Numerical Simulation of NO Reduction by Gases from Coal Pyrolysis at High Temperature

In this study, a detailed reaction mechanism was used to investigate the process of NO reduction by coal volatile gas in a perfect stirred reactor (PSR). Based on the actual condition of boiler reburning zone, the pressure of the reactor was 0.1 Mpa, the temperature ranged from 1273 to 1573 K, reburning fuel percentage varied from 10% to 30%, and the residence time was 0.6 s. The composition of the pyrolysis gas (mixture of CH₄, CO, CO₂, H₂O, H₂, NH₃ and HCN) was predicted by the FG-DVC model. The stoichiometric ratio (SR) was varied from 0.1 to 1.2. It was found that the NO reduction changes from 10-47% as temperature, reburning fuel percentage and SR changing. NO reduction increased as the reburning fuel percentage rising. For a given temperature, the reduction of NO reaches maximum when SR was smaller than 1. As the temperature rising, the SR corresponding to the maximum NO reduction at a certain temperature was smaller and smaller. It was also found that CH₃, H, NH₂ and HCCO are the major reducing agent when SR is small. When SR is more than 1, NH₂ is still the major reducing agent. Some principal reactions consuming or producing NO are also revealed in this paper.