.

In the present invention, the operating pressure for 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 the evaporation process yields sodium chloride crystals of high purity, the amount of SO relative to 1mol of SO contained in the wastewater to be treated ₄ ^2- Cl contained in the wastewater to be treated ^- Is 7.15mol or more, preferably 8mol or more, preferably 10mol or more, preferably 20mol or more, more preferably 30mol or more, and may be, for example, 10 to 20mol. Specific examples thereof include 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, and 50 mol. By reacting SO ₄ ^2- And Cl ^- The molar ratio of the sodium sulfate to the sodium chloride is controlled within the range, pure sodium chloride crystals can be obtained through evaporation, and the separation of the sodium sulfate and the sodium chloride is realized.

According to a preferred embodiment of 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 are saturated in the concentrate 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.

According to another preferred embodiment of the present invention, in order to reduce the amount of circulating water in the treatment system and to increase the efficiency of evaporation and thus the efficiency of wastewater treatment, the evaporation is preferably carried out to such an extent that sodium chloride and sodium sulfate are precipitated simultaneously, that is, the evaporation preferably results in a concentrated solution containing sodium chloride crystals and sodium sulfate crystals. In this case, in order to obtain high-purity sodium chloride crystals, it is preferable that the concentrated solution containing sodium chloride crystals is subjected to a temperature reduction treatment to obtain a treated solution containing sodium chloride crystals before the first solid-liquid separation, and the treated solution containing sodium chloride crystals is subjected to the first solid-liquid separation. At this time, the method of the present invention comprises the steps of:

2) Cooling the concentrated solution containing the sodium chloride crystals to obtain a treatment solution containing the sodium chloride crystals;

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

4) And carrying out second solid-liquid separation on the crystallization liquid containing the sodium sulfate crystals.

In the above-described embodiment, the higher the degree of evaporation is, the better the evaporation is, from the viewpoint of improving the efficiency of wastewater treatment; however, if the evaporation exceeds a certain level, the temperature reduction treatment cannot yield a treatment solution containing only sodium chloride crystals, and in this case, the crystals may be dissolved by adding water to the treatment solution, but the efficiency of wastewater treatment is impaired. Therefore, the evaporation is preferably performed to such an extent that sodium chloride crystals and sodium sulfate crystals are simultaneously precipitated, that is, preferably, the second concentrated solution containing crystals obtained in step 1) is a concentrated solution containing sodium chloride crystals and sodium sulfate crystals, and the temperature reduction treatment dissolves the sodium sulfate crystals in the concentrated solution containing sodium chloride crystals and sodium sulfate crystals. In order to dissolve the sodium sulfate crystals in the concentrated solution containing sodium chloride crystals and sodium sulfate crystals in the temperature-lowering treatment, for example, the evaporation degree of the evaporation may be controlled so that the concentration of sodium sulfate in the treatment solution is equal to or less than Y '(where Y' is the concentration of sodium sulfate when both sodium sulfate and sodium chloride in the treatment solution are saturated under the temperature-lowering treatment condition). In the subsequent temperature-lowering treatment step, the evaporation is preferably performed so that the concentration of sodium sulfate in the treatment solution is 0.9Y 'to 0.99Y', and more preferably 0.95Y 'to 0.98Y', from the viewpoint of precipitating sodium chloride as much as possible and completely dissolving sodium sulfate. By controlling the evaporation degree within the range, sodium chloride can be separated out as much as possible in the evaporation process, and in the cooling treatment, sodium sulfate is completely dissolved, and pure sodium chloride crystals are finally separated. By increasing the evaporation capacity as much as possible, the wastewater treatment efficiency can be improved, and the energy can be saved.

In the present invention, the temperature reduction treatment is performed to dissolve sodium sulfate crystals contained in the concentrated solution containing sodium chloride crystals and further precipitate sodium chloride. The temperature reduction treatment for dissolving the sodium sulfate crystals in the concentrated solution containing the sodium chloride crystals means that the evaporation degree needs to be properly controlled in order to obtain pure sodium chloride crystals, that is, the sodium sulfate in the mixed system is controlled not to exceed the solubility under the corresponding temperature reduction treatment condition. In addition, sodium chloride crystals entrain or adsorb sodium sulfate crystals on the surface during the temperature reduction treatment. In the present invention, the content of sodium sulfate in the obtained sodium chloride crystals is preferably 8 mass% or less, more preferably 4 mass% or less, and in the present invention, it is considered that sodium sulfate is dissolved when the content of sodium sulfate crystals in the obtained sodium chloride crystals is 8 mass% or less.

The conditions for performing the temperature reduction treatment are not particularly limited, and it is sufficient that the sodium sulfate crystals in the concentrated solution containing sodium chloride crystals can be completely dissolved in the temperature reduction treatment process, for example, the conditions for performing the temperature reduction treatment may include: the temperature is 13 ℃ to 100 ℃, preferably 16 ℃ to 45 ℃, more preferably 16.5 ℃ to 35 ℃, and further preferably 17.9 ℃ to 31.5 ℃; more preferably from 17.9 ℃ to 25 ℃. In order to ensure the effect of the temperature reduction treatment, preferably, the conditions of the temperature reduction treatment include: the time is more than 5min, preferably 5min to 120min, more preferably 45min to 90min; more preferably 50 to 70min.

