Hydrate-based technique for natural gas processing: Experimental study of pressure-dropping and continuous modes

Gas hydrate crystallization is perspective and energy-efficient technology for gas mixtures processing, including natural gas. There were compared pressure-dropping and continuous gas hydrate crystallization methods for separation of gas mixture closed to natural gas. The studied mixture has been chosen similar to the natural gas composition: CH₄ (75.68 mol.%) - С₂H₆ (7.41 mol.%) - C₃H₈ (4.53 mol.%) - н-C₄H₁₀ (2.47 mol.%) - CO₂ (5.40 mol.%) - H₂S (1.39 mol.%) - N₂ (3.01 mol.%) - Xe (0.11 mol.%). Experiments were provided in the 4 L high pressure reactor, using water solution of SDS (0.20 wt.%). The experiment conditions were 280.15 K and pressure of 4.25 MPa. The components separation factors and recovery for two modes have been researched and compared for choosing more effective options. After comparing these characteristics, it was concluded that continuous process is more productive than pressure-dropping mode. At the stage cut (θ) of 0.9, the gas components total recovery (R) for the continuous mode have exceeded the total recovery for the pressure-dropping mode by 8.15 %, and at θ = 0.8, exceeded by 6.11 %. The recovery and separation factors have the highest values for H₂S, C₃H₈, Xe in the continuous mode: 97.62 %, 94.90 %, 84.98 % and 8.7, 10.53, 6.36, respectively. Thus, the choosing of the more effective stage cut depends on the aim of the process: the highest purity or the largest recovery.