A plant for chemical or physical treatment of granular solids includes a fluidized-bed reactor, a solids supply conduit and a central gas supply tube. A cooling tube is disposed relative to the gas supply tube so as to form an annular cooling duct, which is configured to cool the gas supply tube and the process gas and is connected with a coolant source configured to supply a coolant with a temperature of below about 400° C. Outlet openings are disposed in the cooling tube. The fluidized-bed reactor is a Venturi reactor in which the cooling tube opens into a flared portion with the outlet openings connecting the annular cooling duct with the reactor interior. The cooling tube adjoins the gas supply tube and extends substantially parallel to the flared portion of the reactor.