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 NOx 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 CO2 in nitrogen at 700−750 °C to yield a nitrogen BET surface area of 200−400 m2/g. The effect of gaseous components such as N2, CO2, SO2, and moisture on the extent of NOx reduction was qualitatively examined. NOx reduction exceeded 99% on simulated flue gas at 525−600 °C. The presence of SO2, even at a concentration of 3600 ppm, did not have any detrimental effect on the extent of NOx reduction. Sodium-enhanced char attained >98% NOx reduction on actual flue gas at a relatively lower temperature of 480−560 °C.