Numerical Study on CO2 Hydrate Formation in a Bubble Column Reactor From Flue Gas Mixtures

Abstract

Abstract Gigascale carbon capture and sequestration (CCS) is increasingly seen as essential to meeting the targets of the Paris Agreement. Sequestration of CO2 as CO2 hydrates (ice-like materials of CO2 and water) has received research attention recently. CO2 hydrates form at medium pressures and temperatures close to freezing from a water-CO2 gas mixture. Bubble column reactors (BCR) are a preferred way of rapidly forming CO2 hydrates. This study uses a recently-developed and validated model to predict performance of a BCR for CO2 hydrate formation from flue gas (CO2/N2). In particular, two performance parameters are analyzed, the gas consumption rate for hydrate formation, and the fraction of CO2 that can be converted to CO2 hydrates (conversion factor). Extensive parametric analysis is conducted to study the influence of pressure, temperature, CO2 mole fraction at inlet, inlet gas flow rate, reactor height and reactor diameter on CO2 hydrate formation rate. Across the range of simulations conducted in this study, the maximum reported hydrate formation rate is 71 ton/yr and the highest conversion efficiency is 67.8%. It is seen that both the performance parameters improve with increasing pressure, decreasing temperature and increasing inlet mole fraction of CO2. Increasing gas flow rate increases the gas consumption rate (i.e., hydrate formation rate) but reduces the conversion factor. This suggests that the operation of BCR for gas separation should involve low flow rates but that high flow rates should be used to synthesize hydrates for CO2 sequestration. An increase in reactor volume by increasing the height or diameter, improves hydrate formation on both performance parameters (rate, conversion factor).