Recycle Sewage Sludge Char as Flue Gas De-NOx Catalyst within Low Temperature Ranges

Sewage sludge chars produced at four different pyrolysis temperatures (550, 650, 750 and 800oC) were investigated to check their CO and SO2 emissions in a hot flue gas flow; and then their catalyst effect on De-NOx process with hydrazine hydrate as reductant was studied. It was found that the chars produced at 750 and 800 oC were highly temperature- and oxidant-resistant and their CO emissions were considerably inhibited in the temperature range of 100 to 400 oC with oxygen level of 5∼10%, at the same time, De-NOx efficiencies were increased by 25% to 50%, suggesting those chars are proper De-NOx catalysts. Chars obtained at pyrolysis temperatures of 650, 750 and 800 oC were also checked their possibilities for absorbing NOx in flue gas, and it was found that they can achieve 20%∼30% of De-NOx efficiency by adsorption within a temperature range of 100∼250 oC at oxygen level around 8%. When hydrazine hydrate was used as a reducing agent together with char catalysts, the De-NOx efficiency was greatly affected by O2 pressure and lower O2 is benefit for the improving De-NOx efficiency. Moreover, it was found that char obtained at 750 oC had the best ability to remove NOx both as an absorbent and as a catalyst.