A gasification system for solid wastes having a thermal reactor and a mechanical gas cleaner, an indirect heat exchange cooler, and an electrostatic precipitator for cleaning and cooling the produced gas. Feed material is continuously fed to the central section of the thermal reactor above an air introduction manifold and nozzles and in an upward direction, forming a stratified charge. As feed material moves upward and outward from the reactor center it is reduced to ash. An agitator assures contact between the hot particulate product and hot gases resulting in gasification of the feed material and net movement to the sidewall of the thermal reactor, forming ash. The air introduction nozzles serve as a grate. Ash descends along the sidewall to the reactor base for removal. The mechanical cleaner has a high speed rotating brush-like gas separator element and scraper combination which removes condensed tars and particulates from the produced gas stream. The device is self cleaning in that condensed tars and particulates agglomerate on the high speed rotating bristle elements and, upon reaching adequate size and mass, are thrown off by centrifugal force to the cylindrical sidewall, where scrapers remove accumulated material which falls to the separator base for removal. An electrostatic precipitator having a cylindrical brush-like electrode suspended from one end by an insulated arm, removes remaining particles or aerosols from the product gas.