CN108726612B

CN108726612B - Method for treating waste water containing ammonium salt

Info

Publication number: CN108726612B
Application number: CN201710266201.XA
Authority: CN
Inventors: 殷喜平; 李叶; 顾松园; 刘志坚; 王涛; 陈玉华; 安涛; 周岩; 苑志伟; 伊红亮
Original assignee: China Petroleum and Chemical Corp; Sinopec Catalyst Co
Current assignee: China Petroleum and Chemical Corp; Sinopec Catalyst Co
Priority date: 2017-04-21
Filing date: 2017-04-21
Publication date: 2022-12-27
Anticipated expiration: 2037-04-21
Also published as: CN108726612A

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 is characterized by comprising the following steps of 1) carrying out first evaporation on wastewater to be treated to obtain first ammonia-containing steam and first concentrated solution containing sodium chloride crystals, wherein the wastewater to be treated contains the wastewater containing ammonium salt; 2) Carrying out low-temperature treatment on the first concentrated solution containing the sodium chloride crystals to obtain a treatment solution containing the sodium chloride crystals; 3) Carrying out first solid-liquid separation on the treatment liquid containing the sodium chloride crystals, and 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 sulfate crystals; 4) And carrying out second solid-liquid separation on the second concentrated solution containing the sodium sulfate crystals. The method can respectively recover the ammonium, the sodium sulfate and the sodium chloride in the wastewater, and furthest recycle resources in the wastewater.

Description

Method for treating 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 the wastewater containing ammonium salt.

Background

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

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

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

Disclosure of Invention

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

To achieve the aboveThe invention aims to provide 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) Performing first evaporation on wastewater to be treated to obtain first ammonia-containing steam and a first concentrated solution containing sodium chloride crystals, wherein the wastewater to be treated contains the wastewater containing ammonium salt;

2) Carrying out low-temperature treatment on the first concentrated solution containing the sodium chloride crystals to obtain a treatment solution containing the sodium chloride crystals;

3) Carrying out first solid-liquid separation on the treatment liquid containing the sodium chloride crystals, and 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 sulfate crystals;

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

wherein the pH value of the wastewater to be treated is adjusted to be more than 9 before the wastewater to be treated is subjected to first evaporation; the second evaporation prevents the crystallization of sodium chloride crystals; relative to 1 mole of SO contained in the wastewater to be treated ₄ ^2- Cl contained in the wastewater to be treated ^- Is 7.15 mol or more.

By the technical scheme, the method aims at the content of NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ The wastewater is obtained by adjusting the pH value of the wastewater to be treated to a specific range in advance, then carrying out evaporation separation by using a first evaporation device to obtain a concentrated solution containing sodium chloride crystals or sodium sulfate crystals and sodium chloride crystals and stronger ammonia water, then carrying out low-temperature treatment to dissolve sodium sulfate in the concentrated solution, further crystallizing and separating out sodium chloride to obtain sodium chloride crystals, and then carrying out evaporation again by using a second evaporation device to obtain the concentrated solution containing sodium sulfate crystals and the thinner ammonia water to obtain sodium sulfate crystals. The method can respectively obtain high-purity sodium chloride and sodium sulfate, avoids the difficulty in the processes of mixed salt treatment and recycling, simultaneously completes the process of separating ammonia and salt, and adopts the same heat exchange mode as the heat exchange modeThe waste water is heated and the ammonia-containing steam is condensed, the heat in the evaporation process is reasonably utilized, the energy is saved, the waste water treatment cost is reduced, the ammonium in the waste water is recovered in the form of ammonia water, the sodium sulfate and the sodium chloride are respectively recovered in the form of crystals, no waste residue and waste liquid are generated in the whole process, and the purpose of changing waste into valuables is realized.

Furthermore, the method combines the first evaporation and the low-temperature treatment, so that the first evaporation can be carried out at a higher temperature, the solid content and the evaporation efficiency in the first evaporation concentrated solution are improved, and the energy-saving effect can be achieved.

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

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

31. First heat exchange device 76 and sixth circulating pump

32. Second heat exchanger 77, seventh circulating pump

33. Third heat exchange device 78, eighth circulating pump

34. Fourth heat exchange device 79 and ninth circulating pump

35. Fifth heat exchange device 80 and tenth circulating pump

36. Sixth heat exchanger 81 and vacuum pump

51. First ammonia water storage tank 82 and circulating water tank

52. Second ammonia storage tank 83 and tail gas absorption tower

53. First mother liquor tank 91 and first solid-liquid separation device

54. Second mother liquor tank 92 and second solid-liquid separation device

61. First pH value measuring device 101 and first compressor

62. Second pH value measuring device 102 and second compressor

71. First circulating pump

Detailed Description

The following describes in detail specific embodiments of the present invention. It should be understood that the detailed description and specific examples, while indicating the 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 numerical ranges, each range between its endpoints and individual point values, and each individual point value can be combined with each other to give one or more new numerical ranges, and such numerical ranges should be construed as specifically disclosed herein.

The present invention will be described below with reference to fig. 1 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,

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 second evaporation prevents the crystallization of sodium chloride crystals; relative to 1 mol of SO contained in the wastewater to be treated ₄ ^2- Cl contained in the wastewater to be treated ^- Is 7.15 mol or more.

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

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

Further preferably, the wastewater to be treated is a 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 ⁺ Except that it contains NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ Furthermore, the ammonium salt-containing wastewater 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 7.15 moles or more, preferably 9.5 moles or more, preferably 10 moles or more, preferably 50 moles or less, more preferably 40 moles or less, further preferably 30 moles or less, and for example, may be 8 to 20 moles, preferably 8 to 12 moles, more preferably 10 to 12 moles. By reacting SO ₄ ^2- And Cl ^- The molar ratio of (b) is controlled within the above range, so that sodium chloride is precipitated and sodium sulfate is completely dissolved in the low-temperature treatment, thereby achieving the purpose of efficiently separating sodium chloride. In addition, as described above and below, it is also possible in the present invention to recycle the second mother liquor obtained in the second evaporation process to the first evaporation, and thereby to treat SO in the wastewater to be treated ₄ ^2- And Cl ^- Can be adjusted and the balance of sodium hydroxide can be maintained.

In the present invention, the first evaporation is preferably performed to precipitate sodium chloride crystals, and in view of improving the treatment efficiency, the first evaporation is preferably performed to precipitate both sodium chloride crystals and sodium sulfate crystals to obtain a first concentrated solution containing sodium sulfate crystals and sodium chloride crystals. In the case of obtaining a first concentrated solution containing sodium sulfate crystals and sodium chloride crystals, the first evaporation requires that the sodium sulfate crystals are dissolved in a low-temperature treatment, and in particular, the first evaporation requires that the first concentrated solution containing sodium sulfate crystals and sodium chloride crystals is obtained, and that the sodium sulfate crystals therein can be completely dissolved in the low-temperature treatment. And (3) controlling the evaporation amount of the first evaporation to simultaneously crystallize and separate out sodium sulfate and sodium chloride (namely, the first evaporation obtains a first concentrated solution containing sodium sulfate crystals and sodium chloride crystals), dissolving the sodium sulfate crystals in the first concentrated solution containing the sodium sulfate crystals and the sodium chloride crystals through the low-temperature treatment, and further crystallizing and separating out sodium chloride to obtain a treated solution only containing the sodium chloride crystals.

Sodium sulfate entrained by or adsorbed on the surface of the sodium chloride crystals is not excluded with respect to the treatment liquid containing sodium chloride crystals. Since the water content of the crystals after the solid-liquid separation is different, the sodium sulfate content in the sodium chloride crystals obtained is usually 8 mass% or less (preferably 4 mass%), and in the present invention, it is considered that the sodium sulfate is dissolved when the sodium sulfate content in the sodium chloride crystals obtained is 8 mass% or less.

