Uptake of NO X by activated carbons: bench-scale and pilot-plant testing

Abstract

The possibility of selectively removing NO x from gas containing CO 2, N 2, O 2, H 2O, SO 2 and NO x has been examined using bench-scale and pilot-scale experimentation. These results have shown that NO can be selectively sequestered from the gas if the oxygen concentration is high enough and the SO 2 concentration is low enough. Oxygen enhances the amount of NO removed, and promotes the conversion of NO to NO 2 (via NO + 1/2O 2 → NO 2) and the adsorption of NO 2 within the carbons' micropores. The carbon is not consumed if during NO 2 desorption its temperature is maintained below about 200 °C. The presence of SO 2 inhibits the oxidation of NO and the subsequent storage of NO 2 within micropores but, at concentrations typical to gases after post-combustion sulfur scrubbers, such inhibition is an immediate effect probably associated with selective site poisoning rather than a cumulative effect associated with pore blocking or sulfur retention. The possibility of removing NO and NO 2 from combustion flue gas and the extent to which fines were produced during pilot-plant testing of activated carbons will also be discussed. Wear patterns on the carbon surface subsequent to the pilot-plant studies and NO x uptake calculated from gas-phase and sorbent analyses are compared to data from the bench-scale experimentation. Information needed for more complete understanding of the interaction of NO + SO 2 on and within carbon is discussed.