Development of a Kinetic Model for In-Situ Combustion and Prediction of the Process Variables using TGA/DSC Techniques

Abstract

ABSTRACT This paper describes the development of a kinetic model of the in-situ combustion process from data obtained from Thermogravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC). The kinetic model was used to predict fuel deposition and combustion rate in a combustion tube. Good agreement was obtained between predicted and observed fuel deposition and combustion rate in two combustion tube runs. A crude oil from Iola County, Kansas, was studied. This oil has a gravity of 19.8° API and a viscosity of 222 cp at 38°C and 89 cp at 54°C. Data from TGA experiments on Iola crude heated in the presence of air were obtained. Analysis of combustion gases from the TGA was done by gas chromatography to determine the nature of the reactions occurring during the TGA runs. Main reactions/transitions identified were distillation, low temperature oxidation, cracking and combustion. A kinetic model of the TGA process was developed from thermograms. The model is based on the weight of crude oil components which undergo main reactions/transitions. The kinetic model was used to predict the percentage of the crude oil deposited as fuel in the combustion process as well as the time for consumption of the fuel within the combustion zone. By estimating the length of the combustion zone from an energy balance across the region where combustion reactions take place in a combustion tube, it was possible to predict the rate at which fuel was consumed during the process. A combustion tube run was made with silica sand containing 8.0% by weight Iola crude oil in order to test the prediction by the kinetic model derived from thermal analysis techniques. Results of the combustion tube run were in good agreement with predicted values of this work and another run from the literature which was performed on the same crude oil. The fuel heating value and heat availability during the process were also estimated by DSC techniques. However, the estimated heating values were low. This was attributed to the Increase in heating value of the crude oil in the combustion tube due to low temperature oxidation and distillation effects downstream of the combustion front.