MODELING OF SULFUR RETENTION IN CIRCULATING FLUIDIZED-BED COMBUSTORS

The effects of operating conditions linear gas velocity, Ca/S molar ra tio, type of coal and limestone, etc.) on sulfur retention efficiency in a circulating fluidized bed combustor were studied. The operating c onditions affect the sulfur retention differently. To explain this, a mathematical model was developed. To determine axial voidage profiles, the model uses a modified exponential decay hydrodynamic model, which divides the bed into a dense region at the bottom of the bed and a di lute region above. In the dilute region a core-annulus structure with solid dispersion from core to annulus is considered. The SO2 retention rate is considered to depend on the bed height through the SO2 profil es generated by the coal devolatilization and char combustion rates, w hich change with the bed height. The model gives good predictions of t he effect of the operating variables on sulfur retention in a CFB pilo t plant of 20 cm i.d. and 6.5 m height, burning two different lignites and an anthracite with four types of Limestone.