Kinetic Parameters For The High-Temperature Oxidation Of In-Situ Combustion Coke

Abstract

Abstract Coke combustion plays a vital role in many thermal recovery methods, whether in-situ or otherwise. Due to this importance, much research has been done into high-temperature coke oxidation. Notwithstanding the extensive studies undertaken to determine the high-temperature coke oxidation model and its kinetic parameters, almost all have used differential analysis in (lie parameter estimation procedure. In addition, the adequacy of the commonly accepted model has never been statistically tested. Because differential analysis requires subjective data manipulation and because a statistical evaluation was sought, an integral-analysis method was developed and applied, with multi-response parameter estimation techniques, to differential reactor data. Kinetic parameters were found for the coke oxidation model using two types of petroleum cokes. It was determined that the commonly accepted coke oxidation model was statistically adequate and that the objective integral-analysis method was superior to the differential analysis technique. Introduction and Literature Survey Thermal recovery methods, including in-situ combustion, the fluidized solids technique(18), the Lurgi Ruhrgas Process(19) and the Taciuk Process(20) depend on high-temperature coke oxidation for their commercial viability. In light of this, much research has been done to determine the form of the combustion model and to estimate the kinetic parameters involved. There have been two approaches to these investigations: a petroleum perspective, done in porous media, and secondly an idealized approach-using a sphere or plate coated with carbon. Dart et al.(18), Lewis et al.(11) and Metcalfe(13), although not done in a porous medium, conducted their experimentation from a global reaction perspective. That is, they analyzed effluent gas compositions and, on that basis, determined reaction rates and the dependence of reaction rate on oxygen and coke concentration. They concluded that the high-temperature coke oxidation reaction is first-order with respect to coke concentration and oxygen partial pressure. Further research was done by Bousaid ef al.(3), Dabbous et al.(7) and Fassihi et al.(9), who conducted their work in porous media, within now-through reactors. In general, their findings indicate that the coke combustion reaction was first-order with respect to coke and oxygen concentration. The reported activation energies varied from 58,850 J/gmole up to 157,300 J/ gmole and the pre-exponential factors ranged from 2.0e-03 to 6.67e05 (g carbon /100 gsand-s). In these studies the reaction rate parameters were obtained by graphical means assuming a differential reactor system. Allag(2) studied coke oxidation from a more numerically rigorous viewpoint. He modelled coke production and burn-off simultaneously and compared the difference between these two (being the residual coke) to his data. He numerically integrated these terms but eventually had to resort to graphical means to minimize convergence problems. Ozomarot(17) investigated the controlling mechanism to coke combustion and the adequacy of the model describing it. He developed a solution routine which solved for the coke combustion parameters by minimizing the error between experimental and calculated reaction rates. However, it was concluded that the technique did not overcome the disadvantages of haphazard data selection and that, judicious choices had to be made as to which data points to include and which to discard.