CN108726759B

CN108726759B - Method for treating ammonium salt-containing wastewater

Info

Publication number: CN108726759B
Application number: CN201710263286.6A
Authority: CN
Inventors: 殷喜平; 李叶; 顾松园; 陈玉华; 刘志坚; 安涛; 张志民; 苑志伟; 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: 2017-04-21
Filing date: 2017-04-21
Publication date: 2023-01-06
Anticipated expiration: 2037-04-21
Also published as: CN108726759A

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) carrying out first evaporation on wastewater to be treated to obtain first ammonia-containing steam and first concentrated solution containing sodium chloride crystals, wherein the wastewater to be treated contains the wastewater containing ammonium salt; 2) Carrying out first solid-liquid separation on the first concentrated solution containing the sodium chloride crystals, and carrying out second evaporation on a liquid phase obtained by the first solid-liquid separation to obtain second concentrated solution containing ammonia vapor and sodium sulfate crystals; 3) And carrying out second solid-liquid separation on the second concentrated solution 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 waste water containing ammonium salt

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 the wastewater containing ammonium salt.

Background

In the production process of the oil refining catalyst, a large amount of inorganic acid alkali salts such as sodium hydroxide, hydrochloric acid, sulfuric acid, ammonium salts, sulfates, hydrochlorides and the like are needed, and a large amount of mixed sewage containing ammonium, sodium chloride, sodium sulfate 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 chloride and sodium sulfate 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 multiple-effect evaporative crystallization to obtain the mixed miscellaneous salt of sodium chloride and sodium sulfate containing ammonium salt. However, these ammonium-containing mixed salts are currently difficult or expensive to treat, and the process of removing ammonium ions at the early stage adds additional cost to the treatment of wastewater.

In addition, the biochemical deamination can only treat wastewater with low ammonium content, and can not directly carry out biochemical treatment due to insufficient COD content in the catalyst sewage, and organic matters such as glucose or starch and the like are additionally added in the biochemical treatment process, so that the ammoniacal nitrogen can be treated by the biochemical method. The most important problem is 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), the wastewater needs to be deeply treated, the salt content of the wastewater is not reduced (20000 mg/L-30000 mg/L), the wastewater cannot be directly discharged, and the wastewater needs to be further desalted.

In order to remove ammonia 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 (20000 mg/L-30000 mg/L), the wastewater cannot be discharged directly, further desalting treatment is needed, the operation cost of wastewater treatment is high, a large amount of alkali remains in the treated wastewater, the pH value is high, the waste is large, and the treatment cost is up to 50 yuan/ton.

Disclosure of Invention

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

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) Carrying out first evaporation on wastewater to be treated to obtain first ammonia-containing steam and first 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 first concentrated solution containing the sodium chloride crystals, and carrying out second evaporation on a liquid phase obtained by the first solid-liquid separation to obtain second concentrated solution containing ammonia vapor and sodium sulfate crystals;

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

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

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, then sodium chloride crystals and stronger ammonia water are obtained by first evaporation and separation, and then sodium sulfate crystals and thinner ammonia water are obtained by second evaporation. The method can respectively obtain high-purity chlorinationSodium and sodium sulfate, the difficulty of mixed salt processing and recycling in-process has been avoided, accomplish the process of separation ammonia and salt simultaneously, and adopt the heat exchange mode to make waste water heat up simultaneously and contain the cooling of ammonia steam, need not the condenser, heat among the rational utilization evaporation process, the energy saving reduces the waste water treatment cost, ammonium in the waste water is retrieved with the form of aqueous ammonia, sodium sulfate and sodium chloride are retrieved with the crystal form respectively, whole process does not have the waste residue waste liquid to produce, the purpose of changing waste into valuables has been realized.

Additional features and advantages of the invention will be set forth in the detailed description which follows.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the 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. Second evaporation device 72 and second circulation pump

2. First evaporation plant 73, third circulating pump

31. First heat exchanger 74, fourth circulating pump

32. Second heat exchanger 75, fifth circulating pump

33. Third heat exchange device 76 and sixth circulating pump

34. Fourth heat exchanger 77, seventh circulating pump

35. Fifth heat exchange device 78, eighth circulating pump

4. Vacuum degassing tank 79 and ninth circulating pump

51. First ammonia water storage tank 81 and vacuum pump

52. Second ammonia storage tank 82 and circulating water tank

53. First mother liquor tank 83 and tail gas absorption tower

54. Second mother liquor tank 91 and first solid-liquid separation device

55. Crystal liquid collecting tank 92 and second solid-liquid separation device

61. First pH value measuring device 101 and first compressor

62. Second pH value measuring device 102 and second compressor

71. First circulating pump

Detailed Description

The following describes in detail specific embodiments of the present invention. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.

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

1) Carrying out first evaporation on wastewater to be treated to obtain first ammonia-containing steam and a first concentrated solution containing sodium chloride crystals, wherein the wastewater to be treated contains the wastewater containing ammonium salt;

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

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.

Further preferably, the wastewater to be treated is a liquid phase mixed solution obtained by the ammonium salt-containing wastewater and the second solid-liquid separation.

Preferably, the pH of the wastewater to be treated is adjusted to be greater than 10.8 before the wastewater to be treated is subjected to the first evaporation. The upper limit 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.

The method provided by the invention can be used for the treatment of the compounds containing NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ Except that it contains NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ In addition, the wastewater to be treated is not particularly limited. From the viewpoint of improving the treatment efficiency of wastewater, the amount of SO contained in the wastewater to be treated is 1 mole per mole ₄ ^2- Cl contained in the wastewater to be treated ^- 9.7 mol or more, more preferably 10 mol or more, more preferably 10.5 mol or more, more preferably 11 mol or more, preferably 50 mol or less, more preferably 40 mol or lessFurther preferably 30 mol or less, for example, 11 to 20 mol, preferably 11 to 15 mol. By reacting SO ₄ ^2- And Cl ^- The molar ratio of (a) to (b) is controlled within the above range, and sodium chloride can be precipitated without precipitating sodium sulfate in the first evaporation, thereby achieving the purpose of efficiently separating sodium chloride. In addition, as described above and below, it is also possible in the present invention to recycle the second mother liquor obtained in the second evaporation process to the first evaporation, and thereby to treat SO in the wastewater to be treated ₄ ^2- And Cl ^- The molar ratio of (a) to (b) is adjusted and the balance of sodium hydroxide can be maintained.

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

In the present invention, the second evaporation to prevent sodium chloride from crystallizing out means that the concentration of sodium chloride in the mixed system is controlled not to exceed the solubility under the second evaporation conditions (including but not limited to temperature, pH value, etc.), and sodium chloride carried by sodium sulfate crystals or adsorbed on the surface is not excluded. When the content of sodium chloride in the obtained sodium sulfate crystals is usually 8 mass% or less (preferably 4 mass% or less) because of the difference in the water content of the crystals after solid-liquid separation, it is considered that sodium chloride is not crystallized out.

In the present invention, it is understood that the first ammonia-containing steam and the second ammonia-containing steam are secondary steam as referred to in the art. The pressures are all pressures in gauge pressure.

According to the present invention, the manner in which the first evaporation and the second evaporation are performed is not particularly limited, and evaporation under the respective evaporation conditions may be performed, and for example, various evaporation apparatuses conventionally used in the art may be used. Specifically, the MVR evaporation device, the multi-effect evaporation device and the single-effect evaporation device can be one or more. Wherein the first evaporation is preferably performed by an MVR evaporation device; the second evaporation is preferably performed by means of an MVR evaporation device.

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 evaporative crystallizer.

As the individual-effect evaporator in the single-effect evaporator or the multi-effect evaporator, for example, one or more selected from falling-film evaporators, rising-film evaporators, wiped-plate evaporators, central-circulation-tube evaporators, basket-suspended evaporators, external-heat evaporators, forced-circulation evaporators, and lien evaporators can be used. Among them, a forced circulation evaporator and an external heating evaporator are preferable. The evaporator may include other evaporation auxiliary components such as a demister for further separating liquid foam, a condenser for condensing all secondary steam, and a vacuum device for pressure reduction operation, if necessary. When the evaporation device is a multi-effect evaporation device, the number of evaporators contained therein is not particularly limited, and may be selected according to the desired evaporation conditions, and may be 2 or more, preferably 2 to 5, and more preferably 2 to 4.

In the present invention, when the first evaporation and/or the second evaporation is performed using a multi-effect evaporation apparatus, the feeding manner of the liquid to be evaporated may be the same or different, and may be a concurrent, countercurrent or advective manner conventionally used in the art. The forward flow is specifically as follows: and sequentially introducing liquid to be evaporated into each effect evaporator of the multi-effect evaporation device, and introducing ammonia-containing steam obtained by evaporation of the former effect evaporator of the multi-effect evaporation device into the latter effect evaporator. The countercurrent is specifically: and sequentially introducing liquid to be evaporated into each effect evaporator of the multi-effect evaporation device, and introducing ammonia-containing steam obtained by evaporation of the latter effect evaporator of the multi-effect evaporation device into the former effect evaporator. The advection specifically comprises the following steps: and independently introducing liquid to be evaporated into each effect evaporator of the multi-effect evaporation device, and introducing ammonia-containing steam obtained by evaporation of the former effect evaporator of the multi-effect evaporation device into the latter effect evaporator. Among them, concurrent feeding is preferred. When concurrent or countercurrent 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 adopted, the evaporation conditions include the evaporation conditions of each effect evaporator of the multi-effect evaporation device.

