Hydrodynamic characteristics of coal in a circulating fluidized bed

Abstract

In a circulating fluidized bed (7.79-ID×260cm-height) flow regime of coal-air system at room temperature has been determined. Bituminous coal having density of 1.4g/㎤ was employed and coal particle sizes were varied 0.725 and 1.03 mm for experiments. The transition velocities between bubbling and turbulent beds and the transition velocities between turbulent and fast beds have determined by means of measuring pressure fluctuations with air velocity and measuring the disappearance time of particle entrainment with air velocity, respectively. The transition velocities between bubbling and turbulent beds and turbulent and fast beds were found to be 103 and 180cm/sec for particle size of 0.725 mm and 130 and 209 cm/sec for particle size of 1.03 mm, respectively. In a circulating fluidized bed, bed density depends primarily on the solid recycle rate and is somewhat uniform with height, respectively. And particle size of 0.725 mm has more uniformity of bed density with height and higher solid contacting than particle size of 1.03 mm. Solid backmixing in a circulating fluidized bed depends slightly not only on gas velocity but also on the solid recycle rate. Choking velocity of transition velocity between dense phase flow and dilute phase flow was found to be 256-259 cm/sec for particle size of 0.725 mm and 290-293 cm/sec for particle size at the solid feeding rate of 30-50 kg/hr.