Abstract: The present invention is a process and associated apparatus for obtaining energy from a fuel source having particles varying in size from fines to coarse. The fuel source is introduced into a passageway formed between an upper combustor and a lower combustor. A gas stream is moved upwardly through the passageway such that the fine particles are entrained in the gaseous stream and carried into the upper combustor.

Abstract: A low BTU, low volatile content, low carbon and high ash fuel is combusted in a combined shaft kiln combustor and fluidized bed combustor to generate heat which is converted to useful energy. The fluidized bed combustor is mounted vertically above the shaft kiln combustor. A venturi is provided in a passageway connecting the shaft kiln combustor and the fluidized bed combustor to produce a gaseous stream moving at a velocity sufficient to separate finer particles from the low BTU, low volatile content, low carbon and high ash fuel so that the coarser particles are burned in the shaft kiln combustor and the finer particles are burned in the fluidized bed combustor.