Experimental investigation of pressure letdown flow characteristics in dense-phase pneumatic conveying at high pressure

• The flow behaviors of pressure letdown are characterized.
• Pressure drops across different sections of the pressure letdown are examined.
• Pressure drop models for the pressure letdown are developed.

Experiments were conducted to investigate the flow characteristics and mechanism of pressure letdown of a conveying facility at pressures up to 3.0 MPa. The effects of operating parameters, particle size and diameter ratio on pressure drops across different sections of the pressure letdown system are examined. Results show that the pressure letdown causes a significant pressure drop in dense-phase pneumatic conveying. The effect of pressure letdown inlet velocity on the pressure drop through different sections is weak at constant solids mass flow rate. With increasing solids mass flow rate, particle size or diameter ratio, the pressure drops for the convergent section and straight pipe section increase, while the pressure drop of a divergent section differs from that of the other sections. The pressure drop of the straight pipe section is responsible for over 70% of the pressure drop through the pressure letdown system. Diameter ratio, length, mass flow rate and powder properties determine the letdown pressure drop. Empirical models, derived based on the Barth additive theory, show good agreement with experimental results, with relative deviations less than ± 15%.

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