Improving the Modeling of Hydrogen Solubility in Heavy Oil Cuts Using an Augmented Grayson Streed (AGS) Approach

The Grayson Streed (GS) method [Grayson H.G. and Streed C.W. (1963) 6th World Petroleum Congress, Frankfurt am Main, Germany, 19-26 June, pp. 169-181] is often used by the industry for calculating hydrogen solubility in petroleum fluids. However, its accuracy becomes very bad when very heavy fluids are considered. An improvement is proposed in this work, based on a Flory-augmented activity coefficient model. Hydrogen solubilities in n-alkanes from n-C-7 up to n-C-36 have been investigated and a decreasing Henry constant with molecular weight is evidenced. The analysis of the Henry constant behaviour with molecular weight suggests a simple improvement to the model, using a Flory entropic contribution, thus keeping its predictive character. This improvement led to the necessity of refitting a number of fundamental hydrogen parameters. The resulting model behaves better for heavy components and for aromatics. The petroleum fractions evaluated with the Augmented Grayson-Streed (AGS) model are taken from Cai et al. [Cai H.Y. et al. (2001) Fuel 80, 1055-1063] and Lin et al. [Lin H.M. et al. (1981) Ind. Eng. Chem. Process Des. Dev. 20, 2, 253-256]. The importance of the petroleum fluid characterization is stressed. A sensitivity analysis has shown that the solubility parameter has a much larger effect than the other parameters: great care must be taken at calculating that property. The predictions of hydrogen solubility in petroleum fractions and in coal liquids were improved compared with the Grayson Streed model, resulting in an Absolute Average Deviation (AAD) of 30% for AGS model compared to 55% for Grayson-Streed model, in the range of 80-380 degrees C and 6.3-258.9 bar.