Preheated combustion characteristics and fuel-nitrogen conversion paths for bituminous coal and anthracite in wide-range preheating temperature

In this study, the characteristics of preheated combustion and fuel-nitrogen (fuel-N) conversion paths in wide-range preheating temperature (700 degrees C-900 degrees C) for bituminous coal and anthracite were revealed during the preheated combustion. The conversion of fuel-N mainly underwent three procedures, including the conversion from fuel-N to char-nitrogen (char-N), tar-nitrogen (tar-N) and gas-nitrogen (gas-N) in the PCFB, the reduction from preheated fuel-N to N2 in the reduction region of combustor and the release of NOx from the char-N in the oxidation region of combustor. During the preheating, the highest conversion ratio from fuel-N to tar-N was 9.94% at the preheating temperature of 700 degrees C for bituminous coal. However, the conversion ratio from fuel-N to tar-N was below 2% for anthracite from 700 degrees C to 900 degrees C. Most of fuel-N was transformed into char-N and N2 during the preheating. Although higher preheating temperature promoted the conversion of fuel-N during the preheating, the reduction of char-N was inhibited due to the lower temperature of reduction region in the combustor for anthracite. The lowest concentration of NOx emission was 226.01 mg/m3(@ 6% O2) at the pre-heating temperature of 850 degrees C for anthracite.