CN108726756B

CN108726756B - Method for treating ammonium salt-containing wastewater

Info

Publication number: CN108726756B
Application number: CN201710263271.XA
Authority: CN
Inventors: 殷喜平; 李叶; 顾松园; 王涛; 高晋爱; 周岩; 杨凌; 苑志伟; 刘夫足; 徐淑朋
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: 2022-12-27
Anticipated expiration: 2037-04-21
Also published as: CN108726756A

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 sulfate 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 sulfate crystals, and carrying out second evaporation on a liquid phase obtained by the first solid-liquid separation to obtain second ammonia-containing steam and a second concentrated solution containing sodium chloride crystals; 3) And carrying out second solid-liquid separation on the second concentrated solution containing the sodium chloride crystals. The method can respectively recover ammonium, sodium sulfate and sodium chloride in the wastewater, and furthest recycle resources in the wastewater.

Description

Method for treating ammonium salt-containing wastewater

Technical Field

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

Background

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

In addition, the biochemical deamination can only treat wastewater with low ammonium content, and can not directly carry out biochemical treatment due to insufficient COD content in the catalyst sewage, and organic matters such as glucose or starch and the like are additionally added in the biochemical treatment process, so that the ammoniacal nitrogen can be treated by the biochemical method. The most important problems are that the total nitrogen of the wastewater subjected to the biochemical deamination treatment often does not reach the standard (the contents of nitrate ions and nitrite ions exceed the standard), advanced treatment is required, 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 sulfate and the sodium chloride in the waste water containing the ammonium salt, and furthest recycle resources in the waste water containing the ammonium salt.

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

3) Carrying out second solid-liquid separation on the second concentrated solution containing the 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 sodium chloride from crystallizing out, and the second evaporation prevents sodium sulfate from crystallizing out; relative to 1 mole of SO contained in the wastewater to be treated ₄ ^2- Cl contained in the wastewater to be treated ^- The molar ratio is 14 mol or less.

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

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 and 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

4. Vacuum degassing tank 78, eighth circulating pump

51. First aqueous ammonia storage tank 79, ninth circulating pump

52. Second ammonia storage tank 81, vacuum pump

53. First mother liquor tank 82 and circulating water tank

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

55. Crystal liquid collecting tank 91 and first solid-liquid separation device

61. First pH value measuring device 92 and second solid-liquid separation device

62. Second pH value measuring device 101 and first compressor

71. First circulation pump 102, second compressor

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 preferred embodiment of the 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 these ranges or values should be understood to encompass values close to these ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.

The present invention will be described below with reference to fig. 1 to 2, but the present invention is not limited to fig. 1 to 2.

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

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

wherein before the wastewater to be treated is subjected to first evaporation, the pH value of the wastewater to be treated is adjusted to be more than 9; the first evaporation prevents sodium chloride from crystallizing out, and the second evaporation prevents sodium sulfate from crystallizing out; relative to 1 mol of SO contained in the wastewater to be treated ₄ ^2- Cl contained in the wastewater to be treated ^- The amount is 14 mol or less.

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 mixed solution of the ammonium salt-containing wastewater and a liquid phase obtained by 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 ⁺ Is treated except for containing 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 based on the total amount of SO ₄ ^2- Cl contained in the wastewater to be treated ^- Is 13.8 mol or less, preferably 13.75 mol or less, more preferably 13.5 mol or less, more preferably 13 mol or less, still more preferably 12 mol or less, and still more preferably 11 mol or lessThe amount of the organic solvent is preferably not more than 10.5 moles, more preferably not less than 2 moles, still more preferably not less than 2.5 moles, still more preferably not less than 3 moles, and may be, for example, 3 to 10.5 moles. By reacting SO ₄ ^2- And Cl ^- The molar ratio of (b) is controlled within the above range and the evaporation conditions described later are combined, so that sodium sulfate is precipitated in the first evaporation without precipitating sodium chloride, thereby achieving the purpose of efficiently separating sodium sulfate. 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 chloride means that the concentration of sodium chloride in the mixed system is controlled not to exceed the solubility under the first evaporation conditions (including but not limited to temperature, pH, etc.), but sodium chloride carried by sodium sulfate crystals or adsorbed on the surface is not excluded. Since the water content of the crystals after the solid-liquid separation is different, the sodium chloride content in the obtained sodium sulfate crystals is usually 8 mass% or less (preferably 4 mass% or less), and in the present invention, it is considered that sodium chloride is not crystallized when the sodium chloride content in the obtained sodium sulfate crystals is 8 mass% or less.

In the present invention, the second 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 second 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. Since the water content of the crystals after the solid-liquid separation is different, the sodium sulfate content in the obtained sodium chloride crystals is usually 8 mass% or less (preferably 4 mass% or less), and in the present invention, it is considered that the sodium sulfate does not crystallize out when the sodium sulfate content in the obtained sodium chloride crystals is 8 mass% or less.

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

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

As each 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 film 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 multiple-effect evaporation device, and introducing ammonia-containing steam obtained by evaporation of the former effect evaporator of the multiple-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 multiple-effect evaporation device, and introducing ammonia-containing steam obtained by evaporation of a subsequent effect evaporator of the multiple-effect evaporation device into a previous effect evaporator. The advection is specifically as follows: and independently introducing liquid to be evaporated into each effect evaporator of the multiple-effect evaporation device, and introducing ammonia-containing steam obtained by evaporation of the former effect evaporator of the multiple-effect evaporation device into the latter effect evaporator. Among them, concurrent feeding is preferred. When feeding is carried out in a forward flow or a reverse flow mode, the evaporation condition refers to the evaporation condition of the last evaporator of the multi-effect evaporation device; when advection feeding is employed, the conditions of evaporation include the evaporation conditions of each effect evaporator of the multi-effect evaporation apparatus.

