Residence time distribution in a structured packing unit for monitoring aerosol emissions

Abstract

Solvent absorption in a structured packed column has been demonstrated as a viable option for post-combustion carbon capture. Amine emissions in the form of aerosol particles pose a major challenge that severely impacts the separation efficiency of the packed column. The aerosol particles quickly achieve the motion of the gas flow. In this context, residence time distribution (RTD) of the gaseous phase will provide insights for managing aerosol particles, thereby controlling amine loss in the packed column. Computational fluid dynamics (CFD) modeling of such columns is a multiscale problem because of a wide range of disparity in length scales. Accordingly, three-dimensional CFD simulations in the representative elementary unit of a structured packing are conducted using OpenFOAM. The RTD is analyzed in terms of residence time distribution function, mean residence time and variance. Effects of the diffusivity and flow rates on RTD are extensively studied, and the dispersion coefficient is calculated using a one-dimensional axial dispersion model. RTDs computed in a smaller domain are extrapolated to a larger domain using the convolution integral. The CFD computed and corresponding CFD models derived from the convolution integral match well at different flow rates and domain sizes. A comparison of RTD among diff ;erent packing designs is presented at a fixed number of repeating units and different flow rates. The mean residence time is found to larger than the superficial time, which is a unique behavior of structure packing. For a fixed number of repeating units, a packed column having higher specific area showed broad dispersion and the axial Péclet number decreases.