Study On Evaporation Crystallization Process Of Ammonium Sulfate

Ammonium sulfate is nitrogenous fertilizer for agriculture. There were some problems in the production of ammonium sulfate, such as uneven crystal size, bad color and morphology etc. So the crystallization process needs to be improved. In order to get better products, the evaporation crystallization process of ammonium sulfate solution made by coke oven gas absorption was studied systematically both in experiment and theory.Crystallization thermodynamics is the key factor for the production yield and the selection of crystallization process. In this thesis, the solubility and metastable zone was determined by laser method. The effects of acidity and impurity on the metastable zone width were studied. The relation between pressure and temperature in vacuum evaporation crystallization process was studied based on the theoretical analysis. The equation of pressure and temperature was inferred to show the relation between them.The nucleation and growth rate can affect the crystal size distribution (CSD). It is the basis for the crystallization operation and scale-up design. According to the crystallization process, the unsteady state method was employed to measure the nucleation and growth kinetics and the equations of nucleation and growth rate in pure water and raw material were got. The effects of acidity of solution and impurity in the raw material on nucleation and growth rate were discussed.Based on thermodynamics and kinetics, the vacuum evaporation crystallization process was optimized experimentally. The effects of parameters, such as seeds added, agitation speed, evaporation temperature, pH of solution etc. on the product quality were studied. And the better operation conditions of crystallization were determined. The better products were produced under the optimized operation condition.Mixing is important to crystallization and reaction processes. Now agitation is a commonly mixing operation in chemical industry. According to the properties of material and operating conditions, the fluid fields of different impellers in crystallizers were simulated with CFD code. The results of simulation were compared and discussed, and the effects on crystallization of two different impellers were analyzed.