Modeling Amine Aerosol Growth at Realistic Pilot Plant Conditions

Abstract

Amine aerosol emissions in carbon capture by amine scrubbing result in solvent loss and environmental impact. Management of the amine aerosol will require understanding the aerosol growth mechanism and quantitative modeling of aerosol growth in the absorber and water wash. An aerosol model was developed by the authors in a separate paper to quantify the aerosol growth inside the absorber and the water wash, and was validated at bench-scale absorber conditions. This work simulates amine aerosol growth at the conditions of the National Carbon Capture Center (NCCC), and will provide guidance for test plans for the April 2017 NCCC pilot plant campaign. The rate-based absorber was modeled using Independence in Aspen Plus® RateSepTM with rigorous thermodynamics and kinetics. Aerosol growth was modeled using gPROMS® ModelBuilder. The solvent used was 5 molal (m) piperazine (PZ). Multiple process configurations were evaluated, including intercoolers, dry bed, and two-stage water wash. At NCCC conditions, with particle number concentration of 107 particle/cm3, aerosol can grow from 0.1μm to 5μm in the absorber and up to 12μm in the water wash. Absorber and water wash operating conditions will have a significant effect on aerosol growth. Amine aerosol growth inside the absorber is driven by amine-limited diffusion, and aerosol is practically at equilibrium with bulk gas CO2, water, and temperature. Higher temperature and higher CO2 driving force result in higher PZ driving force, resulting in faster aerosol growth. In a dry bed, aerosol rapidly approach equilibrium with the bulk gas. In the water wash, aerosol tends to approach equilibrium with bulk gas water activity, and grows rapidly by picking up water. Additional packing results in longer residence time, which allows further aerosol growth. With excessive absorber packing, aerosol growth is inhibited by the mass transfer pinch.