| Potassium nitrate (KNO3) is not only an important industrial raw material, but also can be used as an efficient chlorine-free nitrogen and potassium compound fertilizer. It can be extracted from natural minerals, salt lake, or obtained by synthetic industry. At present, the domestic production of potassium nitrate is widely produced by double decomposition from ammonium nitrate (NH4NO3) and potassium chloride (KC1), and ammonium chloride as a by-product. The technical method is simple and no "three wastes" emissions. But there are still a small number of products containing ammonium chloride and more fine-grained, have wide range of particle size distribution, resulting in the production of potassium nitrate can only reach agricultural grade, and easily caking during storage.The production process and parameters optimization of potassium nitrate by double decomposition method from potassium chloride and ammonium nitrate require the solubility data of K+,NH4+//Cl-,NO3-—H2O system as a theoretical basis. However, the solubility data of this system are incomplete, and there is a big part of the data errors. In this study, on the basis of previous research the data of potassium nitrate and ammonium nitrate crystalline regions involved two-salt eutectic line and three-salt eutectic point at 20 ℃ have been improved. The corresponding equilibrium phase physicochemical properties were measured. And the solubility data of four side points, three three-salt eutectic points, five two-salt eutectic lines were obtained. Based on experimental results draw the dry salt diagram, water diagram, and physicochemical properties-composition diagram of potassium nitrate and ammonium nitrate crystalline regions in this system.The equilibrium phase diagram is the study of the solubility data of two-salt eutectic line and three-salt eutectic point in the complex system. There is a certain deviation between solution state and equilibrium state in the actual production of potassium nitrate. The actual liquid is only saturated solution of potassium nitrate, that is to say the research object is a line of potassium nitrate eutectic plane. So according to enterprise’s three stage flash crystallization process and material composition, the solubility of potassium nitrate in the complex system at different evaporation rates and temperatures were measured. Studies have shown that the solubility of potassium nitrate increases with increasing temperature, and decreases with increasing water evaporation rate. And the supersolvus of potassium nitrate was determined by using cooling balance method in the evaporated to 5% of the raw materials, and obtained the degree of super-cooling is 3.8-3.9℃.Intermittent dynamic method was respectively used to study the cooling crystallization kinetics of potassium nitrate in KNO3—H2O system and in a complex system. The model equations of the nucleation rate and the crystal growth rate of potassium nitrate in two systems were finally obtained. The effects of the operational parameters such as temperature, supersaturation and the stir speed on the nucleation rate and the crystal growth rate were analyzed by these model equations.Single factor experimental method was used to study the relationship among the yield of potassium nitrate in single cycle with mixture ratio (molar ratio of KC1 and NH4NO3 ingredients), the amount of water (water and dry salt molar ratio), and the cooling temperature. Process parameters have been optimized. |
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