Abstract: The present invention relates to a movable catalyst bed reactor provided with catalyst bed supporting and guiding means in the shape of one or more downwardly converging conical surfaces with one or more vertical outlet channels connected to the lower end(s) of the conical surface(s), the supporting and guiding means comprising one or more screen sections for withdrawal of reactor effluent from the catalyst, and separate outlet means for reactor effluent and catalyst, wherein the vessel is further provided with conduit means for forming a protecting layer of substantially spherical particles along the surface(s) of the screen section(s) facing catalyst, which layer is movable along the screen section(s).