Continuous Formation of CO₂ Hydrate via a Kenics-Type Static Mixer

Abstract

Formation of CO2 hydrate using a Kenics-type static mixer was studied experimentally. The flows of liquid CO2 and water were mixed in the static mixer, and CO2 hydrate was formed continuously from the two-phase flow. The patterns of hydrate formation were found to be dependent on the flow velocities of liquid CO2 and water. The flow of agglomerated hydrate chunks in water occurred under relatively CO2-rich conditions, while dispersed flow of tiny particles of CO2 hydrate with small liquid CO2 drops was observed under relatively water-rich conditions. These effects could be explained by two mechanisms occurring in the static mixer, namely, continuous shedding of hydrate films from the interface between liquid CO2 and water induced by the shearing force and breakup of the CO2 drops. The energy consumption by the static mixer for the hydrate formation process was estimated, and it was significantly less than that for a stirring vessel type reactor. A continuous hydrate formation process could be achieved using the static mixer.

Hydrate nucleation in quiescent and dynamic conditions

“…(4) Mechanical agitation: Experiments show that stirring, shaking, or shocking can trigger nucleation in a supersaturated fluid [Mullin, 2001;Mullin and Raven, 1962;Skovborg et al, 1993;Young, 1911;Young and Cross, 1911]. Similarly, mechanical stimulation facilitates ice nucleation and gas hydrate formation [Barrer and Edge, 1967;Skovborg et al, 1993;Sloan and Fleyfel, 1991;Tajima et al, 2004]. Experimental results for other systems show that the nucleation rate and the morphology of precipitates are affected by stirring conditions and rate [Akkermans et al, 2006;Liang et al, 2004;Ting and McCabe, 1934].…”

Gas Hydrate Formation Kinetics in Semi-Batch Flow Reactor Equipped with Static Mixer

“…Static mixers are motionless mixing devices with fixed "mixing elements" arranged in a straight pipe. The Kenics static mixer experiments demonstrated that two fluids (drop/bubble and water) are efficiently agitated with the mixing elements and are subsequently converted to hydrate formed on the drop/bubble surface at specific temperature and pressure conditions (Tajima et al, 2004(Tajima et al, , 2007. Several structures of mixing element are designed for efficient agitation/mixing of fluids more than one.…”

“…Fig. 9 shows the speculated mechanisms for hydrate formation in static mixing-type flow reactor according to experimental results (Tajima et al, 2004(Tajima et al, , 2005(Tajima et al, , 2011b. The r d , r f , and r s are rates of target gas dissociation to water, target gas hydrate nucleation and growth, and target gas hydrate particle/film shedding, respectively.…”

The flow and mass transfer characteristics of concentric gas-liquid flow in an advanced static mixer

“…Some examples of the application of static mixers for dispersive mixing of gaseous phase into liquid phase are ozonation processes in waste water treatment process, scrubbing ammonia or cyanides with water and hydrogenation of vegetable oils [1,6,7,20]. Tajima and his colleagues [21][22][23] analytically and experimentally elucidated the effects of flow division, flow reversal and secondary flow induced by the Kenics static mixer on the formation of CO2 hydrate. The liquefied CO2 was transported through a pipeline and mixed with seawater in a KSM at a depth of 500−1 000 m then released into the ocean.…”