In the present invention, the conditions of the first evaporation may be appropriately selected as needed, and sodium sulfate may be crystallized without precipitating sodium chloride. The conditions of the first evaporation may include: the temperature is above 45 ℃ and the pressure is above-95 kPa. In order to improve evaporation efficiency, it is preferable that the conditions of the first evaporation include: the temperature is 45-365 ℃, and the pressure is-95 kPa-18110 kPa; to further improve the evaporation efficiency, more preferably, the conditions of the first evaporation include: the temperature is 60-365 ℃, and the pressure is-87 kPa-18110 kPa; more preferably, from the viewpoint of reducing equipment cost and energy consumption, the conditions of the first evaporation include: the temperature is 75-175 ℃, and the pressure is-73 kPa-653 kPa; further preferably, the conditions of the first evaporation include: the temperature is 80-130 ℃, and the pressure is-66 kPa-117 kPa; particularly preferably, the conditions of the first 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 first evaporation is more 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, sodium chloride is not crystallized and precipitated while sodium sulfate is ensured to be crystallized, and the purity of the obtained sodium sulfate 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 chloride in the wastewater to be treated (i.e., sodium chloride does not reach supersaturation), and preferably, the first evaporation is performed so that the concentration of sodium chloride in the first concentrated solution is X or less (preferably 0.999X or less, more preferably 0.95X to 0.999X, and still more preferably 0.99X to 0.9967X). Wherein, X is the concentration of sodium chloride when the sodium sulfate and the sodium chloride in the first concentrated solution reach saturation under the condition of the first evaporation. By controlling the degree of the first 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 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 the concentration of the first evaporation-derived liquid, and specifically, the concentration of the first evaporation-derived liquid is controlled within the above range so that the first evaporation does not crystallize sodium chloride 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 to carry out first evaporation, so as to obtain first concentrated solution containing ammonia vapor and sodium sulfate crystals.

According to the invention, the method can also comprise the step of carrying out first crystallization on the first concentrated solution containing the sodium sulfate crystals in a first crystallization device to obtain a crystal slurry containing the sodium sulfate crystals. In this case, the evaporation conditions of the first evaporation are required to satisfy the purpose of crystallizing sodium sulfate without precipitating sodium chloride in the first crystallization process. The first crystallization apparatus is not particularly limited, and may be, for example, a crystal solution tank, a crystal solution collecting tank, a thickener with or without stirring, or the like. The conditions of the first 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 first crystallization of the first concentrated solution containing sodium sulfate crystals can also be carried out in an evaporation device with a crystallizer (e.g. a forced circulation evaporation crystallizer), wherein the temperature of the first crystallization is the corresponding temperature of the first evaporation.

According to the present invention, when the first crystallization is performed using a separate crystallization apparatus, it is further ensured that the first evaporation is performed so that sodium chloride does not crystallize out during the first crystallization (i.e., sodium chloride does not reach supersaturation), and preferably, the first evaporation is performed so that the concentration of sodium chloride in the first 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 first concentrated solution reach saturation 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, as shown in fig. 1, 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 sequentially passes through the second heat exchange device 32 and the first heat exchange device 31, and the wastewater to be treated sequentially passes through the first heat exchange device 31 and the second heat exchange device 32, and the wastewater to be treated is subjected to the first heat exchange by the first ammonia-containing steam and the wastewater to be treated, so as to heat the wastewater to be treated for evaporation, and simultaneously cool the first ammonia-containing steam to obtain a first ammonia water, which 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 third heat exchange device 33, specifically, the first ammonia-containing steam obtained by evaporation in the first evaporation device 2 sequentially passes through the second heat exchange device 32 and the first heat exchange device 31, the second condensed liquid containing ammonia steam obtained by second evaporation (for example, the condensed liquid obtained by second ammonia-containing steam after second heat exchange in the fourth heat exchange device 34) passes through the third heat exchange device 33, and a part of the wastewater to be treated passes through the third heat exchange device 33, 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 liquid 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.

The first heat exchange device 31, the second heat exchange device 32 and the third heat exchange device 33 are not particularly limited, and various heat exchangers conventionally used in the art may be used to achieve the first heat exchange between the first ammonia-containing steam or the condensate of 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 after the first heat exchange is 50 to 370 ℃, more preferably 65 to 370 ℃, still more preferably 75 to 184 ℃, and still more preferably 85 to 139 ℃.

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, in order to adjust the pH. The alkaline substance is preferably NaOH in order not to introduce new impurities in the wastewater to be treated, and to increase 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 a first evaporation apparatus 2, and before the ammonium salt-containing wastewater is fed into a first heat exchange apparatus 31 for first heat exchange, the first pH adjustment is performed by introducing and mixing the aqueous solution containing the alkaline substance in the pipe through which the ammonium salt-containing wastewater is fed into the first heat exchange apparatus 31; and then mixing the ammonium salt-containing wastewater with at least part of a liquid phase obtained by second solid-liquid separation to obtain wastewater to be treated, sending the wastewater to be treated into a second heat exchange device 32 for first heat exchange, introducing the aqueous solution containing the alkaline substance into a pipeline for sending the wastewater to be treated into the second heat exchange device 32, and mixing to perform second pH value 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 carried out so that the pH value of the adjusted wastewater is more than 7 (preferably 7-9), and the second pH adjustment is carried out so that the pH value of the wastewater to be treated is more than 9, preferably more than 10.8.

In order to detect the pH values after the first pH value adjustment and the second pH value adjustment, it is preferable that a first pH value measuring device 61 is provided on a pipe for feeding the ammonium salt-containing wastewater to the first heat exchange device 31 to measure the pH value after the first pH value adjustment, and a second pH value measuring device 62 is provided on a pipe for feeding the wastewater to be treated to the second heat exchange device 32 to measure the pH value after the second pH value 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 mixing of the wastewater to be treated (the wastewater to be treated contains the liquid phase obtained by the ammonium salt-containing wastewater and the second solid-liquid separation as the circulating mother liquor, and the mixing of the wastewater to be treated is required) is not particularly limited, and may be appropriately selected as needed, and may be completed before the first evaporation.

In the invention, the first concentrated solution containing sodium sulfate crystals is subjected to a first solid-liquid separation to obtain sodium sulfate 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 first 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). As shown in fig. 1, after the first solid-liquid separation, the first mother liquor obtained by the first solid-liquid separation device 91 is temporarily stored in the first mother liquor tank 53, and may be sent to the 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 impurities such as chlorine ions, free ammonia, and hydroxide ions are adsorbed on the obtained sodium sulfate crystals, and in order to remove the adsorbed impurities, reduce the odor of solid salts, reduce corrosiveness, and improve the purity of the crystals, it is preferable that the sodium sulfate crystals are first washed with water, the ammonium salt-containing wastewater, or a sodium sulfate 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 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 first washing can be recycled in a counter-current manner when used as the 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 process, the liquid used for elutriation is 1 to 20 parts by weight relative to 1 part by weight of the slurry containing sodium sulfate crystals. In addition, the rinsing is preferably carried out using an aqueous sodium sulfate solution, the concentration of which is preferably such that the sodium chloride and the sodium sulfate reach the concentration of sodium sulfate in the saturated aqueous solution at the same time at the temperature corresponding to the sodium sulfate crystals to be rinsed. In order to further enhance the elutriation effect and obtain sodium sulfate crystals with higher purity, the elutriation is preferably performed using a liquid obtained by rinsing, and preferably using water or a sodium sulfate solution. It is preferable for the liquid produced by the washing to be returned to before the first heat exchange before the first evaporation is completed.

