DISTILLATION CONTROL FOR PACKED AND TRAYED COLUMNS

In this work the dynamic behaviour and control of trayed and packed di stillation columns are studied by rigorous modelling. First, the lambd a parameter to measure the interaction of the internal vapour and liqu id flows is studied for packed columns. The calculated lambda values p redict severe controllability problems at higher internal flow rates c lose to flooding if the vapour flow is manipulated in a packed column. Secondly, open and closed loop simulations are carried out considerin g several control loop devices of different delays. The open loop simu lations show that the packed column is significantly faster than the t rayed column. On the other hand the closed loop simulations prove that average control loop delays have practically no influence on the dyna mic behaviour of the trayed column due to the significantly higher pro cess time constants. In the case of packed columns, however, the avera ge control loop delays are the same order of magnitude as the process time constants. If fast response with dual composition control is need ed it is mandatory to install advanced control loop devices for packed columns.