NOVELTY - The gasifier has a gasifier head (17) designed as a flow control valve facing an opening of a truncated cone such that a flow valve body (23) is arranged in a form of a flow ring (31) with a central guide (24) over a valve seat, and a central annular gap aperture (32) is generated. The truncated cone or the flow valve body is vertically moved and locked such that dimension of the annular gap aperture is adjusted by a vertical position of the truncated cone or the flow valve body, and a perforated plate (35) is provided with a contaminant discharge (5).    USE - Three-zone gasifier for use as an arrangement of thermal decomposition during gas treatment of waste products and/or wastes materials i.e. carbonaceous solid materials or single unit for conversion and gas treatment.    ADVANTAGE - The gasifier achieves prolonged residence time and allowing qualitative and quantitative high carbon conversion, thus increasing performance of the gasification process to prevent procedural blockages, dislocations and overcrowding of the gasifier formed by inert solids or slag impurities and contaminant. The gasifier organizes intensification of convective heat transfer into carbon particles by using a conversion quasi laminar for turbulent flow by using flow-shaping devices and fixation of adaptive gasification zones, thus achieving stabilization during gasification process in a gasification zone. The gasifier realizes differentiated and higher process temperature stability control above a fluidized fixed bed by using flow-technical guides without accumulation of heat, gas and tar and dust-burdening raw gas into the gasification zones.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a method for operating a three-zone gasifier.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic sectional view of a three-zone gasifier.    Contaminant discharge (5)    Gasifier head (17)    Flow valve body (23)    Central guide (24)    Flow ring (31)    Central annular gap aperture (32)    Perforated plate (35)