Cubic Plus Association Equation of State for Flow Assurance Projects

Abstract

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.

Ternary Vapor–Liquid Equilibrium Measurements and Modeling of Ethylene Glycol (1) + Water (2) + Methane (3) Systems at 6 and 12.5 MPa

“…CPA has also been incorporated in industrial process design software, where natural gas dehydration units were modeled. 24 Natural gas hydrate formation has also recently been modeled with the using of machine-learning techniques 25,26 where the best results were achieved using three-layer artificial neural networks.…”

“…Liang et al provide a systematic and extensive comparison of CPA with sPC-SAFT for several systems of interest to this work, while other authors have considered the application of CPA for hydrate inhibition studies. − Folas et al achieved a fair description of their MEG + H 2 O + CH 4 data using CPA. CPA has also been incorporated in industrial process design software, where natural gas dehydration units were modeled . Natural gas hydrate formation has also recently been modeled with the using of machine-learning techniques , where the best results were achieved using three-layer artificial neural networks.…”

New association schemes for mono-ethylene glycol: Cubic-Plus-Association parameterization and uncertainty analysis

“…Gas solubility data are very important for the determination of hydrocarbon carryover into the regeneration processes and the subsequent emissions there [31]. For this purpose, other studies have also investigated mixtures including aromatic (BTEX) compounds [10,32].…”

“…These data were used for deriving new BIPs, which were quite different from those fitted to LLE data. CPA has also been successfully implemented in industrial process simulators[31] specifically for modelling dehydration and hydrate inhibition systems.Due to the intricacies of modelling CO 2 , there have been several studies, including a six-part series[71][72][73][74][75][76], involving acid gas mixtures (H 2 S/CO 2 with alkanes, water, glycols in binary and multicomponent mixtures) and several data are available. The emphasis of this modelling has however been on the description of H MEG parameters remaining unchanged.…”

Simulation and Experimental Study of Methane-Propane Hydrate Dissociation by High Pressure Differential Scanning Calorimetry

“…The experimental results were compared with data obtained by simulations using Multiflash 6.0 (Infochem Computer Services). The program applies the CPA equation of state (Cubic Plus Association) for the liquid and vapor phases (Santos et al, 2015) and the model of Van der Waals and Platteeuw (1959) for the chemical potential of the hydrate phase ( H n~) (Equation 2).…”