(634d) Mass Transfer Intensification Using 3D Printing Novel Dynamic Polarity Packing for Post Combustion Carbon Capture

Global warming has drawn world-wide attention as it impacts global sustainable development. Since fossil fuel are still a major part of energy production in the foreseeable future, CO₂ capture plays a significant role in the mission of reduced CO₂ emissions, or transition to a negative CO₂ emission future ¹. The post combustion carbon capture using amine solutions as the CO₂ absorbent is the most mature and scalable technology to target CO₂ in dilute, low pressure flue gas. Despite this technology having been studied for decades, there still has some limitations that remain unsolved ². A major concern is the high cost in terms of energy and capital investment ³. The energy cost is mostly attributed to the regeneration in the stripper, which strongly depends on the absorbent properties and how the stripper is operated. The capital investment is also significant because of the column size requirement to handle large volume of flue gas.

Herein, we describe the use of 3D printing to develop novel structured packings for the absorber in a CO₂ capture system. 3D printing technique allows for fast and low cost printing of prototypes for objects and patterns, which enjoys various benefits like freedom of design, waste minimization and ability to manufacture complex structures ⁴. Our motivation is to develop new concept of packings with adjustable surface properties to further intensify mass transfer in the absorber column. By doing this, the absorber size can be shrunk to reduce the capital cost or/and a higher CO₂ loading can be achieved in the rich solvent which benefits absorbent regeneration with higher CO₂/H₂O ratio and less energy consumption.

Novel packings, what we call dynamic polarity packings, are shown in this work with similar geometric structure as conventional Mellapak 250Y steel packing (3-inch diameter). The internal structure of dynamic polarity packings has a unique surface that alternatively combines different segments with different material surfaces in order to manipulate the absorbent flow on the packing surface. Due to the inherent properties of these materials, one segment is more hydrophobic and the other one is more hydrophilic. It is known that the aqueous amine CO₂ absorbents will have better wettability (a smaller contact angle) on the hydrophilic surface while it tends to gather and resist spreading on the hydrophobic surface (a larger contact angle). When the absorbent flows down on the packing surfaces, the regular alternation of surface property generates local turbulence within the solvent which will consequently refresh liquid film surface and improve the gas liquid mixing effect. In addition, the proposed dynamic polarity packings are designed with a surrounding hydrophobic shell to reduce the potential wall effect and channeling issues to maintain a better liquid loading on the packing surface.

Based on these considerations, several versions of dynamic polarity packings were printed with dissimilar pattern designs. The printed packings (denoted as DP-1, DP-2 and DP-3) are shown in Figure 1a, along with Mellapak 250Y steel packing. The internal packing surface of dynamic polarity packing has unique design to study the influence of printing pattern on CO₂ absorption. DP-1 and DP-3 packings have 5% of hydrophobic high impact polystyrene (HIPS) surface embedded in hydrophilic nylon-based packing surface, where the HIPS surface pattern differs from each other. The HIPS surface pattern is staggered rectangles for DP-1 packing and “V” shape for DP-3 packing. DP-2 packings have alternative segments with sole HIPS or nylon materials and the height of each segment is 0.5 inch. All the dynamic polarity packings are surrounded by the more hydrophobic HIPS shell. Primary amine 1-amino-2-propanol (1A2P) solution is used as the CO₂ absorbent for the test. To quantify the wettability on different materials, the contact angle of 1A2P solution was measured by sessile drop method as shown in Figure 1b. Depending on the CO₂ loading of the absorbent, there will be around 13 to 18Ëš difference in contact angle serving as driving force to manipulate absorbent flow. The packing performance is tested in an integrated bench scale CO₂ capture unit which mainly includes an absorber column and a stripper column both with ~2 meters of packing height. In these preliminary tests, only the steel packing at the top of the absorber was replaced with dynamic polarity packings to screen the best design for gas absorption (~18” replaced out of 60” total packing height). First a parametric study was carried out to determine the optimal operating conditions in the current unit with absorber filled with the steel packing to be used as a baseline date set. Next, the different 3D printed packing was placed in the absorber and the parametric conditions were repeated. Preliminary testing results of performance including CO₂ absorption efficiency and the energy demand are summarized in Figure 1c. The distribution of data points depends on the operating conditions for the capture system. In general, replacing the steel packings with the dynamic polarity packings shifts the CO₂ capture efficiency higher and leads to lower energy penalty. Comparing with Mellapak 250Y steel packing under similar operating conditions, there is relative 7.8%, 7.7% and 9.1% improvement in CO₂ absorption efficiency and consequential 7.0, 7.9% and 8.4% energy penalty reduction for DP-1, DP-2 and DP-3 packings respectively. Considering only a portion of Mellapak 250Y steel packing is replaced by 3D printing packings during the preliminary test, the improvement will be more prominent after the absorber column is filled with new packings. The testing results imply that the application of these superior packings can potentially decrease the required absorber column size to cut down capital expense. Under some circumstances, it also enables the system to be operated under lower absorbent circulation rate while acquiring richer CO₂ loading to reduce operating expense.

Acknowledgements

Financial support from US Department of Energy (DOE) National Energy Technology Laboratory (NETL) is gratefully acknowledged, DE-FE0031661.

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Figure 1. Steel and dynamic polarity structured packings (a), contact angle of 1A2P solution on nylon and HIPS surface (b) and system CO₂ capture performance evaluation (c, bubble width indicates heat duty)