A method and apparatus for combustion of a solid carbonaceous material in which the solid carbonaceous material is preheated and at least a portion thereof pyrolyzed on a stoker grate disposed in the lower portion of a combustion chamber to produce pyrolysis products. Overfire oxidant is then introduced into the combustion chamber above the stoker grate to ensure complete combustion of combustibles in the products of combustion generated by combustion of the solid carbonaceous material and the pyrolysis products. Preheating and pyrolysis of the solid carbonaceous material is carried out by the introduction of a pyrolysis agent directly into the bed of solid carbonaceous material.