and temperature of the gas flowing into the preparation chamber 2 2 for preparation and flowing out of the preparation chamber 2 2 after prepared controllable metering valves and rate meters for the unburned gases fed into the preparation chamber 2 2 and a programmable control system for processing the measuring data calculating the target variables and relaying the control signals to the actuators such as valves with this system the method according to the invention for preparing the respective process gas 3 at temperatures up to about 1250 u00b0 c that are uncoupled from the temperature in treatment chamber 1 1 is enriched and generated in a preparation step in this example according to a reaction equation and the used process gas 3 is returned to treatment chamber 1 1 after a carburisation process step see fig1 and 2 in this example according to a reaction equation in this context it should be noted again it is within the scope of the central idea of the invention that other reactions may also take place according to the composition of the gas components and depending on the corresponding heat treatment methods for preparing the process gas 3 and its consumption as part of the treatment the sequence of the preparation step and the process step u2014 as here of the carburisation u2014 takes place in a recirculating circuit the preparation step is carried out in preparation chamber 2 2 which is equipped with catalyst 2 2 1 and temperature adjustment device 2 2 2 and separate from industrial furnace 1 but connected to treatment chamber 1 1 via lines 1 5 1 6 the entire recirculation process also encompasses the generation.