Analysis of coupled heat & mass transfer during gas hydrate formation in bubble column reactors

Abstract

Gas hydrates have promising applications in gas separation, carbon capture, desalination and gas storage. Although there exist several studies on modeling hydrate growth, analysis of the coupled role of heat and mass transfer on hydrate formation has been largely neglected. Presently, we develop a fundamentals-based simulations framework which accounts for mass transfer, heat transfer and various interfacial phenomena associated with gas hydrate formation in a bubble column reactor. We model CO2 separation from syngas via CO2 hydrate formation and validate against experiments from another study. This model is used to quantify the impact of various operating parameters (gas flow rate, bubble size, reactor pressure, inlet gas temperature, reactor geometry) on hydrate formation rate and gas-to-hydrate conversion factor. Results provide several insights related to the intricate transport phenomena that underlie hydrate formation. Firstly, we highlight the adverse impact of inadequate heat dissipation on hydrate formation rate and conversion factor. This is particularly important for high gas flow rates, wherein high hydrate formation rate triggers substantial temperature rise. Enhancing thermal conductivity of hydrate forming media can significantly enhance formation, with the conversion factor seen to double. Secondly, simulations show that bubbles < 100 μm diameter are essential to realize high growth rates. Thirdly, increasing reactor pressure can significantly improve the maximum theoretical separation efficiency for CO2 to > 90 %. Fourthly, precooling the inlet gas enhances hydrate formation rates by upto 5 %. Overall, this work outlines a novel approach to modeling hydrate formation and provides a tool for process optimization.