Modeling of SO2 absorption into limestone suspensions

The wet limestone flue gas desulfurization process, and more specifically absorption of SO2 limestone suspensions, was studied. Experiments of SO2 absorption were carried out using a bubbling reactor with a mixture of sulfur dioxide and nitrogen in the gas phase and an aqueous limestone suspension in the liquid phase. The SO2 absorption rate was measured at different compositions of both gas and liquid phases and at different gas flow rates and agitator speeds. A model based on the film theory was proposed to describe liquid-side mass transfer. It was assumed that the liquid-phase diffusional resistance is concentrated in a layer, the thickness of which depends on fluid dynamics, but is independent of the nature of the reactions taking place. The equations considered by the model describe conditions of thermodynamic equilibrium as well as material and electrical balances and use the experimentally determined gas- and liquid-side mass-transfer coefficients, rather than empirical parameters. Model calculations and experimental results were compared, and a good consistency was found. Eventually the model was used to evaluate the absorption enhancement factor as a function of gas- and liquid-phase composition.