A numerical model for simulating a dry forward in-situ combustion process in two dimensions, was developed. The primary focus is on the simulation of the compositional changes that take place inside the porous medium during the running of the process. The model allows any number of hydrocarbon components and six others, namely, liquid water, water vapour. oxygen, nitrogen, carbon dioxide, and carbon monoxide. It describes the flow of water. oil, and gas, and includes the gravity and capillary effects. The vapourisation and condensation effects of both hydrocarbons and water enhanced the heat transfer, primarily by conduction and convection, ahead of the combustion front. Equilibrium calculations are performed on the components in both the liquid and vapour phases. The changes in pressure, temperature, and flUid compositions govern the direction of the interphase mass transfer. Heat is generated by two types of reaction, namely, low temperature oxidation and burning of the crude oil. The model allows the movement of a thin burning front inside the burning cell. It is found to give a better temperature profIle. representative of the combustion process. Oxygen mole fraction is calculated throughout the porous medium according to the reaction kinetics. thus no assumption is made regarding the degree of oxygen consumption. The effects of oxygen bypassing caused by the kinetic-limited combustion is therefore represented. A total of 18 components were used in the computer runs. Results show the preferential vapourisation of the lighter components in the vicinity of the high temperature burning front. The lighter components then move towards the producer. faster than do the heavier ones. This segregation produce fuel that is heavier than the original oil. High temperature in the upstream cells causes a reduction in the oil viscosity. which in turn increases its mobility, thus transporting more heat downstream. The rise in temperature in the condensation cell results in a decrease in the rate of water vapour condensation; extending the condensation zone downstream. In the high pf(>ssure run. all the hydrocarbon in the downstream cells condenses. In the burning cell however. both the vapour and the liquid phases are present due to the high front temperature. The vapour phase is richer in the light components while the liqUid is richer in the heavy components.

Fluidised bed combustion offers potential advantages over conventional power generation systems, particularly with respect to sulphur capture using injected limestone. The stone calcines on entry to the hot bed, forming CaO, and then reacts with SO<SUB>2</SUB> to produce CaSO<SUB>4</SUB>. Regenerative schemes aim to reduce the sorbent loading by stripping off the sulphur from the spent limestone which is then reused. This subject of this dissertation is an investigation into the fundamentals of the regeneration of sulphated limestone by reductive decomposition. Following a detailed discussion of the thermodynamic limitations on the reaction system, attention is focussed on the kinetics of the reductive decomposition scheme. The results of a study on the reaction of CaSO<SUB>4</SUB> powder with CO are reported. This made use of two experimental techniques, X-ray powder diffraction and thermogravimetric analysis. These experiments highlighted the major features of the reaction scheme and allowed the study of two special cases, the sulphidation of CaSO<SUB>4</SUB> to produce CaS only and the solid-solid reaction between CaS and CaSO<SUB>4</SUB>. The major experimental technique used for this work was the batch addition of limestone to a fluidised bed. After a brief discussion of the results of sulphation experiments, typical regeneration experiments are described. By varying the test conditions as well as performing several special experiments, a mechanism for the overall reaction is deduced. The effect of the operating variables on the product split is then explicable. The evidence suggests that the closed pores resulting from the sulphation reaction lead to strong diffusion resistance on regeneration which controls the rate during the early and middle stages. By utilising high CO<SUB>2</SUB> concentrations the formation of CaS was inhibited; the reaction was then amenable to quantitative analysis which revealed an approximate first order dependence on CO concentration and an activation energy of 110kJ/mol. One method for reducing the quantities of CaS produced is to operate the fluidised bed in a two-zone fashion i.e. with oxidising and reducing regions. An investigation into this reactor configuration is included with particular attention paid to the oxidation of CaS. The results obtained are explicable in terms of the results from the single zone bed and allow the effects of operating variables on the reactor performance to be predicted. Finally, the mathematical modelling of the gas-solid reactions is considered. The changing grain size model is introduced by considering the sulphation of limestone. The final conditions from this model then form the initial conditions for the regeneration model, which considers mildly reducing conditions only. The final model then uses as a basis the mechanism proposed in chapter 5 and is applied to the thermogravimetric analysis results.

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