CN108726610B

CN108726610B - Method for treating waste water containing ammonium salt

Info

Publication number: CN108726610B
Application number: CN201710265654.0A
Authority: CN
Inventors: 殷喜平; 李叶; 顾松园; 王涛; 高晋爱; 杨凌; 苑志伟; 刘夫足; 陈玉华
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: CN108726610A

Abstract

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

Description

Method for treating waste water containing ammonium salt

Technical Field

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

Background

In the production process of the oil refining catalyst, a large amount of inorganic acid-base salts such as sodium hydroxide, hydrochloric acid, sulfuric acid, ammonium salts, sulfates, hydrochlorides and the like are needed, and a large amount of mixed sewage containing ammonium, sodium sulfate, sodium chloride and aluminosilicate is generated. For such sewage, the common practice in the prior art is that the pH value is adjusted to be within the range of 6-9, most of suspended matters are removed, then the biochemical method, the blow-off method or the steam stripping method is adopted to remove ammonium ions, then the salt-containing sewage is subjected to pH value adjustment, most of suspended matters are removed, hardness, silicon and part of organic matters are removed, most of organic matters are removed through ozone biological activated carbon adsorption oxidation or other advanced oxidation methods, then the salt-containing sewage enters an ion exchange device for further hardness removal, enters an enrichment device (such as reverse osmosis or electrodialysis) for concentration, and then MVR evaporative crystallization or multiple-effect evaporative crystallization is adopted to obtain mixed miscellaneous salt of sodium sulfate and sodium chloride containing a small amount of ammonium salt; or is; firstly, adjusting the pH value to be within the range of 6.5-7.5, removing most suspended matters, then removing hardness, silicon and part of organic matters, removing most organic matters through ozone biological activated carbon adsorption oxidation or other advanced oxidation methods, then entering an ion exchange device for further removing hardness, entering a thickening device (such as reverse osmosis and/or electrodialysis) for concentration, and then adopting MVR (mechanical vapor recompression) evaporative crystallization or multiple-effect evaporative crystallization to obtain the mixed salt of sodium sulfate and sodium chloride containing ammonium salt. However, these ammonium-containing mixed salts are currently difficult 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 from wastewater by gas stripping deamination, a large amount of alkali is needed to adjust the pH value, the alkali consumption is high, the alkali in the wastewater after deamination cannot be recovered, the pH value of the treated wastewater is high, the treatment cost is high, the COD content in the catalyst wastewater after gas stripping does not change greatly, the salt content in the wastewater is not reduced (20-30 g/L), the wastewater cannot be directly discharged, further desalting treatment is needed, the operation cost of wastewater treatment is high, a large amount of alkali remains in the treated wastewater, the pH value is high, the waste is large, and the treatment cost is up to 50 yuan/ton.

Disclosure of Invention

The invention aims to overcome the defect of NH content in the prior art ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ The wastewater treatment cost is high, and only mixed salt crystals can be obtained, thereby providing a low-cost and environment-friendly NH-containing catalyst ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ The method for treating wastewater can respectively recover ammonium, sodium sulfate and sodium chloride in the wastewater, and furthest recycle resources in the wastewater.

In order to achieve the above object, the present invention provides a method for treating ammonium salt-containing wastewater containing NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ The method comprises the following steps of,

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

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

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

4) Carrying out second solid-liquid separation on the treatment liquid containing the sodium chloride crystals;

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

By the technical scheme, the method aims at the content of NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ The wastewater is obtained by regulating the pH value of the wastewater to be treated to a specific range in advance and then carrying out first evaporation separation to obtain sodium sulfate crystals and relatively concentrated sodium sulfate crystalsAmmonia water, then concentrated solution containing sodium chloride crystals or sodium chloride crystals and sodium sulfate crystals and thinner ammonia water are obtained by secondary evaporation, finally, the sodium sulfate in the concentrated solution is dissolved by low-temperature treatment, and sodium chloride is further crystallized and separated out to obtain sodium chloride crystals. The method can respectively obtain high-purity sodium sulfate and sodium chloride, avoids the difficulty in the processes of mixed salt treatment and recycling, simultaneously completes the process of separating ammonia and salt, simultaneously heats the wastewater and cools the ammonia-containing steam by adopting a heat exchange mode without a condenser, reasonably utilizes the heat in the evaporation process, saves energy, reduces the wastewater treatment cost, recovers the ammonium in the wastewater in the form of ammonia water, recovers the sodium chloride and the sodium sulfate in the form of crystals respectively, does not generate waste residues and waste liquid in the whole process, and achieves the purpose of changing waste into valuable.

Furthermore, the method enables the second evaporation to be carried out at a higher temperature through the matching of the second evaporation and the low-temperature treatment, so that the content of solids in the second evaporation concentrated solution and the evaporation efficiency are improved, and meanwhile, 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

31. First heat exchanger 74 and fourth circulating pump

32. Second heat exchange device 76 and sixth circulation pump

33. Third heat exchanger 77, seventh circulating pump

34. Fourth heat exchange device 78 and eighth circulating pump

35. Fifth heat exchange device 79 and ninth circulating pump

51. First ammonia water storage tank 80 and tenth circulating pump

52. Second ammonia storage tank 81, vacuum pump

53. First mother liquor tank 82 and circulating water tank

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

55. Low-temperature treatment tank 91 and first solid-liquid separation device

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

61. First pH value measuring device 101 and first compressor

62. Second pH value measuring device 102 and second compressor

71. First circulating pump

Detailed Description

The following describes the embodiments of the present invention in detail. 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 waste water containing ammonium salt, wherein the waste water 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 concentrated solution containing ammonia vapor and sodium sulfate crystals, wherein the wastewater to be treated contains the wastewater containing ammonium salt;

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

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

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

Preferably, the pH of the wastewater to be treated is adjusted to be greater than 10.8 before the wastewater to be treated is subjected to the first evaporation. The upper limit of the pH of the wastewater to be treated is not limited, and may be, for example, 14 or less, preferably 13.5 or less, and more preferably 13 or less.

The method provided by the invention can be used for the treatment of the compounds containing NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ Is treated except for containing NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ In addition, 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 per mole ₄ ^2- Cl contained in the wastewater to be treated ^- Is 13.8 moles or less, more preferably 13.75 moles or less, further preferably 13.5 moles or less, further preferably 13 moles or less, further preferably 12 moles or less, further preferably 11 moles or less, further preferably 10.5 moles or less, preferably 2 moles or more, more preferably 2.5 moles or more, further preferably 3 moles or more, and for example, may be 1 to 10 moles, preferably 2 to 8 moles. By reacting SO ₄ ^2- And Cl ^- The molar ratio of sodium sulfate in the first evaporation is controlled within the above range, so that sodium sulfate is precipitated without precipitating sodium chloride, and the purpose of efficiently separating sodium sulfate is achieved. In addition, as described above and below, it is also possible in the present invention to recycle the second mother liquor obtained in the second evaporation process to the first evaporation, and thereby to treat SO in the wastewater to be treated ₄ ^2- And Cl ^- The molar ratio of (a) to (b) is adjusted and the balance of sodium hydroxide can be maintained.

In the present invention, the 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 present invention, the first evaporation to prevent the crystallization of sodium chloride means that the concentration of sodium chloride in the mixed system is controlled not to exceed the solubility under the first evaporation conditions (including but not limited to temperature, pH value, etc.), and sodium chloride carried by sodium sulfate crystals or adsorbed on the surface is not excluded. Since the water content of the crystals after the solid-liquid separation is different, the sodium chloride content in the obtained sodium sulfate crystals is usually 8 mass% or less (preferably 4 mass%), 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, the second evaporation is preferably performed to precipitate sodium chloride crystals, and in view of improving the treatment efficiency, the second evaporation is preferably performed to precipitate both sodium chloride crystals and sodium sulfate crystals to obtain a second concentrated solution containing sodium sulfate crystals and sodium chloride crystals. In the case of obtaining a second concentrated solution containing sodium sulfate crystals and sodium chloride crystals, the second evaporation requires that the sodium sulfate crystals are dissolved in a low-temperature treatment, and in particular, the second evaporation requires that the second concentrated solution containing sodium sulfate crystals and sodium chloride crystals is obtained, and the sodium sulfate crystals in the second concentrated solution can be completely dissolved in the low-temperature treatment. And (3) controlling the evaporation amount of the second evaporation to simultaneously crystallize and separate out sodium sulfate and sodium chloride (namely, the second evaporation obtains a second concentrated solution containing sodium sulfate crystals and sodium chloride crystals), dissolving the sodium sulfate crystals in the second 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.

