Gas separation membrane unit, gas separation system, and method for producing enriched gas

A gas separation membrane unit to which a raw material gas mixture containing CO2 and CH4 is supplied to concentrate and enrich at least CH4 contained in the raw material gas mixture,

• wherein the gas separation membrane unit comprises a plurality of gas separation membrane modules combined in parallel,
• each of the gas separation membrane modules comprises:
• a gas inlet;
• a non-permeated gas outlet;
• and a permeated gas outlet,
• the gas inlets of each of the gas separation membrane modules are shared to constitute the gas inlet of the gas separation membrane unit,
• the non-permeated gas outlets of each of the gas separation membrane modules are shared to constitute the non-permeated gas outlet of the gas separation membrane unit,
• the permeated gas outlets of each of the gas separation membrane modules are shared to constitute the permeated gas outlet of the gas separation membrane unit, and
• each of the gas separation membrane module has a gas separation selectivity (P′CO2/P′CH4) of 5 or more at 40° C., and a coefficient of variation of the gas separation selectivity among the plurality of gas separation membrane modules is 0.01 or more and 0.40 or less, or
• each of the gas separation membrane module has a gas permeability P′CO2 of 1.5×10−5 cm3(STP)/cm2·sec·cmHg or more wherein P′CO2 is a permeation rate of CO2, and a coefficient of variation of the gas permeability among the plurality of gas separation membrane modules is 0.01 or more and 0.40 or less.