According to a preferred embodiment of the present invention, the first concentrated solution containing sodium sulfate obtained by evaporation in the first evaporation apparatus 2 is subjected to preliminary solid-liquid separation by settling, and then subjected to first elutriation in an elutriation tank using the ammonium salt-containing wastewater, and then subjected to second elutriation in another elutriation tank using a liquid obtained in the subsequent washing of sodium sulfate crystals, and finally the slurry subjected to the two elutriations is sent to a solid-liquid separation apparatus to be subjected to solid-liquid separation, the crystals obtained by the solid-liquid separation are subjected to elution with an aqueous sodium sulfate solution, and the eluted liquid is returned to the second elutriation. Through the washing process, the purity of the obtained sodium sulfate crystal is improved, washing liquid cannot be introduced too much, and the efficiency of wastewater treatment is improved.

In the present invention, the evaporation conditions of the second evaporation may be appropriately selected as needed, so that sodium chloride is crystallized and sodium sulfate is not precipitated. The conditions of the second evaporation may include: the temperature is 30-85 ℃, and the pressure is-98 kPa-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 second evaporation include: the temperature is 35 to 60 ℃, and the pressure is-97.5 kPa to-87 kPa; preferably, the conditions of the second evaporation include: the temperature is 40 ℃ to 60 ℃, and the pressure is-97 kPa to-87 kPa; preferably, the conditions of the second evaporation include: the temperature is 45-60 ℃, and the pressure is-95 kPa to-87 kP; preferably, the conditions of the second 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 second evaporation is more 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 be treated and the amount of the wastewater to be treated, and may be, for example, 0.1m ³ More than h (e.g. 0.1 m) ³ /h～500m ³ /h)。

By carrying out the second 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 present invention, the second evaporation does not crystallize sodium sulfate in the second concentrated solution (i.e., sodium sulfate does not reach supersaturation), and preferably, the second evaporation makes the concentration of sodium sulfate in the second concentrated solution to be 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 second concentrated solution reach saturation under the conditions of the second evaporation. By controlling the degree of the second evaporation within the above range, as much sodium chloride as possible can be crystallized out while ensuring that sodium sulfate is not precipitated out. By crystallizing sodium chloride 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 monitored by the concentration of the second evaporation-derived liquid, and specifically, the concentration of the second evaporation-derived liquid is controlled to be in the above range so that the second evaporation does not crystallize sodium sulfate 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 chloride crystals in a second crystallization device to obtain crystal slurry containing the sodium chloride crystals. In this case, the evaporation conditions of the second evaporation need only be satisfied in order to crystallize sodium chloride without precipitating sodium sulfate 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 or without stirring, and the like, and may be carried out, for example, in the crystal solution collecting tank 55. The conditions for the second 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 sufficiently ensure the crystallization effect, the crystallization time may be 5min to 24 hours, preferably 5min to 30min. According to the invention, the second crystallization of the second concentrate containing sodium chloride crystals can also be carried out in a crystallizer evaporator (e.g. a forced circulation evaporator crystallizer), in which case the temperature of the second crystallization is the corresponding second evaporation temperature.

According to the present invention, when a single crystallization device is used for crystallization, it is further ensured that the second evaporation is performed so that sodium sulfate is not crystallized out in the second crystallization process (i.e., sodium sulfate is not supersaturated), and preferably, the second evaporation is performed so that the concentration of sodium sulfate in the second 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 second concentrated solution are saturated under the conditions of the second crystallization.

According to a preferred embodiment of the invention, the second ammonia-containing vapour is subjected to a second heat exchange with the cold medium and ammonia is obtained. The cold medium can be cooling water, glycol water solution and the like. When the conventional cooling water is used, the cooling water is recycled, and when the ammonium salt-containing wastewater is used as the cooling water, the ammonium salt-containing wastewater after heat exchange is preferably directly returned to the treatment process (such as the first pH value adjustment process). 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, and more preferably 2 to 3. Through the heat exchange, the output ammonia water is cooled, and the heat is at the maximum degree at the internal circulation of processing apparatus, rational utilization the energy, it is extravagant to have reduced.

According to a preferred embodiment of the present invention, as shown in fig. 1, the second heat exchange is performed by a third heat exchange device 33 and a 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 washing liquid and the second circulation liquid (i.e. the part of the liquid returned after being evaporated by the second evaporation device (MVR evaporation device) 2) are subjected to the second heat exchange with the second ammonia-containing steam in the fourth heat exchange device 34, and the ammonium salt-containing wastewater is subjected to the second heat exchange with the second ammonia-containing steam condensate in the third heat exchange device 33, so as to further reduce the temperature of the second ammonia-containing steam condensate, improve the heat energy utilization rate, and obtain the second ammonia.

According to a preferred embodiment of the present invention, as shown in fig. 2, the second ammonia-containing vapor obtained from the last evaporator of the second evaporation device (multi-effect evaporation device) 1 undergoes the second heat exchange with the cold medium in the third heat exchange device 33 and obtains the second ammonia water.

The third heat exchanger 33 and the fourth heat exchanger 34 are not particularly limited, and various heat exchangers conventionally used in the art may be used to cool the second ammonia-containing steam. Specifically, the heat exchanger can be a jacketed heat exchanger, a plate heat exchanger, a shell-and-tube heat exchanger, a spiral threaded tube heat exchanger, or the like. The material of the heat exchanger can be specifically selected according to the requirement, for example, the stainless steel spiral thread pipe heat exchanger is preferred because the secondary steam has no corrosivity to the stainless steel.

