CN114409157A - Resource method for preparing chlor-alkali by electrolyzing waste brine - Google Patents
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Abstract
The invention discloses a method for recycling chlor-alkali prepared by electrolyzing waste brine, which comprises the following steps: s1, evaporating and concentrating the salt-containing organic wastewater, and performing fractional crystallization to obtain crystalline sodium sulfate; s2, oxidizing and decomposing organic matters in the concentrated salt-containing organic wastewater to obtain salt-containing wastewater; s3, filtering mechanical impurities in the salt-containing wastewater; s4, refining the filtered salt-containing wastewater for the first time by using an inorganic membrane filter; s5, carrying out secondary refining on the salt-containing wastewater subjected to the primary refining by using chelating resin; s6, electrolyzing the secondary refined salt-containing wastewater by using a zero-pole ionic membrane electrolytic cell to obtain alkali liquor, hydrogen and chlorine. The invention converts the diphenylmethane diisocyanate (MDI) salt-containing organic wastewater into the raw material of the chlor-alkali industry through resource treatment, realizes the cyclic utilization of salt resources in the wastewater, and solves the problem of discharge pollution of the high-salt-containing organic wastewater.
Description
Technical Field
The invention relates to the field of high-salt-content wastewater treatment, in particular to a resource method for preparing chlor-alkali by electrolyzing waste brine.
Background
With the rapid development of petrochemical and chemical industries, China gradually forms relatively complete petrochemical, natural gas chemical, coal chemical, salt chemical and biochemical production systems. However, when a large amount of petrochemical and chemical products are manufactured, a large amount of chemical wastewater is generated, and the chemical wastewater has very complex components and contains a large amount of organic matters, inorganic salts, heavy metals and the like, wherein the high-concentration salt-containing organic wastewater is particularly prominent.
At present, for the treatment of high-concentration salt-containing organic wastewater, harmless measures of dilution discharge or evaporation concentration-incineration are mainly adopted, so that the waste of salt resources is caused. Due to the lack of technical, economic feasibility and reliability, most of the methods still adopt a dilution and discharge mode, particularly discharge of saline wastewater, so that the water resource of fresh water is mineralized and the soil is alkalized.
Diphenylmethane diisocyanate (MDI) salt-containing organic wastewater is used as one of high-concentration salt-containing organic wastewater, has large discharge amount, serious environmental hazard and very difficult resource utilization, and is a difficult problem to be solved in the technical field of domestic and foreign green resources at the present stage.
Disclosure of Invention
In view of the above defects in the prior art, the present invention aims to provide a resource method for producing chlor-alkali by electrolyzing waste brine, which converts diphenylmethane diisocyanate (MDI) salt-containing organic wastewater into raw materials for chlor-alkali industry through resource treatment, realizes the cyclic utilization of salt resources in the wastewater, and solves the problem of discharge pollution of the high salt-containing organic wastewater.
The purpose of the invention is realized by the following technical scheme:
a resource method for preparing chlor-alkali by electrolyzing waste brine comprises the following steps:
s1, evaporating and concentrating the salt-containing organic wastewater, and performing fractional crystallization to obtain crystalline sodium sulfate;
s2, oxidizing and decomposing organic matters in the concentrated salt-containing organic wastewater to obtain salt-containing wastewater;
s3, filtering mechanical impurities in the salt-containing wastewater;
s4, refining the filtered salt-containing wastewater for the first time by using an inorganic membrane filter;
s5, carrying out secondary refining on the salt-containing wastewater subjected to the primary refining by using chelating resin;
s6, electrolyzing the secondary refined salt-containing wastewater by using a zero-pole ionic membrane electrolytic cell to obtain alkali liquor, hydrogen and chlorine.
Further, the step S1 of evaporating and concentrating the salt-containing organic wastewater, and the step S of removing sodium sulfate in the salt-containing organic wastewater by fractional crystallization includes the following steps:
SN1, pre-concentrating the salt-containing organic wastewater;
SN2, evaporating the water of the pre-concentrated salt-containing organic wastewater to obtain sodium chloride salt crystals and concentrated solution, wherein the concentration of sodium sulfate in the concentrated solution reaches a saturated state;
SN3, performing cooling and water evaporation treatment on the concentrated solution to obtain sodium chloride salt crystals and a re-concentrated solution; processing part of the re-concentrated solution in step S2;
and (3) heating and evaporating the SN4 and the rest re-concentrated solution to obtain crystalline sodium sulfate and residual liquid, and treating the residual liquid in the step SN 3.
Further, in the step SN1, the salt-containing organic wastewater is preheated and then subjected to pre-concentration treatment; and saturating sodium chloride in the pre-concentrated saline organic wastewater.
