Abstract: A burner of the double vortex type wherein combustibles travel in an outer spiral during which time the combustibles ignite and burn and the combustion products are expelled from the burner by travelling along an inner spiral. The inner and outer spiral layers are separated by a cylindrical wall to prevent disruption of the currents and countercurrents and adverse turbulence as a result thereof in order that the combustibles and particularly solid fuels are entrained in the combustion stream for a sufficient residence time for maximum combustion and minimum particulate emission. The burner is particularly suitable for operation at slagging temperatures so that the slag can be collected and drawn off to further reduce particulate emission.