Control structure selection for energy integrated distillation column

This paper concerns a case study on control structure selection for an almost binary distillation column. The column is energy integrated with a heat pump to transfer heat from the condenser to the reboiler. This integrated configuration renders the possible control structure somewhat different from what is usually seen. Further the heat pump enables disturbances to propagate faster through the system. The plant has six possible actuators of which three must be used to stabilize the system. Hereby three actuators are left for product purity control and/or pressure control. A MILP screening method based on a linear state space model is used to determine an economically optimal set of controlled and also manipulable variables. The generated set of inputs and outputs are analysed with frequency dependent RGA and singular values to determine the best pairing of the variables in terms disturbance rejection and setpoint tracking. The paring and controller design are implemented and evaluated through nonlinear simulation. The suggested control structure is also compared to a control structure applied experimentally.