Further, clear liquid generated after the sodium chloride salt crystals obtained in the step SN2 are sequentially processed by a salt hydrocyclone and a centrifuge is mixed and diluted with salt-containing organic wastewater to obtain countercurrent saline, and sodium chloride at salt legs of the crystals obtained in the step SN3 is washed;
the concentrated solution is precipitated and then treated in step SN 3.
Further, the counter-current brine portion flushes sodium chloride from the crystallized salt leg in step SN3, and the remaining portion is mixed with the sodium chloride salt crystals obtained in step SN 2.
Further, in step SN3, the concentrated solution is subjected to temperature reduction and moisture evaporation, and the moisture evaporation is performed by using a flash evaporation effect and a mechanical vapor recompression system.
Further, the pre-concentration process of step SN1, the evaporation of water in SN2 and SN4 all utilize a mechanical vapor recompression system.
Further, the step S2 of oxidizing and decomposing the organic matters in the concentrated salt-containing organic wastewater includes the following steps:
adding sodium hypochlorite with the concentration of 3% -6% to ensure that the concentration of the sodium hypochlorite in the reaction tank is 0.8% -1.2%;
adding 10-15% sodium carbonate with the excess of 0.5-1.0 g/L;
adding 0.3-0.5 g/L of 28% -35% sodium hydroxide in excess.
Further, the filtering treatment in the step S3 is to filter and separate mechanical impurities with the grain diameter being more than or equal to 1mm by a filter;
further, in the step S4, the first refining is performed by filtering with three-stage series-connected inorganic membrane filtering units in a cross-flow filtering manner, and each inorganic membrane filtering unit filters the salt-containing wastewater and adds sodium nitrite to remove free chlorine after the salt-containing wastewater is collected.
Due to the adoption of the technical scheme, the invention has the following advantages:
sodium sulfate and sodium chloride are obtained while the salt-containing organic wastewater is treated, so that the resource utilization of the waste salt of the salt-containing organic wastewater of diphenylmethane diisocyanate (MDI) is realized; the membrane method denitration by huge investment construction is avoided; salt and nitrate co-production is realized by fractional crystallization, the current membrane method denitration device greatly influenced by TOC is replaced, and the stable operation of the denitration device is promoted.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.
Drawings
The drawings of the invention are illustrated as follows:
FIG. 1 is a schematic flow chart of a resource method for producing chlor-alkali by electrolyzing waste brine.
Detailed Description
The invention is further illustrated by the following figures and examples.
Example (b):
as shown in figure 1, the resource method for preparing chlor-alkali by electrolyzing waste brine comprises the following steps:
step one, evaporating and concentrating the salt-containing organic wastewater, and crystallizing step by step to obtain crystalline sodium sulfate; the method specifically comprises the following steps:
SN1, preheating the salt-containing organic wastewater, injecting the salt-containing organic wastewater into a first falling film evaporator after preheating, and heating by using recompressed steam of a first mechanical vapor recompression (MVR unit) system. After heating, the evaporation process is started, so that the concentration of the salt-containing organic wastewater is increased, and the water is evaporated and concentrated. The sodium chloride concentration of the pre-concentrated salt-containing organic wastewater approaches or reaches a saturated state.
And SN2, injecting the pre-concentrated salt-containing organic wastewater into a second falling film evaporator, and heating by using recompressed steam of a second mechanical vapor recompression (MVR unit) system. Evaporating the water of the pre-concentrated salt-containing organic wastewater, starting crystallization and gradual deposition of sodium chloride salt crystals, enabling the concentration of sodium sulfate in the remaining concentrated solution to reach a saturated state, and performing precipitation to precipitate and separate the non-adhered crystallized sodium chloride salt;
and (3) treating the crystallized sodium chloride crystal salt by a salt hydrocyclone and a centrifuge in sequence to obtain wet salt, and mixing clear liquid obtained by the salt hydrocyclone and the centrifuge with a small amount of salt-containing organic wastewater to obtain countercurrent salt water.
The countercurrent brine part flushes the sodium chloride deposited on the crystallized salt legs in the step, so that the temperature of sodium chloride salt crystals can be reduced, the centrifugal machine can be protected when the centrifugal machine processes the sodium chloride salt crystals, and the size of the sodium chloride salt crystals can be controlled to obtain the uniform size of the salt crystals suitable for being processed by the propelling type centrifugal machine. The remaining part of the countercurrent brine flows into the crystallized sodium chloride salt.
If the sodium chloride salt is not washed by countercurrent brine, a large amount of NaClO3 will leave the second falling-film evaporator and enter the salt slurry tank and the filtrate storage tank, which will pollute the final sodium chloride salt and negatively affect the sodium chloride crystallization process. On the other hand, too high a concentration of NaClO3 in the sodium chloride salt may cause severe corrosion of the apparatus and significantly increase the boiling point, resulting in a decrease in the evaporation capacity.
