In the present invention, there is disclosed an apparatus for fluidized bed combustion of solid fuels or suspensions, comprising a mixer of gaseous/fluidization/combustion media a preheater of the combustion media disposed behind the gaseous/fluidization/combustion medium mixer or incorporated therein. A mixture of the combustion media is then supplied through the fluidization/combustion medium inlet via at least one electric preheater to a distributor with a pressure gauge disposed therebelow and a pressure gauge disposed thereabove. An inlet of a solid fuel or a suspension and/or a fluidized bed secondary material, along with the pneumatic transportation arrangement and separated from the region above the distributor by a countercurrent cooler, is disposed above the distributor. A reactor comprising boiling, bubbling or spouted fluidized bed is arranged above the solid fuel or suspension inlet. In the reactor lid, there are arranged an inlet of a thermometer passing through the entire structure up to the distributor, and optionally an inlet of a pressure gauge inlet, as well as one outlet for analyses of composition and amount of products. A hot cyclone is arranged in the space after the above-fluidized bed layer area.