In the present invention, the second evaporation is performed so that sodium chloride does not crystallize out, which means that the sodium chloride concentration of the mixed system is controlled not to exceed the solubility under the second evaporation conditions (including but not limited to temperature, pH value, etc.), and sodium chloride entrained 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%), and in the present invention, it is considered that the sodium chloride does not crystallize out when the sodium chloride content in the obtained sodium sulfate 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 secondary steam as referred to in the art. The pressures are all pressures in gauge.

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

As the MVR evaporation means, for example, one or more selected from the group consisting of an MVR falling film evaporator, an MVR forced circulation evaporator, an MVR-FC continuous crystallization evaporator, and an MVR-OSLO continuous crystallization evaporator may be mentioned. Among them, preferred are an MVR forced circulation evaporator and an MVR-FC continuous crystallization evaporator, and more preferred is a falling film + forced circulation two-stage MVR evaporative crystallizer.

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

In the present invention, when the first evaporation and/or the second evaporation is performed using a multi-effect evaporation apparatus, the feeding manner of the liquid to be evaporated may be the same or different, and may be a concurrent, countercurrent or advective manner conventionally used in the art. The forward flow is specifically as follows: and sequentially introducing liquid to be evaporated into each effect evaporator of the 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 specifically comprises the following steps: 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 adopted, the evaporation conditions refer to the evaporation conditions of each effect evaporator of the multi-effect evaporation device.

In the invention, in order to sequentially introduce the wastewater to be treated into each effect evaporator of the multi-effect evaporator, a circulating pump can be arranged between each effect evaporator, and the wastewater evaporated in the previous effect evaporator is introduced into the next effect evaporator through the circulating pump.

In the invention, the circulating pump among the selected evaporators can be various pumps which are conventionally used in the field, in order to uniformly evaporate materials, avoid generating a large number of fine crystal nuclei and prevent crystal grains in the circulating crystal slurry from colliding with an impeller at a high speed to generate a large number of secondary crystal nuclei, the circulating pump is preferably a low-rotating-speed centrifugal pump, and more preferably a high-flow low-rotating-speed guide pump impeller or a high-flow low-lift low-rotating-speed axial pump.

In the present invention, the conditions for the first evaporation may be appropriately selected as needed so that sodium sulfate crystals are not present in the treatment solution. The conditions of the first evaporation may include: the temperature is above 35 ℃ and the pressure is above-95 kPa. In order to improve evaporation efficiency, preferably, the conditions of the first evaporation include: the temperature is 45-175 ℃, and the pressure is-95 kPa-18110 kPa; preferably, the conditions of the first evaporation include: the temperature is 60-175 ℃, and the pressure is-87 kPa-18110 kPa; preferably, the conditions of the first evaporation include: the temperature is 75-175 ℃, and the pressure is-73 kPa-653 kPa; preferably, the conditions of the first evaporation include: the temperature is 80-130 ℃, and the pressure is-66 kPa-117 kPa; preferably, the conditions of the first evaporation include: the temperature is 95-110 ℃, and the pressure is-37 kPa-12 kPa; preferably, the conditions of the first evaporation include: the temperature is 100-110 ℃, and the pressure is-23 kPa-12 kPa.

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

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

By allowing the first evaporation to proceed under the above conditions, the efficiency of evaporation can be improved, and energy consumption can be reduced. The method ensures that the sodium sulfate crystals are completely dissolved after the first concentrated solution is subjected to low-temperature treatment while ensuring the maximum evaporation capacity (concentration multiple), thereby ensuring the purity of the obtained sodium chloride crystals.

According to the invention, by controlling the evaporation conditions of the first evaporation device 2, 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 recycled in the production process of the catalyst, or neutralized by acid to obtain ammonium salt for recycling, or mixed with water and corresponding ammonium salt or ammonia water for use.

According to the invention, the first evaporation is used for crystallizing and separating out sodium chloride in the wastewater to be treated, preferably, sodium chloride and sodium sulfate in the wastewater to be treated are simultaneously crystallized and separated out, and the treatment solution containing sodium chloride crystals with higher purity is obtained after low-temperature treatment. Preferably, the first evaporation is performed so that the concentration of sodium sulfate in the treatment solution is no greater than Y (preferably 0.9Y to 0.99Y, more preferably 0.95Y to 0.98Y), where Y is the concentration of sodium sulfate at which both sodium chloride and sodium sulfate in the treatment solution are saturated under the low-temperature treatment conditions. By controlling the degree of the first evaporation within the above range, as much sodium chloride as possible can be crystallized under conditions that ensure that the low-temperature treatment can dissolve sodium sulfate. By crystallizing sodium chloride in the first evaporation as much as possible, the wastewater treatment efficiency can be improved, and the energy waste can be reduced.

In the present invention, the degree of progress of the first evaporation is determined by monitoring the evaporation amount of the first evaporation, that is, the amount of the liquid, and specifically, the concentration factor is controlled by controlling the evaporation amount of the first evaporation, that is, the amount of the first aqueous ammonia, so that the sodium sulfate crystals precipitated in the first evaporation-concentrated solution can be dissolved during the low-temperature treatment. The degree of the first evaporative concentration is monitored by measuring the evaporation rate, and the flow rate can be measured by using a mass flow meter.

According to a preferred embodiment of the present invention, the first ammonia-containing steam or first ammonia water (first ammonia-containing steam condensate) is subjected to first heat exchange with the wastewater to be treated before the wastewater to be treated is subjected to first evaporation. The first 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 times of the first heat exchange may be one or more, preferably 2 to 4 times, and more preferably 2 to 3 times. 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, a fifth heat exchange device 35 and a second heat exchange device 32, specifically, the first ammonia-containing steam obtained by evaporation in the first evaporation device 2 passes through the second heat exchange device 32 and the first heat exchange device 31 in sequence, the first concentrated solution containing sodium chloride crystals passes through the fifth heat exchange device 35, and the wastewater to be treated is subjected to the first heat exchange by the first heat exchange device 31 or the fifth heat exchange device 35 and then is subjected to the first heat exchange by the second heat exchange device 32. Through first heat exchange makes pending waste water intensification is convenient for evaporate, makes simultaneously the condensation of first ammonia-containing steam obtains first aqueous ammonia, first aqueous ammonia can be stored in first aqueous ammonia storage tank 51.

In the present invention, the first heat exchange device 31, the fifth heat exchange device 35 and the second heat exchange device 32 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 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 made of duplex stainless steel, titanium alloy and hastelloy can be selected, and the heat exchanger made of plastic can be selected when the temperature is lower.

According to the present invention, in order to fully utilize the heat energy of the first ammonia-containing steam, it is preferable that the temperature of the wastewater to be treated after the first heat exchange is 52 to 182 ℃, more preferably 67 to 182 ℃, still more preferably 87 to 137 ℃, and still more preferably 102 to 117 ℃.

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

The manner of adding the 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 the first pH adjustment is performed by introducing and mixing the aqueous solution containing the alkaline substance into the pipe for feeding the wastewater to be treated into the heat exchange apparatus before the wastewater to be treated is fed into the first heat exchange apparatus 31 or the fifth heat exchange apparatus 35 for the first heat exchange; then the wastewater to be treated is sent to the first heat exchange device 31 or the fifth heat exchange device 35 for first heat exchange, and then the aqueous solution containing the alkaline substance is introduced and mixed in the pipeline sending the wastewater to be treated to the second heat exchange device 32 for second pH value adjustment. The pH value of the wastewater to be treated is more than 9, preferably more than 10.8 before the first evaporation is carried out through two pH value adjustments. Preferably, the first pH adjustment is such that the pH of the wastewater to be treated is greater than 7 (preferably 7-9), and the second pH adjustment is such that the pH is greater than 9 (preferably greater than 10.8). According to the present invention, it is preferable that the pH of the wastewater to be treated is adjusted to be greater than 7 before the first heat exchange is performed.

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

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

In the invention, the first concentrated solution containing sodium chloride crystals is subjected to low-temperature treatment to dissolve sodium sulfate crystals, so as to obtain a treated solution containing sodium chloride crystals. By controlling the evaporation amount of the first evaporation so that the concentration of sodium sulfate in the treatment solution is Y or less, the sodium sulfate crystals can be completely dissolved in the low-temperature treatment.

