Energetic assessment of air-steam gasification of sewage sludge and of the integration of sewage sludge pyrolysis and air-steam gasification of char

• Published in: Energy (Oxford) Vol. 76; pp. 652 - 662
• Main Authors: Gil-Lalaguna, N., Sánchez, J.L., Murillo, M.B., Atienza-Martínez, M., Gea, G.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-11-2014; Elsevier
• Subjects: Air-steam gasification; Applied sciences; Assessments; Char; Combustion; Drying; Energy consumption; Exact sciences and technology; Gasification; Liquids; Other industrial wastes. Sewage sludge; Pollution; Pyrolysis; Sewage sludge; Thermal drying; Wastes; Pyrolysis; Air-steam gasification; Thermal drying; Sewage sludge; Char; Gasification
• ISSN: 0360-5442
• DOI: 10.1016/j.energy.2014.08.061

Thermo-chemical treatment of sewage sludge is an interesting option for recovering energy and/or valuable products from this waste. This work presents an energetic assessment of pyrolysis and gasification of sewage sludge, also considering the prior sewage sludge thermal drying and the gasification of the char derived from the pyrolysis stage. Experimental data obtained from pyrolysis of sewage sludge, gasification of sewage sludge and gasification of char (all of these performed in a lab-scale fluidized reactor) were used for the energetic calculations. The results show that the energy contained in the product gases from pyrolysis and char gasification is not enough to cover the high energy consumption for thermal drying of sewage sludge. Additional energy could be obtained from the calorific value of the pyrolysis liquid, but some of its properties must be improved facing towards its use as fuel. On the other hand, the energy contained in the product gas of sewage sludge gasification is enough to cover the energy demand for both the sewage sludge thermal drying and the gasification process itself. Furthermore, a theoretical study included in this work shows that the gasification efficiency is improved when the chemical equilibrium is reached in the process.
•4 MJ kg−1 for thermal drying of sewage sludge (SS) from 65 to 6.5 wt.% of moisture.•0.15 MJ kg−1 for thermal decomposition of sewage sludge during fast pyrolysis.•Not enough energy in gases from SS pyrolysis and char gasification for thermal drying.•Enough energy in SS gasification gas for thermal drying and gasification process.•Gasification efficiency improves when equilibrium is reached in the process.