Generator of endogas for producing a flow of an endothermic gaseous mixture (endogas), optionally with high CO percentages greater than 20% by volume, starting from a gaseous reaction mixture comprising air + methane or another hydrocarbon, said endogas flow being used as feed of one or more furnaces for the heat treatment of metals or their alloys said generator comprising a catalytic reactor contained inside a heating chamber and comprising at least three catalytic tubes arranged in parallel one in relation to the other in the form of a tube bundle, each of said catalytic tubes having an inner diameter smaller than 100 mm and containing, in a section of tube, a catalyst based on noble metal oxides for the partial oxidation of said mixture of air-methane or any other hydrocarbon each catalytic tube being in fluid communication with a respective feed tube, external to said heated chamber, to feed said catalytic tube with a respective flow (Qi) each of said feed tubes being provided with respective selectable regulating means apt to exclude, if required, the respective feed flow (Qi) to said catalytic tube, so as to obtain an overall flow of endogas, exiting from the catalytic reactor that is smaller with respect to a prefixed nominal overall flow rate (Qn) of endogas, said generator further comprising - at least one gas/air exchanger for cooling the endogas exiting from said heating chamber, said exchanger comprising one or more cooling tubes in fluid communication with said catalytic tubes, said generator being characterised in that it further comprises an automated system comprising mixing and control units (501; 502), independent one from the other, apt to feed and control, by means of said selectable regulating means, independent one from the other, one or more of said catalytic tubes with - one or more reaction flows composed of air + methane, added with CO 2 supplied by said unit; and - one or more catalyst regeneration flows of the catalytic tubes not fed with said reaction flows, composed of a mixture of CO 2 + N 2 but also only N 2 for washing/flushing during the normal operation of the generator, supplied by said unit, in such a way that said generator can be modulated simultaneously both in respect of the flow rate produced of endogas, and optionally also in the CO content in the endogas produced, and in the number of catalytic tubes to be regenerated. a catalytic reactor contained inside a heating chamber and comprising at least three catalytic tubes arranged in parallel one in relation to the other in the form of a tube bundle, each of said catalytic tubes having an inner diameter smaller than 100 mm and containing, in a section of tube, a catalyst based on noble metal oxides for the partial oxidation of said mixture of air-methane or any other hydrocarbon each catalytic tube being in fluid communication with a respective feed tube, external to said heated chamber, to feed said catalytic tube with a respective flow (Qi) each of said feed tubes being provided with respective selectable regulating means apt to exclude, if required, the respective feed flow (Qi) to said catalytic tube, so as to obtain an overall flow of endogas, exiting from the catalytic reactor that is smaller with respect to a prefixed nominal overall flow rate (Qn) of endogas, said generator further comprising - at least one gas/air exchanger for cooling the endogas exiting from said heating chamber, - at least one gas/air exchanger for cooling the endogas exiting from said heating chamber, said exchanger comprising one or more cooling tubes in fluid communication with said catalytic tubes, said generator being characterised in that it further comprises an automated system comprising mixing and control units (501; 502), independent one from the other, apt to feed and control, by means of said selectable regulating means, independent one from the other, one or more of said catalytic tubes with - one or more reaction flows composed of air + methane, added with CO 2 supplied by said unit; and - one or more catalyst regeneration flows of the catalytic tubes not fed with said reaction flows, composed of a mixture of CO 2 + N 2 but also only N 2 for washing/flushing during the normal operation of the generator, supplied by said unit, - one or more reaction flows composed of air + methane, added with CO 2 supplied by said unit; and - one or more catalyst regeneration flows of the catalytic tubes not fed with said reaction flows, composed of a mixture of CO 2 + N 2 but also only N 2 for washing/flushing during the normal operation of the generator, supplied by said unit,