Control of quaternary reactive distillation columns: Effects of number and location of temperature loops

The most frequently studied ideal system for reactive distillation columns is the quaternary system with two reactants and two products. The vast majority of reactive distillation literature on control uses two-point inferential control structures with conventional tray selection techniques such as singular value decomposition (SVD) and relative gain array (RGA) analysis. Another common practice for the ideal systems is the assumption of constant relative volatilities. This paper compares two control structures with different number of temperature loops and two alternative sets of tray locations, in terms of the controllability of systems with temperature-dependent relative volatilities. It is observed that a three-point inferential control structure with a new set of tray locations based on a semisystematic method improves the control performance for all three systems studied. This improvement is particularly significant in the purity of the distillate stream as the temperature dependency increases.