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.