CN108726764B

CN108726764B - Treatment method of catalyst production wastewater

Info

Publication number: CN108726764B
Application number: CN201710265383.9A
Authority: CN
Inventors: 殷喜平; 李叶; 杨凌; 陈玉华; 周岩; 安涛; 刘夫足; 吕伟娇; 张志民
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: 2021-09-21
Anticipated expiration: 2037-04-21
Also published as: CN108726764A

Abstract

The invention relates to the field of sewage treatment, and discloses a method for treating catalyst production wastewater, wherein the catalyst production wastewater contains NH₄ ⁺、SO₄ ^2‑、Cl^‑And Na⁺The method comprises the steps of 1) introducing wastewater to be treated into a first multi-effect evaporation device for first evaporation to obtain first concentrated solution containing ammonia vapor and sodium sulfate crystals, wherein the wastewater to be treated contains the catalyst production wastewater; 2) carrying out first solid-liquid separation on the first concentrated solution, and introducing a liquid phase obtained by the first solid-liquid separation into a second multi-effect evaporation device for second evaporation to obtain second ammonia-containing steam and a second concentrated solution containing sodium sulfate crystals and sodium chloride crystals; 3) carrying out low-temperature treatment on the second concentrated solution to dissolve sodium sulfate crystals to obtain a treatment solution containing 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

Treatment method of catalyst production wastewater

Technical Field

The invention relates to the field of sewage treatment, in particular to a method for treating catalyst production wastewater, and especially relates to a catalyst containing NH₄ ⁺、SO₄ ^2-、Cl^-And Na⁺The method for treating wastewater from catalyst production.

Background

In the production process of the oil refining catalyst, a large amount of inorganic acid alkali salts such as sodium hydroxide, hydrochloric acid, sulfuric acid, ammonium salts, sulfates, hydrochlorides and the like are needed, and a large amount of mixed sewage containing ammonium, sodium sulfate, sodium chloride and aluminosilicate is generated. For such sewage, the common method 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 a biochemical method, a blow-off method or a 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 of 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 art₄ ⁺、SO₄ ^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 catalyst₄ ⁺、SO₄ ^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 wastewater from catalyst production, the wastewater containing NH₄ ⁺、SO₄ ^2-、Cl^-And Na⁺The method comprises the following steps of,

1) introducing wastewater to be treated into a first multi-effect evaporation device for first evaporation to obtain first concentrated solution containing ammonia vapor and sodium sulfate crystals, wherein the wastewater to be treated contains the catalyst production wastewater;

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

3) carrying out low-temperature treatment on the second concentrated solution containing the sodium sulfate crystals and the sodium chloride crystals to dissolve the sodium sulfate 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;

before the wastewater to be treated is introduced into a first multi-effect evaporation device, adjusting the pH value of the wastewater to be treated to be more than 9; the first evaporation prevents sodium chloride from crystallizing out; relative to 1 mole of SO contained in the wastewater to be treated₄ ^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 NH₄ ⁺、SO₄ ^2-、Cl^-And Na⁺The wastewater of (1) is prepared by adjusting the pH value of the wastewater to be treated to a specific range in advance and then performing first steamingSeparating to obtain sodium sulfate crystals and stronger ammonia water, then obtaining concentrated solution containing sodium sulfate crystals and sodium chloride crystals and thinner ammonia water by utilizing second evaporation, finally dissolving sodium sulfate in the concentrated solution by utilizing low-temperature treatment, and further crystallizing and separating out sodium chloride 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.

Further, the method carries out first evaporation through the multi-effect evaporation device, and can separately collect the condensate of the first ammonia-containing steam obtained by evaporation in the first-effect evaporator and/or the second-effect evaporator, so that the first ammonia water with higher concentration can be obtained conveniently.

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 wastewater from catalyst production according to an embodiment of the present invention.

Description of the reference numerals

1. Second multi-effect evaporation device 31 and first heat exchange device

2. A first multi-effect evaporation device 32 and a second heat exchange device

33. Third heat exchange device 73 and third circulating pump

34. Fourth heat exchanger 74 and fourth circulating pump

35. Fifth heat exchange device 76 and sixth circulation pump

51. First ammonia water storage tank 78, eighth circulating pump

52. Second ammonia storage tank 79 and ninth circulating pump

53. First mother liquor tank 80 and tenth circulating pump

54. Second mother liquid tank 81, vacuum pump

55. Low-temperature treatment tank 82 and circulating water tank

56. Crystal liquid collecting tank 83 and tail gas absorption tower

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

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

71. First circulating pump

Detailed Description

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

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.

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

The catalysis provided by the inventionMethod for treating wastewater from chemical production, containing NH₄ ⁺、SO₄ ^2-、Cl^-And Na⁺The method comprises the following steps of,

1) introducing wastewater to be treated into a first multi-effect evaporation device 2 for first evaporation to obtain first concentrated solution containing ammonia vapor and sodium sulfate crystals, wherein the wastewater to be treated contains the catalyst production wastewater;

2) carrying out first solid-liquid separation on the first concentrated solution containing the sodium sulfate crystals, and introducing a liquid phase obtained by the first solid-liquid separation into a second multi-effect evaporation device 1 for second evaporation to obtain second ammonia-containing steam and a second concentrated solution containing the sodium sulfate crystals and sodium chloride crystals;

before the wastewater to be treated is introduced into the first multi-effect evaporation device 2, adjusting the pH value of the wastewater to be treated to be more than 9; the first evaporation prevents sodium chloride from crystallizing out; relative to 1 mole of SO contained in the wastewater to be treated₄ ^2-Cl contained in the wastewater to be treated^-The molar ratio is 14 mol or less.

Preferably, the wastewater to be treated is the catalyst production wastewater; or the wastewater to be treated contains the catalyst production 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 catalyst production 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 catalyst production wastewater and the second solid-liquid separation.

Preferably, the pH value of the wastewater to be treated is adjusted to be greater than 10.8 before the wastewater to be treated is passed into the multi-effect evaporation device 2. 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 NH₄ ⁺、SO₄ ^2-、Cl^-And Na⁺Is treated except for containing NH₄ ⁺、SO₄ ^2-、Cl^-And Na⁺In addition, the catalyst production 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 mole₄ ^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 moles or less, preferably 2 moles or more, more preferably 2.5 moles or more, further preferably 3 moles or more, and may be, for example, 2 to 8 moles. By reacting SO₄ ^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 treated₄ ^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 the separation of the catalyst production wastewater and the second solid-liquid, the preparation of the wastewater to be treated needs to be performed) is not particularly limited, and may be appropriately selected as needed, and the first heat exchange, the adjustment of the pH value of the wastewater to be treated, and the preparation of the wastewater to be treated are performed before the wastewater to be treated is introduced into the multi-effect evaporation apparatus 2.