Specific examples of the temperature lowering treatment include: 13 deg.C, 14 deg.C, 15 deg.C, 15.5 deg.C, 16 deg.C, 16.5 deg.C, 17 deg.C, 17.5 deg.C, 17.9 deg.C, 18 deg.C, 18.5 deg.C, 19 deg.C, 19.5 deg.C, 20 deg.C, 21 deg.C, 23 deg.C, 25 deg.C, 27 deg.C, 30 deg.C, 31.5 deg.C, 32 deg.C, 33 deg.C, 34 deg.C, 40 deg.C, 45 deg.C, 50 deg.C, 55 deg.C, etc.

Specific examples of the time for the temperature reduction treatment include: 5min, 6min, 7min, 8min, 10min, 15min, 20min, 25min, 30min, 35min, 40min, 45min, 50min, 52min, 54min, 56min, 58min, 60min, 70min, 100min, 120min.

According to the present invention, the temperature reduction treatment is performed in the low-temperature treatment tank 22, and the treatment solution containing sodium chloride crystals is obtained after the temperature reduction treatment of the concentrated solution containing sodium chloride crystals in the low-temperature treatment tank 22. The low-temperature treatment tank 22 is not particularly limited, and may be, for example, a thickener, a crystallization tank with agitation, a crystallization tank with external circulation, or the like, and among them, a crystallization tank with agitation is preferred. The low-temperature treatment tank 22 is preferably provided with a kneading member for bringing the concentrated solution into a kneaded state in the temperature reduction treatment, and for example, a conventionally used mechanical stirring, electromagnetic stirring and/or external circulation device may be used, and it is preferable that the solid-liquid distribution in the concentrated solution is brought into a uniform state. All parts of the concentrated solution keep uniform temperature and concentration through uniform mixing, thereby avoiding the problem that the dissolution of sodium sulfate crystals cannot be fully carried out and improving the efficiency of cooling treatment. The low-temperature treatment tank 22 is preferably provided with a cooling means for cooling the low-temperature treatment tank 22 to a temperature required for the temperature reduction treatment by introducing a cooling medium, for example.

In the present invention, the degree of progress of the evaporation is performed by monitoring the amount of evaporation (or the amount of the condensate) or the concentration of the concentrated solution, specifically, when the amount of evaporation is measured, the concentration multiple is controlled by controlling the amount of evaporation, that is, the amount of the secondary steam or the amount of the ammonia water, and the degree of evaporation concentration is monitored by measuring the amount of evaporation, so that the sodium sulfate crystals precipitated in the concentrated solution obtained by evaporation can be dissolved during the temperature reduction treatment, specifically, a mass flow meter can be used for flow measurement, the amount of the secondary steam can be measured, and the amount of the condensate can also be measured; in the concentration measurement, the concentration of the concentrated solution obtained by evaporation is controlled to be within the above range, so that the evaporation does not cause crystallization of sodium sulfate in the concentrated solution, and the concentration of the liquid obtained by evaporation is monitored by measuring the density, specifically, the density can be measured by using a densimeter.

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 evaporation 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 refers to: 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 of the evaporation may be, for example, 10 to 200, preferably 40 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 fully utilize the heat of the evaporated ammonia-containing vapor, it is preferable to perform a first heat exchange between the wastewater to be treated and the ammonia-containing vapor before the wastewater to be treated is fed into the MVR evaporation apparatus 2. In order to make full use of the heat in the first mother liquor and/or the concentrate containing sodium chloride crystals, it is more preferred that the wastewater to be treated is subjected to a first heat exchange with the first mother liquor and/or the concentrate containing sodium chloride crystals before said wastewater to be treated is sent to the MVR evaporator 2.

According to a preferred embodiment of the present invention, as shown in fig. 1, the first heat exchange between the wastewater to be treated and the ammonia-containing steam is performed 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 concentrated solution containing sodium chloride crystals is carried out by the 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 concentrated solution containing sodium chloride crystals passes through the fifth heat exchange device 35; meanwhile, one part of the wastewater to be treated exchanges heat with the condensate containing ammonia vapor through the first heat exchange device 31, the other part exchanges heat with the concentrate containing sodium chloride crystals through the fifth heat exchange device 35, and the two parts of wastewater to be treated are combined and then exchanged heat with the ammonia vapor through the second heat exchange device 32, so that the temperature of the wastewater to be treated is raised, the wastewater to be treated is convenient to evaporate, the ammonia vapor is condensed to obtain ammonia water, and the concentrate containing the sodium chloride crystals is cooled, and the temperature of the concentrate containing the sodium chloride crystals is convenient to lower.

