Influence of gas residence time and air ratio on the air gasification of dried sewage sludge in a bubbling fluidised bed

Because little information is available about sewage sludge gasification in a bubbling fluidised bed (BFB), further experiments are required to quantify the power generation potential of dried sewage sludge (DSS) as well as to evaluate the optimum conditions for its gasification. In this work, the influence of the bed height on the process was experimentally determined using a laboratory-scale BFB reactor. The gasification tests were performed at different values of equivalence ratio (λ) and at two values of constant bed height (150 and 300 mm). Attention was focused on the effect of increasing bed height on the gas composition, average cold gas efficiency, and product distribution. Results obtained in this study show that a bed height increase improves the efficiency of the DSS gasification process. This fact could be explained because the high ash content of DSS represents an obstacle to the gas diffusion.