Experimental tests on co-firing coal and biomass waste fuels in a fluidised bed under oxy-fuel combustion

The co-firing of coal and biomass waste in oxy-fuel fluidised beds is an important oxy-fuel combustion technology for CO2 capture and waste disposal. However, practical experience regarding co-firing in an oxy-fuel fluidised bed is still limited. In this study, a 10 kWth oxy-fuel fluidised bed with continuous fuel-feeding and real-time flue gas measurements was developed. The combustion stability and dynamic response during the switch in combustion states were examined. The effect of the combustion atmosphere (air or oxy-fuel combustion), inlet O-2 concentration (V(0)o(2)), combustion temperature, fuel type, and biomass blending mass ratio (Mb) on the combustor temperature distribution, CO2 enrichment, carbon conversion, and combustion residues were systematically investigated. The results indicated that the combustion state can switch quickly during the cofiring process (similar to the rapid switch in combustion states during oxy-coal or oxy-biomass combustion), and stable combustion in the fluidised bed can be maintained when V(0)o(2) is increased to 30% or more. The optimal range of Mb, which is directly related to the fuel type and combustion mode, contributes to a highly uniform temperature distribution, increased CO2 generation, and decreased amount of unburnt carbon in the fly ash. The bottom slag had a honeycomb structure, which became larger than quartz sand (bed material) after 120 h of combustion. Furthermore, no agglomeration of bottom slag, quartz sand, and fly ash was detected during the tests.