Runaway in packed bed reactors operating with periodic flow reversal

An experimental study of periodic reversal of flow direction using a two-recuperator/catalyst bed system is the subject of this paper. Experimental work is extended by modelling and simulation. The objectives of this work were to examine the dynamics of runaway and to locate qualitatively the bounds for stable operation. Runaway behaviour was observed for propene combustion in air over a 0.1 wt% Pt catalyst using air cooling and also occurred for high CO concentrations using a room-temperature proprietary catalyst with water cooling. Both cases revealed a slow runaway over several cycles and a rapid rise in peak temperatures that occurred in the first cycle after start-up. Slow runaway appeared to be retarded by switching flow directions. Cooling the catalyst bed raises combustant concentrations and flow rates that give stable cycling operation, but can lead to quenching at low concentrations or flow rates. Simulation approximated the experimental observations and indicated that what was observed experimentally as runaway eventually achieved stable periodic operation, but at high bed temperatures.