A New Extended Corresponding States Equation of State for Modelling CO2-Water Thermodynamics - A Compromise for CFD
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This PhD work is part of the CO2 Dynamics project in collaboration with Sintef Energy. We investigated the importance of accurate modelling of CO2 thermodynamic properties for process design. The study was conducted for the application of depressurization of a CO2 transport pipeline. In the study we investigated pure CO2 and CO2 mixtures, including the polar mixture of CO2 - water. The study was conducted over pairs of pressure-temperature (PT) complying with two sets of experimental pipeline depressurization data. The results showed a significant impact of the quality of used equation of state (EoS), and the presence of impurities on the predicted thermodynamic behavior and speed of sound. Moreover, we conducted research on the capabilities of the extended corresponding states (ECS) EoS SPUNG when dealing with CO2 - water mixtures. The SPUNG EoS was chosen as it was shown earlier to be a very promising EoS for Carbon Capture and Storage (CCS) non-polar mixtures. We started with a preliminary study followed by a detailed study that showed the potentials and limitations of the method. We also investigated the possibilities to improve or extend the limitations of the SPUNG EoS by changing the reference fluid. The found disadvantages of SPUNG EoS when dealing with CO2 - water mixtures were that it poorly predicted the water-rich phase (even though better than SRK, and SRK-HV) and the CO2 solubility at wide range of conditions. As part of the investigation of the potential of the method, we conducted a reference fluid sensitivity study, which revealed a significant dependency of the density predictions on the chosen reference fluid. Within the set of hydrocarbons, the heavier the hydrocarbon was, the better it predicted the water-rich phase density. However, the reference fluid was found not to play a significant role in phase equilibrium capture. The prediction of phase equilibrium properties was more influenced by the mixing rule used in the approach of calculating the scale factors. Based on these systematic assessments, a new ECS approach was developed, which preserved the advantages of the SPUNG EoS but eliminated the limitations. The proposed EoS accurately captures the phase equilibrium and densities of the CO2 - water systems at wide set of conditions of pressure, temperature and composition. The new model is an ECS that uses Bender’s 20-parameter MBWR as a reference equation, and SRK-HV as bases to the approach used to calculate the shape factors for scaling. The recommended reference fluids were NH3, R23, and R503 with parameters of Polt. All the evaluations in the presented articles were compared to large covering set of experimental data. Since one major advantage of the ECS based approaches is the good capture of transport properties, future work should assess the new model accuracy for predicting the CO2 – water transport properties.
Has partsPaper 1: Ibrahim, Mohamed; Ertesvåg, Ivar Ståle. PVTx Modeling of CO2 Pipeline at Depressurization Conditions Using SPUNG Equation of State (EoS) with a Comparison to SRK. Energy Procedia 2014 ;Volum 63. s. 2467-2474 https://doi.org/10.1016/j.egypro.2014.11.269 This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).
Paper 2: Mohamed Ibrahim, Geir Skaugen, Ivar S. Ertesvåg. The impact of varying reference fluid on the predictability of the extended corresponding state equation SPUNG for modelling CO2 - Water. Energy Procedia 2014; 51:353-362 https://doi.org/10.1016/j.egypro.2014.07.042 This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).
Paper 3: Ibrahim, Mohamed; Skaugen, Geir; Ertesvåg, Ivar Ståle; Haug-Warberg, Tore. Modelling CO2 - water mixture thermodynamics using various equations of state (EoSs) with emphasis on the potential of the SPUNG EoS. Chemical Engineering Science 2014 ;Volum 113. s. 22-34 http://dx.doi.org/10.1016/j.ces.2014.03.025
Paper 4: Ibrahim, Mohamed; Skaugen, Geir; Ertesvåg, Ivar Ståle. An Extended Corresponding States Equation of State (EoS) for CCS Industry. Chemical Engineering Science 2015 ;Volum 137. s. 572-582 http://dx.doi.org/10.1016/j.ces.2015.06.013