SN3 the concentrate was poured into a vacuum flash evaporator and the solubility of sodium sulfate decreased with increasing temperature and the solubility of sodium chloride increased with increasing temperature (standard dissolution profile) over a certain temperature range. By adopting the principle, sodium chloride can be crystallized and separated out at a lower temperature, and sodium sulfate can be crystallized and separated out at a higher temperature.
Therefore, the temperature of the concentrated solution is controlled to be about 50 ℃ so that sodium chloride is precipitated and sodium sulfate is dissolved in the concentrated solution.
And (3) heating the concentrated solution by using a hot vapor recompression (MVR) system while utilizing the flash evaporation effect (the temperature is kept in the range that sodium chloride is separated out and sodium sulfate is dissolved), promoting the evaporation of water in the concentrated solution, and finally obtaining the crystallized sodium chloride and the reconcentrated solution.
In this step, counter-current brine flushes sodium chloride deposited at the crystallized salt legs, serving the same function as in step SN 2.
The re-concentrated solution obtained after partial evaporation is discharged from the system as the final effluent, which contains non-crystallized compounds such as sodium chlorate, iodine, TOC, etc. The discharge of iodine can reduce the influence on the ionic membrane in the subsequent electrolytic process, and is beneficial to stabilizing the operating efficiency of the ionic membrane. The discharged sodium chlorate directly eliminates the operating costs of current chlorate plants. The discharged TOC material may reduce the operating costs of the operation of the TOC removal device.
The SN4, the remaining reconcentrated liquid, enters a third falling film evaporator and is heated with recompressed vapor from a third mechanical vapor recompression (MVR unit). After the water evaporation, the sodium sulfate starts to crystallize, and the remaining liquid is precipitated under the pressure difference of the flash evaporator and then enters the flash evaporator again for treatment.
Heating for evaporating water to obtain crystalline sodium sulfate and residual liquid, and treating the residual liquid in step SN 3.
In the first step, the steam of the MVR system is fully utilized, and the energy consumption is effectively reduced.
Secondly, adding sodium hypochlorite with the concentration of 3% -6% into the discharged reconcentrated liquid serving as the final discharge liquid in the step SN3 to ensure that the concentration of the sodium hypochlorite in the reaction tank is 0.8% -1.2%; adding 10-15% sodium carbonate with the excess of 0.5-1.0 g/L; adding 0.3-0.5 g/L excess sodium hydroxide with concentration of 28% -35% for treatment.
Adding sodium carbonate solution into the re-concentrated solution to react with Ca2+ in the re-concentrated solution to generate insoluble calcium carbonate precipitate; adding sodium hydroxide solution to the reconcentrated solution to react with Mg2+ in the reconcentrated solution to form insoluble Mg (OH)2 precipitate; free chlorine in the sodium hypochlorite oxidizes and decomposes bacteria and algae and other organic matters brought by the re-concentrated solution to finally obtain salt-containing wastewater.
And thirdly, passing the salt-containing wastewater through a coarse filter with the aperture of 1.0mm to remove mechanical impurities.
And fourthly, sequentially passing the salt-containing wastewater for filtering mechanical impurities through three-stage inorganic membrane filtering units connected in series. The inorganic membrane filter adopts a ceramic membrane tube as a filter element, and suspended particles are filtered and removed in a cross-flow filtering mode, so that the contents of SS, Ca2+ and Mg2+ in the brine are ensured to meet the requirements, and finally refined filtered brine is obtained.
And fifthly, pressurizing the refined filtered brine, heating the refined filtered brine to 60 +/-5 ℃ through a heat exchanger, conveying the refined filtered brine to a chelating resin tower, adsorbing Ca2+, Mg2+ and other heavy metal ions in the refined filtered brine, and then trapping and crushing resin through a resin trap to obtain the refined brine.
And sixthly, injecting the refined brine into a zero-polar-distance ion-exchange membrane electrolytic cell for electrolysis, producing qualified chlorine at the anode of the electrolytic cell, and producing qualified alkali liquor and hydrogen at the cathode.
Finally, the above embodiments are only intended to illustrate the technical solutions of the present invention and not to limit the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions, and all of them should be covered by the claims of the present invention.
Claims (10)
1. A resource method for preparing chlor-alkali by electrolyzing waste brine is characterized by comprising the following steps:
s1, evaporating and concentrating the salt-containing organic wastewater, and performing fractional crystallization to obtain crystalline sodium sulfate;
s2, oxidizing and decomposing organic matters in the concentrated salt-containing organic wastewater to obtain salt-containing wastewater;
s3, filtering mechanical impurities in the salt-containing wastewater;
s4, refining the filtered salt-containing wastewater for the first time by using an inorganic membrane filter;
s5, carrying out secondary refining on the salt-containing wastewater subjected to the primary refining by using chelating resin;
s6, electrolyzing the secondary refined salt-containing wastewater by using a zero-pole ionic membrane electrolytic cell to obtain alkali liquor, hydrogen and chlorine.
