CO2 Hydrate Formation in Various Hydrodynamic Conditions

Abstract

Abstract: The influence of hydrodynamics on formation of CO2 hydrate in a column‐type reactor and a stirred‐vessel reactor was investigated experimentally. In the column‐type reactor, the buoyant motion of the CO2 drops released into the reactor was balanced by the counterflow of the water in the reactor and, therefore, the CO2 drops were suspended stably in the test column. The drop Reynolds number affected hydrate formation significantly. For drops with small Reynolds numbers, hydrate formed almost immediately on the drops. For drops with large Reynolds numbers, it took up to 20 minutes for hydrate to cover the drops. In cases where the Reynolds number reached a certain critical value, a continuous process of hydrate formation on the drops and hydrate shedding from the drops was observed. In the stirred‐vessel reactor, the kinetics of hydrate formation was governed by the strength of agitation. In cases without agitation, hydrate formed only at the liquid CO2‐water interface. In cases with a weak agitation, hydrate was shed from the interface; however, the interface was still the only location for hydrate formation. In cases with a strong agitation, the liquid CO2‐water interface broke, liquid CO2 dispersed throughout the water phase, and hydrate particles of about 0.1 mm in size formed in water simultaneously. The hydrate particles and dispersed CO2 drops coagulated, forming a cluster with a dimension of a few centimeters when stirring was stopped. The bulk density of the cluster varied with the duration of agitation. At early stages, the bulk density of the cluster was less than that of water; however, it increased with time under a continuous agitation. The critical time of duration, at which buoyancy of the cluster changed from positive to negative, decreased dramatically with increase in the rate of agitation.