(145e) Optimization of Design and Operating Conditions of Intensified Towers with Internal, Printed Heat Exchangers for CO2 Capture

One of the main bottlenecks for commercialization of CO₂ capture technologies is the high cost. When solvents are used in a tower for CO₂ capture, key contributions to the capital and operating costs are due to the towers and the reboiler duty, respectively. Circulation of large amount of solvent that is often needed to achieve the desired extent of CO₂ capture leads to larger towers as well as larger balance of plant equipment items and higher reboiler duties. Obviously, loading and unloading the solvent to their thermodynamic maximum and minimum, respectively can minimize the solvent circulation rate. For achieving the thermodynamic minimum, one of the important variables is the operating temperature profile in the entire tower. Thus, it will be desired to remove the heat of absorption in the absorber and add the heat of desorption in the desorber to achieve the desired optimal temperature profile. Current practice of removing heat from the absorber is to use 1 or more intercoolers (generally 2-3) that are placed externally where the solvent is extracted from and returned to pre-determined distinct locations¹. This approach does not facilitate achieving the desired temperature profile through the tower. One potential approach to address this issue is through the use of an intensified packing with internal heat exchangers^2,3.

For designing intensified packings with heat exchangers, several considerations need to be made. Simply filling the column with intensified packings of arbitrary size is not desired since for a given volume of the tower, mass transfer area will be sacrificed when heat transfer area is provided thus leading to diminishing return. For optimal design of the intensified packing, several key questions arise: where along the column should such packings be placed? What should be the optimal dimensions of the exchangers? What should be the flow configuration for the utility -co-current or counter-current or mixed? At which locations should the utility enter and exit? In addition, one of the questions for the operating conditions is: what should be the optimal flowrate of the utility to each of the inlet locations for the utility?

To answer these questions, a mathematical optimization problem is solved by using a rigorous model of the towers developed by some of the authors of this abstract^4,5. The tower model includes models of liquid and vapor films and interfacial mass and heat transfer and reactions kinetics. A modified e-NRTL model is developed to capture the highly nonlinear thermodynamic properties of the electrolyte process⁵. Models for interfacial area and mass transfer coefficients and hydrodynamic models are validated with the data from the open literature. A mixed integer nonlinear programming problem is solved to yield optimal values for process and design variables. Results show interesting tradeoffs between capital and operating costs, as well as significant increase in process efficiency when utilizing the intensified packing as compared to the packings with external intercoolers.

References

1. Hanne M. Kvamsdal and Gary T. Rochelle, Industrial & Engineering Chemistry Research 2008 47 (3), 867-875
2. Moore, T., Nguyen, D., Iyer, J., Roy, P., & Stolaroff, J. (2020). Advanced absorber heat integration via heat exchange packings. Separations: Materials, Devices, and Processes.
3. Miramontes, E., Jiang, E. A., Love, L. J., Lai, C., Sun, X., & Tsouris, C. (2020). Process intensification of CO2 absorption using a 3D printed intensified packing device. AIChE Journal, 66(8). https://doi.org/10.1002/aic.16285
4. Akula, P., Eslick, J., Bhattacharyya, D., & Miller, D. C. (2021). Model Development, Validation, and Optimization of an MEA-Based Post-Combustion CO2Capture Process under Part-Load and Variable Capture Operations. Industrial and Engineering Chemistry Research, 60(14), 5176–5193. https://doi.org/10.1021/acs.iecr.0c05035
5. Akula, P, Lee, A, Eslick, J, Bhattacharyya, D, Miller, DC. A modified electrolyte non-random two-liquid model with analytical expression for excess enthalpy: Application to the MEA-H2O-CO2 system. AIChE J. 2023; 69( 1):e17935. doi:10.1002/aic.17935