Experimental study on ultra-low initial NOx emission characteristics of Shenmu coal and char in a high temperature CFB with post-combustion

Abstract

The NOx emission of conventional circulating fluidized bed (CFB) boilers could hardly meet the increasing strict standards in China, so the initial NOx emission and control of Shenmu coal and char were investigated in a 0.5 MWth high temperature CFB test platform with a main combustion zone (MCZ) and a post-combustion zone (PCZ), the reducing atmosphere in MCZ suppressed the formation of NOx, high temperature in PCZ made the residual carbon and CO burnout, the technology of high temperature CFB with post-combustion had the advantage of decreasing the initial NOx emission while maintaining the combustion efficiency of fuel. The experimental results showed that as the injection position of post-combustion air (PCA) moving backward, the reducing zone in PCZ was enlarged so more NOx could be converted to N2. When PCA was injected from PCA1 and PCA3, NOx and CO emission were both relatively lower than other injection positions, the temperature in PCZ of Shenmu char was more uniform and its NOx emission was lower compared to Shenmu coal, the peak temperatures of MCZ and PCC were 968 °C and 936 °C respectively, the initial NOx emission of Shenmu coal was 46 mg/m3 (at 6% O2), meanwhile, the CO emission was 139 ppm. The initial NOx emission of Shenmu char could reach 41 mg/m3 when the temperatures of MCZ and PCZ were 931 °C and 913 °C respectively, the new ultra-low emission requirement (≤50 mg/m3) was successfully achieved without additional denitration equipment, so the technology of high temperature CFB with post-combustion is an effective ultra-low nitrogen combustion technology.