According to another preferred embodiment of the present invention, as shown in fig. 2, the first heat exchange between the wastewater to be treated and the ammonia-containing steam is performed 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 (i.e., a liquid phase obtained by the first solid-liquid separation described later) is performed by the fifth heat exchange means 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; simultaneously with some of pending waste water through first heat transfer device 31 with contain the heat transfer of ammonia steam condensate, the rest passes through fifth heat transfer device 35 and first mother liquor heat transfer, then merges two parts pending waste water back through second heat transfer device 32 with contain the heat transfer of ammonia steam to make pending waste water intensification be convenient for evaporate, make simultaneously contain the ammonia steam condensation and obtain the aqueous ammonia, make the cooling of first mother liquor be convenient for cool off the crystallization.

After the 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, 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 made of duplex stainless steel, titanium alloy and hastelloy can be selected, and the heat exchanger made of plastic 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 of more than 9, preferably more than 10.8, more preferably between 10.8 and 11.5, before the waste water to be treated is subjected to the treatment. 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 subjecting the wastewater to be treated to the treatment 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 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.

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 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 in the pipe for feeding the ammonium salt-containing wastewater to the first heat exchange apparatus 31 before feeding the ammonium salt-containing wastewater to 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 pipe feeding the wastewater to be treated into the MVR evaporation plant 2 and mixing.

The pH value of the wastewater to be treated is more than 9, preferably more than 10.8 before the wastewater is evaporated by two pH value adjustments. Preferably, the first pH adjustment is such that the pH is greater than 7 (preferably 7-9) and the second pH adjustment is such that the pH is greater than 9, preferably greater than 10.8.

In order to detect the pH values after the first pH value adjustment and the second pH value adjustment, it is preferable to arrange a first pH value measuring device 61 on the pipe for feeding the wastewater containing ammonium salt into the first heat exchange device 31 to measure the pH value after the first pH value adjustment, and arrange a second pH value 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 value 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 by 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, the sodium chloride crystals are preferably subjected to first washing with water, the ammonium salt-containing 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 first washing method is preferably performed by elutriation and then rinsing. The first washing liquid obtained from the above washing process is preferably returned to the MVR evaporation device 2 by the eighth circulation pump 78 for evaporation again.

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 is preferably 2 to 4 times in order to obtain 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 washed. 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 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 or the treated solution containing sodium chloride crystals is subjected to preliminary solid-liquid separation by settling, then elutriated in another elutriation tank using a liquid obtained in the subsequent washing of sodium chloride crystals, then the elutriated treated solution containing sodium chloride crystals is sent to a solid-liquid separation apparatus for solid-liquid separation, the crystals obtained by the 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 simultaneously saturated 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 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 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-4-0 ℃; 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 crystallization 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 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.

In the present invention, if SO is present in said first mother liquor ₄ ^2- 、Cl ^- The concentration of (b) is out of the above range, and concentration adjustment may be carried out before cooling crystallization is carried out, and the concentration adjustment is preferably carried out using the ammonium salt-containing waste water, and specifically, the ammonium salt-containing waste water may be 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.

In addition, cl is contained 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, etc.

According to the present invention, the cooling crystallization is carried out in a continuous or batch manner, and the temperature of the first mother liquor is lowered to precipitate sodium sulfate crystals, and the continuous cooling crystallization is preferably carried out. 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 component can lead the first mother liquid in the cooling crystallization tank to be cooled to the condition required for cooling crystallization by introducing a cooling medium. The cooling crystallization device is preferably provided with a blending part, such as a stirrer and the like, and the first mother liquor is blended 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.

In the present invention, it is preferable to adjust Cl in the first mother liquor before the first mother liquor is cooled and crystallized, if necessary ^- 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 crystallization 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. The concentration adjustment can be performed by using the ammonium salt-containing wastewater, a washing solution after washing the sodium sulfate crystals, sodium sulfate, or the like, and the ammonium salt-containing wastewater is preferably used.

By crystallizing said cooled crystals at the above-mentioned temperature, cl ^- The concentration and the pH value can be controlled, sodium sulfate can be fully separated out in cooling crystallization, sodium chloride and the like can not be separated out, and the aim of separating and purifying the sodium sulfate is achieved.

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. In the process of returning the cooling circulation liquid to the cooling crystallization device 1 for crystallization, the cooling circulation liquid may be mixed with the first mother liquid and then enter the cooling crystallization device 1 again for cooling crystallization before returning the cooling circulation liquid to the sixth heat exchange device 36 by the second circulation pump 72, for example. The return amount of the cooling circulation liquid can be defined by a circulation ratio of cooling, and the circulation ratio of the 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 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 of 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 crystal 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 cooling crystallization, and the temperature of the second mother liquor is raised to facilitate evaporation. After the heat exchange is carried out 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 refrigerating fluid. According to a preferred embodiment of the present invention, the heat exchange between the first mother liquid and the refrigerating liquid is performed by the sixth heat exchange device 36, and specifically, the refrigerating liquid and the mixed liquid of the first mother liquid and the cooling circulating liquid are respectively passed through the sixth heat exchange device 36, and heat exchange is performed between the refrigerating liquid and the mixed liquid, so that the temperature of the mixed liquid of the first mother liquid and the cooling circulating liquid 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.

