Abstract: The reactor comprises a plurality of gas-permeable plates, which define reaction stages, which are connected by overflow lines. An annular duct for effecting a gas distribution is provided on at least one plate. The outer wall and the inner wall of the annular duct comprises numerous gas outlet openings. The annular duct is provided with at least one vertical gas-conduction pipe, which extends from the plate and is open at both ends. The top end of the gas-conduction pipe is surrounded by a bell-like cap, which is connected to the annular duct, so that a space through which gases can flow is left between the gas-conducting pipe and the cap.