In the present invention, the conditions of the first evaporation may be appropriately selected as needed, and sodium chloride may be crystallized without precipitating sodium sulfate. The conditions of the first evaporation may include: the temperature is 30-85 ℃, and the pressure is-98 kPa to-58 kPa. In order to improve the evaporation efficiency, and from the viewpoint of reducing the equipment cost and energy consumption, it is preferable that the conditions of the first evaporation include: the temperature is 35-60 ℃, and the pressure is-97.5 kPa to-87 kPa; more preferably, the conditions of the first evaporation include: the temperature is 40 ℃ to 60 ℃, and the pressure is-97 kPa to-87 kPa; further preferably, the conditions of the first evaporation include: the temperature is 45-60 ℃, and the pressure is-95 kPa to-87 kPa; particularly preferably, the conditions of the first evaporation include: the temperature is 45-55 ℃, and the pressure is-95 kPa to-90 kPa.

In the present invention, the operation pressure of the first evaporation is preferably the saturated vapor pressure of the evaporated feed liquid.

In the present invention, the flow rate of the first evaporation may be appropriately selected according to the capacity of the apparatus process, and may be, for example, 0.1m ³ More than h (e.g. 0.1 m) ³ /h～500m ³ /h)。

By carrying out the first evaporation under the above conditions, the sodium sulfate is not crystallized while the crystallization of sodium chloride is ensured, so that the purity of the obtained sodium chloride crystal can be ensured.

According to the invention, by controlling the first evaporation condition, more than 90 mass% (preferably more than 95 mass%) of ammonia contained in the wastewater to be treated can be evaporated, so as to obtain the first ammonia water with higher concentration, and the first ammonia water can be directly reused in the production process of the catalyst, or neutralized by acid to obtain ammonium salt for reuse, or mixed with water and corresponding ammonium salt or ammonia water for use.

According to the present invention, the first evaporation does not crystallize sodium sulfate in the wastewater to be treated (i.e., sodium sulfate does not reach supersaturation), and preferably, the first evaporation is performed so that the concentration of sodium sulfate in the first concentrated solution is Y or less (preferably 0.9Y to 0.99Y, and more preferably 0.95Y to 0.98Y). Wherein Y is the concentration of sodium sulfate at which both sodium chloride and sodium sulfate in the first concentrated solution are saturated under the conditions of the first evaporation. By controlling the degree of the first 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 crystallizing sodium chloride in the first evaporation as much as possible, the wastewater treatment efficiency can be improved, and the energy waste can be reduced.

In the present invention, the degree of progress of the first evaporation is monitored by monitoring the concentration of the first evaporation-yielded liquid, and specifically, the concentration of the first evaporation-yielded liquid is controlled within the above range so that the first evaporation does not crystallize out sodium sulfate in the first concentrated solution. The concentration of the liquid resulting from the first evaporation is monitored by measuring the density, which may be carried out using a densitometer.

According to the invention, said first evaporation is carried out in a first evaporation device 2 (which is as described above). The wastewater to be treated is introduced into the first evaporation device 2 through the first circulating pump 71 for first evaporation, so as to obtain first ammonia-containing steam and first concentrated solution containing sodium chloride crystals.

According to the invention, the method can further comprise the step of carrying out first crystallization on the first concentrated solution containing the sodium chloride crystals in a first crystallization device to obtain crystal slurry containing the sodium chloride crystals. In this case, the evaporation conditions of the first evaporation are required to satisfy the purpose of crystallizing sodium chloride without precipitating sodium sulfate in the first crystallization process. The first crystallization apparatus is not particularly limited, and may be, for example, a solution tank, a solution collecting tank, a thickener with or without stirring, or the like. The conditions for the first crystallization may be appropriately selected, and may include, for example: the temperature is above 30 ℃; preferably 40-60 ℃; more preferably from 45 ℃ to 55 ℃. In order to fully ensure the crystallization effect, the crystallization time can be 5min to 24h, preferably 5min to 30min. According to the invention, the first crystallization of the first concentrated solution containing sodium chloride crystals can also be carried out in a crystallizer evaporator (e.g. a forced circulation evaporator crystallizer), wherein the temperature of the first crystallization is the corresponding temperature of the first evaporation.

According to the present invention, when the crystallization is performed using a separate crystallization apparatus, it is further ensured that the first evaporation is performed so that sodium sulfate is not crystallized out in the first crystallization process (i.e., sodium sulfate is not supersaturated), and preferably, the first evaporation is performed so that the concentration of sodium sulfate in the first concentrated solution is Y or less (preferably, 0.9Y to 0.99Y, and more preferably, 0.95Y to 0.98Y), where Y is the concentration of sodium sulfate at which both sodium sulfate and sodium chloride in the first concentrated solution are saturated under the conditions of the first crystallization.

According to a preferred embodiment of the present invention, before the wastewater to be treated is subjected to the first evaporation, the first ammonia-containing steam or the condensate of the first ammonia-containing steam is subjected to the first heat exchange with the wastewater to be treated and a first ammonia water is obtained. The first heat exchange method is not particularly limited, and may be performed by a conventional heat exchange method in the art. The number of the first heat exchange may be 1 or more, preferably 2 to 4, and more preferably 2 to 3. Through after the first heat exchange, the output ammonia water is cooled, and the heat is circulated in the treatment device to the maximum extent, so that the energy is reasonably utilized, and the waste is reduced.

According to a preferred embodiment of the present invention, the first heat exchange is performed by a first heat exchange device 31 and a second heat exchange device 32, specifically, the first ammonia-containing steam (or the condensate of the first ammonia-containing steam) obtained by evaporation in the first evaporation device 2 passes through the second heat exchange device 32 and the first heat exchange device 31 in sequence, and the wastewater to be treated passes through the first heat exchange device 31 and the second heat exchange device 32 in sequence, the wastewater to be treated is heated for evaporation by the first heat exchange between the first ammonia-containing steam and the wastewater to be treated, and the first ammonia water is obtained by cooling the first ammonia-containing steam, and can be stored in a first ammonia water storage tank 51.

According to another preferred embodiment of the present invention, as shown in fig. 1, the first heat exchange is performed by a first heat exchange device 31, a second heat exchange device 32 and a fifth heat exchange device 35, specifically, the first ammonia-containing steam obtained by evaporation in the first evaporation device 2 passes through the second heat exchange device 32 and the first heat exchange device 31 in sequence, the second condensate containing the second ammonia-containing steam obtained by second evaporation (for example, the condensate obtained by second heat exchange of the second ammonia-containing steam in the third heat exchange device 33 and the fourth heat exchange device 34) passes through the fifth heat exchange device 35, and a part of the wastewater to be treated passes through the fifth heat exchange device 35, and simultaneously another part of the wastewater to be treated passes through the first heat exchange device 31, and then the two parts of the wastewater to be treated are merged and mixed with the second mother liquor to obtain the wastewater to be treated, and then the wastewater to be treated passes through the second heat exchange device 32 to complete the first heat exchange between the first ammonia-containing steam and the wastewater to be treated.

In the present invention, 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 art may be used to achieve the purpose of performing the first heat exchange between the first ammonia-containing steam and the wastewater to be treated. Specifically, a jacketed heat exchanger, a plate heat exchanger, a shell-and-tube heat exchanger, or the like may be mentioned, with the plate heat exchanger being preferred. The material of the heat exchanger can be specifically selected according to the needs, for example, in order to resist the corrosion of chloride ions, the heat exchanger of duplex stainless steel, titanium and titanium alloy, hastelloy can be selected as the material, and the heat exchanger containing plastic material can be selected when the temperature is lower.

According to the present invention, in order to fully utilize the heat energy of the first ammonia-containing steam or the condensate of the first ammonia-containing steam, it is preferable that the temperature of the wastewater to be treated is 41 to 67 ℃, more preferably 47 to 62 ℃ after the first heat exchange.

In the present invention, the method of adjusting the pH is not particularly limited, and for example, the pH of the wastewater to be treated may be adjusted by adding an alkaline substance. The alkaline substance is not particularly limited, and may be, for example, a hydroxide such as sodium hydroxide or potassium hydroxide for the purpose of adjusting the pH. The alkaline substance is preferably NaOH in order not to introduce new impurities in the wastewater to be treated, increasing the purity of the crystals obtained.

The manner of adding the alkaline substance may be any manner known in the art, but it is preferable to mix the alkaline substance with the wastewater to be treated in the form of an aqueous solution, and for example, an aqueous solution containing the alkaline substance may be introduced into a pipe through which the wastewater to be treated is introduced and mixed. The content of the alkaline substance in the aqueous solution is not particularly limited as long as the above-mentioned purpose of adjusting the pH value can be achieved. However, in order to reduce the amount of water used and further reduce the cost, it is preferable to use a saturated aqueous solution of an alkaline substance. 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, as shown in fig. 1, the first evaporation process is performed in the first evaporation apparatus 2, and the first pH adjustment is performed by introducing and mixing the aqueous solution containing the alkaline substance in the pipe for feeding the wastewater to be treated into the first heat exchange apparatus 31 or the fifth heat exchange apparatus 35 before feeding the wastewater to be treated into the first heat exchange apparatus 31 or the fifth heat exchange apparatus 35 for the first heat exchange; then, the wastewater to be treated is sent to the second heat exchange device 32 to perform the first heat exchange, and the aqueous solution containing the alkaline substance is introduced and mixed in the pipe for sending the wastewater to be treated to the second heat exchange device 32 to perform the second pH adjustment. The pH of the wastewater to be treated is greater than 9, preferably greater than 10.8, by two pH adjustments before it is passed into the first evaporator 2. Preferably, the first pH adjustment is performed so that the adjusted pH value of the wastewater to be treated is greater than 7 (preferably 7-9), and the second pH adjustment is performed so that the adjusted pH value of the wastewater to be treated is greater than 9, preferably greater than 10.8.

