A combustion process wherein a fuel, a comburent and component A) are fed to a combustor, component A), comprising low-melting salts and/or oxides having a melting temperature 1,450 K, the ratio by moles A/(AA)0.01, being: A the sum by moles between the amount of metals, under the form of low-melting salts and/or low-melting oxides present in the component A) and the amount of metals under the form of the low-melting salts and/or low-melting oxides or their low-melting mixtures, contained in the fuel, A is the sum of the amount of all the metals contained in the fuel and of those contained in component A), in which the combustor is isothermal type and flameless.