The effect of Ca on distribution of nitrogen species during coal pyrolysis in N2, CO2 and Ar atmospheres

Abstract

ABSTRACTNitrogen species distribution during coal pyrolysis with Ca addition in N2, CO2 and Ar was studied at 1000 °C using a horizontal tube furnace. In particular, the effect of Ca on the distribution of nitrogen species in N2 and CO2 atmospheres, which were closer to pyrolysis processes of conversional air and oxy‐fuel combustion in comparison with inert Ar environment, was investigated for the first time in this work. It was found that Ca has a great effect on nitrogen species distribution during both coal and demineralized coal pyrolysis; on the other hand, CO2 causes the formation of NO. Demineralization increases the formation of HCN and char nitrogen, but there is little effect on NH3 formation during pyrolysis in N2, in contrast to pyrolysis in Ar atmosphere, which decreases NH3 formation. A significant reduction in char yield was found after char gasification in CO2 at 1000 °C. With two different Ca‐based additives, i.e., (CH3COO)2Ca and Ca(OH)2, char yield decreases with the increasing amount of Ca additives in both cases. The effect of Ca on HCN and NH3 formation during pyrolysis depends on both the form of Ca and the amount of addition. In most cases, HCN and NH3 formation decreases with Ca addition in Ar, but increases in N2. Ca addition slightly promotes HCN formation during pyrolysis in CO2. There is no NH3 detected during pyrolysis in CO2 because of the reaction of NH3 and CO2 in the background. In addition, NO concentration decreases sharply with increasing the amount of Ca addition in the atmosphere of CO2, which means that Ca has an effect not only on pyrolysis, but also on gasification of char in CO2. In most cases, char nitrogen increases with Ca addition in N2 or Ar. © 2012 Curtin University of Technology and John Wiley & Sons, Ltd.