Study on sewage sludge pyrolysis using a Fluidized Bed Furnace

Abstract

In this study the performances of sewage sludge pyrolysis using a fluidized bed furnace was investigated, with the oxidation and leaching-out control of Cr in the sewage sludge being main purpose. The fluidized bed furnace was operated at air ratio of 0.56 to 1.10, which had a square (700mm) cross-section at the sand bed. Four kinds of sewage sludge cake which contained about 4, 000ng/kg⋅DS of T-Cr were used. The moisture content of the cakes was adjusted in the range of 40 to 80% by a steam dryer.
From the results of the experiments in a pyrolysis condition the fluidized bed furnace can have a higher sewage sludge feed rate (loading capacity of the furnace) than in ordinary condition. In pyrolysis condition, effective heat load in the sand bed was almost constantly 4.5 to 4.7×10⁵kcal/m²⋅hr whether with polymer cake or calcium cake. The loading capacity and the combustion ratio in the sand bed were strongly influenced by the air ratio. Concerning Cr oxidation and leaching-out control, it was found that a very low air ratio was needed for the calcium cake when the Cr content was high. However for polymer cake control could be carried out in a weak pyrolysis condition in which the air ratio was near 1.0. The effluent gas from the pyrolysis furnace became clean through afterburning.