Mathematical Modeling Of 3d Heat Transfer In Concurrent Fluid Flow In Subseahydrate Gas Harvesting Systemwith Moving Riser Method
The gas hydrate deposits have recently been developed to produce natural gas with risks in economics and gas leakage to seawater. Both of these issues relate to optimal design of gas harvesting system that requires thorough analysis in heat transfer processes. This study demonstrates that, with the Moving Riser Method (MRM), while the heat transfer process along the water injection pipe can be simulated using closed-form analytical solutions, the heat transfer from water to gas hydrates at seabed is a huge challenge due to the complexity of 3D conduction-convection with a moving boundary. In addition to the closed-form analytical solutions for heat transfer along the water injection pipe, a simplified 3-D heat transfer model used for predicting the dynamic mining pit size and thus the required dimension of covering device to collect all dissociated methane gas was developed in this study. It is concluded that with today’s technology applicable to the MRM, the injected water at seafloor level will be hot enough to dissociate gas hydrate at a commercial rate with an affordable gas consumption rate. The gas production to gas combustion ratio (PCR) is greater than 4. According to the simplified 3-D heat transfer mod, even the gas production ship stays at the same location for over 40 hours with continuous water injection, the dynamic pit size will still be within 0.9 meter of the hot water injection point. Therefore it is feasible to use a gas collector of reasonable size (e.g., 2m in diameter) to gather all dissociated gas from the hydrate deposit. However, this issue still requires further investigation due to the assumptions made in the model development.