Experimental Study on Soot Combustion and Its Noncatalyzed Reaction with NO

Abstract

In this paper, the combustion characteristic of soot was investigated in a quartz tube fixed-bed reactor. The soot was generated from the natural gas diffusion flame with different oxygen concentrations (20%, 15%, 10%, and 5%). Noncatalyzed reaction between the soot and NO was also investigated in different NO concentrations (∼200 ppm to ∼1500 ppm). The candle soot, the butane soot, and the coal coke were chosen as references. The ignition temperature of natural gas soot is lower than that of the coal coke. Oxygen concentration has a little influence on the ignition temperature of different samples but a great influence on the combustion process. Reactions of different samples under different NO concentrations have definite initial reaction temperatures and quite good regularities. Compared with other samples, natural gas soot has the highest NO removal rate and lowest initial reaction temperature. Increasing NO concentration will enhance the initial reaction temperature of the soot. On the other hand, the denser the NO concentration is, the lower the reaction rate and the higher reduction proportion of NO. The moisture content plays an important roll in the natural gas combustion, which can increase the soot combustion rate evidently. Moreover, the higher the moisture is, the lower the initial reaction temperature. However, impact of moisture on maximum NO reducing rate of soot is not obvious. Analysis reveals that although soot needs a higher combustion activation energy than the coal coke, it has lower reduction activation with NO. Transmission electron microscopy pictures demonstrate that natural gas soot has a layer microstructure. Both candle and butane soot have quite similar chain microstructures. Such differences among these microstructures lead to the discrepancy of macro-reaction performances among different samples.