Syngas Upgrading Using a Combined Membrane-Methanation Unit: An Exhaustive Study of Critical Process Parameters on the Wobbe Index of the Injected Gas

The refinement of the generated raw synthesis gas in gasifiers plays a vital role in the production of bio SNG (Synthetic Natural Gas) and achieving the concept of CO2 neutral process chain. In the current process design, a practical solution for the conversion of syngas components such as CO₂ and CO to SNG with the required quality of the grid specification is introduced. The syngas undergoes a process chain of pressurized water scrubber to achieve a stochiometric relation of CO₂ and H2 to perform methanation reaction, converting CO and CO₂ to methane. In this process train, the scrubbed gas is utilized as the reactor input in a hydrogenation reactor, combining water-gas-shift and methanation reactions. To achieve appropriate spec quality of the SNG for the gas grid, a concentration of hydrogen below 0.5% vol. and a CO₂ concentration of 1% was achieved by implementing a membrane unit increasing the Wobbe index of the SNG. The optimal operational process condition for the entire process, including the scrubber, the membrane unit, and the methanation unit was achieved. The process was modeled using Aspen Custom Modeler and Aspen plus software. An in-house developed Fortran model was developed for the membrane and methanation units according to experimental data. Finally, the critical process parameters that affect the design of the membrane modules and methanation units were evaluated to achieve calorific heating value for the upgraded SNG gas.

Keywords: Syngas; methanation; membrane; retentate; permeation; methane