Mechanism of wet sewage sludge pyrolysis in a tubular furnace

The main objective of this work was to develop a preliminary mechanistic understanding of wet sewage sludge decomposition from starting constituents to final products, including intermediates formed during the pyrolysis process. Sewage sludge with a moisture content of 84.2 wt% was pyrolyzed at different temperatures in a tubular furnace, the pyrolysis products (hydrogen-rich fuel gas, tar and solid char) were detected by micro-GC, GC-MS, and FTIR, respectively. The high moisture content of wet sewage sludge generated a steam-rich atmosphere at high temperatures, leading to an in situ steam reforming of the volatile compounds and a partial gasification of the solid char, which contributed to the production of hydrogen-rich fuel gas. The pyrolysis process can be divided into two steps: at a relatively low temperature (< 600 degrees C), the breaking of the C-H bonds of alkyl gave rise to the release of CH(4) and C(2) hydrocarbons, and a large amount of CO and CO(2) evolved as the result of C=O decreasing, both processes indicated the decomposition of volatile compounds. The increasing absorbance amount of C-O and C-H(aromatic) demonstrated the formation of tar. As temperature increased further, the diminishing IR absorbance of C-O and C-H(aromatic) was accompanied by a significant reduction of tar yield and an increase of H(2). H(2) was considered as an indicator for the occurrence of tar cracking. The Diels-Alder reaction mechanism followed by dehydrogenation was employed to explain the PAHs formation. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.