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

In the invention, the second concentrated solution containing sodium chloride crystals is subjected to second solid-liquid separation to obtain sodium chloride crystals and a second mother liquor (namely, a liquid phase obtained by the second solid-liquid separation). 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 (i.e., the liquid phase obtained by the second solid-liquid separation) is returned to the first evaporation device 2 for the first evaporation again, and specifically, the second mother liquor can be returned to the first evaporation device 2 by the eighth circulation pump 78 and mixed with the ammonium salt-containing wastewater after the first pH adjustment and before the second pH adjustment to obtain the wastewater to be treated, and then sent to the first evaporation device 2 for the first evaporation. In addition, it is difficult to avoid that the obtained sodium chloride crystals adsorb certain impurities such as sulfate ions, free ammonia, hydroxide ions, etc., and in order to remove the adsorbed impurities, reduce the odor of solid salts, reduce corrosiveness, and improve the purity of the crystals, it is preferable that the sodium chloride crystals are subjected to secondary washing with water, the ammonium salt-containing wastewater, or a sodium chloride solution and dried. In order to avoid dissolution of the sodium chloride crystals during washing, the sodium chloride crystals are preferably washed with an aqueous sodium chloride solution. More preferably, the concentration of the sodium chloride aqueous solution is preferably the concentration of sodium chloride in the aqueous solution at which sodium chloride and sodium sulfate reach saturation simultaneously at the temperature corresponding to the sodium chloride crystals to be washed.

The form of the second solid-liquid separation and the second washing is not particularly limited, and may be carried out, for example, by using a combination of an elutriation apparatus and a solid-liquid separation apparatus which are conventional in the art, or may be carried out on a staged solid-liquid separation apparatus such as a belt filter. Preferably, the second wash comprises elutriation and/or rinsing. The elutriation and rinsing are not particularly limited, and may be performed by a method generally used 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 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, 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. The rinsing is preferably carried out using an aqueous sodium chloride solution, the concentration of which is preferably the concentration of sodium chloride in an aqueous solution in which sodium chloride and sodium sulfate are simultaneously saturated at the temperature corresponding to the sodium chloride crystals to be rinsed. In order to further enhance the elutriation effect and obtain sodium chloride crystals with higher purity, the elutriation may be preferably performed using a liquid obtained by rinsing. For the liquid produced by the washing, preferably, the ammonium salt-containing wastewater elutriation liquid is returned to the second evaporation before the pH value adjustment before the first evaporation is completed. For example, in fig. 1, the second evaporation is performed again by returning the second evaporation apparatus 1 by the ninth circulation pump 79.

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

In the present invention, 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 50 to 100, and the second reflux ratio of the second evaporation may be 0.1 to 50, preferably 7 to 25. 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 returned to the pH value adjustment before the first evaporation, as shown in fig. 1, the first circulating liquid can 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 value adjustment, the first circulating liquid is subjected to heat exchange in the second heat exchange device 32 and finally 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 plant, the process 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 is 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 tail gas and the circulating water in the tail gas absorption tower 83 may be countercurrent or cocurrent, and is preferably countercurrent. 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 wastewater of the present invention may be specifically wastewater from a process for producing a molecular sieve, alumina or a refinery catalyst, or wastewater from a process for producing a molecular sieve, alumina or a refinery 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.

AsSO in the 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 (b) is not particularly limited. SO in the wastewater from the viewpoint of easy access to the wastewater ₄ ^2- 、Cl ^- And Na ⁺ Respectively 200g/L or less, preferably 150g/L or less, and more preferably 120g/L or less; NH in wastewater ₄ ⁺ Is 50g/L or less, preferably 40g/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 waste water containing ammonium salt ^- The lower 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 30 mol or less, preferably 20 mol or less, more preferably 15 mol or less, and further preferably 10 mol or less. 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 0.1 mol or more, more preferably 0.5 mol or more, further preferably 1 mol or more, for example, 1 to 8 mol. By adding SO contained in the waste water containing ammonium salt ₄ ^2- And Cl ^- 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, further preferably 10mg/L or less, and particularly preferably no other inorganic salt ion is contained. By controlling the other inorganic salt ions within the above range, the purity of the sodium sulfate crystals and sodium chloride crystals finally obtained can be further improved. In order to reduce the content of other inorganic salt ions in the ammonium salt-containing wastewater, the following impurity removal is preferably performed.

The TDS of the ammonium salt-containing wastewater may be 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, more preferably 6.2 to 6.8.

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

In the invention, in order to reduce the concentration of impurity ions in the wastewater, ensure the continuous and stable treatment process and reduce the equipment operation and maintenance cost, the 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, either one of a strongly acidic cation resin and a weakly acidic cation resin can be used; as the oxidation, various oxidizing agents conventionally used in the art, such as ozone, hydrogen peroxide, and potassium permanganate, can be used, and in order to avoid introduction of new impurities, ozone, hydrogen peroxide, and the like are preferably used.

The specific impurity removal mode can be specifically selected according to the types of impurities contained in the ammonium salt-containing wastewater. Aiming at suspended matters, a solid-liquid separation method can be selected for removing impurities; for inorganic matters and organic matters, chemical precipitation, ion exchange and adsorption methods can be selected for removing impurities, such as weak acid cation exchange, activated carbon adsorption and the like; for organic matters, impurities can be removed by adopting an adsorption and/or oxidation mode, wherein an ozone biological activated carbon adsorption oxidation method is preferred.

According to a preferred embodiment of the invention, the ammonium salt-containing wastewater is subjected to filtration, weak acid cation exchange method and ozone biological activated carbon adsorption oxidation method for impurity removal 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 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 dosage of the regenerant (calculated by 100%) is 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 Gallery Senno chemical Co., ltd, SNT brand D113 acidic cation exchange resin.

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

The conditions for the concentration of the ED membrane are preferably: the current 145A to 155A and the voltage 45V to 65V. As the ED membrane, for example, an ED membrane manufactured by easton corporation, japan can be used.

The conditions for the reverse osmosis are preferably: the operation pressure is 5.4MPa 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 operation, and if the ion content of the wastewater containing ammonium salt meets the conditions of the invention, the first evaporation can be carried out firstly and then the second evaporation can be carried out according to the conditions of the invention; 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 chloride 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 second concentrated solution is subjected to solid-liquid separation to obtain sodium chloride crystals and a second mother solution, the second mother solution is mixed with the wastewater containing ammonium salt 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 sulfate crystals. Of course, a certain concentration of SO prepared in the initial stage may be used ₄ ^2- 、Cl ^- The solution of (2) adjusts the ion content in the wastewater to be treated as long as the wastewater to be treated satisfies the SO content 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 ammonium salt-containing wastewater is wastewater from the production of molecular sieves, which is subjected to chemical precipitation, filtration, weak acid cation exchange and ozone-activated carbon adsorption oxidation in sequence, and is concentrated by ED membrane concentration and reverse osmosis in sequence.

