Product Liquefaction
Hybrid CO2 capture processes that perform the CO2 purification in multiple stages have shown promise as a way to overcome the limitations of existing adsorbent or membrane materials.17,23,58,59 While the baseline model assumes the primary separation unit can produce 95% pure CO2 at 92% recovery, installation of a liquefaction column when the cooling is available may prove desirable to open up the selection of materials that may not otherwise be able to reach the final target conditions. The proposed process uses a CO2 liquefaction column primarily to allow for more flexible decision making with materials and process design in the first separator.
Figure S3 shows the overall heat balance for the sub-ambient CO2 capture process at one baseline condition. For the sake of clarity, the cooling water used in the process is not shown. In the base case, the minimum temperature approach (5 °C) occurs at the bubble point (TB) liquefaction column. With 16 bar compression, this case resulted in an excess warming requirement of >21 MW in the 12-48 °C range. In this analysis, that excess warming of the product N2 stream is unused and thus is vented to the environment via the stack.