With respect to the treatment liquid containing sodium chloride crystals, sodium sulfate entrained by or adsorbed on the surface of sodium chloride crystals is not excluded. Since the water content of the crystals after solid-liquid separation is different, the sodium sulfate content of the obtained sodium chloride crystals 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 of the obtained sodium chloride crystals is 8 mass% or less.

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

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

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

As each effect evaporator in the single-effect evaporator or the multi-effect evaporator, for example, one or more selected from falling film evaporators, rising film evaporators, wiped film evaporators, central circulation tube evaporators, basket-suspended evaporators, external heat evaporators, forced circulation evaporators and lien evaporators can be used. Among them, a forced circulation evaporator and an external heating evaporator are preferable. The evaporator is composed of a heating chamber and an evaporation chamber, and may further include other evaporation auxiliary components as necessary, such as a demister for further separating liquid foam, a condenser for condensing all secondary steam, and a vacuum device for pressure reduction. 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 carried out using a multi-effect evaporation apparatus, the feeding manner of the liquid to be evaporated may be the same or different, and a concurrent flow, a counter flow or an advection manner conventionally used in the art may be employed. The forward flow is specifically as follows: and sequentially introducing liquid to be evaporated into each effect evaporator of the multi-effect evaporation device, and introducing ammonia-containing steam obtained by evaporation of the former effect evaporator of the multi-effect evaporation device into the latter effect evaporator. The countercurrent is specifically: and sequentially introducing liquid to be evaporated into each effect evaporator of the multi-effect evaporation device, and introducing ammonia-containing steam obtained by evaporation of the latter effect evaporator of the multi-effect evaporation device into the former effect evaporator. The advection specifically comprises the following steps: and independently introducing liquid to be evaporated into each effect evaporator of the multi-effect evaporation device, and introducing ammonia-containing steam obtained by evaporation of the former effect evaporator of the multi-effect evaporation device into the latter effect evaporator. Among them, concurrent feeding is preferred. When concurrent or countercurrent feeding is adopted, the evaporation condition refers to the evaporation condition of the last evaporator of the multi-effect evaporation device; when advection feeding is adopted, the evaporation conditions 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.

According to a preferred embodiment of the present invention, as shown in fig. 1, said first evaporation is carried out in a first evaporation device 2, said first evaporation device 2 being an MVR evaporation device, preferably a falling film + forced circulation two-stage MVR evaporation crystallizer.

According to a preferred embodiment of the present invention, as shown in fig. 2, the first evaporation is performed in a first evaporation apparatus 2, and the first evaporation apparatus 2 is a multi-effect evaporation apparatus, and is composed of a first effect evaporator 2a, a second effect evaporator 2b, a third effect evaporator 2c, and a fourth effect evaporator 2 d. And (3) sequentially introducing the wastewater to be treated into a first effect evaporator 2a, a second effect evaporator 2b, a third effect evaporator 2c and a fourth effect evaporator 2d of the first evaporation device 2 for evaporation to obtain a first concentrated solution containing sodium sulfate crystals. And introducing first ammonia-containing steam obtained by evaporation in the former evaporator of the first evaporation device 2 into the latter evaporator for heat exchange to obtain first ammonia water. More preferably, the first ammonia water and the wastewater to be treated are subjected to first heat exchange in the first heat exchange device 31, so that the energy is fully utilized. Heating steam (namely raw steam conventionally used in the field) is introduced into the first-effect evaporator 2a, the heating steam is condensed in the first-effect evaporator 2a to obtain a condensate, and the condensate is used for preparing a sodium sulfate washing solution after being used for preheating the wastewater to be treated entering the first evaporation device 2.

In the present invention, the conditions of the first evaporation may be appropriately selected as necessary, and the purpose of crystallizing sodium sulfate without precipitating sodium chloride may be achieved. The conditions of the first evaporation include: the temperature is above 35 ℃ and the pressure is above-95 kPa; from the viewpoint of improving the efficiency of evaporation, reducing the cost of equipment, and energy consumption, it is preferable that the conditions of the first evaporation include: the temperature is 45-365 ℃, and the pressure is-95 kPa-18110 kPa; preferably, the conditions of the first evaporation include: the temperature is 60 ℃ to 365 ℃, and the pressure is-87 kPa to 18110kPa; 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 95-105 ℃, and the pressure is-37 kPa to-7 kPa.

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

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

By carrying out the first evaporation under the above conditions, the sodium 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 invention, by controlling the conditions of the first evaporation, more than 90 mass percent (preferably more than 95 mass percent) of ammonia contained in the wastewater to be treated can be evaporated, so as to obtain the first ammonia water with higher concentration, and the first ammonia water can be directly reused in the production process of the catalyst, or neutralized by acid to obtain ammonium salt for reuse, or mixed with water and corresponding ammonium salt or ammonia water for use. When the multi-effect evaporation device is used for first evaporation, in order to obtain stronger ammonia water, the first ammonia-containing steam condensate obtained in the first effect evaporator and/or the second effect evaporator can be collected independently, namely, the ammonia-containing steam condensate obtained in the second effect evaporator and/or the third effect evaporator can be collected. The first ammonia water can be collected independently or in a converging way according to the requirement. In order to control the concentration of ammonia, the evaporation conditions of the individual evaporator effects can be appropriately adjusted.

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

In the present invention, the degree of progress of the first evaporation is performed by monitoring the concentration of the first evaporation-derived liquid, specifically, by controlling the concentration of the first evaporation-derived liquid within the above range, so that the first evaporation does not cause crystallization of sodium chloride in the wastewater to be treated. The concentration of the liquid resulting from the first evaporation is monitored by measuring the density, which may be carried out using a densitometer.

According to a preferred embodiment of the present invention, before the wastewater to be treated is subjected to the first evaporation, the wastewater to be treated is subjected to the first heat exchange with the first ammonia-containing vapor or the first aqueous ammonia (the first ammonia-containing vapor condensate) obtained from the first evaporation apparatus. 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 heat exchanges may be one or more, preferably 2 to 4, more preferably 2 to 3. Through the heat exchange, the output ammonia water is further 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 third heat exchange device 33, a fifth heat exchange device 35 and a second heat exchange device 32, specifically, the first ammonia-containing steam is sequentially passed through the second heat exchange device 32 and the first heat exchange device 31, the second ammonia-containing steam condensate is passed through the third heat exchange device 33, the second concentrated solution containing sodium chloride crystals is passed through the fifth heat exchange device 35, and the wastewater to be treated is simultaneously passed through one or more of the first heat exchange device 31, the third heat exchange device 33 and the fifth heat exchange device 35 and then passed through the second heat exchange device 32 to perform the second first heat exchange with the first ammonia-containing steam.

According to a preferred embodiment of the present invention, as shown in fig. 2, the first heat exchange is performed by a first heat exchange device 31, a third heat exchange device 33 and a fifth heat exchange device 35, specifically, the first ammonia-containing vapor condensate is passed through the first heat exchange device 31, the second ammonia-containing vapor condensate (second ammonia water with higher temperature) obtained by the second evaporation device 1 is passed through the third heat exchange device 33, and a part of the concentrated solution obtained by the second evaporation device 1 is passed through the fifth heat exchange device 35; one part of the wastewater to be treated passes through a first heat exchange device 31, the other part of the wastewater passes through a third heat exchange device 33, and the rest part of the wastewater passes through a fifth heat exchange device 35; and then combining the three parts of wastewater to be treated.

