Stampi-Bombelli Valentina, Mazzotti Marco
Institute of Energy and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland.
Ind Eng Chem Res. 2024 Nov 4;63(45):19728-19743. doi: 10.1021/acs.iecr.4c02303. eCollection 2024 Nov 13.
This study presents a comprehensive comparison between the packed bed and monolith contactor configurations for direct air capture (DAC) via process modeling of a temperature-vacuum swing adsorption (TVSA) process. We investigate various design parameters to optimize performance across different contactor geometries, including pellet size, monolith wall thickness, active sorbent content in monoliths, and packed bed structure configurations, considering both a traditional long column (PB) and multiple shorter columns configured in parallel (PB). Our parametric analysis assesses specific exergy consumption, sorbent, and volume requirements across different operating conditions of a five-step TVSA cycle. For minimizing sorbent requirements, PB and monoliths with over 80% sorbent loading were the best-performing contactor designs with overlapping performance in the low-exergy region. Beyond this region, PB faced limitations in reducing sorbent requirements further and was constrained by a maximum velocity at which it is sensible to operate without substantially increasing the exergy demand. In contrast, monoliths decreased sorbent requirements with minimal exergy increase due to reduced mass transfer resistances and lower pressure drop associated with their thin walls. The analysis of volume requirement-specific exergy Pareto fronts revealed that PB was less competitive with this metric due to the requirements for additional void space in the contactor configuration. The study also revealed that optimal sorbent loading for reducing volume requirements in monoliths differed from those minimizing sorbent usage, with the most effective loading being below 100%. Thus, the optimal contactor design varies depending on the goals of minimizing sorbent and volume requirements, and the choice and design of the contactor will depend on the relative costs of these factors. Lastly, our findings challenge the assumption that higher velocities are always preferable for direct air capture, suggesting instead that the operating velocity depends on the contactor configuration.
本研究通过对变温变压吸附（TVSA）过程进行过程建模，对用于直接空气捕获（DAC）的填充床和整体式接触器配置进行了全面比较。我们研究了各种设计参数，以优化不同接触器几何形状的性能，包括颗粒尺寸、整体式壁厚度、整体式中活性吸附剂含量以及填充床结构配置，同时考虑传统的长柱（PB）和并联配置的多个较短柱（PB）。我们的参数分析评估了五步TVSA循环不同运行条件下的特定火用消耗、吸附剂和体积需求。为了最小化吸附剂需求，吸附剂负载超过80%的PB和整体式是性能最佳的接触器设计，在低火用区域性能重叠。在此区域之外，PB在进一步降低吸附剂需求方面面临限制，并受到在不大幅增加火用需求的情况下合理运行的最大速度的约束。相比之下，由于传质阻力降低和薄壁相关的较低压降，整体式在火用增加最小的情况下降低了吸附剂需求。对特定火用帕累托前沿的体积需求分析表明，由于接触器配置中对额外空隙空间的需求，PB在该指标上竞争力较弱。研究还表明，整体式中降低体积需求的最佳吸附剂负载与最小化吸附剂使用的负载不同，最有效的负载低于100%。因此，最佳接触器设计因最小化吸附剂和体积需求的目标而异，接触器的选择和设计将取决于这些因素的相对成本。最后，我们的研究结果挑战了直接空气捕获中较高速度总是更可取的假设，相反表明运行速度取决于接触器配置。
