(649d) Isotherm Modeling and Techno-Economic Optimization of Contactor Technologies for a New Tetraamine-Appended MOF for CO2 Capture from Ngcc Plants

Natural gas, currently a major source of electricity in the United States (Mondino et al., 2019), is likely to continue to play a significant role in the world’s energy mix. Therefore, new technologies and materials to reduce CO2 emissions will be instrumental in meeting goals for deep decarbonization. Flue gases from natural gas-fired power plants present a significant challenge due to the low CO2 volumetric/molar composition (~4% CO2). To address this challenge, the U.S. Department of Energy’s Carbon Capture Simulation for the Industry Impact (CCSI2) initiative has been developing models and tools that provide insight into cost effective technologies for Carbon Capture Utilization and Storage (CCUS). This work presents development of two rigorous first principles models for gas/solid contactors and techno-economic optimization performed using these models.

Recently, a family of tetraamine-functionalized metal-organic frameworks (MOF) has been reported as promising sorbent materials for capturing CO2 from flue gas conditions relevant to NGCC applications (Kim et al., 2020). The main advantages of these materials are their two-step cooperative CO2 adsorption, which gives rise to unusual two step-shaped CO2 adsorption profiles and their high thermal stability. Isotherm models of the tetraamine-appended MOF, N,N′-bis(3-aminopropyl)-1,4-diaminobutane (3-4-3)-appended Mg2(dobpdc) (Kim et al., 2020) is developed. Due to the unusual isotherm shapes of the experimental CO2 adsorption data for tetraamine-appended Mg2(dobpdc) and the strong nonlinearity of CO2 loading with respect to temperature and pressure, it is challenging to develop accurate isotherm models for these sorbents. In addition to slightly modifying one of the existing isotherm mdoels in the literature (Ga et al., 2021), we also extended the isotherm models developed by some of the co-authors of this work for single-step isotherms (Hughes et al., 2021). By taking into account the effect of physisorption and chemisorption, the model developed based on several logistic functions accurately capture the nonlinearity of the isotherm of these MOFs. In addition, a kinetic model for the MOF was developed and its parameters were optimally estimated using experimental fixed bed breakthrough data.

To make this new class of MOFs economically feasible, the type of contactor used in the capture process will play a critical role. It has also been previously shown that thermal management especially for efficiently rejecting the heat associated with the steps is crucial to realizing the full potential of these sorbents. Therefore, a contactor which can efficiently remove the heat generated during adsorption is needed. Specifically, models of two different contactors, an axial-flow fixed bed and moving bed contactor, were developed as part of this work. These models are dynamic, pressure-driven, and consist of mass, energy, and momentum conservation equations. These models are then used to simulate CO2 capture processes from the flue gas generated from a ~600 gross MW NGCC power plant. A cost model was developed which considers the capital cost of the reactors and the significant operating costs such as steam and electricity. Using NETL’s Framework for the Optimization and Quantification of Uncertainty of Uncertainty and Surrogates tool (FOQUS) (Miller et al., 2016), which has the capability of linking models built using numerous modelling platforms with derivative-free optimization solvers, a techno-economic optimization of the carbon capture processes was performed which minimizes the cost of capture. This work demonstrates the utilization of the rigorous dynamic models for process optimization using the FOQUS tool. It was observed that even for the same MOF, the contactor technology and their operating conditions can significantly affect the economics of CO2 capture.

Disclaimer:
This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Team KeyLogic’s contributions to this work were funded by the National Energy Technology Laboratory under the Mission Execution and Strategic Analysis contract (DE-FE0025912) for support services.

References:

Ga, S.; Lee, S.; Park, G.; Kim, J.; Realff, M.; Lee, J. H. 2021. New model for S-shaped isotherm data and its application to process modeling using IAST. Chemical Engineering Journal, 420, pp.127580
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