Secondary Air Stripper Performance in a Post-Combustion Carbon Capture Pilot Plant Integrated with a Coal-Fired Power Plant

The notion of developing economic power generation with commercially available post-combustion carbon capture (PCCC) technology poses a great challenge to the electric utility industry.  In this sense, the U.S. Department of Energy (US-DOE) has set the goal for the cost of 90% capture to not exceed $40 per ton of CO₂¹.  According to the U.S. Energy Information Administration (EIA), coal-fired power plants emit approximately one ton of CO₂ per MWh². To meet this target, the University of Kentucky Center for Applied Energy Research (UKy-CAER) has designed, constructed, and begun testing of a 0.7 MWe PCCC facility integrated with a coal-fired unit at Kentucky Utilities Company’s E.W. Brown Generating Station. 

The UKy-CAER’s technology employs several process-intensification approaches with added advantage compared to first generation PCCC systems.  First, a liquid-desiccant-based cooling tower is integrated with the system, allowing for enhanced cooling and reduced plant parasitic load.  Second, the use of an advanced proprietary solvent allows for economic savings as compared to traditional MEA-based capture solvents.  Third, a two-stage stripping process has been incorporated to enhance the solvent regeneration process.  In this stripping arrangement, carbon rich solvent first passes through a traditional steam-heated stripping column.  The lean solvent from this primary stripper is subsequently sent to a secondary air stripper where air is used from the liquid desiccant water evaporator.  In theory, the heat is recovered from the CO₂-enriched air before it would be sent back to the plant boiler as secondary combustion air, which in turn would increase the amount of CO₂ entering the absorber (16.6%)³.  The reduction in CO₂ partial pressure of the super-lean solvent going back to the absorber provides an increased driving force for CO₂ transfer from the gas, enhancing the solvent’s efficiency in capturing CO₂.  With the gas entering the absorber at a higher volume percent (vol%) of CO₂ and the solvent at super-lean conditions, the mass transfer of CO₂ into the solvent can be further enhanced.

The performance of the secondary air stripper will be primarily discussed with regard to the amount of additional CO₂ captured compared to a single-step stripping operation.  Furthermore, the capture benefit of utilizing a two-stage stripping process with higher CO₂ concentration at the absorber inlet will also be addressed by analyzing the resulting rich carbon loading of the solvent.  The values given in the preliminary Technical and  Economic Analysis (TEA) will be used for a baseline comparison with performance results to determine if the secondary stripper exhaust air contains the TEA-estimated  3-4 vol% CO₂ and if the amine rich loading is near the TEA-estimated 0.52 mol CO₂/mol MEA³. Additionally, performance will be measured through solvent degradation and emission assessment.  Further topics to be discussed will include power plant integration feasibility, development pathway, and lessons learned from a pilot scale-up at a power plant.

References

1. “Carbon Capture Technology Program Plan”, Office of Fossil Energy – Clean Coal Research Program. U.S. Department of Energy, n.d. Web. 13 July 2015. <https://www.netl.doe.gov/File%20Library/Research/Coal/carbon%20capture/P....
2. "How Much Carbon Dioxide Is Produced per Kilowatthour When Generating Electricity with Fossil Fuels?", U.S. Energy Information Administration - EIA - Independent Statistics and Analysis. U.S. Department of Energy, n.d. Web. 08 July 2015. <http://www.eia.gov/tools/faqs/faq.cfm?id=74&t=11>.
3. Bhown, A., et.al, “Preliminary Technical and Economic Feasibility Study on the Application of a Heat Integrated Post-Combustion CO₂ Capture System with Hitachi Advanced Solvent into Existing Coal-Fired Power Plant,” December 2012.