NOx Formation Characteristics for Cocombustion of Rice Husk and Coal at High Temperature

Abstract

The cocombustion of biomass and coal has the potential to reduce NOx emissions at high temperatures. In this study, an experimental investigation was conducted on a drop-tube furnace to investigate NOx formation characteristics for cocombustion. The effects of temperature, blending ratio, and stoichiometric ratio on NOx formation characteristics were explored. The results indicated that the addition of rice husks had a positive effect on NOx reduction with stoichiometric ratios higher than 1 at temperatures of 1,400°C–1,600°C. Shallow air-staged combustion (stoichiometric ratio slightly lower than 1) effectively reduced NOx formation when the blending ratio was 40%. Regardless of whether rice husk was blended or not, high-temperature air-staged combustion can maintain NOx formation at a low level. When coal was blended with 40% rice husks in the thermal fraction, temperature had a slight effect on NOx formation for the temperature range 1,400°C–1,600°C. The blending of coal and rice husks mainly reduced thermal NOx formation and slightly reduced fuel NOx formation at high temperatures with stoichiometric ratios higher than 1. This study proposed a possible mechanism for NOx reduction by bending coal with rice husks. The reduction of NOx was due to an increase in volatile matter, a reduction in group and biomass char, and a decrease in N content by blending in rice husks.