Impact of air staging along furnace height on NOx emissions from pulverized coal combustion

Experiments were carried out on an electrically heated multi-path air inlet one-dimensional furnace to assess NOx emission characteristics of an overall air-staged (also termed air staging along furnace height) combustion of bituminous coal. The impact of main parameters of overall air-staged combustion technology, including burnout air position, air stoichiometric ratio, levels of burnout air (the number of burnout air arranged at different heights of the furnace), and the ratios of the burnout air flow rates and pulverized coal fineness of industrial interest, on NOx emission were simulated to study in the experimental furnace, as well as the impact of air staging on the carbon content of the fly ash produced. These results suggest that air-staged combustion affects a pronounced reduction in NOx emissions from the combustion of bituminous coal. The more deeply the air is staged, the further the NOx emission is reduced. Two-level air staging yields a greater reduction in NOx emission than single-level air staging. For pulverized coal of differing fineness, the best ratio between the burnout air rates in the two-level staging ranges from 0.6 to 0.3. In middle air-staged degree combustion with fM = 0.75, pulverized coal fineness, R90 (%), has a greater influence on NOx emission, whereas R90 has little influence on NOx emission for deep air-staged degree with fM = 0.61. Air-staged combustion with proper burnout air position has little effect on the burnout. For overall air-staged combustion, proper burnout air position and air-staged rate should be considered together in order to achieve high combustion efficiency.