Gas separation system and enriched gas production method

A method for producing enriched gas by supplying raw material mixed gas to a gas separation system and enriching at least one of gases contained in raw material mixed gas,

• wherein the gas separation system comprises:
• a first gas separation membrane unit;
• a second gas separation membrane unit, and a third gas separation membrane unit,
• the first gas separation membrane unit, the second gas separation membrane unit and the third gas separation membrane unit each include at least a gas inlet, a permeate gas outlet, and a non-permeate gas outlet,
• the non-permeate gas outlet of the first gas separation membrane unit and the gas inlet of the second gas separation membrane unit are connected by a non-permeate gas discharge line,
• the permeate gas outlet of the first gas separation membrane unit and the gas inlet of the third gas separation membrane unit are connected by a permeate gas discharge line,
• a raw material mixed gas supply line is connected to the gas inlet of the first gas separation membrane unit, and a compression part is disposed in the middle of the raw material mixed gas supply line,
• the permeate gas outlet of the second gas separation membrane unit and a position on the suction side of the compression part in the raw material mixed gas supply line are connected by a permeate gas recycle line,
• the non-permeate gas outlet of the third gas separation membrane unit and a position on the suction side of the compression part in the raw material mixed gas supply line are connected by a non-permeate gas recycle line,
• concentrated and enriched gas is taken out from the non-permeate gas outlet of the second gas separation membrane unit, and
• the permeate gas discharge line includes a first permeate gas discard line for discharging a part of the permeate gas discharged from the first gas separation membrane unit to the outside of the gas separation system.