Mercaptan removal from natural gas by the efficient cyclic adsorption process; a simulation study

• Mercaptan removing from natural gas.
• Vacuum pressure swing adsorption process for methane purification.
• Process performance parameters comparison and economic study for PVSA and PTSA processes.

A more efficient and economical cyclic adsorption process was proposed for mercaptan removal from natural gas (NG) to reduce mercaptan content to less than 10 ppm and meet the environmental rules. Continuous sulfur removal is studied for the NG feed stream, with pressure of 6.8 MPa, flow rate of 2850 Nm3/hr and molar composition of 95.98% methane, 0.00182% water vapor, 1% carbon dioxide, 0.0134% mercaptan and 3% heavier hydrocarbons (C3+). The proposed process of Pressure Vacuum Swing Adsorption (PVSA) was designed and simulated as a more efficient alternative process against the current Industrial Pressure-Temperature Swing Adsorption (PTSA). In this work, an improved PVSA process was simulated with sequences of bed pressurization, adsorption, equalization, blow down, bed regeneration by vacuum and purge by product, in each process cycle. Vacuum condition of 10 KPa with the molar purge/feed ratio of 0.06 and temperature of 350 K was required for appropriate bed regeneration from adsorbed mercaptan to approach to the continuous cyclic steady condition. Comparison between PVSA and PTSA, at the same feed characteristics, same packed columns and adsorption operating conditions, revealed that the PVSA process, with less cycle time than PTSA, could achieve the same product purity with 94.8% recovery and 3.90 [mol/kg day] productivity, whereas PTSA has the recovery of 74.04% and productivity of 2.79 [mol/kg day]. At the same time, operating with PVSA, instead of PTSA process, would reduce the operating cost from 88 to 70 [Thousand $/year].

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