Abstract: A process for the generation of mechanical energy in the ammonia oxidation step of process for the production of nitric acid is disclosed, whereby the utilization of process heat is improved, particularly the exploitation of heat contained in NO.sub.x gases and including process heat recovered at low temperature. The process involves evaporating and superheating liquid ammonia upstream of the oxidation step, at a pressure which is a multiple of the pressure required for the combustion, using the process heat of the NO.sub.x gases formed during the the combustion and then expanding the superheated ammonia in a turbine, thus generating mechanical energy.