Experimental investigation of woody and non-woody biomass combustion in a bubbling fluidised bed combustor focusing on gaseous emissions and temperature profiles

Air staging is a well-known effective method to control NOx emissions from solid fuel combustion boilers. However, further research is still needed to clarify the effect of air staging at different injection locations on the gaseous emissions of Fluidised Bed Combustion (FBC) boilers that fire 100% biomass fuels, particularly non-woody biomass fuels. The main objective of this work is to investigate the effect of the staging air injection location on the gaseous emissions (NOx and CO) and temperature profiles of a 20 kW_th bubbling fluidised bed combustor firing three non-woody (straw, miscanthus and peanuts) and two woody biomass fuels. The experimental results showed that injecting the secondary air at the higher location could lead to a greater NOx reduction due to the fact that the biomass combustion reaction mainly took place in the splash zone and/or beginning of the freeboard. Up to 30% of NOx reduction, compared with no air staging, was achieved for the non-woody fuels when the staging air was injected at the higher-location. Air staging also significantly reduced the CO emissions as a result of the higher temperatures in the freeboard and longer residence time in the primary combustion zone.