Gas phase amine depletaion created by aerosol formation and growth

Abstract

Aerosols are systems of droplets or wet particles suspended in gases. In post combustion CO2 absorption systems aerosols can be formed by spontaneous phase transitions in supersaturated gas phases or by droplets or particles entering the absorber with the gas to be treated. Micron and sub-micron mist droplets and fog formed in these processes cannot be removed by conventional demisting devices and because amine may be absorbed in the droplets this may increase dramatically the amine emissions from absorption columns as reported previously (Khakharia et al., 2015; Schaber et al., 2002). Thus, it is important to understand the mechanisms governing droplet growth and amine uptake through absorber as well as the effect large numbers of aerosol droplets can have on the bulk gas phase composition. A model developed and implemented in Matlab, predicts how the gas phase composition and temperature change along the absorber taking into account mass and heat transfer to and from both the bulk liquid and the droplet phase. The objective of this work, compared to earlier work, Majeed et al. (2017), is to study the possible effect of gas phase component depletion on the droplet growth and droplet internal variable profiles and how this varies with initial droplet size and composition, droplet number concentration and amine volatility. For MEA, as a relatively volatile solvent it is seen that gas phase depletion already takes place at number concentrations above 105 droplets/cm3 with an initial droplet radius of 1.5 μ and 5 M MEA initial concentration. For initial droplet radius 0.15 μ and 0.0001 M MEA initial concentration, which may be a more realistic case, hardly any depletion effect is seen up to 107 droplets/cm3. With change in amine volatility it is seen that the gas phase depletion effect is significantly stronger in the case of low volatility than for MEA at high droplet number concentrations. It is found that gas phase amine depletion has a strong effect on droplet growth.