(267e) Effects of Gas Residence Time ON NO Reduction IN Oxy-Coal Combustion

We evaluate the potential benefits of long residence time of gas in a recycle system on NO reduction in oxy-coal combustion. In both single-pass and recycle tests, residence time within a range of 0.26 to 1.6 seconds shows only minimal benefits on NO reduction. Thus, the reverse Zeldovich mechanism appears not a governing factor up to 1700 °C, the peak flame temperature in practical boilers. The NO concentrations under equilibrium are much lower than those experimentally observed. Moreover, addition of 500 ppm NO in the feed for simulating the effects of the recycled NO does not change the estimated equilibrium concentrations in burning coal in O2-CO2 environment. Nevertheless, it is not observed in practical operations. Thus, NO reduction in oxy-coal combustion is highly kinetically controlled, not thermodynamically controlled.