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 needs to dissolve the sodium sulfate crystals in the low-temperature treatment, and specifically, the second evaporation obtains a second concentrated solution containing the sodium sulfate crystals and the sodium chloride crystals, and the sodium sulfate crystals in the second evaporation 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 the solid-liquid separation is different, the sodium sulfate content in the sodium chloride crystals obtained is usually 8 mass% or less (preferably 4 mass%), and in the present invention, it is considered that the sodium sulfate is dissolved when the sodium sulfate content in the sodium chloride crystals obtained is 8 mass% or less.

In the present invention, 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.

In the present invention, the first and second multi-effect evaporation apparatuses 2 and 1 may be the same or different, are not particularly limited, and may be composed of various evaporators conventionally used in the art. For example, it may be selected from one or more of falling film evaporator, rising film evaporator, scraped surface evaporator, central circulation tube evaporator, basket-suspended evaporator, external heating evaporator, forced circulation evaporator and lien evaporator. Among them, a forced circulation evaporator and an external heating evaporator are preferable. The evaporator may include other evaporation auxiliary components such as a demister for further separating liquid foam, a condenser for condensing all secondary steam, and a vacuum device for pressure reduction operation, if necessary. The number of evaporators included in the first and second multi-effect evaporation devices 2 and 1 is not particularly limited, and may be the same or different, and may be 2 or more, preferably 2 to 5, and more preferably 3 to 4.

In the present invention, the feeding manner of the liquid to be vaporized of the first vaporization and the second vaporization may be the same or different, and may employ a co-current, counter-current or advection manner conventionally used in the art. The parallel flow 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 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 is specifically as follows: 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. Wherein, the first evaporation and the second evaporation adopt a parallel flow feeding mode preferably. In a parallel flow or counter flow mode, the evaporation conditions refer to the evaporation conditions of the last effect evaporator; in the advection mode, the evaporation conditions refer to the evaporation conditions of the respective effect evaporators.

And the first multi-effect evaporation device 2 and the second multi-effect evaporation device 1 can be the same multi-effect evaporation device by means of serial connection and the like, as long as one part of the evaporators meets the conditions of the first evaporation and the other part of the evaporators meets the conditions of the second evaporation.

According to a preferred embodiment of the invention, the first evaporation and the second evaporation are both performed in a cocurrent feeding manner, that is, wastewater to be treated is sequentially introduced into each effect evaporator of a first multi-effect evaporation device 2, a liquid phase obtained by the first solid-liquid separation is sequentially introduced into each effect evaporator of a second multi-effect evaporation device 1, first ammonia-containing steam obtained by evaporation of a previous effect evaporator of the first multi-effect evaporation device 2 is introduced into a next effect evaporator, and first ammonia-containing steam obtained by evaporation of a previous effect evaporator of the second multi-effect evaporation device 1 is introduced into a next effect evaporator. Heating steam can be introduced into the first-effect evaporator 2a of the first multi-effect evaporation device 2 and the first-effect evaporator 1a of the second multi-effect evaporation device 1, and the condensate of the heating steam can be used for washing filter cakes or preparing washing solution.

Specifically, the wastewater to be treated is sequentially introduced into a first effect evaporator 2a, a second effect evaporator 2b, a third effect evaporator 2c and a fourth effect evaporator 2d of a first multi-effect evaporation device 2; after the first solid-liquid separation, the liquid phase (first mother liquor) obtained by the first solid-liquid separation is sequentially introduced into a first effect evaporator 1a, a second effect evaporator 1b, a third effect evaporator 1c and a fourth effect evaporator 1d of a second multi-effect evaporation device 1. Heating steam is introduced into the first effect evaporator 2a of the first multi-effect evaporation device 2 and the first effect evaporator 1a of the second multi-effect evaporation device 1. In the first multi-effect evaporation device 2, the first ammonia-containing steam obtained by evaporation in the previous-effect evaporator exchanges heat in the subsequent-effect evaporator to obtain first ammonia water (the condensate of the first ammonia-containing steam), the first ammonia water obtained in each-effect evaporator is collected, optionally exchanges heat with the wastewater to be treated in the first heat exchange device 31, and then is stored in the first ammonia water storage tank 51. In the second multi-effect evaporation device 1, the first ammonia-containing steam obtained by evaporation in the previous-effect evaporator exchanges heat in the subsequent-effect evaporator to obtain second ammonia water (second ammonia-containing steam condensate), and the second ammonia water obtained in each-effect evaporator is collected, optionally exchanges heat with the wastewater to be treated in the fourth heat exchange device 34, and then is stored in the second ammonia water storage tank 52.

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

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

In the present invention, the conditions of the first evaporation may be appropriately selected as needed, and sodium sulfate may be crystallized without precipitating sodium chloride. The conditions of the first evaporation may include: the temperature is above 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; in order to further improve the evaporation efficiency, it is preferable that the conditions of the first evaporation include: the temperature is 60-365 ℃, and the pressure is-87 kPa-18110 kPa; from the viewpoint of reducing the cost of equipment and the energy consumption, it is more preferable that the temperature of evaporation is 75 to 175 ℃ and the pressure is-73 to 653kPa, and it is further preferable that the conditions of the first evaporation include: the evaporation 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 order to fully utilize the heat in the evaporation process, in the first evaporation, the evaporation temperature difference of two adjacent effect evaporators is more than 5 ℃, preferably 5-30 ℃, and more preferably 10-20 ℃.

