A conception and a predesign of a furnace modification of the BB-1150 boiler in order to reduce NOx emission to 200 mg NO2/m(3) (6% O-2) are presented in the article. The effectiveness of lignites from Belchatow and Szczercow as reburning fuels is presented too. Some modifications of combustion chamber design, especially of coal milling and feeding systems, were proposed in order to adjust it for reburning. Results of three-dimensional numerical simulation confirm that the predesigns are correct.