In order to obtain stronger ammonia water and improve the purity and efficiency of the sodium sulfate obtained by cooling crystallization, the wastewater to be treated is preferably concentrated to obtain ammonia-containing steam and concentrated wastewater to be treated before the wastewater to be treated is subjected to the evaporation. The concentration aims at obtaining high-concentration ammonia water, is convenient for controlling the concentration of the ammonia water, and makes the concentration of the wastewater to be treated convenient for cooling and crystallizing. The degree of the concentration to be carried out is not particularly limited as long as it is ensured that the concentrated wastewater to be treated satisfies the above-mentioned requirements for evaporation. The conditions for the concentration and the equipment used are the same as those for the evaporation described later, but the concentration temperature is preferably higher than that for the evaporation described later, so that the wastewater to be treated can be rapidly evaporated, and the evaporation efficiency can be improved while concentrated ammonia water is obtained. Furthermore, the pH of the wastewater to be treated is preferably adjusted to be greater than 9, more preferably greater than 10.8, before the wastewater to be treated is concentrated. The pH adjustment is preferably carried out using NaOH.

By adjusting the pH value of the wastewater to be treated to be greater than 9 before the wastewater is subjected to evaporation, and concentrating, ammonia water with higher concentration can be obtained, the purity of sodium sulfate obtained by cooling crystallization is improved, and the efficiency 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 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 ammonium salt-containing 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. As the inventionThe waste water containing ammonium salt can be waste water from the production process of molecular sieve, alumina or oil refining catalyst, or waste water obtained by removing impurities and concentrating the waste water from the production process of molecular sieve, alumina or oil refining catalyst. 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 said ammonium salt-containing wastewater ₄ ⁺ May be 8mg/L or more, preferably 300mg/L or more.

As Na in said ammonium salt-containing wastewater ⁺ 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 said ammonium salt-containing wastewater 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 said ammonium salt-containing 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 ammonium salt-containing wastewater ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ The upper limit of (3) is not particularly limited. SO in ammonium salt-containing wastewater from the viewpoint of easy access to wastewater ₄ ^2- 、Cl ^- And Na ⁺ The upper limit of (b) is 200g/L or less, preferably 150g/L or less, respectively; NH in ammonium salt-containing wastewater ₄ ⁺ Is 50g/L or less, preferablyLess than 30 g/L.

In the present invention, the inorganic salt ions contained in the ammonium salt-containing 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 ammonium salt-containing wastewater, the following impurity removal is preferably performed.

The TDS of the ammonium salt-containing 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 value of the ammonium salt-containing wastewater is preferably 4 to 7, for example 6 to 7.

In addition, since COD of the wastewater may block a membrane at the time of concentration, affect the purity and color of salt at the time of evaporative crystallization, etc., it is preferable that the COD of the wastewater containing ammonium salt is as small as possible (preferably 20mg/L or less, more preferably 10mg/L or less), and it is preferable that the COD is removed by oxidation at the time of pretreatment, and specifically, it is preferable to perform oxidation by, for example, a biological method, an advanced oxidation method, etc., and it is preferable to perform oxidation by an oxidizing agent such as a Fenton reagent at the time of very high COD content.

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 ammonium salt-containing 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; the chemical precipitation may be pH adjustment, carbonate precipitation, magnesium salt precipitation, or the like; 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 ammonium salt-containing wastewater. For 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 ammonium salt-containing wastewater is subjected to impurity removal by filtration, a weak acid cation exchange method and an ozone biological activated carbon adsorption oxidation method in sequence. 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 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 ammonium salt-containing wastewater is wastewater obtained by performing chemical precipitation, filtration, weak acid cation exchange and ozone biological activated carbon adsorption oxidation on wastewater generated in the molecular sieve production process to remove impurities, and performing ED membrane concentration and reverse osmosis concentration.

The conditions for the above chemical precipitation are preferably: sodium carbonate is used as a treating agent, 1.2-1.4mol 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 20-35 ℃, and the reaction time is 0.5-4h.

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; 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 Tokusan 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. 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 wastewater containing ammonium salt can be directly used for operation, and if the ion content of the wastewater containing ammonium salt meets the condition of the invention, the evaporation can be carried out firstly and then the cooling crystallization can be carried out according to the condition of the invention; if the ion content of the wastewater containing ammonium salt 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 and the wastewater containing ammonium salt are mixed 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, it is also possible to adjust the ion content of the wastewater to be treated in the initial stage by using sodium sulfate or sodium chloride, provided that the wastewater to be treated satisfies the SO content of 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 containing ammonium salt is wastewater generated in the production process of molecular sieve by chemical precipitation, filtration, weak acid cation exchange method and ozone biological activated carbon adsorption oxidation method, and then by ED membrane concentration and reverse osmosis method.

