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 gasification

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, NH₃, and H₂S). 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 H₂, but also to a decrease in impurity contents. The approximately 5 h of gasification proved the activity of AC for tar cracking. The maximum H₂ 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, NH₃, and H₂S contents in producer gas were 27 mg/Nm³, 443, and 470 ppmv, respectively.