According to the present invention, the mode of carrying out the low-temperature treatment is not particularly limited, and it is sufficient to dissolve the sodium sulfate crystals in the first concentrated solution containing sodium chloride crystals obtained by the first evaporation at a temperature controlled appropriately. According to the present invention, the temperature of the low-temperature treatment is lower than the temperature of the first evaporation, and specifically, the conditions of the low-temperature treatment may include: the temperature is 13-100 ℃, preferably 15-45 ℃, more preferably 15-35 ℃, and further preferably 17.9-35 ℃; for example, the temperature can be 18 ℃, 19 ℃, 20 ℃, 21 ℃, 22 ℃, 23 ℃, 24 ℃, 25 ℃, 26 ℃, 27 ℃, 28 ℃, 29 ℃, 30 ℃, 31 ℃, 32 ℃, 33 ℃, 34 ℃, 35 ℃, 36 ℃, 37 ℃, 38 ℃, 39 ℃, 40 ℃, 41 ℃, 42 ℃, 43 ℃, 44 ℃, 45 ℃, 46 ℃, 47 ℃, 48 ℃, 49 ℃,50 ℃, 55 ℃ and 60 ℃. In order to ensure the effect of the low-temperature treatment, the residence time of the low-temperature treatment can be 10min to 600min, preferably 20min to 300min, and preferably 50min to 70min.

In the invention, by controlling the conditions of the first evaporation and the low-temperature treatment, the first evaporation can be carried out at a higher evaporation temperature and an evaporation pressure closer to the normal pressure, so that the problem of low efficiency in evaporation at a lower temperature is solved, the evaporation efficiency is improved, the energy consumption in the evaporation process can be reduced, and the wastewater treatment speed is increased. On the basis, the temperature control of the low-temperature treatment is simpler and more convenient, and the low-temperature treatment temperature can be operated under the condition of being lower than the evaporation temperature (such as below 45 ℃), thereby being more beneficial to the dissolution of sodium sulfate and the precipitation of sodium chloride.

In the present invention, the low-temperature treatment may be performed using various temperature reduction devices conventionally used in the art, and for example, the low-temperature treatment tank 22 may be selected. Preferably, a cooling part, specifically, a part for introducing cooling water, may be provided in the low-temperature treatment tank 22. The first concentrate in the low-temperature treatment tank can be rapidly cooled by the cooling means. Preferably, the low-temperature treatment tank 22 may be provided with a stirring member, and the stirring member can make the solid-liquid phase distribution and the temperature distribution in the first concentrated solution uniform, thereby achieving the purpose of fully dissolving the sodium sulfate crystals and precipitating the sodium chloride crystals to the maximum.

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

According to the present invention, the solid-liquid separation of the first concentrated solution may be performed by using a first solid-liquid separation device (for example, a centrifuge, a belt filter, a plate filter, or the like) 91. After the solid-liquid separation, the first mother liquor obtained by the first solid-liquid separation device 91 is temporarily stored in the first mother liquor tank 53, and can be sent to the second evaporation device 1 by the sixth circulation pump 76 to be subjected to the second evaporation. In addition, it is difficult to avoid that the obtained sodium chloride crystals adsorb certain impurities such as chloride ions, free ammonia, hydroxide ions and the like, and in order to remove the adsorbed impurities, reduce the odor of solid salts, reduce corrosiveness and improve the purity of the crystals, the sodium chloride crystals are preferably subjected to first washing with water, the ammonium salt-containing wastewater or a sodium chloride solution and dried. In order to avoid dissolution of the sodium chloride crystals during washing, preferably the sodium chloride crystals are washed with an aqueous solution of sodium chloride. More preferably, the concentration of the aqueous sodium chloride solution is preferably the concentration of sodium chloride in an aqueous solution in which sodium chloride and sodium sulphate reach saturation simultaneously at the temperature corresponding to the sodium chloride crystals to be washed.

The manner of the first solid-liquid separation and the first washing is not particularly limited, and may be carried out 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 2 to 4 times are preferable for obtaining 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 first washing can be recycled in a counter-current manner when used as the elutriation liquid. Before the elutriation, it is preferable to perform preliminary solid-liquid separation by sedimentation to obtain a slurry containing sodium chloride crystals (the liquid content may be 35% by mass or less). In the elutriation process, 1 to 20 parts by weight of a liquid is used for elutriation with respect to 1 part by weight of a slurry containing sodium chloride crystals. The rinsing is preferably carried out using an aqueous sodium chloride solution. In order to further enhance the elutriation effect and obtain sodium chloride crystals with higher purity, the liquid obtained by rinsing may be preferably used for washing, and water or a sodium chloride solution is preferably used. The liquid generated by washing is preferably returned to the first evaporation device before the second pH adjustment, for example, after being returned to the eighth circulation pump 78 and mixed with the wastewater to be treated before the second pH adjustment, and then returned to the first evaporation device for evaporation after the second pH adjustment and the heat exchange by the second heat exchange device 32.

According to a preferred embodiment of the present invention, after a treatment liquid containing sodium chloride obtained by low-temperature treatment is subjected to preliminary solid-liquid separation by settling, the ammonium salt-containing wastewater is subjected to first elutriation in an elutriation tank, then the liquid obtained in the subsequent washing of sodium chloride crystals is subjected to second elutriation in another elutriation tank, finally the slurry subjected to the two elutriations is sent to a solid-liquid separation device for solid-liquid separation, the crystals obtained by the solid-liquid separation are subjected to elution again with an aqueous sodium chloride solution, and the eluted liquid is returned to the second elutriation. Through the washing process, the purity of the obtained sodium chloride crystal is improved, washing liquid is not excessively introduced, and the efficiency of wastewater treatment is improved.

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

In the present invention, the evaporation conditions of the second evaporation are not particularly limited, and may be appropriately selected as needed to achieve the purpose of concentrating the first mother liquor. The conditions of the second evaporation may include: the temperature is above 35 ℃ and the pressure is above-95 kPa. In order to improve the evaporation efficiency, it is preferable that the conditions of the second evaporation include: the temperature is 45-365 ℃, and the pressure is-95 kPa-18110 kPa; preferably, the conditions of the second evaporation include: the temperature is 60 ℃ to 365 ℃, and the pressure is-87 kPa to 18110kPa; preferably, the conditions of the second evaporation include: the temperature is 75-175 ℃, and the pressure is-73 kPa-653 kPa; preferably, the conditions of the second evaporation include: the temperature is 80-130 ℃, and the pressure is-66 kPa-117 kPa; preferably, the conditions of the second evaporation include: the temperature is 95-110 ℃, and the pressure is-37 kPa-12 kPa; preferably, the conditions of the second evaporation include: the temperature is 95-105 ℃, and the pressure is-37 kPa to-7 kPa.

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

In addition, the evaporation amount of the second evaporation may be determined according to the capacity of the apparatus and the wastewater to be treatedThe amount is suitably selected, and may be, for example, 100L/h or more (e.g., 0.1 m) ³ /h～500m ³ /h)。

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

According to the present invention, the second evaporation does not crystallize sodium chloride in the wastewater to be treated (i.e., sodium chloride does not reach supersaturation), and preferably, the second evaporation makes the concentration of sodium chloride in the second concentrated solution be X or less (preferably 0.999X or less, more preferably 0.95X to 0.999X, and further preferably 0.99X to 0.9967X). Wherein, X is the concentration of sodium chloride when the sodium chloride and the sodium sulfate in the second concentrated solution reach saturation under the second evaporation condition. By controlling the degree of the second evaporation within the above range, as much sodium sulfate as possible can be crystallized out under the condition that sodium chloride is not precipitated out. By crystallizing sodium sulfate in the second evaporation as much as possible, the wastewater treatment efficiency can be improved, and the energy waste can be reduced.

