Insight into the Competitive and Synergistic Effects during Coal/NH<sub>3</sub> Cofiring via Reactive Molecular Dynamics Simulations
Dikun Hong, Lin Yuan, Chunbo Wang, Heyang Wang
Abstract
In this work, reactive force field molecular dynamics (ReaxFF MD) simulations are performed to study competitive and synergistic effects and their impact on CO, CO 2, unburned carbon (UC), and nitrogen oxide (NO) emissions in coal/NH 3 cofiring at different conditions. Simulation results show that cofiring results in higher emissions of UC and NO. Increasing the temperature is helpful in reducing UC emissions but has little effect on NO emissions. Although decreasing the O 2 equivalent ratio can help in reducing NO emissions, UC emissions increase significantly. The conclusion is that the best O 2 equivalent ratio in cofiring is 0.6. Increasing the NH 3 cofiring ratio will reduce NO emissions but seriously increase UC emissions. The competition between coal and NH 3 for O 2 will decrease the coal combustion rate and increase the NH 3 combustion rate. The competition effect is further proved by tracing the OH distribution. The synergistic mechanism is revealed. The free radicals and intermediates generated from coal combustion, such as HO 2, H 2 O 2, H, and OH, will promote NH 3 decomposition and oxidation. The kinetics analysis shows that the competition between NH 3 combustion and coal combustion only influences the combustion rate of coal and NH 3, while the synergistic effect of coal decreases the activation energy of NH 3 combustion. The research results are helpful to further study the mechanism of coal/NH 3 cofiring and guide the technology of NH 3 blending in coal-fired power plants.