TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The sulfur in the fuel is present under the form of elementary sulfur or of organic and/or inorganic compounds containing sulfur. In the combustor the pressure is higher than 101.3-2000 kPa, and the temperature is 1500-2100 K. The comburent is oxygen. The molar ratio B'/A1 is at least 1. The combustion gases at the outlet of the combustor are cooled at less than or equal to 1100 K. The feeding of component B) to the combustor is carried out by feeding the component B) separately from the fuel or in mixture with the fuel. When the component B) is elementary sulfur it is fed to the combustor with aqueous dispersion containing surfactants. The amount of component B) used is such that in the combustion fumes the partial pressure of SO2 is higher than 40 to 300 Pa. The residence time of the fuel in the combustor is 0.5 s up to 30 minutes. The fed oxygen is premixed with recycling fumes, where the amount of fumes in the gaseous mixture is higher than 10 (preferably higher than 50) vol.%. The recycling fumes contain water in the vapor form, and the amount of water calculated with respect to the total volume of the recycling fumes, is higher than 10 vol.% The fuel contains water (up to 80 wt.%). EXAMPLE - The combustion was carried out in an isothermal and flameless 5 MW combustor with walls coated by refractory, operated at 1650 degrees C and 400 kPa, and oxygen (90 vol.%) was used as the comburent so to have an oxygen concentration of 1-3 vol.% in the fumes coming out from the combustor. Olive husk having a content of sulfur, total ashes and humidity as follows (wt.%): sulfur (0.1), total ashes (residue at 600 degrees C) (5), humidity (9), K (18.3), Na (1.1), Ca (12.8) and Mg (1.2), was admixed with water, under stirring, to form a slurry containing water (60 wt.% based on the dry olive husk). In the reactor, under stirring, a water dispersion was prepared by adding a solid mixture formed by sulfur in powder with sodium alkylarylsulfonate surfactant to water. The olive husk slurry was fed to the combustor at a rate of 1200 kg/hour, calculated on the dry olive husk. The aqueous dispersion of sulfur was fed to the combustor in an amount of 18 kg of sulfur/hour. The ratio by moles B'/A1 was 1.1. The combustor has worked for 480 hours. Every 8 hours about 550 kg of vitrified slags, containing the metals K, Na, Ca and Mg in the same ratios and amounts as in the ashes of the fed fuel, were discharged from the combustor. It is found that the fumes emitted into the air contain an ash amount lower than 3 mg/Nm3. At the end of the combustion process no corrosion of the refractory of the combustor walls was noticed. Furthermore, in the vapor superheater made of AISI 304H material and operating with fumes at 800 degrees C and at wall temperatures of 570 degrees C, that is located in the part of the heat recovery plant downhill of the combustor, no surface modification of the wall material was found. A similar comparative combustion was carried out without feeding sulfur for 72 hours. It is noticed that the refractory material made of high-fired bricks (high purity alumina containing chromium (9 wt.%), zirconium (6 wt.%)), has been corroded on the surface. Further the slags discharged from the combustor contained a chromium and zirconium concentration higher than that present in the ashes of the fed fuel.