Slip velocity and axial dispersion measurements in a gas-solid pipeline using particle tracer analysis

Abstract

Pulses of radioactive tracer particles were injected into a dilute phase pneumatic conveying system, and their passage along the pipeline was recorded at a number of points. The pipeline incorporated both horizontal and vertical orientations, and horizontal and vertical bends. Solids slip velocities were calculated from these measurements and showed that the effect of bends on the solids flow can extend for a long distance downstream of the bend exit. The dispersion of the injected pulses along the pipeline is discussed, and dispersion values calculated assuming a simple axial dispersed plug flow model. The results yielded dispersion coefficients higher than those characteristic of turbulent fluid mixing. They also indicated an area about 4 m (50 pipe diameters) downstream from the exit of two consecutive 90° horizontal bends where the solids experienced high localised dispersion. This has been attributed to the resuspension of material which continues to flow in strands or ropes for some distance after the bend exit.