Example 1

As shown in figure 1, the waste water containing ammonium salt (containing 80g/L NaCl and Na) ₂ SO ₄ 82g/L、NH ₄ Cl 50g/L、(NH ₄ ) ₂ SO ₄ 52.1g/L, pH 6.8) at a feed rate of 5m ³ Sending the wastewater to a vacuum degassing tank 4 at a speed of/h for vacuum degassing, introducing a 45.16 mass% sodium hydroxide aqueous solution into a pipeline sent to a first heat exchange device 31 (a titanium alloy plate heat exchanger) for first pH value adjustment, monitoring the adjusted pH value through a first pH value measuring device 61 (a pH meter) (the measured value is 7.5), sending part of the wastewater with ammonium salt after the first pH value adjustment to the first heat exchange device 31 through a first circulating pump 71, carrying out first heat exchange with a recovered first ammonia vapor-containing condensate to heat the wastewater to 98 ℃, sending the other part of the wastewater with the first pH value adjusted to a third heat exchange device 33 through the first circulating pump 71, carrying out first heat exchange with a second ammonia vapor-containing condensate to heat the wastewater to 48 ℃, merging the two parts of the wastewater with ammonium salt, and sending the two parts of the wastewater with the returned second mother liquor (the sending speed is 8.75 m) ³ H) mixing to obtain wastewater to be treated (measuring SO contained in the wastewater ₄ ^2- And Cl ^- In a molar ratio of 1:6.261 Then, a 45.16 mass% aqueous sodium hydroxide solution is introduced into a pipeline for feeding the wastewater to be treated into the second heat exchange device 32 to adjust the pH value for the second time, the adjusted pH value is monitored by a second pH value measuring device 62 (pH meter) (measurement value is 10.8), and then the wastewater to be treated is fed into the second heat exchange device 32 (titanium alloy plate heat exchanger) to perform first heat exchange with the recovered first ammonia-containing steam to heat the wastewater to be treated to 107 ℃, and then the wastewater to be treated after the first heat exchange is fed into a first evaporation device 2 (falling film + forced circulation two-stage MVR evaporation crystallizer) to be evaporated, so that a first concentrated solution containing the first ammonia-containing steam and sodium sulfate crystals is obtained. Wherein, the evaporation conditions of the first evaporation device 2 include: the temperature is 100 ℃, the pressure is-22.82 kPa, and the evaporation capacity is 3.92m ³ H is used as the reference value. The first ammonia-containing vapor obtained by evaporation is compressed by the first compressor 101 (temperature)The temperature of the wastewater rises to 12 ℃) and sequentially passes through the second heat exchange device 32 and the first heat exchange device 31 to exchange heat with the wastewater to be treated, and the wastewater is cooled to obtain first ammonia water which is stored in the 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 77.8). The degree of the first evaporation was monitored by a densitometer provided in the first evaporation apparatus 2, and the concentration of sodium chloride in the first concentrated solution was controlled to 0.9935X (306.2 g/L).

The first concentrated solution obtained by evaporation in the first evaporator 2 was sent to a first solid-liquid separator 91 (centrifuge) to carry out first solid-liquid separation, and 10.58 m/hr was obtained ³ Contains NaCl 306.2g/L and Na ₂ SO ₄ 54.0g/L、NaOH 1.4g/L、NH ₃ 0.27g/L of first mother liquor is temporarily stored in a first mother liquor tank 53, sodium sulfate solid obtained by solid-liquid separation (809.7 kg of sodium sulfate crystal filter cake containing 15 mass% of water is obtained per hour, wherein the content of sodium chloride is less than 6.9 mass%) is eluted by 54g/L of sodium sulfate solution which is equal to the dry basis mass of the sodium sulfate crystal filter cake, 688.25kg of sodium sulfate (the purity is 99.7 weight%) is obtained per hour after drying, and a washing solution is circulated to a pipeline before entering a second heat exchange device 32 through a fifth circulating pump 75 to be mixed with the wastewater, and then enters the first evaporation device 2 again to carry out first evaporation.

The second evaporation process is carried out in a second evaporation device 1 (falling film + forced circulation two-stage MVR evaporative crystallizer). The first mother liquor in the first mother liquor tank 53 is sent to the second evaporation device 1 by the sixth circulation pump 76 for second evaporation to obtain a second concentrated solution containing sodium chloride crystals. Wherein, the evaporation conditions of the second evaporation device 1 include: the temperature is 50 ℃, the pressure is-92.67 kPa, and the evaporation capacity is 1.95m 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 the second circulating liquid to the fourth heat exchange device 34 through the seventh circulating pump 77 to exchange heat with the second ammonia-containing steam, and then enters into the second heat exchange device againThe second evaporation apparatus 1 performs second evaporation (the second reflux ratio is 16). 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 for heat exchange and cooling to obtain second ammonia water, and the second ammonia water is stored in the second ammonia water storage tank 52. The washing liquid after the second solid-liquid separation and part of the first mother liquid after the evaporation in the second evaporation device 1 are respectively pumped out by a ninth circulating pump 79 and a seventh circulating pump 77 and are mixed in a pipeline to perform heat exchange with the second ammonia-containing steam passing through the fourth heat exchange device 34, and part of the wastewater to be treated conveyed by the first circulating pump 71 performs heat exchange with the condensate of the second ammonia-containing steam passing through the third heat exchange device 33. The degree of the second evaporation was monitored by a densimeter provided in the second evaporation apparatus 1, and the concentration of sodium sulfate in the second concentrated solution was controlled to 0.9702Y (65.3 g/L). After the first mother liquor is evaporated in the second evaporator 1, a second concentrated solution containing sodium chloride crystals is obtained.

The second concentrated solution containing sodium chloride crystals is sent to a second solid-liquid separation device 92 (centrifugal machine) for solid-liquid separation, and the solid-liquid separation can obtain 8.75m per hour ³ Contains 293.8g/L NaCl and Na ₂ SO ₄ 65.3g/L、NaOH 1.7g/L、NH ₃ 0.013g/L of the second mother liquor, and the second mother liquor is temporarily stored in the second mother liquor tank 54. The second mother liquor is circulated to a wastewater introduction pipeline before the second pH adjustment by an eighth circulation pump 78 to be mixed with wastewater to obtain wastewater to be treated, sodium chloride solids obtained by solid-liquid separation (785.29 kg of sodium chloride crystal cake with a water content of 14 mass% is obtained per hour, wherein the content of sodium sulfate is 7.1 mass% or less) are subjected to leaching by using 293.8g/L of sodium chloride solution with the same mass as the dry basis of sodium chloride, and are dried in a dryer to obtain 675.35kg of sodium chloride (with a purity of 99.4 wt%) per hour, and a second washing solution obtained by washing is circulated to the second evaporation device 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 of the water for operating the vacuum pump 81 and the ammonia content are reduced. Dilute sulfuric acid is further introduced into the tail gas absorption tower 83 to absorb ammonia and the like in the tail gas.

