CO2-TBAB semi-clathrate hydrate dissociation behaviour in individual capsules: A new two-stage numerical model and parametric study

Abstract

Gas hydrates have a wide implementation in the capture, storage, transport and utilisation of a range of gases, in which the dissociation kinetics is of great importance to gas transport and recovery efficiency. Encapsulation has been proven an effective technique to enhance gas–liquid mass transfer and thus improve gas hydrate formation kinetics. However, the dissociation behaviour of gas hydrate in individual capsules remains unknown. In this work, the dissociation kinetics of encapsulated CO2-TBAB semi-clathrate hydrates in different shapes are experimentally investigated under various operating conditions, and, for the first time, a two-stage numerical model is developed which integrates mass transfer, heat transfer and the intrinsic gas hydrate reaction kinetics to simulate the gas hydrate dissociation process. The effects of temperature, pressure, capsule volume and capsule geometry on gas hydrate dissociation kinetics are investigated. The results reveal that the proposed model is capable of capturing two distinct experimentally-observed dissociation stages, a rapid and subsequently slow stage according to the measured dissociation rate. Surface-to-volume ratio of the capsule and the dissociation driving force are the two main factors influencing the dissociation kinetics. The ring-shaped capsule exhibits the most efficient dissociation process due to its high surface-to-volume ratio and long transition time to the slow dissociation stage. This work enhances the understanding of gas hydrate dissociation behaviour in individual capsules and guides the manipulation of dissociation for efficient hydrate-based gas transport and recovery.