In the methanation section the cleaned and conditioned product gas has to be converted into SNG that meets the specifications after downstream water and CO2 removal.
For methanation of CO and H2 containing gases, commercial processes and catalysts are available; both Lurgi and Haldor-Topsøe can deliver methanation systems. Typically, these methanation processes are carried out at higher pressures than foreseen in the bio SNG plant, i.e. 20 to 30 bar compared to 7 bar. These systems are typically also designed with gas recycles or quenches or internally cooled reactors to control the temperatures to prevent thermal degradation of the catalysts. When the methanation is carried out at lower pressures, the adiabatic temperature increase is correspondingly lower. Resultantly, the methanation can be operated adiabatically without gas recycles and in simple vessels without internal cooling.
Three methanation reactors, with intermediate cooling, are sufficient to reach sufficient CO and H2 conversion. Commercially available nickel-based catalysts are used.