Pulverized coal combustion in air and in O2/CO2 mixtures with NOx recycle

This paper presents experimental results of a 20 kW vertical combustor equipped with a single pf-burner on pulverised coal combustion in air and O2/CO2 mixtures with NOx recycle. Experimental results on combustion performance and NOx emissions of seven international bituminous coals in air and in O2/CO2 mixtures confirm the previous findings of the authors that the O2 concentration in the O2/CO2 mixture has to be 30% or higher to produce matching temperature profiles to those of coal-air combustion while coal combustion in 30% O2/70% CO2 leads to better coal burnout and less NOx emissions than coal combustion in air. Experimental results with NOx recycle reveal that the reduction of the recycled NO depends on the combustion media, combustion mode (staging or non-staging) and recycling location. Generally, more NO is reduced with coal combustion in 30% O2/70% CO2 than with coal combustion in air. Up to 88 and 92% reductions of the recycled NO can be achieved with coal combustion in air and in 30% O2/70% CO2 respectively. More NO is reduced with oxidant staging than without oxidant staging when NO is recycled through the burner. Much more NO is reduced when NO recycled through the burner (from 65 to 92%) than when NO is recycled through the staging tertiary oxidant ports (from 33 to 54%). The concentration of the recycled NO has little influence on the reduction efficiency of the recycled NO with both combustion media—air and 30% O2/70% CO2.