Example 1

As shown in figure 1, the waste water containing ammonium salt (containing 130g/L NaCl and Na) ₂ SO ₄ 26g/L、NH ₄ Cl 40g/L、(NH ₄ ) ₂ SO ₄ 8.1g/L, pH 6.5) at 5.859m ³ The reaction mixture was fed into a line of a treatment system at a rate of/h, and a 45.16 mass% aqueous sodium hydroxide solution was introduced into the line to adjust the pH for the first time, and the adjusted pH was monitored by a first pH measuring device 61 (pH meter) (measurement value was 9)0); wherein, a part of the waste water containing ammonium salt is 5.0m by the first circulating pump 71 ³ The second mother liquor returned from the ninth circulation pump 79 is mixed at a speed of/h to obtain wastewater to be treated (Cl measured therein) ^- Has a concentration of 3.737mol/L, SO ₄ ^2- Has a concentration of 0.197mol/L and Cl ^- /SO ₄ ^2- The molar ratio of 18.97), then sending one part of the wastewater to be treated into a first heat exchange device 31 to exchange heat with the first ammonia-containing steam condensate and heating to 102 ℃, meanwhile sending the rest part of the wastewater to be treated into a fifth heat exchange device 35 to exchange heat with the concentrated solution containing sodium chloride crystals obtained by evaporation and heating to 103 ℃, and then combining two parts of the wastewater to be treated and sending the two parts of the wastewater to be treated into a second heat exchange device 32; 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 the ammonia-containing steam, so that the temperature of the wastewater to be treated is raised to 112 ℃; 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 ammonia-containing steam and concentrated solution containing sodium chloride crystals and sodium sulfate crystals, the evaporation temperature is 105 ℃, the pressure is-7.02 kPa, and the evaporation capacity is 6.116m 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 101 (the temperature is increased by 19 ℃), the ammonia-containing steam exchanges heat with wastewater to be treated 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 again to the MVR evaporation apparatus 2 as a circulation liquid by the seventh circulation pump 77 to be evaporated (reflux ratio is 120). The evaporation degree is monitored by a mass flow meter arranged on the MVR evaporation device 2, and the evaporation amount is controlled to be 6.012m ³ H (corresponding to the control of the sodium sulfate concentration in the treatment solution to 0.9787Y (91.7 g/L)).

And (3) after the concentrated solution containing the sodium chloride crystals and the sodium sulfate crystals exchanges heat with part of the wastewater to be treated through a fifth heat exchange device 35, sending the wastewater to be treated into a low-temperature treatment tank 22 for cooling treatment at the temperature of 17.9 ℃ for 70min to obtain a treatment solution containing the sodium chloride crystals. The low-temperature treatment tank 22 is internally provided with a stirring paddle, and the rotating speed is 60r/min.

The treatment solution containing sodium chloride crystals is sent to a first solid-liquid separation device 91 (centrifugal machine) for solid-liquid separation and leaching, and 2.606m per hour is obtained ³ Contains 277.7g/L NaCl and Na ₂ SO ₄ 91.7g/L、NaOH 2.2g/L、NH ₃ 0.66g/L of the first mother liquor was temporarily stored in the first mother liquor tank 53. The obtained sodium chloride solid (1202.7 kg of sodium chloride crystal cake containing 15 mass% of water per hour, wherein the content of sodium sulfate is 3.1 mass% or less) was subjected to leaching with 277.7g/L of a sodium chloride solution equivalent to the dry mass of sodium chloride, and then dried in a dryer to obtain 1022.3kg of sodium chloride (having a purity of 99.3 mass%) per hour, and the second washing liquid obtained by the washing was circulated to the fifth heat exchange apparatus 35 by the eighth circulation pump 78.

The other part of the waste water containing ammonium salt is treated by the treatment of 0.859m ³ The first mother liquor in the first mother liquor tank 53 was mixed at a rate of/h (NaCl concentration measured therein was 241g/L, na) ₂ SO ₄ The concentration of the sodium sulfate is 69 g/L), the first mother liquor is subjected to heat exchange with the second mother liquor through a third heat exchange device 33 by a sixth circulating pump 76 to be cooled to 2.1 ℃, then is mixed with sodium sulfate crystal eluent and cooling circulating liquid, is subjected to further heat exchange with refrigerating liquid through a sixth heat exchange device 36, and then is sent into a cooling crystallization device 1 (a continuous cooling crystallization tank) to be cooled and crystallized, so that the crystallization liquid containing sodium sulfate crystals is obtained. Wherein the cooling crystallization temperature is-2 deg.C, the time is 130min, and the circulation amount of cooling crystallization is controlled to be 181m ³ And h, controlling the supersaturation degree of sodium sulfate in the cooling crystallization process to be not more than 1.0g/L.