In order to detect the pH values after the first pH adjustment and the second pH adjustment, it is preferable that a first pH measuring device 61 is provided on a pipe for feeding the wastewater to be treated into the first heat exchanging device 31 or the fifth heat exchanging device 35 to measure the pH value after the first pH adjustment, and a second pH measuring device 62 is provided on a pipe for feeding the wastewater to be treated into the second heat exchanging device 32 to measure the pH value after the second pH adjustment.

In the present invention, the sequence of the first heat exchange, the adjustment of the pH value of the wastewater to be treated, and the preparation of the wastewater to be treated (in the case where the wastewater to be treated contains a liquid phase obtained by separating the ammonium salt-containing wastewater from the second solid-liquid, the preparation of the wastewater to be treated needs to be performed) is not particularly limited, and may be appropriately selected as needed, and the first heat exchange, the adjustment of the pH value of the wastewater to be treated, and the preparation of the wastewater to be treated need to be performed before the wastewater to be treated is introduced into the first evaporation apparatus.

In the invention, the first concentrated solution containing sodium chloride crystals is subjected to a first solid-liquid separation to obtain sodium chloride crystals and a first mother liquor (namely, a liquid phase obtained by the first solid-liquid separation). The method of the first solid-liquid separation is not particularly limited, and may be selected from one or more of centrifugation, filtration, and sedimentation.

According to the present invention, the solid-liquid separation of the first concentrated solution may be performed by using a first solid-liquid separation device (for example, a centrifuge, a belt filter, a plate filter, or the like) 91. After the solid-liquid separation, the first mother liquor obtained by the first solid-liquid separation device 91 is temporarily stored in the first mother liquor tank 53, and may be sent to the second evaporation device 1 by the sixth circulation pump 76 to be subjected to the second evaporation. In addition, it is difficult to avoid that the obtained sodium chloride crystals adsorb certain impurities such as chloride ions, free ammonia, hydroxide ions and the like, 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.

The manner of the first solid-liquid separation and the first washing is not particularly limited, and may be carried out by using, for example, a combination of an elutriation apparatus and a solid-liquid separation apparatus which are conventional in the art, or may be carried out on a staged solid-liquid separation apparatus such as a belt filter. Preferably, the first wash comprises panning and/or rinsing. The above-mentioned elutriation and rinsing are not particularly limited and may be carried out by a method conventional in the art. The number of elutriation and rinsing is not particularly limited, and may be 1 or more, and is preferably 2 to 4 times in order to obtain sodium chloride crystals of higher purity. In the elutriation process, the ammonium salt-containing wastewater is generally not recycled when being used as an elutriation liquid, and the washing liquid recovered by the first washing can be recycled in a countercurrent manner when being used as the elutriation liquid. Before the elutriation, a slurry containing sodium chloride crystals is preferably obtained by preliminary solid-liquid separation by sedimentation (the liquid content may be 35% by mass or less, and this step is preferably performed in an apparatus known in the art, such as a sedimentation tank or a sedimentation tank). 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. In addition, the rinsing is preferably performed using an aqueous sodium chloride solution. Preferably, the concentration of the sodium chloride aqueous solution is the concentration of sodium chloride in the aqueous solution that is saturated at the same time with sodium sulfate 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, the elutriation may be preferably performed using a liquid obtained by rinsing, and preferably using water or a sodium chloride solution. It is preferable for the liquid produced by the washing to be returned to before the completion of the first heat exchange before the first evaporation.

According to a preferred embodiment of the present invention, the first concentrated solution containing sodium chloride obtained by evaporation in the first evaporation apparatus 2 is subjected to a preliminary solid-liquid separation by settling, then subjected to a first elutriation in an elutriation tank using the ammonium salt-containing wastewater, and then subjected to a second elutriation in another elutriation tank using a liquid obtained in a subsequent washing of sodium chloride crystals, and finally the slurry subjected to the two elutriations is sent to a solid-liquid separation apparatus for solid-liquid separation, the crystals obtained by the solid-liquid separation are subjected to an elution with an aqueous sodium chloride solution, and the liquid obtained by the elution is returned to the second elutriation. Through the washing process, 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 evaporation conditions of the second evaporation may be appropriately selected as necessary, and the purpose of crystallizing sodium sulfate without precipitating sodium chloride may be achieved. The conditions of the second evaporation may include: the temperature is above 45 ℃ and the pressure is above-95 kPa. In order to improve the evaporation efficiency, and from the viewpoint of reducing the equipment cost and energy consumption, it is preferable that the conditions of the second evaporation include: the temperature is 45-365 ℃, and the pressure is-95 kPa-18110 kPa; preferably, the conditions of the second evaporation include: the temperature is 60-365 ℃, and the pressure is-87 kPa-18110 kPa; preferably, the conditions of the second evaporation include: the temperature is 75-175 ℃, and the pressure is-73 kPa-653 kPa; preferably, the conditions of the second evaporation include: the temperature is 80-130 ℃, and the pressure is-66 kPa-117 kPa; particularly preferably, the conditions of the second evaporation include: the temperature is 95-105 ℃, and the pressure is-37 kPa to-7 kPa.

In the present invention, the operating pressure of the second evaporation is preferably the saturated vapor pressure of the evaporated feed liquid.

Further, the evaporation amount of the second evaporation may be appropriately selected depending on the capacity of the apparatus to treat and the amount of the waste water to be treated, and may be, for example, 0.1m ³ More than h (e.g. 0.1 m) ³ /h～500m ³ /h)。

By carrying out the second evaporation under the above conditions, the sodium chloride is not crystallized while the crystallization of sodium sulfate is ensured, so that the purity of the obtained sodium sulfate crystal can be ensured.

According to the present invention, the second evaporation does not cause crystallization of sodium chloride (i.e., sodium chloride does not reach supersaturation), and preferably, the second evaporation causes the concentration of sodium chloride in the second concentrated solution to be X or less (preferably 0.9X to 0.99X, more preferably 0.95X to 0.999X, and still more preferably 0.99X to 0.9967X), where X is the concentration of sodium chloride at which both sodium chloride and sodium sulfate in the second concentrated solution are saturated under the conditions of the second evaporation. By controlling the degree of the second evaporation within the above range, as much sodium sulfate as possible can be crystallized out under the condition that sodium chloride is not precipitated out. By crystallizing sodium sulfate in the second evaporation as much as possible, the wastewater treatment efficiency can be improved, and the energy waste can be reduced.

In the present invention, the degree of progress of the second evaporation is performed by monitoring the concentration of the second evaporation-yielded liquid, and specifically, by controlling the concentration of the second evaporation-yielded liquid within the above range, the second evaporation does not crystallize out sodium chloride in the second concentrated solution. The concentration of the liquid resulting from the second evaporation is monitored by measuring the density, which may be carried out using a densitometer.

According to the invention, said second evaporation is carried out in a second evaporation device 1 (which is as described above). And introducing the first mother liquor into the second evaporation device 1 for second evaporation to obtain second ammonia-containing steam and second concentrated solution containing sodium chloride crystals.

According to the invention, the method can also comprise a step of carrying out second crystallization on the second concentrated solution containing the sodium sulfate crystals in a second crystallization device to obtain crystal slurry containing the sodium sulfate crystals. In this case, the evaporation conditions for the second evaporation need only be satisfied in order to crystallize sodium sulfate without precipitating sodium chloride in the second crystallization process. The second crystallization apparatus is not particularly limited, and may be, for example, a crystal solution tank, a crystal solution collecting tank, a thickener with stirring or a thickener without stirring, or the like. According to a preferred embodiment of the present invention, the second crystallization is performed in the crystal liquid collection tank 55. The conditions of the second crystallization may be appropriately selected, and may include, for example: the temperature is above 45 ℃; preferably 85-107 ℃; more preferably 95 to 105 ℃. In order to fully ensure the crystallization effect, the crystallization time can be 5min to 24h, preferably 5min to 30min. According to the invention, the second crystallization of the second concentrate containing sodium sulfate crystals can also be carried out in an evaporation device with a crystallizer (e.g. a forced circulation evaporative crystallizer), in which case the temperature of the second crystallization is the corresponding second evaporation temperature.

According to the present invention, when the second crystallization is performed using a separate crystallization apparatus, it is further ensured that the second evaporation is performed so that sodium chloride does not crystallize out during the second crystallization (i.e., sodium chloride does not reach supersaturation), and preferably, the second evaporation is performed so that the concentration of sodium chloride in the second concentrated solution is X or less (preferably, 0.9X to 0.99X, more preferably, 0.95X to 0.999X, and further preferably, 0.99X to 0.9967X), where X is the concentration of sodium chloride at which both sodium chloride and sodium sulfate in the second concentrated solution reach saturation under the conditions of the second crystallization.

According to the invention, the second ammonia-containing steam and the first mother liquor are subjected to second heat exchange to obtain second ammonia water. Preferably, the second ammonia-containing steam is subjected to second heat exchange with the first mother liquor and the wastewater to be treated in sequence to obtain second ammonia water. The second heat exchange method is not particularly limited, and may be performed by a heat exchange method that is conventional in the art. The number of heat exchanges may be 1 or more, preferably 2 to 4, more preferably 2 to 3. Through the heat exchange, the output ammonia water is cooled, and the heat is circulated in the treatment device to the maximum extent, so that the energy is reasonably utilized, and the waste is reduced.

