Use of dynamic simulation for reactor safety analysis

Abstract

Dynamic simulations of chemical processes are widely used to develop effective plantwide control structures that provide stable regulatory control at some desired operating condition. This paper illustrates that they can also serve a very useful role in the analysis of safety problems in the event of emergency situations. The dynamic response of the process when various failures occur is critical to the design of safety systems for the process (alarms, overrides, interlocks, safety valves and rupture disks). For example, a failure of the supply of cooling water will lead to rapid increases in pressures and temperatures in the process. 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.Chemical reactors are typically the most sensitive and potentially the most dangerous units in many processes, particularly when exothermic reactions and low per-pass reactant conversions are involved. This paper illustrates how Aspen Dynamic simulation can be used for predicting the dynamic changes in critical variables. Dynamic emergency safety simulations are presented for five processes with several types of cooled reactors (CSTR and tubular) and residence times varying from 0.16 to 60min. Safety response times vary from several seconds to several minutes, depending on both the reactor, the system in which it is installed and the level of reactant conversion.