We need a hydrogen feed at 3kg/cm2A for one of our newly expanded plant. The main source of the H2 is from a PSA unit (H2>99.9%) available at 30kg/cm2A and another auxiliary source is an off-gas stream (H2=90%)available at 2kg/cm2A.

Since the two H2 sources contain some CO which is a poison to the downstream process, we plan to install a methanation unit to remove the CO. The methanation reaction will be done at 12kg/cm2A. Therefore, main H2 source pressure will need to be reduced while the off-gass pressure will be increased. (see attached file)

When the 30kg/cm2A PSA H2 is reduced to 12 kg/cm2A, there will be choked flow. Also, the post-methanation H2 pressure will once again be reduced to 5 kg/cm2, thus another choked flow. After that, it is desirable that we can control its flowrate by an FCV (flow control valve).

Is the last FCV effective for flow regulation since we already have choked flow upstream of it?
My understanding about choked flow phenomenon is quite blurred, please advise whether the proposed strategy will work.