Fundamental investigation of NO x formation during oxy-fuel combustion of pulverized coal

Abstract

NO x formation was measured during combustion of pulverized coals and pulverized coal char in N 2 and CO 2 environments under isothermal and nearly constant oxygen conditions (i.e. using dilute coal loading). Three different oxygen concentrations (12% O 2, 24% O 2, and 36% O 2) and two representative US coals were investigated, at a gas temperature of 1050 °C. To investigate the importance of NO reburn reactions, experiments were also performed with an elevated concentration (550 ppm) of NO in the gases into which the coal was introduced. For low levels of background NO, the fractional fuel-nitrogen conversion to NO x increases dramatically with increasing bath gas oxygen content, for both N 2 and CO 2 environments, though the fuel conversion is generally lower in CO 2 environments. Char N conversion is lower than volatile N conversion, especially for elevated O 2 concentrations. These results highlight the importance of the volatile flame and char combustion temperatures on NO x formation. For the high background NO x condition, net NO x production is only observed in the 36% O 2 environment. Under these dilute loading conditions, NO reburn is found to be between 20% and 40%, depending on the type of coal, the use of N 2 or CO 2 diluent, the bulk O 2 concentration, and whether or not one considers reburn of volatile-NO x . This dataset provides a unique opportunity to understand and differentiate the different sources and sinks of NO x under oxy-fuel combustion conditions.