Rice Husk Ash/Calcium Oxide/Ceria Sorbent for Simultaneous Removal of Sulfur Dioxide and Nitric Oxide from Flue Gas at Low Temperature

Abstract

The reduction of sulfur dioxide (SO2) and nitric oxide (NO) emissions has become an isssue of great importance to government regulatory agencies and general public due to their negative effect towards the environment and human health. In this work, the simultaneous removal of sulfur dioxide (SO2) and nitric oxide (NO) from simulated flue gas was investigated in a fixed-bed reactor using rice husk ash (RHA)/CaO/CeO2 sorbent. Attention was focused on the major reactor operation parameters affecting sorption capacity of RHA/CaO/CeO2 sorbent, which include feed concentration of SO2 and NO, relative humidity (RH), operating temperature and space velocity (GHSV). This is because such information is unavailable for RHA-based sorbent and the effects of these parameters reported in the literature are also not reliable. Enhancement effect of NO on removal of SO2 was observed and the presence of SO2 was essential to the removal of NO. However, at a high level of SO2/NO concentration, competition in the sorption of NO and SO2 on the sorbent active sites might have occurred. RH was found to significantly enhance the SO2 sorption of the RHA/CaO/CeO2 sorbent. By contrast, NO sorption capacity decreases when RH was further introduced, as it was not easy to sorb NO in the presence of water. Apart from that, the results also shows that there was a threshold value for the RH to ensure higher SO2 and NO removal and this value was observed at 50% RH. Higher operating temperatures were favored for SO2 and NO removal. Nevertheless, beyond 150°C the SO2 removal was found to decrease. On the other hand, a lower space velocity resulted in a higher SO2 and NO removal.