The influence of oxygen-stoichiometry on desulfurization during FBC: A simple sure modeling approach

Abstract

In this paper an extension is presented cf the simple SUlfur REtention SURE model which was published earlier by the authors (Schouten and Van den Bleek, 1987). The present model explains the effect of a decreasing desulfurization efficiency during staged Fluidized Bed Combustion of coal by the relatively fast formation of SO 3 as a gaseous intermediate reactant in the sorbent sulfation reaction. The SURE model provides an analytical expression for the molar (Ca/S) ratio in the reactor feed as a function of the degree of sulfur retention, the maximum sorbent conversion and three dimensionless model parameters. These parameters are functions of fluid bed operating conditions, coal and sorbent properties and the stoichiometric air ratio. It is shown that the oxygen concentration and the decrease in sulfur retention at lower stoichiometric air ratios can readily be described by the model equations. Furthermore, the SURE model is applied as a diagnostic tool for the analysis of plant operational data obtained from the recent literature. It is concluded from an evaluation of SURE model calculations and experimental data that the sorbent residence time is a crucial system parameter. It is demonstrated that the observed neglect of the influence of the sorbent residence time on the steady state character of many retention experimentations gives rise to serious doubt on the reliability and usefulness of these measurements for model verification purposes.