Effects of particle concentration variation in the primary air duct on combustion characteristics and NO_xemissions in a 0.5-MW test facility with pulverized coal swirl burners

The effects on combustion characteristics and NO_xformation of the particle concentration variation in the primary air duct were investigated on a 0.5-MW pulverized-coal combustion test facility with swirl burners. The gas temperature, components and fly ash in the near-burner region and furnace center were sampled and measured. It shows that the pulverized-coal concentration variation in the primary air duct is of great importance as for defining the flame structure, gas temperature profile and gas components. With the burner changing from general type to inner-lean-outer-rich to inner-rich-outer-lean types I and II, the flame diffusion zone shrinks, its color less bright, the O₂concentration in the flame zone decreases and the CO concentration increases significantly. Additionally, the NO_xconcentration decreases, with NO_xemissions at the furnace exit dropping from 1182 to 861 mg/m³(a reduction of 27.15%). Finally, the release rates of carbon, hydrogen and nitrogen and the burnout rate of carbon all decrease. The gas temperatures observed in the inner-rich-outer-lean types I and II burners are lower than those of the general and the inner-lean-outer-rich type burners in the near-burner region. The release rates of elements and the burnout rate of carbon are close to 100% for all four burners.