Non-Stoichiometric crystallization, a thermodynamic flash approach: case of mixed gas hydrates

• Main Authors: Bouillot, Baptiste, Herri, Jean-Michel
• Other Authors: Laboratoire Georges Friedel (LGF-ENSMSE), Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-École des Mines de Saint-Étienne (Mines Saint-Étienne MSE), Institut Mines-Télécom Paris (IMT)-Institut Mines-Télécom Paris (IMT), Département PROcédés Poudres, Interfaces, Cristallisation et Ecoulements (PROPICE-ENSMSE), École des Mines de Saint-Étienne (Mines Saint-Étienne MSE), Institut Mines-Télécom Paris (IMT)-Institut Mines-Télécom Paris (IMT)-SPIN, Centre Sciences des Processus Industriels et Naturels (SPIN-ENSMSE), L'équipe Cristallogénèse du Laboratoire de Sciences et Méthodes Séparatives (SMS) - Université de Rouen, Université de Rouen, Pr. Samuel Petit, Dr. Yohann Cartigny
• Format: Conference Object
• Language: French
• Published: HAL CCSD 2016
• Subjects: Crystallization; gas hydrates; thermodynamics; flash calculations; Cristallisation; Modélisation; Flash thermodynamique; hydrates de gaz; [SPI.GPROC]Engineering Sciences [physics]/Chemical and Process Engineering; Ice; permafrost
• Online Access: https://hal.archives-ouvertes.fr/hal-01327031; https://hal.archives-ouvertes.fr/hal-01327031/document; https://hal.archives-ouvertes.fr/hal-01327031/file/B%20Bouillot%20Cristal%208%202016.pdf

National audience Clathrate Hydrates are ice-like compounds that can be formed under high pressure and low temperature. They are composed of water and small molecules of ‘’gas’’. Hence they are usually called gas hydrates. They are involved in a significant issue of the oil industry, the hydrate plugs in pipelines (flow-assurance), as well as gas capture and storage, air conditioning… Moreover, methane hydrates can be found in sediments in deep sea and permafrost. That is why they are also considered as a significant methane resource on earth.Since they are non-stoichiometric compounds, it is difficult to model these crystals in process simulation. Furthermore, the speed of crystallization seems to influence the hydrate composition. Therefore, a modeling of the hydrate crystallization taking into account the history of the solid formation could be an interesting tool.In this work, a successive thermodynamic flash approach is presented according to two different hypotheses: heterogeneous hydrate phase during the crystal growth, and homogeneous hydrate phase. The main idea of these procedures is to discretize the crystal growth while the hydrate volume is increasing. Hence, three phase flash calculations are performed on the system. Each time, the previous amount of hydrate that has been formed is removed (at each iteration).The results of such algorithms are compared to batch experiments at low and quick crystallization rates ( Duyen et al. 2016). The flash algorithms at given temperature (only one degree of freedom) give accurate results. The predicted final pressure and the hydrate volume are calculated within 7% accuracy. Moreover, the flash calculation results with no hydrate reorganization are closer to experiments at quick crystallization rate, whereas the experiment at low crystallization rate is better predicted with the second hypothesis (reorganization of the hydrate phase during growth). This work and its results provide a more realistic and comprehensive view of gas hydrate crystallization (more ...