Detailed measurements in a pulverized-coal-fired large-scale laboratory furnace with air staging

The aim of the present work was to evaluate the performance of a pulverized-coal-fired large-scale laboratory furnace with air staging. New data are reported for gas phase species concentration, temperature and particle burnout for two primary zone stoichiometric ratios, 1.15 (unstaged flame) and 0.95 (staged flame), other operating conditions being fixed. The results revealed that the reduction in primary zone stoichiometric ratio caused a decrease in NOx emissions from 421 to 180 mg/N m3@6%O2, an increase in CO emissions from 51 to 168 mg/N m3@6%O2 and a reduction in particle burnout from 81.8% to 76.5%. It was concluded that the reduction of the O2 availability in the primary zone inhibits the NO formation, mainly via the fuel mechanism, but it affects negatively both the CO and the char oxidation processes because, under staging conditions, both processes tend to occur in the vicinity of the over fire air injection region, where the temperatures are relatively low.