Kinetics of hydrate formation by CO 2 and mixture of CO 2-C 3 H 8 in concentrated NaCl solution: Effect of impellers

Hydrate-based desalination (HBD) can apply directly to high-salinity water produced with crude oils and gases. For HBD technology to be commercialized, the slow kinetics of hydrate formation must be overcome. This study investigates the effects of type, diameter, number and clearance of impellers on kinetics, i.e. nucleation and growth, of hydrates of pure CO 2 and mixture of CO 2 - C 3 H 8 in a stirred vessel. Concentrated saline solution (8 wt %) was applied to form hydrates at constant temperatures (271.15 - 279.15 K) and pressures (1.73 - 3.6 MPa). Single pitched blade (PB) and straight blade (SB) impellers and also dual combinations of them were applied. With both SB and PB impellers at single mode, lower clearance improved nucleation rates (lower induction times) and higher clearance improved growth rates. The growth rate with SB was higher than that with PB under similar conditions, showing that radial flow is in favor of growth rate. With dual combination of PB and SB, higher nucleation and growth rates were observed compared to single impellers. The presence of PB in dual configuration influenced only the nucleation rate. Using a large diameter SB impeller, resulted in higher growth rate and gas consumption in dual mode. The results with CO 2 - C 3 H 8 mixture were the same as pure CO 2 . Due to the promoting effect of propane on nucleation and growth rates, the effects of variation in propeller characteristics became minor in the presence of propane.