By the first heat exchange, the temperature of the wastewater to be treated is raised for evaporation, and the first ammonia-containing steam is cooled to obtain first ammonia water which can be stored in a first ammonia water storage tank 51; simultaneously cooling the second ammonia-containing steam condensate to obtain second ammonia water, wherein the second ammonia water can be stored in a second ammonia water storage tank 52; and simultaneously, the second concentrated solution is cooled to facilitate low-temperature treatment.

According to a preferred embodiment of the present invention, as shown in fig. 2, the first ammonia-containing vapor evaporated by the last evaporator (fourth evaporator 2 d) of the first evaporation apparatus 2 exchanges heat with the cold medium in the second heat exchange apparatus 32 to obtain ammonia water, and is stored in the first ammonia water storage tank 51. The cooling medium can be cooling water, glycol aqueous solution, etc. When the conventional cooling water is used, the cooling water is recycled, and when the ammonium salt-containing wastewater is used as the cooling water, the ammonium salt-containing wastewater after heat exchange is preferably directly returned to the treatment process (for example, returned to the first pH value adjustment process).

In the present invention, the first heat exchange device 31, the second heat exchange device 32, the third heat exchange device 33 and the fifth heat exchange device 35 are not particularly limited, and various heat exchangers conventionally used in the art may be used to achieve the first heat exchange with the wastewater to be treated. Specifically, a jacketed heat exchanger, a plate heat exchanger, a shell-and-tube heat exchanger, or the like may be mentioned, with the plate heat exchanger being preferred. The material of the heat exchanger can be specifically selected according to the needs, for example, in order to resist the corrosion of chloride ions, the heat exchanger of duplex stainless steel, titanium and titanium alloy, hastelloy can be selected as the material, and the heat exchanger containing plastic material can be selected when the temperature is lower.

According to the present invention, in order to fully utilize the heat energy of the first ammonia-containing steam, it is preferable that the temperature of the wastewater to be treated after the first heat exchange is 50 to 370 ℃, more preferably 72 to 182 ℃, still more preferably 85 to 137 ℃, and still more preferably 102 to 112 ℃.

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

The manner of adding the basic substance may be any manner known in the art, but it is preferable to mix the basic substance with the wastewater to be treated in the form of an aqueous solution, and for example, an aqueous solution containing the basic substance may be introduced into a pipe through which the wastewater to be treated is introduced and mixed. The content of the alkaline substance in the aqueous solution is not particularly limited as long as the above-mentioned purpose of adjusting the pH value can be achieved. However, in order to reduce the amount of water used and further reduce the cost, it is preferable to use a saturated aqueous solution of an alkaline substance. 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 through which the wastewater to be treated is fed to the first heat exchange apparatus 31, the third heat exchange apparatus 33, or the fifth heat exchange apparatus 35, before the wastewater to be treated is fed to the first heat exchange apparatus 31, the third heat exchange apparatus 33, or the fifth heat exchange apparatus 35 for the first heat exchange; then the wastewater to be treated is sent to a second heat exchange device 32 for first heat exchange, and the aqueous solution containing the alkaline substance is introduced and mixed in a pipeline for sending the wastewater to be treated to the second heat exchange device 32 for second pH value adjustment.

According to a preferred embodiment of the present invention, as shown in fig. 2, the first evaporation process is performed in the first evaporation device 2, and the first pH adjustment is performed by introducing and mixing an aqueous solution containing an alkaline substance into the main pipe for feeding the wastewater to be treated into the first heat exchange device 31, the third heat exchange device 33, or the fifth heat exchange device 35 before feeding the wastewater to be treated into the first heat exchange device 31, the third heat exchange device 33, or the fifth heat exchange device 35 for the first heat exchange; then, the second pH adjustment is performed by introducing an aqueous solution containing an alkaline substance into the pipe for feeding the wastewater to be treated into the first evaporation apparatus 2 and mixing.

The pH of the waste water to be treated is greater than 9, preferably greater than 10.8, before it is passed into the first evaporator 2, by two pH 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 of the wastewater to be treated 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 main pipe for feeding the wastewater to be treated into the first heat exchanging device 31 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 first evaporating device 2 to measure the pH value after the second pH adjustment.

According to the invention, the method can also comprise crystallizing the first concentrated solution containing sodium sulfate crystals in a crystallizing device to obtain crystal slurry containing sodium sulfate crystals. In this case, the evaporation conditions for the first evaporation need only be satisfied for the purpose of crystallizing sodium sulfate in the crystallization device without precipitating sodium chloride. 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 56. 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 first concentrated solution containing sodium sulfate crystals can also be carried out in a first evaporator device (e.g. a forced circulation evaporator crystallizer) having a crystallizer, wherein the crystallization temperature is the corresponding first evaporation temperature. In the present invention, the temperature of crystallization is preferably the same as the temperature of the first evaporation.

According to the present invention, when the crystallization is performed using a separate crystallization apparatus, it is further necessary to ensure that the first evaporation does not cause the sodium chloride to crystallize (i.e., sodium chloride does not reach supersaturation), and preferably, the first evaporation causes the concentration of sodium chloride in the first concentrated solution to be X or less (preferably 0.999X or less, more preferably 0.95X to 0.999X, and still more preferably 0.99X to 0.9967X), where X is the concentration of sodium chloride when both sodium chloride and sodium sulfate in the first concentrated solution reach saturation under the conditions of the crystallization.

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

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

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 device and a solid-liquid separation device which are conventional in the art, or may be carried out on a staged solid-liquid separation device such as a belt filter. Preferably, the first wash comprises panning and/or rinsing. The above-mentioned elutriation and rinsing are not particularly limited and may be carried out by a method conventional in the art. The number of elutriation and rinsing is not particularly limited, and may be 1 or more, and is preferably 2 to 4 times in order to obtain sodium sulfate crystals of higher purity. In the elutriation process, the waste water containing ammonium salt is generally not recycled when used as an elutriation liquid, and the washing liquid recovered by the first washing can be recycled in a counter-current manner when used as the elutriation liquid. Before the elutriation, it is preferable to perform a preliminary solid-liquid separation by sedimentation to obtain a slurry containing sodium sulfate crystals (the liquid content may be 35% by mass or less, and this step is preferably performed in an apparatus known in the art such as a sedimentation tank or a sedimentation tank). In the elutriation process, the liquid used for elutriation is 1 to 20 parts by weight relative to 1 part by weight of the slurry containing sodium sulfate crystals. 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, the sodium sulfate crystals may be washed with a liquid obtained by rinsing, preferably with water or a sodium sulfate solution. It is preferable that the liquid generated by the washing is returned to the first evaporation apparatus 2 before the completion of the pH adjustment, for example, returned to the second pH adjustment process by the eighth circulation pump 78.

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

In the present invention, the evaporation conditions of the second evaporation may be appropriately selected as needed so that sodium sulfate crystals are not present in the treatment solution. The conditions of the second evaporation may include: the temperature is above 35 ℃ and the pressure is above-95 kPa; from the viewpoint of improving evaporation efficiency, reducing equipment cost and energy consumption, it is preferable that the conditions of the second evaporation include: the temperature is 45-175 ℃, and the pressure is-95 kPa-18110 kPa; preferably, the conditions of the second evaporation include: the temperature is 60-175 ℃, and the pressure is-87 kPa-18110 kPa; preferably, the conditions of the second evaporation include: the temperature is 75-175 ℃, and the pressure is-73 kPa-653 kPa; preferably, the conditions of the second evaporation include: the temperature is 80-130 ℃, and the pressure is-66 kPa-117 kPa; 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 100-110 ℃, and the pressure is-23 kPa-12 kPa

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

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

According to the present invention, the second evaporation is performed so as to crystallize and precipitate sodium chloride in the liquid phase obtained by the first solid-liquid separation, and preferably, sodium chloride and sodium sulfate in the liquid phase obtained by the first solid-liquid separation are simultaneously crystallized and precipitated, and a treatment solution containing sodium chloride crystals with higher purity is obtained by low-temperature treatment. Preferably, the second 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, and more preferably 0.95Y to 0.98Y), where Y is the concentration of sodium sulfate at which both sodium sulfate and sodium chloride in the treatment solution are saturated under the low-temperature treatment conditions. By controlling the degree of the second evaporation within the above range, it is possible to crystallize sodium chloride as much as possible while ensuring that the precipitated sodium sulfate can be completely dissolved under low-temperature treatment conditions. By crystallizing sodium chloride in the second evaporation as much as possible, the wastewater treatment efficiency can be improved, and the energy waste can be reduced.

