Nitrogen migration and transformation from ammonia to char during ammonia-coal/char co-pyrolysis.

Ammonia (NH 3)-coal co-firing is a promising technology to reduce CO 2 emission. The strong interaction between ammonia and coal during the co-pyrolysis has a considerable impact on nitrogen migration and transformation and will further affect the NO x formation. In this paper, to investigate the effect of the volatile fraction on the migration of N, Shenhua (SH) and Wanxiang (WX) bituminous coals were devolatilized to different levels in the first pyrolysis step and were then co-pyrolyzed with NH 3 in the second pyrolysis step. It is found that the migration of N from the gas to solid is more significant than the release of N with the volatile, especially when the temperature in the first pyrolysis step is low. Given the same pyrolysis condition, WX coal/char has more oxygen-containing functional groups than SH, thus the increase of N content during the NH 3 /coal co-pyrolysis is more significant for WX. The absolute contents of pyridinic N (N-6), pyrrolic N (N-5), and protonated pyridinic N or quaternary N (N-Q) are calculated before and after the co-pyrolysis step according to the results of elemental analysis and X-ray photoelectron spectroscopy. An obvious increase of N-6 is observed in chars with lower degree of devolatilization for both coals. A transformation of N-5 to other types of N is observed for SH coal/char. In contrast, the transformation of N-5 is less obvious for WX, which is due to the presence of alkali metal chlorides in WX. Moreover, WX coal/char has less aromatic structure and more aliphatic groups, which promotes the transformation of N from NH 3 to N-5. Based on these results, possible reaction pathways of N migration and transformation during NH 3 /coal co-pyrolysis are proposed. • Migration of N during ammonia-coal co-pyrolysis are investigated. • Migration of N onto char is more significant than release of N from char. • N that migrates from NH3 to char mainly exists as pyridinic N and pyrrolic N. • Possible reaction pathways of N migration are proposed. [ABSTRACT FROM AUTHOR]