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, 0.1m³More than h (e.g. 0.1 m)³/h～500m³/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 first evaporation condition, more than 90 mass% (preferably more than 95 mass%) of ammonia contained in the wastewater to be treated can be evaporated, so as to obtain the first ammonia water with higher concentration, and the first ammonia water can be directly reused in the production process of the catalyst, or neutralized by acid to obtain ammonium salt for reuse, or mixed with water and corresponding ammonium salt or ammonia water for use. In the first evaporation, in order to obtain stronger ammonia water, the first ammonia vapor-containing condensate obtained in the first effect evaporator and/or the second effect evaporator can be collected separately, namely, the ammonia vapor-containing 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 further 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 under the condition that sodium chloride is not precipitated. 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 liquid obtained by the first evaporation, and specifically, by controlling the concentration of the liquid obtained by the first evaporation within the above range, the first evaporation does not crystallize out 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, the wastewater to be treated is subjected to a first heat exchange with first ammonia water (first ammonia-containing vapor condensate) obtained from the first multi-effect evaporation apparatus before being passed into the first multi-effect evaporation apparatus. Preferably, the first ammonia-containing steam obtained by the evaporation of the last evaporator of the first multi-effect evaporator 2 is subjected to first heat exchange to obtain first ammonia water. 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, the first heat exchange is performed by the first heat exchange device 31, the fourth heat exchange device 34 and the fifth heat exchange device 35, specifically, the first ammonia-containing steam condensate is passed through the first heat exchange device 31, the second ammonia-containing steam condensate obtained by the second multi-effect evaporation device 1 is passed through the fourth heat exchange device 34, and a part of the concentrated solution obtained by the second multi-effect 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 fourth heat exchange device 34, and the rest part of the wastewater passes through a fifth heat exchange device 35; then combining the three parts of wastewater to be treated. Heating the wastewater to be treated for evaporation through first heat exchange, and simultaneously cooling the first ammonia-containing steam condensate to obtain first ammonia water, wherein the first ammonia water can be stored in an 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 an ammonia water storage tank 52; further cooling the second concentrated solution to facilitate low-temperature treatment.

According to a preferred embodiment of the present invention, the first ammonia-containing vapor evaporated by the last evaporator (fourth evaporator 2d) of the first multi-effect evaporation device 2 exchanges heat with the cold medium in the second heat exchange device 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 conventional cooling water is used, the cooling water is recycled, and when the catalyst production wastewater is used as the cooling water, the catalyst production 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 fourth heat exchange device 34 and the fifth heat exchange device 35 are not particularly limited, and various heat exchangers conventionally used in the art may be used to achieve the purpose of performing the first heat exchange between the first ammonia-containing steam and the wastewater to be treated. Specifically, a jacketed heat exchanger, a plate heat exchanger, a shell-and-tube heat exchanger, or the like may be mentioned, with the plate heat exchanger being preferred. The material of the heat exchanger can be specifically selected according to the needs, for example, in order to resist the corrosion of chloride ions, the heat exchanger of duplex stainless steel, titanium and titanium alloy, hastelloy can be selected as the material, and the heat exchanger containing plastic material can be selected when the temperature is lower.

According to the present invention, in order to fully utilize the heat energy of the first ammonia-containing steam condensate, it is preferable that the temperature of the wastewater to be treated is 40 to 364 ℃, more preferably 55 to 364 ℃, even more preferably 65 to 174 ℃, and even more preferably 79 to 99 ℃ after the first heat exchange is performed by the first heat exchange device 31.

According to the present invention, in order to fully utilize the heat energy of the second ammonia-containing vapor condensate, it is preferable that the temperature of the wastewater to be treated is 44 ℃ to 174 ℃, more preferably 79 ℃ to 99 ℃ after the first heat exchange is performed by the fourth heat exchange device 34.

According to the present invention, in order to fully utilize the heat energy of the second concentrated solution, the temperature of the wastewater to be treated is preferably 44 ℃ to 174 ℃, more preferably 79 ℃ to 129 ℃ after the first heat exchange is performed by the fifth heat exchange device 35.

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 the purpose of adjusting the pH value may be achieved. The alkaline substance is preferably NaOH in order not to introduce new impurities in the wastewater to be treated, increasing the purity of the crystals obtained.

The manner of adding the alkaline substance may be any manner known in the art, but it is preferable to mix the alkaline substance with the wastewater to be treated in the form of an aqueous solution, and for example, an aqueous solution containing the alkaline substance may be introduced into a pipe through which the wastewater to be treated is introduced and mixed. The content of the alkaline substance in the aqueous solution is not particularly limited as long as the above-mentioned purpose of adjusting the pH value can be achieved. However, in order to reduce the amount of water used and further reduce the cost, it is preferable to use a saturated aqueous solution of an alkaline substance. In order to monitor the pH value of the wastewater to be treated, the pH value of the wastewater to be treated may be measured after the above-mentioned pH value adjustment.

According to a preferred embodiment of the present invention, the first evaporation process is performed in the first multi-effect 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 through which the wastewater to be treated is fed into the first heat exchange device 31, the fourth heat exchange device 34 or the fifth heat exchange device 35, before the wastewater to be treated is fed into the first heat exchange device 31, the fourth heat exchange device 34 or the fifth heat exchange device 35 for the first heat exchange; the second pH adjustment is then carried out by introducing and mixing an aqueous solution containing alkaline substances in the line which feeds the wastewater to be treated into the first multi-effect evaporation device 2. The pH value of the wastewater to be treated is more than 9, preferably more than 10.8 before the wastewater is introduced into the first multi-effect evaporation device 2 through two pH value adjustments. Preferably, the first pH adjustment is such that the pH of the wastewater to be treated is greater than 7 (preferably 7-9), and the second pH adjustment is such that the pH 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, the fourth heat exchanging device 34, or the fifth heat exchanging device 35 to measure the pH value after the first pH adjustment, and a second pH measuring device 62 is provided on a pipe for feeding the wastewater to be treated into the first multi-effect evaporation 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 30 min. According to the invention, the crystallization of the first concentrated solution containing sodium sulfate crystals can also be carried out in a first multi-effect evaporator with a crystallizer (e.g. a forced circulation evaporator 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 ensured 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 first solid-liquid separation to obtain sodium sulfate crystals and a first mother solution. 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 can be sent to the second multi-effect evaporation device 1 through the sixth circulation pump 76 for second evaporation. In addition, it is difficult to avoid that impurities such as chlorine ions, free ammonia, and hydroxide ions are adsorbed on the obtained sodium sulfate crystals, and in order to remove the adsorbed impurities, reduce the odor of solid salts, reduce corrosiveness, and improve the purity of the crystals, it is preferable that the sodium sulfate crystals are first washed with water, the catalyst production wastewater, or a sodium sulfate solution and dried. In order to avoid the dissolution of sodium sulfate crystals during the washing, the sodium sulfate crystals are preferably washed with an aqueous sodium sulfate solution. More preferably, the concentration of the aqueous sodium sulfate solution is preferably such that the sodium chloride and the sodium sulfate reach the concentration of sodium sulfate in the saturated aqueous solution at the same time at the temperature corresponding to the sodium sulfate crystals to be washed.

