Carbon dioxide low-temperature trapping system combining circulating nitrogen with gradient utilization of cold energy

The invention discloses a carbon dioxide low-temperature trapping system adopting circulating nitrogen in combination with gradient utilization of cold energy. The carbon dioxide low-temperature trapping system comprises a flue gas flow path, an N2 circulating loop and a CO2 collection and storage flow path, n2 in the N2 circulation loop is used as a cooling capacity carrier, so that the temperature of the flue gas is gradually reduced in the heat exchangers in different temperature areas until CO2 in the flue gas is condensed, cold energy of different grades can be better utilized, and gradient utilization of the cold source cooling capacity is achieved. When the system runs, the N2 circulation loop can periodically change the N2 flowing direction; in the flowing direction A, the first heat exchanger is in a desublimation state, and the second heat exchanger is in a sublimation state; in the flowing direction B, the first heat exchanger is in a sublimation state, and the second heat exchanger is in a desubli