Abstract: A regenerative system for purifying mixtures of air and impurities by a combination process. The system includes a plurality of fixed bed regenerative heat exchangers connected to a common combustion chamber. Each of the heat exchangers includes means for diverting selected portions of the gases flowing therethrough out of heat exchange relationship with the heat exchange packing or bed therein. This permits the system to operate with incoming air-impurities mixtures containing high levels of combustibles without generating undesirably high temperatures or changing the mass flow rate through the system.