Nitrogen conversion during the rapid pyrolysis of raw/torrefied wheat straw

Nitrogen functionalities play an important role on the conversion of fuel-N during pyrolysis of raw and torrefied biomass while the influences haven't been clarified yet. The conversion of fuel-N during the rapid pyrolysis of wheat straw (WS) and different torrefied WS was investigated using a fixed-bed reactor at 600-1000 degrees C and the change of fuel characteristics and nitrogen-containing functional groups in samples were analyzed by TG and XPS. Results showed that the N content of samples increased gradually with torrefaction temperature. The main N functionality of WS was amide-N (N-A), while part of the N-A was converted to pyrrole-N (N-5), pyridine-N (N-6), and quaternary-N (N-Q) during torrefaction. CO2 and O-2 can inhibit the transformation of N-A to N-5 and promote the transformation of N-A to N-6. During WS pyrolysis, NH3 was the main NOx precursors at 600-700 degrees C, while HCN became the main nitrogen-containing gas species at 800-1000 degrees C and the conversion of (NH3 + HCN)-N was 18.15%-32.0%. After torrefaction, the conversion of NH3-N decreased in varying degrees, especially at low pyrolysis temperature (600-700 degrees C). The conversion of HCN-N increased with temperature during torrefied WS pyrolysis which was similar to that of WS, but the conversion decreased greatly at 800-1000 degrees C. Torrefaction atmosphere has a substantial effect on the conversion of fuel-N. In particular, WS torrefied in CO2 of O-2 atmosphere can promote the conversion of fuel-N to harmless N-2 during pyrolysis.