For the purpose of the development and introduction of the arrangements aimed at increasing the slagless power, economy, and reliability of the P-67 boiler of the 800 MW unit of the Berezovskaya Power Plant No. 1, the variation of heat-engineering characteristics of the coal (lignite) of the open-cast mine "Berezovsky-1" and its slag properties was investigated, the aerodynamics, heat exchange, formation of nitrogen oxides, and the intensity of local slag formation for different operation regimes and variants of the reconstruction of the furnace-burner device were modelled mathematically, the thermal efficiency of furnace walls was studied experimentally during their long-term operation, including the time after their mechanical cleaning, modernization of the system of water sootblowing, under low air excess, coal dust coarsening, loading the lower rows of burners, and lower air blowing.