Abstract: A method and apparatus for mixing coal char particles with a hot stream of combustion gases containing molten ash particles, in order to prevent build-up of ash in the apparatus. The coal char particles, fluidized with a gas, are discharged as an annulus about the stream of combustion gases, so that the molten ash particles are cooled and solidified by progressive mixing with the char particles and thus prevented from reaching the walls of the apparatus in a molten state.