According to a preferred embodiment of the present invention, the second heat exchange is performed by the third heat exchange device 33 and the fourth heat exchange device 34, specifically, the second ammonia-containing steam is sequentially passed through the fourth heat exchange device 34 and the third heat exchange device 33, the second heat exchange is performed with the mixed liquid of the first mother liquor, the second recycle liquid and the second rinse liquid in the fourth heat exchange device 34, the second heat exchange is performed with the first mother liquor in the third heat exchange device 33, and preferably, the first heat exchange is further performed in the fifth heat exchange device 35, so that the temperature of the second ammonia-containing steam condensate is further reduced, the heat energy utilization rate is improved, and the second ammonia water is obtained, and the second ammonia water is stored in the second ammonia water storage tank 52.

Preferably, after the second heat exchange is performed by the third heat exchange device 33, the temperature of the first mother liquor is 59-364 ℃, and more preferably 69-129 ℃; preferably, after the second heat exchange is performed by the fourth heat exchange device 34, the temperature of the first mother liquor is 67 ℃ to 370 ℃, and more preferably 75 ℃ to 137 ℃.

In the present invention, in order to prevent the sodium sulfate from crystallizing out by the first evaporation and prevent the sodium chloride from crystallizing out by the second evaporation, it is preferable that the conditions of the two-time evaporation (corresponding crystallization conditions when a single crystallization device is used for crystallization) satisfy: the temperature of the first evaporation is at least 5 deg.c lower, preferably 20 deg.c lower, more preferably 35 deg.c to 70 deg.c lower, and especially 40 deg.c to 60 deg.c lower than the temperature of the second evaporation. And respectively crystallizing and separating out sodium chloride and sodium sulfate by controlling the first evaporation and the second evaporation to be carried out at different temperatures, so that the purity of the obtained sodium chloride and sodium sulfate crystals is improved.

In the present invention, the second concentrated solution containing sodium sulfate crystals is subjected to a second solid-liquid separation to obtain sodium sulfate crystals and a second mother liquor (i.e. a liquid phase obtained by the second solid-liquid separation), and the second mother liquor is temporarily stored in the second mother liquor tank 54. 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 a second solid-liquid separation device (e.g., a centrifuge, a belt filter, a plate filter, etc.) 92. After the second solid-liquid separation, the second mother liquor obtained by the second solid-liquid separation device 92 returns to the first evaporation device 2 for the first evaporation again, and specifically, the second mother liquor can be returned to the second pH adjustment process by the eighth circulation pump 78 to be mixed with the ammonium salt-containing wastewater to obtain the wastewater to be treated, and then the wastewater is sent to the first evaporation device 2 for the first evaporation. In addition, it is difficult to avoid that the obtained sodium sulfate crystals adsorb impurities such as sulfate ions, free ammonia, and hydroxide ions to some extent, and in order to remove the adsorbed impurities, reduce the odor of solid salts, reduce corrosiveness, and improve the purity of the crystals, it is preferable that the sodium sulfate crystals are subjected to secondary washing with water, the ammonium salt-containing wastewater, or a sodium sulfate solution and dried. In order to avoid the dissolution of sodium sulfate crystals during the washing, the sodium sulfate crystals are preferably washed with an aqueous sodium sulfate solution. More preferably, the concentration of the aqueous sodium sulfate solution is preferably such that the sodium sulfate and sodium chloride reach the concentration of sodium sulfate in the saturated aqueous solution at the same time at the temperature corresponding to the sodium sulfate crystals to be washed.

The form of the second solid-liquid separation and the second washing is not particularly limited, and may be carried out, for example, by using a combination of an elutriation apparatus and a solid-liquid separation apparatus which are conventional in the art, or may be carried out on a staged solid-liquid separation apparatus such as a belt filter. Preferably, the second wash comprises panning and/or rinsing. The above-mentioned elutriation and rinsing are not particularly limited and may be carried out by a method conventional in the art. The number of elutriation and rinsing is not particularly limited, and may be 1 or more, and is preferably 2 to 4 times in order to obtain sodium sulfate crystals of higher purity. In the elutriation process, the waste water containing ammonium salt is generally not recycled when used as an elutriation liquid, and the washing liquid recovered by the second washing can be recycled in a counter-current manner when used as an elutriation liquid. Before the elutriation, it is preferable to perform a preliminary solid-liquid separation by sedimentation to obtain a slurry containing sodium sulfate crystals (the liquid content may be 35% by mass or less, and this step is preferably performed in an apparatus known in the art such as a sedimentation tank or a sedimentation tank). In the elutriation, 1 to 20 parts by weight of a liquid is used for elutriation per 1 part by weight of a slurry containing sodium sulfate crystals. In addition, the rinsing is preferably carried out using an aqueous sodium sulfate solution (the concentration of the aqueous sodium sulfate solution is preferably such that the sodium sulfate and sodium chloride reach the concentration of sodium sulfate in a saturated aqueous solution at the same time at the temperature corresponding to the sodium sulfate crystals to be rinsed). In order to further enhance the elutriation effect and obtain sodium sulfate crystals with higher purity, the elutriation may be preferably performed using a liquid obtained by rinsing. For the liquid generated by the washing, preferably, the ammonium salt-containing wastewater elutriation liquid is returned to the second evaporation device before being returned to the first evaporation device for the second pH adjustment, and other washing liquid is returned to the second evaporation device, for example, returned to the second evaporation device 1 through the ninth circulation pump 79 in fig. 1 for the second evaporation again.

According to a preferred embodiment of the present invention, after the first solid-liquid separation by settling, the second concentrated solution containing sodium sulfate crystals obtained by the second evaporative crystallization is subjected to a first elutriation in an elutriation tank using the waste water containing ammonium salt, and then the liquid obtained by the subsequent washing of the sodium sulfate crystals is subjected to a second elutriation in another elutriation tank, and finally the slurry subjected to the two elutriations is sent to a solid-liquid separation device for solid-liquid separation, the crystals obtained by the solid-liquid separation are subjected to a leaching with an aqueous sodium sulfate solution (the concentration of the aqueous sodium sulfate solution is the concentration of sodium sulfate in the aqueous solution at which the sodium sulfate and sodium chloride reach saturation at the same time at the temperature corresponding to the sodium sulfate crystals to be washed) and the liquid obtained by the leaching is returned to the second elutriation tank as an elutriation liquid. Through the washing process combining elutriation and leaching, the purity of the obtained sodium sulfate crystals is improved, washing liquid is not excessively introduced, and the efficiency of wastewater treatment is improved.

In the present invention, when the first evaporation and/or the second evaporation is performed by using the MVR evaporation apparatus, in order to increase the solid content in the MVR evaporation apparatus and reduce the ammonia content in the liquid, it is preferable that a part of the liquid (i.e., the liquid located inside the MVR evaporation apparatus, hereinafter also referred to as a circulation liquid) evaporated by the MVR evaporation apparatus is heated and then returned to the MVR evaporation apparatus for evaporation. As a ratio of returning a part of the liquid after evaporation by the MVR evaporation device to the MVR evaporation device, there is no particular limitation, and for example, the first reflux ratio of the first evaporation may be 10 to 200, preferably 40 to 120, and the second reflux ratio of the second evaporation may be 0.1 to 50, preferably 2 to 15. Here, the reflux ratio means: the ratio of the amount of reflux to the total amount of liquid fed to the MVR evaporator minus the amount of reflux. Preferably, before the first circulating liquid in the first evaporation is preferably returned to the second pH adjustment, for example, the first circulating liquid may be returned to the wastewater conveying pipeline between the first heat exchange device 31 and the second heat exchange device 32 by the second circulating pump 72 to be mixed with the wastewater to be treated, and then after the second pH adjustment, the heat exchange is performed in the second heat exchange device 32, and finally the mixture is sent to the first evaporation device 2.

In the present invention, when the first evaporation and/or the second evaporation is performed using an MVR evaporation apparatus, the method further comprises compressing the first ammonia-containing vapor and/or the second ammonia-containing vapor. The compression may be performed by compressors, such as the first compressor 101 and the second compressor 102. 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, the energy is supplied only through the compressor after the continuous running state is achieved, and other energy does not need to be input. The compressor may employ various compressors conventionally used in the art, such as a centrifugal fan, a turbine compressor, or a roots compressor, etc. After being compressed by a compressor, the temperature of the ammonia-containing steam is increased by 5 to 20 ℃.

According to a preferred embodiment of the present invention, the tail gas remaining after the first ammonia-containing steam is condensed by the first heat exchange and the tail gas remaining after the second ammonia-containing steam is condensed by the second heat exchange are discharged after ammonia removal. As shown in fig. 1, the first ammonia-containing steam is subjected to the first heat exchange to condense the remaining tail gas, i.e., the tail gas discharged from the second heat exchange device 32, and the second ammonia-containing steam is subjected to the second heat exchange to condense the remaining tail gas, i.e., the tail gas discharged from the fourth heat exchange device 34. The ammonia in the tail gas is removed, so that the pollutant content in the discharged tail gas can be further reduced, and the tail gas can be directly discharged.

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

In the present invention, the 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-salinity wastewater. The ammonium salt-containing wastewater of the present invention may be specifically wastewater from a process for producing a molecular sieve, alumina or an oil refining catalyst, or wastewater from a process for producing a molecular sieve, alumina or an oil refining catalyst, which is subjected to the following impurity removal and concentration. It is preferable that the wastewater from the production of molecular sieves, alumina or refinery catalysts is subjected to the following impurity removal and concentration.

As NH in 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 1000mg/L or more, more preferably 2000mg/L or more, further preferably 4000mg/L or more, further preferably 8000mg/L or more, further preferably 16000mg/L or more, further preferably 32000mg/L or more, further preferably 40000mg/L or more, further preferably 50000mg/L or more, further preferably 60000mg/L or more.

