Coordinated control of blending systems

Blending is an important unit operation in chemical process industries. Based on Luyben's work, a coordinated control is proposed to overcome the system interaction and process nonlinearity in blending processes. Blending systems with ideal and nonideal mixing (by nonideal mixing we mean the blended property is not a linear function of the inlet properties) are explored. Furthermore, unusual dynamic behavior is observed for blending systems coupled with complex dynamics arisen from the process side. Controlling the blending of streams from different sidestream locations of a distillation column is studied and, based on physical insight, a simple procedure is proposed for the selection of sidedraw locations. Since, the properties of the inlet streams are often subject to changes and disturbance rejection aspects of blending control are discussed and practically important issues such as model uncertainties and measurement noise are also treated in a rigorous manner. Simulation results show that the control of blending systems is not as trivial as it was thought and, more importantly, improvement in the performance can be achieved using the proposed coordinated control.