The manner of the first solid-liquid separation and the first washing is not particularly limited, and may be carried out by using, for example, a combination of an elutriation apparatus and a solid-liquid separation apparatus which are conventional in the art, or may be carried out on a staged solid-liquid separation apparatus such as a belt filter. Preferably, the first wash comprises panning and/or rinsing. The above-mentioned elutriation and rinsing are not particularly limited and may be carried out by a method conventional in the art. The number of elutriation and rinsing is not particularly limited, and may be 1 or more, and is preferably 2 to 4 times in order to obtain sodium sulfate crystals of higher purity. In the elutriation process, the waste water produced by the catalyst 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 liquid obtained by rinsing may be preferably used for washing, and water or a sodium sulfate solution is preferably used. The liquid resulting from the washing is preferably returned to the first multi-effect evaporation device 2 before the pH adjustment before the first evaporation is completed, for example, to the second pH adjustment process by the eighth circulation pump 78.

According to a preferred embodiment of the present invention, after the first concentrated solution containing sodium sulfate obtained by evaporation in the first multi-effect evaporation apparatus 2 is subjected to preliminary solid-liquid separation by settling, the catalyst production wastewater is subjected to first elutriation in an elutriation tank, then the liquid obtained in the subsequent washing of sodium sulfate crystals is subjected to second elutriation in another elutriation tank, finally the slurry subjected to the two elutriations is sent to a solid-liquid separation apparatus for solid-liquid separation, the crystals obtained by the solid-liquid separation are subjected to elution again with an aqueous solution of sodium sulfate, and the liquid obtained by the elution 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 the evaporation amount of the second evaporation can be controlled to simultaneously crystallize and precipitate sodium sulfate and sodium chloride (that is, the second evaporation yields a second concentrated solution containing sodium sulfate crystals and sodium chloride crystals), and then the low-temperature treatment is performed to dissolve the sodium sulfate crystals in the second concentrated solution containing sodium sulfate crystals and sodium chloride crystals, thereby further crystallizing and precipitating sodium chloride, thereby obtaining a treated solution containing only sodium chloride crystals. 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 105-110 ℃, and the pressure is-8 kPa-12 kPa.

In order to fully utilize the heat in the evaporation process, in the second evaporation, the evaporation temperature difference of two adjacent effect evaporators is more than 5 ℃, preferably 5-30 ℃, and more preferably 10-20 ℃.

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

Further, the evaporation amount of the second evaporation may be appropriately selected depending on the capacity of the apparatus and the amount of the wastewater to be treated, and may be, for example, 100L/h or more (e.g., 0.1 m)³/h～500m³/h)。

According to the invention, the second evaporation is used for crystallizing and precipitating sodium chloride and sodium sulfate in the wastewater to be treated simultaneously, and preferably, the second evaporation is used for ensuring that the concentration of sodium sulfate in the treatment liquid after the second concentrated solution is subjected to low-temperature treatment is less than Y (preferably 0.9Y-0.99Y, and more preferably 0.95Y-0.98Y)), wherein Y is the concentration of sodium sulfate when sodium sulfate and sodium chloride in the wastewater to be treated are saturated under the condition of low-temperature treatment. 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.

According to a preferred embodiment of the invention, the second ammonia-containing vapor obtained by the evaporation of the last evaporator of the second multi-effect evaporator 1 is subjected to a second heat exchange to obtain second ammonia water. Specifically, the second ammonia-containing steam obtained by evaporation in the last evaporator of the second multi-effect evaporation device 1 is introduced into the third heat exchange device 33 to exchange heat with cooling water, so as to obtain second ammonia water. Preferably, the catalyst production wastewater is used as cooling water, and the catalyst production wastewater is returned to the pH adjustment process after being heated.

The third heat exchange means 33 is not particularly limited, and various heat exchangers conventionally used in the art may be used for the purpose of condensing 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. The cooling medium can be cooling water, glycol aqueous solution, etc. When conventional cooling water is used, the cooling water is recycled, and when the catalyst production wastewater is used as the cooling water, the wastewater after heat exchange is preferably directly returned to the treatment process (such as to the first pH value adjustment process).

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

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

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

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

In the present invention, the low-temperature treatment may be performed 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 a stirring member, and the stirring member can make the solid-liquid phase distribution and the temperature distribution in the second concentrated solution uniform, thereby achieving the purpose of sufficiently dissolving the sodium sulfate crystals and precipitating the sodium chloride crystals to the maximum.

In the present invention, in order to achieve the object that the first evaporation does not crystallize and precipitate sodium chloride, and the sodium sulfate crystals precipitated in the second evaporation can be dissolved 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 at least 5 ℃ higher than the temperature of the low-temperature treatment, preferably 20 ℃ higher, more preferably 35 ℃ to 90 ℃ higher, still more preferably 35 ℃ to 70 ℃ higher, and particularly preferably 50 ℃ to 60 ℃ higher. By controlling the temperature of the first evaporation and the low-temperature treatment, sodium sulfate in the first evaporation is crystallized and separated out independently, and sodium sulfate crystals separated out by the second evaporation in the low-temperature treatment and sodium sulfate in the sodium chloride crystals can be dissolved, so that the purity of the obtained sodium sulfate and sodium chloride crystals is improved.

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., the circulating wastewater, i.e., the liquid phase obtained by the solid-liquid separation of the sodium chloride crystal-containing treatment liquid). The method of the second solid-liquid separation is not particularly limited, and may be selected from one or more of centrifugation, filtration, and sedimentation, for example.

