Industrial & Engineering Chemistry Research, Vol.57, No.37, 12444-12457, 2018
Economic Comparison of Crystallization Technologies for Different Chemical Products
Crystallization is an ancient unit operation that remains vital for the chemical process industry. Traditional single-effect evaporation consumes a great deal of energy, and various alternatives to this method have been proposed. In this work, the total cost of producing a fixed quantity of different solid chemicals by crystallization from water is determined for several different technologies: evaporative crystallization, membrane distillation with porous hydrophobic membranes, reverse osmosis membrane-assisted crystallization, and eutectic freeze crystallization (EFC). Among the solute properties, the solubility has the greatest effect on the cost of the process since it determines the amount of water that must be removed per unit product produced. If waste heat is available at a unit price lower than that of low-pressure steam produced using coal or natural gas, then the assumed price of waste heat also has a significant effect on the economics. The results indicate that, if feasible, reverse osmosis has the lowest total annual cost. On the other hand, for high osmotic pressure cases, EFC has the lowest cost when cheap heating energy (waste heat) is not available. On the contrary, a conventional single or multiple effect evaporative crystallization has the lowest cost among the remaining options when heating energy is cheap or solubility is high. Moreover, eutectic temperature plays important role when determining the best technology when solubility is between 0.2 and 0.6 kg/kg solution.