Investigation on pyrolysis characteristics and kinetics of sewage sludge with different heat-mass transfer rates

Abstract

The pyrolysis process of sewage sludge (SS) in fluidized bed has the characteristics of high speed heat-mass transfer rate, which challenges the reliability of thermal analysis methods. In this study, TGA and fast-reaction thermogravimetric analysis (FR-TGA) were used to investigate the pyrolysis characteristics of SS. The apparent kinetic parameters of pyrolysis at constant heating rate (β) and excellent heat-mass transfer rate were obtained, respectively. Resuls shows that, the pyrolysis of SS under both conditions showed multi-step reaction characteristics. The apparent activation energy (Eα) of pyrolysis of SS determined by FR-TGA was significantly lower than that determined by TGA. With the increase in temperature of the FR-TGA reactor, E decreased further. The excellent heat-mass transfer rate could improve the reactivity during SS pyrolysis. In addition, FR-TGA experiments showed that moisture could promote the pyrolysis of organic components in SS and further reduce Eα. Based on these conclusions, a kinetic model of SS pyrolysis under excellent heat-mass transfer rate was established. This study can serve as a reference for predicting the pyrolysis behavior of SS in a fluidized bed reactor.