HIGH-PRESSURE VERTICAL PNEUMATIC TRANSPORT INVESTIGATION

Vertical pneumatic transport was investigated in a 0.026 m i.d. Lucite tube at various pressures. Nitrogen was the conveying gas at pressure s of 101, 790, 2170 and 4238 kPa. Pressure drop, particle velocity, pr essure fluctuations and flow patterns were measured or visually observ ed and recorded. Choking velocity, velocity at minimum pressure drop a nd the particle friction factor were also investigated at these elevat ed pressures. Glass beads (97 and 545 mum) and coal (89 and 505 mum) w ere used as the conveyed solids. The use of Lucite tubing was made pos sible 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 pe r unit length versus superficial gas velocity was plotted at all press ures investigated. As pressure increased, the curve shifted toward a h igher pressure drop at a given gas velocity. Gas velocity at minimum p ressure drop thereby decreases as the pressure increases. The same tre nd 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. Investi gation of the friction factors for the small particles (89 and 97 mum) at elevated pressures revealed that the friction factors due to the g as 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 parti cle velocity, choking velocity, particle friction factor and velocity at minimum pressure drop are recommended for designing dilute-phase (i .e. epsilon > 0.9) high-pressure transport systems.