As SO in said ammonium salt-containing wastewater ₄ ^2- May be 1000mg/L or more, preferably 2000mg/L or more, more preferably 4000mg/L or more, further preferably 8000mg/L or more, further preferably 16000mg/L or more, further preferably 32000mg/L or more, further preferably 40000mg/L or more, further preferably 50000mg/L or more, further preferably 60000mg/L or more, further preferably 70000mg/L or more.

As Cl in said ammonium salt-containing wastewater ^- May be 970mg/L or more, more preferably 2000mg/L or more, further preferably 4000mg/L or more, further preferably 8000mg/L or more, further preferably 16000mg/L or more, further preferably 32000mg/L or more, further preferably 40000mg/L or more, further preferably 50000mg/L or more, further preferably 60000mg/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. From waste waterFrom the viewpoint of easy operation, SO in wastewater ₄ ^2- 、Cl ^- And Na ⁺ The upper limit of (b) is 200g/L or less, preferably 150g/L or less, respectively; NH in wastewater ₄ ⁺ Is 50g/L or less, preferably 20g/L or less.

From the viewpoint of improving the efficiency of the first evaporation and reducing the energy consumption of the treatment process, the method is relative to the SO contained in the wastewater containing ammonium salt ₄ ^2- Cl in ammonium salt-containing wastewater ^- The higher the content, the better, for example, relative to 1 mole of SO contained in the ammonium salt-containing wastewater ₄ ^2- Cl contained in the ammonium salt-containing wastewater ^- Is 1 mole or more, preferably 2 moles or more, preferably 5 moles or more, more preferably 9.5 moles or more, and further preferably 10 moles or more. From the viewpoint of practicality, the amount of SO contained in the ammonium salt-containing wastewater is 1 mol ₄ ^2- Cl contained in the ammonium salt-containing wastewater ^- Preferably 200 moles or less, more preferably 150 moles or less, further preferably 100 moles or less, further preferably 50 moles or less, and further preferably 30 moles or less. By adding Cl contained in the ammonium salt-containing wastewater ^- And SO ₄ ^2- The molar ratio of (a) to (b) is limited to the above range, most of water can be evaporated in the first evaporation, the amount of circulating liquid in a treatment system is reduced, energy is saved, and the treatment process is more economical.

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. To reduceThe content of other inorganic salt ions in the ammonium salt-containing wastewater is preferably subjected to the following impurity removal.

The TDS of the ammonium salt-containing wastewater may be 1600mg/L or more, preferably 4000mg/L or more, more preferably 8000mg/L or more, further preferably 16000mg/L or more, further preferably 32000mg/L or more, further preferably 40000mg/L or more, further preferably 50000mg/L or more, further preferably 60000mg/L or more, further preferably 100000mg/L or more, further preferably 150000mg/L or more, further preferably 200000mg/L or more.

In the present invention, the pH of the ammonium salt-containing wastewater is preferably 4 to 8, and more preferably 6.4 to 6.6.

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; as the chemical precipitation, pH adjustment, carbonate precipitation, magnesium salt precipitation, and the like may be mentioned; the adsorption can be physical adsorption and/or chemical adsorption, and the specific adsorbent can be selected from activated carbon, silica gel, alumina, molecular sieve, natural clay and the like; as the ion exchange, any 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 ammonium salt-containing wastewater treatment process is ensured.

In the present invention, the ammonium salt-containing 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 treatment by the treatment method of the present invention (preferably, after the above-mentioned impurity removal). Preferably, the concentration is selected from ED membrane concentration and/or reverse osmosis; more preferably, the concentration is performed by ED membrane concentration and reverse osmosis, and the order of performing the ED membrane concentration and the reverse osmosis is not particularly limited. The ED membrane concentration and reverse osmosis treatment apparatus and conditions may be performed in a manner conventional in the art, and may be specifically selected according to the condition of wastewater to be treated. Specifically, as the concentration of the ED membrane, a one-way electrodialysis system or a reversed electrodialysis system can be selected for carrying out; as the reverse osmosis, a roll membrane, a plate membrane, a disc-tube membrane, a vibrating membrane or a combination thereof can be selected for use. Through the concentration, the efficiency of treating the waste water containing ammonium salt can be improved, and energy waste caused by a large amount of evaporation is avoided.

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 to 1.4 mol of sodium carbonate is added relative to 1 mol of calcium ions in the wastewater, the pH value of the wastewater is adjusted to be more than 7, the reaction temperature is between 20 and 35 ℃, and the reaction time is between 0.5 and 4 hours.

The conditions for the filtration are preferably: the filtering unit adopts a double-layer filtering material multi-medium filter consisting of anthracite and quartz sand, the grain diameter of the anthracite is 0.7-1.7 mm, the grain diameter of the quartz sand is 0.5-1.3 mm, and the filtering speed is 10-30 m/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 10-15 h.

The conditions for the weak acid cation exchange method are preferably: the pH value range is 6.5-7.5; the temperature is less than or equal to 40 ℃, the height of the resin layer is 1.5-3.0 m, the HCl concentration of the regeneration liquid is as follows: 4.5 to 5 mass percent; the amount of the regenerant (calculated by 100%) was 50kg/m ³ ～60kg/m ³ Wet resin; the flow rate of the regeneration liquid HCl is 4.5 m/h-5.5 m/h, and the regeneration contact time is 35 min-45 min; the forward washing flow rate is 18 m/h-22 m/h, and the forward washing time is 20 min-30 min; the running flow rate is 15 m/h-30 m/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 50min to 70min, and the empty bed filtration rate is 0.5m/h to 0.7m/h.

The conditions for concentrating the ED membrane are preferably: the current 145A to 155A and the voltage 45V to 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 5.4MPa to 5.6MPa, the water inlet temperature is 25 ℃ to 35 ℃, and the pH value is 6.5 to 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 start-up, and if the ion content of the wastewater containing ammonium salt meets the condition of the invention, the wastewater containing ammonium salt can be treated according to the inventionCarrying out first evaporation and then carrying out second evaporation under the bright conditions; if the ion content of the wastewater containing ammonium salt does not meet the conditions of the invention, the first evaporation can be controlled to ensure that the concentration of sodium sulfate in the first concentrated solution is close to the precipitation concentration, then the first concentrated solution is subjected to the second evaporation to obtain a second concentrated solution, the solid-liquid separation is carried out to obtain sodium sulfate crystals and a second mother solution, the second mother solution 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 then the first evaporation is carried out to obtain sodium chloride crystals. Of course, na may be used in the initial stage ₂ SO ₄ Or NaCl, as long as the ion content of the wastewater to be treated is adjusted SO that the wastewater to be treated satisfies SO in the wastewater to be treated in the 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 NaCl 160g/L, na) ₂ SO ₄ 50g/L、NH ₄ Cl 39g/L、(NH ₄ ) ₂ SO ₄ 12.4g/L, pH 6.5) at a feed rate of 5m ³ The reaction mixture was fed to a vacuum degassing tank 4 at a rate of/h to be vacuum degassed, an aqueous sodium hydroxide solution having a concentration of 45.16 mass% was introduced into the line to adjust the pH value for the first time, the adjusted pH value was monitored by a first pH value measuring device 61 (pH meter) (measured value: 7.5), and a part (1 m) of the ammonium salt-containing wastewater having been adjusted by the first pH value was subjected to the first pH value adjustment by a first circulating pump 71 ³ H) sending the waste water into a fifth heat exchange device 35 (a titanium alloy plate heat exchanger) to perform first heat exchange with the recovered second ammonia-containing steam condensate so as to heat the waste water containing ammonium salt to 48 ℃, and sending the rest of the waste water into a first heat exchange device 31 to perform first heat exchange with the recovered first ammonia-containing steam condensate so as to heat the waste water containing ammonium salt to 49 ℃; then, two are put intoPart of the wastewater containing ammonium salt is merged and mixed with the second mother liquor to obtain wastewater to be treated (SO contained in the wastewater is measured) ₄ ^2- And Cl ^- In a molar ratio of 1:12.656 Introducing a sodium hydroxide aqueous solution with the concentration of 45.16 mass% into a pipeline for conveying the wastewater to be treated into the second heat exchange device 32 to carry out secondary pH value adjustment, monitoring the adjusted pH value through a second pH value measuring device 62 (a pH meter) (the measured value is 11), conveying the wastewater to be treated into the second heat exchange device 32 (a titanium alloy plate type heat exchanger) to carry out first heat exchange with the recovered first ammonia-containing steam so as to heat the wastewater to be treated to 57 ℃, conveying the wastewater to be treated into the first evaporation device 2 (a falling film and forced circulation two-stage MVR evaporation crystallizer) to carry out evaporation, and obtaining first ammonia-containing steam and a first concentrated solution containing sodium chloride crystals. Wherein the evaporation temperature of the first evaporation device 2 is 50 ℃, the pressure is-92.7 kPa, and the evaporation capacity is 4.56m ³ H is used as the reference value. The first ammonia-containing steam obtained by evaporation is compressed by a first compressor 101 (the temperature is increased by 10 ℃) and then sequentially passes through a second heat exchange device 32 and a first heat exchange device 31, and is respectively subjected to heat exchange with wastewater to be treated and wastewater containing ammonium salt, cooled to obtain first ammonia water, and the first ammonia water is stored in a first ammonia water storage tank 51. In addition, in order to increase the solid content in the first evaporation apparatus 2, part of the liquid evaporated in the first evaporation apparatus 2 is circulated as a first circulation liquid to the second heat exchange apparatus 32 by the second circulation pump 72, and then enters the first evaporation apparatus 2 again to perform the first evaporation (the first reflux ratio is 95.4). The degree of the first evaporation was monitored by a densimeter provided in the first evaporation apparatus 2, and the concentration of sodium sulfate in the first concentrated solution was controlled to be 0.9705Y (65.7 g/L).

