NOVELTY - Combustion process comprises feeding a comburent; a fuel; and (i) component (B) sulfur or compounds containing sulfur in an amount to have a molar ratio of B1/C1 of greater than or equal to 0.5; and (ii) component (A) comprising low-melting salts and/or oxides having melting temperature of less than or equal to 1450 K, to a combustor, which is isothermal and flameless.    USE - The combustion process is useful for preparing fumes (claimed).    ADVANTAGE - The process shows a low impact on both the environment and on health of human and animal beings and allows to use also low ranking fuels, as biomasses and waste, also in plants having a high thermal recovery yield and a high transformation yield of thermal energy into electric energy, built with conventional materials (non high alloyed). The process is operated at combustion temperatures of 1500000-1670000, to reduce the amount of vanadium in fumes. The basic ashes are transformed into inert compounds, mainly sulfates, which neither attack the refractories of the combustor walls nor the metallic materials, in particular steels and metal alloys.    DETAILED DESCRIPTION - Combustion process comprises feeding a comburent; a fuel; and (i) component (B) sulfur or compounds containing sulfur in an amount to have a molar ratio of B1/C1 of greater than or equal to 0.5, where the B1 is the sum by moles between the total amount of sulfur present in (B) + the total amount of sulfur contained in the fuel, and the C1 is the sum by moles between the total amount of alkaline and/or alkaline-earth metals contained in the fuel + the amount of alkaline and/or alkaline-earth metals in the form of salts and/or oxides contained in (B); and (ii) component (A) comprising low-melting salts and/or oxides having melting temperature of less than or equal to 1450 K, where the ratio by moles of A1/(A2-A1) is greater than or equal to 0.01, where the A1 is the sum by moles between the metals under the form of low-melting salts and/or oxides in (A) and the amount of metals of low-melting salts and/or oxides contained in the fuel, and A2 is the sum of the amount of all the metals contained in the fuel and of those contained in (A) to a combustor, which is isothermal and flameless. An INDEPENDENT CLAIM is included for fumes obtained by the process.