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

By allowing the second evaporation to proceed under the above conditions, the efficiency of evaporation can be improved and the energy consumption can be reduced. The method ensures that the sodium sulfate crystals are completely dissolved after the 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 a preferred embodiment of the present invention, the second evaporation process is performed in a second evaporation device 1, and the first mother liquor is introduced into the second evaporation device 1 through a sixth circulation pump 76 to perform a second evaporation, so as to obtain a second ammonia-containing vapor and a second concentrated solution containing sodium chloride crystals.

According to the present invention, the low-temperature treatment may be performed at a temperature controlled to a suitable level so as to dissolve the sodium sulfate crystals in the second concentrated solution containing sodium chloride crystals obtained by the second evaporation. Preferably, the temperature of the low-temperature treatment is lower than that of the second evaporation, and specifically, the conditions of the low-temperature treatment may include: the temperature is 13 ℃ to 100 ℃, preferably 15 ℃ to 45 ℃, more preferably 15 ℃ to 35 ℃, further preferably 17.9 ℃ to 35 ℃, and further preferably 20 ℃ to 30 ℃; 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 may be 10min to 600min, preferably 20min to 300min, preferably 50min to 70min, and more preferably 55min to 65min.

In the invention, the conditions of the second evaporation and the low-temperature treatment are controlled, so that the second evaporation can be carried out at a higher evaporation temperature and an evaporation pressure closer to the normal pressure, 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 improved. 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 by using various temperature reduction devices conventionally used in the art, and for example, the low-temperature treatment tank 55 may be selected. Preferably, a cooling part, specifically, a part for introducing cooling water, may be provided in the low temperature treatment tank 55. The second concentrated solution in the low-temperature treatment tank can be rapidly cooled by the cooling part. Preferably, the low-temperature treatment tank 55 may be provided with an agitation member, and the solid-liquid phase distribution and the temperature distribution in the second concentrated solution can be made uniform by the agitation member, so that the sodium sulfate crystals can be sufficiently dissolved, and the sodium chloride crystals can be precipitated to the maximum extent.

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

According to a preferred embodiment of the present invention, as shown in fig. 2, the second ammonia-containing vapor evaporated by the second evaporator 1 undergoes second heat exchange with the first mother liquor (or a mixed solution of the first mother liquor, the circulating liquid, and the second rinse liquid) in the fourth heat exchanger 34 to obtain second ammonia water. According to the present invention, the temperature of the first mother liquor (or the mixed solution of the first mother liquor, the circulating solution, and the second rinse solution) after the second heat exchange is 35 ℃ or higher, more preferably 50 to 200 ℃, still more preferably 75 to 184 ℃, and still more preferably 102 to 117 ℃.

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

In the present invention, the sodium chloride crystal-containing treatment liquid obtained by the low-temperature treatment is subjected to a second solid-liquid separation to obtain sodium chloride 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, for example, one or more of centrifugation, filtration, and sedimentation.

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.). After the second solid-liquid separation, the second mother liquor obtained by the second solid-liquid separation device 92 is temporarily stored in the second mother liquor tank 54, and may return to the first evaporation device 2 to perform the first evaporation again, and specifically, the second mother liquor may return to the waste water containing ammonium salt before the first pH adjustment or before the second pH adjustment by the ninth circulation pump 79 to be mixed with the waste water containing ammonium salt, so as to obtain the waste water to be treated. In addition, it is difficult to avoid that the obtained sodium chloride crystals adsorb certain impurities such as sulfate ions, free ammonia, hydroxide ions, etc., and in order to remove the adsorbed impurities, reduce the odor of solid salts, reduce corrosiveness, and improve the purity of the crystals, it is preferable that the sodium chloride crystals are subjected to secondary washing with water, the ammonium salt-containing wastewater, or a sodium chloride solution and dried. In order to avoid dissolution of the sodium chloride crystals during washing, preferably the sodium chloride crystals are washed with an aqueous solution of sodium chloride. More preferably, the concentration of the sodium chloride aqueous solution is preferably the concentration of sodium chloride in the aqueous solution at which sodium chloride and sodium sulfate reach saturation simultaneously at the temperature corresponding to the sodium chloride crystals to be washed.

The form of the second solid-liquid separation and the second washing is not particularly limited, and may be carried out, for example, by using a combination of an elutriation apparatus and a solid-liquid separation apparatus which are conventional in the art, or may be carried out on a staged solid-liquid separation apparatus such as a belt filter. Preferably, the second wash comprises panning and/or rinsing. The above-mentioned elutriation and rinsing are not particularly limited and may be carried out by a method conventional in the art. The number of elutriation and rinsing is not particularly limited, and may be 1 or more, and 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 second washing can be recycled in a counter-current manner when used as an elutriation liquid. Before the elutriation, a slurry containing sodium chloride crystals is preferably obtained by preliminary solid-liquid separation by sedimentation (the liquid content may be 35% by mass or less, and this step is preferably performed in an apparatus known in the art, such as a sedimentation tank or a sedimentation tank). In the elutriation process, 1 to 20 parts by weight of a liquid is used for elutriation per 1 part by weight of a slurry containing sodium chloride crystals. The rinsing is preferably carried out using an aqueous sodium chloride solution, the concentration of which is preferably the concentration of sodium chloride in an aqueous solution in which sodium chloride and sodium sulfate are simultaneously saturated at the temperature corresponding to the sodium chloride crystals to be rinsed. In order to further enhance the elutriation effect and obtain sodium chloride crystals with higher purity, it is preferable to wash the sodium chloride crystals with the liquid obtained by rinsing. For the liquid generated by washing, preferably, the elutriation liquid of the ammonium salt-containing wastewater is returned to the second evaporation device for second evaporation before being returned to the first evaporation device for second pH adjustment, for example, as shown in fig. 2, and is returned to the second evaporation device 1 by the tenth circulation pump 80.

According to a preferred embodiment of the present invention, after the treatment solution containing sodium chloride crystals obtained by low-temperature treatment is subjected to preliminary solid-liquid separation by sedimentation, the treatment solution is subjected to first elutriation in an elutriation tank using the ammonium salt-containing wastewater, then subjected to second elutriation in another elutriation tank using a liquid obtained by subsequent washing of sodium chloride crystals, and finally the slurry subjected to the two elutriations is sent to a second solid-liquid separation apparatus for solid-liquid separation, the crystals obtained by the solid-liquid separation are subjected to elution with an aqueous sodium chloride solution (the concentration of the aqueous sodium chloride solution is the concentration of sodium chloride in an aqueous solution in which sodium chloride and sodium sulfate are both saturated at a temperature corresponding to the sodium chloride crystals to be washed), and the eluted liquid is returned to the second elutriation as an elutriation solution. Through the washing process combining elutriation and leaching, the purity of the obtained sodium chloride crystal is improved, washing liquid cannot be introduced too much, and the efficiency of wastewater treatment is improved.