According to the present invention, the second solid-liquid separation may be performed by a second solid-liquid separation device (for example, a centrifuge, a filter, or the like) 92. After the second solid-liquid separation, the second mother liquor obtained by the second solid-liquid separation device 92 returns to the first multi-effect evaporation device 2 for the first evaporation again, and specifically, the second mother liquor can be returned to the second pH adjustment process by the ninth circulation pump 79. In addition, it is difficult to avoid that the obtained sodium chloride crystals adsorb certain impurities such as sulfate ions, free ammonia, hydroxide ions, etc., and in order to remove the adsorbed impurities, reduce the odor of solid salts, reduce corrosiveness, and improve the purity of the crystals, the sodium chloride crystals are preferably subjected to secondary washing with water 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 second washing method is preferably performed by performing the elutriation before the rinsing. The second washing liquid obtained in the above washing process is preferably returned to the second multi-effect evaporation device 1 by the tenth circulation pump 80 to be subjected to the second evaporation again.

The form of the second solid-liquid separation and the second washing is not particularly limited, and may be carried out by using, for example, a combination of an elutriation apparatus and a solid-liquid separation apparatus which are conventional in the art, or may be carried out in a staged solid-liquid separation apparatus. The above-mentioned elutriation and rinsing are not particularly limited and may be carried out by a method conventional in the art. The number of elutriation and rinsing is not particularly limited, and may be 1 or more, and is preferably 2 to 4 times in order to obtain sodium chloride crystals of higher purity. In the elutriation process, the catalyst production wastewater is generally not recycled when being used as an elutriation liquid, and the washing liquid recovered by the second washing can be recycled in a counter-current manner when being used as the elutriation liquid. Before the elutriation, it is preferable to perform preliminary solid-liquid separation by sedimentation to obtain a slurry containing sodium chloride crystals (the liquid content may be 35% by mass or less). In the elutriation process, 1 to 20 parts by weight of a liquid used for elutriation is used with respect to 1 part by weight of a slurry containing sodium chloride crystals. The rinsing is preferably carried out using an aqueous sodium chloride solution, the concentration of which is preferably the concentration of sodium chloride in an aqueous solution in which sodium chloride and sodium sulfate are simultaneously saturated at the temperature corresponding to the sodium chloride crystals to be rinsed. In order to further enhance the elutriation effect and obtain sodium chloride crystals with higher purity, 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 catalyst production wastewater is returned to the second multi-effect evaporation device before the elutriation liquid is returned to the first multi-effect evaporation device for second pH value adjustment before evaporation, and the water or the washing liquid of the sodium chloride water solution and the elutriation liquid are returned to the second multi-effect evaporation device.

According to a preferred embodiment of the present invention, after performing a preliminary solid-liquid separation by settling on a treatment liquid containing sodium chloride crystals obtained by low-temperature treatment, a first elutriation is performed in an elutriation tank using the catalyst production wastewater, then a second elutriation is performed in another elutriation tank using a liquid obtained when sodium chloride crystals are subsequently washed, finally, a slurry obtained by the two elutriations is sent to a second solid-liquid separation device for solid-liquid separation, crystals obtained by the solid-liquid separation are eluted with an aqueous sodium chloride solution (the concentration of the aqueous sodium chloride solution is the concentration of sodium chloride in an aqueous solution in which sodium chloride and sodium sulfate are simultaneously saturated at a temperature corresponding to the sodium chloride crystals to be washed), and the eluted liquid is returned to the second elutriation as an elutriation liquid. Through the washing process combining elutriation and leaching, the purity of the obtained sodium chloride crystal is improved, washing liquid is not excessively introduced, and the efficiency of wastewater treatment is improved.

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 subjected to the first heat exchange to condense the remaining tail gas, namely the tail gas discharged from the second heat exchange device 32, and the second ammonia-containing steam is subjected to the second heat exchange to condense the remaining tail gas, namely the tail gas discharged from the third heat exchange device 33. 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 catalyst production wastewater is not particularly limited as long as it contains NH₄ ⁺、SO₄ ^2-、Cl^-And Na⁺The wastewater is obtained. In addition, the wastewater of the invention is particularly suitable for the treatment of high-salinity wastewater. The wastewater of the present invention may be specifically wastewater from a process for producing a molecular sieve, alumina or a refinery catalyst, or wastewater from a process for producing a molecular sieve, alumina or a refinery catalyst, which is subjected to the following impurity removal and concentration. It is preferable that the wastewater from the production of molecular sieves, alumina or refinery catalysts is subjected to the following impurity removal and concentration.

As NH in the catalyst production wastewater₄ ⁺May be 8mg/L or more, preferably 300mg/L or more.

As Na in the wastewater from the catalyst production⁺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 wastewater from the production of said catalyst₄ ^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 the catalystCl in production wastewater^-It 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 catalyst production wastewater₄ ⁺、SO₄ ^2-、Cl^-And Na⁺The upper limit of (3) is not particularly limited. SO in the wastewater from the viewpoint of easy access to wastewater₄ ^2-、Cl^-And Na⁺The upper limit of (b) is 200g/L or less, preferably 150g/L or less, respectively; NH in wastewater₄ ⁺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 of the treatment process, the amount of SO contained in the wastewater is relatively small₄ ^2-Cl in catalyst production wastewater^-The lower the content, the better, for example, relative to 1 mole of SO contained in the catalyst production wastewater₄ ^2-Cl contained in the catalyst production 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 wastewater from the catalyst production is 1 mole₄ ^2-Cl contained in the catalyst production 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 8 mol. By adding SO contained in the catalyst production wastewater₄ ^2-And Cl^-The molar ratio of (a) to (b) is limited to the above range, most of water can be evaporated in the first evaporation, the amount of circulating liquid in a treatment system is reduced, energy is saved, and the treatment process is more economical.

In the present invention, the inorganic salt ions contained in the catalyst production wastewater are other than NH₄ ⁺、SO₄ ^2-、Cl^-And Na⁺In addition, it may contain Mg²⁺、Ca²⁺、K⁺、Fe³⁺Inorganic salt ions such as rare earth element ions, Mg²⁺、Ca²⁺、K⁺、Fe³⁺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 catalyst production wastewater, the following impurity removal is preferably performed.

The TDS of the catalyst production 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 catalyst production wastewater is preferably 4 to 8, preferably 6 to 7.

