Multicomponent distillation dynamics

Abstract

This dissertation is a study of the composition dynamics of multicomponent distillation in a plate column. A ten-plate bubble-cap distillation column 21 feet in length with a two-foot inside diameter and a one-foot plate spacing was used. There were 22 two-inch bubble caps per plate. The feed system consisted of benzene, n-heptane, toluene, and xylene.

Three experimental tests were analyzed; (1) a steady state test in which there was no forcing of the feed stream composition, (2) a transient test in which the feed stream benzene concentration was increased for a twenty-minute period, and (3) a pulse test in which the feed stream benzene concentration was increased for a five-minute period. The sampling frequency for the steady state and transient tests was one sample per minute from the.liquid of each of the plates and the feed, bottoms, and reflux streams. The sampling frequency for the pulse test was one sample every thirty seconds from the liquid and vapor of each plate and from the three terminal streams.

The dynamic periods of the transient and pulse tests were simulated by means of a digital computer program. The program was written to solve by a finite difference method the differential equations describing the composition dynamics of the column. The transient and pulse composition response functions were transformed into the frequency domain by means of numerical methods. Simple lumped parameter transfer functions were then fit to the frequency response plots derived from the experimental data.

It was determined that the digital computer program used to simulate the composition variations gave satisfactory results in comparison with the experimental data. The method of determining the initial conditions of the dynamic simulation program by means of a steady state multicomponent distillation computer program proved to be satisfactory.