Research on purification, combustion and NOx emission characteristics of pulverized coal preheated by a novel self-sustained purifying burner

Abstract

To more quickly achieve the breakthrough of minimum NOx emission, this study focused on purification, combustion and NOx emission characteristics of pulverized coal preheated by a novel self-sustained purifying burner, and deeply explored the effect of purifying temperature (Tp) in a 30 kW purification-combustion system. In the purifying burner, the main combustible gases in the reductive coal gas were CO and H2, and their concentrations ranked as CO > H2. Increasing Tp rose their yields. By contrast, the CH4 concentration was always extremely low. This burner effectively improved the particle properties of pulverized coal (including particle size, macrostructure, carbon microcrystalline structure and fuel conversion rate), and was superior over the previous self-preheating burner. Properly increasing Tp optimized the particle properties of reductive coal char except pore diameter, and there might be an optimal Tp. The pore diameter always decreased as Tp increased. Increasing Tp reduced the relative content of N-X in the reductive coal char, and its content was extremely low when Tp was above 1083 °C. Moreover, N-Q was the main form of nitrogen functional groups in the reductive coal char at an extremely high Tp. In the subsequent combustion, NO2 and NO were the main forms of nitrogen oxides in the reduction and burnout regions respectively, while N2O was not. In the whole purification-combustion system, the burning efficiency was always about 99.50 %, and its change was extremely small as Tp increased, while the NOx emission decreased first and then increased. Moreover, the adverse effect of higher Tp on the emission was more significant compared to lower Tp.