Method and system for refining crude brine

Abstract

The invention relates to a method and a system for refining crude brine. The method comprises the following steps of: performing pre-reaction; pressurizing and dissolving gas; pretreating; performing post reaction; filtering by using a membrane; and filtering off residual slag particles by using a membrane filter to obtain the refined brine. By the method and the system for refining crude brine, under the condition of not introducing new impurities, various metal impurity ions are efficiently flocculated and precipitated, so that problems of great mineral salt impurity fluctuation and overproof Fe and Al ions are solved, the high quality of the finished brine product and the high-efficiency and normal operation of subsequent ion-exchange membrane electrolysis can be ensured, and the aim that mineral salt replaces sea salt to serve as chlor-alkali electrolysis raw salt is fulfilled; moreover, brine sludge emission and treatment cost can be obviously reduced, and the method and the system have good emission reduction effect and good environment-friendly property.

Description

technical field [0001] The present invention relates to chemical raw material and its preparation, more specifically, the present invention relates to chlor-alkali salt and its preparation process and equipment system. Background technique [0002] Raw salt, as the main raw material in the chlor-alkali industry, accounts for about 30% of the cost of making alkali. Chlor-alkali enterprises need a large amount of raw salt every day, and its quality and price affect the market competitiveness of chlor-alkali enterprises. The raw salt used by foreign chlor-alkali enterprises is basically refined salt (its purity is above 99%, or even 99.5%); while the raw salt used by domestic chlor-alkali enterprises is mainly divided into sea salt, lake salt, and mineral salt according to their sources. Wait. [0003] From crude salt to chlor-alkali products, the first process that must be passed through is brine refining. Its main task is to dissolve solid crude salt and remove impurities ha...

AI Technical Summary

Problems solved by technology

[0007] However, sea salt (including lake salt) has the following serious disadvantages: (1) its salt content (sodium chloride) is 92%, which is lower than 97.5% of mineral salt. For a long time, its price is higher than that of mineral salt, while chlor-alkali The average daily consumption of raw salt in enterprises is tens or even hundreds of tons, and its high price leads to high costs; (2) For the majority of inland chlor-alkali enterprises, sea salt still has the problems of difficult transportation and easy stock out of stock, which will give enterprises Production and operation have serious consequences

Usually, in order to stabilize the supply and production, the majority of inland chlor-alkali enterprises purchase raw salt for about 2-3 months each time, and the quantity reaches thousands or even tens of thousands of tons.

(3) Because the salt content of sea salt (92%) is lower than that of mineral salt (97.5%), and its impurity content is higher, the amount of salt mud formed during the purification process accounts for about 7% of the raw material, and more salt mud is needed Expenses are used for environmental protection treatment, which also affects the operation and development of enterprises

[0009] The problem of ion adsorption method: because the brine is alkaline, various metals basically exist in the form of hydroxide, it is difficult to remove them by adsorption resin, and the special adsorption equipment is expensive and costly, which is not conducive to market competition. , the ion adsorption method has no practical production value

[0010] Flocculation problems: commonly used flocculants are FeCl 3 , aluminum chloride, iron sulfate, sodium polyacrylate, etc., but because the electrolysis process has strict requirements on the content of organic impurities, it is required that no organic impurities harmful to electrolysis be introduced during flocculation. Therefore, sodium polyacrylate cannot be used, and it is currently preferred. FeCl 3 as flocculant

However, increasing FeCl for mineral salt 3 As a result of the dosage, although most of the metal ions can be separated from the solid and liquid, the stubborn problem of iron and aluminum exceeding the standard in the primary brine is difficult to solve; and this will lead to an increase in the electrolysis voltage of the ion membrane in subsequent electrolysis, reducing the ion membrane The efficiency of electrolysis will increase the energy consumption, even damage the ion membrane, shorten the service life of the ion membrane, which is very unfavorable to the production of chlor-alkali

[0011] In order to solve the problems caused by the different advantages and disadvantages of sea salt and mineral salt in the above-mentioned production process, some domestic enterprises have adopted the method of mixing part of sea salt with mineral salt, which has achieved certain results in improving the quality of primary brine, but this method needs to be adjusted according to the quality of mineral salt. The proportion of sea salt, firstly, the production of sea salt is greatly affected by the climate, the transportation is inconvenient, the supply is unstable, and the problem of out-of-stock cannot be solved fundamentally; secondly, this method greatly increases the links and costs of the production and operation management of the enterprise, making it difficult to continue to implement

Third, after mixing part of sea salt, the amount of salt mud will increase, which will increase the cost of environmental protection treatment at the same time

[0012] At the same time, some domestic enterprises adopt the method of recycling part of the salt mud produced by a brine filtration in the pre-filtration system to increase the adsorption capacity of impurities during the filtration of the brine system. Practice has proved that the salt mud circulation technology has a certain effect on the above-mentioned raw salt problem. Relief, you can reduce the amount of sea salt, but when it is reduced to about 15%, the impurity content is abnormal, and the treatment effect is not ideal

[0013] It can be seen from the above that in the traditional process, mineral salt alone cannot meet the quality requirements of ion membrane electrolysis production, and cannot be used as raw salt for ion membrane electrolysis

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