Output of fossil fuel fired industrial boilers is usually designed to meet expected maximum heat requirements of heated system. This design solution cannot be applied on biomass boilers since operational range of standard industrial biomass boilers is set to operate above 30 % of boiler nominal capacity. Biomass boilers must be operated in the most stable mode possible, without any major changes to the output, in order to achieve expected efficiency and low amounts of pollutants in flue gas. Biomass boilers operated in real-life premises are often designed to meet a significant portion of the maximum expected heat requirements of the system, which leads to oversized boilers with serious operational problems. This paper sums up recommendations for selection of optimum biomass boiler output which have been published in literature, and also presents major undesirable features associated with operation of oversized boilers. The presented study focuses on research of 1 - 5 MW biomass boilers with inclined moving grate. But majority of obtained results may be applied on all types of energy sources combusting biomass. A case study from wood-processing industry demonstrates concrete operational difficulties. The paper further discusses possible measures for improvement of operational features of oversized boilers.
