Pilot-Scale Studies of NOx Reduction by Activated High-Sodium Lignite Chars: A Demonstration of the CARBONOX Process

Pilot-scale experiments were carried out to quantify the extent of NO x reduction attained by activated lignite chars on simulated and lignite-coal-combustion derived flue gas. Lignite chars, obtained by devolatilizing high-sodium lignite coal in pure nitrogen, were activated by their reaction with a gas mixture consisting of steam and CO 2 in nitrogen at 700−750 °C to yield a nitrogen BET surface area of 200−400 m 2 /g. The effect of gaseous components such as N 2, CO 2, SO 2, and moisture on the extent of NO x reduction was qualitatively examined. NO x reduction exceeded 99% on simulated flue gas at 525−600 °C. The presence of SO 2, even at a concentration of 3600 ppm, did not have any detrimental effect on the extent of NO x reduction. Sodium-enhanced char attained >98% NO x reduction on actual flue gas at a relatively lower temperature of 480−560 °C.