Variation of No Emissions with Char Burn-Off Levels in a Fluidised Bed Reactor

Previous studies on NO emissions from the combustion of coal in fluidised beds have shown that nitric oxide is partially reduced in pores and on the char surface. Moreover, competition between NO and N₂O for active sites on the char has been suggested. Other authors have also reported the influence of coal rank and specific surface area on NO reduction (2). Consequently, the textural characteristics of the char may exert, a strong influence on the overall heterogeneous reactions involved in the reduction of NO in fluidised bed coal combustion conditions. In addition char reactivity is an important factor in the conversion of fuel-N to NO since the rates of NO formation and destruction are strongly dependent on the intrinsic reactivity of char and its textural characteristics. In this work combustion chars of different burnout levels were prepared in a fluidised bed reactor. The evolution of the chars textural characteristics with burn-off level was measured and related with their reactivity to oxygen and NO emissions. TG/MS was used to determine char reactivity and for evolved gas analysis.