Analysis of energetics and economics of sub-ambient hybrid post-combustion carbon dioxide capture

Adsorption of CO2 from post-combustion flue gas is one of the leading candidates for globally impactful carbon capture systems. This work focused on understanding the opportunities and limitations of sub-ambient CO2 capture processes utilizing a multistage separation process. A hybrid process design using a combination of pressure-driven separation of CO2 from flue gas (e.g., adsorption- or membrane-based separation) followed by CO2-rich product liquefaction to produce high-purity (>99%) CO2 at pipeline conditions is considered. The operating pressure of the separation unit is a key cost parameter and also an important process variable that regulates the available heat removal necessary to reach the sub-ambient operating conditions. The economic viability of applying pressure swing adsorption (PSA) processes using fiber sorbent contactors with internal heat management was found to be most influenced by the productivity of the adsorption system, with productivities as high as 0.015 molCO2/kg(sorb)(-1) sec(-1) being required to reduce costs of capture below $60/ton CO2 captured. This analysis was carried out using a simplified two-bed process, and thus there is opportunity for further cost reduction with exploration of more complex cycle designs. Three exemplar fiber sorbents (MIL-101(Cr), UiO-66, and zeolite 13X) were considered for application in the sub-ambient process of PSA unit. Among the considered sorbents, zeolite 13X fiber composites were found to perform better at ambient temperatures as compared to sub-ambient. MIL-101(Cr) and UiO-66 fiber composites had improved purity, recovery, and productivity at colder temperatures reducing costs of capture as low as $61/ton CO2. Future economic improvement could be achieved by reducing the required operating pressure of the PSA unit and pushing the Pareto frontier closer to the final pipeline requirement via a combination of PSA cycle design and material selection.

Automated summary

This study focuses on understanding the opportunities and limitations of sub-ambient CO2 capture processes using a multistage separation process, proposing a hybrid process design involving pressure-driven separation and CO2-rich product liquefaction. Among the considered sorbents, zeolite 13X fiber composites were found to perform better at ambient temperatures compared to sub-ambient, while MIL-101(Cr) and UiO-66 fiber composites showed improved purity, recovery, and productivity at colder temperatures, reducing costs of capture to as low as $61/ton CO2.