Experimental studies of a biomass boiler suitable for small district heating systems

Extensive experiments have been carried out in a newly developed furnace suitable for small district heating networks. The fuel is wood-chips with moisture content in the range of 30–58%. One of the unique features of this new furnace is the broad thermal output span, which makes it possible to run the boiler down to 10% of maximum heat load, with maintained low emissions of CO and total hydrocarbons (THC). The aim of this study has been to evaluate the performance of the combustion chamber during steady-state operation in the complete thermal output range. The experiments show very good results over the entire thermal output range. In the range 60 kW up to 500 kW, the average CO content in the stack gases is typically below 25 mg Nm−3 (20 ppm) and the NOx concentration below 195 mg Nm−3 (95 ppm) during steady state conditions. At lower thermal outputs, the average CO content is below 105 mg Nm−3 (84 ppm). (All values standardised to 10 vol% O2.)