Effects of Mixing Functions of Static Mixers on the Formation of CO2 Hydrate from the Two-Phase Flow of Liquid CO2 and Water

Abstract

Formation experiments of CO2 hydrate from the two-phase flow of liquid CO2 and water were carried out using static mixers with different types of mixing elements to elucidate the effects of mixing functions of the static mixer on CO2 hydrate formation. The mixing principle of the Kenics type static mixer is composed of three mixing functions, flow division, flow reversal, and radial mixing. In this study, three types of mixing elements in addition to the basic Kenics type static mixer were applied for CO2 hydrate formation; each mixing element lacked at least one mixing function among three mixing functions. The observed behaviors of CO2 hydrate formation could be classified into six patterns: (1) hydrate chunks, (2) CO2 drops agglomerated through the hydrate film, (3) dispersed liquid CO2 drops covered with hydrate film, (4) mixture of tiny liquid CO2 drops and hydrate particles, (5) mixture of hydrate chunks and agglomerated CO2 drops, and (6) mixture of agglomerated and dispersed CO2 drops. Occurrences of the above patterns depended on the type of the mixing element as well as the flow rates of liquid CO2 and water. From the observations, flow division was suggested to be important for the formation of hydrate chunks but not essential, and flow reversal was essential for the formation of dispersed hydrate particles. The formation mechanisms of CO2 hydrate with the static mixer are discussed according to the results.