Seawater Scrubbing Desulfurization: A Model for SO2 Absorption in Fall-Down Droplets

An unsteady model of SO2 absorption in fall-down spherical seawater droplets is presented, focused on marine diesel engine exhaust gas scrubbing. The model evaluates the amount of sulfur dioxide absorbed by a single droplet, with given initial velocity, diameter, and alkalinity, falling counter-flow with respect to the exhaust gas stream. Kinematics of the droplet, heat exchange, and evaporation has been considered, taking into account internal circulation. Neutralization of absorbed sulfur species in the droplet has been modeled with a global and fast reaction mechanism. Transport equations for species inside the droplet have been solved on a nonuniform computational grid, which is regenerated at every time step to account for droplet diameter reduction. The single-droplet model has been incorporated in a simple scrubber plug-flow model, to evaluate the desulfurization efficiency and the seawater supply rate under realistic marine engine exhaust gas desulfurization conditions. The influence of flue gas inlet temperature, flue gas velocity, initial droplet size, and velocity on the scrubbing process were investigated. Results of this model are valuable for judging the feasibility and operating costs of this SO2 scrubbing technique compared with alternative methods. (C) 2011 American Institute of Chemical Engineers Environ Prog, 31: 277-287, 2012