Installation of a combined air fluid producing device and a unit in which a chemical reaction occurs and implementation method

The invention concerns a combined installation of fluid producing apparatus (P) with a main air compressor (44) and a fluid consuming unit (2), wherein a gas coming from the unit is expanded in a turbine (10, 20, 30, 40, 150) or another device capable of generating mechanical energy driving the compressor (14, 24, 34, 44, 154). Another turbine or device can expand another gas or the same gas coming from the unit to drive another compressor.