fraction stream 48 benefits from interacting with the oxygen rich outer oxidant stream 26 accelerated heating at this interface further improves stability while increasing thermal radiation from the outer flame and reducing carbon carryover persons skilled in the art will recognize that there may be other methods of mixing the reactant streams using the present invention and respective benefits may be derived therefrom an important feature of the present invention is that the solid fuel transport gas stream 38 contacts the two oxidant streams 20 26 on two interfaces at two distinct radii this increases the surface contact area between the fuel transport gas and oxidant while also reducing the effective thickness of the fuel transport gas stream over which the oxidant and the fuel mutually diffuse this accelerates reaction of the fuel compared to conventional burners in which fuel and oxidant share only a single interface an additional advantage of this configuration lies in the ability to vary the flow rate and velocity of the oxidant streams 20 26 and thereby control the shear force at both the inner and outer interfaces of the fuel transport gas stream 38 hence for example if a low volatile solid fuel is employed or a relatively short flame is desired then the velocities.