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

In the invention, in order to reduce the concentration of impurity ions in the wastewater, ensure the continuous and stable operation of the treatment process and reduce the equipment operation and maintenance cost, the catalyst production 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 catalyst production wastewater. For suspended matters, a solid-liquid separation method can be selected for removing impurities; for inorganic matters and organic matters, chemical precipitation, ion exchange and adsorption methods can be selected for removing impurities, such as weak acid cation exchange, activated carbon adsorption and the like; for organic matters, impurities can be removed by adopting an adsorption and/or oxidation mode, wherein an ozone biological activated carbon adsorption oxidation method is preferred. According to a preferred embodiment of the invention, the wastewater is subjected to filtration, weak acid cation exchange method and ozone biological activated carbon adsorption oxidation method for removing impurities in sequence. Through the impurity removal process, most suspended matters, hardness, silicon and organic matters can be removed, the scaling risk of the device is reduced, and the continuous and stable operation of the wastewater treatment process is ensured.

In the present invention, the wastewater having a low salt content may be concentrated to have a salt content within a range required for the wastewater of the present invention before the wastewater is treated by the treatment method of the present invention (preferably, after the above-mentioned impurity removal). Preferably, the concentration is selected from ED membrane concentration and/or reverse osmosis; more preferably, the concentration is performed by ED membrane concentration and reverse osmosis, and the order of performing the ED membrane concentration and 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 can improve the efficiency of waste water treatment, avoid the energy waste that a large amount of evaporations caused.

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

The conditions for the above chemical precipitation are preferably: sodium carbonate is used as a treating agent, 1.2-1.4 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 0.5-4 h.

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 10-30 m/h. After the filter material is used, the regeneration method of 'gas back flushing-gas and water back flushing-water back flushing' is adopted to regenerate the filter material, and the regeneration period is 10-15 h.

The conditions for the weak acid cation exchange method are preferably: the pH value range is 6.5-7.5; the temperature is less than or equal to 40 ℃, the height of the resin layer is 1.5-3.0m, 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/m³Wet resin; the flow rate of the regeneration liquid HCl is 4.5-5.5m/h, and the regeneration contact time is 35-45 min; the forward washing flow rate is 18-22m/h, and the forward washing time is 2-30 min; the running flow rate is 15-30 m/h; as the acidic cation exchange resin, for example, there can be used a Gallery Senno chemical Co., Ltd, SNT brand D113 acidic cation exchange resin.

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

The conditions for the concentration of the ED membrane are preferably: current 145-155A, voltage 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 catalyst production wastewater can be used for direct operation, and if the ion content of the catalyst production wastewater 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 catalyst production wastewater 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 low-temperature treatment and second evaporation to obtain a second concentrated solution, the second concentrated solution is subjected to solid-liquid separation to obtain sodium chloride crystals and a second mother solution, the second mother solution is mixed with the catalyst production wastewater 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, the ion content of the wastewater to be treated can be adjusted by using sodium sulfate or sodium chloride in the initial stage as long as the wastewater to be treated satisfies the SO content in the wastewater to be treated in the present invention₄ ^2-、Cl^-The requirements are met.

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

In the following examples, the wastewater is obtained by sequentially removing impurities from wastewater generated in the production process of the molecular sieve by chemical precipitation, filtration, weak acid cation exchange method and ozone biological activated carbon adsorption oxidation method, and sequentially concentrating the wastewater by ED membrane concentration and reverse osmosis method.

Example 1

As shown in FIG. 1, wastewater (containing NaCl 48g/L, Na)₂SO₄ 90g/L、NH₄Cl 47g/L、(NH₄)₂SO₄89.6g/L, pH of 6.8) at a feed rate of 5m³The speed of the second mother liquor is fed into a pipeline of a treatment system, and the second mother liquor is mixed with the second mother liquor to obtain wastewater to be treated (containing SO)₄ ^2-And Cl^-In a molar ratio of 1: 2.404) in the conduit leading to the first heat exchange means 31 (titanium alloy plate heat exchanger) by means of the first pH measuring means 61(pH meter)The pH value is then monitored (measurement value 9.2), and a part (3 m) of the wastewater to be treated is fed through the first circulation pump 71³H) 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 102 ℃, and carrying out the other part (1 m)³H) sending the waste water to a fourth heat exchange device 34, carrying out first heat exchange with the recovered second ammonia-containing steam condensate to heat the waste water to be treated to 108 ℃, sending the rest part of the waste water to a fifth heat exchange device 35, and carrying out first heat exchange with the second concentrated solution to heat the waste water to be treated to 103 ℃; introducing a sodium hydroxide aqueous solution with the concentration of 45.16 mass% into a pipeline for conveying the wastewater to be treated after the first heat exchange into the first multi-effect evaporation device 2 to carry out secondary pH value adjustment, monitoring the adjusted pH value through a second pH value measuring device 62 (a pH meter) (the measured value is 11), and conveying the wastewater to be treated after the second pH value adjustment into each effect evaporator of the first multi-effect evaporation device 2 in sequence to carry out evaporation to obtain a first concentrated solution containing ammonia vapor and sodium sulfate crystals. The first multi-effect 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). And introducing first ammonia-containing steam obtained by evaporation of the previous-effect evaporator into the next-effect evaporator for heat exchange to obtain condensate, further cooling in the first heat exchange device 31 to obtain first ammonia water, performing heat exchange on the first ammonia-containing steam obtained by the fourth-effect evaporator 2d and the catalyst production wastewater in the second heat exchange device 32 to obtain first ammonia water, and combining the first ammonia water and storing in the 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 the first evaporation is monitored by a densimeter provided on the first multi-effect evaporation device 2, and the concentration of the sodium chloride in the first evaporation concentrate is controlled to be 0.9935X (305.8 g/L). Wherein, the evaporation conditions of the first multi-effect evaporation device 2 are as shown in the following table 1.

TABLE 1

Crystallizing the first concentrated solution obtained by evaporation in the first multi-effect evaporation device 2 in a crystal liquid collecting tank 56 at the crystallization temperature of 100 ℃ for 5min to obtain crystal slurry containing sodium sulfate crystals.

The above-mentioned crystal slurry containing sodium sulfate crystals was fed into a first solid-liquid separation apparatus 91 (centrifuge) to carry out a first solid-liquid separation to obtain 3.66m per hour³Contains NaCl 305.8g/L, Na₂SO₄ 53.8g/L、NaOH 2.2g/L、NH₃0.5g/L of the first mother liquor is temporarily stored in the first mother liquor tank 53, sodium sulfate solids obtained by solid-liquid separation (1098.27 kg of sodium sulfate crystal cake containing 15 mass% of water per hour, wherein the content of sodium chloride is 2.1 mass% or less) are eluted with 53g/L of a sodium sulfate solution having the same dry basis mass as the sodium sulfate crystal cake, and dried in a dryer to obtain 933.53kg of sodium sulfate (the purity is 99.5 wt%) per hour, and the washing liquid is sent to the first multi-effect evaporation device 2 by the eighth circulation pump 78 to be subjected to first evaporation.

