A novel CO2 cryogenic liquefaction and separation system

In this paper, the phase transition characteristics of CO2 and CO2/H2 mixture are analyzed, and ideas for improving the cryogenic separation method are drawn. On this basis, a novel CO2 cryogenic liquefaction and separation system is put forward. In the novel system, two-stage compression, two-stage refrigeration, two-stage separation, and sufficient recovery of cryogenic energy are adopted. Two-stage compression can increase the total pressure of gas mixture and liquefaction temperature of CO2. Two-stage refrigeration and two-stage separation can reduce the cryogenic energy demand and compression work in subsequent steps. Sufficient recovery of the cryogenic energy can reduce refrigeration duties. All these measures decrease the total energy consumption. As a result, under a CO2 recovery ratio of 90%, the total energy consumption is only 0.395 MJ/kgCO2 with over 99% CO2 purity. Further analysis indicates that the proposed CO2 cryogenic liquefaction and separation system is more suitable for separating liquid CO2 from gas mixtures with high CO2 concentration, and that the high initial pressure of the mixture presents better performance. The proposed system can serve as a new approach to CO2 removal with low energy penalty.