(245g) Optimal Design and Operation of Solvent-Based Capture Systems with Novel Configurations for High CO2 Capture

Achieving ultra-high CO₂ capture that exceeds 99% at minimal cost is a crucial challenge for post-combustion carbon capture. CO₂ capture using amine solvents is one of the most widely used technologies due to its high reactivity with CO₂. The high energy consumption due to the solvent regeneration process remains a significant drawback for amine-based solvents in carbon capture. Most of the research done in this field focuses on capture rates of up to 90%, as this has been the benchmark previously. However, achieving capture rates up to 99.9% is gaining attention and remains a technological challenge. Most of the existing publications on solvent systems for high capture have mainly focused on simulations followed by economic analysis or optimization of a surrogate objective such as the stripper reboiler duty¹. This limitation prevents the simultaneous optimization of both energy consumption and cost, leading to suboptimal process designs. In this work, a techno-economic optimization framework is used to optimize the cost of CO₂ capture at very high capture rates of up to 99.9%. Novel configurations are also proposed and optimized.

An equation-oriented modeling framework is developed for the techno-economic analysis of the capture process². Other than detailed thermodynamic, chemistry, and kinetic models for the capture process, the framework also includes the cost model. The framework enables simultaneous optimization of process design variables such as the absorber and desorber dimensions and operational variables such as solvent circulation flowrate, lean solvent loading, etc.

One of the optimization strategies investigated is the use of intercoolers in the absorption section³. A portion or the entire solvent from a packing section is extracted, sent through the intercooler and returned to the tower. Higher heat removal in the intercoolers can lower the tower temperature that adversely affects the reaction and mass transfer kinetics, but favors thermodynamics. In addition, due to the placement of the intercoolers, the temperature bulge may shift to a different location for some operational regime making the impact of the intercoolers negligible. Therefore, the intercooler flowrate and return temperature profiles are optimized. To further minimize the costs, a novel split-flow configuration is proposed⁴. In this configuration, semi-lean solvent from the stripper column is extracted from one or more locations and injected into one or more locations in the absorber column with novel configuration for heat exchange between the lean/rich solvents. Optimal decisions for the proposed configuration include the locations and flowrate of extraction points, locations and flowrate of injection points, and heat exchanger configuration and design. This leads to a mixed integer nonlinear programming (MINLP) problem that is ill-conditioned due to potential tower flooding/weeping and temperature cross in heat recovery exchangers. The model is reformulated, and an initialization algorithm is developed for improved convergence of the optimization problem. Our results show that the split flow and intercooler modifications can considerably lower energy and economic penalty at high capture rate compared to the conventional configuration. Sensitivity studies are undertaken for various inlet CO₂ loadings and variable capture rates.

Acknowledgement

The authors graciously acknowledge funding from the U.S. Department of Energy, Office of Fossil Energy and Carbon Management, through the Carbon Capture Program.

Disclaimer

This project was funded by the Department of Energy, National Energy Technology Laboratory an agency of the United States Government, in part, through a support contract. Neither the United States Government nor any agency thereof, nor any of its employees, nor the support contractor, nor any of their employees, makes any warranty, expressor 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, or any of their contractors.

References

(1) Du, Y.; Gao, T.; Rochelle, G. T.; Bhown, A. S. Zero- and Negative-Emissions Fossil-Fired Power Plants Using CO2 Capture by Conventional Aqueous Amines. Int. J. Greenh. Gas Control 2021, 111, 103473. https://doi.org/10.1016/j.ijggc.2021.103473.

(2) Akula, P.; Eslick, J.; Bhattacharyya, D.; Miller, D. C. Model Development, Validation, and Optimization of an MEA-Based Post-Combustion CO ₂ Capture Process under Part-Load and Variable Capture Operations. Ind. Eng. Chem. Res. 2021, 60 (14), 5176–5193. https://doi.org/10.1021/acs.iecr.0c05035.

(3) Plaza, J. M.; Wagener, D. V.; Rochelle, G. T. Modeling CO2 Capture with Aqueous Monoethanolamine. Energy Procedia 2009, 1 (1), 1171–1178. https://doi.org/10.1016/j.egypro.2009.01.154.

(4) Bhattacharyya, D.; Miller, D. C. Post-Combustion CO 2 Capture Technologies — a Review of Processes for Solvent-Based and Sorbent-Based CO 2 Capture. Curr. Opin. Chem. Eng. 2017, 17, 78–92. https://doi.org/10.1016/j.coche.2017.06.005.