NOx adsorption on char in presence of oxygen and moisture Original Research Article

The char produced from a subbituminous coal is a cheap and effective adsorbent to remove nitrogen oxides (NOx) from flue gas. This paper addresses the NOx adsorption on char in the presence of oxygen and moisture since there are both water vapor and oxygen present in flue gas. The experimental results of this study show that nitric oxide (NO) is catalytically oxidized to nitrogen dioxide (NO2) on the char surface. When the oxygen concentration in the feed gas is greater than 5% and H2O concentration is less than 1%, the moles of NOx removed from the feed gas per 100 moles of carbon are almost independent of concentrations of oxygen and water in the feed gas. The breakthrough time of NO increased and that of NO2 decreased slightly with an increase in the concentration of oxygen. When moisture is present, a part of the adsorbed NO2 is further converted into nitric acid which is adsorbed on char. The amount of NOx adsorbed as HNO3 increases as both oxygen and moisture concentration in the feed gas increase. The removal of NOx was almost independent of water vapor concentration in the feed gas (0.23–0.95% by volume) probably due to the fact that the promotion effect of water vapor on NOx adsorption was balanced by the inhibition effect.