Hydrodynamic modeling of downward gas-solids flow. Part I: Counter-current flow

Abstract

The one-dimensional model of accelerating turbulent downward counter-current gas-solids flow of coarse particles was formulated and experimentally verified by measuring the pressure distribution along the transport tube. The continuity and momentum equations were used in the model formulation and variational model was used for the prediction of the fluid-particle interphase drag coefficient. Experiments were performed by transporting spherical glass particles 1.94 mm in diameter in a 16 mm i.d. acrylic tube at constant solids mass flux of 392.8 kg/m(2)s. Tube Reynolds number ranged from 170 to 5300 and the slip Reynolds number from 650 to 1060. Under these conditions loading ratio (G(p)/G(f)) varied between 66 and 2089. Visual observations show that particles flow downward in apparently homogenous dispersion. Experimental data for the static fluid pressure distribution along the transport tube agree quite well with the model predictions. The mean voidage and the particle velocity decrease, while the slip velocity increases with the increase in gas superficial velocity. The values of the pressure gradient, porosity, particle velocity and slip velocity along the tube were calculated according to the formulated model. In these calculations, particle-wall friction coefficient was determined indirectly by adjusting the f(p) value to agree with the experimental data. The effect of the value of fp on the model calculations was significant. Calculations show that the acceleration length for the same particles (1.94 mm) in downward counter-current gas-solids flow is about two times higher than the acceleration length in upward co-current gas-solids flow. In the system investigated, "choking" occurs at slip velocity which is about 73% of the single particle terminal velocity.