Abstract: The invention is to be used for afterburning of polydisperse high-ash thermal decomposition residues, as well as in the construction of the first stage of power utility furnaces for burning fuel with a low yield of volatile products and with a low reactivity.The furnace comprises a chamber having its bottom part narrowing downwards which is provided with an inlet pipe for admission of air and fuel to the chamber, and the top part of the chamber is provided with an outlet pipe for removal of combustion products from the chamber.A combustion stabilizer is accommodated in the chamber which comprises a blade-type stream swirling device having its blades arranged in the cross-section of the top part of the chamber upstream the outlet pipe in the path of flow of combustion products.