Carbon Capture in Molten Salts A new process for CCS based on Ca-looping chemistry

1. Carbon Capture in Molten Salts A new process for CCS based on Ca-looping chemistry Espen Olsena, Viktorija Tomkutea, Asbjørn Solheimb aDep. Mathematical Sciences and Technology, UMB, N-1432 Ås, Norway bDep. Energy Conversion and Materials, SINTEF Materials and Chemistry, N-0314 Oslo, Norway Summary Experimental Results Carbon Capture in Molten Salts (CCMS) has been demonstrated on the laboratory scale. Absorption of CO2 from a simulated combustion gas is shown to exhibit extremely efficient characteristics, absorbing up to 99.97% of CO2 from a simulated flue gas in a reactor column of 10 cm length. Desorption proceeds to 100% so all CaO is regenerated in reactive state overcoming the main challenge in conventional Ca-looping. If the process characteristics are scalable to larger scale reactors exhibiting similar efficiency, selective capture and release of CO2 from a wide range of gas compostitions is possible. This opens for a large number of applications. A dedicated laboratory set up involving a high-sensitivity FTIR gas analyzer and TGA functionality is used. A simulated flue gas (0-100% CO2 in N2) is fed to a 10 cm column of molten salt containing CaO. The gas composition before and after absorption is analyzed with high accuracy Figure 5: Repeated absorption-desorption cycling (4x, 800°C/950°C) from a simulated flue gas (N2+27% CO2) in a chloride based absorbing liquid (CaCl2+5%CaO). The content of CO2 in the gas emitted is shown in the bottom panelwhile the mass of the reaction vessel (―) as well as temperature (―) is shown in the top panel. Introduction and Theory The Ca-looping principle1 relies on displacement of the equilibrium described by Eq.(1) (M denotes an alkaline-earth metal) by thermal cycling at elevated temperatures (650 - 1000°C). This minimizes fundamental losses due to low temperature waste heat. (1) Figure 2: The experimental setup, schematically depicted. The absorption-desorption processes are monitored by gravimetry (TGA) and mass balance by gas analysis (FTIR). Figure 6: The conversion efficiency of the cycling between CaO and CaCO3 during absorption (•) and desorption (•) in each of the cycles from Fig.5. The decarbonation of CaCO3 by forming CaO and CO2 is reaching 100% efficiency in all the cycles while the conversion of CaO to CaCO3 during absorption shows a rising trend with each cycle, contrary to the loss in reactivity experienced in solid state Ca-looping. Figure 1: The Gibbs free energy of reaction (1) vs. temperature and alkali-earth cation. The process is performed in FBR-reactors and is being developed on the demonstration scale2. The main obstacles for successful commercial implementation is deactivation of CaO powders by decomposition and sintering introduced by thermal cycling. Figure 3: Details of the reaction chamber. Outer sleeve of steel, inner crucible and feed tube of Ni. • The CCMS idea: By (partly) dissolving the active substances in a supersaturated molten salt, highly reactive absorbing CaO is constantly regenerated as described by Eq.(2).(M denotes an alkaline-earth metal) • The CCMS project aims at: • To develop a new and patented process for carbon capture. 3 • Establish the scientific foundation for industrialization. Time frame: 5-10 years. Figure 7: Absorption with subsequent desorption of CO2 from a simulated flue gas (N2+27% CO2) in a fluoride based liquid (NaF/CaF2/10% CaO) at 820°C. Desorption at 1150°C. The content of CO2 in the gas emitted from the reactor (―) and temperature (―). Figure 4: Schematic set up of a pilot scale reactor for continous operation. (2) Conclusions and further work The CCMS process works as predicted from fundamental thermodynamic modeling. 5 cycles has been completed with 100% conversion efficiency from CaCO3 to CaO. The present results are promising indicating the potential for CCS from a wide variety of gas compositions from different sources. Focus will be now be directed towards construction of a lab pilot reactor for continous operation References: 1 Chem. Eng. Res. Des. 89, (2011), 836-855 2 www.caoling.eu 3 Norwegian patent No. 20092083