Abstract. The aim of paper is to study the combustion processes of organizing non-standard fuel burning using a numerical approach in a boiler unit BKZ-210-140 with steam capacity of 210 t/h. The EulerLagrange aerothermochemical technique of describing physical and chemical processes in the furnace volume by the FIRE 3D application package on the base was used. Special attention is paid to the numerical modeling results conclusion of the aerodynamics processes, heat exchange, and combustion in the furnace volume.