Modelling solubility of solid sulphur in natural gas

The purpose of this work is to propose a model able to estimate the solubility of sulphur in natural gas transmission and distribution networks. Thus, we developed a model to predict the equilibrium solubility of elemental sulphur in natural gas containing low amount of H2S, at pressure and temperature ranges lower than those encountered in production conditions. We established a reactive flash model. The constitutive equations are classically the chemical and physical equilibriums and partial mass balances. We chose the Peng–Robinson equation of state to describe the phase behaviour coupled with the van der Waals one-fluid mixing rules with one binary interaction coefficient. This approach needed critical parameters for each component. We determined the set of critical parameters for S8 specie from three thermodynamic intrinsic properties including the description of sulphur dissociation reactions. Binary interaction parameters between CH4, CO2, H2S and sulphur are obtained by optimisation from binary and ternary solubility data. Comparisons with experimental values of solid sulphur solubility show that the model is able to describe the sulphur solubility in synthetic natural gases. The application of our model to different natural gases indicated that under transport conditions sulphur solubility is less than 0.005 mg per normal cubic meter.