While one crystallization step can be sufficient to provide pure components in case of eutectic systems, multistage operation is required to resolve solid solutions. A recently published equilibrium stage model was adopted here and generalized to simplify the description of the corresponding solid‐liquid equilibrium (SLE). The equilibria of the system potassium sulfate/ammonium sulfate/water were studied at different temperatures. The existence of a controversially discussed miscibility gap below 25 °C could not be confirmed. Using the equilibrium stage model and the studied specific SLE data, process variants considering different evaporation strategies were simulated.