Thermodynamic hydrate inhibitors such as methanol, ethanol, (mono) ethylene glycol (MEG), and triethylene glycol (TEG) are widely used in the oil and gas industry. On modeling these compounds, we show here how the CPA equation of state was implemented in an in-house process simulator as an in-built model. To validate the implementation, we show calculations for binary systems containing hydrate inhibitors and water or hydrocarbons using the Cubic Plus Association (CPA) and Soave−Redlich−Kwong (SRK) equation of states, also comparing against experimental data. For streams containing natural gas and water, CPA was applied to calculate the loss of the inhibitor to the vapor phase as a function of temperature and pressure. Simulations of dehydration units using TEG were conducted, and the CPA results were compared with that of two commercial simulators which used their available thermodynamic packages for glycol applications, proving that the CPA calculations are in good agreement with these models and showing that this is an adequate way to simulate complex mixtures containing natural gas, water, and hydrate inhibitors.

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Since the discovery of the Pre-Salt layer in Brazilian waters, production of high gas–oil ratio (GOR) has increased considerably. This gas has a high content of water, CO2, and sometimes H2S. A study in different conditions was conducted using several equations of state (EoS) such as Peng–Robinson, GERG-modified Peng–Robinson (PR-ISO-04), Soave–Redlich–Kwong, and Cubic Plus Association (CPA). Petrobras’ Process Simulator has been used to perform the phase equilibrium calculations. All the EoS except for CPA used parameters from the literature. A new parameter estimation procedure for CPA has been proposed using a particle swarm optimization algorithm followed by the SIMPLEX method presenting themselves together as an optimal approach. The results show that PR-ISO-04 can be considered to be an improvement compared to the original Peng–Robinson but CPA appears to be the most promising approach to be used for predicting dew points for water-containing mixtures, especially at high pressures.

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