Air gasification of dried sewage sludge in a fluidized bed:: Effect of the operating conditions and in-bed use of alumina

Sewage sludge has recently become a particularly important problem all over the world because of its harmful impact on the environment. The consequent need to develop alternative processes for the use of dried sewage sludge for energy purposes, such as gasification, requires experimental tests in order to quantify the potential energy power of the sludge, as well as to evaluate the optimum conditions for its gasification. There is, however, little information available. In this study, the gasification with air of dried sewage sludge was experimentally investigated using a bubbling fluidized bed. Attention was focused on the influence of the temperature (750-850 degrees C), the equivalence ratio (25-35%), and the fluidizing velocity (5, 8, and 11 times the value of u(mf)) on the product yields, gas composition, thermal efficiency, and tar content. The results obtained show the potential for using sewage sludge gasification with air as an option for energy recovery and waste treatment. However, the high tar yield obtained needs to be reduced. Consequently, experiments involving the in-bed use of alumina were carried out. This primary measure has proven effective for tar removal (the content decreases by nearly 40% with in-bed use of alumina at 5 wt%).