AIR STAGING AND REBURNING MECHANISMS FOR NOX ABATEMENT IN A LABORATORY COAL COMBUSTOR

Mechanisms that govern the formation and destruction of nitrogenous sp ecies in fuel rich zones caused by air staging and reburning were expl ored in a laboratory coal combustor. The objective was to determine wh ether the same simplified, but fundamentally based, gas phase mechanis m would predict time resolved profiles of all nitrogenous species, for both NO(x) abatement procedures. Experimentation was conducted on a 1 7 kW down-fired pulverized coal combustor, burning a variety of coals, under various air staged and fuel staged configurations. In the fuel rich pulverized coal post-flame, HCN appearance in the bulk gas phase was not due to the slow release of nitrogen from the coal residue, as was previously hypothesized. HCN formation and destruction in fuel ric h regimes were governed by homogeneous gas phase kinetics alone. The f ixation of N2 by hydrocarbons to form HCN, together with reactions of hydrocarbon radicals with either NO or N atoms, could explain HCN form ation, during both air and fuel staging. The interconversion of nitrog enous species in the fuel rich zones of air or fuel staging configurat ions could be adequately described by a simplified mechanism based on known detailed gas phase reactions and partial equilibrium assumptions . Profiles of NO, HCN and NH3 were adequately predicted for both air a nd fuel staged NO(x) abatement configurations, and the proposed mechan ism should prove useful for incorporation into more complicated furnac e models to predict NO emissions from practical coal combustion system s.