(610b) Heat and Mass Transport in a Reactive Porous Medium: Application to Heavy Oil and Oil Shales Combustion

We are interested by heat and mass transport in a reactive porous media and particularly by oxidation reactions that occur inside it.

First materials used were oil shales because they were a good candidate for a kinetic study. Indeed, from the chemical point of view, they are more complex than coal for example, because they contain various organic components but the presence of a large fraction of inert inorganic matter in the rock induces a big simplification that is the combustion does not affect the bed structure. Moreover, oil shales are in solid form and contain a little fraction of water.

Second candidate was heavy oil. Its study is more difficult than for oil shales because they are three miscible phases.

Major difficult in both cases was to obtain a good reactional mechanism which can reproduce with a good agreement both oxidation reactions: LTO reactions and HTO reactions. Water seems to modify chemical behaviours. Experiments will be designed to check it.

Families of oxidation reactions are the same ones for both cases but the study of oil shales is simpler because there is little water fraction then we can't observe water phase. Moreover, for the heavy oil, coke is due to the fuel deposition through oil vaporization and cracking of the heavy components of the oil while for oil shales coke is only due to cracking.

In the first part, we introduce the oil shales study. We have designed a transient one dimensional numerical tool taking into account various transport and chemistry mechanisms and simulating oil shale combustion in a fixed bed. The main issue of this work is to find a simplified chemical model able to represent as well as we can do different processes like heterogeneous oxidation. Another important point is to consider the possible thermal disequilibrium between solid and gas phase revealed in previous studies. This aspect was treated through a two phase heat balance equation, one for the gas and the other for the solid. This modelling used results coming from series of experiments. During this study, the main matter was to model oxidation. The first approach was to use a coal model considering pyrolysis producing char, which is burned during the oxidation; this way has not been showed here. Finally, we employ an ?oil? approach using thermogravimetric analysis and reactor results to obtain a single equation reaction mechanism. Thereafter, this last method was enriched with another oxidation reaction.

In the second part, we discuss about combustion of heavy oil in a reactor and particularly modeling and additional difficulties compared to the preceding study.