A pressurized cyclonic combustion method and a cylindrical burner apparatus for pressurized combustion of particulate solid fuels to produce a pressurized clean effluent gas. In the burner, the particulate solids such as wood chips are fed tangentially into a primary combustion chamber at its inlet end and flow at high tangential velocity in a helical path through the burner. Oxygen-containing combustion gas such as air is supplied tangentially at high velocity through multiple ports spaced along the burner length to maintain and/or increase the high tangential velocity and produce high centrifugal forces on the particulate solids and provide for prolonged combustion and produce high burner volumetric heat release rates exceeding about 400,000 Btu/hr ft.sup.3. A choke opening is provided centrally located at the combustion chamber outlet end for promoting prolonged combustion of solid fuel particles upstream of a quench zone. A secondary combustion chamber is provided downstream of the choke opening. Also, a quench gas stream is introduced into the choke zone preferably in a tangential flow direction opposite to the helical flow in the burner primary combustion chamber, so as to effectively mix the quench gas with the hot effluent gas and reduce its temperature, usually to about 1400.degree.-2000.degree. F. as determined by downstream metallurgy considerations. The resulting pressurized effluent gas can be further processed to remove any existing fine solids, and the clean pressurized gas can then be expanded in a gas turbine to produce useful power.