A new type three-stage gasification of dried sewage sludge: Effects of equivalence ratio, weight ratio of activated carbon to feed, and feed rate on gas composition and tar, NH₃, and H₂S removal and results of approximately 5 h gasi

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<P><B>Abstract</B></P> <P>A new three-stage gasifier consisting of an auger gasifier, a fluidized bed gasifier, and a tar-cracking zone was applied for the gasification of dried sewage sludge to obtain a high-quality producer gas with low levels of impurities (tar, NH<SUB>3</SUB>, and H<SUB>2</SUB>S). In the experiments, the effects of activated carbon (AC), equivalence ratio, the weight ratio of AC to fuel, and feed rate were investigated. In particular, approximately 5 h of gasification was conducted to see the deactivation behavior of AC and changes in gas compositions. The experiments showed that the equivalence ratio had a strong influence on impurity contents in producer gas, lowering them at a high equivalence ratio of 0.5. The increase in the ratio of AC to fuel not only led to an increase in the production of H<SUB>2</SUB>, but also to a decrease in impurity contents. The approximately 5 h of gasification proved the activity of AC for tar cracking. The maximum H<SUB>2</SUB> content in producer gas (29 vol%) was obtained at the AC/fuel ratio of 3:1 and at an equivalence ratio of 0.35. The minimum tar, NH<SUB>3</SUB>, and H<SUB>2</SUB>S contents in producer gas were 27 mg/Nm<SUP>3</SUP>, 443, and 470 ppmv, respectively.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A successful three-stage gasification of dried sewage sludge was performed. </LI> <LI> A ∼5 h gasification showed a high possibility for clean gas production. </LI> <LI> Activated carbon played a crucial role in tar removal. </LI> <LI> The minimum tar content in producer gas were 27 mg/Nm<SUP>3</SUP>. </LI> <LI> The minimum NH<SUB>3</SUB> and H<SUB>2</SUB>S contents in producer gas were 443 and 470 ppmv. </LI> </UL> </P>