Comparative study of carbon-deNO process by different sewage sludge chars.

Sewage sludge char (SC) reduces NO to N at high temperatures thus acting as a potential reducing agent in flue gas cleaning systems. However, SC needs to be modified to enhance the carbon-deNO performance. In this study, coal char (CC) and different types of SCs, i.e., original (SC-R), pyrolytic volatiles activated (SC-V) and KOH activated (SC-K), were compared in terms of their carbon-deNO performance, including NO removal rate and secondary pollution discharged. The results showed that when the oxygen content in the flue gas was 5-6%, the carbon-deNO efficiency of the three types of SCs was greater than 70%, which was higher than that of the CC. SC-V has lower emissions of CO and gaseous nitrogen-containing compounds (NH, HNCO, HCN) among the three types of SCs. For the oxygen content of 8-11% in the flue gases, the NO conversion performance was found in the order of SC-K > SC-R > SC-V > CC. The physical and chemical characterization of activated carbon shows that pyrolytic-volatile activation increases the ratio of C-O and C=O functional groups on its surface of SC-V, which not only facilitates the chemisorption of NO but are also easily converted under high oxygen conditions. SC-V is found as a suitable reductant for carbon-deNO within the temperature range of 300-350 °C.