Evaluation of pyrolysis residue of oil sludge for recycling as bed material

Abstract Pyrolysis is an appealing technique to convert oil sludge into valuable products such as gaseous and liquid fuels, however, there is lack of research on the use of solid residue after sludge pyrolysis. This work investigated the possibility of recycling solid residue as bed material for the pyrolysis process. The thermogravimetric analysis of the raw sludge in both the pyrolysis condition and combustion condition found that part of the heavy organic compounds in the oil sludge was difficult to recover by pyrolysis, though could be combusted easily in the presence of oxygen. Therefore, by leaving the heavy compound in the solid residue, the solid residue can be self‐heated by combustion and cycled to the pyrolysis process to enhance heat transfer and catalysis. A series of pyrolysis residues at varies temperatures and holding times were collected after pyrolyzing oil sludge in this study. To examine whether there is sufficient potential heat remaining in the pyrolytic residue, the residue was further investigated by FTIR, proximate, ultimate analysis, and TGA in air to study the combustion characteristics and combustion kinetics. Higher pyrolysis temperature and longer pyrolysis time resulted in more ash and fixed carbon in the residue, though less volatile matter. Residue pyrolyzed at a lower temperature was easier to combust and showed lower combustion activation energy, though the recovery of organic fuel was not significant. Pyrolysis time had very minor effect on the solid residue combustion behaviour. It is more appropriate to control the residue property by governing the pyrolysis temperature.