An efficient modelling technique based on the representation of the precipitated asphaltene as a pure dense phase is presented. The success of the approach is based on the division of the heaviest component in the oil into a nonprecipitating and a precipitating component.The characterization of these components is discussed. This model was able to make quantitative predictions of experimental data from the literature as well as additional data from industry. This was achieved with only a small number of adjustable parameters (two or three). The mechanistic aspect of the model with regards to colloidal nature of asphaltene/resin micelles is also discussed. An algorithm for three-phase flash calculations with asphaltene precipitation is described.

Diffusion and reactions in a porous pellet are treated as transient, nonisothermal, nonisobaric processes. Continuity and energy balance equations are solved simultaneously for temperature and concentration profiles in the pellet. Conductive, convective as well as radiative heat transfer are included. The ‘dusty gas’ flux model is used to describe the transport of diffusing gases. Viscous, bulk and concentration gradient terms have been included. Structural changes with reaction are accounted by considering the effect of changing grain radius on porosity and pore diameter. The model predictions match conversion trends for carbon gasification over a temperature range of 800 to 1100°C investigated experimentally.

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