Parameter setting method for control system of cryogenic distillation column

A computer code is developed for analysis of dynamic behavior of a single cryogenic distillation column. A dynamic simulation study is performed for the lead column in a typical column cascade which consists of four columns and two catalytic equilibrators. The atom fraction of protium in the bottom product and the reflux ratio are regarded as the controlled variable and the manipulated variable, respectively. Fluctuation or change of the feed composition is considered as the disturbance and the PI control scheme is introduced for a constant value control. The criteria are derived, which can be used in setting the choice of the two PI controller parameters. Investigated are the effects of the controller parameters on the response of the controlled variable to a step change in the feed composition, and the validity of the criteria is verified. The parameter setting method proposed in the present study has two advantages: it accounts for the strong nonlinearity of the column and it predicts the unstable region which must be avoided in the actual operation. (author)