Temperature influence on product distribution and characteristics of derived residue and oil in wet sludge pyrolysis using microwave heating.

ABSTRACT

Sludge taken from a wastewater treatment plant of the petrochemical industry was dewatered and pyrolyzed to produce liquid oil as an alternative fuel via microwave heating. Element contents of dried sludge were 45.9±3.85wt.% carbon, 7.70±1.43wt.% hydrogen, 4.30±0.77wt.% nitrogen and 3.89±0.52wt.% sulfur. Two major thermal degradation peaks of sludge were determined during the microwave pyrolysis process, one at 325-498K (most of the water was vaporized, and the weight loss was over 85wt.%) and the other at 548-898K for sludge constituent decomposition. Zn content was high in the dried raw material and residues. Other toxic elements such as Ni, Cr, Pb, As and Cd contents were 0.61-0.99, 0.18-0.46, 0.15-0.25, 0.018-0.034, and 0.006-0.017mg/g, respectively. About 14-20wt.% of oil was produced based on the dried sludge cake, and the oil major elements were C (69-72wt.%), H (5.7-6.7wt.%), N (1.9-2.2wt.%), and S (0.58-0.82wt.%). The heat values of liquid oils were 8700-9200kcal/kg at 400-800°C.