Abstract
A mathematical model of a pressure crystallizer for high-temperature crystallization of inorganic compounds from aqueous solutions is presented. The model is a result of long-term research which has led to the design of the new type continuous pressure crystallizer for high-temperature crystallization. High-temperature crystallization from aqueous solutions, also called crystallization under elevated temperature and pressure or thermal crystallization, can be used for salts characterized by inverse solubility (the solubility of some salts, mainly sulphates, decreases as the temperature rises). In order to crystallize such salts their solutions are heated up to appropriately high temperatures (in the order of 473 K). For this reasons the process of high- temperature crystallization takes place under elevated pressure (about 1.6 MPa). One of the main advantages of this process is lower energy consumption in comparison with evaporation crystallization, especially in the case of low-concentration solutions. The mathematical model is based on the results of investigations into the high-temperature crystallization of magnesium, manganese (II) and zinc sulphates conducted in the developed continuous pressure crystallizer with a working volume of 0.006 m3. The crystallizer working space is divided into two parts. The upper part works similarly to the MSMPR crystallizer. From the crystallizer’s upper part the crystal slurry flows to its lower part where the process is continued and where the crystal slurry thickens as some of the mother liquor with fines is discharged. Population balances for the crystallizer’s upper part and its lower part, and kinetics parameters are entered into the mathematical model. Using the mathematical model one can simulate the effect of the operating parameters on the size of the produced crystals and generate designs of the pressure crystallizer.