In the present invention, when the first evaporation and/or the second evaporation is performed by using the MVR evaporation apparatus, in order to increase the solid content in the MVR evaporation apparatus and reduce the ammonia content in the liquid, it is preferable that a part of the liquid (i.e., the liquid located inside the MVR evaporation apparatus, hereinafter also referred to as a circulation liquid) evaporated by the MVR evaporation apparatus is heated and then returned to the MVR evaporation apparatus for evaporation. As a ratio of returning a part of the liquid after evaporation by the MVR evaporation device to the MVR evaporation device, there is no particular limitation, and for example, the first reflux ratio of the first evaporation may be 10 to 200, preferably 40 to 100, 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 plant, the process further comprises compressing the first ammonia-containing vapor and/or the second ammonia-containing vapor. The compression may be performed by compressors, such as the first compressor 101 and the second compressor 102. The ammonia-containing steam is compressed, energy is input into the MVR evaporation system, the continuous process of waste water heating, evaporation and cooling is guaranteed, the starting steam needs to be input when the MVR evaporation process is started, the energy is supplied only through the compressor after the continuous operation state is achieved, and other energy does not need to be input any more. 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 remained after the second ammonia-containing steam is condensed through the second heat exchange after ammonia removal. The first ammonia-containing steam is tail gas discharged from the second heat exchange device 32 after being condensed by the first heat exchange, and the second ammonia-containing steam is tail gas discharged from the fourth heat exchange device 34 after being condensed by the second heat exchange. The ammonia in the tail gas is removed, so that the pollutant content in the discharged tail gas can be further reduced, and the tail gas can be directly discharged.

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

In the present invention, the ammonium salt-containing wastewater is not particularly limited as long as it contains NH ₄ ⁺ 、SO ₄ ^2- 、Cl ^- And Na ⁺ The wastewater is obtained. In addition, the method is particularly suitable for treating high-salinity wastewater. The ammonium salt-containing wastewater of the present invention may be specifically wastewater from a process for producing a molecular sieve, alumina or an oil refining catalyst, or wastewater from a process for producing a molecular sieve, alumina or an oil refining catalyst, which is subjected to the following impurity removal and concentration. It is preferably a wastewater obtained by subjecting a wastewater from a molecular sieve, alumina or oil refining catalyst production process to impurity removal and concentration as described below.

As NH in said ammonium salt-containing wastewater ₄ ⁺ May be 8mg/L or more, preferably 300mg/L or more.

As Na in said ammonium salt-containing wastewater ⁺ May be 510mg/L or more, preferably 1g/L or more, more preferably 2g/L or more, further preferably 4g/L or more, further preferably 8g/L or more, further preferably 16g/L or more, further preferably 32g/L or more, further preferably 40g/L or more, further preferably 50g/L or more, further preferably 60g/L or more.

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

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

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

From the viewpoint of improving the efficiency of the first evaporation and reducing the energy consumption in the treatment process, relative to SO contained in the wastewater containing ammonium salt ₄ ^2- Cl in waste water containing ammonium salt ^- The lower the content, the better, for example, relative to 1 mole of SO contained in the ammonium salt-containing wastewater ₄ ^2- Cl contained in the ammonium salt-containing wastewater ^- Is 30 mol or less, preferably 20 mol or less, more preferably 15 mol or less, and still more preferably 10 mol or less. From the viewpoint of practicality, the amount of SO contained in the ammonium salt-containing wastewater is 1 mol ₄ ^2- Cl contained in the ammonium salt-containing wastewater ^- Preferably 0.1 mol or more, more preferably 0.5 mol or more, further preferably 1 mol or more, for example, 0.5 to 10 mol, preferably 1 to 9 mol. By adding SO contained in the ammonium salt-containing wastewater ₄ ^2- And Cl ^- The molar ratio of (b) is limited to the above range, most of the water can be distilled out in the first evaporation, the amount of the circulating liquid in the treatment system is reduced, the energy is saved, and the treatment process is more economical.

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

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

In the present invention, the pH of the ammonium salt-containing wastewater is preferably 4 to 8, for example, 6 to 7.

In addition, since COD of the waste water containing ammonium salt 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 waste water containing ammonium salt has less COD (preferably 20mg/L or less, more preferably 10mg/L or less), and is preferably removed by oxidation at the time of pretreatment, and specifically, it may be carried out by, for example, a biological method, an advanced oxidation method, etc., and it is preferable to oxidize by an oxidizing agent such as Fenton's 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. Aiming at suspended matters, a solid-liquid separation method can be selected for removing impurities; for inorganic matters and organic matters, chemical precipitation, ion exchange and adsorption methods can be selected for removing impurities, such as weak acid cation exchange, activated carbon adsorption and the like; for organic matters, impurities can be removed by adopting an adsorption and/or oxidation mode, wherein an ozone biological activated carbon adsorption oxidation method is preferred. According to a preferred embodiment of the invention, the ammonium salt-containing wastewater is subjected to impurity removal by sequentially carrying out filtration, a weak acid cation exchange method and an ozone biological activated carbon adsorption oxidation method. Through the impurity removal process, most suspended matters, hardness, silicon and organic matters can be removed, the scaling risk of the device is reduced, and the continuous and stable operation of the wastewater treatment process is ensured.

In the present invention, the 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 one-way electrodialysis system or a reversed electrodialysis system can be selected for carrying out; as the reverse osmosis, a roll membrane, a plate membrane, a disc-tube membrane, a vibrating membrane or a combination thereof can be selected for use. Through the concentration, the efficiency of wastewater treatment can be improved, and energy waste caused by a large amount of evaporation is avoided.

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

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

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

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

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

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

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

According to the invention, when the wastewater treatment is started, the wastewater containing ammonium salt can be directly used for operation, and if the ion content of the wastewater containing ammonium salt meets the conditions of the invention, the first evaporation can be carried out firstly and then the second evaporation can be carried out according to the conditions of the invention; if the ion content of the wastewater containing ammonium salt does not meet the conditions of the invention, the first evaporation can be controlled to ensure that the concentration of sodium chloride in the first concentrated solution is close to the precipitation concentration, then the first concentrated solution is subjected to second evaporation and low-temperature treatment to obtain a treated solution, solid-liquid separation is carried out to obtain sodium chloride crystals and a second mother solution, the second mother solution is mixed with the wastewater containing ammonium salt to adjust the ion content of the wastewater to be treated to be in the range required by the invention, and then the first evaporation is carried out to obtain sodium sulfate crystals. Of course, sodium sulfate and sodium chloride may be used in the initial stage to adjust the ion content of the wastewater to be treated SO long as the wastewater to be treated satisfies the SO content of the wastewater to be treated in the present invention ₄ ^2- 、Cl ^- The requirements are met.

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

In the following examples, the ammonium salt-containing wastewater is wastewater from the production of molecular sieves, which is subjected to chemical precipitation, filtration, weak acid cation exchange and ozone-activated carbon adsorption oxidation in sequence, and is concentrated by ED membrane concentration and reverse osmosis in sequence.

Example 1

As shown in figure 1, the waste water containing ammonium salt (containing 80g/L NaCl and Na) ₂ SO ₄ 81g/L、NH ₄ Cl 48g/L、(NH ₄ ) ₂ SO ₄ 49.4g/L, pH 6.2) at a feed rate of 5m ³ Mixing the second mother liquor with the speed of/h to obtain the wastewater to be treated (containing SO) ₄ ^2- And Cl ^- In a molar ratio of 1:3.7487 After that), the first pH value is measured in the main conduit fed to the first heat exchange unit 31, the third heat exchange unit 33 and the fifth heat exchange unit 35 (all titanium alloy plate heat exchangers)The pH value after mixing was monitored by a pH meter 61 (measurement value: 9.2), and a part (3 m) of the wastewater to be treated was circulated by a first circulation pump 71 ³ H) sending the waste water to the first heat exchange device 31 to carry out first heat exchange with the first ammonia-containing steam condensate so as to heat the waste water to be treated to 99 ℃, and the other part (2 m) ³ H) sending the wastewater to the third heat exchange device 33 to perform first heat exchange with the second ammonia-containing steam condensate to heat the wastewater to be treated to 99 ℃, sending the rest of the wastewater to the fifth heat exchange device 35 to perform first heat exchange with the second concentrated solution obtained by second evaporation to heat the wastewater to be treated to 102 ℃, and then converging the wastewater to be treated and sending the wastewater to the second heat exchange device 32; introducing a sodium hydroxide aqueous solution with the concentration of 45.16 mass percent into a pipeline for conveying the wastewater to be treated into a second heat exchange device 32 to adjust the pH value for the second time, monitoring the adjusted pH value through a second pH value measuring device 62 (a pH meter) (the measured value is 10.8), conveying the wastewater to be treated into the second heat exchange device 32 (a titanium alloy plate type heat exchanger) to perform first heat exchange with the recovered first ammonia-containing steam to heat the wastewater to be treated to 107 ℃, conveying the wastewater to be treated into a first evaporation device 2 (a falling film and forced circulation two-stage MVR evaporation crystallizer) to evaporate, and obtaining first ammonia-containing steam and a first concentrated solution containing sodium sulfate crystals. Wherein the evaporation temperature of the first evaporation device 2 is 100 ℃, the pressure is-22.82 kPa, and the evaporation capacity is 3.82m 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 is raised by 12 ℃) and then passes through the second heat exchange device 32 and the first heat exchange device 31 in sequence to exchange heat with the wastewater to be treated, and is condensed to obtain first ammonia water which is stored in the first ammonia water storage tank 51. In addition, in order to increase the solid content in the first evaporation apparatus 2, part of the liquid evaporated in the first evaporation apparatus 2 is circulated as a first circulation liquid to the second heat exchange apparatus 32 by the second circulation pump 72 to exchange heat, and then enters the first evaporation apparatus 2 again to perform the first evaporation (the reflux ratio is 75.9). The degree of the first evaporation was monitored by a densitometer provided in the first evaporation apparatus 2, and the concentration of sodium chloride in the first evaporation concentrate was controlled to 0.9935X (306.2 g/L).

