Development and Evaluation of a Novel Integrated Vacuum Carbonate Absorption Process

Abstract

This project was aimed at obtaining process engineering and scale-up data at a laboratory scale to investigate the technical and economic feasibility of a patented post-combustion carbon dioxide (CO{sub 2}) capture process?the Integrated Vacuum Carbonate Absorption Process (IVCAP). Unique features of the IVCAP include its ability to be fully-integrated with the power plant?s steam cycle and potential for combined sulfur dioxide (SO{sub 2}) removal and CO{sub 2} capture. Theoretical and experimental studies of this project were aimed at answering three major technical questions: 1) What additives can effectively reduce the water vapor saturation pressure and energy requirement for water vaporization in the vacuum stripper of the IVCAP? 2) What catalysts can promote CO{sub 2} absorption into the potassium carbonate (PC) solution to achieve an overall absorption rate comparable to monoethanolamine (MEA) and are the catalysts stable at the IVCAP conditions and in the flue gas environment? 3) Are any process modifications needed to combine SO{sub 2} and CO{sub 2} removal in the IVCAP? Lab-scale experiments and thermodynamic and process simulation studies performed to obtain detailed information pertinent to the above three technical questions produced the following results: 1) Two additives were identified that lower the saturation pressure of water vapor over the PC solution by about 20%. 2) The carbonic anhydrase (CA) enzyme was identified as the most effective catalyst for promoting CO{sub 2} absorption. The absorption rate into the CO{sub 2}-lean PC solution promoted with 300 mg/L CA was several times slower than the corresponding 5 M MEA solution, but absorption into the CO{sub 2}-rich PC solution was comparable to the CO{sub 2}-rich MEA solution. The tested CA enzymes demonstrated excellent resistance to major flue gas impurities. A technical-grade CA enzyme was stable at 40{degrees}C (104{degrees}F) over a six-month test period, while its half-life was about two months at 50{degrees}C (122{degrees}F). Enzyme immobilization improved the CA enzyme?s thermal stability by up to three times compared to its free counterpart. 3) Two process modifications were proposed to improve the technical performance of the IVCAP for combined SO{sub 2} removal and CO{sub 2} capture. The results from a techno-economic study of a 528 MWe (gross) pulverized coal-fired, subcritical steam power plant revealed that the cost of CO{sub 2} avoidance with the IVCAP was about 30% lower than conventional MEA-based processes. The levelized cost of electricity (LCOE) of the IVCAP ranged from $40 to 46/MWh, an increase of 60 to 70% compared to a reference power plant without CO{sub 2} capture. The overall conclusion of this study is that the IVCAP is a technically feasible and economically more attractive process than available MEA-based processes. A scale-up study using the slipstream of an actual coal-derived flue gas and development of a more stable CA enzyme are recommended for future studies.