Practical evaluation of hold-up for passive decoupling in distillation column

Decisions made during the steady-state design of distillation columns have a large influence on the dynamic characteristics of the operating unit. Conventionally, steady-state design is often completed before dynamics and control issues are considered. Additional complexity in the active control system must as a result be used to compensate for any resulting shortcomings in dynamic performance. Here, our aim is to improve control system performance not through more complex active control but through passive improvements arising from more favourable equipment design. An extra liquid hold-up, the middle vessel, was placed in the middle of the column by connecting the feed to an external vessel via a circulating system. To exploit and demonstrate the potential performance of this new modified design, our study was focussed on an existing pilot Scale distillation column at Nottingham University. This new design was shown to be very effective in rejecting both feed composition and feed flowrate step changes.