The second evaporation process is carried out in a second multi-effect evaporation device 1, and the second multi-effect evaporation device 1 consists of a first effect evaporator 1a, a second effect evaporator 1b, a third effect evaporator 1c and a fourth effect evaporator 1d (all of forced circulation evaporators). The first mother liquor in the first mother liquor tank 53 is sequentially sent to the respective evaporators of the second multi-effect evaporation device 1 by a sixth circulating pump 76 for second evaporation to obtain a second concentrated solution containing ammonia vapor and sodium sulfate crystal and sodium chloride crystal, wherein the evaporation conditions are as shown in table 1 above. Introducing second ammonia-containing steam obtained by evaporation in the previous evaporator into the next evaporator for heat exchange to obtain condensate, and further condensing in a fourth heat exchange device 34 to obtain second ammonia water; the second ammonia-containing steam obtained by evaporation in the fourth effect evaporator 1d exchanges heat with the catalyst production wastewater in a third heat exchange device 33 to obtain second ammoniaAnd water, the second ammonia water is combined and stored in the second ammonia water tank 52. Heating steam (namely raw steam conventionally used in the field) is introduced into the first-effect evaporator 1a, and the condensate obtained after the heating steam is condensed in the first-effect evaporator 1a is used for preparing a washing solution. The degree of the first evaporation is monitored by a densimeter arranged on the second multi-effect evaporation device 1, and the evaporation capacity of the second evaporation is controlled to be 1.50m per hour³(corresponding to a sodium sulfate concentration in the treatment solution of 0.978Y, i.e., 88.5 g/L).

After the first mother liquor is evaporated in the second multi-effect 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 60min 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) for solid-liquid separation to obtain 2.22 m/hr³Contains 279.2g/L, Na NaCl₂SO₄ 88.5g/L、NaOH 3.62g/L、NH₃0.01g/L of the second mother liquor is temporarily stored in the second mother liquor tank 54. And circulating the second mother liquor to a wastewater introducing pipeline through a ninth circulating pump 79 to be mixed with the catalyst production wastewater to obtain wastewater to be treated. Sodium chloride solid obtained by solid-liquid separation (582.66 kg of sodium chloride crystal cake with the water content of 15 mass% is obtained per hour, wherein the content of sodium sulfate is below 2.0 mass%) is washed by 279g/L of sodium chloride solution with the same dry mass as sodium chloride, and is dried in a drier, 495.26kg of sodium chloride (with the purity of 0.994 weight%) is obtained per hour, and the washing liquid is circulated to the second multi-effect evaporation device 1 through a tenth circulating pump 80.

In addition, the tail gas discharged by the second heat exchange device 32 and the third heat exchange device 33 is introduced into a tail gas absorption tower 83 through a vacuum pump 81 for absorption, circulating water is introduced into the tail gas absorption tower 83, the circulating water circulates in the tail gas absorption tower 83 under the action of the fourth circulating pump 74, water is supplemented into the tail gas absorption tower 83 from a circulating water tank 82 through a third circulating pump 73, and fresh water is supplemented into the circulating water tank 82, so that the temperature and the ammonia content of the working water of the vacuum pump 81 are reduced. Dilute sulfuric acid is further introduced into the tail gas absorption tower 83 to absorb ammonia and the like in the tail gas. In addition, the starting phase of the MVR evaporation was started by steam at a temperature of 143.3 ℃.

In this example, 4.57m of ammonia water having a concentration of 3.9 mass% was obtained per hour in the first ammonia water tank 51³1.50m of aqueous ammonia having a concentration of 0.12% by mass per hour was obtained in the second aqueous ammonia tank 52³The ammonia water can be reused in the production process of the molecular sieve.

Example 2

The treatment of the waste water was carried out according to the method of example 1, except that: for NaCl containing 109g/L, Na₂SO₄ 105g/L、NH₄Cl 23g/L、(NH₄)₂SO₄22.5g/L, pH of 6.3 was treated to obtain SO in the wastewater to be treated₄ ^2-And Cl^-In a molar ratio of 1: 4.37. the temperature of the wastewater to be treated after heat exchange by the first heat exchange device 31, the fourth heat exchange device 34 and the fifth heat exchange device 35 is 108 ℃. The evaporation conditions of the first and second multi-effect evaporation devices 2 and 2 are as follows in table 3. The low-temperature treatment temperature is 25 deg.C, and the retention time is 58 min.

TABLE 2

The first solid-liquid separation device 91 obtained 750.45kg of a sodium sulfate crystal cake containing 14 mass% of water per hour, and finally obtained 645.39kg of sodium sulfate (purity: 99.6 wt%) per hour; the mother liquor tank 54 gave 5.64m per hour³The concentration of NaCl is 305.6g/L, Na₂SO₄ 55.2g/L、NaOH 1.15g/L、NH₃0.1g/L of the first mother liquor.

The second solid-liquid separation device 92 obtained 780.84kg of sodium chloride crystal cake with a water content of 14 mass% per hour, and finally 671.52kg of sodium chloride (purity 99.5 wt%) per hour; the second solid-liquid separation device 92 gave 3.58 m/hour³NaCl concentration 280.9g/L, Na₂SO₄ 83g/L、NaOH 1.7g/L、NH₃0.3g/L of the second mother liquor.

In this example, 3.55m of ammonia water having a concentration of 1.7% by mass per hour was obtained in the first ammonia water tank 51³2.00m of aqueous ammonia having a concentration of 0.03 mass% was obtained per hour in the second aqueous ammonia tank 52³The ammonia water can be reused in the production process of the molecular sieve.

Example 3

The treatment of the waste water was carried out according to the method of example 1, except that: for NaCl-containing 162g/L, Na₂SO₄ 69g/L、NH₄Cl 30g/L、(NH₄)₂SO₄13g/L, pH of 6.6 to obtain SO in the wastewater to be treated₄ ^2-And Cl^-In a molar ratio of 1: 7.198. the temperature of the wastewater to be treated after heat exchange by the first heat exchange device 31, the fourth heat exchange device 34 and the fifth heat exchange device 35 is 110 ℃. The evaporation conditions of the first and second multi-effect evaporation devices 2 and 2 are as follows in table 3. The low-temperature treatment temperature is 30 deg.C, and the retention time is 55 min.

