Effect of Na, Ca and Fe on the evolution of nitrogen species during pyrolysis and combustion of model chars

The catalytic effects of Na, Ca and Fe on the formation of HCN and NH3 during pyrolysis of nitrogen-containing model chars and on the emission of NOx during the char combustion have been investigated in a fixed bed reactor. The results show that fuel-type nitrogen is mainly retained in char under the pyrolysis conditions (∼900 °C). The presence of Na favors the transformation of char-nitrogen to volatile-nitrogen at high temperature, but the influence of Ca and Fe is negligible. The NH3:HCN ratio under catalytic pyrolysis conditions is higher than that under non-catalytic pyrolysis conditions. It was also found that the emission of NOx was restrained under catalytic conditions at high combustion temperature, but was favored at low temperature. The conversion of char-N to NOx depended on a number of factors including the properties of char, the types of catalysts and the combustion conditions. The influence of catalysts on the emission levels of NOx reflects the relative importance of the catalytic effect on char-N oxidation and on NO-char reaction during the combustion of nitrogen-containing char.