Influence of tray hydraulics on tray column dynamics

To column control, in contrast to column design, tray hold-up and dependenc ies of tray hold-up on the operating conditions play an important role. The essence of this article is the development of an improved model of tray hy draulics over a broad operating range and its experimental validation by me ans of batch distillation. First, the column dynamics are related to tray c olumn design parameters and operating conditions. The model parameters are fitted by column residence time measurements. Two tray load regimes are dis tinguished: an aeration regime and an obstruction regime. At low column loa d a vapour increase will decrease the tray mass since the liquid is driven out by larger aeration. At high load the opposite is the case, since the li quid is driven up by stowage. The resulting dynamic behaviour is studied by linearising the rigorous tray model in an operating point. Especially the influence of the vapour flow on the column dynamics is investigated. For th e influence of the tray composition change on the molar mass, a new composi tion-shift parameter kappa is defined. The influence appeared to be small. (C) 1998 Elsevier Science Ltd. All rights reserved.