Further Experiments on Sewage Sludge Air Gasification: Influence of the Nonstationary Period on the Overall Results

In the present study, the gasification with air of dried sewage sludge (DSS) was experimentally investigated using a bubbling fluidized bed reactor. The experimental work analyzed the effect on the DSS gasification tests of the gas residence time (as a function of both the bed height and the superficial air velocity) and the potential catalytic role of the DSS ashes. Furthermore, the influence of the nonstationary period on the accumulated tar production was analyzed. The results show that a longer gas residence time improves the gas efficiency process. A decrease in tar production and an increase in H2 content in the raw gas were observed when a mixture of sand and DSS ashes was used as an initial bed. These results confirm the catalytic effect of DSS ashes, which would be able for catalytic applications. The influence of the nonstationary period on the accumulated tar production was minimized when the experiment length was extended. This finding could confirm the higher tar production during this period.