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.