Modeling flue gas desulfurization by spray-dry absorption

A detailed model for flue gas desulfurization by spray-dry absorption with a lime slurry is presented. The model combines a steady state one-dimensional spray-dryer model with a single-drop model for SO2 absorption with instantaneous irreversible reaction in a rigid droplet containing uniformly dispersed fine lime particles. The fate of the droplets is followed from atomization until formation of a porous coherent shell around the drying droplets. The model results were validated against available experimental spray-dry FGD results, showing excellent agreement at low to medium Ca/S feed ratios. The model was then used to study the relevance of the different resistances to SO2 absorption and to predict the influence of the main operating variables on the spray-dryer desulfurization performance. Analysis of variables profiles along the spray-dry column showed that the initial droplet velocity has no influence on model results and that the initial droplets decelerating phase always accounts for negligible SO2 capture. Results further showed that the controlling resistance to SO2 absorption shifts from a liquid-phase one near the atomizer to a gas-phase one at the column exit. The operating variables that exert the largest influence on the overall desulfurization efficiency are the Ca/S molar feed ratio, the mean initial droplet size and the mean lime particle size. In particular, careful control of the last two variables is critical in order to obtain a good spray-dryer performance. (C) 2003 Elsevier B.V. All rights reserved.