Structured gas-solid contactors for CO2 removal from air
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Min, Youn Ji
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Abstract
In recent decades, the exponential rise in anthropogenic greenhouse gas emissions has propelled atmospheric CO2 concentrations to levels not seen in millions of years, and without precedence in human history. These escalated concentrations significantly contribute to global warming and climate change, underscoring the urgent need for mitigation strategies. Atmospheric CO2 removal, often referred to under the umbrella of negative emission technology, can play a significant role in limiting global warming if implemented on a large scale. Direct air capture (DAC) is a scalable approach for removing atmospheric carbon, yet the true scope of its scalability remains unclear due to the early stage of technology development and high first plant costs.
Our research group has worked on the development of novel structured gas-solid contactors for air capture applications, partnering with W.L. Gore & Associates. In this partnership, we have developed and proposed an air capture system utilizing solid-supported amines uniformly dispersed in expanded poly(tetrafluoroethylene)-based laminate structure, and steam as a regeneration medium. This particular technology is the subject of the thesis dissertation with the goal of establishing its potential technical and economic feasibility.
In this context, the three main objectives are addressed in this dissertation: i) develop and evaluate a scalable ePTFE-based laminate system for air capture applications, ii) establish a metric to evaluate the economic feasibility of the proposed DAC system and understand the interplay between DAC performance and the system design parameters, iii) demonstrate the proposed laminate system in a practical steam regeneration process, and iv) identify options for process optimization in varying system design parameters.
The work on the first objective showed that the ePTFE-based laminate system can be processed practically into scalable gas-solid contactors for capturing CO2 from ultra dilute sources. Commercial amino polymer was infused into the ePTFE/silica composite, yielding adsorbed CO2 quantities competitive with other DAC technologies and enhanced kinetics thanks to its porous nature. The composite materials showed excellent material stability during multicyclic dry and humid CO2 adsorption analysis, as well as in the small-scale cyclic steam regeneration. The incorporation of hydrophobic domain in the contactor system restricted total H2O uptake, and its concomitant regeneration energy penalty.
In the second objective, a first-principle transient mass and energy balance model was developed for the laminate contactors. The model described the different phases of the process, adsorption, evacuation, desorption, and cooling, and included detailed and experimentally calibrated representation of mass transfer phenomena. This model was implemented in a gPROMS, a process modeling software package. The model was simulated over a wide range of system design parameters and used to evaluate the system performance. A high-level techno-economic analysis was conducted to understand the complex interplay between the system performance and the system design parameters. Specifically, this work provides an initial investigation into identifying the significance of the geometrical design parameters on system performance. Using the laminate contactor model with optimized geometry, the trade-offs between operational process parameters were identified and visualized. The resulting productivity and energy were translated into cost of CO2 capture at scale of 1 Mt CO2 captured/y. The main cost driver changed over different process conditions, from capital to operating costs. The operating cost governs the Pareto optimal front between cost and productivity. Overall, the model establishes that there is the potential to operate below 150 $/tonne CO2. This work provides a robust computational tool for evaluating DAC systems based on cost and energy analysis.
Lastly, for the third objective, the laminate composites were installed in an efficient gas-solid contactor and demonstrated in a practical steam-assisted temperature vacuum swing adsorption process. Sorbent regeneration using steam was demonstrated to be effective, rapidly providing required regeneration energy through condensation. The dynamic behavior of the ePTFE-based laminate contactors was captured and studied in a range of design parameters, including inlet gas velocity and contactor channel length. The addition of surface hydrophobicity enhanced the multicyclic hydrothermal stability of the laminate contactors, providing a potential design strategy to enhance the sorbent lifetime. The practical demonstration of the ePTFE-based laminate gas-solid contactors provided a baseline for rational system design and process optimization.
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Date
2024-02-14
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Dissertation