In this example, 3.92m of ammonia water having a concentration of 3.53 mass% was obtained per hour in the first ammonia water tank 51 ³ 1.95m of 0.144 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.

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 waste water was carried out according to the method of example 1, except that: for NaCl-containing 60g/L, na ₂ SO ₄ 130g/L、NH ₄ Cl 15g/L、(NH ₄ ) ₂ SO ₄ Treating the wastewater with 33.0g/L and pH of 6.8 to obtain SO contained in the wastewater to be treated ₄ ^2- And Cl ^- In a molar ratio of 1:4.462. the temperature of the wastewater after heat exchange by the first heat exchange device 31 was 67 deg.C, and the temperature of the wastewater to be treated after heat exchange by the second heat exchange device 32 was 102 deg.C. The evaporation conditions of the first evaporation device 2 include: the temperature is 95 ℃, the pressure is-36.36 kPa, and the evaporation capacity is 4.48m ³ H is used as the reference value. The evaporation conditions of the second evaporation apparatus 1 include: the temperature is 55 ℃, the pressure is-90.15 kPa, and the evaporation capacity is 1.05m ³ /h。

The first solid-liquid separation device 91 gave 978.40kg of a sodium sulfate crystal cake containing 15% by mass of water per hour, and finally gave 831.63kg of sodium sulfate (purity 99.3% by weight) per hour; 7.25 m/hr ³ The concentration of NaCl is 307.2g/L and Na ₂ SO ₄ 54.5g/L、NaOH 1.8g/L、NH ₃ 0.18g/L of the first mother liquor.

The second solid-liquid separation device 92 obtained 444.79kg of sodium chloride crystal cake with a water content of 15 mass% per hour, and finally 378.07kg of sodium chloride (purity 99.5 wt%) per hour; yield 6.30m per hour ³ Concentration ofIs NaCl 295.5g/L and Na ₂ SO ₄ 63.1g/L、NaOH 2.1g/L、NH ₃ 0.01g/L of a second mother liquor.

In this example, 4.48m of ammonia water having a concentration of 1.4 mass% was obtained per hour in the first ammonia water tank 51 ³ 1.05m of aqueous ammonia having a concentration of 0.11 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 waste water was carried out according to the method of example 1, except that: for NaCl-containing 160g/L and Na ₂ SO ₄ 55g/L、NH ₄ Cl 32g/L、(NH ₄ ) ₂ SO ₄ Treating the wastewater with the pH value of 6.2 and 11.2g/L to obtain SO contained in the wastewater to be treated ₄ ^2- And Cl ^- In a molar ratio of 1:9.249. the temperature of the wastewater after heat exchange by the first heat exchange means 31 was 73 deg.c and the temperature of the wastewater to be treated after heat exchange by the second heat exchange means 32 was 112 deg.c. The evaporation conditions of the first evaporation device 2 include: the temperature is 105 ℃, the pressure is-7.02 kPa, and the evaporation capacity is 2.63m ³ H is used as the reference value. The evaporation conditions of the second evaporation apparatus 1 include: the temperature was 45 ℃, the pressure was-94.69 kPa, and the evaporation capacity was 2.86m ³ /h。

The first solid-liquid separation device 91 gave 385.26kg of a sodium sulfate crystal cake containing 14 mass% of water per hour, and finally gave 331.32kg of sodium sulfate (purity: 99.4% by weight) per hour; yield 11.98m per hour ³ The concentration of NaCl is 306.4g/L and Na ₂ SO ₄ 52.5g/L、NaOH 2.6g/L、NH ₃ 0.11g/L of the first mother liquor.

1151.57kg of sodium chloride crystal cake with a water content of 15 mass% is obtained by the second solid-liquid separation device 92 per hour, and 978.83kg of sodium chloride (purity 99.4 wt%) is finally obtained per hour; obtained at 9.18m per hour ³ The concentration of NaCl is 291.2g/L and Na ₂ SO ₄ 67.9g/L、NaOH 3.4g/L、NH ₃ 0.0084g/L of second mother liquor.

In this example, 2.63m of aqueous ammonia having a concentration of 2.3 mass% was obtained per hour in the first aqueous ammonia tank 51 ³ Second ammonia storage2.86m of ammonia water having a concentration of 0.043% by mass per hour was obtained in the tank 52 ³ The ammonia water can be reused in the production process of the molecular sieve.

Example 4

As shown in FIG. 2, the waste water containing ammonium salt (containing NaCl 156g/L, na) ₂ SO ₄ 50g/L、NH ₄ Cl 60g/L、(NH ₄ ) ₂ SO ₄ 19.55g/L, pH 6.3) at a feed rate of 5m ³ A rate of/h was fed to a pipe line of a treatment system, a sodium hydroxide aqueous solution having a concentration of 45.16 mass% was introduced into the pipe 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 was 7.5), and a part (2.5 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 carry out first heat exchange with the first ammonia-containing steam condensate to heat the waste water containing ammonium salt to 99 ℃, sending the rest part of the waste water into a fourth heat exchange device 34 (a duplex stainless steel plate heat exchanger) to carry out first heat exchange with the second ammonia-containing steam condensate to heat the rest part of the waste water containing ammonium salt to 60 ℃, combining the two parts of waste water, and mixing the two parts of waste water with a second mother solution (the sending speed is 15.31 m) ³ H) mixing to obtain wastewater to be treated (SO contained in the wastewater to be treated) ₄ ^2- And Cl ^- In a molar ratio of 1: 10.356). Then, the wastewater to be treated is sent to a second heat exchange device 32 (titanium alloy plate heat exchanger), first heat exchange is carried out with the recovered first ammonia-containing steam to heat the wastewater to be treated to 113 ℃, then the wastewater to be treated is sent to a pipeline of a first evaporation device 2 (falling film + forced circulation two-stage MVR evaporation crystallizer), sodium hydroxide aqueous solution with the concentration of 45.16 mass% is introduced for second pH value adjustment, the adjusted pH value is monitored by a second pH value measurement device 62 (pH meter) (the measured value is 10.8), the wastewater to be treated after the second pH value adjustment is sent to the first evaporation device 2 for evaporation, and first ammonia-containing steam and a first concentrated solution containing sodium sulfate crystals are obtained. Wherein the evaporation temperature of the first evaporation device 2 is 105 ℃, the pressure is-7.02 kPa, and the evaporation capacity is 2.53m ³ H is used as the reference value. The first ammonia-containing vapor obtained by evaporation is compressed by a compressor 10 (temperature rise 14 ℃ C.) and then evaporatedAnd the wastewater passes through the second heat exchange device 32 and the first heat exchange device 31 again, exchanges heat with the wastewater to be treated, is cooled to obtain ammonia water, and is stored in the 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 circulated as a circulation liquid to the second heat exchange apparatus 32 by the second circulation pump 72, and then entered the first evaporation apparatus 2 again to perform the first evaporation (reflux ratio of 56.2). The degree of the first evaporation was monitored by a densitometer provided in the first evaporation apparatus 2, and the concentration of sodium chloride in the first concentrated solution was controlled to 0.99352X (307.0 g/L).

