The fate of char-N at pulverized coal conditions

Abstract The fate of char-N (nitrogen removed from the coal matrix during char oxidation) has been widely studied at fluidized bed conditions. This work extends the study of char-N to pulverized coal conditions. Coal chars from five parent coals were prepared and burned in a laboratory-scale pulverized coal combustor in experiments designed to identify the parameters controlling the fate of char-N. The chars were burned with natural gas (to simulate volatiles combustion) in both air and in a nitrogen-free oxidant composed of Ar, CO 2 , and O 2 . In some experiments, the char flames were doped with various levels of NO or NH 3 to simulate formation of NO x from volatile-N (nitrogen removed during coal devolatilization). The conversion of char-N to NO x in chars burned in the nitrogen-free oxidant was 50–60% for lignites and 40–50% for bituminous coals. In char flames doped with NO x , the apparent conversion of char-N to NO x (computed using the NO x measurements made before and after the addition of char to the system) decreased significantly as the level of NO x doping increased. With 900 ppm NO x present before the addition of char, apparent conversion of char-N to NO x was close to 0% for most chars. While there is no clear correlation between nitrogen content of the char and char-N to NO x conversion at any level of NO x in the flame, the degree of char burnout within a given family of chars does play a role. Increasing the concentration of O 2 in the system in both air and nitrogen-free oxidant experiments increased the conversion of char-N to NO x . The effects of temperature on NO x emissions were different at low (0 ppm) and high (900 ppm) levels of NO x present in the flame before char addition.