A kind of evaporation crystallization method to ammonium chloride when producing potassium nitrate

Abstract

The invention discloses an evaporative crystallization method of ammonium chloride in potassium nitrate production, which belongs to the technical field of evaporative crystallization of solutions. The evaporative crystallization method comprises a multiple-effect countercurrent falling film evaporation process and a DTB flash crystallization process, i.e. an ammonium chloride mother liquid enters a final-effect evaporator firstly, and then enters a previous-effect evaporator until the mother liquid enters a first-effect evaporator to heat for evaporating, then feed liquor obtained in the first-effect evaporator is pumped into a DTB flash crystallizer to carry out cooling crystallization so as to obtain primary crystal mush and a fine-crystal containing primary clear liquid, the primary clear liquid is pumped into a fine-crystal eliminator to heat and dissolve fine-crystals, and the primary crystal mush is pumped into a thickener to thicken, so that secondary crystal mush and a secondary clear liquid are obtained; and the secondary crystal mush is subjected to centrifugal drying treatment so as to obtain solid ammonium chloride, and the secondary clear liquid enters a settler to carry out settling treatment, so that potassium nitrate mother liquid and a settling liquid are obtained. The method disclosed by the invention is low in process investment operating cost, uniform in crystal size of products, and good in quality.

Description

technical field [0001] The invention relates to the technical field of evaporative crystallization of solutions, in particular to a method for evaporative crystallization of ammonium chloride during the production of potassium nitrate. Background technique [0002] Potassium nitrate is an important inorganic chemical raw material. The production method of potassium nitrate in my country mainly adopts the metathesis conversion method of ammonium nitrate and potassium chloride. This method also generates a by-product ammonium chloride while generating potassium nitrate. Discharging ammonium chloride waste liquid will cause great pollution to the environment, so it is generally necessary to separate the by-product ammonium chloride. Generally speaking, when separating ammonium chloride, it is usually necessary to evaporate, crystallize and centrifuge the ammonium chloride mother liquor A series of steps such as separation. [0003] Most of the existing ammonium chloride mother l...

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Problems solved by technology

[0005] (2) High investment and operating costs

Since the liquid flow rate in the heat exchange tube of the forced external circulation evaporator is generally large, the forced external circulation evaporator is often equipped with a high-power circulation pump with a large flow rate and a low lift, which greatly increases investment and operating costs.

[0006] (3) The product crystal particle size distribution is wide and the quality is poor

Crystals are often produced in the final effect of the forced external circulation evaporator. When using a forced circulation pump, the crystal grains in the slurry will collide with the high-speed rotating impeller, causing damage to the crystal itself. More than 80% of the product crystal grain size Between 0.08 and 0.2mm, the crystal particle size distribution is wide, the quality is poor, and the yield of the product is low; at the same time, during the collision process, the crystal will also cause certain wear and tear on the pump body itself, thus increasing maintenance. cost

[0007] (4) For a single-effect evaporator, since the heat exchange surface is relatively small, it is necessary to maintain a large temperature difference between the medium on both sides of the heat exchange surface, but the large temperature difference is likely to cause the solution to contact with the heat exchange surface. Local overheating causes materials to accumulate on the heat exchange surface, resulting in poor heat transfer effect on the heat exchange surface and increased labor for subsequent processing

[0008] In addition, there are also problems such as large footprint of the device

Due to the above shortcomings in the existing ammonium chloride mother liquor evaporation and crystallization production process, the process has obtained low production capacity under the condition of high cost operation

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