The first concentrated solution was fed to a first solid-liquid separation apparatus 91 (centrifuge) to carry out first solid-liquid separation, whereby 18.43 m/hr was obtained ³ Contains NaCl 307.0g/L and Na ₂ SO ₄ 52.7g/L、NaOH 1.67g/L、NH ₃ 0.13g/L of the first mother liquor is temporarily stored in the first mother liquor tank 53, sodium sulfate solids obtained by solid-liquid separation (wherein 407.73kg of sodium sulfate crystal cake containing 14 mass% of water is obtained per hour, and the content of sodium chloride is 6.8 mass% or less) are eluted by 52.7g/L of sodium sulfate solution equal to the dry basis mass of the sodium sulfate crystal cake, 350.64kg of sodium sulfate (the purity is 99.4 wt%) is obtained per hour after drying, and the eluted eluate is circulated to the second heat exchange device 32 by the eighth circulation pump 78, and then enters the first evaporation device 2 again for first evaporation.

The second evaporation process is carried out in a second evaporation device (a multiple-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 (all of forced circulation evaporators). And (3) feeding the first mother liquor into a second evaporation device 1 through a fifth circulating pump 75, feeding the first mother liquor into a second effect evaporator 1b for evaporation after the first mother liquor is evaporated in a first effect evaporator 1a, and feeding the first mother liquor into a third effect evaporator 1c for evaporation to finally obtain a second concentrated solution containing sodium chloride crystals. Wherein the evaporation temperature of the first effect evaporator 1a is 86 ℃, the pressure is-55.83 kPa, and the evaporation capacity is 1.08m ³ H; the evaporation temperature of the second effect evaporator 1b is 71 ℃, the pressure is-77.40 kPa, and the evaporation capacity is 1.07m ³ H; evaporation temperature of third effect evaporator 1cThe temperature is 56 ℃, the pressure is-89.56 kPa, and the evaporation capacity is 1.06m 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 a second-effect evaporator 1b for heat exchange to obtain second ammonia water, introducing second ammonia-containing steam obtained by evaporation in the second-effect evaporator 1b into a third-effect evaporator 1c for heat exchange to obtain first ammonia water, and storing the second ammonia water in a second ammonia water storage tank 52 after the second ammonia water exchanges heat with the 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, and a condensate obtained after the heating steam is condensed in the first-effect evaporator 1a is used for preparing washing brine. The second ammonia-containing vapor evaporated by the third effect evaporator 1c exchanges heat with the cold medium in the third heat exchange device 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 was monitored by a densimeter provided in the second evaporation apparatus 1, and the concentration of sodium sulfate in the second concentrated solution was controlled to 0.9693Y (63.1 g/L). After the first mother liquor is evaporated in the second evaporator 1, the finally obtained second concentrated solution containing sodium chloride crystals is crystallized in the crystal liquid collecting tank 55 (crystallization temperature is 55 ℃, crystallization time is 30 min) to obtain crystal slurry containing sodium chloride crystals.

The crystal slurry containing sodium chloride crystals is sent to a second solid-liquid separation device 92 (centrifugal machine) for solid-liquid separation, and the solid-liquid separation can obtain 15.31m per hour ³ Contains 295.6g/L NaCl and Na ₂ SO ₄ 63.1g/L、NaOH 2.0g/L、NH ₃ 0.13g/L of second mother liquor, circulating the second mother liquor to a wastewater introduction pipeline through a seventh circulating 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 chloride solid (1293.73 kg of sodium chloride crystal filter cake with the water content of 14 mass% per hour, wherein the content of sodium sulfate is less than 7.0 mass%), washing the sodium chloride solid with 295g/L of sodium chloride solution with the same dry basis mass as the sodium chloride, drying the sodium chloride solid in a dryer, and obtaining 1112.6kg of sodium chloride (with the purity of 99.4 weight%) per hour, wherein the washing liquid obtained by washing is circulated to the second evaporation device 1 through a sixth circulating 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, 2.53m of ammonia water having a concentration of 4.44 mass% was obtained per hour in the first ammonia water tank 51 ³ 3.21m of 0.072 mass% ammonia water is obtained in the second ammonia water tank 52 every hour ³ The ammonia water can be reused in the production process of the molecular sieve.

In this example, 2.64m of ammonia water having a concentration of 2.4 mass% was obtained per hour in the first ammonia water tank 51 ³ 3.1m of aqueous ammonia having a concentration of 0.084 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 5

The treatment of the ammonium salt-containing wastewater was carried out in the same manner as in example 4, except that: for NaCl 71g/L and Na ₂ SO ₄ 132g/L、NH ₄ Cl 16g/L、(NH ₄ ) ₂ SO ₄ 30.24g/L of ammonium salt-containing wastewater with the pH value of 7.0 is treated to obtain SO contained in the wastewater to be treated ₄ ^2- And Cl ^- In a molar ratio of 1:4.163. the temperature of the wastewater to be treated after heat exchange by the first heat exchange means 31 was 64 deg.c, and the temperature of the wastewater to be treated after heat exchange by the second heat exchange means 32 was 102 deg.c. The evaporation conditions of the first evaporation device 2 include: the temperature is 95 ℃, the pressure is-36.36 kPa, and the evaporation capacity is 2.53m ³ H is used as the reference value. The evaporation conditions of the first effect evaporator 1a of the second evaporation device 1 include: the temperature is 80 ℃, the pressure is-65.87 kPa, and the evaporation capacity is 0.43m ³ H; the evaporation conditions of the second effect evaporator 1b include: steaming at 64 deg.C and-84.0 kPaThe hair output is 0.43m ³ H; the evaporation conditions of the third effect evaporator 1c include: the temperature was 46 ℃, the pressure was-94.33 kPa, and the evaporation capacity was 0.42m ³ /h。

The first solid-liquid separation device 91 obtained 970.09kg of sodium sulfate crystal cake containing 15 mass% of water per hour, and finally obtained 824.57kg of sodium sulfate (purity: 99.5 wt%) per hour; yield 6.59m per hour ³ The concentration of NaCl is 305.6g/L and Na ₂ SO ₄ 55.15g/L、NaOH 1.15g/L、NH ₃ 0.19g/L of the first mother liquor.

