NO formation and destruction during combustion of high temperature preheated pulverized coal

Abstract

Preheating of pulverized coal (PC) has previously been verified as an effective method for reducing NO emission during coal combustion. However, studies on NO formation and destruction characteristics related to the combustion of high-temperature preheated PC are rare. In this study, two drop tube furnaces were connected in series to model the preheating-combustion process, and the effect of combustion temperature on NO emission during the oxidation of high-temperature preheated PC was studied in detail through experiment and kinetic modeling. Results confirmed the effectiveness of preheating on NO reduction with a maximum efficiency as high as 71.73%. Results also indicated that increasing the combustion temperature promoted both the formation and destruction of NO, while the increase in the NO formation rate was steeper than its destruction. This led to an increase in NO from 223 to 273 mg·m−3 as the combustion temperature increasing from 1273 K to 1473 K at preheating temperature of 1673 K. In addition, the rate of production (ROP) of NO formation increased from 8.54E-9 to 3.49E-7 mol·cm−3·s−1 with an elevated temperature from 1073 K to 1873 K, whereas the rate of NO destruction increased only from 1.40E-9 to 7.45E-8 mol·cm−3·s−1. Finally, the ROP analysis also indicated that the presence of background NO posed heavy impact on conversion of char-N and significantly improved the NO destruction rate.