The first concentrated solution is sent to a first solid-liquid separation apparatus 91 (centrifuge) to carry out first solid-liquid separation for every small periodThen 4.48m is obtained ³ Contains 306.2g/L NaCl and Na ₂ SO ₄ 54.0g/L、NaOH 1.3.8g/L、NH ₃ 0.60g/L of first mother liquor is temporarily stored in a first mother liquor tank 53, sodium sulfate solid obtained by solid-liquid separation (664.41 kg of sodium sulfate crystal filter cake containing 15 mass% of water is obtained per hour, wherein the content of sodium chloride is less than 5.0 mass%) is eluted by 54g/L of sodium sulfate solution which is equal to the dry basis mass of the sodium sulfate crystal filter cake, 664.41kg of sodium sulfate (the purity is 99.4 wt%) is obtained per hour after drying, and the washing liquid is circulated by an eighth circulating pump 78 to be mixed with the wastewater to be treated before the second pH adjustment, and then enters the 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 second evaporation device 1 by the sixth circulating pump 76 for second evaporation to obtain a second ammonia-containing steam and a second concentrated solution containing sodium sulfate crystals and sodium chloride crystals. Wherein the evaporation temperature of the second evaporation device 1 is 105 ℃, the pressure is-7.02 kPa, and the evaporation capacity is 2.01m ³ H is the ratio of the total weight of the catalyst to the total weight of the catalyst. In order to increase the solid content in the second evaporation device 1, part of the first mother liquor evaporated in the second evaporation device 1 is circulated as a second circulating liquid to the fourth heat exchange device 34 through the seventh circulating pump 77 for heat exchange, and then enters the second evaporation device 1 again for second evaporation (the reflux ratio is 42.3). The second ammonia-containing steam obtained by evaporation is compressed by the second compressor 102 (the temperature is raised by 12 ℃) and then sequentially passes through the fourth heat exchange device 34 and the third heat exchange device 33, and is respectively subjected to heat exchange with the first mother liquor and part of wastewater to be treated conveyed by the first circulating pump 71, and is cooled to obtain second ammonia water, and the second ammonia water is stored in the second ammonia water storage tank 52. The degree of the second evaporation is monitored by a mass flow meter arranged on the second evaporation device 1, and the evaporation capacity of the second evaporation is controlled to be 2.01m ³ H (corresponding to the control of the sodium sulfate concentration in the treatment solution to 0.979Y, i.e., 91.6 g/L). Evaporating the first mother liquor in the second evaporator 1 to obtain a second concentrated solution containing sodium sulfate crystals and sodium chloride crystals, and treating at 17.9 deg.C in a low temperature treatment tank 55 for 70min to obtain a second concentrated solution containing chlorineAnd (3) treating liquid of sodium chloride crystals.

The treated liquid containing sodium chloride crystals was sent to a second solid-liquid separation apparatus 92 (centrifuge) to conduct solid-liquid separation, yielding 2.58m per hour ³ Contains 277.6g/L NaCl and Na ₂ SO ₄ 91.6g/L、NaOH 2.34g/L、NH ₃ 0.01g/L of a second mother liquor, temporarily stored in a second mother liquor tank 54. And circulating the second mother liquor to a wastewater introduction pipeline through a ninth circulating pump 79 to be mixed with the ammonium salt-containing wastewater to obtain wastewater to be treated. After sodium chloride solid obtained by solid-liquid separation (769.43 kg of sodium chloride crystal cake with a water content of 14 mass% is obtained per hour, wherein the sodium sulfate content is less than 6.0 mass%) is subjected to spray washing by 277.6g/L of sodium chloride solution which is equal to the dry basis mass of sodium chloride, part of the sodium chloride crystal cake is used for preparing 277.6g/L of sodium chloride solution, the sodium chloride crystal cake is dried in a drier to obtain 661.71kg of sodium chloride (with a purity of 99.5 wt%) per hour, and a washing solution is returned to the fourth heat exchange device 34 through a tenth circulating pump 80 to exchange heat and then returned to the second evaporation device 1.

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, 3.83m of ammonia water having a concentration of 3.45 mass% was obtained per hour in the first ammonia water tank 51 ³ 2.01m of ammonia water having a concentration of 0.137 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 2

The treatment of the ammonium salt-containing wastewater was carried out in the same manner as in example 1, except that: for the NaCl-containing 65g/L and Na ₂ SO ₄ 130g/L、NH ₄ Cl 12g/L、(NH ₄ ) ₂ SO ₄ Treating the ammonium salt-containing wastewater with the pH value of 6.5 of 24.4g/L to obtain SO contained in the wastewater to be treated ₄ ^2- And Cl ^- In a molar ratio of 1:2.291. a portion (4 m) of the waste water to be treated ³ H) carrying out first heat exchange by the first heat exchange device 31 to heat the wastewater to be treated to 94 ℃, and carrying out the other part (1 m) ³ And h) carrying out first heat exchange through the third heat exchange device 33 to heat the wastewater to be treated to 99 ℃, carrying out first heat exchange on the rest part through the fifth heat exchange device 35 to heat the wastewater to be treated to 99 ℃, and carrying out heat exchange through the second heat exchange device 32 after the wastewater to be treated is converged to obtain 107 ℃. The evaporation temperature of the first evaporation device 2 is 95 ℃, the pressure is-36.36 kPa, and the evaporation capacity is 4.31m ³ H is the ratio of the total weight of the catalyst to the total weight of the catalyst. The evaporation temperature of the second evaporation device 1 is 100 ℃, the pressure is-22.83 kPa, and the evaporation capacity is 1.17m ³ H is the ratio of the total weight of the catalyst to the total weight of the catalyst. The low-temperature treatment temperature is 20 deg.C, and the retention time is 55min.

The first solid-liquid separation device 91 obtained 911.15kg tons of sodium sulfate crystal cake containing 14 mass% of water per hour, and finally 783.59kg of sodium sulfate (purity of 99.5 wt%) per hour; obtained 2.68m per hour ³ The concentration of NaCl is 307.2g/L and Na ₂ SO ₄ 54.5g/L、NaOH 1.83g/L、NH ₃ 0.35g/L of the first mother liquor.

The second solid-liquid separation device 92 obtained 456.76kg of a sodium chloride crystal cake having a water content of 15 mass% per hour, and finally 38.24kg of sodium chloride (purity 99.6 wt%) per hour; 1.67 m/h ³ The concentration of NaCl is 279.5g/L and Na ₂ SO ₄ 88.7g/L、NaOH 4.13g/L、NH ₃ 0.011g/L of the second mother liquor.

