Preventing hot-spot formation in the exhaust system of deposition reactors

The chemical reactions occurring in the exhaust systems of the deposition reactors can potentially lead to the formation of problematic reactive compounds on the exhaust surfaces. The accumulation of this deposit can cause clogging of the system and, more importantly, lead to some uncontrolled highly exothermic reactions. Under certain conditions, these reactions become self-accelerating and form hot spots that would damage or even destroy the exhaust components. These catastrophic events have been observed and reported by industry and are the focus of this fundamental study. A comprehensive process model is developed that includes reactions as well as heat and mass transport processes that contribute to these energetic events. The results show that the self-acceleration of these reactions takes place primarily due to the accumulation of reacting species on the surfaces, leading to conditions where the net generation of heat by the gas-solid reactions is greater than its dissipation by convective flow of gas and losses to the surroundings through the exhaust walls. The model is shown to be valuable for predicting the range of safe operating conditions and for developing methods to mitigate the undesirable energetic events.