The influence of the impeller on carbonation performances in carbon capture using industrial by-products

Abstract

This study investigates the performances of radial flow (Rushton turbine and Parabolic) and axial flow (Pitch Blade Down-pumping [PBD] and Pitch Blade Up-pumping [PBU]) impellers in promoting CO₂ capture via carbonation in various alkaline absorbents such as NaOH in ethanol, black liquor, and green liquor dregs. We performed experiments in a lab-scale reactor that show that the Rushton turbine exhibits superior effectiveness in industrial by-product-derived solutions such as 5% w/v aqueous green liquor dregs and black liquor, albeit at a high energy cost. However, in ethanol–NaOH mixtures, where the carbonation process inherently leads to an increase in viscosity, the PBD demonstrates superior efficiency. For example, in aqueous green liquor dregs at 400 rpm, down-pumping operation achieved pH = 8.5 with 13% improved performance at 25% w/v, whereas the up-pumping mode showed a 23% advantage at 5% w/v. In addition, power number reductions of up to 70% were observed with PBD compared to the Rushton impeller. Our main results are supported by numerical simulations that link impeller performances to mixing and vortical structures of the flow inside the reactor. The unique adaptability of the pitch blade, capable of mode-switching between down-pumping and up-pumping, offers distinct advantages through various stages of carbonation. The findings underscore the importance of analyzing the optimal impeller design for enhancing CO₂ absorption efficiently, considering operational factors and the inherent variations in the process, especially in view of designing a large-scale reactor.