Fully-resolved simulations of volatile combustion and NO X formation from single coal particles in recycled flue gas environments

The interaction of coal particles and recycled/recirculated flue gas (RFG) with elevated temperatures and low levels of oxygen occurs in various pulverised coal combustion scenarios. In this work, the effect of oxygen level and temperature on single coal particle combustion characteristics and NO X formation in N 2 diluent is studied by means of fully-resolved particle simulations. Comprehensive gas-phase kinetics are utilised to consider the critical pathways of NO X formation including tar-N. Results show that higher RFG temperatures decrease the time to reach the peaks of temperature and species profiles and increase the corresponding peak values. When decreasing O 2 , irrespective of the RFG temperature, the fuel release period is prolonged, the volatile combustion time increases and the combustion process becomes overall less intense. The reduction of O 2 in RFG results in a significant decrease of NO production, while the reduction of the RFG temperature has a smaller effect. The analysis of the key reactions that contribute to NO production in the region around stoichiometry shows that fuel-NO X is the major contributor. Both NH 3 and HCN in fuel-N play a major role, while tar-N only contributes in the case with the lowest temperature and O 2 concentration. The classical NO X formation pathways are negligible and the initiation reaction of the Zeldovich mechanism is even reversed, i.e. NO -& RARR; N 2 is dominant and contributes to NO destruction. The destruction of NO mainly occurs in a rich region close to the particle surface where abundant tar species and their derivatives play a major role for NO

Automated summary

This study investigates the influence of oxygen level and temperature on single coal particle combustion characteristics and NO X formation using fully-resolved particle simulations. The results show that higher RFG temperatures result in faster temperature and species profile peaks, while decreasing O 2 prolongs fuel release period and increases volatile combustion time. The reduction of O 2 in RFG significantly decreases NO production, while the reduction of RFG temperature has a smaller effect.