Results from Process Modeling of the Mixed-salt Technology for CO2 Capture from Post-combustion-related Applications

Mixed-salt technology, a solvent-based technology for removing CO2 from flue gas streams offers a significant advantage over conventional amine-based CO2 removal technologies (e.g., Fluor Econamine FG PlusSM technology). SRI International (SRI) is currently investigating the application of mixed-salt technology for pulverized coal combustion (PCC) power plant retrofit applications for removing >90% CO2 at a cost not to exceed $40/tonne of CO2 captured. The research was performed at a large bench-scale level with funding from the United States Department of Energy (DOE), National Energy Technology Laboratory (NETL). Very recently, a successful demonstration of mixed-salt technology at 0.25 tonne/day system was conducted in the USA, and the data obtained from the tests was used to develop a rate-based model to determine the mass and energy balance for a carbon dioxide recovery (CDR) removing 90% CO2 from a 550-MW supercritical power plant. In this paper, we present the process modeling data including the preliminary techno-economic evaluation (TEA) of mixed-salt technology. CO2 capture and CO2 pipeline purity specifications were met in all the process configurations investigated in this study. SRI's mixed-salt process can strip CO2 at high pressure as the stripper for rich-solvent regeneration is operated at higher pressure than the Fluor Econamine FG PlusSM process. Thus, the electrical power required for compressing CO2 to delivery pressures (> 130 atm) is greatly reduced in the mixed-salt process compared to other solvent-based technologies operating with lower-pressure regenerations. Ammonia-based technologies require absorber solvent cooling and treated gas washing to reduce ammonia emissions, and the raw water consumption of the process combines the water being used in the two water-wash sections. The Fluor Econamine FG PlusSM technology requires a large water recycle in the CDR unit for cooling purposes (1,173,350-1,286,900 lpm or 310,000-340,000 gpm), which greatly exceeds the PC plant cooling water requirement (643,450-757,000 lpm or 170,000-200,000 gpm). SRI's mixed-salt process requires a relatively smaller recycle for cooling purposes, and the overall cooling water recycled was 71% less in the mixed-salt process compared to the baseline case. As such, the auxiliary power required for mixed-salt process CDR unit was 60% less than the baseline case. The heat duty for the mixed-salt process was calculated to be 2.0 MJ/Kg of CO2 recovered (in the stripper reboiler). This accounts for a 44% decrease in the heat duty requirement in the mixed-salt process compared to the baseline case. Published by Elsevier Ltd.