TABLE 3

The first solid-liquid separation device 91 gave 485.29kg of a sodium sulfate crystal cake containing 15% by mass of water per hour, and finally 412.50kg of sodium sulfate (purity: 99.4% by weight) per hour; 8.17m per hour³The concentration of NaCl is 306.4g/L, Na₂SO₄ 52.5g/L、NaOH 2.64g/L、NH₃0.07g/L of the first mother liquor.

The second solid-liquid separation device 92 obtained 1135.37kg of sodium chloride crystal cake with a water content of 14 mass% per hour, and finally 976.42kg of sodium chloride (purity 99.5 wt%) per hour; obtained 5.41m per hour³The concentration of NaCl is 282.5g/L, Na₂SO₄ 79.3g/L、NaOH 3.98g/L、NH₃0.002g/L of second mother liquor.

In this example, 2.61m of ammonia water having a concentration of 2.3 mass% was obtained per hour in the first ammonia water tank 51³Second ammonia storage2.92m of aqueous ammonia having a concentration of 0.02 mass% was obtained per hour in the tank 52³The ammonia water can be reused in the production process of the molecular sieve.

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

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

In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.

Claims

1. Method for treating catalyst production wastewater containing NH₄ ⁺、SO₄ ^2-、Cl^-And Na⁺Characterized in that the method comprises the following steps,

1) introducing the wastewater to be treated into a first multi-effect evaporation device for first evaporation to obtain first concentrated solution containing ammonia vapor and sodium sulfate crystals;

before the wastewater to be treated is introduced into a first multi-effect evaporation device, adjusting the pH value of the wastewater to be treated to be more than 9;

the first evaporation prevents sodium chloride from crystallizing out;

the conditions of the second evaporation include: the conditions of the second evaporation include: the temperature is 75-175 ℃, and the pressure is-73 kPa-653 kPa; the temperature of the low-temperature treatment is 15-45 ℃; the temperature of the first evaporation is higher than that of the low-temperature treatment by more than 5 ℃;

relative to 1 mole of SO contained in the wastewater to be treated₄ ^2-Cl contained in the wastewater to be treated^-14 mol or less;

the wastewater to be treated contains the catalyst production wastewater and a liquid phase obtained by the second solid-liquid separation, and NH in the catalyst production wastewater₄ ⁺Is more than 8mg/L, SO₄ ^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 treated₄ ^2-Cl contained in the wastewater to be treated^-Is 13.8 mol or less.

3. The method as recited in claim 1, wherein the pH of the wastewater to be treated is adjusted to be greater than 10.8 prior to passing the wastewater to be treated to the first multi-effect evaporation device.

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 method of claim 1, wherein the first evaporation is conducted such that the concentration of sodium chloride in the first concentrated solution is no greater than X, where 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.

6. The method according to claim 5, 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.

7. A process as claimed in claim 5, wherein the first evaporation provides a concentration of sodium chloride in the first concentrate of from 0.95X to 0.999X.

8. The method of claim 6, wherein the second evaporation provides a sodium sulfate concentration in the treatment solution of 0.9Y to 0.99Y.

9. The method of any one of claims 1-8, wherein the conditions of the first evaporation comprise: the temperature is above 35 ℃ and the pressure is above-95 kPa.

10. The method of claim 9, wherein the conditions of the first evaporation comprise: the temperature is 45-365 ℃, and the pressure is-95 kPa-18110 kPa.

11. 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.

12. The method of claim 11, wherein the conditions of the first evaporation comprise: the temperature is 75-175 ℃, and the pressure is-73 kPa-653 kPa.

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

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

15. The method of any one of claims 1-8, wherein the conditions of the second evaporation comprise: the temperature is 80-130 ℃, and the pressure is-66 kPa-117 kPa.

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

17. The method according to any one of claims 1 to 8, wherein the temperature of the cryogenic treatment is between 15 ℃ and 35 ℃.

18. The method of claim 17, wherein the cryogenic treatment is at a temperature of 17.9 ℃ to 35 ℃.

19. The method according to claim 9, wherein the temperature of the first evaporation is 20 ℃ or more higher than the temperature of the low-temperature treatment.

20. The method of claim 19, wherein the temperature of the first evaporation is 35 ℃ to 90 ℃ higher than the temperature of the low-temperature treatment.

21. The method of claim 1, wherein the wastewater to be treated is subjected to a first heat exchange with first ammonia water obtained from a first multi-effect evaporation device prior to passing the wastewater to be treated into the first multi-effect evaporation device.

22. The method of claim 21, wherein the first ammonia-containing vapor evaporated by the last evaporator of the first multi-effect evaporator is subjected to a first heat exchange to obtain a first ammonia water.

23. A method according to claim 21, wherein the pH of the wastewater to be treated is adjusted to be greater than 7 prior to the first heat exchange.

24. The method according to claim 21, wherein the first ammonia-containing vapor is discharged after ammonia removal from the tail gas remaining from the condensation of the first heat exchange.

25. The method of claim 1, wherein the second ammonia-containing vapor evaporated by the last evaporator of the second multi-effect evaporator is subjected to a second heat exchange to obtain a second ammonia water.

26. The method according to claim 25, wherein the second ammonia-containing steam is discharged after ammonia removal from the tail gas remaining from the condensation of the second heat exchange.

27. The method according to any one of claims 1 to 8, further comprising subjecting the first concentrated solution containing sodium sulfate crystals to a first solid-liquid separation to obtain sodium sulfate crystals.

28. The method of claim 27, further comprising washing the resulting sodium sulfate crystals.

29. The method according to any one of claims 1 to 8, further comprising subjecting the treatment liquid containing sodium chloride crystals to a second solid-liquid separation to obtain sodium chloride crystals.

30. The method of claim 29, further comprising washing the obtained sodium chloride crystals.

31. The process of any one of claims 1 to 8, wherein the catalyst production wastewater is wastewater from a molecular sieve, alumina or refinery catalyst production process.

32. The method of claim 31, further comprising removing impurities and concentrating the catalyst process wastewater.