Method and apparatus for heat treatment in a fluidized bed

A method for the heat treatment of fine-grained solids wherein the solids are heated to a temperature of 150 to 1000° C. in a fluidized bed reactor, comprising introducing a first gas or gas mixture from below through a gas supply tube into a mixing chamber of the reactor located above an annular stationary fluidized bed, the stationary annular fluidized bed being fluidized by supplying fluidizing gas, wherein the gas flowing through the gas supply tube entrains solids from the fluidized bed into the mixing chamber when passing through the upper orifice region of the gas supply tube, wherein the bed height of the solids in the reactor is adjusted such that the annular fluidized bed extends beyond the upper orifice end of the gas supply tube, and adjusting the gas velocities of the first gas or gas mixture as well as of the fluidizing gas for the annular fluidized bed such that the particle Froude numbers in the gas supply tube are between 1 and 100, in the annular fluidized bed between 0.02 and 2 and in the mixing chamber between 0.3 and 30.