The first concentrated solution was sent to a first solid-liquid separation apparatus 91 (centrifuge) to carry out first solid-liquid separation, and 20.87m per hour was obtained ³ Contains NaCl 294.6g/L, na ₂ SO ₄ 65.7g/L、NaOH 0.22g/L、NH ₃ 0.11g/L of the first mother liquor is temporarily stored in a first mother liquor tank 53, sodium chloride solids obtained by solid-liquid separation (15 mass% of sodium chloride crystal cake containing water 1196.17kg which contains 3.9 mass% or less of sodium sulfate is obtained per hour) are leached by 295g/L of sodium chloride solution which is equal to the dry basis mass of the sodium chloride crystal cake,after drying, 1016.74kg of sodium chloride (purity of 99.5 wt%) is obtained every hour, and the washing liquid is circulated by a fifth circulating pump 75 to be mixed with the wastewater to be treated before the second pH value adjustment, and then enters the first evaporation device 2 again for first evaporation.

The second evaporation process is carried out in a second evaporation device 1 (falling film + forced circulation two-stage MVR evaporative crystallizer). And (3) enabling the first mother liquor in the first mother liquor tank 53 to exchange heat with the second ammonia-containing steam condensate through a third heat exchange device 33 by a sixth circulating pump 76, then enabling the first mother liquor to exchange heat with the second ammonia-containing steam through a fourth heat exchange device 34, and finally sending the second mother liquor into the second evaporation device 1 for second evaporation to obtain second concentrated solution containing second ammonia-containing steam and sodium sulfate crystals. Wherein the evaporation temperature of the second evaporation device 1 is 105 ℃, the pressure is-7.0 kPa, and the evaporation capacity is 1.05m ³ H is used as the reference value. In order to increase the solid content in the second evaporation device 1, part of the first mother liquor evaporated in the second evaporation device 1 is circulated as a second circulation liquid to the fourth heat exchange device 34 by the seventh circulation pump 77, and then enters the second evaporation device 1 again for second evaporation (the second reflux ratio is 4). The second ammonia-containing steam obtained by evaporation is compressed by the second compressor 102 (the temperature is raised by 12 ℃) and then sequentially passes through the fourth heat exchange device 34 and the third heat exchange device 33 to perform second heat exchange with the first mother liquor, and then passes through the fifth heat exchange device 35 to perform first heat exchange with part of the ammonium salt-containing wastewater conveyed by the first circulating pump 71, and is cooled to obtain second ammonia water, and the second ammonia water is stored in the second ammonia water storage tank 52. The degree of the second evaporation was monitored by a densimeter provided in the second evaporation apparatus 1, and the concentration of sodium chloride in the second concentrated solution was controlled to 0.99355X (307.9 g/L). After the first mother liquor is evaporated in the second evaporation apparatus 1, a second concentrated solution containing sodium sulfate crystals is obtained.

The second concentrated solution containing sodium sulfate crystals was sent to a second solid-liquid separation apparatus 92 (centrifuge) for solid-liquid separation to obtain 20.21 m/hr ³ Contains NaCl 307.9g/L, na ₂ SO ₄ 53.0g/L、NaOH 0.30g/L、NH ₃ 0.0035g/L of a second mother liquor, temporarily stored in a second mother liquor tank 54. The second mother liquor is entirely circulated to the eighth circulation pump 78And mixing the wastewater with preheated ammonium salt-containing wastewater to obtain wastewater to be treated before the pH value is adjusted for the second time. The sodium sulfate solid obtained by solid-liquid separation (sodium sulfate crystal cake having a water content of 14 mass% 364.15kg, wherein the sodium chloride content is 3.8 mass% or less, obtained per hour) was washed with 53g/L of a sodium sulfate solution equivalent to the dry basis mass of sodium sulfate, and then dried in a dryer to obtain 313.17kg (purity of 99.5 wt%) of sodium sulfate per hour, and the second washing liquid obtained by washing was circulated to the second evaporation apparatus 1 by a ninth circulation pump 79.

In addition, the tail gas discharged by the vacuum degassing tank 4, the second heat exchange device 32 and the fourth heat exchange device 34 is introduced into a tail gas absorption tower 83 through a vacuum pump 81 for absorption, circulating water is introduced into the tail gas absorption tower 83, the circulating water circulates in the tail gas absorption tower 83 under the action of 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 working water of 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.

In this example, 4.56m of ammonia water having a concentration of 1.63 mass% was obtained per hour in the first ammonia water tank 51 ³ 1.05m of aqueous ammonia having a concentration of 0.21 mass% was obtained per hour in the second aqueous ammonia tank 52 ³ The ammonia water can be reused in the production process of the molecular sieve.

In addition, the starting phase of the MVR evaporation was started 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 sample containing NaCl 60g/L, na ₂ SO ₄ 130g/L、NH ₄ Cl 15g/L、(NH ₄ ) ₂ SO ₄ Treating the ammonium salt-containing wastewater with the concentration of 33.04g/L, pH being 6.6 to obtain SO contained in the wastewater to be treated ₄ ^2- And Cl ^- In a molar ratio of 1:11.496. the temperature of the ammonium salt-containing wastewater subjected to heat exchange by the fifth heat exchange device 35 is 53 ℃, the temperature of the ammonium salt-containing wastewater subjected to heat exchange by the first heat exchange device 31 is 54 ℃, and the temperature of the ammonium salt-containing wastewater is controlled by the second heat exchange deviceThe temperature of the wastewater to be treated after heat exchange is carried out at 32 is 62 ℃. The evaporation temperature of the first evaporation device 2 is 55 ℃, the pressure is-90.2 kPa, and the evaporation capacity is 2.76m ³ H is used as the reference value. The evaporation temperature of the second evaporation device 1 is 95 ℃, the pressure is-36.4 kPa, and the evaporation capacity is 2.93m ³ /h。

The first solid-liquid separation device 91 obtains 445.34kg of sodium chloride crystal filter cake containing 15 mass% of water every hour, and finally obtains 378.54kg of sodium chloride (the purity is 99.6 weight%); the hourly yield of 82.63m is ³ The concentration of NaCl 296.6g/L, na ₂ SO ₄ 63.6g/L、NaOH 0.29g/L、NH ₃ 0.032g/L of the first mother liquor.

The second solid-liquid separation device 92 obtains 977.85kg of sodium sulfate crystal cake with a water content of 15 mass% per hour, and finally obtains 831.17kg of sodium sulfate (with a purity of 99.4 wt%) per hour; the hourly yield of 80.07m is ³ The concentration of NaCl is 306.1g/L, na ₂ SO ₄ 55.3g/L、NaOH 0.3g/L、NH ₃ 0.0013g/L of second mother liquor.

In this example, 2.76m of aqueous ammonia having a concentration of 2.26 mass% was obtained per hour in the first aqueous ammonia tank 51 ³ 2.93m of aqueous ammonia having a concentration of 0.087 mass% was obtained per hour in the second aqueous ammonia tank 52 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 the NaCl-containing 81g/L, na ₂ SO ₄ 79g/L、NH ₄ Cl 32g/L、(NH ₄ ) ₂ SO ₄ 31.72g/L, pH ammonium salt-containing wastewater of 6.4 is treated, and SO contained in the obtained wastewater to be treated ₄ ^2- And Cl ^- In a molar ratio of 1:11.123. the temperature of the ammonium salt-containing wastewater subjected to heat exchange by the fifth heat exchange device 35 is 43 ℃, the temperature of the ammonium salt-containing wastewater subjected to heat exchange by the first heat exchange device 31 is 44 ℃, and the temperature of the wastewater to be treated subjected to heat exchange by the second heat exchange device 32 is 52 ℃. The evaporation temperature of the first evaporation device 2 is 45 ℃, the pressure is-94.7 kPa, and the evaporation capacity is 3.73m ³ H is used as the reference value. Evaporation temperature of the second evaporation device 1At 100 deg.C, under-22.9 kPa, and with an evaporation capacity of 1.99m ³ /h。

The first solid-liquid separation device 91 obtains 675.13kg of sodium chloride crystal filter cake containing 14 mass% of water every hour, and finally obtains 580.61kg of sodium chloride (the purity is 99.4 wt%) every hour; obtained 36.26m per hour ³ The concentration of NaCl is 292.4g/L, na ₂ SO ₄ 67.3g/L、NaOH 0.1g/L、NH ₃ 0.076g/L of the first mother liquor.

The second solid-liquid separation device 92 obtained 657.0kg of sodium sulfate crystal cake with a water content of 14 mass% per hour, and finally obtained 580.6kg of sodium sulfate (purity of 99.5 wt%); yield 34.52m per hour ³ The concentration is NaCl 307.1g/L, na ₂ SO ₄ 54.3g/L、NaOH 0.105g/L、NH ₃ 0.0039g/L of a second mother liquor.

In this example, 3.73m of ammonia water having a concentration of 2.3 mass% was obtained per hour in the first ammonia water tank 51 ³ 1.99m of ammonia water having a concentration of 0.13 mass% is obtained per hour in the second ammonia water tank 52 ³ The ammonia water can be reused in the production process of the molecular sieve.

