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′/(A″−A′)≧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.