Understanding aerosol based emissions in a Post Combustion CO2 Capture process: Parameter testing and mechanisms

Abstract

Solvent emissions from a Post Combustion CO2 Capture (PCCC) process can lead to environmental hazards and higher operating cost. Aerosol based emissions in the order of grams per Nm3 have been reported from PCCC plants. These emissions are attributed to the presence of particles such as sulphuric acid aerosol droplets in the flue gas. Recently, we confirmed the relation between particle number concentration in the inlet flue gas and aerosol based emissions of monoethanolamine (MEA) as the solvent. The operating parameters and especially the presence of CO2 were found to influence the extent of aerosol based emissions. In this study, the following parametric experimental tests were performed in a mini CO2 capture plant: changing the lean solvent temperature, the pH of the lean solvent, and the CO2 concentration in the flue gas. Moreover, other commonly used CO2 capture solvents, a mixture of 2-amino-2-methyl-propanol (AMP) with piperazine (Pz), and AMP with potassium taurate (KTau), were evaluated for their potential for aerosol formation. Increasing the temperature of the lean solvent resulted in a lowering of the amine emissions. Aerosol based emissions were observed only at a relatively high lean pH. As the CO2 content of the flue gas was reduced from 12.7 to 0.7vol.%, a maximum in the emissions was observed at 6vol.% of CO2. Aerosol based emissions for both AMP (1500–3000mg/Nm3) and Pz (200–400mg/Nm3) were measured, while no aerosol based emissions were observed for AMP-Ktau as a solvent even in the presence of sulphuric acid aerosols in the flue gas. The ratio of AMP:Pz emissions was found to be much lower in the presence of aerosols (5–12) as compared to only volatile emission (∼26). This indicated that Pz has a preference to be in the aerosol phase over AMP. Three aspects were found to be important for aerosol based emissions in a CO2 capture absorber: (i) the particle number concentration, (ii) the supersaturation, and (iii) the reactivity of the amine. These observations add to the existing understanding of aerosol formation and growth by heterogeneous nucleation in counter-current gas liquid absorption processes, by considering the reactivity of the components.