Dynamic effects of temperature control tray location in distillation columns

AbstractThis paper presents the results of theoretical and experimental studies of the dynamic effects of varying the location of the temperature control tray in a distillation column. The binary methanol‐water system was studied in a 24‐tray, 8‐in. I.D. column with reflux manipulated to hold the temperature on various trays in the rectifying section of the column.The ultimate gain and ultimate frequency of the temperature feedback control loops were found to decrease as the temperature control tray was moved down the column away from the top. This confirmed the qualitative statements made by many workers and the quantitative work recently reported by Beaverstock.The process natural frequency (or breakpoint frequency) was found, unexpectedly, to increase somewhat as the temperature control tray was moved down the column. This meant that the open‐loop response of tray liquid composition to reflux flow changes was slightly slower for trays near the top of the column. Because of the increasing purity near the top, adjacent trays differed little in composition and the slope of the equilibrium line was flatter. Both contributed to slower dynamic response.In developing a theoretical model for the real system studied, the linear model and solution techniques of Lamb, Pigford, and Rippin and were extended to include nonequimolal overflow effects.