Example 4

As shown in figure 2, the waste water containing ammonium salt (containing NaCl 156g/L, na) ₂ SO ₄ 49g/L、NH ₄ Cl 62g/L、(NH ₄ ) ₂ SO ₄ 19.8g/L, pH 6.7) by means of a first circulation pump 71 at a feed rate of 5m ³ The reaction mixture was fed into a line of a treatment system at a speed of/h, an aqueous sodium hydroxide solution having a concentration of 45.16 mass% was introduced into the line to adjust the pH value for the first time, the adjusted pH value was monitored by a first pH value measuring device 61 (pH meter) (measured value: 7.4), and a part (3 m) of the ammonium salt-containing wastewater having been subjected to the first pH value adjustment was treated ³ H) sending the waste water into a first heat exchange device 31 (a plastic plate heat exchanger) to perform heat exchange with the recovered first ammonia-containing steam condensate to heat the waste water containing ammonium salt to 54 ℃, sending the rest part of the waste water into a fourth heat exchange device 34 (a duplex stainless steel plate heat exchanger) to perform heat exchange with the recovered second ammonia-containing steam condensate to heat the waste water containing ammonium salt to 70 ℃, combining the two parts of waste water containing ammonium salt, and mixing the two parts of waste water containing ammonium salt with the second mother solution to obtain the waste water to be treatedWater (measuring SO contained therein) ₄ ^2- And Cl ^- In a molar ratio of 1:12.444 Then, the wastewater to be treated is sent into a second heat exchange device 32 (a titanium alloy plate heat exchanger), first heat exchange is carried out between the wastewater to be treated and the recovered first ammonia-containing steam to heat the wastewater to be treated to 62 ℃, then the wastewater to be treated after two times of first heat exchange is sent into a pipeline of a first evaporation device 2, sodium hydroxide aqueous solution with the concentration of 45.16 mass% is led in for second pH value adjustment, the adjusted pH value is monitored through a second pH value measuring device 62 (a pH meter) (the measured value is 10.8), and the wastewater to be treated after the second pH value adjustment is sent into the first evaporation device 2 (a falling film and forced circulation two-stage MVR evaporation crystallizer) for evaporation to obtain first ammonia-containing steam and a first concentrated solution containing sodium chloride crystals. Wherein the evaporation temperature of the first evaporation device 2 is 55 ℃, the pressure is-90.2 Pa, and the evaporation capacity is 4.63m ³ H is used as the reference value. The first ammonia-containing steam obtained by evaporation is compressed by a first compressor 101 (the temperature is increased by 10 ℃) and then sequentially passes through a second heat exchange device 32 and a first heat exchange device 31, and is respectively subjected to heat exchange with wastewater to be treated and wastewater containing ammonium salt, cooled to obtain first ammonia water, and the first ammonia water is stored in a first ammonia water storage tank 51. In addition, in order to increase the solid content in the first evaporation apparatus 2, part of the liquid evaporated in the first evaporation apparatus 2 was returned to the second heat exchange apparatus 32 as a circulation liquid by the second circulation pump 72, and then again entered the first evaporation apparatus 2 to perform the first evaporation (the reflux ratio was 96.4). The degree of the first evaporation was monitored by a densimeter provided in the first evaporation apparatus 2, and the concentration of sodium sulfate in the first concentrated solution was controlled to 0.9707Y (66.25 g/L).

The first concentrated solution obtained by evaporation in the first evaporator 2 was fed to a first solid-liquid separator 91 (centrifuge) to carry out first solid-liquid separation, thereby obtaining 24.13 m/hr ³ Containing NaCl 293.8g/L, na ₂ SO ₄ 66.25g/L、NaOH 0.18g/L、NH ₃ 0.10g/L of the first mother liquor was temporarily stored in the first mother liquor tank 53, and the sodium chloride solids obtained by solid-liquid separation (14 mass% aqueous sodium chloride crystal cake 1306.96 kg/hr, sodium sulfate content of 3.9 mass% or less) were used as a dry substrate together with the sodium chloride crystal cakeAnd leaching 293g/L sodium chloride solution with equal amount, drying to obtain 1124kg of sodium chloride (with the purity of 99.4 wt%) per hour, circulating the washing solution to the second heat exchange device 32 through the eighth circulating pump 78, and then entering the first evaporation device 2 again for first evaporation.

The second evaporation process is carried out in a second evaporation device (a multi-effect evaporation device) 1, and the second evaporation device 1 consists of a first effect evaporator 1a, a second effect evaporator 1b and a third effect evaporator 1c (both forced circulation evaporators). And (3) feeding the first mother liquor in the mother liquor tank 54 into the second evaporation device 1 through a fifth circulating pump 75, evaporating the first mother liquor in the first-effect evaporator 1a, introducing the first mother liquor into the second-effect evaporator 1b for evaporation, introducing the first mother liquor into the third-effect evaporator 1c for evaporation, and finally obtaining a second concentrated solution containing sodium sulfate crystals. Wherein the evaporation temperature of the first effect evaporator 1a is 128 ℃, the pressure is 103.53kPa, and the evaporation capacity is 0.41m ³ H; the evaporation temperature of the second effect evaporator 1b is 114 ℃, the pressure is 28.07kPa, and the evaporation capacity is 0.40m ³ H; the evaporation temperature of the third effect evaporator 1c is 100 ℃, the pressure is-22.83 kPa, and the evaporation capacity is 0.40m ³ H is used as the reference value. And introducing second ammonia-containing steam obtained by evaporation in the first effect evaporator 1a of the second evaporation device 1 into the second effect evaporator 1b to perform second heat exchange to obtain first ammonia water, introducing second ammonia-containing steam obtained by evaporation in the second effect evaporator 1b into the third effect evaporator 1c to perform second heat exchange to obtain first ammonia water, and storing the ammonia water obtained from the second effect evaporator 1b and the first effect evaporator 1c in a second ammonia water storage tank 52 after heat exchange with ammonium salt-containing wastewater through a fourth heat exchange device 34. Heating steam (namely raw steam conventionally used in the field) is introduced into the first-effect evaporator 1a, the heating steam is condensed in the first-effect evaporator 1a to obtain a condensate, and the condensate is used for preparing a washing solution after being used for preheating the wastewater (raw material) to be treated entering the first evaporation device 2. The second ammonia-containing steam evaporated by the third effect evaporator 1c of the second evaporator 1 exchanges heat with cooling water (ammonium salt-containing wastewater) in the third heat exchanger 33 to obtain second ammonia water, and the second ammonia water is stored in the second ammonia water storage tank 52. The degree of the second evaporation is monitored by a densitometer provided in the second evaporation apparatus 1The concentration of sodium chloride in the second concentrated solution was controlled to be 0.99353X (307.1 g/L). After the first mother liquor is evaporated in the second evaporation device 1, the finally obtained second concentrated solution containing sodium sulfate crystals is crystallized in the crystal liquid collecting tank 55 (the crystallization temperature is 100 ℃, and the crystallization time is 10 min) to obtain a crystal slurry containing sodium sulfate crystals.

The crystal slurry containing sodium sulfate crystals is sent to a second solid-liquid separation device 92 (centrifugal machine) for solid-liquid separation, and 20.13m is obtained per hour ³ Contains NaCl 307.1g/L, na ₂ SO ₄ 54.2g/L、NaOH 0.19g/L、NH ₃ 0.0053g/L of a second mother liquor, circulating the second mother liquor to a wastewater introduction line by a seventh circulation pump 77, mixing the second mother liquor with ammonium salt-containing wastewater to obtain wastewater to be treated, performing solid-liquid separation to obtain sodium sulfate solids (sodium sulfate crystal cake containing 15 mass% of water 407.7kg in which the content of sodium chloride is 4 mass% or less per hour), washing the sodium sulfate solids with 54g/L of a sodium sulfate solution having a mass equivalent to the dry basis mass of sodium sulfate, drying the sodium sulfate solids in a dryer to obtain 346.54kg of sodium sulfate (having a purity of 99.5 wt%) per hour, and returning the washed second washing liquid to the second evaporation apparatus 1 by a sixth circulation pump 76.

In addition, the tail gas discharged by the second heat exchange device 32 and the third heat exchange device 33 is introduced into a tail gas absorption tower 83 through a vacuum pump 81 for absorption, circulating water is introduced into the tail gas absorption tower 83, the circulating water circulates in the tail gas absorption tower 83 under the action of the fourth circulating pump 74, water is supplemented into the tail gas absorption tower 83 from a circulating water tank 82 through a third circulating pump 73, and fresh water is supplemented into the circulating water tank 82, so that the temperature and the ammonia content of the working water of 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.

In this example, 4.63m of ammonia water having a concentration of 2.56 mass% was obtained per hour in the first ammonia water tank 51 ³ 1.21m of 0.19 mass% ammonia water was obtained per hour in the second ammonia water tank 52 ³ The ammonia water can be reused in the production process of the molecular sieve.

