THE CONTROL OF AZEOTROPIC DISTILLATION COLUMNS

A steady state analysis is used to design control systems for azeotropic distillation columns. A simulation based on the Naphtali-Sandholm solution method is developed and a procedure based on step averaging is used to improve the convergence of the solution method. The success of the step averaging procedure in promoting convergence is demonstrated on various examples including those for which multiple solutions exist.;The control schemes suggested by the steady state analysis are then studied using a dynamic simulation. The dynamic results confirm the conclusions of the steady state analysis.;Using the steady state simulation, a steady state analysis is performed on two azeotropic distillation columns. The steady state gains are rigorously calculated for an isopropanol drying column and an ethanol drying column. The resulting process gain matrices are then decomposed using the singular value decomposition (SVD). Information derived from the SVD is interpreted in light of the column control problem and is compared to results obtained using Bristol's relative gain array (RGA). The SVD analysis indicates where to locate temperature sensors, which manipulated variables to use for control and the number of independent inputs and outputs. The RGA is used in conjunction with the SVD to pair the inputs and outputs in a single-input, single-output fashion.