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OS4C-3：FORMATION AND STABILITY OF HYDRATES ON SUSPENDED GAS BUBBLES
发布时间:2014-07-28
Litao CHEN, E. Dendy SLOAN, Carolyn A. KOH, Amadeu K. SUM
Centre for Hydrate Research, Chemical & Biological Engineering Department, Colorado School of Mines, USA
A high pressure water tunnel (HPWT) was designed and built to study hydrate formation and dissociation on suspended gas bubbles. The purpose of the studies using this system is to understand the impact of hydrates on gas bubbles rising in an open ocean as a result of an oil/gas blowout. Little is known on the process of hydrate formation on gas bubbles, in particular the changes on the rising gas bubbles induced by the hydrates in terms of the dissolution of gas in water and the hydrodynamics of the hydrated gas bubble. To develop the fundamental understanding of hydrates on suspended gas bubbles, a systematic set of experiments have been performed in the HPWT. In the experiments to be discussed in this contribution, methane gas was injected into the counter flowing water to form hydrate shell on the suspended gas bubbles. The stability of methane hydrate shells on these gas bubbles was studied in two manners: 1) observations of the hydrate shell formation at constant pressure and temperature, 2) observations of hydrate shell dissociation during depressurization of the system at constant temperature. Hydrate shells were formed on methane gas bubbles at 277 K and 7.0, 10.4, 13.9 and 17.3 MPa. Before hydrates were formed, the water in the HPWT was saturated with methane gas. Methane gas bubbles were directly injected into a tetragonal cone with a cylinder base, used to restrict the flow and trap the gas bubbles in the viewing area. The measured methane concentration needed to form hydrate shell on the gas bubbles was around 0.0014 mole fraction. In most experiments, it was initially observed that the hydrate on the gas bubbles formed rough shells. Over time, the hydrate shells became smooth and wrinkled (collapsed of gas bubble) due to the shear induced by the flow water. It was also found that the hydrate shells on the suspended gas bubbles were unstable in the system with counter flowing water at constant pressure and temperature, meaning that the hydrates were gradually sheared from the gas bubble surface, resulting in a constant decrease of the gas bubble until it completely vanished. It was observed that the hydrate shells became wrinkled and smaller over time. During depressurization of the system at constant temperature, the hydrate shells on the gas bubbles were seen to expand as the pressure decreased. Cracks on the hydrate shell appeared at around 5.6 MPa and 277.2 K, but a hydrate film quickly re-formed on the gap created by the cracks. Hydrates completely dissociated around 4.5 MPa and 277.2 K.
Centre for Hydrate Research, Chemical & Biological Engineering Department, Colorado School of Mines, USA
A high pressure water tunnel (HPWT) was designed and built to study hydrate formation and dissociation on suspended gas bubbles. The purpose of the studies using this system is to understand the impact of hydrates on gas bubbles rising in an open ocean as a result of an oil/gas blowout. Little is known on the process of hydrate formation on gas bubbles, in particular the changes on the rising gas bubbles induced by the hydrates in terms of the dissolution of gas in water and the hydrodynamics of the hydrated gas bubble. To develop the fundamental understanding of hydrates on suspended gas bubbles, a systematic set of experiments have been performed in the HPWT. In the experiments to be discussed in this contribution, methane gas was injected into the counter flowing water to form hydrate shell on the suspended gas bubbles. The stability of methane hydrate shells on these gas bubbles was studied in two manners: 1) observations of the hydrate shell formation at constant pressure and temperature, 2) observations of hydrate shell dissociation during depressurization of the system at constant temperature. Hydrate shells were formed on methane gas bubbles at 277 K and 7.0, 10.4, 13.9 and 17.3 MPa. Before hydrates were formed, the water in the HPWT was saturated with methane gas. Methane gas bubbles were directly injected into a tetragonal cone with a cylinder base, used to restrict the flow and trap the gas bubbles in the viewing area. The measured methane concentration needed to form hydrate shell on the gas bubbles was around 0.0014 mole fraction. In most experiments, it was initially observed that the hydrate on the gas bubbles formed rough shells. Over time, the hydrate shells became smooth and wrinkled (collapsed of gas bubble) due to the shear induced by the flow water. It was also found that the hydrate shells on the suspended gas bubbles were unstable in the system with counter flowing water at constant pressure and temperature, meaning that the hydrates were gradually sheared from the gas bubble surface, resulting in a constant decrease of the gas bubble until it completely vanished. It was observed that the hydrate shells became wrinkled and smaller over time. During depressurization of the system at constant temperature, the hydrate shells on the gas bubbles were seen to expand as the pressure decreased. Cracks on the hydrate shell appeared at around 5.6 MPa and 277.2 K, but a hydrate film quickly re-formed on the gap created by the cracks. Hydrates completely dissociated around 4.5 MPa and 277.2 K.
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