Thermodynamic Modeling of Natural Gas Systems Containing Water

Abstract

As the need for dew point specifications remains very urgent in the natural gas industry, the development of accurate thermodynamic models, which will match experimental data and will allow reliable extrapolations, is needed. Accurate predictions of the gas phase water content in equilibrium with a heavy phase were previously obtained using cubic plus association (CPA) coupled with a solid phase model in the case of hydrates, for the binary systems of water–methane and water–nitrogen and a few natural gas mixtures. In this work, CPA is being validated against new experimental data, both water content and phase equilibrium data, and solid model parameters are being estimated for four natural gas main components (methane, ethane, propane, and carbon dioxide). Different tests for the solid model parameters are reported, including vapor-hydrate-equilibria (VHE) and liquid-hydrate-equilibria (LHE) calculations, structural transitions, and predictions at low temperatures. Furthermore, model predictions for representative multicomponent mixtures are presented and compared against the ISO-standard GERG-water model and other selected models. In most cases, very good agreement with experimental data is obtained.