The crystal liquid containing sodium sulfate crystals obtained in the cooling crystallization device 1 is sent to a second solid-liquid separation device 92 (centrifugal machine) for solid-liquid separation and leaching, and 2.793m is obtained every hour ³ Contains NaCl 299g/L and Na ₂ SO ₄ 15.8g/L、NH ₃ Temporarily storing the first mother liquor of 5.08g/L in a second mother liquor tank 54, and returning and mixing the first mother liquor and the wastewater containing ammonium salt to obtain wastewater to be treated; mixing the obtained sodium sulfate decahydrate crystal (wherein the content of sodium chloride is 3.0 wt% or less) withAfter washing with 15.8g/L sodium sulfate solution of the same dry mass of sodium sulfate, 797.2kg of sodium sulfate decahydrate crystal cake having a purity of 98.6 mass% and a water content of 75 mass% was obtained per hour.

In this example, 6.012m of ammonia water having a concentration of 1.39 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 ammonium salt-containing wastewater was carried out in the same manner as in example 1, except that: for the NaCl containing 68g/L and Na ₂ SO ₄ 68g/L、NH ₄ Cl 25g/L、(NH ₄ ) ₂ SO ₄ 25.4g/L of ammonium salt-containing wastewater with pH of 6.3 is treated, and the feeding amount is 6.84m ³ H; part of the wastewater is treated at 5.0m ³ Cl in the wastewater to be treated obtained by mixing the speed of/h with the second mother liquor returned by the ninth circulating pump 79 ^- And SO ₄ ^2- Is 10.848; the concentration of NaCl in the wastewater to be treated, which is obtained by mixing the rest part of wastewater containing ammonium salt with the first mother liquor in the first mother liquor tank 53, is 237.85g/L, na ₂ SO ₄ The concentration of (B) was 71.39g/L.

The evaporation temperature is 100 ℃, the pressure is-22.83 kPa, and the evaporation capacity is 5.530m ³ H; the temperature of the cooling treatment is 20 ℃, and the time is 65min; the cooling crystallization temperature is 0 ℃ and the time is 120min.

The first solid-liquid separation device 91 produced 755.64kg of sodium chloride crystal cake having a water content of 14.5 mass% per hour, and finally produced 646.08kg of sodium chloride (purity 99) per hour2 mass%); the second solid-liquid separation device 92 obtained 7.433m per hour ³ The concentration of NaCl is 279.9g/L and Na ₂ SO ₄ 88.9g/L、NaOH 2.2g/L、NH ₃ 0.27g/L of the first mother liquor.

The second solid-liquid separation device 92 obtained 2531.56kg (purity: 98.3 mass%) of a sodium sulfate decahydrate crystal cake containing 74 mass% of water per hour; obtained 7.265m per hour ³ The concentration of NaCl 303.9g/L and Na ₂ SO ₄ 17g/L、NH ₃ 3.86g/L of the second mother liquor.

Ammonia water of 5.530m in a concentration of 1.7 mass% was obtained 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 ammonium salt-containing wastewater was carried out in the same manner as in example 1, except that: for NaCl-containing 50g/L, na ₂ SO ₄ 100g/L、NH ₄ Cl 21g/L、(NH ₄ ) ₂ SO ₄ 42.69g/L of ammonium salt-containing wastewater with the pH value of 6.7 is treated, and the feeding amount is 9.39m ³ H; part of the waste water containing ammonium salt is treated by the treatment of 5.0m ³ Cl in the wastewater to be treated obtained by mixing the speed of/h with the second mother liquor returned by the ninth circulating pump 79 ^- And SO ₄ ^2- Is 11.640; the concentration of NaCl in the wastewater to be treated, which is obtained by mixing the rest part of wastewater containing ammonium salt with the first mother liquor in the first mother liquor tank 53, is 224.49g/L, na ₂ SO ₄ The concentration of (B) was 62.84g/L. The temperature of the wastewater to be treated after heat exchange by the second heat exchange means 32 was 105 ℃.

The evaporation temperature is 110 ℃, the pressure is 11.34kPa, and the evaporation capacity is 5.999m ³ H; the temperature of the cooling treatment is 25 ℃, and the time is 60min; the cooling crystallization temperature is-4 deg.C, and the time is 120min.

The first solid-liquid separation device 91 obtained 775.47kg of a sodium chloride crystal cake having a water content of 14 mass% per hour, and finally 666.90kg of sodium chloride (purity of 99.4 mass%) per hour; the second solid-liquid separation device 92 obtains 13.876m per hour ³ The concentration of NaCl is 279.7g/L and Na ₂ SO ₄ 82.4g/L、NaOH 2.2g/L、NH ₃ 0.23g/L of the first mother liquor.

The second solid-liquid separation device 92 yielded 5445.10kg of a sodium sulfate decahydrate crystal cake containing 74.5 mass% of water (purity: 98.4 mass%); obtained at 13.900m per hour ³ The concentration of NaCl is 295g/L and Na ₂ SO ₄ 14.5g/L、NH ₃ 5.70g/L of the second mother liquor.

