System and method used to recycle exhaust gas during olefin polymer production

A method for recycling an exhaust gas in olefin polymer production comprising:

• a compression cooling step, wherein after an olefin polymer exhaust gas is fed into a compression cooling mechanism, the olefin polymer exhaust gas is processed by a compression cooling unit to form a remaining exhaust gas stream which is outputted via a first outlet of the compression cooling mechanism, and a C4+ high carbon hydrocarbon stream as a liquid phase which is outputted via a second outlet of the compression cooling mechanism, and the remaining exhaust gas stream is fed into a hydrocarbon membrane separation mechanism;
• a hydrocarbon membrane separation step, wherein the remaining exhaust gas stream fed into the hydrocarbon membrane separation mechanism is processed by a hydrocarbon membrane module to form a product discharge system (PDS) transport gas stream which is outputted via a first outlet of the hydrocarbon membrane separation mechanism, and a C4+ high carbon hydrocarbon stream which is outputted via a second outlet of the hydrocarbon membrane separation mechanism, and the remaining exhaust gas is fed into a hydrogen membrane separation mechanism;
• a hydrogen membrane separation step, wherein the remaining exhaust gas fed into the hydrogen membrane separation mechanism is processed by a hydrogen membrane module to form a remaining tail gas stream which is outputted via a first outlet of the hydrogen membrane separation mechanism, and a mixed non-condensable gas stream containing hydrogen gas which is outputted via a second outlet of the hydrogen membrane separation mechanism, and the remaining tail gas stream is fed into a deep cooling mechanism;
• and
• a deep cooling step, wherein the remaining tail gas stream fed into the deep cooling mechanism is processed by a deep cooling unit to form a nitrogen gas stream which is outputted via a first outlet of the deep cooling mechanism, a C2+ low carbon hydrocarbon stream which is outputted via a second outlet of the deep cooling mechanism, and a C4+ high carbon hydrocarbon stream which is outputted via a third outlet of the deep cooling mechanism,
• wherein, the deep cooling mechanism is used for receiving the remaining tail gas stream from the hydrogen membrane separation mechanism and recycling a C2+ low carbon hydrocarbon stream and a nitrogen gas stream,
• the deep cooling mechanism comprises at least one deep cooling unit, wherein the deep cooling unit comprises a second heat exchanger, a second gas-liquid separator, a first throttle valve, a third heat exchanger, a third gas-liquid separator, a second throttle valve, a turbo expander, and a turbo expander pressurization end.