(112a) Emissions Control Technologies for RTI’s Non-Aqueous Solvent for Carbon Capture

Advanced water-lean solvents (WLS) for post-combustion CO₂ capture have been gaining interest due to their ability to reduce the parasitic penalty from energy needed for solvent regeneration. RTI International, with funding from the US Department of Energy, has been involved in development of its non-aqueous solvent (NAS), eCO₂Sol^TM. The solvent has demonstrated specific reboiler duties as low as 2.3 GJ/t-CO₂ at pilot plant scale CO₂ capture system at Tiller, Norway. Commercial implementation of these novel CO₂ capture technologies hinges on successful control of amine emissions. Vapor phase emissions can be controlled through use of water wash that scrub the amine components out of the treated gas as it exits the absorber column. While significant research work has been done to characterize and control aerosol-based emissions from aqueous solvents, similar information is not available for emissions from use of these novel water-lean solvents.

RTI has been conducting studies from fundamental and operational aspects to reduce the overall amine emissions from the WLS systems, specifically RTI’s non-aqueous solvent eCO₂Sol^TM. The work has been carried out at 4-6 kW equivalent using the RTI’s bench-scale gas absorption system (BsGAS). It consists of a CO₂ absorber column with intercoolers and water wash section, and a solvent regenerator column with a thermosiphon reboiler and inter-stage heaters. RTI’s BsGAS was modified to add the aerosol generation system and monitoring equipment to determine the aerosol characteristics during the eCO₂Sol CO₂ capture process. The system is now capable of producing aerosols with the peak diameter and concentration of 50 mm and 1.2 x10⁷ cm^-3, similar to those observed in the actual coal-fired power plant flue gas at the inlet of the CO₂ capture system.

RTI has conducted over 1,300 hours of parametric testing to evaluate the impact of the aerosols and operating conditions during the CO₂ capture with NAS on the overall amine emissions in the treated flue gas. A simulated flue gas, with 15% CO₂, 2.3-4.2% H₂O and balance air, was used in the study. SO₃ particulates were generated by reacting SO₂ with O₂ in air over a silica supported vanadium pentoxide (V₂O₅/SiO₂) catalyst at 450°C. The generated SO₃ particulates were injected into the simulated flue gas fed to the absorber. The SO₃ particulates mimic the presence of SO_X, fly ash and other particulates in the flue gas exiting the direct contact cooler and provides nucleation sites for growth of aerosols in the CO₂ capture process. A Scanning Mobility Particle Sizer and an Aerodynamic Particle Sizer were used to monitor the aerosol particles size and number distribution at various locations in the CO₂ capture system. The amine emissions at the absorber outlet and water wash outlet were monitored using a MKS MultiGasâ„¢ FTIR spectroscopy gas analyzer. Initial testing found that the CO₂ capture rate and water wash temperature were the two most dominant process factors on vapor emissions. Further testing fixed those two process variables to evaluate other variables including liquid/gas ratio (L/G, mass basis), intercooling profile (extent of intercooling at the top and bottom intercooler), temperature of the lean solvent to the absorber, the water wash L/G, temperature of the water wash return stream, and the inlet saturation temperature of the flue gas (which dictates both the extent of water in the flue gas, and the water wash temperature required to maintain water balance in the system). The CO₂ capture rate was maintained close to 90% capture rate.

Results from parametric testing suggested that the presence of the aerosols in the flue gas could increase the overall emissions by 10X compared to the baseline emissions from NAS’s vapor pressure. The temperature difference between the temperature bulge seen in the absorber column and the water wash temperature impacts the particle growth, with the aerosol emissions increasing with the increase in the temperature difference. Most of the aerosols did not grow substantially in the system, and the particle concentrations remained nearly constant between the absorber inlet and wash outlet. Only a small portion of the particles were found to grow significantly. A second water-lean solvent was also tested and elicited insights into how to minimize vapor and aerosol emissions through solvent modification.

Results from parametric testing have established the emission baseline from water-lean solvent processes. The BsGAS has been modified to add in vapor and aerosol control technologies such as a water wash acidifier, an amine sorbent removal and regeneration system, high efficiency demisters, and a lime-coated filter which mimics a filter baghouse. Testing of the control technologies has shown their ability to significantly reduce the emissions from the water-lean solvents. Results from emission studies post-BsGAS modifications will be presented to show the effectiveness of the emission control strategies to minimize emissions from the CO₂ capture process using water-lean solvents.