This paper gives a general method to calculate solid and liquid equilibrium (SLE) stage by identifying the number of phases and the species of crystals existing at equilibrium automatically. An effective and rapid algorithm is proposed to obtain the result at equilibrium. Meanwhile this algorithm also gives the sequence of each crystal being precipitated and the composition of each phase at the time of crystal precipitation. This is important for the need of process simulation for solid - liquid separation. Especially

the method proposed does not depend on the phase diagram. On the contrary

the phase diagram of solid and liquid equilibrium could be obtained-by this method. Several examples are given to show that this method is capable of predicting the composition of SLE for systems with hydrate

multi -ion and complex salts.