A Simple Kinetic Model for Coke CombustionDuring an In Situ Combustion (ISC) Process

摘要

Although coke combustion studies have been longconducted, literature is still lacking an accurate understandingof reaction kinetics. To this end, the thermo-oxidative behaviorsof Neilburg oil and its asphaltene fraction were examined in thepresence of core sand. Thermogravimetric analysis (TGA) wasperformed in a flowing atmosphere at the heating rate of10°C/min up to 750°C. Both nitrogen and air were used at aflow rate of 45ml/min in the experiments. As earlier researchershave observed, at least two main regions of reactions wereidentified by the thermogravimetric (TG) and derivativethermogravimetric (DTG) thermograms. Various effects,including distillation, low-temperature oxidation (LTO),thermal cracking, high-temperature oxidation (HTO) orcombustion, even mineral decomposition were observed.In this study, Neilburg oil and asphaltenes were completelycracked in nitrogen atmosphere at 425°C to produce coke.Subsequently, the fresh coke was subjected to isothermalcombustion at several temperatures from 374°C to 519°C. Atwo-step oxidation reaction model was applied to describe thiscombustion process. The chemical reactions were simplifiedinto two oxidations occurring in series. In the first reaction,coke was partially oxidized to form an intermediate product,which was then burned in the second reaction. Based on theTGA data, kinetic parameters were estimated with the aid ofcustom written software. For comparison, the one-stepoxidation reaction model was also employed to predict thecombustion process. The two-step oxidation reaction modelgave a better fit to the experimental data. It was also found thatthe coke derived from Neilburg oil and asphaltenes might havesimilar thermo-oxidative behaviors.