The invention discloses a cryogenic
separation system for separating a
mixed gas. The
system mainly comprises two parts, that is, a
molecular sieve purification unit and a cold box of a cryogenic separation device, wherein the
mixed gas at least containing
carbon monoxide,
hydrogen,
methane and a small amount of
nitrogen communicates with an inlet pipeline of the
molecular sieve purification unit, the
molecular sieve purification unit sequentially communicates with a first main
heat exchanger, a
tower bottom
reboiler of a stripping
tower, a
tower bottom
reboiler of a demethanizing tower, and a second main
heat exchanger in the cold box of the cryogenic separation device through a first pipeline and then is connected to a middle inlet of a
hydrogen separation tank after impurities easy to condense at a low temperature, of
carbon dioxide, methyl
alcohol and water, are removed, and three
hydrogen-enriched gas pipelines are connected out from the top of the hydrogen separation tank and communicate with an external hydrogen-enriched gas
collection system after a hydrogen-enriched gas is reheated by the two main heat exchangers to recover a cold quantity; and two liquid pipelines are connected out from the bottom of the hydrogen separation tank, one liquid pipeline communicates with a middle inlet pipeline of the stripping tower through a first
throttle valve and the second main
heat exchanger, and the other liquid pipeline communicates with an upper inlet pipeline of the stripping tower through a second
throttle valve.