Study of pyrolysis and combustion kinetics of oil sludge

Abstract

ABSTRACT In order to deal with the shortage of oil and natural gas, the supplement energies, such as oil sludge, waste plastics, waste rubber needed to be studied. The pyrolysis and combustion methods have advantages when they are chosen to treat oil sludge. The investigation of kinetics is significantly important to know the kinetic parameters and the reaction mechanisms and to provide important theoretical basis for the process design of pyrolysis and combustion to treat oil sludge. Most previous studies on pyrolysis and combustion kinetics of oil sludge regarded pyrolysis process or combustion process, and rarely split pyrolysis or combustion process to calculate kinetic parameters separately. In this work, the experiment of pyrolysis and combustion were carried out by thermal gravimetric analyzer. After splitting the pyrolysis and combustion processes into two stages, respectively, the methods of Coats-Redfern and distributed activation energy model (DAEM) were used to calculate the kinetic parameters. Based on the results of thermogravimetric analysis, the pyrolysis and combustion process can be divided into two stages. For the pyrolysis process, the first stage is mainly with the evolution of adsorbed volatile hydrocarbon and the rupture of weaker chemical bond and the second stage is the cracking of organic macromolecules. Meanwhile, in the first stage of combustion process, small molecular organic matter in dry basis oil sludge will volatilize and then burn on the surface of the crucible and the gas phase outside the crucible, and in the second stage, macromolecular organic matter will volatilize, pyrolyze and burn, and the diffusion of oxygen into the crucible will cause the fixed carbon to burn. According to the kinetic results of the pyrolysis process, the activation energy of the first stage calculated by the Coats-Redfern model are all less than 40 kJ/mol, and that of the second stage increases from 148.14 kJ/mol to 184.97 kJ/mol with the increase of the heating rate. The results of DAEM model show that with the increase of the conversion rate, the activation energy of the first stage increases from 60.82 kJ/mol to 81.05 kJ/mol, and that of the second stage increases from 120.60 kJ/mol to 237.07 kJ/mol. For the combustion process, the activation energy calculated using Coats-Redfern model decreases from 120.18 kJ/mol to 73.48 kJ/mol in the first stage, and that of the second stage is relatively low. The results of DAEM model show that with the increase of the conversion rate, the activation energy decreases from 129.53 kJ/mol to 62.36 kJ/mol in the first stage and that in the second stage is stable at about 70 kJ/mol.