In this example, 4.31m of ammonia water having a concentration of 1.1 mass% was obtained per hour in the first ammonia water tank 51 ³ 1.17m of aqueous ammonia having a concentration of 0.085 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 ammonium salt-containing waste water was treated in the same manner as in example 1 without further treatmentThe method comprises the following steps: for the sample containing NaCl168g/L and Na ₂ SO ₄ 35g/L、NH ₄ Cl 40g/L、(NH ₄ ) ₂ SO ₄ Treating the ammonium salt-containing wastewater with 8.47g/L and pH of 6.6 to obtain SO contained in the wastewater to be treated ₄ ^2- And Cl ^- In a molar ratio of 1:9.3964. the temperature of the wastewater to be treated after heat exchange by the first heat exchange device 31 is 99 ℃, the temperature of the wastewater to be treated after heat exchange by the third heat exchange device 33 is 99 ℃, the temperature of the wastewater to be treated after heat exchange by 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 112 ℃. The evaporation temperature of the first evaporation device 2 is 105 ℃, the pressure is-7.02 kPa, and the evaporation capacity is 2.36m ³ H is used as the reference value. The second evaporator 1 had an evaporation temperature of 110 deg.C, a pressure of 11.34kPa, and an evaporation capacity of 3.16m ³ H is used as the reference value. The low-temperature treatment temperature is 25 deg.C, and the retention time is 50min.

The first solid-liquid separation device 91 gave 251.35kg of a sodium sulfate crystal cake containing 14% by mass of water per hour, and finally gave 216.16kg of sodium sulfate (purity: 99.6% by weight) per hour; 8.22 m/hr ³ The concentration of NaCl is 306.4g/L and Na ₂ SO ₄ 52.5g/L、NaOH 2.64g/L、NH ₃ 0.18g/L of the first mother liquor.

The second solid-liquid separation device 92 obtained 1236.21kg of sodium chloride crystal cake with a water content of 14 mass% per hour, and finally obtained 1063.14kg of sodium chloride (purity 99.5 wt%) per hour; obtained 5.03m per hour ³ The concentration of NaCl is 279.5g/L and Na ₂ SO ₄ 82.2g/L、NaOH 4.13g/L、NH ₃ 0.017g/L of second mother liquor.

In this example, 2.36m of ammonia water having a concentration of 3.0 mass% was obtained per hour in the first ammonia water tank 51 ³ 3.16m of aqueous ammonia having a concentration of 0.044 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 4

As shown in FIG. 2, the wastewater containing ammonium salt (containing NaCl 158g/L, na) ₂ SO ₄ 46g/L、NH ₄ Cl 57g/L、(NH ₄ ) ₂ SO ₄ 16.9g/L, pH 6.4) at a feed rate of 5m ³ The reaction solution is fed into a pipeline of a treatment system at a speed of/h, a sodium hydroxide aqueous solution with a concentration of 45.16 mass% is introduced into a wastewater conveying pipeline for pH value adjustment, and then the wastewater is mixed with a second mother liquor to obtain wastewater to be treated (containing SO) ₄ ^2- And Cl ^- In a molar ratio of 1:7.9515 And the adjusted pH value is monitored by a first pH value measuring device 61 (pH meter) before being sent to the first heat exchanging device 31, the third heat exchanging device 33 and the fifth heat exchanging device 35 (all titanium alloy plate heat exchangers) (the measured value is 9); a portion (2 m) of the waste water to be treated is then passed through the first circulation pump 71 ³ H) sending the wastewater to a first heat exchange device 31, carrying out first heat exchange with the recovered first ammonia-containing steam condensate to heat the wastewater to be treated to 99 ℃, and carrying out the other part (3 m) ³ H) sending the wastewater to a third heat exchange device 33, carrying out first heat exchange with the recovered second ammonia-containing steam condensate to heat the wastewater to be treated to 99 ℃, sending the rest of the wastewater to a fifth heat exchange device 35, carrying out first heat exchange with the second concentrated solution to heat the wastewater to be treated to 103 ℃, then converging the wastewater to be treated, and sending the wastewater to a first evaporation device 2; the wastewater to be treated is introduced into a pipe for feeding the wastewater to be treated into the first evaporation apparatus 2, an aqueous sodium hydroxide solution having a concentration of 45.16 mass% is introduced to adjust the pH value, the adjusted pH value is monitored by a second pH value measuring apparatus 62 (pH meter) (measurement value is 10.8), and then the wastewater to be treated after pH value adjustment is sequentially fed into the respective evaporators of the first evaporation apparatus 2 to be evaporated, thereby obtaining a first concentrated solution containing ammonia vapor and crystals containing sodium sulfate. The first evaporation device 2 consists of a first effect evaporator 2a, a second effect evaporator 2b, a third effect evaporator 2c and a fourth effect evaporator 2d (all of forced circulation evaporators). Wherein, the evaporation conditions of the first evaporation device 2 are as the following table 1:

TABLE 1

The first ammonia-containing steam obtained by evaporation of the previous-effect evaporator is introduced into the next-effect evaporator to carry out heat exchange to obtain first ammonia water, and further carries out heat exchange with wastewater to be treated in a first heat exchange device 31, the first ammonia-containing steam obtained by evaporation in the fourth-effect evaporator 2d carries out heat exchange with cooling water (wastewater containing ammonium salt) in a second heat exchange device 32 to obtain first ammonia water, and the first ammonia water is combined and stored in a first ammonia water storage tank 51. Heating steam (namely raw steam conventionally used in the field) is introduced into the first-effect evaporator 2a, and the condensate obtained after the heating steam is condensed in the first-effect evaporator 2a is used for preparing the washing solution. The degree of first evaporation was monitored by a densimeter provided in the first evaporation apparatus 2, and the concentration of sodium chloride in the first evaporation concentrate was controlled to 0.99353 × (307 g/L). Crystallizing the first concentrated solution obtained by evaporation in the first evaporation device 2 in a crystal liquid collecting tank 56 at 105 ℃ for 5min to obtain crystal slurry containing sodium sulfate crystals.

The above-mentioned crystal slurry containing sodium sulfate crystals was fed to a first solid-liquid separation apparatus 91 (centrifuge) to carry out a first solid-liquid separation to obtain 7.743m per hour ³ Contains 307g/L NaCl and Na ₂ SO ₄ 52.73g/L、NaOH 1.67g/L、NH ₃ 0.287g/L of first mother liquor is temporarily stored in a first mother liquor tank 53, sodium sulfate solid obtained by solid-liquid separation (371.47 kg of sodium sulfate crystal filter cake containing 15 mass% of water is obtained per hour, wherein the content of sodium chloride is less than 5.8 mass%) is leached by 52.5g/L of sodium sulfate solution which is equal to the dry basis mass of the sodium sulfate crystal filter cake, the sodium sulfate solid is dried in a drier, 315.74kg of sodium sulfate (the purity is 99.5 weight%) is obtained per hour, and a washing liquid is circulated by an eighth circulating pump 78 to be mixed with the wastewater to be treated before the second pH adjustment, and then the mixture is sent to the first evaporation device 2 again for first evaporation.

The first mother liquor in the first mother liquor tank 53 is sent to the second evaporation device 1 (falling film + forced circulation two-stage MVR evaporation crystallizer) by the sixth circulation pump 76 for second evaporation, so as to obtain a second ammonia-containing vapor and a second concentrated solution containing sodium sulfate crystals and sodium chloride crystals, wherein the evaporation conditions are as shown in table 1 above. The second ammonia-containing vapor evaporated by the second evaporator 1 is compressed by the second compressor 102 (temperature is raised)After the temperature is 14 ℃, exchanging heat with the first mother liquor in a fourth heat exchange device 34, exchanging heat with part of wastewater to be treated in a third heat exchange device 33 to obtain second ammonia water, and storing the second ammonia water in a second ammonia water storage tank 52. In order to increase the solid concentration in the second evaporation apparatus 1, part of the liquid evaporated in the second evaporation apparatus 1 is sent again to the second evaporation apparatus 1 as a circulation liquid by the seventh circulation pump 77 to be subjected to second evaporation (the reflux ratio is 41.8). The degree of the second evaporation is monitored by a mass flow meter arranged on the second evaporation device 1, and the evaporation capacity of the second evaporation is controlled to be 3.354m per hour ³ (corresponding to the control of the concentration of sodium sulfate in the treatment solution to 0.978Y, i.e., 88.7 g/L). After the first mother liquor is evaporated in the second evaporation device 1, the obtained second concentrated solution containing sodium sulfate crystals and sodium chloride crystals is subjected to low-temperature treatment in a low-temperature treatment tank 55 at the temperature of 20 ℃ for 55min to obtain a treatment solution containing sodium chloride crystals.

