NOx and N2O precursors (NH3 and HCN) in pyrolysis of biomass residues

Nitrogen release is a little known aspect of pyrolysis of biomass. In this study on thermally thick samples of three biomass residues with high N-content, the NOx precursors NH3 and HCN were measured with a Fourier transform infrared (FTIR) analyzer at different heating rates (low and high) and temperatures (400-900 degrees C). The feedstocks investigated have been given scarce or no attention. At a high heating rate, (1) NH3 is the main N-compound with increasing yield with increasing temperature until reaching a plateau at 825-900 degrees C at a conversion level of 31-38%; (2) HCN release is increasing sharply with temperature to reach a conversion of 9-18%; (3) the (HCN + NH3) conversion levels of all samples are close; (4) N-selectivity is affected by temperature and particle size; (5) release patterns and thermal behaviors of N and C are different and influence of fuel properties (intrinsic and physical) may be inferred; (6) the intricate structure of biomass indicates that decomposition paths may include (N-compounds + non-N-compounds) reactions. At a low heating rate, (1) NH3 is the main N-compound; (2) HCN and NH3 release are significantly different for the various fuels (7.9-19.2%) and fuel properties (intrinsic and physical) might be of importance; (3) the release pattern of N is affected by fuel properties.