Abstract
Comparison of different regeneration options for direct air capture (DAC) has usually been limited to only consider pure CO2 production, limiting the process options to e.g. temperature-vacuum swing adsorption (TVSA) or steam-stripping. In this work, detailed experimental comparison is conducted of temperature swing adsorption (TSA/TCSA) and TVSA for DAC. Particularly, TVSA is assessed with air or inert gas purge flow (TVCSA) and without purge flow. The working capacity, regeneration specific energy requirement (SER) and adsorbent regenerability of these processes was compared. For all other studied regeneration options except TVSA without purge flow, over 85% regeneration was obtained already at 60 °C. Isobaric TSA at 60 °C had the lowest regeneration SER of 4.2 MJ/kgCO2. Coupling TSA with mild vacuum improved desorption rate and increased working capacity from 0.47 to 0.51 mmolCO2/gsorbent, requiring 7.5 MJ/kgCO2 for regeneration. Without purge flow, TVSA resulted in only 0.39 mmolCO2/gsorbent with the SER of 8.6 MJ/kgCO2 at 100 °C. Due to lower allowable regeneration temperature of 60 °C, mild vacuum TVSA with air flow also had a lower cyclic capacity decrease rate of 0.26%/cycle compared to 0.38%/cycle with TVSA without purge flow at 100 °C. However, using 100 °C with air flow in the TVSA process lead to a significant capacity decrease of 0.6%/cycle. Therefore, using either air or inert purge flow below 100 °C coupled with mild vacuum has benefits over the TVSA process with no inflow in terms of CO2 productivity, specific energy requirement and adsorbent regenerability. For utilization purposes that require low-concentration CO2, TVSA with purge flow should thus be considered as a viable regeneration option for direct air capture along with isobaric TSA.
Highlights
For carbon capture and storage (CCS) or utilization (CCU) purposes, CO2 capture from flue gases or air has been proposed using various technologies
The purpose of this analysis is to assess whether using re generation methods with inlet flow such as Temperature swing adsorption (TSA), leading to low-purity CO2, show significant working capacity or specific energy requirement benefits compared to the temperature-vacuum swing adsorption (TVSA) process without inlet flow during re generation
Because the total desorption capacities are equal or higher than the adsorption capacities with uncertainty taken into account, regeneration of the adsorbent was complete after each 4-step re generation process
Summary
For carbon capture and storage (CCS) or utilization (CCU) purposes, CO2 capture from flue gases or air has been proposed using various technologies. TVSA with inert gas purge has been compared to steam stripping with vacuum as a re generation method for DAC in terms of desorption rate [30], but the energy requirement or adsorbent regenerability using this process has not been compared to other options to the authors’ best knowledge. An automated and modifiable fixed-bed ad sorption–desorption device is used for studying the regeneration op tions for DAC using temperature-swing adsorption (TSA) and tem perature-vacuum swing adsorption (TVSA) processes with and without inlet flow The purpose of this analysis is to assess whether using re generation methods with inlet flow such as TSA, leading to low-purity CO2, show significant working capacity or specific energy requirement benefits compared to the TVSA process without inlet flow during re generation. The progress of cyclic adsorption and desorption capacities are studied over multiple experimental cycles for TCSA and TVSA processes to see the effect of different process options on the regenerability of the amine-based adsorbent
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