In the present invention, the degree of progress of the second evaporation is performed by monitoring the concentration of the liquid obtained by the second evaporation, and specifically, by controlling the concentration of the liquid obtained by the second evaporation to be in the above range, the second evaporation does not cause crystallization of sodium chloride in the wastewater to be treated. 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, the method can also comprise crystallizing the second concentrated solution containing sodium sulfate crystals in a crystallizing device to obtain crystal slurry containing sodium sulfate crystals. In this case, the evaporation conditions of the second evaporation need only be satisfied in order to crystallize sodium sulfate without precipitating sodium chloride in the crystallization apparatus (the concentration of sodium chloride in the second concentrated solution is X or less in the second evaporation). The crystallization apparatus is not particularly limited, and may be, for example, a crystal solution tank, a crystal solution collecting tank, a thickener with stirring or a thickener without stirring, or the like. According to a preferred embodiment of the present invention, the crystallization is performed in the crystal liquid collection tank 55. The crystallization conditions are not particularly limited, and may include, for example: the temperature is 45 ℃ or higher, preferably 95 to 107 ℃, and more preferably 85 to 105 ℃; the crystallization time may be 5min to 24h, preferably 5min to 30min. According to the invention, the crystallization of the second concentrated solution containing sodium sulfate crystals can also be carried out in a second evaporator with a crystallizer (e.g. a forced circulation evaporator crystallizer), wherein the crystallization temperature is the corresponding second evaporation temperature. In the present invention, the temperature of crystallization is preferably the same as the temperature of the second evaporation.

According to a preferred embodiment of the present invention, the second ammonia-containing vapor is subjected to a second heat exchange with the first mother liquor and a second aqua ammonia is obtained. The second heat exchange method is not particularly limited, and may be performed by a conventional heat exchange method in the art. The number of times of the second heat exchange may be one or more, preferably 2 to 4 times, more preferably 2 to 3 times, and particularly preferably 2 times. Through the second heat exchange, the output aqueous ammonia is cooled, and the heat furthest is at processing apparatus internal recycle, rational utilization the energy, the waste has been reduced.

According to the present invention, preferably, 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 evaporated in the second evaporation device 1 passes through the fourth heat exchange device 34 and the third heat exchange device 33 in sequence, the first mother liquor passes through the third heat exchange device 33 and then is mixed with the first mother liquor and the second circulation liquid (part of the concentrated liquid in the second evaporation device 1), and the obtained mixed liquid passes through the fourth heat exchange device 34 to perform the second heat exchange, so that the temperature of the first mother liquor is raised for evaporation, and the second ammonia-containing steam is condensed to obtain the second ammonia, and the second ammonia can be stored in a second ammonia storage tank 52.

According to the present invention, after the second heat exchange, the temperature of the first mother liquor is 42 ℃ or higher, more preferably 52 to 372 ℃, still more preferably 82 to 182 ℃, and still more preferably 102 to 112 ℃.

According to a preferred embodiment of the present invention, the second evaporation process is performed in the second evaporation apparatus 1, and the first mother liquor is passed into the second evaporation apparatus 1 through the sixth circulation pump 76 to perform the second evaporation, so as to obtain a second concentrated solution containing ammonia vapor and sodium sulfate crystals.

In the present invention, in order to prevent the sodium chloride from crystallizing and precipitating by the second evaporation and to dissolve the sodium sulfate crystals precipitated by the first evaporation in the low-temperature treatment process, it is preferable that the conditions of the second evaporation and the low-temperature treatment satisfy: the temperature of the second evaporation is at least 5 ℃ higher than the temperature of the low-temperature treatment, preferably 20 ℃ higher, more preferably 35 ℃ to 90 ℃ higher, still more preferably 35 ℃ to 70 ℃ higher, and particularly preferably 50 ℃ to 60 ℃ higher. By controlling the temperature of the second evaporation and the low-temperature treatment, when the sodium sulfate crystals and the sodium chloride crystals separated out by the first evaporation in the low-temperature treatment are dissolved, the sodium sulfate in the sodium sulfate crystals and the sodium chloride crystals separated out by the second evaporation are independently crystallized, so that the purity of the obtained sodium sulfate crystals and the sodium chloride crystals is improved.

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

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

The form of the second solid-liquid separation and the second washing is not particularly limited, and may be carried out, for example, by using a combination of an elutriation apparatus and a solid-liquid separation apparatus which are conventional in the art, or may be carried out on a staged solid-liquid separation apparatus such as a belt filter. Preferably, the second wash comprises panning and/or rinsing. The 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 sulfate crystals of higher purity. In the elutriation process, the waste water containing ammonium salt is generally not recycled when used as an elutriation liquid, and the washing liquid recovered by the second washing can be recycled in a countercurrent manner when used as the elutriation liquid. Before the elutriation, it is preferable to perform preliminary solid-liquid separation by sedimentation to obtain a slurry containing sodium sulfate crystals (the liquid content may be 35% by mass or less). 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. The rinsing is preferably carried out using an aqueous sodium sulfate solution. In order to further enhance the elutriation effect and obtain sodium sulfate crystals with higher purity, it is preferable to wash the sodium sulfate crystals with a liquid obtained by rinsing. For the liquid generated by the washing, it is preferable that the other washing liquid is returned to the second evaporation device 1 before the ammonium salt-containing wastewater elutriation liquid is returned to the first evaporation device 2 for the second pH adjustment before evaporation, for example, the other washing liquid is returned to the second evaporation device 1 by the tenth circulation pump 80 for the second evaporation again.

According to a preferred embodiment of the present invention, the second concentrated solution containing sodium sulfate crystals obtained by the second evaporation is subjected to a preliminary solid-liquid separation by settling, and then subjected to a first elutriation in an elutriation tank using the ammonium salt-containing wastewater, and then subjected to a second elutriation in another elutriation tank using a liquid obtained by subsequently washing sodium sulfate crystals, and finally the slurry after the two elutriations is sent to a second solid-liquid separation device to be subjected to solid-liquid separation, the crystals obtained by the solid-liquid separation are subjected to an elution with an aqueous sodium sulfate solution, and the eluted liquid is returned to the second elutriation as an elutriation liquid. Through the washing process combining elutriation and leaching, 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, when the MVR evaporation device is used to perform the first evaporation and/or the second evaporation, in order to increase the solid content in the MVR evaporation device 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 device, also referred to as a circulation liquid) evaporated by the MVR evaporation device is heated and then returned to the MVR evaporation device to be evaporated. As a ratio of returning a part of the liquid after evaporation by the MVR evaporation device to the MVR evaporation device, there is no particular limitation, and for example, the first reflux ratio of the first evaporation may be 10 to 200, preferably 40 to 150, and the second reflux ratio of the second evaporation may be 0.1 to 100, preferably 5 to 50. Here, the reflux ratio means: the ratio of the amount of reflux to the total amount of liquid fed to the MVR evaporator minus the amount of reflux. Preferably, before the first circulating liquid in the first evaporation is preferably returned to the pH adjustment before the first evaporation, as shown in fig. 1, the first circulating liquid may be returned to the wastewater conveying pipeline between the first heat exchange device 31 and the second heat exchange device 32 by the second circulating pump 72 to be mixed with the wastewater to be treated, and then after the second pH adjustment, the heat exchange is performed in the second heat exchange device 32, and finally the mixture is sent to the first evaporation device 2. Preferably, before the second circulating liquid in the second evaporation returns to the second heat exchange, as shown in fig. 1, the second circulating liquid may be returned to the fourth heat exchange device 34 by a seventh circulating pump 77 for heat exchange, and then sent to the second evaporation device 1.

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

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

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

In the present invention, the ammonium salt-containing wastewater is not particularly limited as long as it contains NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ The wastewater is obtained. In addition, the method is particularly suitable for treating high-salinity wastewater. The waste catalyst production water of the present invention may be specifically wastewater from a molecular sieve, alumina or oil refining catalyst production process, or wastewater obtained by subjecting wastewater from a molecular sieve, alumina or oil refining catalyst production process 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 1g/L or more, more preferably 2g/L or more, further preferably 4g/L or more, further preferably 8g/L or more, further preferably 16g/L or more, further preferably 32g/L or more, further preferably 40g/L or more, further preferably 50g/L or more, further preferably 60g/L or more.

