NOVELTY - A downdraft gasification process involves contacting shredded municipal waste in a downdraft with an air supply which has been preheated by heat exchange with a pyrolysis reactor (1); and further heating pre-heated air supply by heat exchange with combustible exhaust gas from the pyrolysis reactor using a heat exchanger (22). In the gasification process, the shredded municipal waste is allowed to descend through a pyrolysis reactor and the waste is pyrolyzed in the reactor to form a combustible gas.    USE - For gasification of shredded municipal waste, preferably a loose shredded unpelletized feedstock, to form a combustible gas used for generating energy (claimed), for direct firing of gas turbines and gas engines and for powering high temperature fuel cells.    ADVANTAGE - Pre-heating of the air improves the efficiency of the gasification process and allows introduction of unpelletized feedstock at up to 30% moisture. The high moisture content can be turned into superheated steam because of the high temperatures in the reactor, thus improving gas quality in the water gas reaction. The higher moisture content and the introduction of hot air increases superheating of steam to improve the water gas reaction, which therefore reduces tar and increases hydrogen production (i.e. produces gas of higher calorific value gas). The process can permit inhomogeneous waste to be converted into a homogenous combustible gas, in a continuous operation. The mixer device with an air supply shaft within the reactor, allows air to be directed into the oxidation zone resulting in more even heat distribution and improved combustible gas quality which has smaller quantities of tars. The process permits direct use of municipal waste without densification, and the product gas may, without cleaning, be used for gas-fired steam boilers combined with steam turbines or for increased steam superheating.    DETAILED DESCRIPTION - A downdraft gasification process involves contacting shredded municipal waste in a downdraft with an air supply which has been preheated by heat exchange with a pyrolysis reactor (1); and further heating pre-heated air supply by heat exchange with combustible exhaust gas from the pyrolysis reactor using a heat exchanger (22). In the gasification process, the shredded municipal waste is allowed to descend through a pyrolysis reactor and the waste is pyrolyzed in the reactor to form a combustible gas. A high temperature mixer system is employed with a central hollow shaft, which allows the air supply to be directed into an oxidation zone of the pyrolysis reactor. The air supply is preheated by passing around an outer wall of the pyrolysis reactor so as to cool the outer wall. The preheated air supply is further heated by passing through a heat exchanger in countercurrent to the exhaust gas. An INDEPENDENT CLAIM is included for a gasification apparatus for pyrolyzing shredded municipal waste, comprising a reactor having a pyrolysis zone in which the waste is allowed to descend through the pyrolysis zone, an air supply for pyrolysis zone such that the air pass through the zone in downdraft, a unit permitting pre-heating of the air supply by the pyrolysis zone, and heat exchanger for further heating pre-heated air supply with exhaust gas from the pyrolysis zone.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic cross-sectional view of a gasifier.    Pyrolysis reactor (1)    Inlet (2)    Shaft (3)    Hopper inlet (5)    Passageway (15)    Hot gas outlet (20)    Heat exchanger (22)