(60a) The Effect of Stirring on Gas Hydrate Formation in High Pressure Reactor Systems

The liquefaction of natural gas (LNG) is one of the major modes of natural gas transportation between different regions. The liquefaction of natural gas requires cooling up to -161^oC and the cost of liquefaction can range from 3 $ to 10 $ per MMBtu (millions of British thermal units). So unless there is a demand for higher LNG prices, the liquefaction cost could negatively affect LNG business and make liquefaction projects unprofitable.

In order to cut down liquefaction cost, the researchers are trying to study gas hydrates as a potential mode of natural gas transportation and storage in future. Gas hydrates are crystalline meta-stable compounds, made up of water and gas molecules. One volume of hydrate can store up to 180 volumes of natural gas at STP (standard temperature and pressure). Therefore, the development of hydrate production plants holds particular importance in future.

In this work, the formation rate of gas hydrates in a high pressure reactor system has been studied at different stirring rates using a magnetic stirrer. In the first phase, the system was first cooled from 20 ^o C to 2 ^o C at a constant pressure for 18 hours. Then immediately in second phase, the system was left stable at 2 ^o C for another 18 hours at constant stirring rate to allow hydrate crystals to grow in size. The stirring rates were varied between 100-1400 Rpm (Rotations per minute) for each experiment and the gas hydrate crystal formation was observed by measuring pressure drop across the system during the second phase. The experimental results show that for a chosen system, the stirring rate does have significant effect on the rate of gas hydrate crystal formation. The maximum gas hydrate crystal formation was observed within the systen at the stirring range of 550-750 RPM. It was found that for a chosen system there exists a threshold stirring limit, above or below which little or no hydrate crystal formation takes place. This fundamental study can be useful for modeling purposes and designing of a pilot scale hydrate production plant.