Ammonia water of 5.999m in a concentration of 2.6 mass% is obtained per hour in the ammonia water tank 51 ³ The ammonia water can be reused in the production process of the molecular sieve.

Example 4

As shown in FIG. 2, the wastewater containing ammonium salt (containing NaCl 120g/L and Na) ₂ SO ₄ 48g/L、NH ₄ Cl 23g/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 ammonium salt-containing wastewater is fed into a first mother liquor tank 53 to be mixed, the other part of the ammonium salt-containing wastewater is fed into a first heat exchange device 31 to exchange heat with the first ammonia-containing steam condensate, the rest part of the ammonium salt-containing wastewater is mixed with a second mother liquor returned by a ninth circulating pump 79 and then fed into a fifth heat exchange device 35 to exchange heat with the first mother liquor, then the wastewater after heat exchange by 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 to 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 evaporationObtaining 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 a compressor 101 (the temperature rises by 17 ℃), the ammonia-containing steam exchanges heat with wastewater to be treated and wastewater containing ammonium salt in a second heat exchange device 32 and a first heat exchange device 31 in sequence to obtain ammonia water, and the ammonia water is stored in an 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 again to the MVR evaporation apparatus 2 as a circulating liquid by the seventh circulating pump 77 to be evaporated (reflux ratio is 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、NaOH 2.2g/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 ammonium salt-containing wastewater was mixed with the first mother liquor in the first mother liquor tank 53 (NaCl concentration measured therein was 260g/L, na) ₂ SO ₄ Is 38.2 g/L), the first mother liquor is subjected to heat exchange with a mixed solution of ammonium salt-containing wastewater and the second mother liquor through a fifth heat exchange device 35 by a sixth circulating pump 76, then is subjected to heat exchange with the second mother liquor by a third heat exchange device 33 to reduce the temperature to 0 ℃, then is mixed with sodium sulfate crystal eluent and cooling circulating liquid, then is subjected to further heat exchange with refrigerating liquid by a sixth heat exchange device 36, and then is sent into a cooling crystallization device 1 (continuous freezing crystallization device 1)A crystallizing tank) to obtain a crystallization liquid containing sodium sulfate crystals. 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.

The crystal liquid containing sodium sulfate crystals obtained from the cooling crystallization device 1 is sent to a second solid-liquid separation device 92 (centrifugal machine) for solid-liquid separation and leaching, and 11.60m is obtained every 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 of the water for operating the vacuum pump 81 and the ammonia content 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 5

The treatment of the ammonium salt-containing wastewater was carried out in the same manner as in example 4, except that: for the NaCl containing 68g/L and Na ₂ SO ₄ 100g/L、NH ₄ Cl 24g/L、(NH ₄ ) ₂ SO ₄ 35.9g/L of ammonium salt-containing wastewater with the pH value of 6.7 is treated, and the feeding amount is 13.3m ³ H; will be 5.0m ³ H waste water containing ammonium salt is mixed with the second mother liquor returned by the ninth circulating pump 79Cl in wastewater to be treated ^- And SO ₄ ^2- Is 18.948; mixing the rest part of wastewater containing ammonium salt 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 is contained in the mixed liquor ₂ SO ₄ The concentration of (2) 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 separation device 91 obtained 1462.30kg of sodium chloride crystal cake with a water content of 15 mass% per hour, and finally 1242.96kg of sodium chloride (purity of 99.5 mass%) per hour; yield 25.58m per hour ³ The concentration is NaCl 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; obtained 28.02m per hour ³ The concentration of NaCl is 298.9g/L and Na ₂ SO ₄ 15.7g/L、NH ₃ 5.11g/L of the 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 6

The treatment of the ammonium salt-containing wastewater was carried out in the same manner as in example 4, 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 ammonium salt-containing 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 ammonium salt-containing wastewater with second mother liquor returned by the ninth circulating pump 79 ^- And SO ₄ ^2- Is 16.938; mixing the rest part of the wastewater containing ammonium salt with the first mother liquor in the first mother liquor tank 53 to obtain a mixed liquor with the NaCl concentration of 238.5g/L and Na ₂ SO ₄ The concentration of (2) was 47.1g/L.

The evaporation temperature is 50 ℃, the pressure is-92.67 kPa, and the evaporation capacity isIs 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 sodium chloride crystal cake with 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.

6113.15kg (purity: 98.9 mass%) of a sodium sulfate decahydrate crystal cake containing 74 mass% of water was obtained in the second solid-liquid separation device 92 per hour; obtained at 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 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 ammonium salt-containing wastewater containing NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ Characterized in that the method comprises the following steps,

1) Evaporating the wastewater to be treated to obtain ammonia-containing steam and concentrated solution containing sodium chloride 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 ^- 7.15mol or more;

the sodium chloride is not crystallized and separated out by the cooling crystallization;

the wastewater to be treated contains the ammonium salt-containing wastewater and a liquid phase obtained by the second solid-liquid separation;

NH in the ammonium salt-containing 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 8mol or more.