As SO in said ammonium salt-containing wastewater ₄ ^2- May be 1g/L or more, preferably 2g/L or more, more preferably 4g/L or more, further preferably 8g/L or more, further preferably 16g/L or more, further preferably 32g/L or more, further preferably 40g/L or more, further preferably 50g/L or more, further preferably 60g/L or more, further preferably 70g/L or more.

As Cl in said ammonium salt-containing wastewater ^- May be 970mg/L or more, more preferably 2g/L or more, further preferably 4g/L or more, further preferably 8g/L or more, further preferably 16g/L or more, further preferably 32g/L or more, further preferably 40g/L or more, further preferably 50g/L or moreAbove all, 60g/L or more is more preferable.

NH contained in the ammonium salt-containing wastewater ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ The upper limit of (3) is not particularly limited. SO in ammonium salt-containing wastewater from the viewpoint of easy access to wastewater ₄ ^2- 、Cl ^- And Na ⁺ The upper limit of (b) is 200g/L or less, preferably 150g/L or less, respectively; NH in waste water containing ammonium salt ₄ ⁺ Is 100g/L or less, preferably 50g/L or less.

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

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

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

In the present invention, the pH value of the ammonium salt-containing wastewater is preferably 4 to 8, for example 6.5 to 7.5.

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

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

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

The specific impurity removal mode can be specifically selected according to the types of impurities contained in the ammonium salt-containing wastewater. For suspended matters, a solid-liquid separation method can be selected for removing impurities; for inorganic matters and organic matters, chemical precipitation, ion exchange and adsorption methods can be selected for removing impurities, such as weak acid cation exchange, activated carbon adsorption and the like; for organic matters, impurities can be removed by adopting an adsorption and/or oxidation mode, wherein an ozone biological activated carbon adsorption oxidation method is preferred. According to a preferred embodiment of the invention, the ammonium salt-containing wastewater is subjected to impurity removal by filtration, a weak acid cation exchange method and an ozone biological activated carbon adsorption oxidation method in sequence. Through the impurity removal process, most suspended matters, hardness, silicon and organic matters can be removed, the scaling risk of the device is reduced, and the continuous and stable operation of the 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 ammonium salt-containing wastewater of the present invention before the treatment by the treatment method of the present invention (preferably, after the above-mentioned impurity removal). Preferably, the concentration is selected from ED membrane concentration and/or reverse osmosis; more preferably, the concentration is performed by ED membrane concentration and reverse osmosis, and the order of performing the ED membrane concentration and the reverse osmosis is not particularly limited. The ED membrane concentration and reverse osmosis treatment apparatus and conditions may be performed in a manner conventional in the art, and may be specifically selected according to the condition of wastewater to be treated. Specifically, as the concentration of the ED membrane, a unidirectional electrodialysis system or a reverse electrodialysis system can be selected; as the reverse osmosis, a roll membrane, a plate membrane, a disc-tube membrane, a vibrating membrane or a combination thereof can be selected for use. Through the concentration can improve the efficiency of waste water treatment, avoid the energy waste that a large amount of evaporations caused.

In a preferred embodiment of the invention, the wastewater is wastewater obtained by performing chemical precipitation, filtration, weak acid cation exchange and ozone biological activated carbon adsorption oxidation on wastewater generated in a molecular sieve production process to remove impurities, and performing ED membrane concentration and reverse osmosis concentration on the wastewater.

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

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

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

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

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

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

According to the invention, when the wastewater treatment is started, the wastewater containing ammonium salt can be directly usedStarting up, if the ion content of the waste water containing ammonium salt meets the conditions of the invention, carrying out first evaporation, low-temperature treatment and then second evaporation 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 sulfate in the first concentrated solution is close to the precipitation concentration, then the first concentrated solution is subjected to low-temperature treatment and second evaporation to obtain a second concentrated solution, the second concentrated solution is subjected to solid-liquid separation to obtain sodium sulfate 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 chloride crystals. Of course, na may be used in the initial stage ₂ SO ₄ Or NaCl, as long as the ion content of the wastewater to be treated is adjusted SO that the wastewater to be treated satisfies SO in the wastewater to be treated in the invention ₄ ^2- 、Cl ^- The requirements are met.

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

In the following examples, the wastewater containing ammonium salt is wastewater generated in the production process of molecular sieve by chemical precipitation, filtration, weak acid cation exchange method and ozone biological activated carbon adsorption oxidation method, and then by ED membrane concentration and reverse osmosis method.

Example 1

As shown in FIG. 1, the waste water containing ammonium salt (containing NaCl 159g/L, na) ₂ SO ₄ 48g/L、NH ₄ Cl 39g/L、(NH ₄ ) ₂ SO ₄ 12g/L, pH 7) at a feed rate of 5m ³ The reaction is carried out by feeding the reaction mixture into a treatment system at a speed of/h by a first circulation pump 71, introducing a sodium hydroxide aqueous solution with a concentration of 45.16 mass% into a main pipeline fed into a first heat exchange device 31 and a fifth heat exchange device 35 (titanium alloy plate heat exchangers) to carry out primary pH value adjustment, monitoring the adjusted pH value by a first pH value measuring device 61 (pH meter) (the measured value is 7.8), feeding the ammonium salt-containing wastewater subjected to the primary pH value adjustment into the first heat exchange device 31 and the fifth heat exchange device 35 respectively, and mixing the ammonium salt-containing wastewater with a first ammonia-containing steam condensate and sodium sulfate-containing crystals and chloride crystals obtained by first evaporation and a first ammonia-containing steam condensate and the ammonium salt-containing crystals and chloride crystals obtained by first evaporation respectivelyCarrying out first heat exchange on the first concentrated solution of the sodium crystals to heat the wastewater containing ammonium salt to 102 ℃; then mixing with the second mother liquor to obtain the wastewater to be treated (containing SO) ₄ ^2- And Cl ^- In a molar ratio of 1:11.346 Then, the wastewater to be treated is sent into a pipeline of a second heat exchange device 32, a sodium hydroxide aqueous solution with the concentration of 45.16 mass percent is introduced for second pH value adjustment, the adjusted pH value is monitored by a second pH value measuring device 62 (a pH meter) (the measured value is 11), then the wastewater to be treated is sent into the second heat exchange device 32 (a titanium alloy plate type heat exchanger) to carry out first heat exchange with the recycled first ammonia-containing steam so as to heat the wastewater to be treated to 112 ℃, and then the wastewater to be treated after the two times of first heat exchange is treated at 476.5m ³ And/h, sending the mixture into a first evaporation device 2 (a falling film and forced circulation two-stage MVR evaporation crystallizer) for evaporation to obtain first ammonia-containing steam and first concentrated solution containing sodium sulfate crystals and sodium chloride crystals. Wherein, 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 4.82m ³ H is used as the reference value. The first ammonia-containing steam obtained by evaporation is compressed by the first compressor 101 (the temperature rises by 18 ℃) and then 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 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 of the concentrated solution in the first evaporation apparatus 2, part of the liquid evaporated in the first evaporation apparatus 2 is circulated to the second heat exchange apparatus 32 by the second circulation pump 72, and then enters the first evaporation apparatus 2 again to perform the first evaporation (the first reflux ratio is 95.3). The degree of the first evaporation is monitored by a mass flow meter arranged on the first evaporation device 2, and the evaporation capacity of the first evaporation is controlled to be 4.82m ³ H (corresponding to the control of the sodium sulfate concentration in the treatment solution to 0.978Y (88.9 g/L)).

And (3) carrying out low-temperature treatment on the obtained first concentrated solution containing the sodium sulfate crystals and the sodium chloride crystals in a low-temperature treatment tank 22 at the temperature of 20 ℃ for 60min to obtain a treatment solution containing the sodium chloride crystals.

