The combustion device according to the invention produces gases containing CO2 and water vapor and comprises a circulating fluidized bed reaction chamber (1, 2), a separator (10, 20), heat recovery means of which a part is situated in a dense fluidized bed (12, 12a, 22), wherein the part located in the bed of the heat recovery system(s) is composed of catalyst tubes (120, 120a, 220) through which a gas mixture flows. The gas mixture is composed of natural gas and/or naphtha or refinery gas or two or more of these gases. The gas undergoes reformation which converts it into a synthesis gas containing hydrogen. The fact of the catalyst tubes being situated in the dense fluidized bed made up of ashes from the combustion allows the catalyst to be reheated in a homogenous manner and the reforming reaction of the natural gas mixture to be stimulated.