New Adsorption Cycles for Carbon Dioxide Capture and Concentration
The objective of this three-year project was to study new pressure swing adsorption (PSA) cycles for CO{sub 2} capture and concentration at high temperature. The heavy reflux (HR) PSA concept and the use of a hydrotalcite like (HTlc) adsorbent that captures CO{sub 2} reversibly at high temperatures simply by changing the pressure were two key features of these new PSA cycles. Through the completion or initiation of nine tasks, a bench-scale experimental and theoretical program has been carried out to complement and extend the process simulation study that was carried out during Phase I (DE-FG26-03NT41799). This final report covers the entire project from August 1, 2005 to July 31, 2008. This program included the study of PSA cycles for CO{sub 2} capture by both rigorous numerical simulation and equilibrium theory analysis. The insight gained from these studies was invaluable toward the applicability of PSA for CO{sub 2} capture, whether done at ambient or high temperature. The rigorous numerical simulation studies showed that it is indeed possible to capture and concentrate CO{sub 2} by PSA. Over a wide range of conditions it was possible to achieve greater than 90% CO{sub 2} purity and/or greater than 90% CO{sub 2} recovery, depending on the particular heavy reflux (HR) PSA cycle under consideration. Three HR PSA cycles were identified as viable candidates for further study experimentally. The equilibrium theory analysis, which represents the upper thermodynamic limit of the performance of PSA process, further validated the use of certain HR PSA cycles for CO{sub 2} capture and concentration. A new graphical approach for complex PSA cycle scheduling was also developed during the course of this program. This new methodology involves a priori specifying the cycle steps, their sequence, and the number of beds, and then following a systematic procedure that requires filling in a 2-D grid based on a few simple rules, some heuristics and some experience. It has been tested successfully against several cycle schedules taken from the literature, including a 2-bed 4-step Skarstrom cycle, a 4-bed 9-step process with 2 equalization steps, a 9-bed 11-step process with 3 equalization steps, and a 6-bed 13-step process with 4 equalization steps and 4 idle steps. With respect to CO{sub 2} capture and concentration by PSA, this new approach is now providing a very straightforward way to determine all the viable 3-bed, 4-bed, 5-bed, n-bed, etc. HR PSA cycle schedules to explore using both simulation and experimentation. This program also touted the use of K-promoted HTlc as a high temperature, reversible adsorbent for CO{sub 2} capture by PSA. This program not only showed how to use this material in HR PSA cycles, but it also proposed a new CO{sub 2} interaction mechanism in conjunction with a non-equilibrium kinetic model that adequately describes the uptake and release of CO{sub 2} in this material, and some preliminary fixed bed adsorption breakthrough and desorption elution experiments were carried out to demonstrate complete reversibility on a larger scale. This information was essentially missing from the literature and deemed invaluable toward promoting the use of K-promoted HTlc as a high temperature, reversible adsorbent for CO{sub 2} capture by PSA. Overall, the objectives of this project were met. It showed the feasibility of using K-promoted hydrotalcite (HTlc) as a high temperature, reversible adsorbent for CO{sub 2} capture by PSA. It discovered some novel HR PSA cycles that might be useful for this purpose. Finally, it revealed a mechanistic understanding of the interaction of CO{sub 2} with K-promoted HTlc.
- Research Organization:
- Univ. of South Carolina, Columbia, SC (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FG26-05NT42545
- OSTI ID:
- 958277
- Country of Publication:
- United States
- Language:
- English
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