Rigorous Simulation Model of a KCl Food Production Plant to Address Impurity Precipitation

Potassium chloride (KCl) is widely used in many fields of the processing industry. The application in the food industry, as well the one in the pharmaceutic sector, requires very pure KCl crystals (not less than 99.0%), therefore the elimination of impurities in the production process is a mandatory task. The case study analyzed in this work is a real pilot plant for producing high-purity KCl developed by an Italian chemical company. The major issue of this process is given by the occasional presence of potassium sulfate (K2SO4) in the final product which invalidates the stringent purity specifications required. The actual socio-economic situation linked to the energy and raw materials markets makes it very difficult for the industries to spend efforts for experimental investigations that are normally often long and expensive. Therefore, a rigorous simulation model of the plant has been built using UniSim Design® with the thermodynamic package OLI® that enables the possibility to consider different liquid-solid equilibria. The developed model has been used to verify the formation of the impurities in three different ways: checking the process normal operation, verifying the fluid dynamics design of the crystallization unit, and investigating the start-up conditions. The analysis shows a potential source of formation of K2SO4 nucleus under the actual brine concentration recirculated in the crystallizer during the start-up phase, albeit further investigations have to be performed on the pilot plant to confirm such a hypothesis.