Kinetics Of Methane Clathrate Hydrate Formation In Water-in-oil Emulsion

The theoretical and experimental research on kinetics of clathrate hydrate formation in water-in-oil emulsion is the design basis of natural gas hydrate formation equipment and gases separation equipment for the absorption-hydration hybrid method, also is the basis of anti-plug of gas and oil transport pipeline. It is critical for the gas transport and storage, the guarantee of pipeline transport, and the application of gas separation technology. In this thesis, the theoretical and experimental research system of hydrate formation kinetics in water-in-oil is established, and the experimental and model work has been carried out as following:(1) The experimental apparatus was established for the research of methane hydrate formation kinetics in water-in-oil(w/o) emulsion using the pressurevolume-temperature(PVT) method. The effects of agitation rates of 300-1100 rpm, average water droplet diameters at 30% water cut, and temperatures of 269.15-277.15 K on the induction time and hydrate formation rate were systematically studied. The experimental results show that the induction time of hydrate formation initially decreased as the agitation rate increased and then increased when higher agitation rates were used. Increasing the temperature increased the induction time. The rate of hydrate formation increased as the agitation rate increased and the average diameter and temperature decreased. The methane consumption was affected by the average diameter and temperature: above 273.15 k, the gas consumption goes up as temperature decrease; while under 273.15 k, the gas consumption goes down as temperature decrease. Under the same experimental conditions, the methane hydrate formation rate in 30% water cut w/o emulsion was 5 times than that in pure water.(2) Apply the Johnson-Mehl-Avrami-Komogorov(JMAK) kinetic equation to the description of methane hydrate formation kinetics in the w/o emulsion. The parameters of the JMAK model were determined by correlating the experimental data with the model data. The agreement between the experimental data and the calculated results of the model was satisfactory(R=0.9635~0.9907). Based on the range of Avrami index, the methane hydrate formation kinetics in the w/o emulsion was proposed.(3) Considering the effects of hydrate amount on emulsion viscosity, one equation was added to describe the effects of hydrate amount on the methane mass transfer coefficient, which was taken into account effect of emulsion viscosity on mass transfer process, on the basis of Dalmmazone’s model. This model was correlated with the experimental data of methane consumed by hydrate formation under various conditions. The model parameters were calculated using nonlinear least square method. The agreement between the experimental data and the calculated results of the model was satisfactory. To make the model more reasonable, we take the following conditions into consideration-where rate of nucleation changes with driving force, and where site saturation nucleation-based on the multi-nucleation process.(4) On basis of the shrinking-core model and the assumption that the time of hydrate formation from water droplet in emulsion is different, hydrate formation kinetics in w/o emulsion was established through calculating the formed hydrate droplet number in unit time using nucleation time distribution function. Then the methane hydrate formation gas consumption in w/o emulsion was calculated. This model was regressed with the methane hydrate formation gas consumption data. It was found that shear rate greatly affect the droplet nucleation distribution in the emulsion: the bigger the shear rate is, the narrower the nucleation time distribution will be. At 700 rpm or above, nucleation time showed normal distribution. While under 700 rpm, nucleation time deviated from the normal distribution. Above the freezing point, nucleation time distribution became narrower with the temperature decreasing.