Method for preparing anhydrous sodium sulphate from mirabilite hydrate in chlor-alkali production and related nitre melting equipment

Abstract

The invention provides a method for preparing anhydrous sodium sulphate from mirabilite hydrate in chlor-alkali production and related nitre melting equipment. According to the method, the target of producing the anhydrous sodium sulphate from the mirabilite hydrate is achieved through the steps of nitre melting liquid introduction, reasonable nitre melting, heating and warming, salting-out crystallization and solid-liquid separation. The adopted nitre melting equipment comprises a nitre melting tank and a mixing melter, wherein an inner cavity of the nitre melting tank is divided into a solid-phase area and a melting area by a grating; the mixing melter communicates with the lower part of the melting area; and one path of the nitre melting liquid enters the melting area to melt the mirabilite hydrate, and the other path enters the mixing melter to be mixed and melted with nitrate slurry settled from the melting area. The process is creatively fused with a whole chlor-alkali system, a new production process is created for co-production of caustic soda of chlor-alkali enterprises, refined salt and anhydrous sodium sulphate and large-scale use of underground cheap high-SO4<2-> brine. Compared with a currently running mirabilite hydrate technology, the method has the characteristics of continuous efficient and stable operation, environment protection, energy conservation and production of high-quality anhydrous sodium sulphate.

Description

technical field [0001] The invention belongs to the technical field of inorganic salt separation, and in particular relates to the production of sodium ion membrane caustic soda, which involves melting, heating, salting out and crystallizing separation of Glauber's salt decahydrate separated by membrane method denitrification, recovering nitrate salt co-saturated solution, freezing denitrification, and dechlorination. The dehydration process of Glauber's salt decahydrate in the process of producing caustic soda in the production system. Background technique [0002] Na 2 SO 4 As an accompanying substance, it always exists in the original salt. In the dechlorination process of light brine, a certain amount of Na should also be added. 2 SO 3 As a reducing agent to reduce free chlorine in light brine, a small amount of Na 2 SO 4 . During the production of caustic soda by ion membrane electrolysis of salt water, Na 2 SO 4 It will gradually accumulate and affect the solu...

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Problems solved by technology

[0004] ①Salt-out dehydration method of molten nitrate in kettle, intermittent operation, adding salting-out agent NaCl at one time after melting Glauber’s salt decahydrate, concentrated supersaturated precipitation of Anhydrous Glauber’s salt, input amount of salting-out agent NaCl, solution composition after salting-out, reaction Factors such as time control and determination of the reaction end point are uncertain, and the crystal particles of the product are unstable and of poor quality

[0005] ② Evaporation and concentration method, after melting and separating the decahydrate Glauber’s salt, then evaporating and concentrating the saturated solution to produce Anhydrous Glauber’s salt, during the whole process of evaporating and concentrating the Glauber’s salt saturated solution to precipitate anhydrous Glauber’s salt, the solution is in a supersaturated state, and the operation is difficult. Steam consumption and various costs are quite high, only seen in reports without industrialized examples

[0006] ③Hot-melt method, after melting Glauber’s salt decahydrate, separate out Glauber’s salt decahydrate, then freeze the saturated solution to separate Glauber’s salt decahydrate, then melt Glauber’s salt decahydrate to separate Anhydrous Glauber’s salt, the maximum precipitation rate of Glauber’s salt in one cycle is 33.79%, and the circulation in the whole device The materials are all in a saturated state, the operation is difficult, the blockage of each link is serious, the start and stop are frequent, and the basic conditions for continuous operation are not met.

[0007] Judging from the above processing techniques, various dehydration techniques of Glauber's salt decahydrate are immature and do not meet the conditions for industrialized continuous production. The use of Glauber's salt decahydrate is quite limited compared to Anhydrous Glauber's salt, resulting in by-products of membrane denitrification in chlor-alkali enterprises Glauber's salt decahydrate is seriously unsalable, and there is basically no way out, which to a large extent also restricts the use value of low-cost Gaomans brine as a raw material for caustic soda

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