Case study: effects of reboiler and overhead condenser behaviors during overfilling of debutanizer column to PRV sizing: article

Overfilling or flooding is a condition where vapor flow is higher in comparison with the liquid flow thus prevents liquid from flowing into the downcomer effectively. This condition couples with a failure at the downcomer side of debutanizer column further creates an overpressure scenario. Such failure occurs when the control valve is in fail closed position causing a blocked liquid outlet. The degree of fatality caused by these failures and inability to properly address an overfilling event will affect the plant performance, create casualty and in worst case scenario significant loss of life. Therefore, this work studies the effect of overfilling at thermosyphon reboiler and overhead condenser and its impact to PRV sizing, safety feature essentials for any distillation column. The columns’ parameters namely phase flow, temperature and flowrate are analyzed using Aspen HYSYS simulation and also manual calculation under four different debutanizer column’s case profiles. Results obtained confirm that sizing of the PRVs varied according to each profile and that the mass flux of the incoming feed into a column is significant contributor to accurately size the PRV.