The treated liquid containing sodium chloride crystals was sent to a first solid-liquid separation apparatus 91 (centrifuge) to carry out solid-liquid separation for every hourYield 7.17m ³ Contains 279.8g/L NaCl and Na ₂ SO ₄ 88.9g/L、NaOH 2.64g/L、NH ₃ 0.31g/L of first mother liquor is temporarily stored in a first mother liquor tank 53, sodium chloride solid obtained by solid-liquid separation (1190.32 kg of sodium chloride crystallization filter cake containing 15 mass% of water is obtained every hour, wherein the content of sodium sulfate is less than 3.9 mass%) is eluted by 279.8g/L of sodium chloride solution which is equal to the dry basis mass of the sodium chloride crystallization filter cake, the sodium chloride is dried in a drier, 1011.78kg of sodium chloride (the purity is 99.5 wt%) is obtained every hour, and after the washing liquid is sent into a second heat exchange device 32 through an eighth circulating pump 78, the washing liquid enters a first evaporation device 2 again for first evaporation.

The second evaporation process is carried out in a second evaporation plant 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 third heat exchange device 33 and the fourth heat exchange device 34 in sequence by the sixth circulation pump 76, and then sent to the second evaporation device 1 for second evaporation to obtain a second concentrated solution containing sodium sulfate crystals. Wherein, the evaporation conditions of the second evaporation device 1 include: the temperature is 105 ℃, the pressure is-7.02 kPa, and the evaporation capacity is 0.78m ³ H is used as the reference value. In order to increase the solid content of the concentrated solution in the second evaporation device 1, part of the first mother liquor evaporated in the second evaporation device 1 is circulated as a second circulating liquid to the fourth heat exchange device 34 through the seventh circulating pump 77, and then enters the second evaporation device 1 again for second evaporation (the second reflux ratio is 9.6). The second ammonia-containing steam obtained by evaporation is compressed by the second compressor 102 (the temperature is raised by 18 ℃) and then sequentially passes through the fourth heat exchange device 34 and the third heat exchange device 33 to exchange heat with the first mother liquor, and the second ammonia water is obtained by cooling and stored in the second ammonia water storage tank 52. The degree of the second evaporation is monitored by a mass flow meter arranged on the second evaporation device 1, and the concentration of the sodium chloride in the second evaporation concentrated solution is controlled to be 0.9935X (306.5 g/L).

Feeding the second concentrated solution containing sodium sulfate crystals into a second solid-liquid separation device 92 (centrifuge) for solid-liquid separation to obtain 6.70m per hour ³ Contains NaCl 306.5g/L and Na ₂ SO ₄ 52.5g/L、NaOH 2.89g/L、NH ₃ 0.01g/L of a second mother liquorIs stored in the second mother liquor tank 54. And (3) circulating the second mother liquor to a wastewater pipeline between the first heat exchange device 31 and the second heat exchange device 32 through a ninth circulating pump 79, and mixing the second mother liquor with the wastewater containing ammonium salt to obtain the wastewater to be treated. After solid-liquid separation, the obtained sodium sulfate solid (349.84 kg of a sodium sulfate crystal cake with a water content of 14 mass% or less, wherein the sodium chloride content is 3.9 mass% or less, obtained per hour) was washed with a sodium sulfate solution of 52.5g/L, which was equal to the dry mass of sodium sulfate, and dried in a dryer, 300.87kg of sodium sulfate (purity of 99.5 wt%) was obtained per hour, and the washing solution was circulated to the second evaporation apparatus 1 by the tenth circulation pump 80.

In addition, the tail gas discharged by 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 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 addition, the starting phase of the MVR evaporation was started by steam at a temperature of 143.3 ℃.

In this example, 4.82m of ammonia water having a concentration of 1.5 mass% was obtained per hour in the first ammonia water tank 51 ³ 0.78m of 0.28 mass% ammonia water was obtained per hour in the second ammonia water tank 52 ³ The ammonia water can be reused in the production process of the molecular sieve.

Example 2

The treatment of the ammonium salt-containing wastewater was carried out in the same manner as in example 1, except that: for NaCl containing 58g/L and Na ₂ SO ₄ 120g/L、NH ₄ Cl 19g/L、(NH ₄ ) ₂ SO ₄ Treating the ammonium salt-containing wastewater with the concentration of 40g/L and the pH value of 7.1 to obtain SO contained in the wastewater to be treated ₄ ^2- And Cl ^- In a molar ratio of 1:8.665. the temperature of the ammonium salt-containing wastewater after heat exchange through the first heat exchange device 31 and the fifth heat exchange device 35 is 97 ℃, and heat exchange is carried out through the second heat exchange device 32The temperature of the wastewater to be treated is 97.5 ℃. The evaporation conditions of the first evaporation apparatus 2 include: the temperature is 100 ℃, the pressure is-22.83 kPa, and the evaporation capacity is 3.47m ³ H is used as the reference value. The low temperature treatment temperature is 25 deg.C, and the retention time is 55min. The evaporation conditions of the second evaporation apparatus 1 include: the temperature is 95 ℃, the pressure is-36.36 kPa, and the evaporation capacity is 2.28m ³ /h。

454.10kg tons of sodium chloride crystallization filter cakes containing 14 mass percent of water are obtained by the first solid-liquid separation device 91 every hour, and 390.53kg of sodium chloride (with the purity of 99.6 weight percent) is finally obtained every hour; yield 25.59m per hour ³ The concentration of NaCl is 280.6g/L and Na ₂ SO ₄ 82.9g/L、NaOH 2.2g/L、NH ₃ 0.12g/L of the first mother liquor.

The second solid-liquid separation device 92 gave 962.68kg of a sodium sulfate crystal cake containing 15% by mass of water per hour, and finally 818.28kg of sodium sulfate (purity: 99.5% by weight) per hour to give 23.56m ³ The concentration is NaCl 303.2g/L and Na ₂ SO ₄ 55.3g/L、NaOH 2.4g/L、NH ₃ 0.005g/L of second mother liquor.

In this example, 3.47m of aqueous ammonia having a concentration of 2.2 mass% was obtained per hour in the first aqueous ammonia tank 51 ³ 2.28m of aqueous ammonia having a concentration of 0.13% by mass per hour was obtained in the second aqueous ammonia tank 52 ³ The ammonia water can be reused in the production process of the molecular sieve.

Example 3

The treatment of the ammonium salt-containing wastewater was carried out in the same manner as in example 1, except that: for the NaCl content of 80g/L and Na ₂ SO ₄ 78g/L、NH ₄ Cl 29g/L、(NH ₄ ) ₂ SO ₄ 28.7g/L of ammonium salt-containing wastewater with pH of 6.6 is treated to obtain SO contained in the wastewater to be treated ₄ ^2- And Cl ^- In a molar ratio of 1:8.745. the temperature of the wastewater containing ammonium salt after heat exchange by the first heat exchange device 31 and the fifth heat exchange device 35 is 105 ℃, and the temperature of the wastewater to be treated after heat exchange by the second heat exchange device 32 is 117 ℃. The evaporation conditions of the first evaporation device 2 include: the temperature is 110 ℃, the pressure is 11.34kPa, and the evaporation capacity is 4.26m ³ H is used as the reference value. Second steamingThe evaporation conditions of the hair apparatus 1 include: the temperature is 100 ℃, the pressure is-22.82 kPa, and the evaporation capacity is 1.40m ³ H is used as the reference value. The low temperature treatment temperature is 20 deg.C, and the retention time is 60min.

657.86kg of sodium chloride crystal filter cake containing 15 mass percent of water per hour is obtained by the first solid-liquid separation device 91, and 559.18kg of sodium chloride (with the purity of 99.4 weight percent) is finally obtained per hour; yield 13.55m per hour ³ The concentration of NaCl is 280.2g/L and Na ₂ SO ₄ 89.1g/L、NaOH 1.7g/L、NH ₃ 0.18g/L of the first mother liquor.

