The models of two process system networks in an alumina refinery are developed in this paper. These models have been used in the numerical simulations in previous work. They are the washing circuits widely used in the mineral processing plants. The process modeling here is to derive a state space model for the multi-variable feedback control design purpose. The complex process system is modelled as an interconnected system having a mixed connection configuration. The interactions between equipment and sub-processes via the material flows within an unit operation are modelled as interactive variables of subsystems under the auspices of interconnected system formulation