Example 5

The treatment of the ammonium salt-containing wastewater was carried out in the same manner as in example 4, except that: for NaCl-containing 160g/L, na ₂ SO ₄ 25g/L、NH ₄ Cl 39g/L、(NH ₄ ) ₂ SO ₄ 6.2g/L, pH is 6.5, the temperature of the ammonium salt-containing wastewater subjected to heat exchange by the first heat exchange device 31 is 44 ℃, the temperature of the ammonium salt-containing wastewater subjected to heat exchange by the fourth heat exchange device 34 is 100 ℃, the temperature of the wastewater to be treated subjected to heat exchange by the second heat exchange device 32 is 52 ℃, and the obtained SO contained in the wastewater to be treated ₄ ^2- And Cl ^- In a molar ratio of 1:14.438. the evaporation temperature of the first evaporation device 2 is 45 ℃, the pressure is-94.69 kPa, and the evaporation capacity is 4.94m ³ H is used as the reference value. The first effect evaporator 1a of the second evaporation device 1 has an evaporation temperature of 130 ℃, a pressure of 116.77kPa, and an evaporation capacity of 0.19m ³ H; the evaporation temperature of the second effect evaporator 1b is 117 ℃, the pressure is 41.92kPa, and the evaporation capacity is 0.19m ³ H; the evaporation temperature of the third effect evaporator 1c is 105 ℃, the pressure is-7.02 kPa, and the evaporation capacity is 0.18m ³ /h。

The first solid-liquid separation device 91 obtains 1198.31kg of sodium chloride crystallized filter cake containing 15 mass% of water per hour, and finally obtains 1018.57kg of sodium chloride (the purity is 99.4 weight percent) per hour; obtained 9.49m per hour ³ The concentration of NaCl is 291.8g/L, na ₂ SO ₄ 67g/L、NaOH 0.16g/L、NH ₃ 0.07g/L of the first mother liquor.

The second solid-liquid separation device 92 obtained 177.95kg of sodium sulfate crystal cake with a water content of 14 mass% per hour, and finally obtained 153.04kg of sodium sulfate (purity of 99.5 wt%); obtained at 9.00m per hour ³ The concentration is NaCl 307.9g/L, na ₂ SO ₄ 53.1g/L、NaOH 0.17g/L、NH ₃ 0.0031g/L of a second mother liquor.

In this example, 4.94m of ammonia water having a concentration of 1.38 mass% was obtained per hour in the first ammonia water tank 51 ³ 0.56m of 0.118 mass% ammonia water was obtained per hour in the second ammonia water tank 52 ³ 。

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 105g/L, na ₂ SO ₄ 108g/L、NH ₄ Cl 20g/L、(NH ₄ ) ₂ SO ₄ 20.91g/L, pH is 6.7, a portion (2.5 m) of the ammonium salt-containing wastewater was treated ³ H) the temperature after heat exchange by the first heat exchange device 31 is 49 ℃, the temperature after heat exchange by the other part by the fourth heat exchange device 34 is 85 ℃, the temperature after heat exchange by the wastewater to be treated by the second heat exchange device 32 is 57 ℃, and the obtained SO contained in the wastewater to be treated ₄ ^2- And Cl ^- In a molar ratio of 1:11.333. the evaporation temperature of the first evaporation device 2 is 50 ℃, the pressure is-92.7 kPa, and the evaporation capacity is 3.35m ³ H is used as the reference value. The first effect evaporator 1a of the second evaporation device 1 has an evaporation temperature of 125 ℃, a pressure of 84.91kPa, and an evaporation capacity of 0.77m ³ H; the second effect evaporator 1b has an evaporation temperature of 110 deg.C, a pressure of 11.34kPa, and an evaporation capacity of 0.75m ³ H; the evaporation temperature of the third effect evaporator 1c is 95 ℃, the pressure is-36.37 kPa, and the evaporation capacity is 0.75m ³ /h。

The first solid-liquid separation device 91 obtains 745.41kg of sodium chloride crystal filter cake containing 15 mass% of water every hour, and finally obtains 633.59kg of sodium chloride (the purity is 99.5 weight%); the hourly yield of 52.06m is ³ The concentration is NaCl 294.6g/L, na ₂ SO ₄ 65.7g/L、NaOH 0.22g/L、NH ₃ 0.056g/L of the first mother liquor.

The second solid-liquid separation device 92 obtains 768.53kg of sodium sulfate crystal cake with a water content of 15 mass% per hour, and finally obtains 653.25kg of sodium sulfate (with a purity of 99.4 wt%) per hour; yield 50.07m per hour ³ The concentration of NaCl is 306.2g/L, na ₂ SO ₄ 55.3g/L、NaOH 0.229g/L、NH ₃ 0.0017g/L of second mother liquor.

In this example, 3.35m of ammonia water having a concentration of 1.63 mass% was obtained per hour in the first ammonia water tank 51 ³ 2.27m of 0.12 mass% ammonia water was obtained per hour in the second ammonia water tank 52 ³ 。

The preferred embodiments of the present invention have been described in detail, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.

It should be noted that the various features described in the foregoing embodiments may be combined in any suitable manner without contradiction. The invention is not described in detail in order to avoid unnecessary repetition.

In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present 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) Carrying out first evaporation on the wastewater to be treated to obtain first ammonia-containing steam and a first concentrated solution containing sodium chloride crystals;

wherein the pH value of the wastewater to be treated is adjusted to be more than 9 before the wastewater to be treated is subjected to first evaporation;

the first evaporation prevents the crystallization of sodium sulfate, and the second evaporation prevents the crystallization of sodium chloride;

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

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- Over 1000mg/L, cl ^- Over 970mg/L of Na ⁺ Is more than 510 mg/L.

2. The method according to claim 1, wherein the SO contained in the wastewater to be treated is 1 mole relative to the SO contained in the wastewater to be treated ₄ ^2- Cl contained in the wastewater to be treated ^- Is 10 mol or more.

3. The method according to claim 2, wherein the SO contained in the wastewater to be treated is 1 mole relative to the SO contained in the wastewater to be treated ₄ ^2- Cl contained in the wastewater to be treated ^- Is 10-15 mol.

4. A method as claimed in claim 3, wherein the pH of the wastewater to be treated is adjusted to be greater than 10.8 before passing it to the first evaporation plant.

5. The method as claimed in claim 1, wherein the pH adjustment of the wastewater to be treated is carried out with NaOH.

6. The process of claim 1, wherein the first evaporation is conducted such that the concentration of sodium sulfate in the first concentrated solution is Y or less, wherein Y is the concentration of sodium sulfate at which both sodium chloride and sodium sulfate in the first concentrated solution are saturated under the conditions of the first evaporation.

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

8. The method of claim 1, wherein the second evaporation provides a concentration of sodium chloride in the second concentrate of X or less, wherein X is the concentration of sodium chloride at which both sodium chloride and sodium sulfate in the second concentrate are saturated under the conditions of the second evaporation.

9. The process of claim 8, wherein the second evaporation provides a concentration of sodium chloride in the second concentrate of 0.95X to 0.999X.

10. The method of any one of claims 1-9, wherein the conditions of the first evaporation comprise: the temperature is 30-85 ℃, and the pressure is-98 kPa to-58 kPa.

11. The method of claim 10, wherein the conditions of the first evaporation comprise: the temperature is 35 to 60 ℃, and the pressure is-97.5 kPa to-87 kPa.

12. The method of claim 10, wherein the conditions of the first evaporation comprise: the temperature is 40-60 ℃, and the pressure is-97 kPa to-87 kPa.

13. The method of claim 10, wherein the conditions of the first evaporation comprise: the temperature is 45-60 ℃, and the pressure is-95 kPa to-87 kPa.

14. The method of claim 10, wherein the conditions of the first evaporation comprise: the temperature is 45-55 ℃, and the pressure is-95 kPa to-90 kPa.

15. The method of any one of claims 1-8, wherein the conditions of the second evaporation comprise: the temperature is above 45 ℃ and the pressure is above-95 kPa.

16. The method of claim 15, wherein the conditions of the second evaporation comprise: the temperature is 45-365 ℃, and the pressure is-95 kPa-18110 kPa.

17. The method of claim 15, wherein the conditions of the second evaporation comprise: the temperature is 60-365 ℃, and the pressure is-87 kPa-18110 kPa.

18. The method of claim 15, wherein the conditions of the second evaporation comprise: the temperature is 75-175 ℃, and the pressure is-73 kPa-653 kPa.

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

20. The method of claim 15, wherein the conditions of the second evaporation comprise: the temperature is 95-105 ℃, and the pressure is-37 kPa to-7 kPa.

21. The method of claim 10, wherein the temperature of the first evaporation is more than 5 ℃ lower than the temperature of the second evaporation.

22. The method of claim 21, wherein the temperature of the first evaporation is 20 ℃ or more lower than the temperature of the second evaporation.

23. The method of claim 21, wherein the temperature of the first evaporation is 35 ℃ to 70 ℃ lower than the temperature of the second evaporation.

24. The method of claim 21, wherein the temperature of the first evaporation is 50 ℃ to 59 ℃ lower than the temperature of the second evaporation.

25. The method of any one of claims 1-9, wherein the first and second evaporations are performed by one or more of an MVR evaporation device, a single-effect evaporation device, and a multi-effect evaporation device, respectively.

26. The method of claim 25, wherein the first evaporation is performed by an MVR evaporation device.

27. The method of claim 25, wherein the second evaporation is performed by an MVR evaporation device.

28. The method according to claim 1, wherein the first ammonia-containing steam or the condensate of the first ammonia-containing steam is subjected to a first heat exchange with the wastewater to be treated and a first ammonia water is obtained before the first evaporation is performed.

29. A method as set forth in claim 28 wherein the pH of the wastewater to be treated is adjusted to be greater than 7 prior to the first heat exchange.

30. The method according to any one of claims 1 to 9, further comprising subjecting the first concentrated solution containing sodium chloride crystals to a first solid-liquid separation to obtain sodium chloride crystals.

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

32. The method according to any one of claims 1 to 9, further comprising subjecting the second concentrated solution containing sodium sulfate crystals to a second solid-liquid separation to obtain sodium sulfate crystals.

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

34. The process of any one of claims 1 to 9, wherein the ammonium salt-containing wastewater is wastewater from a molecular sieve, alumina or refinery catalyst production process.

35. The method of claim 34, further comprising removing impurities and concentrating the ammonium salt-containing wastewater.