The second solid-liquid separation device 92 obtained 632.55kg of a sodium sulfate crystal cake with a water content of 14 mass% per hour, and finally obtained 543.99kg of sodium sulfate (purity of 99.5 wt%); yield 12.39m per hour ³ The concentration of NaCl is 306.1g/L and Na ₂ SO ₄ 53.9g/L、NaOH 1.85g/L、NH ₃ 0.0099g/L of second mother liquor.

In this example, 4.26m of ammonia water having a concentration of 1.8 mass% was obtained per hour in the first ammonia water tank 51 ³ 1.40m of ammonia water having a concentration of 0.16 mass% is obtained per hour in the second ammonia water tank 52 ³ The ammonia water can be reused in the production process of the molecular sieve.

Example 4

As shown in FIG. 2, the waste water containing ammonium salt (containing 149g/L NaCl and Na) ₂ SO ₄ 49g/L、NH ₄ Cl 45g/L、(NH ₄ ) ₂ SO ₄ 15g/L, pH 7.0) at a feed rate of 5m ³ A flow rate of 45.16 mass% sodium hydroxide aqueous solution was introduced into a pipe of the treatment system at a rate of/h, and a first pH value was adjusted by introducing 45.16 mass% sodium hydroxide aqueous solution into the pipe before the pipe was introduced into the first heat exchanger 31 or the fifth heat exchanger 35 (both of which are titanium alloy plate heat exchangers), and the mixed pH value was monitored by a first pH value measuring device 61 (pH meter) (measured value was 8), and a part (4.5 m) of ammonium salt-containing wastewater was circulated by a first circulation pump 71 (measured value was 8) ³ H) sending the waste water into a first heat exchange device 31, carrying out first heat exchange with the recovered first ammonia-containing steam condensate to heat the waste water containing ammonium salt to 103 ℃, sending the rest part into a fifth heat exchange device 35, carrying out first heat exchange with the first concentrated solution to heat the waste water containing ammonium saltHeating to 103 ℃, mixing the wastewater containing ammonium salt with the second mother liquor after converging the wastewater to obtain wastewater to be treated (containing SO) ₄ ^2- And Cl ^- In a molar ratio of 1:11.227 And then the wastewater to be treated is sent into a second heat exchange device 32 to carry out first heat exchange with the first ammonia-containing steam, so that the temperature of the wastewater to be treated is raised to 112 ℃; then, a sodium hydroxide aqueous solution with a concentration of 45.16 mass% is introduced into a pipeline for feeding the wastewater to be treated into the first evaporation device 2 to carry out second pH value adjustment, the adjusted pH value is monitored by a second pH value measuring device 62 (pH meter) (the measured value is 10.8), and the wastewater to be treated after the second pH value adjustment is fed into the first evaporation device 2 (falling film + forced circulation two-stage MVR evaporation crystallizer) to carry out evaporation, so that first ammonia-containing steam and first concentrated solution containing sodium sulfate crystals and sodium chloride crystals are obtained. The first ammonia-containing steam obtained by evaporation is compressed by the first compressor 101 (the temperature is raised by 17 ℃) and then sequentially passes through the second heat exchange device 32 and the first heat exchange device 31, and is respectively subjected to heat exchange with wastewater to be treated and wastewater containing ammonium salt, cooled to obtain first ammonia water, and the first ammonia water is stored in the first ammonia water storage tank 51. In addition, in order to increase the crystal content of the concentrated solution in the first evaporation apparatus 2, a part of the liquid evaporated in the first evaporation apparatus 2 is circulated as a 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 reflux ratio is 92.6). The degree of the first evaporation is monitored by a mass flow meter arranged on the first evaporation device 2, and the evaporation capacity of the first evaporation is controlled to be 4.69m ³ H (corresponding to the control of the sodium sulfate concentration in the treatment solution to 0.976Y (83 g/L)). Wherein, the evaporation conditions of the first evaporation device 2 are as the following table 1:

TABLE 1

And (3) carrying out low-temperature treatment on the obtained first concentrated solution containing the sodium sulfate crystals and the sodium chloride crystals in a low-temperature treatment tank 22 at the temperature of 25 ℃ for 55min to obtain a treatment solution containing the sodium chloride crystals.

The above-mentioned treatment liquid containing sodium chloride crystals was fed to a first solid-liquid separation apparatus 91 (centrifuge) to carry out a first solid-liquid separation to obtain 9.38m per hour ³ Contains NaCl 281g/L and Na ₂ SO ₄ 83g/L、NaOH 1.66g/L、NH ₃ 0.18g/L of the first mother liquor is temporarily stored in a first mother liquor tank 53, sodium chloride solids obtained by solid-liquid separation (1157.43 kg of sodium chloride crystal cake containing 14 mass% of water per hour, wherein the content of sodium sulfate is 3.6 mass% or less) are leached by 281g/L of a sodium chloride solution having the same dry basis mass as the sodium chloride crystal cake, and are dried in a dryer to obtain 995.39kg of sodium chloride (having a purity of 99.4 wt%) per hour, and the washing liquid is sent to a second heat exchange device 32 by an eighth circulating 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 1, and the second evaporation device 1 consists of a first effect evaporator 1a, a second effect evaporator 1b, a third effect evaporator 1c and a fourth effect evaporator 1d (all of forced circulation evaporators). The first mother liquor in the first mother liquor tank 53 is sequentially sent to the fourth heat exchange device 34 and the sixth heat exchange device 36 through the sixth circulation pump 76 for heat exchange, and then sequentially sent to the single-effect evaporators of the second evaporation device 1 for second evaporation to obtain a second concentrated solution containing sodium sulfate crystals, wherein the evaporation conditions are as shown in table 1 above. And introducing second ammonia-containing steam obtained by evaporation in the previous-effect evaporator into the next-effect evaporator for heat exchange to obtain condensate, further exchanging heat with the first mother liquor in a fourth heat exchange device 34 to obtain second ammonia water, exchanging heat between the second ammonia-containing steam obtained by evaporation in the fourth-effect evaporator 1d and cooling water (the ammonium salt-containing wastewater) in a third heat exchange device 33 to obtain second ammonia water, and combining the second ammonia water in a second ammonia water storage tank 52 for storage. Heating steam (namely raw steam conventionally used in the field) is introduced into the first-effect evaporator 1a, and condensate obtained after the heating steam is condensed in the first-effect evaporator 1a is introduced into the sixth heat exchange device 36, and the first mother liquor is further preheated and then used for preparing a washing solution. The degree of the first evaporation was monitored by a densitometer provided in the second evaporation apparatus 1, and the concentration of sodium chloride in the second evaporation concentrate was controlled to 0.9935X (308.1 g/L). Crystallizing the second concentrated solution obtained by evaporation in the second evaporation device 1 in a crystal liquid collecting tank 55 at the crystallization temperature of 100 ℃ for 5min to obtain crystal slurry containing sodium sulfate crystals.

The crystal slurry containing the sodium sulfate crystals is sent to a second solid-liquid separation device 92 (centrifugal machine) for solid-liquid separation, and 8.70m is obtained per hour ³ Contains NaCl 308.1g/L and Na ₂ SO ₄ 53.9g/L、NaOH 1.82g/L、NH ₃ And (3) temporarily storing 0.01g/L of second mother liquor in a second mother liquor tank 54, and circulating all the second mother liquor to a wastewater pipeline between the first heat exchange device 31 and the second heat exchange device 32 through a ninth circulating pump 79 to be mixed with the wastewater containing ammonium salt to obtain the wastewater to be treated. After solid-liquid separation, the obtained sodium sulfate solid (378.37 kg of a sodium sulfate crystal cake containing 15 mass% of water per hour, wherein the content of sodium chloride was 4.3 mass% or less) was washed with 53.9g/L of a sodium sulfate solution equivalent to the dry mass of sodium sulfate, and dried in a dryer to obtain 321.62kg of sodium sulfate (purity: 99.5 wt%) per hour, and the washing solution was circulated to the second evaporation apparatus 1 by the tenth circulation pump 80.

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 addition, the starting phase of the MVR evaporation was started by steam at a temperature of 143.3 ℃.

