The invention concerns a process for using a facility in which circulates at least one oxide which is reduced and then oxidized in each of both reactors (1, 4) and including a first reactor (1) for reducing oxide in which enter a grounded solid fuel material (E1) and oxide (E2), a first separation device (2) receiving entrained solids from this reactor for reducing oxide, a carbon separator (3) installed at the outlet of this first separation device in order to send the carbonaceous particles into the reactor (1) for reducing oxide and the oxide into a second reactor (4) for oxidizing oxide and a second separation device (5) receiving entrained solids from this reactor for oxidizing oxide. According to the invention, the average particle diameter of the entering solid fuel material (E1) is controlled to be different from the average particle diameter of the entering oxide (E2), with a rate of relating average particle diameters of at least two.
Preferably, the average particle diameter of the entering solid fuel material (E1) is smaller than the average particle diameter of the entering oxide (E2).