High-pressure vertical pneumatic transport investigation

Abstract

Vertical pneumatic transport was investigated in a 0.026 m i.d. Lucite tube at various pressures. Nitrogen was the conveying gas at pressures of 101, 790, 2170 and 4238 kPa. Pressure drop, particle velocity, pressure fluctuations and flow patterns were measured or visually observed and recorded. Choking velocity, velocity at minimum pressure drop and the particle friction factor were also investigated at these elevated pressures. Glass beads (97 and 545 μm) and coal (89 and 505 μm) were used as the conveyed solids. The use of Lucite tubing was made possible by encapsulating the entire transport system in a high-pressure containment vessel and pressurizing the outside and the inside of the transport tube simultaneously. A Zenz-type diagram of pressure drop per unit length versus superficial gas velocity was plotted at all pressures investigated. As pressure increased, the curve shifted toward a higher pressure drop at a given gas velocity. Gas velocity at minimum pressure drop thereby decreases as the pressure increases. The same trend is observed for the choking velocity. Average particle velocity of the gas—solid flow mixture approaches the superficial gas velocity at higher pressures more readily than it does at lower pressures. Investigation of the friction factors for the small particles (89 and 97 μm) at elevated pressures revealed that the friction factors due to the gas and solid were dependent on the loading of the system. Expressions were developed for predicting the frictional pressure drop for the gas and solid at low loadings for small particles. Correlations for particle velocity, choking velocity, particle friction factor and velocity at minimum pressure drop are recommended for designing dilute-phase (i.e. ϵ>0.9) high-pressure transport systems.