CIRCULATING FLUIDIZED BED COMBUSTION IN THE TURBULENT REGIME: MODELLING OF CARBON COMBUSTION EFFICIENCY AND SULPHUR RETENTION

摘要

In this work carbon combustion efficiencies and sulphur retentions in CFBC under the turbulent regime were studied. Experimental results were obtained from the combustion of a lignite and an anthracite with a limestone in a CBF pilot plant with 20 cm internal diameter and 6.5 m height. The effect of operating conditions such as coal and limestone particle size distributions, temperature, excess air, air velocity and Ca/S molar ratio on carbon combustion efficiency and sulphur retention was studied. On the other hand, a mathematical model for the carbon combustion efficiencies and sulphur retentions in circulating fluidized bed combustors operating under the turbulent regime was developed. The model has been developed considering the hydrodynamics behaviour of a turbulent bed, the kinetics of carbon combustion and sulphur retention in the riser. The hydrodynamics characteristics of the turbulent regime were previously studied in a cold pilot plant and equations to determine the axial and radial voidage in the bed were proposed. A core-annulus structure in the dilute region of the bed was found in this regime. Carbon combustion and sulphur retention were modelled by modifying a model developed for fast beds and taking into account turbulent regime characteristics. The experimental results of carbon combustion efficiencies and sulphur retentions were compared with those predicted by the model and a good correlation was found for all the conditions used.