Modelling of absorption process by seawater droplets for flue gas desulfurization application

Abstract

• A new model for calculating the mass transfer coefficient between the droplet and the gaseous phase has been implemented. • The new model takes additional physical parameters such as surface renewal intensity. • With the newly-implemented model in 3D CFD simulations better results are achieved. Flue gas desulfurization technology for sulfur dioxide removal from exhausts of combustion processes is becoming more widespread as allowed emission levels keep getting lowered. Spray scrubbers have gained traction in coastal and maritime applications, where seawater can be used as a scrubbing liquid. Detailed numerical models are required for accurate replication of processes in these applications, with complex physical and chemical phenomena considered. Among them, mass transfer modeling between phases has proven to be particularly important for obtaining accurate simulation results. Present work investigates a new model for calculating liquid side mass transfer coefficient in falling droplets, which considers additional parameters such as surface renewal rate, Reynolds number, and droplet diameter, compared to simplified and more common approaches. Initial modelling was performed on a single droplet level, followed by the implementation in the computational fluid dynamics framework and expansion to the entire spray. Desulfurization efficiencies for real cases modelled with the new approach were compared with the experimental data and the previously used penetration theory model results. The newly implemented model investigated the influence of operational parameters such as water and gas flow, sulfur dioxide concentration, droplet size, and distribution on desulfurization efficiency. The results obtained by the new model showed the expected trend of increased efficiency with the water flow increase, as well as greater sensitivity to operational conditions in different cases. Furthermore, compared to the previously used model, the present work more accurately replicated removal efficiencies in simulations of seawater spray scrubber applications, which is beneficial in designing new and more efficient equipment.