The treated liquid containing sodium chloride crystals was sent to a second solid-liquid separation apparatus 92 (centrifuge) to carry out solid-liquid separation to obtain 4.371 m/hr ³ Contains 279.6g/L NaCl and Na ₂ SO ₄ 88.7g/L、NaOH 2.81g/L、NH ₃ 0.287g/L of second mother liquor is temporarily stored in the second mother liquor tank 54, and the whole second mother liquor is circulated to the wastewater introduction pipeline through the ninth circulating pump 79 to be mixed with the wastewater containing ammonium salt to obtain the wastewater to be treated. Sodium chloride solid obtained by solid-liquid separation (1286.86 kg of sodium chloride crystal filter cake with the water content of 14 mass% is obtained per hour, wherein the content of sodium sulfate is less than 5.2 mass%) is subjected to leaching by using 279.6g/L of sodium chloride solution which is equal to the dry basis mass of sodium chloride, and then is dried in a drier, 1106.70kg of sodium chloride (with the purity of 99.4 weight%) is obtained per hour, and the washing liquid returns to the fourth heat exchange device 34 through the tenth circulating pump 80, exchanges heat, and then returns to the second evaporation device 1.

In this example, 2.353m of ammonia water having a concentration of 4.46% by mass was obtained per hour in the first ammonia water tank 51 ³ The second ammonia water tank 52 was filled with 3.354m of 0.064 mass% ammonia water per hour ³ The ammonia water can be reused in the production process of the molecular sieve.

Example 5

The treatment of the ammonium salt-containing wastewater was carried out in the same manner as in example 4, except that: for the solution containing NaCl 76g/L and Na ₂ SO ₄ 128g/L、NH ₄ Cl 16g/L、(NH ₄ ) ₂ SO ₄ Treating the waste water containing ammonium salt with the pH value of 6.7 at 27.4g/L to obtain SO contained in the waste water to be treated ₄ ^2- And Cl ^- In a molar ratio of 1:2.9034. the temperature of the wastewater after heat exchange by the first heat exchange device 31 is 95 ℃, the temperature of the wastewater to be treated after heat exchange by the third heat exchange device 33 is 93 ℃, and the temperature of the wastewater to be treated after heat exchange by the fifth heat exchange device 35 is 93 ℃. 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 25 deg.C, and the retention time is 60min.

TABLE 2

The first solid-liquid separation device 91 yielded 918.33kg of a sodium sulfate crystal cake containing 14 mass% of water per hour, and finally yielded 789.76kg of sodium sulfate (purity: 99.4 wt%) per hour; yield 3.73m per hour ³ The concentration of NaCl is 305.6g/L and Na ₂ SO ₄ 55.15g/L、NaOH 1.15g/L、NH ₃ 0.308g/L of the first mother liquor.

The second solid-liquid separation device 92 obtains a sodium chloride crystal cake 547 having a water content of 15 mass% per hour.13kg, finally 465.06kg of sodium chloride (purity 99.5 wt%) are obtained per hour; obtained 2.493m per hour ³ The concentration of NaCl is 280.9g/L and Na ₂ SO ₄ 83g/L、NaOH 1.73g/L、NH ₃ 0.023g/L of second mother liquor.

In this example, 4.147m of ammonia water having a concentration of 1.41 mass% was obtained per hour in the first ammonia water tank 51 ³ The second aqueous ammonia tank 52 receives 0.083 mass% aqueous ammonia 1.386m per hour 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 1, except that: for NaCl-containing 118g/L, na ₂ SO ₄ 116g/L、NH ₄ Cl 19g/L、(NH ₄ ) ₂ SO ₄ Treating the ammonium salt-containing wastewater with the pH value of 6.8 at 19g/L to obtain SO contained in the wastewater to be treated ₄ ^2- And Cl ^- In a molar ratio of 1:4.4621. the temperature of the wastewater after heat exchange by the first heat exchange device 31 is 98 ℃, the temperature of the wastewater to be treated after heat exchange by the third heat exchange device 33 is 103 ℃, and the temperature of the wastewater to be treated after heat exchange by the fifth heat exchange device 35 is 103 ℃. 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 30 deg.C, and the retention time is 65min.

TABLE 3

The first solid-liquid separation device 91 gave 793.13kg of a sodium sulfate crystal cake containing 14 mass% of water per hour, and finally 682.09kg of sodium sulfate (purity 99.5 wt%) per hour; yield 5.886m per hour ³ The concentration of NaCl is 305.8g/L and Na ₂ SO ₄ 53.84g/L、NaOH 2.2g/L、NH ₃ 0.18g/L of the first mother liquor.

806.90kg of sodium chloride crystal cake with a water content of 14 mass% was obtained per hour by the second solid-liquid separation device 92, and finally 693.93kg of sodium chloride was obtained per hour (seePurity 99.5 wt%); the obtained product has a particle size of 3.925m per hour ³ The concentration of NaCl is 282.9g/L and Na ₂ SO ₄ 79.6g/L、NaOH 2.76g/L、NH ₃ 0.016g/L of second mother liquor.

In this example, 3.448m of ammonia water having a concentration of 1.53 mass% was obtained per hour in the first ammonia water tank 51 ³ 2.074m of aqueous ammonia having a concentration of 0.05% 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.

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 all within the protection 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 sulfate crystals;

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

the first evaporation prevents sodium chloride from crystallizing out;

the conditions of the second 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 ℃;

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

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

NH in the ammonium salt-containing wastewater ₄ ⁺ Is more than 8mg/L, SO ₄ ^2- 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 mole relative to the SO contained in the wastewater to be treated ₄ ^2- Cl contained in the wastewater to be treated ^- Is 13.8 mol or less.

3. The method according to claim 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.

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

5. The process of claim 1, wherein the second concentrate comprising sodium chloride crystals further comprises sodium sulfate crystals; and when the second 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.

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

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

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

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

10. The method of any one of claims 1-9, wherein the conditions of the first evaporation comprise: the temperature is above 35 ℃ and the pressure is above-95 kPa.

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

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

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

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

15. The method of claim 10, wherein the conditions of the first evaporation comprise: the temperature is 95-110 ℃, and the pressure is-37 kPa-12 kPa.

16. The method of any one of claims 1-9, wherein the conditions of the second evaporation comprise: the temperature is 75-175 ℃, and the pressure is-73 kPa-653 kPa.

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

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

19. The method of any of claims 1-9, wherein the conditions of the cryogenic process comprise: the temperature is 15-35 ℃.

20. The method of claim 19, wherein the conditions of the cryogenic process comprise: the temperature is 17.9-35 ℃.

21. The method according to claim 10, wherein the temperature of the first evaporation is higher than the temperature of the low-temperature treatment by 5 ℃ or more.

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

23. The method of claim 21, wherein the temperature of the first evaporation is 35 ℃ to 90 ℃ higher than the temperature of the cryogenic treatment.

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

25. The method of claim 24, wherein the first evaporation is performed by an MVR evaporation device.

26. The method of claim 24, wherein the second evaporation is performed by an MVR evaporation device.

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

28. The method as set forth in claim 27, wherein the pH of the wastewater to be treated is adjusted to be greater than 7 prior to the first heat exchange.

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

30. The method of claim 29, further comprising washing the resulting sodium sulfate crystals.

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

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

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

34. The method of claim 33, further comprising decontaminating and concentrating the ammonium salt-containing wastewater.