(227g) Experimental and Theoretical Evaluation of a Direct Steam Based Direct Air Capture (DAC) Process Using Honeycomb Sorbents

Based on recent assessments [1], represents the removal of CO₂ from the ambient air, typically referenced as Direct Air Capture (DAC), one of the technology pathways required to meet the targets set with respect to global warming. While different DAC technologies are considered, the adsorptive separation of CO₂ using solid sorbents combined with a temperature swing adsorption (TSA) process represent an approach pursued by many players active in this field. Structured sorbents, for example in form of honeycomb structures, are often preferred, independent of the active sorbent material selected. This is driven by their favorable characteristics with respect to pressure drop and heat and mass transfer [2], both being of crucial importance with respect to the overall process and capture economics.

While the desorption using direct steam is common practice and significant practical relevance, as it allows for very high energy densities and an easy separation of the product gas by condensation of the water, very limited experimental data are available in the literature [3-5]. Most academic research work is done with indirect heating or with diluted steam, which is not trivial to scale economically and cannot be directly applied to processes using direct steam heating.

In this presentation we will report on extensive experimental work on laboratory scale using saturated steam for the direct heating of honeycomb structured sorbents. In the experimental work amine based materials are used as active sorbents, coated onto ceramic honeycomb substrates. As these amine materials are sensitive to oxidation, the experiments also include the evaporative cooling step as well as the subsequent adsorption. Furthermore, will we discuss the cyclic operation (adsorption – evacuation – steaming - cooling), in addition to the results from the individual process steps. The experimental work is supplemented by detailed numerical modeling. Besides the normal adsorption and desorption phenomena, the process of steam condensation and evaporation of the condensed water in the porous honeycomb sorbents is considered. Based on the results from the experimental work and the simulations some critical learnings will be provided as well as suggestions for an optimized process and structured sorbent selection.

Literature

[1] PCC, 2023: Climate Change 2023: Synthesis Report. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, H. Lee and J. Romero (eds.)]. IPCC, Geneva, Switzerland, pp. 35-115

[2] R. Mennitto et al., Extruded monoliths for gas separation processes: height equivalent to a theoretical plate and pressure drop correlations, AIChE J 68 (2022) e17650.

[3] X. Zhu et al., Design of steam-assisted temperature vacuum-swing adsorption processes for efficient CO2 capture from ambient air, Renewable and Sustainable Energy Reviews (2021), 137, 110651

[4] J. Gu, H.-J. Bart, Heat and mass transfer in steam desorption of an activated carbon adsorber, Int. Commun. Heat and Mass Transf. (2005), 35, 296–304

[5] W. Li et al., Steam-Stripping for Regeneration of Supported Amine-Based CO2 Adsorbents, ChemSusChem (2010), 3, 899 – 903