518.3kg of sodium chloride crystallized filter cake with the water content of 15 mass percent is obtained by the second solid-liquid separation device 92 every hour, and finally 440.5kg of sodium chloride (with the purity of 99.5 weight percent) is obtained every hour; 5.42 m/hr ³ The concentration of NaCl 292.6g/L and Na ₂ SO ₄ 67.4g/L、NaOH 1.4g/L、NH ₃ 0.012g/L of the second mother liquor.

In this example, 4.26m of ammonia water having a concentration of 1.46% by mass was obtained per hour in the first ammonia water tank 51 ³ 1.28m of aqueous ammonia having a concentration of 0.095 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 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 118g/L, na ₂ SO ₄ 116g/L、NH ₄ Cl 19g/L、(NH ₄ ) ₂ SO ₄ Treating the ammonium salt-containing wastewater with the pH value of 6.8 at 18.99g/L to obtain SO contained in the wastewater to be treated ₄ ^2- And Cl ^- In a molar ratio of 1:6.419. the temperature of the wastewater to be treated after heat exchange by the first heat exchange means 31 was 97 deg.c, and the temperature of the wastewater to be treated after heat exchange by the second heat exchange means 32 was 107 deg.c. The evaporation conditions of the first evaporation device 2 include: the temperature is 100 ℃, the pressure is-22.83 kPa, and the evaporation capacity is 3.52m ³ H is used as the reference value. The evaporation conditions of the first effect evaporator 1a of the second evaporation apparatus 1 include: the temperature is 86 ℃, the pressure is-55.83 kPa, and the evaporation capacity is 0.667m ³ H; the evaporation conditions of the second effect evaporators 1b include: the temperature was 71 ℃ and the pressure was-77 ℃.4kPa, evaporation 0.666m ³ H; the evaporation conditions of the third effect evaporator 1c include: the temperature is 56 deg.C, the pressure is-89.56 kPa, and the evaporation capacity is 0.665m ³ /h。

The first solid-liquid separation device 91 produced 792.33kg of a sodium sulfate crystal cake containing 14 mass% of water per hour, and finally produced 681.41kg of sodium sulfate (purity 99.5 wt%) per hour; obtained 10.95m per hour ³ The concentration of NaCl is 305.8g/L and Na ₂ SO ₄ 53.84g/L、NaOH 2.2g/L、NH ₃ 0.099g/L of the first mother liquor.

The second solid-liquid separation device 92 yielded 817.22kg of sodium chloride crystal cake with a water content of 14 mass% per hour, and finally 694.64kg of sodium chloride (purity 99.4 wt%) per hour; obtained 9.06m per hour ³ The concentration of NaCl is 293.3g/L and Na ₂ SO ₄ 65g/L、NaOH 2.656g/L、NH ₃ 0.0072g/L of the second mother liquor.

In this example, 3.515m of ammonia water having a concentration of 1.5 mass% was obtained per hour in the first ammonia water tank 51 ³ The second ammonia water tank 52 receives 1.998m of 0.051 mass% ammonia water per hour ³ The ammonia water can be reused in the production process of the molecular sieve.

The preferred embodiments of the present invention have been described 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 above embodiments may be combined in any suitable manner without departing from the scope of the invention. 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 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 sodium chloride from crystallizing out, and the second evaporation prevents sodium sulfate from crystallizing out;

relative to 1 mol of SO contained in the wastewater to be treated ₄ ^2- Cl contained in the wastewater to be treated ^- 14 mol or less;

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 13.8 mol or less.

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 4-10 mol.

4. The method as claimed in claim 1, wherein 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.

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

7. A process as claimed in claim 6, wherein the first evaporation provides a concentration of sodium chloride in the first concentrate of from 0.95X to 0.999X.

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

9. The method of claim 8, wherein the second evaporation provides a sodium sulfate concentration in the second concentrated solution of 0.9Y to 0.99Y.

10. The method of any one of claims 1-9, wherein the conditions of the first evaporation comprise: the temperature is above 45 ℃ and the pressure is above-95 kPa.

11. The method of claim 10, wherein the conditions of the first evaporation comprise: the temperature is 45-365 ℃, and the pressure is-95 kPa-18110 kPa.

12. The method of claim 10, wherein the conditions of the first evaporation comprise: the temperature is 60-365 ℃, and the pressure is-87 kPa-18110 kPa.

13. The method of claim 10, wherein the conditions of the first evaporation comprise: the temperature is 75-175 ℃, and the pressure is-73 kPa-653 kPa.

14. The method of claim 10, wherein the conditions of the first evaporation comprise: the temperature is 80-130 ℃, and the pressure is-66 kPa-117 kPa.

15. The method of claim 10, wherein the conditions of the first evaporation comprise: the temperature is 95-105 ℃, and the pressure is-37 kPa to-7 kPa.

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

17. The method of claim 16, wherein the conditions of the second evaporation comprise: the temperature is 35-60 ℃, and the pressure is-97.5 kPa to-87 kPa.

18. The method of claim 16, wherein the conditions of the second evaporation comprise: the temperature is 40-60 ℃, and the pressure is-97 kPa to-87 kPa.

19. The method of claim 16, wherein the conditions of the second evaporation comprise: the temperature is 45-60 ℃, and the pressure is-95 kPa to-87 kPa.

20. The method of claim 16, wherein the conditions of the second evaporation comprise: the temperature is 45-55 ℃, and the pressure is-95 kPa to-90 kPa.

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

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

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

24. The method of claim 21, wherein the temperature of the first evaporation is 40-60 ℃ higher 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. The 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 sulfate crystals to a first solid-liquid separation to obtain sodium sulfate crystals.

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

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

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

34. The process of any 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 decontaminating and concentrating the ammonium salt-containing wastewater.