In this example, 4.69m of ammonia water having a concentration of 1.8 mass% was obtained per hour in the first ammonia water tank 51 ³ 0.99m of 0.17 mass% ammonia water was obtained per hour in the second ammonia water tank 52 ³ The ammonia water can be reused in the production process of the molecular sieve.

Example 5

Ammonium salt-containing waste water was conducted in accordance with the procedure of example 4Processing is carried out by the following steps: for NaCl-containing 69g/L, na ₂ SO ₄ 138g/L、NH ₄ Cl 12g/L、(NH ₄ ) ₂ SO ₄ Treating the ammonium salt-containing wastewater with 24.4g/L and pH of 7.1 to obtain SO contained in the wastewater to be treated ₄ ^2- And Cl ^- In a molar ratio of 1:9.085. the temperature of the ammonium salt-containing wastewater subjected to heat exchange by the first heat exchange device 31 and the fifth heat exchange device 35 is 104 ℃, and the temperature of the wastewater to be treated subjected to heat exchange by the second heat exchange device 32 is 114 ℃. The evaporation conditions of the first evaporation apparatus 2 and the second evaporation apparatus 1 are as follows in table 2. The low-temperature treatment temperature is 30 deg.C, and the retention time is 50min.

TABLE 2

The first solid-liquid separation device 91 obtained 475.12kg tons of sodium chloride crystal cake containing 14 mass% of water per hour, and finally obtained 408.95kg of sodium chloride (purity 99.4 wt%); yield 26.11m per hour ³ The concentration of NaCl is 283.4g/L and Na ₂ SO ₄ 79.9g/L、NaOH 2.66g/L、NH ₃ 0.077g/L of the first mother liquor.

The second solid-liquid separation device 92 obtained 968.12kg of a sodium sulfate crystal cake having a water content of 15 mass% per hour, and finally 822.91kg of sodium sulfate (purity of 99.5 wt%) per hour; obtained 24.04m per hour ³ The concentration of NaCl is 306.3g/L and Na ₂ SO ₄ 52.5g/L、NaOH 2.97g/L、NH ₃ 0.003g/L of the second mother liquor.

In this example, 3.31m of ammonia water having a concentration of 1.4 mass% was obtained per hour in the first ammonia water tank 51 ³ 2.32m of 0.08 mass% ammonia water per hour is obtained from the second ammonia water 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 106g/L and Na ₂ SO ₄ 103g/L、NH ₄ Cl 21g/L、(NH ₄ ) ₂ SO ₄ Treating the ammonium salt-containing wastewater with the concentration of 20.7g/L and the pH value of 7.2 to obtain SO contained in the wastewater to be treated ₄ ^2- And Cl ^- In a molar ratio of 1:9.189. the temperature of the wastewater containing ammonium salt after heat exchange by the first heat exchange device 31 and the fifth heat exchange device 35 is 103 ℃, and the temperature of the wastewater to be treated after heat exchange by the second heat exchange device 32 is 112 ℃. The evaporation conditions of the first evaporation apparatus 2 and the second evaporation apparatus 1 are as follows in table 3. The low temperature treatment temperature is 25 deg.C, and the retention time is 55min.

TABLE 3

The first solid-liquid separation device 91 obtained 757.97kg ton of sodium chloride crystal cake containing 15 mass% of water per hour, and finally 644.27kg of sodium chloride (purity 99.4 wt%) per hour; yield 19.57m per hour ³ The concentration of NaCl is 280.4g/L and Na ₂ SO ₄ 82.7g/L、NaOH 2.64g/L、NH ₃ 0.15g/L of the first mother liquor.

The second solid-liquid separation device 92 obtained 737.81kg of sodium sulfate crystal cake having a water content of 15 mass% per hour, and finally 627.14kg of sodium sulfate (purity of 99.5 wt%) per hour; obtained 18.09m per hour ³ The concentration is NaCl 303.2g/L and Na ₂ SO ₄ 55.1g/L、NaOH 2.85g/L、NH ₃ 0.0049g/L of a second mother liquor.

In this example, 3.86m of ammonia water having a concentration of 1.4% by mass was obtained per hour in the first ammonia water tank 51 ³ 1.76m of 0.16 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.

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 can be made, and the same should be considered as the disclosure of the present invention as long as the idea of the present invention is not violated.

Claims

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

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

wherein 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 conditions of the first evaporation include: the temperature is 60-175 ℃, and the pressure is-87 kPa-18110 kPa; the temperature of the low-temperature treatment is 15-45 ℃;

the second evaporation prevents sodium chloride crystals 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 ^- 7.15 mol or more;

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

NH in the waste water containing ammonium salt ₄ ⁺ Is more than 8mg/L, SO ₄ ^2- Is more than 1g/L, cl ^- Over 970mg/L of Na ⁺ Is more than 510 mg/L.

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

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

4. The method according to 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 concentrate comprising sodium chloride crystals further comprises sodium sulfate crystals; and when the first concentrated solution containing sodium chloride crystals also contains sodium sulfate crystals, dissolving the sodium sulfate crystals by the low-temperature treatment to obtain the treated solution containing the sodium chloride crystals.

7. The method according to claim 1, wherein the first evaporation is performed so that a concentration of sodium sulfate in the treatment solution is Y or less, where Y is a concentration of sodium sulfate at which both sodium chloride and sodium sulfate in the treatment solution are saturated under the low-temperature treatment condition.

8. The method of claim 7, wherein the first evaporation provides a sodium sulfate concentration in the treatment solution of 0.9Y to 0.99Y.

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

10. A process as claimed in claim 9, wherein the second evaporation provides a concentration of sodium chloride in the second concentrate of 0.95X to 0.999X.

11. The method of any one of claims 1-10, wherein the conditions of the first evaporation comprise: the temperature is 75-175 ℃, and the pressure is-73 kPa-653 kPa.

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

13. The method of claim 11, wherein the conditions of the first evaporation comprise: the temperature is 95-110 ℃, and the pressure is-37 kPa-12 kPa.

14. The method of any of claims 1-10, wherein the conditions of the second evaporation comprise: the temperature is above 35 ℃ and the pressure is above-95 kPa.

15. The method of claim 14, wherein the conditions of the second evaporation comprise: the temperature is 45-365 ℃, and the pressure is-95 kPa-18110 kPa.

16. The method of claim 14, wherein the conditions of the second evaporation comprise: the temperature is 60-365 ℃, and the pressure is-87 kPa-18110 kPa.

17. The method of claim 14, wherein the conditions of the second evaporation comprise: the temperature is 75-175 ℃, and the pressure is-73 kPa-653 kPa.

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

19. The method of claim 14, wherein the conditions of the second evaporation comprise: the temperature is 95-110 ℃, and the pressure is-37 kPa-12 kPa.

20. The method of any of claims 1-3, wherein the conditions of the cryogenic process comprise: the temperature is 15-35 ℃.

21. The method of claim 20, wherein the conditions of the cryogenic process comprise: the temperature is 17.9-35 ℃.

22. The method of claim 14, wherein the temperature of the second evaporation is more than 5 ℃ higher than the temperature of the low temperature treatment.

23. The method of claim 22, wherein the temperature of the second evaporation is more than 20 ℃ higher than the temperature of the low temperature treatment.

24. The method of claim 22, wherein the temperature of the second evaporation is 35 ℃ to 90 ℃ higher than the temperature of the low temperature treatment.

25. The method of any one of claims 1-10, 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 wastewater to be treated is subjected to a first evaporation.

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 10, further comprising subjecting the treatment liquid containing sodium chloride crystals to a first solid-liquid separation to obtain sodium chloride crystals.

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

32. The method according to any one of claims 1 to 10, further comprising subjecting the second concentrated solution containing sodium sulfate crystals to a second solid-liquid separation to obtain sodium sulfate crystals.

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

34. The process according to any one of claims 1 to 10, wherein the ammonium salt-containing wastewater is wastewater from a molecular sieve, alumina or refinery catalyst production process.

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