(634e) Optimization of a High Temperature PSA Process for Pre-Combustion CO2 Capture

In a U.S. Department of Energy (DOE) sponsored project, TDA Research, Inc. is developing a novel sorbent that removes CO₂ well above the dew point of synthesis gas stream generated by commercial gasifiers using a pressure swing adsorption (PSA) process. The relatively strong affinity of the sorbent to CO₂ enables effective operation at temperatures up to 300°C. However, because the sorbent and the CO₂ do not form a true covalent bond, the energy needed to regenerate TDAâ??s sorbent (5.4 kcal per mol of CO₂) is much lower than that observed for either chemical absorbents (e.g., 29.9 kcal/mol CO₂ for sodium carbonate) or amine-based solvents (e.g., 14.2 kcal/mol CO₂ for monoethanolamine). TDAâ??s sorbent can be regenerated isothermally and CO₂ could be recovered at pressures as high as 150 psia. Thus, the energy needed to regenerate the sorbent and compress the CO₂ for sequestration is significantly lower than that for any technology reported to date. In this presentation we will summarize the results of collaboration between TDA Research and the University of Alberta to develop PSA models for TDAâ??s precombustion CO_2 capture sorbent.

High-pressure dynamic column breakthrough experiments have been performed using a bench scale fixed bed reactor system over a wide range of temperatures. The adsorption isotherms and kinetic parameters for CO₂ and H₂ were measured by fitting the experimental breakthrough responses with those simulated using a detailed adsorption model. Based on these parameters, a variety of PSA cycles, that include pressure equalization, blow down and steam purge steps were designed. Using a detailed model coupled with a genetic algorithm toolbox, these PSA cycles were optimized for maximizing CO₂ purity and recovery. Using this approach, we were able to show that many cycle configurations do achieve high CO₂ purity (>95%) and recovery (>90%) that are recommended by the DOE for sequestration. For those cycles that satisfied the high purities and recoveries, the problem of minimizing parasitic energy was studied. Factors such as energy consumption for CO₂ compression, loss of H₂ into the desorption product, steam utilization were all combined into a single objective function. The cycle parameters such as various pressure levels, step time and feed velocities were used as decision variable while the CO₂ purity and recovery were used as a constraint. The results of this optimization study will be discussed at the meeting.