A systematic method is presented for improving the recovery of the desirable product in an existing fractional crystallization process. Solid-liquid-phase behaviors and techniques relevant to product recovery are discussed. Retrofit targets are identified through an analysis of the phase diagram of the mixture under consideration. Conceptual design techniques consisting of heat and mass balances, heuristics, and short-cut unit models are used to determine the necessary changes in flow sheet structure and equipment design in order to meet the retrofit objective. The method is illustrated with an adipic acid plant.