(617d) Multi-Scale Dynamic Modeling, and Techno-Economic Optimization of a Radial Flow Fixed Bed Contactor for Post-Combustion CO2 Capture

Solid sorbent-based CO₂ capture has strong potential for reducing the cost of post combustion capture. An optimal contactor technology is critical for minimizing the cost for solid-sorbent CO₂ capture. While fluidized or moving beds can enhance heat and mass transfer, they may lead to higher capital cost, reduce the mass transfer driving force especially in fluidized beds, are more complex to operate, and requires attrition-resistant properties¹. Fixed bed contactors can address several of these shortcomings. However, traditional fixed bed contactors are of axial flow configuration that can lead to large vessel volumes and high pressure drops, especially when treating high volumes of low CO₂ concentration². Since the flue gas is available from power plants at nearly atmospheric pressure, higher pressure drop through the bed will lead to higher compression cost, which can quickly grow high due to the large amount of flue gas that needs to be treated. Radial flow fixed bed (RFFB) contactors are a promising alternative. In RFFBs, as the gas flows radially in the reactor, either towards the center or the extremity of the cylindrical vessel, they offer higher surface area for gas-solid contact and shorter path length compared to an axial flow bed of same volume thus reducing the pressure drop, and therefore the cost. While RFFB contactors have been investigated for many applications, including direct air capture^{3, 4}, oxygen generation⁵, and various pressure swing adsorption processes⁵, dynamic multi-scale modeling of RFFBs, techno-economic analysis and techno-economic optimization of these types of beds for post-combustion CO₂ capture is lacking in the existing literature.

The solid sorbent used in this work is a MOF functionalized with 2,2-dimethyl-1,3-diaminopropane (dmpn) Mg₂(dobpdc) (dobpdc^4– = 4,4′-dioxidobiphenyl-3,3′-dicarboxylate) [dmpn-Mg₂(dobpdc)]⁶ that exhibits unique step-shaped isoterm⁶. In addition to development of the isotherm model and the kinetic models for the solid, a multi-scale model that includes a particle level model coupled with a bulk-scale model is developed and validated against the lab-scale breakthrough experimental data. The model is scaled up to the commercial-scale size of RFFBs and used to simulate a temperature swing adsorption process. For efficiently removing/adding the heat of adsorption, an embedded heat exchanger is modeled. An economic model of the process is developed. For undertaking techno-economic optimization of the process, dynamic optimization is desired due to the transient characteristics of the adsorption/desorption process. Due to the cyclic operation of this bed, multiple spatial and time scales of the process, steepness of the system of equations, and large number of equations, it is challenging to perform dynamic optimization. Reactor design parameters such as the dimensions of the contactor, embedded exchanger size, flow configuration, and operating conditions including cycle time are considered as decision variables. Comparisons with fixed bed contactors are also made.

References:

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[2] Kareeri, A.A., Zughbi, H.D., and Al-Ali, H.H., Simulation of Flow Distribution in Radial Flow Reactors. Ind. Eng. Chem. Res. 2006; 45, 2862-2874

[3] Yu, Q., Brilman, W., A Radial Flow Contactor for Ambient Air CO2 Capture. Appl. Sci. 2020; 10, 1080

[4] Schellevis, M., Jacobs, T., and Brilman, W., CO2 Capture From Air in a Radial Flow Contactor: Batch or Continuous Operation?. Frontiers in Chemical Engineering. 2020; 2.

[5] Wang, H., Yang, X., Li, Z., Liu, Y., Zhang, C., Xiaojun Ma, X., and Chunwang Li, C., 3-D Modeling of Gas–Solid Two-Phase Flow in a π-Shaped Centripetal Radial Flow Adsorber. Appl. Sci. 2020, 10, 614.

[6] Forse, A.C., Milner, P.J., Lee, J., Redfearn, H.N., Oktawiec, J., Siegelman, R.L., Martell, J.D., Dinakar, B., Porter-Zasada, L.B., Gonzalez, M.I., Neaton, J.B., Long, J.R., Reimer, J.A., Elucidating CO₂ Chemisorption in Diamine-Appended Metal-Organic Frameworks. J. Am. Chem. Soc. 2018; 140(51), 18016-18031