(66g) Probing the Effect of Stirring on Natural Gas Hydrate Formation-a Future Energy Fuel

The transport of natural gas through liquefaction is one of the major modes of natural gas export across different regions in the world. The process of liquefaction of natural gas is costly and consume large sum of energy as it requires cooling of up to -161^oC. Normally, the liquefaction cost vary from 3 $ to 10 $ per MMBtu (millions of British thermal units). So if the market prices of crude oil are down, the liquefaction cost could negatively affect LNG business and make liquefaction projects unprofitable.

In order to avoid liquefaction cost, the scientists are trying to study gas hydrates as potential mode of natural gas transportation and storage in future. Gas hydrates are crystalline compounds, formed 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 experimental based work, the formation rate of gas hydrates in a high pressure cell has been studied at different stirring rates using a magnetic stirrer. In the first stage, the system was first cooled from 20 ^o C to 2 ^o C at constant pressure for 18 hours. Then in second stage, the system was left stable at 2 ^o C for another 18 hours at constant stirring rate. The stirring rates were varied between 100-1400 Rpm (Rotations per minute) for each experiment and the gas hydrate crystal formation was observed by calculating pressure drop across the high pressure cell during the second stage.

The experimental result shows that for a chosen high pressure cell, the stirring rate has a significant effect on the rate of gas hydrate crystal formation. The maximum gas hydrate crystal formation was observed within the stirring range of 550-750 RPM. It was found that there exists a threshold stirring limit, above or below which little or no hydrate crystal formation takes place. This fundamental study is a significant step forward and it can be useful for modeling purposes and designing of a pilot scale hydrate production plant to study the economical and safety factors associated with natural gas hydrate storage and transportation phenomena.

Acknowledgement

This work was made possible by NPRP grant # 6-330-2-140 and GSRA # 2-1-0603-14012 from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors.