Abstract: A furnace is provided with a separate cyclone chamber for combusting the fuel, provided with a double-sided outlet for heating gases. The heat release of this chamber having relatively small overall dimensions can reach the order of 40.multidot.10.sup.6 kcal/m.sup.3.h. The outlets of the heating gases are on both opposite sides of the chamber are connected with cyclone reaction chambers where the processing of the mineral raw material occurs at temperatures established by the technology in the range up to 2500.degree. C. The furnace products flow down into a lower precipitation chamber where the non-gaseous content is finally separated from the gaseous components of the product.Depending on the process parameters and the type of the mineral raw material, the furnace product can be molten or sintered, or have a gaseous form. The waste heat of exhaust gases and heat originated by cooling of the furnace is utilized in utilizing arrangements.