Biomass Diversification for District Heating: Trade- Off between Biomass Sustainability and Heat Production Efficiency

Biomass diversification in district heating is driven by resource constraints and sustainability requirements under European Union policy, yet variability in fuel properties complicates procurement and operational planning. This study evaluates nine biomass fuels available on the local market, including wood chips, residues from intensified forest harvesting, and alternative biomass blends, to link fuel quality with economic and environmental performance. Fuels were characterized by proximate and ultimate analysis, calorific value, ash melting temperature, and chemical composition, and ash utilization potential was assessed through oxide mapping and heavy-metal analysis. Combustion tests were conducted in a large-scale moving-grate boiler under real operating conditions, with flue-gas measurements used to calculate efficiency and heat losses. WC3 achieved the highest net calorific value due to low moisture, also the highest combustion efficiency and lowest particulate matter concentration in flue gas, while WM3 and WM4 showed severe CO peaks and combustion efficiency losses under tested conditions. WM3 had the highest ash content and lowest melting point, while WM4 contained a large fines fraction, raising dust and segregation concerns. Heavy-metal concentrations were lowest in WC3 and highest in WR2.