an apparatus for supporting and starting up a fluidized bed in which a grate is disposed in a housing for receiving a single bed of particulate material , portions of which are combustible . the interior of the housing below the grate is divided into a plurality of compartments , and an air damper is disposed in each for selectively controlling the flow of air through the compartments and through the respective portions of the grate to selectively fluidize the corresponding portions of the bed of particulate material . a start - up burner is provided for igniting that portion of the combustible portion of the bed of particulate material extending above one of the compartments and additional combustible particulate material is selectively supplied to the portions of the bed .