3. The method according to claim 2, wherein the SO contained in the wastewater to be treated is 1mol with respect to the SO ₄ ^2- Cl contained in the wastewater to be treated ^- 9.5mol or more.

4. The method according to claim 1, wherein the pH of the wastewater to be treated is adjusted to 10.8 or more before the wastewater to be treated is evaporated.

5. 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 cooled and crystallized ₄ ^2- Has a concentration of 0.01mol/L or more, cl ^- The concentration of (b) is 5.2mol/L or less.

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

7. The method according to claim 1, wherein the concentrated solution containing sodium chloride crystals is subjected to a temperature reduction treatment to obtain a treated solution containing sodium chloride crystals before the first solid-liquid separation, and the treated solution containing sodium chloride crystals is subjected to the first solid-liquid separation.

8. The method according to claim 7, wherein the concentrated solution containing sodium chloride crystals obtained in step 1) is a concentrated solution containing sodium chloride crystals and sodium sulfate crystals, and the temperature reduction treatment dissolves the sodium sulfate crystals in the concentrated solution containing sodium chloride crystals and sodium sulfate crystals.

9. The method according to claim 1, wherein the wastewater to be treated is concentrated before being subjected to said evaporation, resulting in ammonia-containing steam and concentrated wastewater to be treated.

10. 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.

11. The method of claim 10, wherein the evaporating provides a sodium sulfate concentration in the concentrate of 0.9Y to 0.99Y.

12. The method of any one of claims 1-11, wherein the conditions of evaporation comprise: the temperature is above 35 ℃ and the pressure is above-98 kPa.

13. The method of claim 12, wherein the conditions of evaporation comprise: the temperature is 45-175 ℃ and the pressure is-95 kPa-653 kPa.

14. The method of claim 13, wherein the conditions of evaporation comprise: the temperature is 60-160 ℃, and the pressure is-87 kPa-414 kPa.

15. The method of claim 14, wherein the conditions of evaporation comprise: the temperature is 75-150 ℃, and the pressure is-73-292 kPa.

16. The method of claim 15, wherein the conditions of evaporation comprise: the temperature is 80-130 ℃, and the pressure is-66 kPa-117 kPa.

17. The method of claim 16, wherein the conditions of evaporation comprise: the temperature is 95-110 ℃, and the pressure is-37 kPa-12 kPa.

18. The method according to claim 7, wherein the temperature of the temperature reduction treatment is 13-100 ℃.

19. The method according to claim 18, wherein the temperature of the temperature reduction treatment is 16 ℃ to 45 ℃.

20. The method of claim 19, wherein the temperature of the temperature reduction treatment is 16.5-35 ℃.

21. The method according to claim 20, wherein the temperature of the temperature reduction treatment is 17.9-31.5 ℃.

22. The method according to claim 18, wherein the time of the temperature reduction treatment is 5min or more.

23. The method of claim 22, wherein the time of the temperature reduction treatment is 5min to 120min.

24. The method of claim 23, wherein the time of the temperature reduction treatment is 45-90 min.

25. The method according to any one of claims 1 to 11, wherein the temperature of the cooling crystallization is from-21.7 ℃ to 17.5 ℃.

26. The method of claim 25, wherein the temperature of the cooling crystallization is from-20 ℃ to 5 ℃.

27. The method of claim 26, wherein the temperature of the cooling crystallization is from-10 ℃ to 5 ℃.

28. The method of claim 27, wherein the temperature of the cooling crystallization is from-10 ℃ to 0 ℃.

29. The method according to claim 25, wherein the cooling crystallization time is 5min or more.

30. The method of claim 29, wherein the cooling crystallization time is 60min to 180min.

31. The method of claim 30, wherein the cooling crystallization time is 90min to 150min.

32. The method according to any one of claims 1 to 11, wherein the wastewater to be treated is subjected to a first heat exchange with the ammonia-containing steam and to obtain ammonia water before the wastewater to be treated is subjected to evaporation.

33. The process according to any one of claims 1 to 11, 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.

34. The method according to any one of claims 1 to 11, further comprising subjecting the concentrated solution containing sodium chloride crystals or the treated solution containing sodium chloride crystals to a first solid-liquid separation to obtain sodium chloride crystals.

35. The process of claim 34, further comprising washing the obtained sodium chloride crystals.

36. The method according to any one of claims 1 to 11, further comprising subjecting the sodium sulfate crystal-containing crystal liquid to a second solid-liquid separation to obtain sodium sulfate crystals.

37. The method of claim 36, further comprising washing the resulting sodium sulfate crystals.

38. The process of any one of claims 1 to 11, wherein the ammonium salt-containing wastewater is wastewater from a molecular sieve, alumina or refinery catalyst production process.

39. The method of claim 38, further comprising removing impurities and concentrating the ammonium salt-containing wastewater.