Control of the ignited steady state in autothermal fixed-bed reactors for catalytic combustion

Since autothermal reactors are always operated in the ignited steady state, control measures must be taken to prevent the reactor from extinction during times of lean feed as well as from overheating during times of rich feed. Respective control measures are discussed for autothermal reactors with integrated heat exchange for the case of catalytic combustion of traces of organics in exhaust air. They are shown to differ from control measures for conventional autothermal reactors with external heat exchange. Two types of autothermal reactors with integrated heat exchange are the fixed-bed reactor with periodic flow reversal and the countercurrent fixed-bed reactor. Control measures which proved successful in simulations were verified experimentally on a reverse flow laboratory reactor. They consist of adding supporting fuel or hot gas in times of lean feed and of using central heat exchange, cold gas injection or hot sidestream withdrawal in times of rich feed. Since none of these measures was able to prevent the reactor from Overheating, a new concept using a structured fixed bed and sidestream withdrawal was developed and tested. It allows for an efficient heat recovery during times of lean feed as well as for the prevention of excess temperatures and the utilization of almost all of the heat of reaction during times of rich feed.