Detailed analysis of early-stage NOx formation in turbulent pulverized coal combustion with fuel-bound nitrogen

A carrier-phase direct numerical simulation (CP-DNS) of pulverized coal combustion in a mixing layer is performed, considering three NOx formation mechanisms (fuel-NOx , thermal-NOx and prompt-NOx ). Detailed analyses, including reaction path analysis, chemical timescale analysis, and a priori and budget analyses are conducted to investigate the NOx production mechanisms and the performance of the flamelet model. Considering the high computational cost of CP-DNS, this work focuses on the early phase governed by devolatilization, where char reactions are less important. The reaction path analyses show that the principal thermal-NO reaction contributes to the net consumption of NO in fuel-bound nitrogen pulverized coal flames, which is essentially different from fuel-nitrogen-free flames. The chemical timescale analyses show that the production rates of NOx species are faster than those of major species, which confirms the suitability of the flamelet tables. The a priori analyses show that the gas temperature and major/intermediate species can be predicted well by the flamelet model, while the NOx species show significant discrepancies in certain regions. Finally, the budget analyses explain why the flamelet model performs differently for major/intermediate and NOx species. (c) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

A carrier-phase direct numerical simulation (CP-DNS) was conducted to investigate pulverized coal combustion and NOx formation mechanisms in a mixing layer, focusing on the early devolatilization phase. The study found that different reaction pathways and chemical timescales can affect the production rates and consumption rates of NOx species.