Abstract: The invention relates to a process for preparing a heat treatment atmosphere by a catalytic reaction in a catalytic reactor (16) between a first gas mixture (12) containing oxygen and a second gas mixture (26) containing a hydrocarbon, characterized in that the catalytic reactor is arranged in substantially vertical position and in that the reaction mixtures are introduced into the catalytic reactor through the bottom (19) of the reactor with recovery of the heat treatment atmosphere resulting from the reaction at the top (20) of the reactor.

Abstract: Process for the preparation of a heat treatment atmosphere by a catalytic reaction in a catalytic reactor including an inlet and an outlet between a first gas mixture comprising oxygen and a second gas mixture comprising a hydrocarbon for the purpose of supplying said atmosphere to a user site comprising at least one user location, comprising the steps of:a) feeding said first and second gas mixture at a given flowrate into the inlet of said catalytic reactor;b) continuously measuring the pressure of the heat treatment atmosphere obtained at the reactor outlet;c) comparing the pressure measured during step b) with a setpoint pressure level P.sub.