Abstract Using biomass in combustion, as a renewable source of energy, from ecological and economic considerations, sets special demands for control of the co-firing process. The paper aimed to study the problems like slugging, clogging and ash deposits formed on heat exchange surfaces during the co-firing process of agricultural biomass with coal. There are identifies the main factors that influence the formation of flying ash deposits and corrosion process. Most problems of co-firing process of biomass with coal have their origins in fuels properties. The problems related to the ash management have a strong impact on the life time of heating equipment and environment, therefore has economic and ecological relevance.