Freeze Crystallization Processes: Efficiency by Flexibility

Abstract

Energy consumption in fractionating solutions by distillation and evaporation can be reduced by 70% to 90% by using freeze crystallization processes. The thermodynamic bases for the substantially lower energy requirements include: 1) The phase change is required only once in freeze processes, as opposed to the high reflux ratios needed in most distillation separations. 2) The latent heat of fusion is less than the heat of vaporization, and the process operates at a lower temperature, so the entropy of the separation is less. 3) A heat pump is used in the freeze crystallization process to transfer heat from the freezer to the melter, providing advantages similar to the vapor compression evaporator cycle. Freeze crystallization should be considered an alternative to all distillation and evaporation separation processes. The factors which affect the relative efficiency and economics of the process are discussed in this paper.