Investigation of N Transfer during Coal Char Oxidation by Reactive Molecular Dynamics

Abstract

This work employs large-scale simulations of reactive molecular dynamics to investigate influences of coal char structures, O 2 concentration, and temperature on NO x formation during coal char oxidation processes, which are facilitated by combining high-performance computing and cheminformatics-based reaction analysis. The char property models are constructed by using a new strategy on the basis of nascent structures taken from different pyrolysis stages individually from a large coal model. Analysis results of the char model structures show that nitrogen atoms would transform into N-containing six-membered ring groups from coal to a matured char structure at the high temperature of the late pyrolysis stage. Analysis of the simulation trajectories reveals that fuel/O 2 ratio and temperature play important roles in NO x emission, while the N-gas generation in the oxidation of char is not sensitive to the nascent coal char structure. NO formed in char oxidation tends to be reduced to N 2 at high temperature for a fuel/O 2 ratio of 1.0, which is an optimal condition for NO reduction in decoupling combustion. The reaction pathways revealed for the transformation of N-containing functionalities and generation of NO/N 2 show the vital roles of NH 3 , HCN, char-CNO, and char-NCO in NO x emission. Particularly, the intermediate structures of CNO at coal char provide the very first N to react with NO, leading to N 2 generation. It should be noted that the N 2 in the air would not affect the conclusion regarding fuel-N transfer in the pure oxidation system of O 2 obtained.

Insight into the Competitive and Synergistic Effects during Coal/NH3 Cofiring via Reactive Molecular Dynamics Simulations

“…The simulation temperature is artificially increased to allow the chemical reaction to occur normally within an acceptable time range. It has been shown in a number of previous studies that the increasing temperature strategy in molecular dynamics simulations can accurately make the phenomenon of the hydrocarbon thermochemical reaction process reappear at experimental temperatures. − ReaxFF MD simulations were conducted via the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) package. The atomic labeling method was adopted in the simulation of cofiring systems to identify whether the atoms are from coal or NH 3 to deeply understand the mechanisms of the competition and synergetic between coal combustion and NH 3 combustion.…”

Investigation of N Migration during Municipal Sludge/Coal Co-Pyrolysis via ReaxFF Molecular Dynamics

“…Moreover, the reactive force field molecular dynamics (ReaxFF MD) method has recently gained acceptance and accreditation as an effective approach to exploring and investigating intricate chemical reactions within large-scale reaction systems (>1000 atoms) . In particular, the ReaxFF MD method has been successfully employed to examine the nitrogen-containing hydrocarbons pyrolysis. , Liu and Guo investigated the nitrogen behavior during pyridine pyrolysis by adopting the ReaxFF MD method and discovered the pathways for nitrogen gas conversion in pyridine.…”