Fluidized Bed Combustion and Desulfurization of a Heavy Liquid Fuel

An experimental and theoretical study on the combustion and desulfurization of liquid fuels in fluidized beds is proposed in the paper. Tests with a high sulfur liquid fuel (Egyptian mazut) have been performed in a bubbling fluidized bed combustor equipped with a special fuel injector at different operating conditions. Limestone is used as sorbent at various Ca/S ratio. The experiments evidenced that efficient combustion and desulfurization can be achieved under operating conditions that maximize the mixing of fuel vapors and bed materials and depress the spontaneous formation of endogenous fuel rich bubbles. A tall bed and high fuel dispersion velocity largely improve the process efficiency. The design and operation of the fuel feeding device also have a key role. The theoretical study was aimed at developing a predictive model for estimating the desulfurization efficiency in a fluidized bed fed with liquid fuels. The model is based on a novel three phases schematization of the bed. It accounts for the mechanism of bubble coalescence, the diffusion between bubbles and the emulsion, the sulfation reaction, the sorbent attrition and elutriation. A macro-kinetics of fuel oxidation is adopted for the prediction of the O2 partial pressure in the bed. Model results are presented in the paper. The trend and the measured values obtained from the experiments are well predicted by the model, even if some refinements are needed in order to have a very accurate estimation of the sulfur retention. © 2004 Elsevier B.V. All rights reserved.