Pyrolysis kinetics of perfusion tubes under non-isothermal and isothermal conditions

Abstract

The waste-to-energy (WTE) conversion of solid waste including perfusion tubes becomes interesting, with potential advantages of reducing the volume and mass of solid waste, and exploiting new energy sources. First, the non-isothermal pyrolysis experiments of perfusion tubes with the heating rates (β) of 5, 10, 20, 40°Cmin−1 were conducted in a thermogravimetric analyzer (TGA) under nitrogen atmosphere. The TGA results indicated that the pyrolysis temperature of perfusion tubes is mainly between 200°C and 500°C, and the pyrolysis process of perfusion tubes under non-isothermal conditions can be divided into two stages. Next, the isothermal pyrolysis experiments of perfusion tubes were carried out on a batch fluidized bed at four temperatures (850, 875, 900, 925°C), which is close to the practical pyrolysis processes of perfusion tubes. The batch fluidized bed results demonstrated that the pyrolysis process of perfusion tubes under isothermal conditions only has a rapid conversion stage, which is dissimilar to that under non-isothermal conditions (two-stage conversion). Last, the pyrolysis kinetic parameters of perfusion tubes under non-isothermal and isothermal conditions were calculated, respectively by the isoconversional methods (the Flynn–Wall–Ozawa (FWO) method and the Kissinger–Akahira–Sunose (KAS) method) and the isothermal model fitting methods. Noted that the isothermal pyrolysis kinetics of perfusion tubes were for the first time investigated according to the gas compositions at different isothermal conditions, and the contracting volume (R3) mechanism model was determined as the most probable model to describe the pyrolysis process of perfusion tubes among six potential mechanism models. The apparent activation energies of perfusion tube pyrolysis under non-isothermal conditions were between 97.81 and 209.62kJmol−1 using the FWO method and between 85.63 and 214.28kJmol−1 using the KAS method, while it was calculated as 74.54kJmol−1 under isothermal conditions. The decrease of apparent activation energy in isothermal fluidized bed experiments could be due to less limitation to external transfer of mass and heat. Overall, these results suggested that this research can provide an understanding of pyrolysis kinetics of perfusion tubes and some useful information for the design of pyrolytic processing system using perfusion tubes as feedstock.