EXPERIMENTAL STUDY OF DISSOLUTION RATE OF A CO_2 DROPLET AND CO2 SOLUBILITY IN HIGH PRESSURE AND LOW TEMPERATURE SEAWATER WITH HYDRATE FREE

摘要

Against the background of carbon dioxide (CO_2) ocean sequestration technology, we investigated the solubility of CO_2 in seawater at a thermodynamic state similar to that at an ocean depth of 1000 m. The experiment was performed in two steps. In the first step, we reexamined and modified the fundamental relationship between Sherwood (Sh) number and Rayleigh (Ra) number in a natural convective flow over an up-down CO_2 droplet. We derived a new expression of the Grashof number for CO_2dissolution in water and seawater with the aid of the relation between the density of CO_2 solution and CO_2 concentration. In the second step, this new expression was applied to the estimation of solubility of CO_2 from experiments examining the dissolution of an individual CO_2 droplet in seawater at hydrate-formable pressure and temperature states. We found from our experiments: that at hydrate-formable conditions (step two), no hydrate appeared at interface between liquid CO_2 and seawater throughout the experiments within 5 hours, which suggested that a thermodynamic state (pressure and temperature) is indispensable but not a complete condition for hydrate formation; and associated with this dual nature, the data of CO_2 solubility estimated from this experiment are much larger than those obtained by Kimuro et al from experiments of hydrate coexistence. Our data ranged from 0.052 to 0.062 in mass fraction.