Study On Evaporation-Cooling Crystallization Process Of Ammonium Chloride

Ammonium chloride is an important inorganic salt and is widely used in many fields, such as agriculture, food ,medicine, et al. In view of the quality problems of the ammonium chloride product made in China, such as the poor crystal morphology, asymmetry CSD and the low yield, the crystallization process of ammonium chloride were investigated and analyzed systematically.The solubility of ammonium chloride adding impurities(such as sodium chloride, potassium chloride) in water was measured by the laser method and the equations were fitted via the solid-liquid equilibrium experiential equation.The concentration of impurities is 0g/L-10g/L.According to the crystallization process,the unsteady state method was employed to measure evaporation crystallization kinetics and the equations of nucleation and growth rate of ammonium chloride in pure water were got.The effect of operation parameters on nucleation and growth rate was discussed.On the basis of thermodynamics and kinetics study,the couping crystallization process of vacuum evaporation and cooling was optimized experimentally.The effect of parameters,such as evaporation rate, agitation speed,cooling rate, seeds added,on the product quality were studied,and the crystallization process was optimized at last.Also the effect of impurities on the crystal morphology was studied. The quality of ammonium chloride accords with the nation standard, and the crystal size and crystal size distribution are superior to the product of factory.To reduce the production cost and energy use effectively, a mathematical model of a continuous multistage evaporation crystallizer is established in this work,involving equations of mass balance, heat balance, population balance, solubility and crystallization kinetics.