(47e) Bench-Scale Evaluation of a Post-Combustion Carbon Dioxide Capture Process Enabled By a Combination of Low-Energy Solvents, Enzymes and Vacuum Regeneration

Authors: 
Salmon, S., Novozymes North America, Inc.
Liu, K., Center for Applied Energy Research, University of Kentucky
Qi, G., University of Kentucky
Frimpong, R. A., University of Kentucky
Liu, K., University of Kentucky
Freeman, C. J., Pacific Northwest National Laboratory
Bearden, M., Pacific Northwest National Laboratory

The objective of this project is to demonstrate a post-combustion carbon dioxide capture process with the goal of improved efficiency, economics and sustainability compared with existing CO2 scrubber technologies. Tests are being conducted in an integrated bench-scale system that pairs the bio-renewable enzyme catalyst carbonic anhydrase with a low-enthalpy aqueous potassium carbonate solvent, and uses low temperature vacuum regeneration in a recirculating solvent-based process. Rationale for use of carbonic anhydrase is to promote inter-conversion between dissolved CO2 and bicarbonate ion, which is the rate-limiting step for absorption and desorption in solutions that rely on ionic complexation of CO2. Rationale for low temperature vacuum regeneration is that preliminary simulations have shown the use of very low pressure steam as thermal energy input during regeneration could lead to 43% lower parasitic power from a coal-fired power plant compared to MEA reference technology, including accounting for the compression penalty that comes with application of vacuum, which is required to increase the overall driving force for solvent regeneration at moderate temperatures (70-80°C bulk liquid temperature). Testing on the bench-scale unit is being carried out to compare experimental findings to simulated values, and update the simulation accordingly to enable predictions for a full-scale system. The bench-scale absorber (ID=7.6 cm; Raschig ring packed height = 2 m) is sized to treat 30 SLPM of simulated flue gas containing ~15% CO2, and is well-instrumented to monitor system performance. System shakedown tests demonstrated > 90% CO2 capture upon enzyme addition, corresponding to >75% improvement in % CO2 capture and 36% reduction in regeneration energy demand relative to the no enzyme case. The lowest energy demand (a further 30% reduction) achieved during unit shakedown testing occurred during an initial test of the simulated very low pressure steam (85°C) condition, albeit with 70% CO2 capture, versus < 25% capture in absence of enzyme. Parametric testing is currently in progress to determine conditions for conducting a 500 hour test with 90% CO2 capture, as well as provide data for kinetic-based ASPEN simulation. Enzyme replenishment is controlled by adding dissolved enzyme to the working solvent, meaning the enzyme travels along with the solvent as it recirculates through the absorber and stripper, and enzyme longevity under CO2 scrubbing conditions is being monitored. A description of the bench-scale unit, operational considerations, and results of the evaluations will be presented. This project is supported by funding from the U.S. Department of Energy’s National Energy Technology Laboratory.
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