Pressurized pyrolysis of sewage sludge: Process performance and products characterization

Pyrolysis is a promising method for sewage sludge (SS) management by co-producing syngas, tar and char. However, in atmospheric pyrolysis, low-heating value syngas and low-quality tar are main barriers for widely application. In this study a series of pyrolysis experiments were carried out at elevated pressure of 0.1, 1.0, 3.0, 5.0, 7.0 MPa to treat SS. The effect of pressure on pyrolysis product yields, syngas composition, properties of tar and char were systematically investigated. The results indicated that the elevated pyrolysis pressure promoted the tar cracking to produce more energy-dense syngas. As for syngas composition, when the pressure was increased from 0.1 MPa to 7.0 MPa, noncombustible CO2 content decreased and simultaneously energy-dense CH4 content increased as well as the lower heating value (LHV) of syngas was greatly increased. According to GC-MS and FTIR results, the quality of tar was greatly improved in terms of high esters, phenols and aromatics contents. The quality of char was improved in terms of LHV and atomic O/C and H/C ratios. These findings suggested that the pressurized pyrolysis is an attractive strategy to upgrade conventional pyrolysis for SS treatment.