Abstract: The firing performance of a radial, scroll, or vortex cyclone furnace can be improved when firing difficult to burn materials having a relatively low heating value or a relatively high moisture content, such as sub-bituminous and lignite coals. This can be achieved by introducing additionally heated primary air into the burner of the radial and vortex cyclone furnace or separately introducing preheated or additionally heated auxiliary air into the scroll burner. Moreover, additionally heated tertiary air can be introduced into the radial and scroll burners to further improve firing performance. Moreover, additionally heated primary air can be mixed with the coal before introducing the mixture into the scroll burner to further improve firing performance.