Dissociation experiment and dissociation rate model of CO2 hydrate

Abstract

Applying CO2 hydrate (referred to as hydrate) to CO2 storage and sequestration can alleviate global greenhouse effect, which is currently a hot spot of hydrate research. In order to explore the dissociation mechanism and rate, this paper carries out hydrate dissociation experiments under different working conditions of depressurization stage, temperature and initial hydrate volume fraction by using the reactor. Then, based on the experimental results, the influences of pressure, temperature, hydrate volume fraction, mass exchange and energy exchange on the dissociation rate are analyzed. Finally, a hydrate dissociation rate model considering the influences of intrinsic dissociation dynamics, mass transfer and other comprehensive mechanisms is established. And the following research results are obtained. First, two dissociation phenomena appear in the process of hydrate dissociation, including adsorption of gas bubble and shedding of flaky hydrate from the edge. Second, hydrate dissociation is a process of intrinsic dissociation dynamic driving, mass and heat transfer. According to the dissociation rate variation, it can be divided into two stages, i.e., stable dissociation stage and dissociation weakening stage. In the stable dissociation stage, the dissociation rate is maintained constant. And in the dissociation weakening stage, the dissociation rate decreases gradually with the increase of dissociation resistance (mass exchange). Third, both pressure and temperature drive the dissociation by influencing the difference between the actual hydrate surface fugacity and the phase equilibrium fugacity. The increase of depressurization range can lead to the increase of dissociation rate while the duration of stable dissociation is extending. The increase of temperature can also lead to the increase of the dissociation rate, but its influence is less than that of depressurization. In conclusion, this newly established dissociation rate model can well predict the value and variation trend of hydrate dissociation rate. And under the working condition of 2.0 MPa, the maximum relative error of the experimental results is 5.1%.