TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Process: From 10-100% of the gaseous fuel stream is returned to the chamber, through at least one venturi inlet below the vanes. It is mixed with steam prior to its reintroduction without supplemental pumping. The feed is introduced under the influence of a compressed gas or a gravity feed mechanism. The heating fluid comprises steam and/or a fuel combustion gas stream. The heating fluid is at a temperature of 300-1000 degreesC. Part of the fuel stream that exits the chamber in each cycle is collected. It is then subject to particulate removal, drying, compression and/or sweetening. The pressure drop through the chamber is less than 400 Pa. Heating of the feed in the first chamber results in drying, devolatization, gasification and/or pyrolysis. Two or three chambers may be used in series, with some of the char formed in the first chamber fed to the second chamber, where it undergoes another combustion step to produce another gaseous fuel stream, and some of the fuel stream fed to the third chamber and is heated in a tar cracking step to produce a gaseous fuel stream. At least part of the gaseous fuel stream formed in a chamber that is fed to a preceding chamber contributes to the upward flow of the heating fluid through the vanes at the chamber's base.Preferred Device: The chamber contains a resident bed of particulate material which circulates about an axis of the chamber when the flow of the heating fluid is generated. The inlet is located adjacent to the base of the chamber, or above the vanes, and the outlet is spaced downstream.Preferred Feed: The waste and/or premium fuel comprises a solid and/or a liquid. The waste is sewage sludge, by-product waste, waste wood, wood shavings, clean wood, agricultural waste, animal litter, municipal waste and/or refuse-derived fuel. The premium fuel is coal, petrochemical derivatives and/or refinery residues.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Material: The particulate material contains a solid absorbent for removal of acidic gases from the gaseous fuel stream that exits the chamber. It is a catalytic material, which acts to increase the rate of tar decomposition in the gaseous fuel stream. The particulate comprises dolomite, a nickel-bearing catalyst, a zeolite, a magnesium-calcium carbonate and/or a calcined magnesium-carbonate.