Computational fluid dynamics approach to study methane hydrate formation in stirred reactor

Abstract

Hydrate formation management in oil and gas industries needs a detailed understanding of hydrate formation phenomena in terms of dynamics and kinetics aspects. Stirred reactors are one of the popular experimental systems to study hydrate formation/dissociation in terms of kinetics and thermodynamics mechanisms. Various processes/systems such as gas hydrate formation and decomposition phenomena in oil and gas facilities are simulated using computational fluid dynamics (CFD). This research examines the hydrate formation in a stirred reactor for a water-methane system using the Eulerian multiphase flow model by employing CFD software (STAR CCM +). The developed numerical model incorporates the conservation equations of momentum, mass, and energy, where the hydrate equations, including mass transfer, hydrate kinetics, and heat of hydrate formation, are included in the governing equations. In this paper, the methane hydrate formation in the stirred reactor for the stirring rate of 300 RPM and volume fraction of 0.04 with a pressure of 5,500 kPa is simulated. Then, the simulation results are validated using the experimental data collected from the literature, resulting in an overall absolute average deviation percentage (AAD%) of 15.6 %. The influences of stirring rate (300 to 500 RPM), methane volume fraction (0.04 to 0.4), pressure (3,500 to 7,500 kPa), and subcooling (1.96 to 9.23 °C) are studied on the hydrate formation in the agitated reactor. The results reveal that the developed CFD model can predict the methane hydrate formation in the stirred reactor with acceptable precision. According to the simulation runs, methane hydrate is formed mainly near the walls and around the stirrer blades. In addition, an increase in subcooling, gas volume fraction, pressure, and stirring rate leads to more hydrate formation in the reactor with a constant temperature of 274.3 K. The maximum mass fraction of hydrate is observed for the case when the gas volume fraction and stirring rates are 0.4 and 900 RPM, respectively. However, the minimum value of methane hydrate is 0.092 g, where the volume fraction and impeller speed are 0.04 and 300 RPM.The findings of this study can help to further understand hydrate formation phenomena in oil and gas facilities. This model can provide oil and gas engineering sectors with effective strategies to control and manage gas hydrates. In addition, the proposed CFD model can be helpful for engineers and researchers in the petroleum industry to simulate hydrate formation in other complicated geometries in petroleum facilities.