CFD-Based Model to Study Shortstopping Runaway Reactions in a Batch Reactor

Thermal runaway has been a major and persistent safety problem to reactor operations. It is partly due to lack of awareness of runaway reactions and management, but more importantly because of the inherent transport-kinetic complex behavior inside the stirred reactor. Shortstopping runaway reactions, conventionally known as injection of small quantity of chemical inhibitors to react with reactants or catalysts so as to interrupt the generation process of reaction heat and cool the system down in a short time, has been recognized as an effective measure for runaway emergency response.

Runaway kinetics can be studied with RC1 equipment, but it is hazardous and costly to investigate flow behavior inside the reactor, especially the interactions between kinetics and flow conditions. As shown in the work in 2004 by Louvar, a CFD-based model was first used to simulate flow conditions coupled with a basic kinetic model in a stirred vessel for propylene oxide (PO) polymerization. CFD simulations were applied to compare the effectiveness of impeller and jets on shortstopping runway reactions in 2006 and hotspot distribution was emphasized by Dakshinamoorthy. However, some important issues were under-stressed in these work. (1) The experimentally-fitted kinetic model is too coarse to capture major reaction pathways. (2) How physical properties of components change with temperature was completely ignored, which actually plays a vital role in polymerization process. (3) Local phase condition, caused by viscosity-temperature dependency, was not considered inside the reactor.

To study the unaddressed issues, a CFD-based model was established using ANSYS Fluent 16.0 to describe the flow behavior of acrylic polymerization process within a lab-scale batch reactor. The flow model and energy models, with component property (especially viscosity) change taken into consideration, are to study the velocity and temperature distribution inside the reactor. Then reaction kinetics model from literature are coupled in the simulation to explore the kinetic-transport interactions, and predict runaway behaviors. Finally, certain amount of chemical inhibitors are injected to simulate the shortstopping scenario. In conclusion, this study will give insights on hotspot evolution inside the reactor and lead to the development of effective guideline for reaction shortstopping.