2. The resource method for preparing chlor-alkali by electrolyzing waste brine as claimed in claim 1, wherein the step S1 comprises the following steps:
SN1, pre-concentrating the salt-containing organic wastewater;
SN2, evaporating the water of the pre-concentrated salt-containing organic wastewater to obtain sodium chloride salt crystals and concentrated solution, wherein the concentration of sodium sulfate in the concentrated solution reaches a saturated state;
SN3, performing cooling and water evaporation treatment on the concentrated solution to obtain sodium chloride salt crystals and a re-concentrated solution; processing part of the re-concentrated solution in step S2;
and (3) heating and evaporating the SN4 and the rest re-concentrated solution to obtain crystalline sodium sulfate and residual liquid, and treating the residual liquid in the step SN 3.
3. The resource method for preparing chlor-alkali by electrolyzing waste brine as claimed in claim 2, wherein in step SN1, the organic wastewater containing salt is pre-heated and then pre-concentrated; and saturating sodium chloride in the pre-concentrated saline organic wastewater.
4. The resource method for preparing chlor-alkali by electrolyzing waste brine as claimed in claim 2, wherein the clear solution produced by the treatment of the sodium chloride salt crystals obtained in step SN2 sequentially through the salt hydrocyclone and the centrifuge is mixed and diluted with the organic wastewater containing salt to obtain the counter-current brine, and the sodium chloride at the salt leg of the crystallization in step SN3 is washed;
the concentrated solution is precipitated and then treated in step SN 3.
5. A resource utilization method for electrolytic production of chlor-alkali from waste brine as claimed in claim 4, characterized in that the part of the countercurrent brine flushes the sodium chloride in the crystallized salt leg of step SN3, and the rest part is mixed with the sodium chloride salt crystals obtained in step SN 2.
6. The resource method for preparing chlor-alkali from waste brine through electrolysis as claimed in claim 2, wherein in step SN3, the concentrated solution is subjected to temperature reduction and water evaporation treatment, and the water evaporation treatment is carried out by utilizing a flash evaporation effect and a mechanical vapor recompression system.
7. The resource method for preparing chlor-alkali from waste brine by electrolysis as claimed in claim 2, wherein the pre-concentration treatment of step SN1 and the water evaporation treatment in steps SN2 and SN4 all utilize mechanical vapor recompression system.
8. The method as claimed in claim 1, wherein the step S2 of oxidizing and decomposing the organic substances in the concentrated organic wastewater containing salt comprises the following steps:
adding sodium hypochlorite with the concentration of 3% -6% to ensure that the concentration of the sodium hypochlorite in the reaction tank is 0.8% -1.2%;
adding 10-15% sodium carbonate with the excess of 0.5-1.0 g/L;
adding 0.3-0.5 g/L of 28% -35% sodium hydroxide in excess.
9. The method as claimed in claim 1, wherein the step S3 is carried out by filtering with a filter to separate mechanical impurities with particle size not less than 1 mm.
10. The resource method for preparing chlor-alkali by electrolyzing waste brine as claimed in claim 1, wherein in step S4, the first refining is performed by filtering with three-stage inorganic membrane filter units connected in series in a cross flow manner, and each inorganic membrane filter unit filters salt-containing wastewater to be collected and then sodium nitrite is added to remove free chlorine.
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| CN115417491A (en) * | 2022-08-16 | 2022-12-02 | 龙佰集团股份有限公司 | Method for synergistically removing TOC and ammonia nitrogen in sodium chloride wastewater |
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| CN107364877A (en) * | 2017-08-09 | 2017-11-21 | 深圳市瑞升华科技股份有限公司 | A kind of solventing-out Processes and apparatus of zero discharge of industrial waste water |
| CN207933534U (en) * | 2017-12-15 | 2018-10-02 | 江苏久吾高科技股份有限公司 | A kind of purification devices of abraum salt |
| US20210101815A1 (en) * | 2018-02-14 | 2021-04-08 | Covestro Intellectual Property Gmbh & Co. Kg | Process for the work-up and reuse of salt-containing process water |
| CN109293089A (en) * | 2018-10-29 | 2019-02-01 | 甘肃银光聚银化工有限公司 | A kind of processing method of TDI production neutral and alkali brine waste |
| CN109292797A (en) * | 2018-11-02 | 2019-02-01 | 江苏中圣高科技产业有限公司 | A kind of brine waste sub-prime recovery method |
| CN111661886A (en) * | 2019-03-07 | 2020-09-15 | 广州市迈源科技有限公司 | MVR evaporation salt separation system |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115417491A (en) * | 2022-08-16 | 2022-12-02 | 龙佰集团股份有限公司 | Method for synergistically removing TOC and ammonia nitrogen in sodium chloride wastewater |
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