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

摘要

Sewage sludge chars produced at four different pyrolysis temperatures (550, 650, 750 and 800°C) 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 °C were highly temperature-and oxidant-resistant and their CO emissions were considerably inhibited in the temperature range of 100 to 400 °C 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 pyro lysis temperatures of 650, 750 and 800 °C 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 °C 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 °C had the best ability to remove NOx both as an absorbent and as a catalyst.