An effect of CO2 on the characteristic of gas hydrate in a vessel tank

Gas hydrate represents a mixture of natural gas and water molecules formed at high pressures and low temperatures near the freezing point of water. Physically, the hydrates are ice-shaped and among the water molecules, there is a cavity filled by a hydrate gas called clathrate. The hydrates can be formed because there is gas injected in water molecules at high pressure condition having temperature above the freezing point of water. Then it is exposed to a force that can dissolve gas inside the water. A lot of research has been conducted to investigate the performance of the gas hydrate itself. The performances include the rate of hydrate formation, the hydrate stability, and the hydrate storage capacity. Several studies have been studied, among others, to observe the effect of initial gas injection pressure on gas hydrate process, the effect of rotation in a vessel tank as a container for gas hydrate formation, and the hydrate formation process on stirrer tank. One of the most important things in the gas hydrate process is how the hydrate can be formed, which can be seen from the rate of hydrate formation by investigating how much the gas pressure will penetrate into water molecules. It is due the hydrate formation requires low temperature and high pressure. However, a conditioning of the gas hydrate formation at high pressure and low temperature is a matter that requires considerable energy. Therefore, it is needed a system in which the pressure of hydrate formation is not too high. One method to lower the hydrate pressure in order to the hydrate-forming pressure is not too high, CO2 will be mixed to the gas hydrate. It is because CO2 is soluble in water molecules. It make an effect that the pressure of gas formation will be lower. In the previous research, it is showed that CO2 was able to make the pressure in methane gas mixture lower. By decreasing its pressure, CO2 is expected to improve the hydrate performances. The study was conducted by varying the percentage of CO2 volume from 0% to 100%. Each percentage of CO2 will be seen as its effect on the gas hydrate performance. The gas used in this experiment were propane-butane gas mixture of 50% each. The mixture of propane-butane gas and CO2 were then fed into the water molecules. The water used was a demine water of 50 cm3. The initial pressure of the formation rate was 0.3 MPa and the temperature formation was 273 K. Meanwhile, the temperature used to stabilize the hydrate was 268 K. The vessel tank, used to process the occurrence of hydrate has the capability of high pressure has a cavity diameter material of 4 cm, height 12 cm, 0.5 cm thick and total volume of 150 cm3. The vessel tanks were inserted into the cooling bath that was set at a temperature of 273 K. The results showed that as greater the CO2 content, as smaller the initial hydrate initiation phase, However, it has an impact to decrease the hydrate stability. For hydrate storage capacity performance, pure CO2 hydrate has the highest storage capacity, while the lowest storage capacity was CO2 with gas-CO2 mixed percentage of 50%. It shows that CO2 is capable to decrease the pressure effect on 50% composition variation.