Rigorous dynamic models for distillation safety analysis

Dynamic simulations of distillation columns are widely used to develop effective control structures. The normal distillation models assume instantaneous heat transfer in the condenser and reboiler. However, when dynamic simulations are used in the analysis of safety problems in the event of emergency situations, the basic model does not accurately represent the dynamic response. Accurate response times are essential in the design of safety systems for the column. For example, a failure of the supply of cooling water will lead to rapid increases in pressures and temperatures that occur in seconds. Accurately determining the rates of increase in these important variables and the time period to reach critical limits (safety response time) permits the engineer to quantitatively design effective safety systems.This paper illustrates how rigorous condenser and reboiler models can be developed in Aspen Plus and their dynamics evaluated in Aspen Dynamics.

► Dynamic simulation used to explore distillation safety response times.
► Aspen column models must be modified to accurately predict rapid pressure dynamics.
► Must use multiunit models with external heat exchangers for reboiler and condenser.
► Condenser cooling failures and surges of reboiler heat input explored.